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HAND-BOOK
PHYSIOLOGY.
“ «Aetiga —_ — FSi gce. |. ee a
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HAND-BOOK
OF
PHYSIOLOGY.
BY WILLIAM SENHOUSE KIRKES, M.D.
EDITED BY
W. MORRANT BAKER, F.R.C.S.
LECTURER ON PHYSIOLOGY, AND ASSISTANT SURGEON TO ST. BARTHOLOMEW’S HOSPITAL SURGEON TO THE EVELINA HOSPITAL FOR SICK CHILDREN,
WITH TWO HUNDRED AND FORTY-EIGHT ILLUSTRATIONS.
WA
Gighth Gdition. es A$
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LONDON: JOHN MURRAY, ALBEMARLE STREET. | 1872.
iy t ‘? f ore, .# ris Oy «OP. ; ' a | - BRADBURY, AGNEW, & ©0., PRINTERS, ETA, ; ai Re ‘ : f
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at
PREFACE TO THE EIGHTH EDITION.
+
THE Eighth Edition is the result of an increased ‘demand for this work, involving the necessity for a reprint at an earlier period after the publication of the Seventh Edition than was anticipated, The oppor- ' tunity has been seized for making corrections and addi tions where they appeared to be most needed ; but the ~ present issue must be regarded as, in great part, a
reprint of the Edition of 1869.
W. MORRANT BAKER.
THe CoLLEGE, St. BARTHOLOMEW’S HOSPITAL, October, 1872.
ibe
Digitized by the te Archive in, 2007 with func lime sai
CONTENTS.
peed Yaa
CHAPTER I.
THe GENERAL AND DISTINCTIVE CHARACTERS OF LIVING BEINGS
CHAPTER II,
CHEMICAL COMPOSITION OF THE HumMAN Bopy
CHAPTER III.
StTrucTURAL COMPOSITION OF THE HumMAN Bopy
CHAPTER IV.
' STRUCTURE OF THE ELEMENTARY TISSUES. ; < Epithelium . ‘ ‘ : ; Areolar, Cellular, or Connective Tissue
Adipose Tissue Pigment Cartilage . ‘ . Bones and Teeth : : CHAPTER V. Ture BLoop .
Quantity of Blood Coagulation of the Blood
PAGE
19
Vili CONTENTS.
THE Boop, continued. Conditions affecting Coagulation ‘ : ; ose 66 Chemical Composition of the Blood : ; : : 68 The Blood-Corpuscles, or Blood-Cells . yeas sree 69 Chemical Composition of Red Blood-Cells if 5 ‘ 74 Blood-Crystals . ; , ; , ‘ ; ote, ib. The White Corpuscles . . poet, ae é 76
The Serum 78 Variations in the Prinekpal Constizhents of the Ticade Sanguinis . 79
Variations in Healthy Blood reece Different Cirenmabatioes 83 Variations in the Composition of the Blood in Different
‘parts of the Body . ‘ : : : ; 5 ae 84. Gases contained in the Blood . ; é : ‘ ¢ 89 Development of the Blood . ‘ ‘ ; ‘ Ya go Uses of the Blood . ‘ ee 95: Uses of the various Cenniitaunka of the Blood ; Bl ia ab...
CHAPTER VI.
CIRCULATION OF THE BLoop . ; > ae 99 _ The Systemic, Pulmonary, and Portal Gireulation ‘ ; 10B
THE Heart. ‘ ‘ ; *+? 102 Structure of the Valves of the Heart : ; 4 : 104 The Action of the Heart . > . ce < y 109 Function of the Valves of the Heart A eine > 4 112 Sounds of the Heart . ; ‘ : ‘ ; rh 119 Impulse of the Heart. . ‘ ‘ ; 122 Frequency and Force of the Heart’s heladh ; a: 124. Cause of the Rhythmic Action of the Heart . , : 128 Effects of the Heart’s Action . : ; : pF ee 132
THE ARTERIES . ; : : : ; : 133 Structure of the ‘Arteries ; _ ; ‘ ‘ 5 and ib. The Pulse : ; ; ; ; ‘ ‘ ‘ ‘ 143 Sphygmograph . : ; Sen ee 146 Force of the Blood in the Arteries : ° ‘ o Bhd 152 Velocity of the Blood inthe Arteries. . . oie 155
CONTENTS. 1X
PAGE
Tue CAPILLARIES . é ‘ F 155 The Structure and Avvehaesaurt of Capillaries: , PSR 156 Circulation in the Capillaries . ‘ : ‘ ‘ ‘ 160.
THE VEINS : , : ‘ P ; ; . rth 167
Structure : . ‘ . ab. Agents concerned in ith Oireulation of the Blood ae 173 Velocity of Blood in the Veins ; ; : ; ‘ 175 Velocity of the Circulation ; ‘ - , c's 176
PECULIARITIES OF THE CIRCULATION IN DIFFERENT PARTS 180. Cerebral Circulation ‘ 2 - 4 az : ‘ tb. Erectile Structures. , ; é ? - winx 183,
CHAPTER VIE.
RESPIRATION , ; : ; ; ; 186 Position and Str pethare of the tain ‘ j : tee ib. Mechanism of Respiration i é . 5 , ‘ 194. Respiratory Movements . ; < : i wy 195 Respiratory Khythm : . ‘ . : ; 200 Respiratory Movements of Glottis 3 ‘ b Way tb. Quantity of Air respired ‘ : ’ 205 Movements of the Blood in eenieatary Organs 4 aig 208 Changes of the Air in Respiration . : d 210 Changes produced in the Blood by Waspination’ i ims 219 Mechanism of various Respiratory Actions .- . ; 220 Influence of the Nervous System in Respiration . gts 225 Effects of the Suspension and Arrest of Respiration . ‘ 227
CHAPTER VIII.
ANIMAL HEAT , : ‘ : : . Pid 231 Variations in Penbiainde ‘ , 232 Sources and Mode of Production of Heat in the Rody ‘ 236 Regulation of Temperature. ana ‘ ‘ ‘ 238 Influence of Nervous System. ; . ‘ aT 243
,
x i CONTENTS.
CHAPTER IX.
DIGESTION . : 4 .: . : : ’ Food * Starvation
PASSAGE OF FoopD THROUGH THE ALIMENTARY CANAL The Salivary Glands and the Saliva Passage of Food into the Stomach
DIGESTION OF Foop IN THE STOMACH . Structure of the Stomach ‘ Secretion and Properties of the Gabtrie Fluid . Changes of the Food in the Stomach . Movements of the Stomach : Influence of the Nervous System on Cesise Digestion Digestion of the Stomach after Death
DIGESTION IN THE INTESTINES ; Structure and Secretion of the Small Intestines Valvule Conniventes . ; Glands of the Small Intestine P The Villi . Structure of the Laie Iotmutine- The Pancreas and its Secretion . Structure of the Liver Functions of the Liver The Bile : Glycogenic Function of the Liver Summary of the Changes which take inte in the Food during its Passage through the small Intestine Summary of the Process of Digestion in the large Intestine Gases contained in the Stomach and Intestines Movements of the Intestines .
CHAPTER X.
ABSORPTION Structure and Office of the Leste and Uymphatic Vessel and Glands . . . 3 : , Lymphatic Glands
354
CONTENTS.
ABSORPTION, continued. Properties of Lymph and Chyle Absorption by the Lacteal Vessels Absorption by the Lymphatics Absorption by Blood- Vessels
CHAPTER XI. NvuTRITION AND GROWTH NUTRITION GROWTH CHAPTER XII. SECRETION
SECRETING MEMBRANES Srrovus MEMBRANES . Mucous MEMBRANES SECRETING GLANDS PROCESS OF SECRETION .
CHAPTER XIII.
VASCULAR GLANDS; OR GLANDS WITHOUT DucTs .
Structure of the Spleen Functions of the Vascular Glands
CHAPTER XIV.
Tuer SKIN AND ITs SECRETIONS Structure of the Skin Structure of Hair and Nails Excretion by the Skin Absorption by the Skin .
394 395 396 398 401
404,
410 4il 414
419
ab. 428 432 437
xii CONTENTS.
CHAPTER XV.
Tue KIDNEYS AND THEIR SECRETION . ‘ : . Structure of the Kidneys Secretion of Urine ; The Urine ; its general Brovextion : : ‘ . ‘ Chemical Composition ofthe Urine .° . - gy
CHAPTER XVI.
Tue Nervous SystEM ; Elementary Structures of the N ervous ‘ayatom Functions of Nerve-Fibres Functions of Nerve-Centres
CEREBRO-SPINAL NERVOUS SysTEM. : ; Spinal Cord and its Nerves . ‘ : : é Functions of the Spinal Cord
THE MEDULLA OBLONGATA . ; Its Structure 4 Distribution of the Fibres of the Medulla Oblonaaia Functions of the Medulla Oblongata . , ‘ ‘
STRUCTURE AND PuHysIOLOGy OF THE Pons VAROLII, CRURA CEREBRI, CORPORA QUADRIGEMINA, CorroRA GENICU- LATA, Optic THALAMI, and Corpora STRIATA .
Pons Varolii
Crura Cerebri
Corpora Quadrigemina The Sensory Ganglia
STRUCTURE AND PHYSIOLOGY OF THE CEREBELLUM
STRUCTURE AND PHYSIOLOGY OF THE CEREBRUM
PHYSIOLOGY OF THE CEREBRAL AND SPprnAL NERVES ‘ Physiology of the Third, Fourth, and Sixth Cerebral or Cranial Nerves . A ‘ Physiology of the Fifth or Trigeratoel Werve Physiology of the Facial Nerve . ‘
PAGE 440 ab. 446 448 450
463 464 474. 483
488 tb. 495
509
tb. 511 513.
CONTENTS. Xill
PAGE
PHYSIOLOGY OF THE CEREBRAL AND SPINAL NERVES, continued. Physiology of the Glosso-Pharyngeal Nerve. ; : 553 Physiology of the Pneumogastric Nerve . : are 557 Physiology of the Spinal Accessory Nerve ; : . 564 Physiology of the Hypoglossal Nerve . . : sofa 565 Physiology of the Spinal Nerves. ‘ : ; : 567
-PHYSIOLOGY OF THE SYMPATHETIC NERVE . r i ab,
CHAPTER XVII.
CAUSES AND PHENOMENA OF MOTION . F ; ; ; 578 Cin1ARY Morion . ; : ; ; ; ae ab. Muscutar Motion » | RE. 5 a 309; BBO Muscular Tissue : , ‘ p . 5 grees ab. Properties of Muscular issue : . : ; ‘ 587 Action of the Voluntary Muscles : ‘ ‘ ae 595 Action_of the Involuntary Muscles ? ‘ : ‘ 602 Source of Muscular Action j i : : ave g tb.
CHAPTER XVIII.
Or Voice AND SprEcH ; : ; : 604 Mode of Production of the Bunn Veioe . . Se ib. The Larynx . ‘ ‘ : 606 papeeatian of the Vanes in Shaving: and Sealkine eid 614
Risin , . ‘ ; ; ; ; - ; ; 619
CHAPTER XIX.
THE SENSES . ‘ ; ; ; : ; 7% 622
» Tue SENSE OF ices: : ; - ; ; ‘ ; 630 Tue SENSE OF SIGHT ‘ ays : 4 ‘wr 636
Structure of the Eye . ‘ , d ‘ ‘ ‘ ib. Phenomena of Vision . dey 645
Reciprocal Action of different Sachs of the Rating ‘ 661 Simultaneous Action of the two Eyes . : sist 664.
Xiv
CONTENTS.
THE SENSE OF HEARING
Anatomy of the Organ of Biatng
Physiology of Hearing
Functions of the External Ear:
Functions of the Middle Ear ; the Tympanum, Ossicul and Fenestre :
Functions of the Internal Ear
Sensibility of the Auditory Nerve
THE SENSE OF TASTE. : Z ‘ : i
THE SENSE oF TovucH
CHAPTER XX.
GENERATION AND DEVELOPMENT
Generative Organs of the Female Unimpregnated Ovum Discharge of the Ovum
Corpus Luteum .
IMPREGNATION OF THE OvuM
Male Sexual Functions
DEVELOPMENT
Changes of the Ovum sieevioits to the oemation of the Embryo . ‘ : ‘ af As
Changes of the Ovum withi the icra ‘ ; ,
The Umbilical Vesicle
The Amnion and Allantois
The Chorion
Changes of the Macsils $etitenns of the Tierne aud Formation of the Placenta
DEVELOPMENT OF ORGANS
Development of the Vertebral Calan and Cisalnna: Development of the Face and Visceral Arches © Development of the Extremities
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758
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CONTENTS.
DEVELOPMENT OF ORGANS, continued. ° Development of the Vascular System Circulation of Blood in the Foetus Development of the Nervous System Development of the Organs of Sense Development of the Alimentary Canal Development of the Respiratory Apparatus The Wolffian Bodies, Urinary Apparatus, and Sexual Org gans
THE MAMMARY GLANDS . INDEX
List OF WORKS REFERRED TO
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HANDBOOK OF PHYSIOLOGY.
CHAPTER I.
ON THE GENERAL AND DISTINCTIVE CHARACTERS OF LIVING BEINGS.
Human Puystotoey is the science which treats of the life of man—of the way in which he lives, and moves, and has his being. It teaches how man is begotten and born; how he attains maturity ; and how he dies.
Having, then, man as the object of its study, it is un- necessary to speak here of the laws of life in general, and the means by which they are carried out, further than is requisite for the more clear understanding of those of the life of man if particular. Yet it would be impossible to understand rightly the working of a complex machine without some knowledge of its motive power in the sim- plest form; and it may be well to see first what are the so-called essentials of life—those, namely, which are mani- fested by all living beings alike, by the lowest vegetable and the highest animal, before proceeding to the consider- ation of, the structure and endowments of the organs and tissues belonging to man.
The essentials of life are these,—birth, growth and development, decline and death—and an idea of what life is, will be best gained by sketching these events, each in succession, and their relations one to another.
The term, birth, when employed in this general sense of one of the conditions essential to life, without reference
a f Bo
2 GROWTH.
to any particular kind of living being, may be taken to mean, separation from a parent, with a greater or less power of independent existence as a living being.
Taken thus, the term, although not defining any par- ticular stage in development, serves well enough for the expression of the fact, to which no exception has yet been proved to exist, that the capacity for life in all living beings is got by inheritance.
Growth, or inherent power of increasing in size, although essential to our idea of life, is not a property of living beings only. A crystal of sugar or of common salt, or of any other substance, if placed under appropriate conditions for obtaining fresh material, will grow in a fashion as definitely characteristic and as easily to be foretold as that of a living creature. It is, therefore, necessary to explain the distinctions which exist in this respect between living and lifeless structures; for the manner of growth in the two cases is widely different.
First, the growth of a crystal, to use the same example as before, takes place merely by additions to its outside; the new matter is laid on particle by particle, and layer by layer, and, when once laid on, it remains unchanged. The growth is here said to be superjicial. In a living structure, on the other hand, as, for example, a brain or a muscle, where growth occurs, it is by addition of new matter, not to the surface only, but throughout every part of the mass; the growth is not superficial, but interstitial. In the second place, all living structures are subject to constant decay ; and life consists, not as once supposed, in the power of pre- venting this never-ceasing decay, but rather in making up for the loss attendant on it by never-ceasing repair. Thus, a man’s body is not composed of exactly the same particles day after day, although to all intents he remains the same individual, Almost every part is changed by degrees; but the change ‘is so gradual, and the renewal of that which is lost.so exact, that no difference may be noticed, except at
DEVELOPMENT. | 3
long intervals of time. A lifeless structure, as a crystal, is subject to no such laws; neither decay nor repair is a necessary condition of its existence. That which is true of ‘structures which never had to do with life is true also with respect to those which, though they are formed by living parts, are not themselves alive. Thus, an oyster shell is formed by the living animal which it encloses, but it is as lifeless as any other mass of saline matter; and in accord- ance with this circumstance its growth takes place not in- terstitially, but layer by layer, and it is not subject to the constant decay and reconstruction which belong to the living. ‘The hair and nails are examples of the same fact.
' Thirdly. In connection with the growth of lifeless masses there is no alteration in composition or properties of the material which is taken up and added to the pre- viously existing mass. For example, when a crystal of common salt grows on being placed in a fluid which con- tains the same material, the properties of the salt are not changed by being taken out of the liquid by the crystal and added to its surface in a solid form. But the case is essentially different from this in living beings, both animal and vegetable. A plant, like a crystal, can only grow when fresh material is presented to it; and this is absorbed by its leaves and roots; and animals for the same purpose of getting new matter for growth and nutrition, take food into their stomachs. But in both these cases the materials are much altered before they are finally assimilated by the structures they are destined to nourish. * Fourthly. The growth of all living things has a definite limit, and the law which governs this limitation of increase in size is so invariable that we should be as much astonished to find an individual plant or animal without: limit as to growth as without limit to life.
Development is as constant an accompaniment of life as
growth. The term is used to indicate that change to : "Bz
4 ANIMALS CONTRASTED
which, before maturity, all living parts are constantly sub- ject, and by which they are made more and more capable of performing their several functions. For example, a full-grown man is not simply a magnified child; his tissues and organs have not only grown, or increased in size, they have also developed, or become better in quality.
No very accurate limit can be drawn between the end of development and the beginning of decline; and the two processes may be often seen together in the same individual. But after a time all parts alike share in the tendency to degeneration, and this is at length succeeded by death.
The decline of living beings is as definite in its occur- rence as growth or development. Death—not by disease or injury—so far from being a violent interruption of the course of life, is but the fulfilment of a purpose in view from the commencement.
It has been already said that the essential features of life are the same in all living things; in other words, in the members of both the animal and vegetable kingdoms. It may be well now to notice briefly the distinctions which exist between the members of these two kingdoms. ~ It wnay seem, indeed, a strange notion’that it is possible to confound vegetables with animals, but it is true with respect to the lowest of them, in which but little is mani- fested beyond the essentials of life, which are the same in both.
I. Perhaps the most essential distinction is the presence or absence of power to live upon inorganic material; in other words, to act chemically on carbonic acid, ammonia and water, so as to make use of their cumponent elements as food. Indeed one ought probably to say that a question concerning the capability of the lower kinds of animal to live in this way cannot be entertained; and that such a manner of life should decide at once in favour of a vegetable nature, whatever might be the attributes which seemed to point to an opposite conclusion. The power of
WITH VEGETABLES. 5
living upon organic matter would: seem to be less decisive of an animal nature, for some fungi appear to derive support almost entirely from this source.
II. There is, commonly, a marked difference in general chemical composition between vegetables and animals, even in their lowest forms; for while the former consist mainly of a substance containing carbon, hydrogen, and oxygen only, arranged so as to form a compound closely allied to starch, and called cellulose, the latter are com- monly composed in great part of the three elements just named, together with a fourth, nitrogen; the proxi- mate principles formed from these being identical, or nearly so, with albumen. It must not be supposed, how- ever, that either of these typical compounds alone, with its allies, is confined to one kingdom of nature. Nitro- genous or albuminous compounds are freely produced by vegetable structures, although they form an infinitely smaller proportion of the whole organism than cellulose or starch. And while the presence of the latter in animals is much more rare than is that of the former in vegetables, there are many znimals in which traces of it may be dis- covered, and some, the Ascidians, in which it is found in considerable quantity.
III. Inherent power of movement is a quality which we so commonly consider an essential indication of animal nature, that it is difficult at first to conceive it existing in any other. The capability of simple motion is now known, however, to exist in so many vegetable forms, that it can no longer be held as an essential distinction between them and animals, and ceases to be a mark by which the one can be distinguished from the other. Thus the zoospores of many of the Cryptogamia exhibit movements of a like kind to those seen in animalcules; and even among the higher orders of plants, many exhibit such motion, either at regular times, or on the application of external irrita- tion, as might lead one, were this fact taken by itself, to
6 ANIMALS CONTRASTED
regard them as sentient beings. Inherent power of move- ment, then, although especially characteristic of animal nature, is, when taken by itself, no proof of it. Of course, if the movement were such as to indicate any kind of purpose, whether of getting food or any other, the case would be different, and we should justly call a being ex- hibiting such motion, an animal. But low down in the scale of life, where alone there exists any difficulty in distinguishing the two classes, movements, although almost always more lively, are scarcely or not at all more pur- posive in one than the other; and even if we decide on the animal nature of a being, it by no means follows that we are bound to acknowledge the presence of sensation or volition in the slightest degree. There may be at least no evidence of its possessing a trace of those tissues, nervous and muscular, by which, in the higher members of the animal kingdom, these qualities are manifested. Probably there is no more of either of them in the lowest animals than in vegetables. In both, movement is effected by the same means—ciliary action, and hence the greater value, for purposes of classification, of the power to live on this or that kind of food,—on organic or inorganic matter. As the main purpose of the lowest members of the vegetable kingdom is doubtless to bring to organic shape the elements of the inorganic world around, so the function of the lowest animal is, in like manner, to act on degenerating organic matter,—‘“to arrest the fugitive organized particles, and turn them back into the ascending stream of animal life.” And, because sensation and voli- tion are accompaniments of life in somewhat higher animal forms, it is needless to suppose that these qualities exist under circumstances in which, as we may believe, they could be of no service. It is as needless as to dogmatise — on the opposite side, and say that no feeling or voluntary movement is possible without the presence of those tissues which we call nervous and muscular.
WITH VEGETABLES. 7
IV. The presence of a stomach is a very general mark
by which an animal can be distinguished from a vegetable.
But the lowest animals are’ surrounded by material that they can take as food, as a plant is surrounded by an atmosphere that it can usein like manner. And every part of their body being adapted to absorb and digest, they have no need of a special receptacle for nutrient matter, and accordingly have no stomach. ‘This distinction, then, is not a cardinal one. |
It would be tedious as well as unnecessary to enumerate
‘the chief distinctions between the more highly developed
animals and vegetables. They are sufficiently apparent. It is necessary to compare, side by side, the lowest mem- bers of the two kingdoms, in order to understand rightly how faint are the boundaries between them.
CHAPTER II.
.
CHEMICAL COMPOSITION OF THE HUMAN BODY.
Tue following Elementary Substances may be obtained by chemical analysis from the human body: Oxygen, Hydro- gen, Nitrogen, Carbon, Sulphur, Phosphorus, Silicon, Chlorine, Fluorine, Potassium, Sodium, Calcium, Magne- sium, Iron, and, probably as accidental constituents, Man- ganesium, Aluminium, Copper, and Lead. Thus, of the sixty-three or more elements of which all known matter is composed, more than one-fourth are present in the human body. F
Only one or two elements, and in very minute amount, are present in the body uncombined with others; and even these are present much more abundantly in various states of combination. The most simple compounds formed
8 CHEMICAL COMPOSITION OF HUMAN BODY.
by union in various proportions of these elements are termed prowimate principles; while the latter are classified as the organic and the inorganic proximate principles.
The term organic was once applied exclusively to those substances which were thought to be beyond the compass of synthetical chemistry and to be formed only by or- ganized or living beings, animal or vegetable; these being called organized, inasmuch as they are charac- terized by the possession of different parts called organs. But with advancing knowledge, both distinctions have dis- appeared; and while the title of living organism is applied to numbers of living things, having no trace of organs in the old sense of the term, and in some, so far as can be now seen, in no other sense, the term organic has long ceased to be applied to substances formed only by living tissues. In other words, substances, once thought to be formed only. by living tissues, are still termed organic, although they can be now made in the laboratory. The term, indeed, in its old meaning, becomes year by year applicable to fewer substances, as the chemist adds to his conquests over inorganic elements and compounds, and moulds them to more complex forms.
Although a large number of so-called organic com- pounds have long ceased to be peculiar in being formed only by living tissues, the terms organic and inorganic are ~ still commonly used to denote distinct classes of chemical substances, and the classification of the matters of which the human body is composed into the organic and the inorganic is-convenient, and will be here employed.
No very accurate line of separation can be drawn between organic and inorganic substances, but there are certain peculiarities belonging to the former which siny be: here briefly noted.
I. Organic compounds are composed of a larger number of Elements than are present in the more common kinds of inorganic matter. Thus, albumen, fibrin, and gelatin, the
CHEMICAL COMPOSITION OF HUMAN BODY. 9
most abundant substances of this class, in the more highly organized tissues of animals, are composed of five elements, —carbon, hydrogen, oxygen, nitrogen, and sulphur. The most abundant inorganic substance, water, has but two elements, hydrogen and oxygen.
2. Not only are a large number of elements usually combined in an organic compound, but a large number of equivalents or atoms of each of the elements are united to form an equivalent or atom of the compound. In the case of carbonate of ammonium, as an example among inorganic substances, one equivalent of carbonic acid is united with two of ammonium; the equivalent or atom of carbonic acid consists of one of carbon with two of oxygen; and that of ammonium of one of nitrogen with three of hydrogen. But in an equivalent or atom of fibrin, or of albumen, there are of the same elements, respectively, 72, 22, 18, and 112 equivalents. . And together with this union of large numbers of equivalents in the organic compound, it is further observable, that the several numbers stand in no simple arithmetical relation one with another, as the numbers of equivalents combining in an inorganic com- pound do.
With these peculiarities in the chemical composition of organic bodies we may connect two other consequent facts; first, the large number of different compounds that. are formed out of comparatively few elements; secondly, their great proneness to decomposition. For it is a general rule, that the greater the number of equivalents or atoms of an element that enter into the formation of an atom of a compound, the less is the stability of that compound. Thus, for example, among the various oxides of lead and other metals, the least stable in composition are those in which each equivalent has the largest number of equiva- _lents of oxygen. So, water, composed of one equivalent of oxygen and two of hydrogen, is not changed by any slight force; but peroxide of hydrogen, which has two
Io CHEMICAL COMPOSITION OF HUMAN BODY,
equivalents of oxygen to two of hydrogen, is among the substances most easily decomposed.
The instability, on this ground, belonging to organic compounds, is, in those which are most abundant in the highly organized tissues of animals, augmented, Ist, by their containing nitrogen, which, among all the elements, may be called the least decided in its affinities, and that which maintains with least tenacity its combinations with other elements; and, 2ndly, by the quantity of water which, in their natural state, is combined with them, and the presence of which furnishes a most favourable con- dition for the decomposition of nitrogenous compounds. Such, indeed, is the instability of animal compounds, arising from these several peculiarities in their constitu- tion, that, in dead and moist animal matter, no more is requisite for the occurrence of decomposition than the presence of atmospheric air and a moderate temperature; — conditions go commonly present, that the decomposition of dead animal bodies appears to be, and is generally called, spontaneous. The modes of such decomposition vary ac- cording to the nature of the original compound, the tem- perature, the excess of oxygen, the presence of microscopic organisms, and other circumstances, and constitute the several processes of decay and putrefaction ; in the results of which processes the only general rule seems to be, that the several elements of the original compound finally unite to form those substances, whose composition is, under the circumstances, most stable. |
The organic compounds existing in the human body may be arranged in two classes, namely, the azotized or nitro- genous, and the non-azotized, or non-nitrogenous principles,
The non-azotized principles include the several fatty, oily, or oleaginous substances, as olein, stearin, cholesterin, and others. In the same category of non-nitrogenous substances may be included lactic and formic acids, animal glucose, sugar of milk, &e.
GELATINOUS SUBSTANCES. II
The oily or fatty matter which, enclosed in minute cells, forms the essential part of the adipose or fatty tissue of the human body (p. 38), and which is mingled in minute par- ticles in many other tissues and fluids, consists of a mixture of stearin, palmitin, and olein. The mixture forms a clear yellow oil, of which different specimens congeal at from 45° to 35°.
Cholesterin, a fatty matter which melts at 293° F., and is therefore, always solid at the natural temperature of the body, may be obtained in small quantity from blood, bile, and nervous matter. It occurs abundantly in many biliary calculi; the pure white crystalline specimens of these con- cretions being formed of it almost exclusively.. Minute rhomboidal scale-like crystals of it are also often found in morbid secretions, as in cysts, the puriform matter of softening and ulcerating tumours, &c. It is soluble in ether and boiling alcohol; but alkalies do not change it; it is one of those -fatty substances which are not saponifiable.
The azotized or nitrogenous principles in the human body include what may be called the proper gelatinous and albu- ninous substances, besides others of less definite rank and composition, as pepsin and ptyalin, horny matter or keratin, many colouring and extractive matters, &c.
The gelatinous substances are contained in several of the tissues, especially those which serve a »passive mechanical office in the economy; as the cellular, or fibro-cellular tissue in all parts of the body, the tendons, ligaments, and other fibrous tissues, the cartilages and bones, the skin and serous membranes. These, when boiled in water, yield a material, the solution of which remains liquid while it is hot, but becomes solid and jelly-like on cooling.
Two varieties of these substances are described, gelatin and chondrin, the latter being derived from cartilages, the former from all the other tissues enumerated above,
12 CHEMICAL COMPOSITION OF HUMAN.BODY.
and in its purest state, from isinglass, which is the swim- ming bladder of the sturgeon, and which, with the excep- tion of about 7 per cent. of its weight, is wholly reducible into gelatin. The most characteristic property of gelatin is that already mentioned, of its solution being liquid when warm, and solidifying or setting when it cools. The tem- perature at which it becomes solid, the proportion of gela- tin which must be in solution, and the firmness of the jelly when formed, are various, according to the source, the quantity, and the quality of the gelatin; but, as a general rule, one part of dry gelatin dissolved in 100 of water, will become solid when cooled to 60°. The solidi- fied jelly may be again made liquid by heating it, and the transitions from the solid to the liquid state by the alter- nate abstraction and addition of heat, may be repeated several times ; ,but at length the gelatin is so far altered, and, apparently, oxydized by the process, that it no longer becomes solid on cooling. Gelatin in solutions too weak to solidify when cold, is distinguished by being precipitable with alcohol, ether, tannic acid, and bichloride of mercury, and not precipitable with the ferrocyanide of potassium. The most delicate and striking of these tests is the tannic acid, which is conveniently supplied in an infusion of oak- bark or gall-nuts; it will detect one part of gelatin in 5,000 of water; and if the solution of gelatin be strong it forms a singularly dense and heavy precipitate, which has been named tanno-gelatin, and is completely insoluble in water.
Chondrin, the kind of gelatin obtained from cartilages, agrees with gelatin in most of its characters, but its solution solidifies on cooling much less firmly, and, unlike gelatin, it is precipitable with acetic and the mineral and other acids, and with alum, persulphate of iron and acetate of lead.
Albuminous substances, or proteids, as they are sometimes called, exist abundantly in the human body. The chief
ALBUMEN. 13
among them are albumen, fibrin, casein, syntonin, myosin, and globulin.
tbumen exists in most of the-tissues of the body, but especially in the nervous, in the lymph, chyle, and blood, and in many morbid fluids, as the serous secretions of _dropsy, pus, and others. In the human body it is most abundant, and most nearly pure, in the serum of the blood. In all the forms in which it naturally occurs, it is com- bined with about six per cent. of fatty matter, phosphate of lime, chloride of sodium, and other saline substances. Its most- characteristic property is, that both in solution and in the half-solid state in which it exists in white-of- egg, it is coagulated by heat, and.in thus becoming solid, becomes insoluble in water. ‘The temperature required for the coagulation of albumen is the higher the less the proportion of albumen in the solution submitted to heat. Serum and such strong solutions will begin to coagulate at from 150°.to 170°, and these, when the cheat is maintained, become almost solid and opaque. But weak solutions require a much higher temperature, even that of, boiling, for their coagulation, and either only become milky or opaline, or produced flocculi which are precipitated.
Albumen, in the state in which it naturally occurs, ap- pears to be but little soluble in pure water, but is soluble in water containing a small proportion of alkali. In such solutions it is probably combined chemically with the alkali; it is precipitated from them by alcohol, nitric, and other mineral acids, by ferrocyanide of potassium (if before or after adding it the alkali combined with the albumen be neutralised), by bichloride of mercury, acetate of lead, and most metallic salts.
Coagulated albumen, i.c., albumen made solid with heat, is soluble in solutions of caustic alkali, and in acetic acid if it be long digested or boiled with it. With the.aid of heat, also, strong hydrochloric acid dissolves albumen pre-.
a
*
14 CHEMICAL COMPOSITION OF HUMAN BODY.
viously coagulated, and the solution ‘has a beautiful purple or blue colour.
Fibrin is found most abundantly in the blood and the more perfect portions of the lymph and chyle. It is very doubtful, however, whether fibrin, as such, exists in these fluids,—whether, that is to say, it is not itself formed at the moment of coagulation. (See Chapter on the Blood.)
Tf a common clot of blood be pressed in fine linen while a stream of water flows upon it, the whole of the blood- colour is gradually removed, and strings and various pieces | remain of a soft, yet tough, elastic, and opaque-white sub-_ stance, which consist of fibrin, impure, with a mixture of fatty matter, lymph-corpuscles, shreds of the membranes of red blood-corpuscles, and some saline substances. Fibrin somewhat purer than this may be obtained by stirring blood while it coagulates, and collecting the shreds that attach themselves to the instrument, or by retarding the coagula- tion, and, while the red blood-corpuscles sink, collecting the fibrin unmixed with them. But in neither of these cases is the fibrin perfectly pure.
Chemically, fibrin and albumen can scarcely be distin- guished ; the only difference apparently being that fibrin contains 1°5 more oxygen in every 100 parts than albumen does. Mr. A. H. Smee has, indeed, apparently converted albumen into fibrin, by exposing a solution to the prolonged influence of oxygen. Nearly all the changes, produced by various agents, in coagulated albumen, may be repeated with coagulated fibrin, with no greater differences of result than may be reasonably ascribed to the differences in the mechanical properties of the two substances. Of such dif- ferences, the principal are, that fibrin immersed in acetic acid swells up and becomes transparent like gelatin, while albumen undergoes no such apparent change; and that deutoxyde of hydrogen is decomposed when in contact with coagulated fibrin, but not with albumen.
Casein, which is said to be albumen in combination with
SYNTONIN: MYOSIN. 15
soda, exists largely in milk, and forms one of its most im- portant constituents.
Syntonin is obtained from muscular tissue, both of the striated and organic kind. It differs from ordinary fibrin in several particulars, especially in being less soluble in nitrate and carbonate of potash, and more soluble in dilute hydrochloric acid.
Myosin is the substance which spontaneously Seagulates in the juice of muscle. It is closely allied to syntonin ; indeed, in the act of solution in eee acid, it is converted into it.”
The per-centage composition of albumen, fibrin, gelatin, and chondrin, is thus given by Mulder:—
Albumen. Fibrin. Gelatin. | Chondrin.
Carbon. 53°5 52°7 50°40 49°97 Hydrogen 7°O 69 6°64 6°63 Nitrogen : 15°5 15"4 18°34 14°44 Oxygen... 22'0 235. Ib aang | tL 28°58 Sulphur ae 1°6 12 |f 74 f 0°38 Phosphorus . : 0"4. 0°3
| 100°0 100°0 100'00 100'00
Horny Matter.—The substance of the horny tissues, in- cluding the hair and nails (with whale-bone, hoofs, and horns), consists of an albuminous substance, with larger proportions of sulphur than albumen and fibrin contain. Hair contains 10 per cent. and nails 6 to 8 per cent. of sulphur.
The horny substances, to which Simon applied the name of keratin, are insoluble in water, alcohol, or ether; soluble in caustic alkalies, and sulphuric, nitric, and hydrochloric acids; and not precipitable from the solution in acids by ferrocyanide of potassium.
Mucus, in some of its forms, is related to these horny
~ substances, consisting, in great part, of epithelium detached
16 CHEMICAL COMPOSITION OF HUMAN BODY. .
from the surface of mucous membrane, and floating in a peculiar clear and viscid fluid. But under the name of mucus, several various substances are included of which some are morbid albuminous secretions containing mucus and pus-corpuscles, and others consist of the fluid secretion variously altered, concentrated, or diluted. Mucus contains an albuminous substance, termed mucin. It differs from albumen chiefly in not containing sulphur.
Pepsin and other albuminous ferments, as they are some- times called, will be described in connection with the secre- tions of which they are the active principles. And the various colouring matters, as of the blood, bile, &c., will be also considered with the fluids or tissues to which they belong.
Besides the above-mentioned organic nitrogenous com- pounds, other substances are formed in the living body, chiefly by decomposition of nitrogenous materials of the food and of the tissues, which must be reckoned rather as temporary constituents than essential component parts of the body; although from the continual change, which is a necessary condition of life, they are always to be found in greater or less amount. Examples of these are urea, uric, and hippuric acid, creatin, creatinin, leucin, and many others.
_ Such are the chief organic substances of which the human body is composed. It must not be supposed, how- ever, that they exist naturally in a state approaching that of chemical purity. All the fluids and tissues of the body appear to consist, chemically speaking, of mixtures of several of these principles, together with saline matters: Thus, for example, a piece of muscular flesh would yield fibrin, albumen, gelatin, fatty matters, salts of soda, potash, lime, magnesia, iron, and other substances, such as creatin, which appear passing from the organic towards the inorganic state. This mixture of substances may be explained in some measure by the existence of many
WATER: POTASH’; SODA. ~~. 17
different structures or tissues in the muscles; the gelatin may be referred principally to the cellular tissue between the fibres, the fatty matter to the adipose tissue in the same position, and part of the albumen to the blood and the fluid by which the tissue is kept moist. But, beyond these general statements, little can be said of the mode in which the chemical compounds are united to form an organized structure; or of how, in any organic body, the several incidental substances are combined with. those which are essential.
The inorganic matters which exist as such in the human body are numerous.
Water forms a large proportion, probably more than
two-thirds of the weight of the whole body. _~ Phosphorus occurs in combination,—as in the neutral phosphate of sodium in the blood and saliva, the acid phosphates of the muscles and urine, the basic phosphates of calcium and magnesium in the bones and teeth.
Sulphur is present chiefly in the sulphocyanide of potas- sium of the saliva, and in the sulphates of the urine and sweat. : ,
A very small quantity of silica exists, according to Berzelius, in the urine, and, according to others, in the blood. Traces of it have also been found in bones, in hair, and in some other parts of the body.
Chlorine is abundant in combination with sodium, potas- sium, and other bases in all parts, fluid as well as solid, of the body. A minute quantity of fluorine in combination with calcium has been found in the bones, teeth, and urine.
Potassium and sodium are constituents of the blood and all the fluids, in various quantities and proportions. They exist in the form of chlorides, sulphates, and phosphates, and probably, also, in combination with albumen, or certain organic acids. Liebig, in his work on the Chemistry of Food, has shown that the juice expressed from muscular
C
18 CHEMICAL COMPOSITION OF HUMAN BODY.
flesh always contains a much larger proportion of potash- salts than of soda-salts; while in the blood and other fluids, except the milk, the latter salts always preponderate over the former; so that, for example, for every 100 parts of soda-salts in the blood of the chicken, ox, and horse, there are only 40°8, 5°9, and 9°5 parts of potash-salts ; but for every 100 parts of soda-salts in their muscles, there are 381, 279, and 285 parts of potash-salts.
The salts of calcium are by far the most abundant of the earthy salts found in the human body. They exist in the lymph, chyle, and blood, in combination with phosphoric acid, the phosphate of calcium being probably held in solu- tion by the presence of phosphate of sodium. Perhaps no tissue is wholly void of phosphate of calcium; but its especial seats are the bones and teeth, in which, together with carbonate and fluoride of calcium, it is deposited in minute granules, in a peculiar compound, named bone-earth, containing 51°55 parts of lime, and 48°45 of phosphoric acid. Phosphate of calcium, probably the neutral phosphate, is also found in the saliva, milk, bile, and most other secretions, and acid phosphate in the urine, and, according to Blondlot, in the gastric fluid. |
Magnesium appears to be always associated with calcium, but its proportion is much smaller, except in the juice expressed from muscles, in the ashes of which magnesia preponderates over lime.
The especial place of iron is in the hemo-globin, the colouring-matter of the blood, of which a further account will be given with the chemistry of the blood. Peroxyde © of iron is found, in very small quantities, in the ashes of bones, muscles, and many tissues, and in lymph and chyle, albumen of serum, fibrin, bile, and other fluids; and a salt of iron, probably a phosphate, exists in considerable quantity in the hair, black pigment, and other deeply coloured epithelial or horny substances.
Aluminium, Manganese, Copper, and Lead.—It seems most
PROTOPLASM. . IG
likely that in the human body, copper, manganesium, alumi- nium, and lead are merely accidental elements, which, being taken in minute quantities with the food, and not excreted at once with the feeces, are absorbed and deposited in some tissue or organ, of which, however, they form no necessary
part. In the same manner, arsenic, being absorbed, may
be deposited in the liver and other parts.
CHAPTER III. STRUCTURAL COMPOSITION OF THE HUMAN BODY.
In the investigation of the structural composition of the human body, it will be well to consider in the first place, what are the simplest anatomical elements which enter into its formation, and then proceed to examine those more complicated tissues which are produced by their union.
It may be premised, that in all the living parts of all living things, animal and vegetable, there is invariably to be discovered, entering into the formation of their anato- mical elements, a greater or less amount of a substance, which, in chemical composition and general characters, is indistinguishable from albumen. As it exists, in a living tissue or organ, it differs essentially from mere albumen in the fact of its possessing the power of growth, develop- ment, and the like; but in chemical composition it is identical with it.
This albuminous substance has received various names according to the structures in which it has been found, and
the theory of its nature and uses which may have pre- c2
20 STRUCTURAL COMPOSITION OF HUMAN BODY.
sented itself most strongly to the minds of its observers. In the bodies of the lowest animals, as the Rhizopoda or Gregarinida, of which it forms the greater portion, it has been called ‘‘ sarcode,” from its chemical resemblance to the flesh of the higher animals. When discovered in vegetable cells, and supposed to be the prime agent in their con- struction, it was termed “‘ protoplasm.” As the presumed formative matter in animal tissues it was called ‘‘ blastema;”’ and, with the belief that wherever found, it alone of all matters has to do with generation and nutrition, Dr. Beale has surnamed it ‘‘ germinal matter.”
So far as can be discovered, there is no difference in chemical composition between the protoplasm of one part or organism and that of another. The movements which can * be seen in certain vegetable cells apparently belong to a sub- stance which is identical in composition with that which constitutes the greater portion of the bodies of the lowest animals, and which is present in greater or less quantity in all the living parts of the highest. So much appears to be a fact ;—that in all living parts there exists an albu- minous substance, in which in favourable cases for observa- tion in vegetable and the lower animal organisms, there can be noticed certain phenomena which are not to be accounted for by physical impressions from without, but are the result of inherent properties we call vital. For example, if a hair of the Tradescantia Virginica, or of many other plants, be examined under the microscope, there is seen in each individual cell a movement of the pro- toplasmic contents in a certain definite direction around the interior of the cell. Each cell is a closed sac or bag, and its contents are therefore quite cut off from the direct influence of any motive power from without. The motion of the particles, moreover, in a circuit around the interior of the cell, precludes the notion of its being due to any other than those molecular changes which we call vital. Again, in the lowest animals, whose bodies resemble more than
PROTOPLASM. } 21
anything else a minute mass of jelly, and which appear to be made up almost solely of this albuminous protoplasm, there are movements in correspondence with the needs of the organism, whether with respect to seizing food or any other purpose, which are unaccountable accord-
vital. In many, too, “there is a kind of molecular cur- | rent, exactly arasecsicam: that which is seen in a vegetable | cell.
In the higher animals, phenomena such as these are so subordinate to the more complex manifestations of life that they are apt to be overlooked; but they exist nevertheless. The mere nutrition of each part of the body in man or in the higher animals, is performed after a fashion which is strictly analogous to that which holds good in the case of a vegetable cell, or a rhizopod ; or, in other words, the life of each anatomical element in a complex structure, like the human body, resembles very closely the life of what in the lowest organisms constitutes the whole being. For example, the thin scaly covering or epidermis, which forms the outér part of a man’s skin, is made up of minute cells, which, when living, are composed in part of pro- toplasm, and which are continually wearing away and. being replaced by new similar elements from beneath ; and this process of quick waste and repair could only take place under the very complex conditions of nutrition which exist in man. One working part of the organism of an animal is so inextricably interwoven with that of another, that any want or defect in one, is soon or immediately felt by the whole ; and the epidermis, which only subserves a mechanical function, would be altered very soon by any defect in the more essential parts concerned in circulation, respiration, &c. But if we take simply the life-history of one of the small cells which constitute the epidermis, we find that it absorbs nourishment from the parts around, grows, and developes in a manner analogous to that which
22 STRUCTURAL COMPOSITION OF HUMAN BODY.
belongs to a cell which constitutes part of a vegetable structure, or even a cell which by itself forms an indepen- dent being. |
Remembering, however, the invariable presence of a living albuminous matter or protoplasm of apparently identical composition in all living tissues, animal and vegetable, we must not forget that its relations to the parts with which it is incorporated are still very doubtfully known; and all theories concerning it must be considered only tentative and of uncertain stability.
Among the anatomical elements of the human body, some appear, even with the help of the best microscopic apparatus, perfectly uniform and simple: they show no trace of structure, z.¢., of being composed of definitely arranged dissimilar parts. These are named simple, structureless, or amorphous substances. Such is the simple membrane which forms the walls of most primary cells, of the finest gland- ducts, and of the sarcolemma of muscular fibre; and such | is the membrane enveloping the vitreous humour of the eye. Such also, having a dimly granular appearance, but no really granular structure, is the intercellular sub- stance of the so-called hyaline cartilage.
In the parts which present determinate structure, certain primary forms may be distinguished, which, by their various modifications and modes of combination make up the tissues and organs of the body. Such are, I. Gra- nules or molecules, the simplest and minutest of the primary forms. ‘They are particles of various sizes, from immea- surable minuteness to the 10,000th of an inch in diameter; of various and generally uncertain composition, but usually so affecting light transmitted through them, that at dif- ferent focal distances their centre, or margin, or whole substance, appears black. From this character, as well as from their low specific gravity (for in microscopic examina- tions they always appear lighter than water), and from their solubility in ether when they can be favourably
NUCLEI. 23
tested, it is probable that most granules are formed of fatty or oily matter; or, since they do not coalesce as minute drops of oil would, that they are particles of oil coated over with albumen deposited on them from the - fluid in which they float. In any fluid that is not too viscid, they exhibit the phenomenon of molecular motion, shaking and vibrating incessantly, and sometimes moving through the fluid, probably, in great measure, under the influence of external vibration.
Granules may be either free, as in milk, chyle, milky serum, yelk-substance, and most tissues containing cells with granules; or enclosed, as are the: granules in nerve-corpuscles, gland-cells, and epithelium-cells, the pigment granules in the pigmentum nigrum and me- dullary substance of the hair; or imbedded, as are the granules of phosphate and carbonate of lime, in bones and teeth.
_ 2. Nuclei, or cytoblasts (fig. 1, 6), appear to be the simplest elementary structures, next to granules. They were thus - named in accordance with the hypothesis that they are always connected with cells, or tissues formed from cells, and that in the development of these, each nucleus is the germ or centre around which the cell is formed. The hypothesis is only partially true, but the terms based on it are too familiarly accepted to make it advisable to change them till some more exact and comprehensive theory is formed. |
Of the corpuscles called nuclei some are minute cellules or vesicles, with walls formed of simple membrane, enclos- ing often one or more particles, like minute granules, called nucleoli (fig. 1,'c). Other nuclei, again, appear to be simply small masses of protoplasm, with no trace of vesicular structure.
One of the most general characters of the nucleus, and the most useful in microscopic examinations, is, that it is neither dissolved nor made transparent by acetic acid, but
24 STRUCTURAL COMPOSITION OF HUMAN BODY.
acquires, when that fluid is in contact with it, a darker and more distinct outline. It is commonly, too, the part of the mature cell which is capable of being stained by an ammo- niacal solution of carmine—the test, it may be remarked,
by which, according to Dr. Beale, protoplasm or germinal matter may be always known.
Nuclei may be either free or attached. ree nuclei are such as either float in fluid, like those in some of the secre- tions, which appear to be derived from the secreting cells of the glands, or lie loosely embedded in solid substance, as in the grey matter of the brain and spinal cord, and most abundantly in some quickly-growing tumours. Aiétached nuclet are either closely imbedded in homogeneous pellucid substance, as in rudimental cellular tissue ; or are fixed on the surface of fibres, as on those of organic muscle and organic nerve-fibres ; or are enclosed in cells, or in tissues formed by the extension or junction of cells. Nuclei en- closed in cells appear to be attached to the inner surface of the cell-wall, projecting into the cavity. . Their position in relation to the centre or axis of the cell is uncertain; often when the cell lies on a flat or broad surface, they appear central, as in blood corpuscles, epithelium-cells, whether tesselated or cylindrical; but, perhaps, more often their position has no regular relation to the centre of the cell. In most instances, each cell contains only a single nucleus; but in cartilage, especially when it is growing or ossifying, two or more nuclei in each cell are common; and the development of new cells is often effected. by a division or multiplication of nuclei in the cavity of a parent cell; as in
the primary blood-cells of the embryo in the germinal
vesicle, and others.
When cells extend and coalesce, so that their walls form tubes or sheaths, the nuclei commonly remain attached to the inner surface of the wall. Thus they are seen imbedded n the walls of the minutest capillary blood-vessels of, for example, the retina and brain; in the sarcolemma of
at ert’ ela
pi sosieke Ere
CELLS. 26
_ transversely striated muscular fibres; and in minute gland- tubes.
Nuclei are most commonly oval or round, and do not generally conform themselves to the diverse shapes which the cells assume; they are altogether less variable ele- ments, even in regard, to size, than the cells are, of which fact one may see a good example in the uniformity of the nuclei in cells so multiform as those of epithelium. . But sometimes they appear to be developed into filaments, elongating themselves and becoming solid, and uniting end.to end for greater length, or by lateral branches to form a network. So, according to Henle, are formed the filaments of the striated and fenestrated coats of arteries; and, according to Beale, the so-called connective tissue cor- puscles are to be considered branched nuclei, formed of protoplasm or germinal matter.
3. Cells.—The word ‘‘ cell’’ of course implies strictly a hollow body, and the term was a sufficiently good one when all so-called cells were considered to be small bags with a membranous envelope, and more or less liquid contents. Mathy bodies, however, which are still called cells do not answer to this description, and the term, there- fore, if taken in its literal signification, is very apt to lead astray, and, indeed, very frequently does so. It is too widely used, however, to be given up, at least for the present, and we must therefore consider the term to indi- cate, either a membranous closed bag with more or less liquid contents, and almost always a nucleus; or a small semi- solid mass of protoplasm, with no more definite boundary- wall than such as has been formed by a condensation of its outer layers, but with, most commonly, a small granular substance in the centre, called, as in the first place, a nucleus. In both cases the nucleus may contain a nucleolus. Fat cells (fig. 11) are examples of the first kind of cells ; white blood-corpuscles (fig. of the second.
The cell-wall, when there one, never presents any
26 STRUCTURAL COMPOSITION OF HUMAN BODY.
appearance of structure: it appears sometimes to be an albuminous substance; sometimes a horny matter, as in thick and dried cuticle. In almost all cases (the dry cells of horny tissue, perhaps, alone excepted) the cell-wall is made transparent by acetic acid, which also penetrates into the interior and distends it, so that it can hardly be discerned. But in such cases the cell-wall is usually not dissolved ; it may be brought into view again by merely neutralizing the acid with soda or potash.
The simplest shape of cells, and that which is prokably the normal shape of the primary cell, is oval or spheroidal, as in cartilage-cells and lymph-corpuscles; but in many in- stances they are flattened and discoid, as in the red blood- corpuscles (fig. 26) or scale-like, as in the epidermis and tesselated epithelium (fig. 2). By mutual pressure they may become many-sided, as are most of the pigment-cells of the choroidal pigmentum nigrum (fig. 12), and those in close-textured adipose tissue; they may assume a conical or cylindriform or prismatic shape, as in the varieties of cylinder-epithelium (fig. 4); or be caudate, as in certain bodies in the spleen; they may send out exceedingly fine processes in the form of vibratile cilia (fig. 6), or larger processes, with which they become stellate, or variously caudate, as in some of the ramified pigment-cells of the choroid coat of the eye (fig. 13).
The contents of all living cells, including the nucleus, are formed in a greater or less degree of protoplasm,—less as the cell grows older. But, besides, cells contain matters almost infinitely various, according to the position, office, and age of the cell. In adipose tissue they are the oily matter of the fat; in gland-cells, the contents are the proper substance of the secretion, bile, semen, &c., as the case may be; in pigment-cells they are the pigment-gra- nules that give the colour; and in the numerous instances in which the cell-contents can be neither seen because they are pellucid, nor tested because of their minute quantity,
INTERCELLULAR SUBSTANCE. 27
they are yet, probably, peculiar in each tissue, and con- stitute the greater part of the proper substance of each. Commonly, when the contents are pellucid, they contain granules which float in them; and when water is added and the contents are diluted, the granules display an active molecular movement within the cavity of the cell. Such a movement may be seen by adding water to mucus-, or granulation-corpuscles, or to those of lymph. In a few cases, the whole cavity of the cell is filled with granules: it is so in yelk-cells and milk-corpuscles, in the large diseased corpuscles often found among the products of inflammation, and in some cells when they are the seat of extreme fatty degeneration. All cells containing abundant granules appear to be either lowly organized, as for nutri- ment, ¢.g., yelk-cells, or degenerate, ¢.g., granule-cells of inflammation, or of mucus. The peculiar contents of cells may be often observed to accumulate first around or di- rectly over the nuclei, as in the cells of black pigment, in those of melanotic tumours, and in those of the liver during - the retention of bile.
Intercellular*substance is the material in which, in certain tissues, the cells are imbedded. Its quantity is very variable. In the finer epithelia, especially the columnar epithelium on the mucous membrane of the intestines, it can be just seen filling the interstices of the close-set cells; here it has no appearance of structure. In cartilage and bone, it forms a large portion of the whole substance of the tissue, and is either homogeneous and finely granular (fig. 14), or osseous, or, as in fibro-cartilage, resembles fine fibrous tissue (fig. 15). In some cases, the cells are very loosely connected with the intercellular substance, and may be nearly separated from it, as in fibro-cartilage: but in some their walls seem amalgamated with it.
The foregoing may be regarded as the simplest, and the nearest to the primary forms assumed in the organization of animal matter; as the states into which this passes in
28 - STRUCTURAL COMPOSITION OF HUMAN BODY.
becoming a solid tissue living or capable of life. By the further development of tissue thus far organized, higher or secondary forms are produced, which it will be sufficient in this place merely to enumerate. Such are,
4. Filaments, or jfibrils—Threads of exceeding fineness, from 5;1,,th of an inch upwards. Such filaments are cylindriform, as are those of the striated muscular and the fibro-cellular or areolar tissue (fig. 8); or flattened, as are those of the organic muscles. Filaments usually lie | in parallel fasciculi, as in muscular and tendinous tissues ; but in some instances are matted or reticular with branches and intercommunication, as are the filaments of the middle coat, and of the longitudinally-fibrous coat of arteries; and in other instances, are spirally wound, or very tortuous, as in the common fibro-cellular-tissue (fig. 9).
5. Fibres in the instances to which the name is commonly applied are larger than filaments or fibrils, but are by no essential general character distinguished from them. The flattened band-like fibres of the coarser varieties of organic muscle or elastic tissue (fig. 10) are the simplest examples of this form; the toothed fibres of the crystalline lens are more complex; and more compound, so as hardly to permit of being classed as elementary forms, are the striated mus- cular fibres, which consist of bundles of filaments enclosed in separate membranous sheaths, and the cerebro-spinal nerve-fibres, in which similar sheaths enclose apparently two varieties of nerve substance.
6. Tubules are formed of simple, or structureless mem- brane, such as the investing sheaths of striated muscular and cerebro-spinal nerve-fibres, and the basement mem- brane or proper wall of the fine ducts of secreting glands; or they may be formed, as in the case of the minute capil- lary lymph and blood-vessels, by the apposition, edge to edge, in a single layer, of. variously shaped flattened cells (fig. 48).
With these simple materials, the various parts of the
Yo 7 ——— ————————
EPITHELIUM. 29
s
body are built up; the more elementary tissues being, so |
to speak, first compounded of them; while these again are variously mixed and interwoven to form more intricate combinations. Thus are constructed epithelium and its modifications, connective tissue, fat, cartilage, bone, the fibres of muscle and nerve, etc. ; and these again, with the more simple structures before mentioned, are used as mate- rials wherewith to form arteries, veins, and lymphatics, secreting and vascular glands, lungs, heart, liver, and other parts of the body.
CHAPTER IV.* STRUCTURE OF THE ELEMENTARY TISSUES.
Epithelium.
OnE of the simplest of the elementary structures of which the human body is made up, is that which has received the name of Epithelium. Composed of nucleated cells which are arranged most commonly in the form of a continuous membrane, it lines the free surfaces both of the inside and outside of the body, and its varieties, with one exception, have been named after the shapes which the individual cells in different parts assume. Classified thus, Epithelium presents itself under four principal forms, the characters of each of which are distinct enough in well-marked ex- amples; but when, as frequently happens, a continuous
* The following Chapter, containing an outline-description of the elementary tissues, has been inserted for the convenience of students. For a much fuller and better account, the reader may be referred to Dr, Sharpey’s admirable descriptions in Quain’s Anatomy.
’
lye ELEMENTARY TISSUES.
surface possesses at different parts two or more different epithelia, there is a very gradual transition from one to the other.
1. The first and most common variety is the squamous or tesselated epithelium (figs. I and 2), which is composed of flat, oval, roundish, or polygonal nucleated cells, of various size, arranged in one, or in many superposed layers. Arranged in several superposed layers this form of
Fig. 1.* Fig. 2.*
epithelium covers the skin, where it is called the Epidermis, and is spread over the mouth, pharynx, and csophagus, the conjunctiva covering the eye, the vagina, and entrance of the urethra in both sexes; while, as a single layer the same kind of epithelium lines the interior of most of the serous and synovial sacs, and of the heart, blood-vessels, and lymph-vessels. é
2. Another variety of epithelium named spheroidal, from the usually more or less rounded outline of the cells com-
* Fig. 1. Fragment of epithelium from a serous membrane (peri- toneum) ; magnified 410 diameters. a. cell; 0. nucleus; c. nucleoli (Henle).
+ Fig. 2. Epithelium scales from the inside of the mouth ; magnified 260 diameters (Henle).
Se
ee ot ee Se
see 2s
fe dt
EPITHELIUM. 31
posing it (d, fig. 3), is found chiefly lining the interior of the ducts of the compound glands, and more or less completely filling the small sacculations or acini, in which they ter- minate. It commonly indeed occupies the true secreting parts of all glands, and hence is sometimes called glandular epithelium (b,c, and d, fig. 3). Often, from mutual pressure,
Fig. 3.* *
the cells acquire a polygonal outline. From the fact, how- ever, of the term spheroidal epithelium being a generic one for almost all gland-cells, the shapes and sizes of the cells composing this variety of epithelium are, as might be ex- pected, very diverse in different parts of the body.
3. The third variety is the cylindrical or columnar
* Fig. 3. The gastric glands of the human stomach (magnified). a, deep part of a pyloric gastric gland (from Kolliker) ; the cylindrical epithelium is traceable to the cecal extremities. 06 and ¢, cardiac gastric glands (from Allen Thomson) ; 8, vertical section of a small portion of the mucous membrane with the glands magnified 30 diameters ; ce, deeper portion of one of the glands, magnified 65 diameters, showing a slight division of the tubes, and a sacculated appearance produced by the large glandular cells within them ; d, cellular elements of the cardiac glands magnified 250 diameters.
32 ELEMENTARY TISSUES.
epithelium (figs. 4 and 5), which extends from the cardiac
orifice of the stomach along the whole of the digestive canal to the anus, and lines the principal gland-ducts which
open upon the mucous surface of this tract, sometimes throughout their whole extent (a, fig. 3), but in some cases only atthe part nearest to the orifice (o and). It is also
Fig. 5.+
Mir, By oe Sait
found in the gall-bladder and in the greater portion of the urethra, and in some other parts, as the duct of the parotid gland and of the testicle. It is composed of oblong cells closely packed, and placed perpendicularly to the surface they cover, their deeper or attached extremities being most
* Fig. 4. Cylindrical epithelium from intestinal villus of a rabbit ; magnified 300 diameters (from Kolliker).
{ Fig. 5. Cylinders of the intestinal epithelium (after Henle) :— B. from the jejunum; c. cylinders of the intestinal epithelium as seen when looking on their free extremities ; D. ditto, as seen ona transverse section of a villus.
a OG REP TS Pt
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EPITHELIUM. 33
commonly smaller than those which are free. Each of such cells encloses, at nearly mid distance between its base and apex, a flat nucleus with nucleoli (x, fig. 5); the nuclei being arranged at such heights in contiguous cells as not to interfere with each other by mutual pressure. |
4. The fourth variety of epithelium cells, usually cylindrical, but occasionally of some other shape, are pro- vided at their free extremities with several fine pellucid pliant processes or cilia (figs. 6 and 7). This form of epi- thelium lines the whole respiratory tract of mucous mem- brane and its prolongations. It occurs also in some parts
Fig. 6.*
of the generative apparatus; in the male, lining the vasa efferentia of the testicle, and their prolongations as far as the lower end of the epididymis; and, in the female com- mencing about the middle of the neck of the uterus, and ex- tending to the fimbriated extremities of the Fallopian tubes, _ and for a short distance along the peritoneal surface of the latter. A tesselated epithelium, with scales partly covered with cilia, lines, in great part, the interior of the cerebral ventricles,
If a portion of ciliary mucous membrane from a living or recently dead animal be moistened and examined with a microscope, the cilia are observed to be in constant motion,
* Fig. 6. Spheroidal ciliated cells from the mouth of the frog ;
magnified 300 diameters (Sharpey). + Fig. 7. Columnar ciliated epithelium cells from the human nasal membrane ; magnified 300 diameters (Sharpey). D
34 ELEMENTARY TISSUES.
moving continually backwards and forwards, and alter- nately rising and falling with a lashing or fanning movement. The appearance is not unlike that of the waves in a field of corn, or swiftly running and rippling water. The general result of their movements is to pro- duce a continuous current in a determinate direction, and this direction is invariably the same on the same surface, being usually in the case of a cavity towards its external orifice.
Uses of Epithelium.—The various kinds of epithelium serve one general purpose, namely, that of protecting, and at the same time rendering smooth, the surfaces on which they are placed. But each, also, discharges a special office in relation to the particular function of the membrane on which it is placed.
In mucous and synovial membranes it is highly probable
_ that the epithelium-cells, whatever be their forms and what- ever their other functions, are the organs in which by a regular process of elaboration and secretion, such as will be afterwards described, mucus and synovial fluid are formed and discharged. (See chapter on Secretion).
Ciliated epithelium has another superadded function. By means of the current set up by its cilia in the air or fluid in contact with them, it is enabled to propel the fluids or minute particles of solid matter, which come within the range of its influence, and aid in their expulsion from the body. In the respiratory tract of mucous mem- brane the current set up in the air may also assist in the diffusion and change of gases, on which the due aération of the blood depends. In the Fallopian tube the direction of the current excited by the cilia is towards the cavity of the uterus, and may thus be of service in aiding the progress of the ovum. Of the purposes served by the cilia which line the ventricles of the brain nothing is known.
The nature of ciliary motion and the circumstances by
AREOLAR TISSUE. 35
which it is influenced will be considered hereafter. (See chapter on Motion.)
Epithelium is devoid of blood-vessels, and lymphatics. The cells composing it are nourished by absorption of nutrient matter from the tissues on which they rest; and as they grow old they are cast off and replaced by new cells from beneath.
Areclar, Cellular, or Connective Tissue.
This tissue, which has received various names according to the qualities which seemed most important to the authors who have described it, is met with in some form or otherin every region of the body; the areolar tissue of one dis- trict being, directly or indirectly, continuous with that of
Fig. 8.*
all others. In most parts of the body this structure 2 contains fat, but the quantity of the latter is very variable, and in some few regions it is absent altogether (p. 38).
« Fig. 8. -Filaments of areolar tissue, in larger and smaller bundles, as seen under a magnifying power of 400 diameters (Sharpey). D 2
36 ELEMENTARY TISSUES.
Probably no nerves are distributed to areolar tissue itself, although they pass through it to other structures; and although blood-vessels are supplied to it, yet they are sparing in quantity, if we except those destined for the fat which is held in its meshes.
Under the microscope areolar tissue seems composed of a mesh-work of fine fibres of two kinds. The first, which makes up the greater part of the tissue, is formed of very fine white structureless fibres, arranged closely in bands and bundles, of wave-like appearance when not stretched out, and crossing and intersecting in all directions (fig. 8). The ' second kind, or the yellow elastic fibre (fig. 10), has a much
Fig. 9.*
sharper and darker outline, and is not arranged in bundles, but intimately mingled with the first variety, as more or less separate and well-defined fibres, which twist among and around the bundles of white filaments (fig. 9). Sometimes
* Fig. 9. Magnified view of areolar tissues (from different parts) treated with acetic acid. The white filaments are no longer seen, and the yellow or elastic fibres with the nuclei come into view. At ¢, elastic fibres wind round a bundle of white fibres, which, by the effect
ofthe acid, is swollen out between the turns, Some connective tissue.
corpuscles are indistinctly represented in c (Sharpey).
Ee ee ee ee ee
AREOLAR TISSUE. 37
the yellow fibres divide at their ends and anastomose with each other by means of the branches. Among the fibrous parts of areolar or connective tissue are little nuclear bodies of various shapes, called connective-tissue corpuscles (fig. 9, c.), some of which are prolonged at various points of their outline into small processes which meet and join others like them proceeding from their neighbours.
The chief functions of areolar tissue seem to consist in the investment and mechanical support of various parts, and as a connecting bond between such structures as may need it. The connective-tissue corpuscles, which, accord- ing to Beale, are small branched particles of germinal matter or protoplasm, probably minister to the nutrition of the texture in which they are seated.
In various parts of the body, each of the two constituents of areolar tissue which have been just mentioned, may exist sepa- rately, or nearly so. ‘Thus ten- dons, fascize, and the like more or less inelastic structures, are formed almost exclusively of the white fibrous tissue, arranged ac- cording to the purpose required, either. in parallel bundles or membraneous meshes; while the yellow elastic fibres are found to make up almost alone such elas- tic structures as the vocal cords, the ligamenta subflava, etc., and to enter largely into the composition of the blood-vessels, the trachea, the lungs, and many other parts of the body.
Fig. 10.*
* Fig. 10. Elastic fibres from the ligamenta subflava, magnified about 200 diameters (Sharpey).
38 ELEMENTARY TISSUES.
Adipose Tissue.
In almost all regions of the human body a larger or smaller quantity of adipose or fatty tissue is present; the chief exceptions being the subcutaneous tissue of the eye- lids, penis and scrotum, the nymphe and the cavity of the cranium. Adipose tissue is also absent from the sub- stance of many organs, as the lungs, liver and others.
Fatty matter, not in the form of a distinct tissue, is also widely present in the body, as the fat of the liver and brain, of the blood and chyle, ete.
Adipose tissue is almost always found seated in areolar tissue, and forms in its meshes little masses of unequal size and irregular shape, to which the term, lobules, is commonly applied. Under the, microscope it is found to
Fig. 11.*
consist essentially of little vesicles or cells about =1,th or toth of an inch in diameter, each composed of a struc- tureless and colourless membrane or bag, filled with fatty matter which is liquid during life, but in part solidified after death. A nucleus is always present in some part or other of the cell-walli ; but in the ordinary condition of the
* Fig. 11. A small cluster of fat-cells; magnified 150 diameters (Sharpey).
PIGMENT-CELLS. 39
cell it is not easily or always visible. The ultimate cells are
held together by capillary blood-vessels; while the little clusters thus formed are grouped into small masses, and held so, in most cases, by areolar tissue. The oily matter contained in the cells is composed chiefly of the compounds of fatty acids with glycerin, which are named olein, stearin, and palmitin.
It is doubtful whether lymphatics or nerves are supplied to fat, although both pass through it on their way to other structures.
Among the uses of fat, these seem to be the chief :—
1. It serves as a store of combustible matter which may be re-absorbed into the blood when occasion re- quires, and being burnt, may help to preserve the heat of the body.
2. That part of the fat which is situate beneath the skin must, by its want of conducting power, assist in preventing undue waste of the heat of the body by escape from the surface.
3. As a packing material, fat serves very admirably to fill up spaces, to form a soft and yielding yet elastic mate- rial wherewith to wrap tender and delicate structures, or form a bed with like qualities on which such structures may lie, unendangered by pressure. As good examples of situations in which fat serves such purposes may be men- tioned the palms of the hands, and soles of the feet, and the orbits.
4. In the long bones, fatty tissue, in the form known as marrow, serves to fill up the medullary canal, and to sup- port the small blood-vessels which are distributed from it to the inner part of the substance of the bone.
Pigment. In various parts of the body there exists a considerable
quantity of dark pigmentary matter, ¢.g., in the choroid coat of the eye, at the back of the iris, in the skin, etc.
40 . ELEMENTARY TISSUES.
In all these cases the dark colour is due tothe presence of so-called pigment-cells. |
Pigment-cells are for the most part polyhedral (fig. 12) or spheroidal, although sometimes they have irregular processes, as shown in fig. 13. The cell-wall itself is colourless,—the dark tint being produced by small dark granules heaped closely together, and more or less con- cealing the nucleus, itself colourless, which each cell contains. The dark tint of the skin, in those of dark com- plexion and in the coloured races, is seated chiefly in the
Fig. 12.* Fig. 13.
epidermis, and depends on the presence of pigment-cells,
which, except in the presence of the dark granules in their
interior, closely resemble the colourless cells with which they are mingled. The pigment-cells are situate chiefly in the deep layer of the epidermis, or the so-called rete mucosum. (See chapter on the Skin.)
* Fig. 12. Pigment-cells from the choroid ; magnified 370 diameters.
(Henle). A, cells still cohering, seen on their surface ; a, nucleus indistinctly seen. In the other cells the nucleus is concealed by the
pigment granules. B, two cells seen in profile ; a, the outer or posterior
part containing scarcely any pigment.
+ Fig. 13. Ramified pigment cells, from the tissue of the choroid . coat ofthe eye ; magnified 350 diameters (after Kolliker). a, cells with pigment ; 4, colourless fusiform cells.
% = 4 E , i § ‘ : ‘ 5 s
ee ee ee ne Pa
CARTILAGE, | Cp ae
The pigmentary matter is a very insoluble compound of carbon, hydrogen, nitrogen and oxygen,—the carbon largely predominating ; besides, there is a small quantity of saline matter.
The uses of pigment in most parts of the body are not clear. In the eyeball it is evidently intended for the absorption of superfluous rays of light.
Cartilage.
Cartilage or gristle exists in different forms in the human body, and has been classified under two chief heads, namely, temporary and permanent cartilage; the former term being applied to that kind of cartilage which, in the foetus and in young subjects, is destined to be con- verted into bone. The varieties of permanent cartilage have been arranged in three classes, namely, the cellular, the hyaline, and the jibrous cartilages,—the last-named, being again capable of subdivision into two kinds, namely, elastic or yellow cartilage, and the so-called jibro- cartilage.
Elastic cartilage, however, contains fibres, and fibro- cartilage is more or less elastic; it will be well, therefore, for distinction’s sake to term those two kinds white fibro- cartilage and yellow fibro-cartilage respectively.
The accompanying table represents the classification of the varieties of cartilage :—
1. Temporary. A. Cellular. B. Hyaline. nee White fibro-cartilage. C. Fibrous: Yellow fibro-cartilage.
2. Permanent.
All kinds of cartilage are composed of cells imbedded in a substance ealled the matrix: and the apparent differences of structure met with in the various kinds of cartilage are more due to differences in the character of the matrix than of the cells. Among the latter, however, there is also considerable diversity of form and size.
42 ELEMENTARY TISSUES.
With the exception of the articular variety, cartilage is invested by a thin but tough and firm fibrous membrane called the perichondrium. On the surface of the articular cartilage of the foetus, the perichondrium is represented by a film of epithelium; but this is gradually worn away up to the margin of the articular surfaces, when by use the parts begin to suffer friction.
1. Cellular cartilage may be readily obtained from the external ear of rats, mice, or other small mammals. It is composed almost entirely of cells (hence its name), with little or no matrix. The latter, when present, consists of very fine fibres, which twine about the cells in various directions and enclose them in a kind of network. The cells are packed very closely together,—so much so that it is not easy in all cases to make out the fine fibres often encircling them.
Cellular cartilage is found in the human subject, only in early foetal life, when it constitutes the Chorda dor- salis. (See chapter on Genera- tion.) ~ 2. Hyaline cartilage is met with largely in the human body,—investing the articular ends of bones, and forming the costal cartilages, the nasal 'Y cartilages, and those of the larynx, with the exception of the epiglottis and cornicula laryngis. Like other cartilages it is composed of cells imbedded in a matrix (fig. 14). _
Fig. 14.*
_ * Fig. 14. A thin layer peeled off from the surface of the cartilage of the head of the humerus, showing flattened groups of cells. The
shrunken cell-bodies are distinctly seen, but the limits of the capsular
cavities, where they adjoin one another, are but faintly indicated. Magnified 400 diameters (after Sharpey).
Of ti eel
nigeria hh
er a te. uy Me ee, ee or and
4S p>
9h elie pes
CARTILAGE. 43
The cells, which contain a nucleus with nucleoli, are irregular in shape, and generally grouped together in patches. The patches are of various shapes and sizes, and placed at unequal distances apart. They generally appear flattened near the free surface of the mass of cartilage in which ‘they are placed, and more or less perpendicular to the surface in the more deeply seated portions.
The matrix in which they are imbedded has a dimly granular appearance, like that of ground glass.
In the hyaline cartilage of the ribs, the cells are mostly larger than in the articular variety, and there is a tendency to the development of fibres in the matrix. The costal cartilages also frequently become ossified in old age, as also do some of those of the larynx.
Temporary cartilage closely resembles the ordinary hyaline kind; the cells, however, are not grouped together after the fashion just described, but are more uniformly distributed throughout the matria.
Articular hyaline cartilage is reckoned among the so- called non-vascular structures, no blood-vessels being sup- plied directly to its own substance; it is nourished by those of the bone beneath. When hyaline cartilage is in thicker masses, as in the case of the cartilages of the ribs, a few blood-vessels traverse its substance. The distinction, however, between all so-called vascular and non-vascular parts, is at the best a very artificial one. (See chapter on Nutrition. ) |
Nerves are probably not supplied to any variety of cartilage.
Fibrous cartilage, as before mentioned, occurs under two chief forms, the yellow and the white fibro-cartilage.
Yellow fibro-cartilage is found in the external ear, in the epiglottis and cornicula laryngis, and in the eyelid. The cells are rounded or oval, with well-marked nuclei and nucleoli. The matrix in which they are seated is composed almost entirely of fine fibres, which form an intricate inter-
~
Aa ELEMENTARY TISSUES.
lacement about the cells, and in their general characters are allied to the yellow variety of fibrous tissue (fig. 15).
White fibro-cartilage, which is much more widely distri- buted throughout the body, than the foregoing kind, is - composed, like it, of cells and a matrix; the latter, however, being made up almost entirely of fibres closely resembling those of white fibrous tissue.
In this kind of fibro-car- tilage it is not unusual to find a great part of its mass composed almost exclusively of fibres, and deserving the name of cartilage only from the fact that in another por- tion, continuous with it, cartilage cells may be pretty freely distributed.
The different situations in which white fibro-cartilage is formed have given rise to the following classification :—
1. Inter-articular fibro-cartilage, e.g., the semilunar car- tilages of the knee-joint.
2. Circumferential or marginal, as on the edges of the acetabulum and glenoid cavity of the scapula.
3. Connecting, e.g., the inter-vertebral fibro-cartilages.
4. Fibro-cartilage is found in the sheaths of tendons, and sometimes in their substance. In the latter situation, the nodule of fibro-cartilage is called a sesamoid fibro-carti- lage, of which a specimen may be found in the tendon of the tibialis posticus, in the sole of the foot, and usually in the neighbouring tendon of the peroneus longus.
The uses of cartilage are the following :—in the joints, to form smooth surfaces for easy friction, and to act as a buffer, in shocks; to bind bones together, yet to allow a certain degree of movement, as between the vertebrae; to
* Fig. 15. Section of the epiglottis, magnified 380 diameters (Dr. Baly).
BONE. | 45
form a firm framework and protection, yet without undue stiffness or weight, as in the larynx and chest walls; to deepen joint-cavities, as in the acetabulum, yet not so as to restrict the movements of the bones; to be, where such qualities are required, firm, tough, flexible, elastic, and strong. et Structure of Bones and Teeth.
Bone is composed of earthy and animal matter in the proportion of about 67 per cent. of the former to 33 per cent. of the latter. The earthy matter is composed chiefly of phosphate of lime, but besides there is a small quantity, about 11 of the 67 per cent., of carbonate of lime, with minute quantities of some other salts. The animal matter is resolved into gelatine by boiling. The earthy and animal constituents of bone are so intimately blended and incorporated the one with the other, that it is only by chemical action, as for instance, by heat in one case, and by the action of acids in another, that they can be sepa- rated. Their close union, too, is further shown by the fact that when by acids the earthy matter is dissolved out, or, on other Fand, when the animal part is burnt out, the general shape of the bone is alike preserved.
To the naked eye there appear two kinds of structure in different bones, and in different parts of the same bone, namely, the dense or compact, and the cancellous tissue. Thus, in making a longitudinal section of a long bone, as the humerus or femur, the articular extremities are found capped on their surface by a thin shell of compact bone, while their interior is made up of the spongy or cancellous
tissue. The shaft, on the other hand, is formed almost
entirély of a thick layer of the compact bone, and this sur-
rounds a central canal, the medullary cavity—so called from
its containing the medulla or marrow (p. 39). ‘In the flat bones, as the parietal bone or the scapula, one layer of the cancellous structure lies between two layers of the
compact tissue, and in the short and irregular bones, as
those of the carpus and tarsus, the cancellous tissue alone
46 ELEMENTARY TISSUES.
fills the interior, while a thin shell of compact bone forms the outside. The spaces in the cancellous tissue are filled by a species of marrow, which differs considerably from that of the shaft of the long bones. It is more fluid, and of a reddish colour, and contains very few fat cells.
The surfaces of bones, except the parts covered with articular cartilage, are clothed by a tough fibrous mem- brane, the periosteum; and it is from the blood-vessels which are distributed first in this membrane, that the
Fig. 16.*
Pipes : SZ, “GZ =
\ dt ae
bones, especially their more compact tissue, are in great part supplied with nourishment,—minute branches from the periosteal vessels entering the little foramina on the surface of the bone, and finding their way to the Haversian canals, to be immediately described. The long bones are
* Fig. 16. Transverse section of compact tissue (of humerus) mag- nified about 150 diameters. Three of the Haversian canals are seen, with their concentric rings ; also the corpuscles or lacune, with the canaliculi extending from them across the direction of the lamelle. The Haversian apertures had got filled with débris in grinding down the section, and therefore appear black in the figure, which represents the object as viewed with transmitted light (after Sharpey).
a oe a ee ee ee sth Niet
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BONE. 47
supplied also by a proper nutrient artery, which entering at some part of the shaft so as to reach the medullary canal, breaks up into branches for the supply of the marrow, from which again small vessels are distributed to the inte- rior of the bone. Other small blood-vessels pierce the arti- cular extremities for the supply of the cancellous tissue. Notwithstanding the differences of arrangement just mentioned, the structure of all bone is found, under the microscope, to be essentially the same. Examined with a rather high power, its substance is found occupied by a multitude of little spaces, called lacune, with very minute ’ canals or canaliculi, as they are termed, leading from them, and anastomosing with similar little prolongations from other lacunee (fig. 16). In very thin layers: of bone, no other canals than these may be visible; but on making a transverse section of the compact tissue, ¢.g., of a long bone, as the humerus or ulna, the arrangement shewn in . fig. 16can be seen. The bone seems mapped out into small circular dis- tricts, at or about the centre of each of which is a hole, and around this an appearance as of concentric layers—the lacune and canaliculi fol- lowing the same concentric plan of distribution around the small hole in the centre, with which, indeed, they communicate. On making a longitudinal section, the central holes are found to be simply the cut extremities of small canals which run lengthwise through the bone (fig. 17), and
* Fig. 17. Haversian canals, seen in a longitudinal section of the compact tissue of the shaft of one of the long bones. a. Arterial canal ; b. Venous canal; ¢. Dilatation of another venous canal.
48 ELEMENTARY TISSUES.
are called Haversian canals, after the name of the physician, Clopton Havers, who first accurately described them.
The Haversian canals, the average diameter of which is ~1., of an inch, contain blood-vessels, and by means of them, blood is conveyed to all, even the densest parts of the bone; the minute canaliculi and lacunee absorbing nutrient maiter from the Haversian blood-vessels, and con- veying it still more intimately to the very substance of the bone which they traverse. The blood-vessels enter the Haversian canals both from without, by traversing the small holes which exist on the surface of all bones beneath the periosteum, and from within by means of small channels, which extend from the medullary cavity, or from the can- cellous tissue. According to Todd and Bowman, the arteries and veins usually occupy separate canals, and the veins which are the larger, often present, at irregular intervals, small pouch-like dilatations (fig. 17).
The lacune are occupied by nucleated cells, or, as Dr. Beale expresses it, minute portions of protoplasm or germinal matter; and there is every reason to believe that the lacunar cells are homologous with the corpuscles of the connective tissue, each little particle of protoplasm ministering to the nutrition of the bone immediately surrounding it, and one lacunar particle communicating with another, and with its surrounding district, and with the blood-vessels of the Haversian canals, by means of the minute streams of fluid nutrient matter which occupy the canaliculi.
Besides the concentric lamelle of bone tissue which surround the Haversian canal in the shaft of a long bone, are others, especially near the circumference, which surround the whole bone, and are arranged concentrically with regard to the medullary canal.
The ultimate structure of the lamelig appears to be reticular. If a thin film be peeled off the surface of a bone from which the earthy matter has been removed by acid,
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BONE. - - 49
and examined with a high power of the microscope, it will be found composed, according to Sharpey, of a finely reticular structure, formed appa- rently of very slender fibres decus-
sating obliquely, but coalescing at Up tii ie ny the points of intersection, as if here | TE ae the fibres were fused rather . than \ ma BRO woven together (fig. 18). ZnS SRP In many places these reticular Mine RCNA lamellee are perforated by tapering PSR. ES fibres, resembling in character the LUA AMOR ordinary white or rarely the elastic 4 ii HN fibrous tissue, which bolt the neigh- RWRRN DRY
bouring lamelle together, and may be drawn out when the latter are torn asunder (fig. 19). -
Bone is developed after two different fashions. In one, the tissue in which the earthy matter is laid down is a membrane, composed mainly of fibres and granular cells, like imperfectly developed connective-tissues.. Of this kind of ossification in membrane, the flat bones of the skull are examples. «in the other, and much more common case, of which a long bone may be cited as an instance, the ossification takes place in cartilage.
In most. bones ossification begins at more than one point; and from these centres of ossification, as they are called, the process of deposition of calcareous matter advances in all directions. Bones grow by constant de- velopment of. the cartilage or membrane between these centres of ossification, until by the process of calcification advancing at a quicker rate than the development of the softer structures, the bone becomes impregnated through-
* Fig. 18. Thin layer peeled off from a softened bone, as it appears under a magnifying power of 400.—This figure, which is intended to represent the reticular structure of a lamella, gives a better idea of the object when held rather farther off than usual from the eye (from
Sharpey). E
50 | ELEMENTARY TISSUES.
out with calcareous matter, and can grow no more. In the long bones the main centres of ossification are seated at the middle of’ the shaft, and at each of the extremities. Increase of the length of bones, therefore, occurs at the part which intervenes between the ossifying centre in the shaft
Fig. 19.*
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and that at each extremity; while increase in thickness takes place by the formation of layers of osseous tissue beneath the periosteum. The former is an example of ossification in cartilage; the latter of ossification in membrane. Teeth.—A tooth is generally described as possessing a crown, neck, and fang, or fangs. The crown is the portion which projects beyond the level of the gum. The neck is that constricted portion just below the crown which is
* Fig. 19. Lamelle torn off from a decalcified human parietal bone at some depth from the surface. «, a lamella, showing reticular fibres ; b, 6, darker part, where several lamellz are superposed ; ¢, ¢, perforating fibres. Apertures through which perforating fibres had passed, are seen especially in the lower part, a, a, of the figure. Magnitude as seen - under a power of 200, but not drawn to a scale (from a drawing by : Dr. Allen Thomson).
TEETH. 51
embraced by the free edges of the gum, and the fang includes all below this.
On making a longitudinal section through the centre of a tooth (figs. 20 and 21), it is found to be princi- pally composed of a hard matter, dentine or ivory ; while in the centre this (22% dentine is hollowed out into a cavity resembling in general shape the outline of the tooth, and called the pulp-cavity, from its containing a very vascular and sensi- tive little mass composed of connective tissue, blood-vessels and nerves, which is called the tooth-pulp. The pulp is continuous below, through an opening at the end of the fang, with the mucous membrane of the gum. Capping that part of the dentine which projects beyond the level of the gum, is a layer of very hard calcareous matter, the enamel, while sheathing the portion of dentine which is beneath the level of the gum, is a layer of true bone, called the cement or crusta petrosa. At the neck of the tooth the cement is exceedingly thin, but it gradually becomes thicker as it approaches and covers the lower end or apex of the _ fang.
Dentine or ivory in chemical composition closely re- sembles bone. It contains, however, rather less animal matter; the proportion in 100 parts being about 28 of animal matter to 72 of earthy. The former, like the animal matter of bone, may be resolved into gelatin by boiling. The
4
* Fig. 20. Sections of an Incisor and Molar Tooth.—The longitudinal sections show the whole of the pulp-cavity in the incisor and molar teeth, its extension upwards within the crown, and its prolongation downwards into the fangs, with the small aperture at the point of each : these and the cross section show the relation of the dentine and enamel.
E 2
52 ELEMENTARY TISSUES.
earthy matter is made up chiefly of phosphate of lime, with a small portion of the carbonate, and traces of some other salts.
- Under the microscope, dentine is seen to be finely channelled by a mul- titude of fine tubes, which, by their inner ends, communicate with the pulp-cavity, and by their outer extre- mities come into contact with the under part of the enamel and cement, and sometimes even penetrate them for a greater or less distance. In their course from the pulp-cavity to the surface of the dentine, these mi- nute tubes form gentle and nearly parallel curves, and divide and sub- divide dichotomously, but without much lessening of their calibre until they are approaching their peripheral termination. From their sides proceed other exceedingly minute secondary canals, which extend into the dentine between the tubules.
The tubules of the dentine, the average diameter of which at their inner and larger extremity is ,=);>, of an inch, contain fine prolongations from the tooth-pulp which give the dentine a certain faint sensitiveness under ordinary circumstances, and, without doubt, have to do also with its nutrition.
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(after Retzius)—1, the ivory or dentine, showing the direction and ~
primary curves of the dental tubuli; 2, the pulp-cavity, with the small apertures of the tubuli into it ; 3, the cement or crusta petrosa, covering the fang as high as the border of the enamel at the neck, exhibiting lacune ; 4, the enamel resting on the dentine ; this has been worn away by use from the upper part.
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TEETH. 53
The enamel, which is by far the hardest portion of a tooth, is composed, chemically, of the same elements that enter into the composition of dentine and bone. Its animal matter, however, amounts only to about 2 or 3 per cent.
Examined under the microscope, _ Fig. 22.* | enamel is found composed of fine 7 hexagonal fibres (figs. 22 and 23), which are set on end on the sur- face of the dentine, and fit into corresponding depressions in the same. ‘They radiate in such a manner from the dentine, that at the top of the tooth they are more or less vertical, while towards the sides they tend to the horizontal direction. Like the dentine-tu- bules, they are not straight, but disposed in wavy and parallel curves. The fibres are marked by transverse lines, and are mostly solid, but some of them contain a MIG IA A very minute canal. Te - yy, PRT
The enamel itself is coated on Gb; | the outside by a very thin calcified WN) | Yi,
membrane, sometimes termed the : i ; cuticle of the enamel.
The crusta petrosa, or cement, is composed of true bone, and in it are lacune and canaliculi which sometimes communicate with the outer finely-branched ends of the dentine-tubules.
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* Fig. 22. Thin section of the enamel and a part of the dentine {from K6lliker) *£2. a, cuticular pellicle of the enamel ; 0, enamel fibres, or columns with fissures between them and cross strie ; ¢, larger cavities in the enamel, communicating with the extremities of some of
the tubuli (¢).
54 ELEMENTARY TISSUES.
Development of T. veth.—The teeth are developed after the |
following manner :—Along the free edge of the tooth- less gum in the foetus, there extends a groove, or small
¥G 70
trench, the primitive dental groove (Goodsir), and, from the bottom of this, project ten small processes of mucous mem- brane, or papille, containing blood-vessels and nerves. As these papille grow up from below, the edges of the small trench begin to grow in towards each other, and over- shadow them, at the same time that each papilla is cut off from its neighbour by the extension of a partition wall from the gum, which grows in from each side to separate the one from the other. Thus closed in above and all around, each dental papilla is at length contained in a separate sac, and gradually assumes the character of a tooth by deposition on its surface of the various hard matters which have been just enumerated as composing the greater part of a tooth’s substance. The small vascular
* Fig. 23. Enamel fibres ( from Ko6lliker) **°. A, fragments and single fibres of the enamel, isolated by the action of hydrochloric acid. B, surface of a small fragment of enamel, showing the hexagonal ends of the fibres.
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DEVELOPMENT OF TEETH. 55
papilla is gradually encroached upon and imprisoned by the calcareous deposit, until only a small part of it is left as the tooth-pulp, which remains shut up in the harder substance, with only the before-mentioned small communi- cation with the outside, through the end of the fang. In this manner the first set of teeth,,or the milk-teeth, are formed; and each tooth, by degrees developing, presses at length on the wall of the sac enclosing it, and causing its absorption, is cut, to use a familiar phrase.
The temporary or milk-teeth, having only a very limited term of existence, gradually decay and are shed, while the permanent teeth push their way from beneath, by gradual increase and development, so as to succeed them.
The temporary teeth are ten in each jaw, namely, four incisors, two canines, and four molars, and are replaced by ten permanent teeth, each of which is developed from a small sac set by, so to speak, from the sac of the temporary tooth which precedes it, and called the cavity of reserve. The number of the permanent teeth is, however, increased to sixteen, by the development of three others on each side of the jaw aftermuch the same fashion as that by which the milk teeth were themselves formed. The beginning of the development of the permanent teeth of course takes place long before the cutting of those which they are to succeed; one of the first acts of the newly-formed little dental sac of a milk-tooth being to set aside a portion of itself as the germ of its successor.
The following formula shows, at a glance, the com- parative arrangement and number of the temporary and permanent teeth :—
MO. CA. IN. CA. MO, ) Upper re es" fi'-o4 80 Temporary Teeth . = 20 Lower 2 4° 4k i
MO.BI. CA. IN. CA. BI. MO. Upper 3 2 I 4 I 2 3=16
Permanent Teeth. 32
Lower 3 2 1t-.4° 1 12 3=16
56 | THE BLOOD.
From this formula it will be seen that the two bicuspid teeth in the adult are the successors of the two molars in thechild. They differ from them, however, in some respects, the temporary molars having a stronger likeness to the permanent than to their immediate descendants, the so-called bicuspids. The temporary incisors and canines differ but little, except in their smaller size, from their . successors.
CHAPTER V. THE BLOOD.
ALTHOUGH it may seem, in some respects, unadvisable to describe the blood before entering upon the physiology of those subservient processes which have for their end or purpose its formation and development, yet there are many reasons for taking such a course, and we may there- fore at once proceed to consider the structural and chemical composition of this fluid.
Wherever blood can be seen under a moderately high microscope-power as it flows in the vessels of a living part, it appears a colourless fluid containing minute coloured particles. The greater part of these particles are red, when seen en masse, and they are the source of the colour which, so far as the naked eye can see, belongs to every part of the blood alike. The colourless fluid is named liquor sanguinis ; the particles are the blood corpuscles or blood-cells. The struc- tural composition of the blood may be thus expressed :—
, Clot (containing also Liquid Blood Corpuscles . * * / more or less serum). rqure 21000" +) Liquor Sanguinis § Fibrin \ or Plasma. Serum When blood flows from the living body, it is a thickish heavy fluid, of a bright scarlet colour when it comes from
an artery ; deep purple, or nearly black, when it flows from
ODOUR OF BLOOD. 57
a vein. Its specific gravity at 60° F. is, on an average, 1055, that of water being reckoned as 1000; the extremes consistent with health being 1050 and 1059. Its tempera- ture is generally about 100° F.; but it is not the same in all parts of the body. ‘Thus, while the stream is slightly warmed by passing through the liver and some other parts, itis slightly cooled, according to Bernard, by traversing the capillaries of the skin. The temperature of blood in the left side of the heart is, again 1° or 2° higher than in the right (Savory).
The blood has a slight alkaline reaction; and emits an odour similar to that which issues from the skin or breath of the animal from which it flows, but fainter. The alka- -line reaction appears to be a constant character of blood in all animals and under all circumstances. An exception has been supposed to exist in the case of menstrual blood ; but the acid reaction which this sometimes presents is due to the mixture of an acid mucus from the uterus and vagina. Pure menstrual blood, such as may be obtained with a speculum, or from the uteri of women who die during menstruation, is always alkaline, and resembles ordinary blood. According to Bernard, blood becomes spontaneously acid after removal from the body, ORE to conversion of its sugar into lactic acid.
The odour of blood is easily perceived in the watery vapour, or hulitus as it is called, which rises from blood just drawn; it may also be set free, long afterwards, by adding to the blood a mixture of equal parts of sulphuric acid and water. It is said to be not difficult to tell, by the likeness of the odour to that of the body, the species of domestic animal from which any specimen of blood has been taken: the strong odour of the pig or cat, and the peculiar milky smell of the cow, are especially easy to be thus discerned in their blood (Barruel).
58 THE BLOOD.
Quantity of Blood.
Only an imperfect indication of the whole quantity of blood in the body is afforded by measurement of that which escapes, when an animal is rapidly bled to death, inasmuch as a certain amount always remains in the blood- vessels. In cases of less rapid bleeding, on the other hand, when ‘life is more prolonged, and when, therefore, sufficient time elapses before death to allow some absorp- tion into the circulating current of the fluids of the body (p. 84), the whole quantity of blood that escapes may be greater than the whole average amount naturally present in the vessels.
Various means have been devised, therefore, for obtain- ing a more accurate estimate than that which results from merely bleeding animals to death.
Welcker’s method is the following. An animal is.
rapidly bled to death, and the blood which escapes is col- lected and measured, The blood remaining in the smaller vessels is then removed by the injection of water through them, and the mixture of blood and water thus obtained, is also collected. The animal is then finely minced, and infused in water, and the infusion is mixed with the com- bined blood and water previously obtained. Some of this fluid is then brushed on a white ground, and the colour compared with that of mixtures of blood and water whose proportions have been previously determined by measure- ment. In this way the materials are obtained for a fairly exact estimate of the quantity of blood actually existing in the body of the animal experimented on.’
Another method (that of Vierordt) consists in estimating the amount of blood expelled from the ventricle, at each beat of the heart, and multiplying this quantity by the number of beats necessary for completing the ‘round’ of the circulation. This method is ingenious, but open to various objections, the most conclusive being the uncer-
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QUANTITY OF BLOOD. 59
tainty of all the premisses on which the conclusion is founded.
Other methods depend on the results of injecting a known quantity of water (Valentin) or of saline matters (Blake) into the blood-vessels; the calculation being founded in the first case, on the diminution of the specific gravity which ensues, and in the other, on the quantity of the salt found diffused in acertain measured amount of the blood abstracted for experiment.
A nearly correct estimate was probably made by Weber and Lehmann, from the following data. A criminal was weighed before and after decapitation; the difference in the weight representing, of course, the quantity of blood which escaped. The blood-vessels of the head and trunk, were then washed out by the injection of water, until the fluid which escaped had only a pale red or straw colour. This fluid was then also weighed; and the amount of blood which it represented was calculated, by comparing the proportion of solid matter contained in it, with that of the first blood which escaped on decapitation. Two experi- ments of this kind gave precisely similar results.
The most reliable of these various means for estimating the quantity of blood in the body yield as nearly similar results as can be expected, when the sources of error un- avoidably present in all, are taken into consideration; and it may be stated that in man, the weight of the whole quantity of blood, compared with that of the body, is from about 1 to 8, to 1 to 10.
It must be remembered, however, that the whole quan- tity of blood varies, even in the same animal, very consider- ably, in correspondence with the different amounts of food and drink, which may have been recently taken in, and the equally varying quantity of matter given out. Bernard found by experiment, that the quantity of blood obtainable from a fasting animal is scarcely more than a half of that which is present soon aftera full meal. The estimate above
60).> THE BLOOD
given, must therefore be taken to represent only an ap- proximate average.
Coagulation of the Blood.
When blood is drawn from the body, and left at rest, certain changes ensue, which constitute a kind of rough analysis of it, and are instructive respecting the nature of some of its constituents. After about ten minutes, taking a general average of many observations, it gradually clots or coagulates, becoming solid like a soft jelly. The clot thus formed has at first the same volume and appearance as the fluid blood had, and,-like it, looks quite uniform; the only change seems to be, that the blood which was fluid is now solid. But presently, drops of transparent yellowish fluid begin to ooze from the surface of the solid clot; and these gradually collecting, first on its upper surface, and then all around it, the clot or “ crassamentum,” diminished jn size, but firmer than it was before, floats in a quantity of yellowish fluid, which is named serum, the quantity of which may continually increase for from twenty-four to forty-eight hours after the clotting of the blood.
7
The changes just described may be thus explained. The |
liquor sanguinis, or liquid part of the blood (p. 56), consists of a thin fluid called serum, holding fibrin in solution.* The peculiar property of fibrin, as already said, is its ten- dency to become solid when at rest, and in some other conditions. When, therefore, a quantity of blood is drawn from the vessels, the fibrin coagulates, and the blood cor- puscles, with part of the serum, are held, or, as it were, entangled in the solid substance which it forms.
But after healthy fibrin has thus coagulated, it always
* This statement has been left unaltered in the text ; but, as will be seen farther on, it requires modification.—(Ep.)
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COAGULATION OF BLOOD. > 61
contracts ; and what is generally described as one process of coagulation should rather be regarded as consisting of two parts or stages; namely, first, the simple act of clot- ting, coagulating, or becoming solid; and, secondly, the contraction or condensation of the solid clot thus formed, By this second act much of the serum which was soaked in the clot is gradually pressed out; and this collects in the vessel around the contracted clot.
Thus, by the observation of blood within the vessels, and of the changes which commonly ensue when it is drawn from them, we may distinguish in it three principal consti- tuents, namely, Ist, the fibrin, or coagulating substance ; 2nd, the serum; 3rd, the corpuscles.
That the fibrin is the only spontaneously coagulable material in the blood, may be proved in many ways; and most simply by employing any means whereby a portion of the liquor sanguinis, z.¢., the serum and fibrin, can be separated from the red corpuscles before coagulation. Under ordinary circumstances coagulation occurs before the red corpuscles have had time to subside; and thus, from their beiny entangled in the meshes of the fibrin, the clot is of a deep dark red colour throughout,—somewhat darker, it may be, at the most dependent part, from accu- » mulation of red cells, but not to any very marked degree. If, however, from any cause, the red cells sink more quickly than usual, or the fibrin contracts more slowly, then, in either of these cases, the red corpuscles may be observed, while the blood is yet fluid, to sink below its surface; and the layer beneath which they have sunk, and which has usually an opaline or greyish white tint, will coagulate without them, and form a white clot consisting _ of fibrin alone, or of fibrin with entangled white cor- puscles; for the white corpuscles, being very light, tend upwards towards the surface of the fluid. The layer of white clot which is thus formed rests on the top of a coloured clot of ordinary character, i.c., of one in which
62 THE BLOOD.
the coagulating fibrin has entangled the red corpuscles while they were sinking: and, thus placed, it constitutes what has been called a buffy coat.
When a buffy coat is formed in the manner just de- scribed, it commonly contracts more than the rest of the clot does, and, drawing in at its sides, produces a cupped appearance on the top of the clot. :
In certain conditions of the system, and especially when
there exists some local inflammation, this buffed and.
cupped condition of the clot is well marked, and there has been much discussion concerning its origin under these circumstances. It is now generally agreed that two causes combine to produce it.
In the first place, the tendency of the red corpuscles to form rouleaux: (see p. 73) is much exaggerated in inflam- matory blood; and as their rate of sinking increases with their aggregation, there is a ready explanation, at least in part, of the colourless condition of the top of the clot. And in the next place, inflammatory blood coagulates less rapidly than usual, and thus there is more time for the already rapidly sinking corpuscles to subside. ‘The colour- _ less or buffed condition of the upper part of the clot is there- fore, readily accounted far; while the cupped appearance is easily explained by the greater power of contraction pos- sessed by the fibrin of inflammatory blood, and by its contraction being now not interfered with by the presence of red corpuscles in its meshes.
Although the appearance just described is commonly the result of a condition of the blood in which there is an increase in the quantity of fibrin, it need not of necessity be so. For a very different state of the blood, such as that which exists in chlorosis, may give rise to the same appearance; but in this case the pale layer is due to a relatively smaller amount of ‘red corpuscles, not to any increase in the quantity of fibrin.
It is thus evident that the coagulation of the blood is due
COAGULATION OF BLOOD. 63
to its fibrin. The cause of the coagulation of the fibrin, however, is still a mystery.
The theory of Prof. Lister, that fibrin has no natural tendency to clot, but that its coagulation out of the body is due to the action of foreign matter with which it happens to be brought into contact, and, in the body, to conditions of the tissues, which cause them to act towards it like foreign matter, is insufficient; because even if it be true, it still leaves unexplained the manner in which the fibrin, fluid in the living blood-vessels, can, by foreign matter, be thus made solid. If it be a fact, it is a very important one, but it is not an explanation.
The same remark may be applied also to another theory which differs from the last, in that while it admits a natural tendency on the part of the blood to coagulation, it supposes that this tendency in the living body is re- strained by some inhibitory power resident in the walls of _ the containing vessels. This also may, or may not, be true; but it is only a statement of a possible fact, and leaves unexplained the manner in which living tissue can thus restrain coagulation.
Dr. Draper believes that coagulation takes place in the living body, as out of it, or as in the dead; but in the one case the fibrin is picked out in the course of the circu- lation by tissues which this particular constituent of the blood is destined to nourish; in the others, it remains and becomes evident asa clot. This explanation is inge- nious, but requires some kind of proof before it can be adopted.
Concerning other theories, as for instance, that coagu- lation is due to the escape of carbonic acid, or of ammonia, it need only be said that they have been completely disproved.
We must, therefore, for the edit believe that the cause of the coagulation of the blood has yet to’ be dis-
64 THE BLOOD.
covered; but some very interesting observations in con- nexion with the subject have been recently made, and seem not unlikely to lead in time to a solution of this difficult and most. vexed question. The observations referred to have been made independently by Alexander Schmidt, although he was forestalled in regard to some of his ex- periments by Dr. Andrew Buchanan of Glasgow, many
_ years ago.
When blood-serum, or washed blood-clot, is added to the fluid of hydrocele, or any other serous effusion, it speedily causes coagulation, and the production of true fibrin. And this phenomenon occurs also on the ad-
mixture of serous effusions from different parts of the
body, as that of hydrocele with that of ascites, or of either with fluid from the cavity of the pleura. Other sub- stances also, as muscular or nervous tissue, skin, etc., have been found also able to excite coagulation in serous fluids. Thus, fluids which have little or no tendency to coagulate when left to themselves, can be made, to produce. a clot, apparently identical with the fibrin of blood by the addition to them of matter which, on its part, was not known to have any special relation to fibrin. As may be supposed, the coagulation is not alike in extent under all these circumstances. Thus, although it occurs when ap-
parently few or no blood-cells exist in either constituent of
the mixture, yet the addition of these very much increases the effect, and their presence evidently has a very close connexion with the process. From the action of the buffy coat of a clot, in causing the appearance of fibrin in serous effusions, it may be inferred that the pale as well as the red corpuscles are influential in coagulation under these circumstances. Blood-crystals are also found to be effec- tive in producing a clot in serous fluids.
The true explanation of these very curious phenomena is, probably, not fully known; but Schmidt supposes that in the act of formation of fibrin there occurs the union
FORMATION OF FIBRIN. 65
of two substances, which he terms fibrino-plastin and fibrinogen.
The substance which he terms fibrino-plastin, and which he has obtained, not only from blood, but from many other liquids and solids, as the crystalline lens, chyle and lymph, connective tissue, etc., which are found capable of exciting coagulation in serous fluids, is probably identical with the globulin of the red corpuscles.
The fibrinogenous matter obtained from serous effusions differs but little, chemically, from the fibrino-plastin.
Thus in the experiment before mentioned, the globulin or fibrino-plastic matter of the blood-cells, in the clot, causes coagulation by uniting with the fibrinogen present in the hydrocele-fluid. And whenever there occurs coagu- lation with the production of fibrin, whether in ordinary blood-clotting, or in the admixture of serous effusions, or in any other way, a like union of these two substances may be supposed to occur. ©
The main result, therefore, of these very interesting experiments and observations has been to make it probable that the idea of fibrin existing in a liquid state in the blood is founded on a mistaken notion of its real nature, and that, probably, it does not exist at all in solution as fibrin, but is formed at the moment of coagulation by the union of two substances which, in fluid blood, exist separately. bob
The theories before referred to, concerning the coagu- lation of the blood, will therefore, if this be true, resolve themselves into theories concerning the causes of the union of fibrino-plastin and fibrinogen ; and whether, on the one hand, itis an inhibitory action of the living blood-vessels that naturally restrains, or a catalytic action of foreign matter that excites, the union of these two substances.
66 =. (HE BLOOD.
Conditions affecting Coagulation.
Although the coagulation of fibrin appears to be spon- taneous, yet it is liable to be modified by the conditions in which it is placed ; such as temperature, motion, the access of air, the substances with which it is in contact, the mode of death, etc. All these conditions need to be considered in the study of the coagulation of the blood.
The coagulation of the blood is hastened by the eapid ing means :—
1. Moderate warmth,—from about 100° F. to 120° F.
2. Rest is favourable to the coagulation of blood. Blood, of which the whole mass is kept in uniform motion, as when a closed vessel completely filled with it is constantly moved, coagulates very slowly and imperfectly. But rest. is not essential to coagulation; for the coagulated fibrin may be quickly obtained from blood by stirring it with a bundle of small twigs;. and whenever any rough points of earthy matter or foreign bodies are introduced into the blood-vessels, the blood soon coagulates upon them.
3. Contact with foreign matter, and especially multi- |
plication of the points of contact. Thus, when all other conditions are unfavourable, the blood will coagulate upon rough bodies projecting into the vessels; as, for example,
- upon threads passed through arteries or aneurismal sacs,
or the heart’s valves roughened by inflammatory deposits or calcareous accumulations. And, perhaps, this may explain the quicker coagulation of blood after death in the heart with walls made irregular by the fleshy columns, than in the simple smooth-walled arteries and veins.
4. The free access of air.
5. Coagulation is quicker in shallow, than in tall and narrow vessels.
6. The addition of less than twice the bulk of water.
The blood last drawn is said to coagulate more quickly than that which is first let out.
CONDITIONS AFFECTING COAGULATION, 67
The coagulation of the blood is retarded by the following means :—
1. Cold retards the coagulation of blood; and it is said that, so long as blood is kept at a temperature below 40° F., it will not coagulate at all. Freezing the blood, ‘of course, prevents its coagulation; yet it will coagulate, though not firmly, if thawed after being frozen; and it will do so, even after it has been frozen for several months. Coagulation is accelerated, but the subsequent contraction of the clot is hindered, by a temperature between 100° and 120°: a higher temperature retards coagulation, or, by coagulating the albumen of the serum, prevents if altogether.
2. The addition of water in greater proportion than twice the bulk of the blood.
3. Contact with living tissues, and especially with the interior of a living blood-vessel, retards coagulation, although if the blood be at rest it does not prevent it, .
4. The addition of the alkaline and earthy salts in the proportion of 2 or 3 per cent. and upwards. ‘When added in large proportion most of these saline substances pre- vent coagulation altogether. Coagulation, however, en- sues on dilution with water. The time that blood can be thus preserved in a liquid state and coagulated by the _ addition of water, is quite indefinite.
5. Imperfect aération,—as in the blood of those who die by asphyxia.
6. In Inflammatory states of the system, the blood coa- gulates more slowly although more firmly.
7. Coagulation is retarded by exclusion of the blood from the air, as by pouring oil on the surface, etc. In vacuo, the blood coagulates quickly; but Prof. Lister thinks that the rapidity of the process is due to the bub- bling which ensues from the escape of gas, and to the blood being thus brought more freely into contact with the
containing vessel. F 2
68 THE BLOOD.
The coagulation of the blood is prevented altogether by the addition of strong acids and caustic alkalies.
It has been believed, and chiefly on the authority of Mr. Hunter, that, after certain modes of death, the blood does not coagulate; he enumerates the death by lightning,
over-exertion (as in animals hunted to death), blows on the ©
stomach, fits of anger. He says, ‘‘ I have seen instances of them all.’”’ Doubtless he had done so; but the results of such events are not constant. The blood has been often observed coagulated in the bodies of animals killed by lightning or an electric shock; and Mr. Gulliver has published instances in which he found clots in the hearts of hares and stags hunted to death, and of cocks killed in fighting.
Chemical Composition of the Blood.
Among the many analyses of the blood that have been published, some, in which all the constituents are enume- rated, are inaccurate in their statements of the proportions of those constituents; others, admirably accurate in some particulars, are incomplete. The two following Tables, constructed chiefly from the analyses of Denis, Lecanu, Simon, Nasse, Lehmann, Becquerel, Rodier, and Gavarret, are designed to combine, as far as possible, the advan- tage of accuracy in numbers with the convenience of presenting at one yiew, a list of all the constituents of the blood.
Average proportions of the principal constituents of the blood in 1,000 parts :—
Water . : : ; , ‘ = - Nae 5 Red corpuscles (solid residue) . ; : ag et See Albumen of serum . ; : ; : ; eats tx Saline matters . : ‘ ; : s eae 6°03 Extractive, fatty, and other matters : 3 : 7°77 Fibrin ; : . ‘ ; : i eth 22 1C00*
=. fio
we were
COMPOSITION OF BLOOD. 69
Average proportions of all the constituents of the blood in 1,000 parts :—
Water . F : / ; ; ‘ ; er ae Albumen. . ; ‘ , : i ies 70° Fibrin : ae : , . . . 2°2 Red corpuscles (dry). ° ; : é ‘7 Es6! _ Fatty matters . steer . . I°4 ‘Inorganic salts: Cliloride of sodium . ; ; 3°6 Chloride of potassium . ee 0°35 Tribasic phosphate of soda . : o'2 Carbonate of soda . i Gh. 0°28 Sulphate of soda . : : ‘ 0°28 Phosphates of lime and magnesia. 0°25 Oxide and phosphate of iron , O°5 Extractive matters, biliary colouring matter, gases, and accidental substances : ; : E 6°40 1000° Elementary composition of the dried blood of the ox :— Carbon ‘ . 2 ‘ ‘ ; ; s 57°9 Hydrogen ; : ‘ ; ‘ ; mah ped Nitrogen ., : ' : ‘ ; ; Pay y hy Oxygen .. 4 - P : Bs be i i 2 iO! Ashes . ‘ ‘ ; ‘ : : j . ae
These results of the ultimate analysis of ox’s blood afford a remarkable illustration of its general purpose, as supply- ing the materials for the renovation of all the tissues. For the analysts (Playfair and Boeckmann) have found that the flesh of the ox yields the same elements in so nearly the same proportions, that the elementary composition of the organic constituents of the blood and flesh may be con- sidered identical, and may be represented for both by the formula C,;H..N,0,;.
The Blood-Corpuscles or Blood-Cells.'
It has been already said, that the clot of blood contains, with the fibrin and the portion of the serum that is soaked in it, the blood-corpuscles, or blood-cells. Of these there are
70 THE BLOOD.
two principal forms, the red and the white corpuscles.
When coagulation has taken place quickly, both kinds of Fig. 24.*
Mammals. Birds. Reptiles. Amphibia. Fish.
tl i i a
OSTRICH
CROCODILE
K DEEF 8
MUSK D
PIGEON ELECTRIC EEL..
PROTEUS
- 2 < 0 < wW p x a
TRITON
LIZARD
HUMMING BIRD
* The above illustration is somewhat altered from a drawing, by Mr. Gulliver, in the Proced. Zool. Society, and exhibits the typical characters of the red-blood cells in the main divisions of the Vertebrata. The fractions are those of an inch, and represent the average diameter. In
RED BLOOD-CORPUSCLES. v5:
corpuscles may be uniformly diffused through the clot; but, when it has been slow, the red corpuscles, being the heaviest constituent of the blood, tend by gravitation to accumulate at the bottom of the clot; and the white cor- puscles, being among the lightest constituents, collect in the upper part, and contribute to the formation of the buffy coat.
The human red blood-cells or blood corpuscles (figs. 25 and 29) are circular flattened disks of different sizes, the majority varying in diameter from +}, to <5/5> of an inch, and about sotss of an inch in thickness. When viewed singly, they appear of a pale yellowish tinge ; the deep red colour which they give to the blood being observable in them only when they are seen en masse. Their borders are rounded; their surfaces, in the perfect and most usual state, slightly con- caye; but they readily acquire flat or convex surfaces when, the liquor sanguinis being diluted, they are swollen by absorption of fluid. They are composed of a colourless, structureless, and transparent filmy framework or stroma infiltrated in all parts by a red colouring-matter termed hemoglobin. « The stroma is tough and elastic, so that, as the cells circulate, they admit of elongation and other changes of form, in adaptation to the vessels, yet recover their natural shape as soon as they escape from compres- sion. The term cell, in the sense of a bag or sac, is inap- plicable to the red blood-corpuscle; and it must be con-
the case of the oval cells, only the long diameter is here given. It is remarkable, that although the size of the red blood-cells varies 80 much in the different classes of the vertebrate kingdom, that of the white corpuscles remains comparatively uniform, and thus they are, in some animals, much greater, in others much less than the red corpuscles existing side by side with them.
It may be here remarked, that the appearance of a nucleus in the red blood-cells of birds, reptiles, amphibia and fish has been shown by Mr. Savory to be the result of post-mortem change ; no nucleus being visible in the cells as they circulate in the living body, or in those which have just escaped from the blood-vessels.
72 THE BLOOD.
sidered, if not solid throughout, yet as having no such variety of consistence in different parts as to justify the notion of its being a membranous sac with fluid contents. — The stroma exists in all parts of its substance, and the colouring-matter uniformly pervades this, and is not merely surrounded by and mechanically enclosed within the outer wall of the corpuscle. The red corpuscles have no nuclei, although, in their usual state, the unequal refraction of transmitted light gives the appearance of a central spot, brighter or darker than the border, according as it is viewed in or out of focus. Their specific gravity is about 1088.
In examining a number of red corpuscles with a micro- scope, it is easy to observe certain natural diversities among them, though they may have been all taken from the same part. The great majority, indeed, are very uniform; but some are rather larger, and the larger ones generally appear paler and less exactly circular than the rest; their surfaces also are, usually, flat or slightly convex, they often contain a minute shining particle like a nucleolus, and they are lighter than the rest, floating higher in the fluid in which they are placed. Other deviations from the general characters assigned to the corpuscles, depend on changes that occur after they are taken from the body. Very com- monly they assume a granulated or mulberry-like form, in consequence, apparently, of a peculiar corrugation of their cell-walls. Sometimes, from the same cause, they present a very irregular, jagged, indented, or star-like appearance. The larger cells are much less liable to this change than the smaller, and the natural shape may be restored by diluting the fluid in which the corpuscles float; by such dilution the corpuscles, as already said, may be made to swell up, by absorbing the fluid; and, if much water be added, they will become spherical and pellucid, their colouring-matter being dissolved, and, as it were, washed . out of them. Some of them may thus be burst; the others
RED BLOOD-CORPUSCLES. 73
are made obscure ; but many of these latter may be brought into view again by evaporating, or adding saline matter to, the fluid, so as to restore it to its previous density. The - changes thus produced by water are more quickly effected by weak acetic acid, which immediately makes the cor- puscles pellucid, but dissolves few or none of them, for
7 _ the addition of an alkali, so as to neutralise the acid, will
restore their form though not their colour.
A peculiar property of the red corpuscles, which is exag- gerated in inflammatory blood, and which appears to exist in a marked degree in the blood of horses, may be here noticed. It gives them a great tendency to adhere together in rolls or columns, like piles of coins, and then, very quickly, these rolls fasten together by their ends, and cluster; so that, when the blood is spread out thinly on a glass, they form a kind of irregular network, with crowds of corpuscles at the several points corresponding with the knots of the net (fig. 25). Hence, the clot formed in such a thin layer of blood looks mottled with blotches*of pink upon a white ground : in a larger quan- tity of such blood, as soon as the corpuscles have clustered and collected in rolls (that is, generally in two or three minutes _ after the blood is drawn), they begin to sink very quickly; for in the aggregate they pre- sent less surface to the resistance of the liquor sanguinis than they would if sinking separately. Thus, quickly sink- ing, they leave above them a layer of liquor sanguinis, and this coagulating, forms a buffy coat, as before de- scribed, the volume of which is augmented by the white corpuscles, which have no tendency to adhere to the red ones, and by their lightness float up clear of them.
* Fig. 25. Red corpuscles collected into rolls (after Henle).
74 THE BLOOD.
Chemical Composition of Red Blood-cells.
It has been before remarked that the red blood-corpuscles are formed of a colourless stroma, infiltrated with a colour- ing matter termed hemoglobin. As they exist in the blood they contain about three-fourths of their weight of water.
The stroma appears to be composed of a nitrogenous proximate principle termed protagon, combined with albu- minous matter (paraglobulin. or fibrinoplastin), fatty mat- ters including cholesterin, and salts, chiefly phosphates, of potash, soda and lime.
Heemoglobin, which enters far more largely into the com- position of the red corpuscles than any other of their con- stituents, is allied to albumen in some respects, but differs remarkably from it in others. One of its most marked
distinctive characters is its tendency under certain arti-.
ficial conditions to crystallize; the so-called blood-crys- tals being but the natural so hae ai forms assumed by this substance.
Heemoglobin can be obtained in a crystalline form with various degrees of difficulty from the blood of different animals, that of man holding an intermediate place in this respect. Among the animals whose blood colouring-matter crystallizes most readily, are the guinea-pig and the dog ; and in these cases to obtain crystals it is generally suffi- cient to dilute a drop of recently drawn blood with water and expose it for a few minutes to the air. In many instances, however, a somewhat less simple process must be adopted; as theaddition of chloroform or ether, rapid freezing and then thawing, or other means which separate the colour- ing-matter from the other constituents of the corpuscles.
Different forms of blood-crystals are shown in the accom- panying figures,
Another and most important character of heemoglobin is its attraction for oxygen, and some other gases, as carbonic
ot had a ee
BLOOD-CRYSTALS. 75
and nitrous oxides, with all of which it appears to form ~ definite chemical combinations. The combination with oxygen is that which is of most physio- logical importance. During the passage of the blood through the lungs, it is con- stantly formed; while it is as constantly decomposed, in con- sequence of the rea- diness with which hemoglobin _ parts with oxygen, when the latter is exposed to other attractions in its circulation through the — sys- temic capillaries. Thus, the red cor- puscles, in virtue of their colouring mat- ter, which readily absorbs oxygen and as readily gives it up again, are the chief means by which oxygen is carried in the blood (see also
p. 85).
Fig. 26." ~.
* Figs. 26, 27, and 28, illustrate some of the principal forms of blood-erystals :-—
Fig. 26, Prismatic, from human blood.
+ Fig. 27, Tetrahedral, from blood of the guinea-pig.
76 THE BLOOD.
By heat, mineral and other acids, alkalies, etc., hamo-
Fig. 28.* globin is decomposed into an albuminous matter (resembling globulin) and hema- tin. The latter, now known to be a pro- duct of the decom- position of hzemo- globin, was once thought to be the natural _ colouring matter of the blood.
The White Corpuscles of the Blood or Blood Leucocytes.
The white corpuscles are much less numerous than the red. Onan average, in health, there may be’one white to 400 or 500 red corpuscles ; but in disease, the propor- tion is often as high as one to ten, and sometimes even much higher.
In health, the proportion varies considerably even in the course of the same day. The variations appear to
depend chiefly on the amount and probably also on the -
kind of food taken; the number of leucocytes being very considerably increased by a meal, and diminished again on fasting.
They present greater diversities of form than the red
ones do; but the gradations between the extreme forms are so regular, that no sufficient reason can be found for
supposing that there is in healthy blood more than one
species of white corpuscles. In their most general appear-
* Fig. 28. Hexagonal crystals from blood of squirrel. On these six-sided plates, prismatic crystals, grouped in a stellate manner, not unfrequently occur (after Funke).
ee
; a Te
WHITE BLOOD-CORPUSCLES. 77
ance, they are circular and nearly spherical, about 5.1, of an inch in diameter (fig. 29). ‘They have a greyish, pearly look, appearing variously shaded or nebulous, the shading being much darker in some than in others. They seem to be formed of Reopen (p. 19), containing granules which are in
some specimens few and Fig. 29.*
very distinct, in others (though rarely) so nu- merous that the whole corpuscle looks like a mass of granules.
These corpuscles can- not be said to have any true cell-wall. Ina few instances an apparent cell-membrane can be traced around them; but, much more commonly, even this is not discernible till after the addition of water or dilute acetic acid, which penetrates the* corpuscle, and lifts up and distends what looks like a cell-wall, to the interior of which the mate- rial, that before appeared to form the whole corpuscle, remains attached as the nucleus of the cell (fig. 29).
A remarkable property of the white corpuscles, first observed by Mr. Wharton Jones, consists in their capa- bility of assuming different forms, irrespective of any external influence. If a drop of blood be examined with a high microscope power under conditions by which loss of moisture is prevented, at the same time that the temperature is maintained at about the degree natural to ‘the blood as it circulates in the living body, the leu-
* Fig. 29. Red and white blood-corpuscles. a, White corpuscle of natural aspect. 6, Three white corpuscles acted on by weak acetic acid. ¢, Red blood corpuscles.
78 THE BLOOD. . y
cocytes can be seen alternately contracting and dilating
very slowly at various parts of their circumference,—shoot- ing out irregular processes, and again withdrawing them partially or completely, and thus in succession assuming various irregular forms.
These movements, called ameboid, from their resem- blance to the movements exhibited by an animal called the Ameba, the structure of which is as simple as that of a white blood-corpuscle, are characteristic of the living leucocyte, and form a good example of the contractile pro- perty of protoplasm, before referred to. Indeed, the unchang- ing rounded form which the corpuscles present in specimens of blood examined in the ordinary manner under the micro- scope, must be looked upon as the shape natural to a dead corpuscle, or one whose vitality is dormant, rather than as the proper shape of one living and active.
Besides the red and white corpuscles, the microscope reveals numerous minute molecules or granules in the blood, circular or spherical, and varying in size from the most minute visible speck to the =, of an inch (Gulliver). These molecules are very similar to those found in the lymph and chyle, and are, some of them, fatty, being soluble in ether, others probably albuminous, being soluble in acetic acid. Generally, also, there may be detected in the blood, especially during the height of digestion, very minute equal-sized fatty particles, similar to those of which the molecular base of chyle is constituted (Gulliver). |
The Serum.
The serum is the liquid part of the blood remaining after the coagulation of the fibrin. In the usual mode of coagulation, part of the serum remains soaked in the clot, and the rest, squeezed from the clot by its contraction, lies around and over it. The quantity of serum that appears around the clot depends partly on the total quantity in the blood, but partly also on the degree to which the clot con-
ee
sre”? S wet
ah
lant iain:
i n
SERUM OF BLOOD. 79
tracts. This is affected by many circumstances : generally, the faster the coagulation the less is the amount of con- traction ; and, therefore, when blood coagulates quickly, it will appear to contain a small proportion of serum. Hence, theserum always appears deficient in blood drawn slowly into a shallow vessel, abundant in inflammatory blood drawn into a tall vessel. In all cases, too, it should be remembered, that, since the contraction of the clot may continue for thirty-six
_ or more hours, the quantity of serum in the blood cannot
be even roughly estimated till this period has elapsed.
The serum is an alkaline, slimy or viscid, yellowish fluid, often presenting a slight greenish, or greyish hue, and with a specific gravity of from 1025 to 1030. It is composed of a mixture of various substances dissolved in about nine times their weight of water. It contains, indeed, the greater part of all the substances enumerated as existing in the blood, with the exception of the fibrin and the red corpuscles. Its principal constituent is albumen, of which it contains about 8 per cent., and the coagulation of which, when heated, converts nearly the whole of the serum into a solid mass. «Ihe liquid which remains uncoagulated, and which is often enclosed in little cavities in the coagu- lated serum, is called serosity: it contains, dissolved in water, fatty, extractive, and saline matters.
Variations in the principal Constituents of the Liquor Sanguinis.
The water of the blood is subject to hourly variations in its quantity, according to the period since the taking of food, the amount of bodily exercise, the state of the atmosphere, and all the other events that may affect either the ingestion or the excretion of fluids. According to these conditions, it may vary from 700 to 790 parts in the thousand. Yet uniformity is on the whole maintained; because nearly all those things which tend to lower the proportion of water in the blood, such as active exercise, or the addition of saline and other solid matter, excite thirst; while, on the
Ba": THE BLOOD.
other hand, the addition of an excess of water to the blood is quickly followed by its more copious excretion in sweat and urine. And these means for adjusting the proportion of the water find their purpose in maintaining certain im- portant physical conditions in the blood; such as its proper viscidity, and the degree of its adhesion to the vessels through which it ought to flow with the least possible resistance from friction. On this also depends, in great measure, the activity of absorption by the blood-vessels, into which no fluids will quickly penetrate, but such as are of less density than the blood. Again, the quantity of water in the blood determines chiefly its volume, and thereby the fulness and tension of the vessels and the quantity of fluid that will exude from them to keep the tissues moist. Finally, the water is the general solvent of all the other materials of the liquor sanguinis.
It is remarkable, that the proportion of water in the blood may be sometimes increased even during its abstrac- tion from an artery or vein. Thus Dr. Zimmerman in bleeding dogs, found the last drawn portion of blood contain 12 or 13 parts more of water in 1000 than the blood first drawn; and Polli noticed a corresponding diminution in the specific gravity of the human blood during venesection, and suggested the only probable ex- planation of the fact, namely, that during bleeding, the blood-vessels absorb very quickly a part of the serous fluid with which all the tissues are moistened. |
The albumen may vary, consistently with health, from 60 to 70 parts in the 1000 of blood. The form in which it exists in the blood is not yet certain. It may be that of simple solution as pure albumen: but it is, more probably, in combination with soda, as an albuminate of soda; for, if serum be much diluted with water, and then neutralized with acetic acid, pure albumen is deposited. Another view entertained by Enderlin is that the albumen is dis- solved in the solution of the neutral phosphate of sodium,
FATTY MATTERS IN THE BLOOD. 8I
to which he considers the alkaline reaction of the blood to be due, and solutions of which can dissolve large quantities of albumen and phosphate of lime.
The proportion of jibrin in healthy blood may vary be- tween 2 and 3 parts in 1000. In some diseases, such as typhus, and others of low type, it may be as little as 1:034; in other diseases, it is said, it may be increased to as much as 7°528 parts in 1000. But, in estimating the quantity of fibrin, chemists have not taken account of the white corpuscles of the blood. These cannot, by any mode of analysis yet invented, be separated from the fibrin of mammalian blood: their composition is unknown, but their weight is always included in the estimate of the fibrin. In health, they may, perhaps, add too little to its weight to merit consideration, but in many diseases, espe- cially in inflammatory and other blood diseases in which the fibrin is said to be increased, these corpuscles become so numerous that a large proportion of the supposed increase of the fibrin must be due to their being weighed with it. On this account all the statements respecting the increase of fibrin in certain diseases need revision.
The enumeration of the fatty matters of the blood makes it probable that most of those which are found in the tissues or secretions exist also ready-formed in the blood ; for it contains the cholesterin of the bile, the cerebrin and phosphorised fat of the brain, and the ordinary saponi- fiable fats, stearin, olein, and palmatin. A volatile fatty acid is that on which the odour of the blood mainly de- pends; and it is supposed that when sulphuric acid is added (see p. 57), it evolves the odour by combining with the base with which, naturally, this acid is neutra- lized. According to Lehmann, much of the fatty matter of the blood is accumulated in the red corpuscles.
These fatty matters are subject to much variation in quantity, being commonly increased after every meal in
which fat, or starch, or saccharine substances have been : G
82 THE BLOOD.
taken. At such times, the fatty particles of the chyle, added quickly to the blood, are only gradually assimilated ; and their quantity may be sufficient to make the serum of the blood opaque, or even milk-like.
As regards the inorganic constituents of the blood,—the substances which remain as ushes after its complete burning _—one may observe in general their small quantity in pro- portion to that of the animal matter contained in it.
Those among them of peculiar interest are the phosphate and carbonate of sodium, and the phosphate of calcium.
It appears most probable, that the blood owes its alkaline reaction to both these salts of sodium. The existence of the neutral phosphate (Na,H.PO,) was proved by Enderlin : the presence of carbonate of sodium has been proved by Lehmann and others. )
In illustration of the characters which the blood may derive from the phosphate of sodium, Liebig points out the _ large capacity which solutions of that salt have of absorb- ing carbonic acid gas, and then very readily giving it off
again when agitated in atmospheric air, and when the
atmospheric pressure is diminished. It is probably, also, by means of this salt, that the phosphate of calcium is held in solution in the blood in a form in which it is not soluble in water, or in a solution of albumen. Of the remaining inorganic constituents of the blood, the oxide and phos- phate of iron referred to, exist in the liquor sanguinis, independently of the iron in the corpuscles.
Schmidt’s investigations have shown that the inorganic constituents of the blood-cells somewhat differ from those contained in the serum; the former possessing a consider- able preponderance of phosphates and of the salts of potas- sium, while the chlorides, especially of sodium, with phos- phate of sodium, are particularly abundant in the latter.
Among the extractive matters of the blood, the most noteworthy are Creatin and Creatinin. Besides these, other organic principles have been found either constantly
-_ 7 ~ =
tt Peet
VARIATIONS OF BLOOD. 83
or generally in the blood, including casein, especially in women during lactation: glucose, or grape-sugar, found in the blood of the hepatic vein, but disappearing during its transit through the lungs (Bernard); urea, and-in very minute quantities, wric acid (Garrod) ; hippurie and lactic acids ; ammonia (Richardson); and lastly, certain colouring and odoriferous matters.
Variations in healthy Blood under different Circumstances.
As the general condition of the body depends so much on the condition of the blood, and as, on the other hand, anything that affects the body must sooner or later, and . to a greater or less degree, affect the blood also, it might be expected that considerable variations in the qualities of this fluid would be found under different circumstances of disease ; and such is found to be the case. Even in health, however, the general composition of the blood varies con- siderably. |
The conditions which appear most to influence the com- position of the blood in health, are these: sex, pregnancy, age, and temperament. The composition of the blood is
also, of course, much influenced by diet. 1. Sex.—The blood of men differs from that of women,
chiefly in being of somewhat higher specific gravity, from its containing a relatively larger quantity of red corpuscles.
2. Pregnancy.—The blood of pregnant women has a rather lower specific gravity than the average, from de- ficiency of red corpuscles. The quantity of white corpuscles, on the other hand, and of fibrin, is increased.
3. Age.—From the analysis of Denis it appears that the blood of the foetus is very rich in solid matter, and espe- cially in red corpuscles; and this condition, gradually diminishing, continues for some weeks after birth. The quantity of solid matter then falls during childhood below the average, again rises during adult life, and in old age
falls again. G2
84 THE BLOOD.
4. Temperament.—But little more is known concerning the connection of this with the condition of the blood, than that there appears to be a relatively larger quantity of solid matter, and particularly of red corpuscles, in those of a plethoric or sanguineous temperament.
5. Diet.—Such differences in the composition of the blood as are due to the temporary presence of various matters absorbed with the food and drink, as well as the more lasting changes which must result from generous or poor diet respectively, need be here only referred to.
Effects of Bleeding.—The result of bleeding is to diminish the specific gravity of the blood; and so quickly, that in a single venesection, the portion of blood last drawn has often a less specific gravity than that of the blood that flowed first (J. Davy and Polli). This is, of course, due to ab- sorption of fluid from the tissues of the body. The physio- logical import of this fact, namely, the instant absorption of liquid from the tissues, is the same as that of the intense thirst which is so common after either loss of blood, or the abstraction from it of watery fluid, as in cholera, diabetes, and the like. |
For some little time after bleeding, the want of red
-blood-cells is well marked; but, with this exception, no considerable alteration seems to be produced in the com- position of the blood for more than a very short time, the loss of the other constituents, including the pale corpuscles, being very quickly repaired.
Variations in the Composition of the Blood, in different Parts.
of the Body.
The composition of the blood, as might be expected, is found to vary in different parts of the body. Thus arterial blood differs from venous; and although its composition and general characters are uniform throughout the whole course of the systemic arteries, they are not so throughout
: 7 : y
VARIATIONS OF BLOOD. 85
the venous system,—the blood contained in some veins differing remarkably from that in others.
1. Differences between arterial and venous blood.—These may be arranged under two heads,—differences in colour, and in general composition.
a. Colour.—Concerning the cause of the difference in colour between arterial and venous blood, there has been much doubt, not to say confusion. For while the scarlet colour of the arterial blood has been supposed by some observers, and for some reasons, to be due to the chemical action of oxygen, and the purple tint of that in the veins to the action of carbonic acid, there are. facts which made it seem probable that the cause was a mechanical one rather than a chemical, and that it depended on a difference in the shape of the red corpuscles, by which their power of transmitting and reflecting light was altered. Thus, car- bonie acid was thought to make the blood dark by causing the red cells to assume a bi-convex outline, and oxygen was supposed to reverse the effect by contracting them and rendering them bi-concave. We may believe, however, that, at least ‘for the present, this vexed question has, by the results of investigations undertaken by Professor Stokes and others, been now set at rest.
The colouring matter of the blood, or heemoglobin (p. 74), is capable of existing in two different states of oxidation, and the respective colours of arterial and venous blood are caused by differences in tint between these two varieties— oxidised or scarlet hemoglobin and de-oxidised or purple hemoglobin... The change of colour produced by the passage ‘of the blood through the lungs, and its consequent exposure to oxygen, is due, probably, to the oxidation of purple, and its conversion into scarlet hemoglobin; while the readiness with which the latter is de-oxidised offers a reasonable explanation of the change, in regard to tint, of
arterial into venous blood, —the transformation being effected by the delivering up of oxygen to the tissues, by
86 THE BLOOD.
the scarlet hemoglobin, during the blood’s passage through the capillaries. The changes of colour are more probably due to this cause, namely, a varying quantity of oxygen chemically combined with the hemoglobin, than to any mechanical effect of this gas, or to the influence of carbonic acid, either chemically, on the colouring matter, or me- chanically, on the corpuscles which contain it. We are not, perhaps, in a position to deny altogether the possible influence of mechanical conditions of the red corpuscles on the colour of arterial and venous blood respectively ; but it is probable that this cause alone would be quite insufficient to explain the differences in the colour of the two kinds of blood, and therefore if it be an element at all in the change, it must be allowed to take only a subordinate position.
The distinction between the two kinds of hemoglobin naturally present in the blood, or, in other words, the proof that the addition or subtraction of oxygen involves the production respectively of two substances having funda- mental differences of chemical constitution, has been made out chiefly by spectrum-analysis,—the effects produced by placing oxidised and de-oxidised solutions of heemoglobin in the path of a ray of light traversing a spectroscope being different. For while théoxidised solution causes the ap- pearance of two absorption bands in the yellow and the green part of the spectrum, these are replaced by.a single band intermediate in position, when the oxidised or scarlet solution is darkened by de-oxidising agencies,—or, in other words, when the change which naturally ensues in the ‘conversion of arterial into venous blood is artificially produced.*
The greater part of the hemoglobin in both arterial and venous blood probably exists in the scarlet or more highly oxidised condition, and only a small part is de-oxidised and made purple in its passage from the arteries into the veins.
* The student to whom the terms employed in connection with spectrum analysis are not familiar, is advised to consult, with reference to the preceding paragraph, an elementary treatise on Physics.
=
BLOOD OF PORTAL VEIN. 87
A 4
The differences in regard to colour between arterial and venous blood are sometimes not to be observed. If blood runs very slowly from an artery, as from the bottom of a deep and devious wound, it is often as dark as venous blood. “In persons nearly asphyxiated also, and some- times, under the influence of chloroform or ether, the arterial blood becomes like the venous. In the fcetus also both kinds of blood are dark. But, in all these cases, the dark blood becomes bright on exposure to the air. Bernard has shown that venous blood returning from a gland in active secretion is almost as bright as arterial blood.
b. General Composition.—The chief differences between arterial and ordinary venous blood are these. Arterial blood contains rather more fibrin, and rather less albumen and fat. It coagulates somewhat more quickly. Also, it contains more oxygen, and less carbonic acid. According to Denis, the fibrin of venous blood differs from arterial, in that when it is fresh, and has not been much exposed to the air, it may be dissolved in a slightly heated solution of nitrate of potassium.
Some of the veins, however, contain blood which differs from the ordinary standard considerably. These are the
portal, the hepatic, and the splenic veins.
Portal vein.—The blood which the portal vein conveys to the liver is supplied from two chief sources; namely, that in the gastric and mesenteric veins, which contains the soluble elements of food absorbed from the stomach and intestines during digestion, and that in the splenic vein; it must, therefore, combine the qualities of the blood from each of these sources.
The blood in the gastric and mesenteric veins will vary much according to the stage of digestion and the nature of the food taken, and can therefore be seldom exactly the same. Speaking generally, and without considering the sugar, dextrine, and other soluble matters which may have been absorbed from the alimentary canal, this blood |
88 THE BLOOD,
appears to be deficient in solid matters, especially in red corpuscles, owing to dilution by the quantity of water ab- sorbed, to contain an excess of albumen, though chiefly of a lower kind than usual, resulting from the digestion of ni- trogenised substances, and termed albuminose, and to yield a less tenacious kind of fibrin than that of blood generally.
The blood from the splenic.vein is probably more definite in composition, though also liable to alterations according to the stage of the digestive process, and other circum- stances. It seems generally to be deficient in red cor- puscles, and to contain an unusually large proportion of albumen. The fibrin seems to vary in relative amount, but to be almost always above the average. The propor- tion of colourless corpuscles appears also to be unusually large. The whole quantity of solid matter is decreased, the diminution appearing to be chiefly in the proportion of red corpuscles.
The blood of the portal vein, combining the peculiarities of its two factors, the splenic and mesenteric venous blood, is usually of lower specific gravity than blood generally, is more watery, contains fewer red corpuscles, more albumen, chiefly in the form of albuminose, and yields a less firm clot than that yielded by other blood, owing to the deficient tenacity of its fibrin. These characteristics of portal blood refer to the composition of the blood itself, and have no reference to the extraneous substances, such as the absorbed materials of the food, which it may contain; neither, indeed, has any complete analysis of these been given.
Comparative analyses of blood in the portal vein and blood in the hepatic veins have also been frequently made, with the view of determining the changes which this fluid undergoes in its transit through the liver. Great diversity, however, is observable in the analyses of these two kinds of blood by different chemists. Part of this diversity is no doubt attributable to the fact pointed out by Bernard, that
GASES OF THE BLOOD. 89
unless the portal vein is tied before the liver is removed from the body, hepatic venous blood is very liable to regurgitate into the portal vein, and thus vitiate the result of the analysis. Guarding against this source of error, recent observers seemed to have determined that hepatic venous blood contains less water, albumen, and salts, than the blood of the portal vein; but that it yields a much larger amount of extractive matter, in which, according to Bernard and others, is one constant element, namely, grape- sugar, which is found, whether saccharine or farinaceous matter have been present in the food cr not. |
Besides the rather wide difference between the composi- tion of the blood of these veins and of others, it must not be forgotten that in its passage through every organ and tissue of the body, the blood’s composition must be varying con- stantly, as each part takes from it or adds to it such matter as it, roughly speaking, wishes either to have or to throw away. Thus the blood of the renal vein has been proved by experiment to contain less water than does the blood of the artery, and doubtless its salts are diminished also. The blood in the renal vein is said, moreover, by Bernard and Brown-Séquard not to coagulate.
This then is an example of the change produced in the blood by its passage through a special excretory organ. But all parts of the body, bones, muscles, nerves, etc., must act on the blood as it passes through them, and leave in it some mark of their action, too slight though it may be, at any given moment, for analysis by means now at our disposal.
On the Gases contained in the Blood.
The gases contained in the blood are carbonic acid, oxygen, and nitrogen, 100 volumes of blood containing from 40 to 50 volumes of these gases collectively.
Arterial blood contains relatively more oxygen and less carbonic acid than venous. But the absolute quantity of carbonic acid is in both kinds of blood greater than that of
‘
90 DEVELOPMENT OF BLOOD. the oxygen. The proportion of nitrogen is in both very small. |
It is most probable that the carbonic acid of the blood is partly in a state of simple solution, and partly in a state of weak chemical combination. The portion of the car- bonic acid which is chemically combined, is contained partly in a bicarbonate of soda, and partly is united with phosphate of the same base. ~The oxygen is combined chemically with the hemoglobin of the red corpuscles (pp. 75 and 85).
That the oxygen is absorbed chiefly by the red corpuscles is proved by the fact that while blood is capable of _ absorbing oxygen in considerable quantity, the serum alone has little or no more power of absorbing this gas than pure water.
Development of the Blood.
In the development of the blood little more can be traced than the processes by which the corpuscles are formed.
The first formed blood-cells of the human embryo differ much in their general characters from those which belong to the latter periods of intra-uterine, and to all periods of extra-uterine life. Their manner of origin differs also, and it will be well perhaps to consider this first. ~ In the process of development of the embryo, the plan, so to speak, of the heart and chief blood-vessels is first laid out in cells. Thus the heart is at first but a solid mass of cells, resembling those which constitute all other parts of the embryo; and continuous with this are tracts of similar cells—the rudiments of the chief blood-vessels.
The formation of the first blood corpuscles is very simple. While the outermost of the embryonic cells, of which the rudimentary heart and its attendant vessels are composed, gradually develop into the muscular and other tissues which form the walls of the heart and blood-vessels, the inner cells simply separate from each other, and form
DEVELOPMENT OF BLOOD. QI
blood-cells; some fluid plasma being at the same time secreted. Thus, by the same process, blood is formed, and the originally solid heart and blood-vessels are hollowed out.
The blood-cells produced in this way, are from about sss> tO zs Of an inch in diameter, mostly spherical, pellucid, and colourless, with granular contents, and of well-marked nucleus. Gradually, they acquire a red colour, at the same time that the nucleus becomes more defined, and the granular matter clears away. Mr. Paget describes them, as, at this period, circular, thickly disc- shaped, full-coloured, and, on an average, about =, of an inch in diameter; their nuclei, which are about +, of an inch in diameter, are central, circular, very little pro- minent on the surfaces of the cell, and apparently slightly granular or tuberculated.
Before the occurrence, however, of this change—from the colourless to the coloured state—in many instances, probably, during it, and in many afterwards, a process of multiplication takes place by division of the nucleus and subsequently of the cell, into two, and much more rarely,
Fig. 30.*
D ¥ F
three or four new cells, which gradually acquire ‘the characters of the original cell from which they sprang Fig. 30 (B, c, D, E).
* Fig. 30. Development of the first set of blood-corpuscles in the
92 DEVELOPMENT OF BLOOD,
When, in the progress of embryonic development, the liver begins to be formed, the multiplication of blood- cells in the whole mass of blood ceases, according to Kolliker, and new blood-cells are produced by this organ. Like those just described, they are at first colourless and nucleated, but afterwards acquire the ordinary blood- tinge, and resemble very much those of the first set. Like them they may also multiply by division. In whichever way produced, however, whether from the original for- mative cells of the embryo, or by the liver, these coloured nucleated cells begin very early in foetal life to be mingled with coloured non-nucleated corpuscles resembling those of the adult, and about the fourth or fifth month of embryonic existence are completely replaced by them.
The manner of origin of these perfect non-nucleated corpuscles must be now considered.
I. Concerning the cells from which they arise.
a. Before Birth—It is uncertain whether they are derived only from the cells of the lymph, which, at about the period of their appearance, begins to be poured into the blood; or whether they are derived also from the nucleated red cells, which they replace, or also from similar nucleated cells, which K6lliker thinks are produced by the liver during the whole time of foetal existence. —
b. After Birth.—Itis generally agreed that after birth the red corpuscles are derived from the smaller of the nucleated lymph or chyle-corpuscles,—the white corpuscles of the blood.
II. Concerning the Manner of their Development.
There is not perfect agreement among physiologists
mammalian embryo. A. A dotted, nucleated embryo-cell in process of conversion into a blood-corpuscle ; the nucleus provided with a nucle- olus. 3. A similar cell with a dividing nucleus ; at c, the division of the nucleus is complete ; at p, the cell also is dividing. x. A blood- corpuscle almost complete, but still containing a few granules. F. Per- fect blood-corpuscle.
DEVELOPMENT OF BLOOD. 93
concerning the process by which lymph-globules or white corpuscles (and in the foetus, perhaps the red. nucleated cells) are transformed into red non-nucleated blood-cells. For while ‘some maintain that the whole cell is changed into a red one by the gradual clearing up of the con- tents, including the nucleus, it is believed by Mr. Wharton Jones and many others, that only the nucleus becomes the red blood-cell, by escaping from its envelope and acquiring
_ the ordinary blood-tint.
Of these two theories, that which supposes the nucleus of the lymph or chyle globule to be the germ of the future red blood-corpuscle is the theory now generally adopted.
The development of red blood-cells from the corpuscles of the lymph and chyle continues throughout life, and there is no reason for supposing that after birth they have any other origin.
Without doubt, these little bodies have, like all other parts of the organism, a tolerably definite term of existence, and in a like manner die and waste away when the portion of work allotted to them has been performed. Neither the length of their life, however, nor the fashion of their decay, has been yet clearly made out, and we can only surmise that in these things they resemble more or less closely those parts of the body which lie more plainly within our observation.
From what has been said, it will have appeared that when the blood is once formed, its growth and maintenance are effected by the constant repetition of the development of new portions. Inthe same proportion that the blood yields its materials for the maintenance and repair of the several solid tissues, and for secretions, so are new materials sup- plied to it in the lymph and chyle, and by development made likeit. The part of the process which relates to the formation of new corpuscles has been described, but it is probably only a small portion of the whole process ; for the assimilation of the new materials to the blood must be
‘
94 ASSIMILATION OF BLOOD.
perfect, in regard to all those immeasurable minute par- ticulars by which the blood is adapted for the nutrition of every tissue, and the maintenance of every peculiarity of each. How precise the assimilation must be for such an adaptation, may be conceived from some of the cases in — which the blood is altered by disease, and by assimilation is maintained in its altered state. For example, by the insertion of vaccine matter, the blood is for a short time , manifestly diseased; however minute the portion of virus, it affects and alters, in some way, the whole of the blood. And the alteration thus produced, inconceivably slight as it must be, is long maintained; for even very long after a successful vaccination, a second insertion of the virus may have no effect, the blood being no longer amenable to its influence, because the new blood, formed after the vaccina- tion, is made like the blood as altered by the vaccine virus ; in other words, the blood exactly assimilates to its altered self the materials derived from the lymph and chyle. In health we cannot see the precision of the adjustment - of the blood to the tissues; but we may imagine it from the small influences by which, as in vaccination, it is disturbed; and we may be sure that the new blood is as perfectly assimilated to the healthy standard as in disease it is assimilated to the most minutely altered standard.* How far the assimilation of the blood is affected by any formative power which it may possess in common with the solid tissues, we know not. That this possible formative power is, however, if present, greatly ministered to and ‘assisted by the actions of other parts there can be no doubt ; as Ist, by the digestive and absorbent systems, and pro- bably by the liver, and all of the so-called vascular glands ; and, 2ndly, by the excretory organs, which separate from the blood refuse materials, including in this term not only
* Corresponding facts in relation to the maintenance of the tissues by assimilation will be mentioned in the chapter on NUTRITION .
;
USES OF THE BLOOD. | 95
the waste substance of the tissues, but also such matters as, having been taken with food and drink, may have been absorbed from the digestive canal, and have been sub- sequently found unfit to remain in the circulating current. And, 3rdly, the precise constitution of the blood is adjusted by the balance of the nutritive processes for maintaining the several tissues, so that none of the materials appro- priate for the maintenance of any part may remain in excess in the blood. Each part, by taking from the blood the materials it requires for its maintenance, is, as has been observed, in the relation of an excretory organ to all the rest; inasmuch as by abstracting the matters proper for its nutrition, it prevents excess of such matters as effectually as if they were separated from the blood and cast out altogether by the excreting organs specially present for such a purpose.
Uses of the Blood.
‘The purposes of the blood, thus developed and main- tained, appear, in the perfect state, to be these; Ist, to be a source whencc the various parts of the body may abstract the materials necessary for their nutrition and mainte- nance; and whence the secreting organs may take the materials for their various secretions; 2nd, to be a constantly replenished store-house of latent chemical force, which in its expenditure will maintain the heat of the body, or be transformed by the living tissues, and mani- fested by them in various forms as vital power; 3rd, to convey oxygen to the several tissues which may need it, either for the discharge of their functions, or for combination with their refuse matter ; 4th, to bring from all parts refuse matters, and convey them to places whence they may be dis- charged; 5th, to warm and moisten all parts of the body.
Uses of the various Constituents of the Blood.
Regarding the uses of the various constituents of the
96 USES OF THE BLOOD. |
blood it may be said that the matter almost resolves itself into an analysis of the different parts of the body, and of the food and drink which are taken for their nutrition, with a subsequent consideration of how far any given con- stituent of the blood may be supposed to be on its way to the living tissues, to be incorporated with and nourish them, or, having fulfilled its purpose, to be on its way ina more or less changed condition to the excretory organs to be cast out. It must be remembered, however, that the blood contains also matters which serve by their combustion to produce heat, and, again, others which possibly sub- serve only a mechanical, although most important, purpose ; as for instance the preservation of the due specific gravity of the blood, or some other quality by which it is enabled to maintain its proper relation to the vessels containing it and to the tissues through which it passes. Lastly, among the constituents of the blood, are the gases, oxygen and carbonic acid, and the substances specially adapted to carry them, which can scarcely be said to take part in the nutri- tion of the body, but are rather the means and evidence of the combustion before referred to, on which, to a great
extent, directly or indirectly, all vitality depends. Albumen.—The albumen, which exists in so large a
proportion among the chief constituents of the blood, is without doubt mainly for the nourishment of those tex- tures which contain it or other compounds nearly allied to it. Besides its purpose in nutrition, the albumen of the liquor sanguinis is doubtless of importance also in the maintenance of those essential physical properties of the blood to which reference has been already made.
Fibrin.—It has been mentioned in a previous part of this chapter that the idea of fibrin existing in the blood, as fibrin, is probably founded in error ; and that it is formed in the act of coagulation by the union of two substances, which before existed separately (p. 64). In considering, therefore, the functions of fibrin, we may exclude the notion
a
USES OF BLOOD. | 97
of its existence, as such, in the blood in a fluid state, and of its use in the nutrition of certain special textures, and look for the explanation of its functions to those circumstances, whether of health or disease, under which it is produced.
‘In hemorrhage, for example, the formation of fibrin in the
clotting of blood, is the means by which, at least for a time, the bleeding is restrained or stopped; and the material which is produced for the permanent healing of the injured part, contains a coagulable material probably identical, or very nearly so, with the fibrin of clotted blood.
‘atty Matters.—The fatty matters of the blood subserve more than one purpose. For while they are the means, at least in part, by which the fat of the body, so widely dis- tributed in the proper adipose and other textures, is re- plenished, they also, by their union with oxygen, assist in maintaining the temperature of the body. In certain secre- tions also, notably the milk and bile, fat is an important constituent. | |
' Saline Matter—The uses of the saline constituents of the blood are, first, to enter into the composition of such textures and s2cretions as naturally contain them, and, secondly, to assist in preserving the due specific gravity and alkalinity of the blood and, perhaps, also in preventing its decomposition. The phosphate and carbonate of sodium, besides maintaining the alkalinity of the blood, are said especially to preserve the liquidity of its albumen, and to favour its circulation through the capillaries, at the same time that they increase the absorptive power of the serum for gases. But although, from the constant presence of a certain quantity of saline matter in the blood, we may believe that it has these last-mentioned important functions in connection with the blood itself, apart from the nutri- tion of the body, yet, from the amount which is daily separated by the different excretory organs, and especially by the kidneys, we must also believe that a considerable quantity simply passes through the blood, both from the
H
98 | USES OF BLOOD.
food and from the tissues, as a temporary and useless con - stituent, to be excreted when opportunity offers. Corpuscles.—The uses of the red corpuscles are probably not yet fully known, but they may be inferred, at least in part, from the composition and properties of their contents. The affinity of hemoglobin for oxygen has been already ' mentioned; and the main function of the red corpuscles seems to be the absorption of oxygen in the lungs by means of this constituent, and its conveyance to all parts of the body, especially to those tissues, the nervous and mus- - cular, the discharge of whose functions depends in so great a degree upon a rapid and full supply of this element. The readiness with which hemoglobin absorbs oxygen, and
delivers it up again to a reducing agent, so well shown by —
the experiments of Prof. Stokes, admirably adapts it for this purpose. How far the red corpuscles are concerned in the nutrition of the tissues is quite unknown.
The relation of the white to the red corpuscles of the blood has been already considered (p. 92); of the functions of the former, other than are concerned in this relationship, nothing is positively known. Recent observations of the migration of the white corpuscles from the interior of the blood-vessels into the surrounding tissues (see Section, On the Circulation in the Capillaries) have, however, opened out a large field for investigation of their probable fune- tions in connection with the nutrition of the textures, in which, even in health, they appear to wander.
gts elt tee AS
a te
A att
THE CIRCULATION. 99
CHAPTER VI. CIRCULATION OF THE BLOOD.
Tux body is divided into two chief cavities—the chest or thorax and abdomen, by a curved muscular partition, called the diaphragm (fig. 31). The chest’is almost entirely filled by the lungs and heart; the latter being fitted in, so to speak, between the two lungs, nearer the front than - the back of the chest, and partly overlapped by them (fig. 31). Each of these organs is contained in a distinct bag, called respectively the right and left pleura and the pericardium, the latter being fibrous in the main, but lined on the inner aspect by a smooth shining epithelial covering, on which can glide, with but little friction, the equally smooth surface of the heart enveloped by it. In fig. 31 the containing bags of pleura and pericardium are sup- posed to have been removed, Entering the chest from above is a lerge and long air-tube, called the trachea, which divides into two branches, one for each lung, and through which air passes and repasses in respiration, Springing from the upper part or base of the heart may be seen the large vessels, arteries, and veins, which convey blood either to or from this organ.
In the living body the heart and lungs are in constant rhythmic movement, the result of which is an unceasing stream of air through the trachea alternately into and out of the lungs, and an unceasing stream of blood into and - out of the heart.
It is with this last event that we are concerned especially in this chapter,—with the means, that is to say, by which the blood which at one moment is forced out of the heart, is in a few moments more returned to it, again to depart, and again pass through the body in course of what is
H 2
100 THE CIRCULATION.
technically called the circulation. The purposes for which
this unceasing current is maintained, are indicated in the
uses of the blood enumerated in the preceding chapter. The blood is conveyed away from the heart by the
arteries, and returned to it by the veins; the arteries and.
veins being continuous with each other, at one end by means of the heart, and at the other by a fine network of vessels called the capillaries. The blood, therefore, in its passage from the heart passes first into the arteries, then into the capillaries, and lastly into the veins, by which it is conveyed back again to the heart,—thus completing a revolution, or circulation.
Fig. 31.*
As generally described there are two circulations by which all the blood must pass; the one, a shorter circuit
* Fig, 31. View of heart.and lungs in situ. The front portion of the chest-wall, and the outer or parietal layers of the pleure and peri- cardium have been removed. The lungs are partly collapsed.
>t ee
a
THE CIRCULATION. IOI
from the heart to the lungs and back again; the other and larger circuit, from the heart to all parts of the body and back again; but more strictly speaking, there is only one complete circulation, which may be diagrammatically repre- sented by a double loop, as in the accompanying figure. On reference to Fig. 32.*
this figure and noticing the di- rection of the ar- rows which repre- sent the course of the stream of blood, it will be observed that while there is a smaller and a larger circle both of which pass through the heart, yet that these are not distinct, “one from the other, but are formed really by one con- tinuous’ stream, the whole of which must, at i [7 _ 77 one part of ‘its course, pass through the lungs. Subor- dinate to the two principal circulations, the pulmonary and systemic as they are named, it will be noticed also in the same figure, that there is another, by which a portion of the stream of blood having been diverted once into the capillaries of the intestinal~canal, and some other organs, and gathered up again into a single stream, is a second time divided in its passage through the liver,
* Fig. 32. Diagram of the circulation.
102 THE CIRCULATION.
before it finally reaches the heart and completes a revolu- tion. This subordinate stream through the liver is called the portal circulation.
The principal force provided for constantly moving the blood through this course is that of the muscular substance of the heart; other assistant forces are (2) those of the elastic walls of the arteries, (3) the pressure of the muscles among which some of the veins run, (4) the movements of the walls of the chest in respiration, and probably, to some extent, (5), the interchange of relations between the blood and the tissues which ensues in the capillary system during the nutritive processes. The right direction of the blood’s. course is determined and maintained by the valves of the heart to be immediately described; which valves open to permit the movement of the blood in the course described, but close when any force tends to move it in the contrary direction.
We shall consider separately each member of the system of organs for the circulation: and first—
The Heart.
The heart is a hollow muscular organ, the interior of which is divided by a partition in such a manner as to form two chief chambers as cavities—right and left. Each of these chambers is again subdivided into an upper and a lower portion called respectively the auricle and ventricle, which freely communicate one with the other ; the aperture of communication, however, being guarded by valvular curtains, so disposed so as to allow blood to pass freely from theauricle into the ventricle, but not in the opposite direc- tion. There are thus four cavities altogether in the heart —two auricles and two ventricles; the auricle and ventricle of one side being quite separate from those of the other. The right auricle communicates, on the one hand, with the veins of the general system, and, on the other, with the right ventricle, while the latter leads directly into the pul- monary artery, the orifice of which is guarded by valves.
THE HEART. 103 The eft auricle again communicates, on the one hand, with the pulmonary veins, and on the other, with the left ventricle, while the latter leads directly i large artery which conveys blood to the general system, the orifice of which, like that of the pulmonary artery, is guarded by valves.
The arrangement of the heart’s valves is such that the blood can pass only in one definite direction, and this is as follows (fig. 33):—From the right auricle the blood passes into the right ventricle, and thence into the pulmo- nary artery, by which it is con- veyed to the ca- | pillaries of the | lungs. From the | lungs the blood, | whichis nowpuri- | fied and altered | in colour, is ga- thered by thepul- monary veins and | taken to the left auricle. Fromthe left auricle it | passes into the | left ventricle, and thence into the L ———_a_— aorta, by which it is distributed to the capillaries of every portion of the body. The branches of the aorta, from being distributed to the general system, are called systemic arteries; and from these the blood passes into the sys- temic capillaries, where it again becomes dark and impure, and thence into the branches of the systemic veins, which
* Fig. 33. Diagram of the circulation through the heart (after Dalton)
104 THE CIRCULATION.
forming by their union two large trunks, called the supe- rior and inferior vena cava, discharge their contents into the right auricle, whence we supposed the blood to start
(fig. 33). Structure of the Valves of the Heart.
It will be well now to consider the structure of the
Fig. 34.*
* Fig. 34. The right auricle and ventricle opened, and a part of
their right and anterior walls removed, so as to show their interior. 4. —lI, superior vena cava; 2, inferior vena cava; 2’, hepatic veins cut short ; 3, right auricle; 3’, placed in the fossa ovalis, below which is the Eustachian valve ; 3", is placed close to the aperture of the coronary
STRUCTURE OF HEART’S VALVES. 105
valves of the heart, and the manner in which they perform their function of directing the stream of blood in the course which has been just described. The valve between the right auricle and ventricle is named tricuspid (fig. 34), because it presents three principal cusps or pointed portions, and that between the left auricle and ventricle bicuspid or mitral, because it has two such portions (fig. 35). But in both valves there is between each two principal portions a smaller one; so that more properly, the tricuspid may be described as consisting of six, and the mitral of four, por- tions. Each portion is of triangular form, its apex and sides lying free in the cavity of the ventricle, and its base, which is continuous with the bases of the neighbouring portions, so as to form an annular membrane around the auriculo-ventricular opening, being fixed to a tendinous ring, which encircles the orifice between the auricle and ventricle, and receives the insertions of the muscular fibres of both. In each principal portion of the valve may be distinguished a middle-piece, extending from its base to its apex, and including about half its width; this piece is thicker, and: much tougher and tighter than the border-
_ pieces which are attached loose and flapping at its sides. While the bases of the several portions of the valves are fixed to the tendinous rings, their ventricular surfaces
vein; +, +, placed in the auriculo-ventricular groove, where a narrow portion of the adjacent walls of the auricle and ventricle has been pre- ‘served ; 4, 4, cavity of the right ventricle, the upper figure is imme- diately below the semilunar valves ; 4’, large columna carnea or mus- culus papillaris ; 5, 5’, 5", tricuspid valve ; 6, placed in the interior of the pulmonary artery, a part of the anterior wall of that vessel having been removed, and a nayrow portion of it preserved at its commence- ment where the semilunar valves are attached; 7, concavity of the aortic arch close to the cord of the ductus arteriosus ; 8, ascending part or sinus of the arch covered at its commencement by the auricular appendix and pulmonary artery ; 9, placed between the innominate and left carotid arteries ; 10, appendix of the left auricle ; 11, 11, the outside of the left ventricle, the lower figure near the apex. (From Quain’s Anatomy.)
106 THE CIRCULATION.
and borders are fastened by slender tendinous fibres, the chord@ tendinea, to the walls of the ventricles, the muscular fibres of which project into the ventricular cavity in the
Fig. 35.*
* Fig. 35. The left auricle and ventricle opened and a part of their anterior and left walls removed so as to show theirinterior. 4.—The pulmonary artery has been divided at its commencement so as to show the aorta ; the opening into the left ventricle has been carried a short distance into the aorta between two of the segments of the semilunar valves ; the left part of the auricle with its appendix has been removed.
STRUCTURE OF HEART’S VALVES. 107
form of bundies or columns—the columne@ carnee. These columns are not all of them alike, for while some of them are attached along their whole length on one side, and by their extremities, others are attached only by their extremities; and a third set, to which the name musculi papillares has been given, are attached to the wall of the ventricle by one extremity only, the other projecting, papilla-like, into the cavity of the ventricle (5, fig. 35), and having attached to it chorde tendinee. Of the tendinous cords, besides those which pass from the walls of the ven- tricle and the musculi papillares, to the margins of the valves both free and attached, there are some of especial strength, which pass from the same parts to the edges of the middle pieces of the several chief portions of the valve. The ends of these cords are spread out in the substance of the valve, giving its middle piece its peculiar strength and toughness; and from the sides numerous other more slender and branching cords are given off, which are
The right auriele has been thrown out of view. 1, the two right pul- monary veins cut short’; their openings are seen within the auricle ; 1’, placed within the cavity of the auricle on the left side of the septum and on the part which forms the remains of the valve of the foramen
: ovale, of which the crescentic fold is seen towards the left hand of 1’ ;
2, a narrow portion of the wall of the auricle and ventricle preserved round the auriculo-ventricular orifice ; 3, 3/, the cut surface of the walls of the ventricle, seen to become very much thinner towards 3", at the apex ; 4, a small part of the anterior wall of the left ventricle which has been preserved with the principal anterior columna carnea or musculus papillaris attached to it; 5, 5, musculi papillares ; 5’, the left side of the septum between the two ventricles, within the cavity of the left ventricle; 6, 6, the mitral valve ; 7, placed in the interior of the aorta near its commencement and above the three segments of its semilunar valve which are hanging loosely together ; 7’, the exterior of the great aortic sinus ; 8, the root of the pulmonary artery and its semilunar valves ; 8’, the separated portion of the pulmonary artery remaining attached to the aorta by 9, the cord of the ductus arteriosus ; 10, ‘the arteries rising from the summit of the aortic arch. (From Quain’s Anatomy.)
108 THE CIRCULATION.
attached all over the ventricular surface of the adjacent border-pieces of the principal portions of the valves, as well as to those smaller portions which have been mentioned as lying between each two principal ones. Moreover, the musculi papillares are so placed that from the summit of each tendinous cords may proceed to the adjacent halves of two of the principal divisions, and to one intermediate or smaller division, of the valve.
It has been already said that while the ventricles com- municate, on the one hand, with the auricles, they communi- cate, on the other, with the large arteries which convey the blood away from the heart; the right ventricle with the pul- monary artery (6, fig. 34), which conveys blood to the lungs, and the left ventricle with the aorta, which distributes it to the general system (7, fig. 35). And as the auriculo- ventricular orifice is guarded by valves, so are also the mouths of the pulmonary artery and aorta (figs. 34, 35).
The valves, three in number, which guard the orifice of each of these two arteries, are called the semilunar valves. They are nearly alike on both sides of the heart; but those of the aorta are altogether thicker and more strongly con- structed than those of the pulmonary artery. Like the tricuspid and mitral valves, they are formed by a dupli- cature of the lining membrane of the heart, strengthened by fibrous tissue. Each valve is of semilunar shape, its convex margin being attached to a fibrous ring at the place of junction of the artery to the ventricle, and the concave or nearly straight border being free (fig. 35). In the centre of the free edge of the valve, which contains a fine cord of fibrous tissue, is a small fibrous nodule, the
corpus Arantii, and from this and from the attached border .
fine fibres extend into every part of the mid substance of the valve, except a small lunated space just within the free edge, on each side of the corpus Arantii. Here the valve is thinnest, and composed of little more than the endocardium. Thus constructed and attached, the three
any, ay all
ACTION OF THE HEART. 109
semilunar valves are placed side by side around the arterial orifice of each ventricle, so as to form three little pouches, which can be thrown back and flattened by the blood pass- ing out of the ventricle, but which belly out immediately so as to prevent any return (6, fig. 34). This will be again referred to immediately.
The muscular fibres of the heart; unlike those of most involuntary muscles, present a striated appearance under the microscope. (See Chapter on Motion.)
THE ACTION OF THE HEART.
The heart’s action in propelling the blood consists in the successive alternate contractions and dilatations of the mus- cular walls of its two auricles and two ventricles. The auricles contract simultaneously ; so do the ventricles ; their dilatations also are severally simultaneous; and the con- tractions of the one pair of cavities are synchronous with the dilatations of the other.
- The description of the action of the heart may best be commenced at that period in each action whichimmediately precedes the beat of the heart against the side of the chest, and, by a very small interval more, precedes the pulse at the wrist. For at this time the whole heart is in a passive state, the walls of both auricles and ventricles are relaxed, and their cavities are being dilated. The auricles are gradually filling with blood flowing into them from the veins ; and a portion of this blood passes at once through them into the ventricles, the opening between the cavity of each auricle and that of its corresponding ventricle being, during all the pause, free and patent. The auricles, however, receiving more blood than at once passes through them to the ventricles, become, near the end of the pause, fully distended ; then, in the end of the pause, they con- tract and empty their contents into the ventricles. The contraction of the auricles is sudden and very quick; it commences at the entrance of the great veins into them,
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110. THE CIRCULATION.
and is thence propagated towards the ariculo-ventricular opening; but the last part which contracts is the aricular appendix. The effect of this contraction of the auricles is to propel nearly the whole of their blood into the ventricles. The reflux of blood into the great veins is resisted not only by the mass of blood in the veins and the force with which it streams into -the auricles, but also by the simultaneous contraction of the muscular coats with which the large veins are provided for some distance before their entrance into the auricles; a resistance which, however, is not so complete but that a small quantity of blood does regurgi4 tate, i.e., flow backwards into the veins, at each auricular contraction. The effect of this regurgitation from the right auricle is limited by the valves at the junction of the subclavian and internal jugular veins, beyond which the blood cannot move backwards; and the coronary vein, or vein which brings back to the right auricle the blood which has circulated in the substance of the heart,