stoke a ito tet os ate S| Meee Nan a i Meehan be hin eoreeny i tee ah Ne bn re ne 133 3333 i eas EPEE EEE S he ive + HEE eetete! tre tF E : tee + 2534 ET EEEE 44 hoe Nee 83 E FS La prergrerexprpes ‘ 4 fe le *, te vn -F; + sy ($5 a3: re. $3: a3 Laas 3 -F: 24 t is 34 “5 +. ¢ te. eft 1% ok -t iss ies :3 33 p33 FLEE 233 se state i atititatal ir I, meetrins : oe i a iit et ra iss praia ae oe Le be re — ha ide : . ry = —_ oe ere |. a fi fj e RSs § ’ Weg re tie eae ee) ere i ie | ry 4 , é " yet , S ae) | i ae » ia Shiny . Ad r Seas } Ves 2 Raab’ led 4 hai VAN) rh ah Lia He a ih Uh i Orr: iid il ie ™ a ea Rae ree Ls : ) cae i sa Ay ) Ove ae Ana 4 Li 1 i) pee y i 1 Z : ; 5 QUAIN’S ANATOMY, at ony) : ¥2 QUAIN’S Re O\s ‘ELEMENTS OF ANATOMY ~ =e ere NS YMNL NN Ns s\ EDITED Ns Sade Ss [EQ WILLIAM SHARPEY, MD, LL.D, F.RS.°L. & E, EMERITUS PROFESSOR OF ANATOMY AND PHYSIOLOGY IN UNIVERSITY COLLEGE, LONDON ALLEN THOMSON, M.D., LL.D. F.RS. L & E, PROFESSOR OF ANATOMY IN THE UNIVERSITY OF GLASGOW AND EDWARD ALBERT SCHAFER ASSISTANT PROFESSOR OF PHYSIOLOGY IN UNIVERSITY COLLEGE, LONDON IN TWO VOLUMES. ILLUSTRATED BY UPWARDS OF 950 ENGRAVINGS ON WOOD. VOLS ET. Cigqhth Endttton. NEW YORK WILLIAM WOOD AND CO., PUBLISHERS | 27 GREAT JONES STREET 1878. CONTENTS. GENERAL ANATOMY. GENERAL CONSIDERATIONS ON THE TEXTURES ‘ Enumeration of the Textures Organic Systems Structural Elements Physical Properties . Chemical Composition . Vital Properties DEVELOPMENT OF THE TEXTURES The Vegetable Cell The Animal Cell . , Nutrition and Regeneration of the Textures . 5 THE BLoop . Physical and Organic Constitu- tion : Chemical Composition P Coagulation of the Blood . THE LyMPH AND CHYLE Formation of the Corpuscles of the Lymph and Chyle . : Formation of the Blood-Cor- puscles EPITHELIAL, EPIDERMIC, oR Cu- TICULAR TISSUE ; Ciliated Epithelium. PIGMENT : CONNECTIVE TrssvE The Areolar Tissue Adipose Tissue Fibrous Tissue . Yellow or Elastic Tissue Special Varieties of Connective Tissue . Development of the Connective Tissue : CARTILAGE . Hyaline Cartilage . : : Elastic or Yellow Cartilage White Fibro-Cartilage . Bone oR Ossrous Tissur . Physical Properties Chemical Composition Structure Periosteum Marrow PAGE CONII DP WN N SH Blood-Vessels, &c. . Formation and Growth of Bone. Ossification in Membrane . Ossification in Cartilage . Growth and Absorption of Bone Muscutar TIssuE Structure of Voluntary Muscles. Sheath : : nae Fasciculi Fibres : Blood- Vessels, ke. Involuntary Muscles Development and Growth Muscle . Composition and Properties of Muscular Tissue Te Nervous SYSTEM 5 Structural Elements : White or Medullated F ibres : Grey Fibres : Ganglia. The Cerebro- ‘Spinal Nerves The Sympathetic or Canghoa Nerves : Chemical Composition Vital Properties : Development of Nerves Bioop- VESSELS ‘ Arteries Veins . Smaller Arteries and Veins and Capillaries . - Development of Blood-Vessels . "of - LYMPHATIC SYSTEM Lymphatic Glands Srrous MEMBRANES SynoviAL MEMBRANES Mucous MEMBRANES Tue SKIN . Epidermis, Cuticle, or Scarf Skin Corium Nails and Hairs Glands of the Skin SECRETING GLANDS DucTLess oR VASCULAR Ganps. PAGE 92 94 94 97 103 107 108 108 109 III 116 118 SPECIAL ANATOMY ’ PAGE Tur THORACIC VISCERA. 239 The Pericardium 239 Tue HEART 242 Position of the Parts of the Heart with Relation to the Wall of the Thorax 253 Intimate Structure of the Heart. 255 Dimensions and Weight of the Heart 262 Orcans oF RESPIRATION 263 The Trachea and Bronchi 263 Structure 266 The Lungs and Pleure . 268 The Pleurze 268 The Lungs 269 Root of the Lung . 273 Structure . : 5 ea The Larynx or Organ of Voice . 280 Cartilages of the Larynx 280 Ligaments end Joints 283 Interior of the Larynx . 285 Muscles of the Larynx . A Aste) Mucous Membrane and Glands 293 Vessels and Nerves 294 Formation and Growth of the Larynx . 294. Dvuctirss GLANDS oF ‘THE LA- RYNX AND TRACHEA 295 The Thyroid Body 295 The Thymus Gland . 207 ORGANS OF DIGESTION 300 The Mouth 300 The Teeth 301 General Characters 301 Structure . 306 Formation of the Teeth. 313 Secondary Dentine. oh oe SLE: The Tongue. : ese Mucous Membrane 32 Muscular Substance . 331 The Palate . : . . d 333 The Tonsils : 335 The Salivary Glands 33 Parotid Gland 335 Submaxillary Gland . 337 Sublingual gland : ses Structure of the Salivary Glands . . : ee 80 The Pharynx . : 2 9340 The @sophagus . ee sa3 THB ABDOMINAL VISCERA : - 346 The Abdomen. : en o46 The Peritoneum ; = 349 The Stomach : By Bile) Structure. , 2 B50 Tur Smauu INTEsTiINE . Bw st Structure . 358 Special Characters and Connec- tions of the Different Parts of the Small Intestine . ‘$360 CONTENTS. OF THE VISCERA. PAGE The Large Intestine . B7t Structure . 371 Special Characters and Con- nections of the Different Parts of the Large Intestine 374 The Anus and its Muscles 379 The Liver : 380 Structure 386 The Pancreas 394, The Spleen 397 Structure . : 398 THE URINARY ORGANS 402 Kidneys 402 Suprarenal Bodies 413 The Ureters. 417 The Urinary Bladder. 419 Structure . 23 The Urethra 427 REPRODUCTIVE ORGANS IN THE MALE ; 427 The Prostate Gland 427 The Penis ; 430 Corpora Cavernosa 431 Corpus Spongiosum . 435 Urethra of the Male . 436 Testicles and Accessory Strue- tures . 440 Coverings of the Testis and Cord . 440 The Testicles 445 Vas Deferens . 450 Seminal Vessels and Ejacula- tory Ducts : 451 Vessels and Nerves of the Testis . 453 REPRODUCTIVE ORGANS IN THE FEMALE The Vulva 456 The Female Urethra _ 459 The Vagina 460 The Uterus . : 462 Fallopian Tubes 470 The Ovaries . 471 Structure 472 THE PERITONEUM 481 MAMMARY GLANDS 486 Structure 486 | Tur CEREBRO-SPINAL AXIS 489 SPINAL Corp . 489 External Form 489 Internal Structure 494 Minute Structure 497 THE ENCEPHALON . 502 The Medulla Oblongata 503 The Pons Varolii . Sit Internal Structure . SII The Cerebellum 515 Internal Structure. 518 Minute Structure 520 The Cerebrum . 5 ; 522 Exterior of the Cerebrum . Internal or Median and Ten- torial Surface. ae Base of the Cerebrum 2 Internal Parts of the Cerebrum Internal Structure of the Cere- brumi = : ; White Matter Grey Matter Meynert’s Terminology Origin of the Cranial Nerves . Membranes of the Brain and Spinal Cord . 5 4 The Dura Mater The Pia Mater . The Arachnoid Membrane Blood-Vessels of the Brain and Spinal Cord : : Blood-Supply of the Brain Size and Weight of the has alon : Weight of the Spinal Cord Specific Gravity of the En- cephalon a it ORGANS OF THE SENSES THe Eyre . The Kyelids and Conjunctiva . The Lachrymal Apparatus. The Globe of the Kye The Sclerotic Coat. PAGE 522 531 533 537 553 553 556 564 565 569 569 571 572 576 576 577 582 CONTENTS. The Cornea 3 The Choroid Coat . The Iris Retina or Nervous Tunic The Vitreous “ae The Lens Aqueous Humour and its Chamber ; , THe Har. ; External Ear. The Pinna The External Canal The Middle Ear or Tympanam Small Bones of the Ear. Ligaments and Muscles of the Tympanum . : The Lining Membrane Vessels and Nerves : The Internal Ear or Labyrinth. _ The Osseous Labyrinth The Membranous ase Vestibule Semicircular C anals Cochlea . p Organ of Corti . THE NOsE . ; Cartilages of the Nose . Nasal F ossee Mucous Membrane. Auditory EMBRYOLOGY ; OR, DEVELOPMENT OF THE F@TUS AND ITS ORGANS. THE OvuM: ITs MATURATION, FE- CUNDATION, AND SEGMENTA- TION: FORMATION OF THE BLASTODERM. F The Mature Ovarian Ovum : Distinction of the Germ Disappearance of the Germinal Vesicle P Fecundation . Segmentation of the Yolk In the Mammal’s Ovum . In the Bird’s Ovum . Tue BLASTODERM: ITs STRUC- TURE AND RELATION TO THE DEVELOPMENT OF THE EM- BRYO . 5 Z Position and Extent — Trilaminar Structure Relation of the Layers to De- velopment : Discovery of the Blastodermic Elements Snort OUTLINE oF THE “MORE GENERAL PHENOMENA OF DEVELOPMENT OF THE OvuM Distinction of Embryonic and Peripheral Phenomena . . INTRA-EMBRYONIC PHENOMENA OF DEVELOPMENT Axial Rudiment of the Em- bryo : Cerebro-Spinal Axis. The Notochord . ; Protovertebre Pleural Cleavage of the Lateral Parts of the “Mesoblast : Inflection of the Walls of the Body of the Embryo . The Cerebro- oe Nervous Centre . The Nerves Organs of the Senses Vascular System Alimentary Canal Reproductive and Organs . The Limbs ExtTrRA-EMBRYONIC PHENOMENA oF DEVELOPMENT. Foetal Membranes . The Yolk-Sac The Amnion , The Allantois : Urinary Vesicle The Chorion Villi of the Chorion a PAGE Endochorion or Vascular zene of the Allantois . : 709 UTEROGESTATION: PLACENTAT ION 710 Incapsulation of the Ovum in the Decidua : 710 Earliest Observed Human Ova 710 Formation of Decidua_ . WII Structure of the Placenta . . 718 Circulation of Blood in the Placenta . 719 Further Consideration of the Structure of the Placenta . 721 General Conclusion i 723 Separation at Birth and Resto- ration of the Mucous Mem- brane of the Uterus 2A DEVELOPMENT OF PARTICULAR ORGANS AND SYSTEMS . 725 THE SKELETON AND ORGANS OF VotunTary Morion. . 725 VertebralColumn and Trunk 725 Segmentation of the Proto- ° vertebre . ; 2S Formation of Vertebral Matrices . : : 730 The Head . : ‘ | eee The Cranium . ; 3 7382 The Cranial Flexures . 733 Formation of the Mouth and Hypophysis Cerebri a get Suberanial, Facial, or Pha- ryngeal Plates or Arches. 738 Relations of Cranial Nerves. 740 Origin and Formation of the Limbs Ae Development of the Muscles . 744. Formation of the Joints. . 745 DEVELOPMENT OF THE ORGANS OF THE Nrervous Systrem . 746 The Spinal Marrow . 5 WES The Brain or Encephalon . . 750 General Phenomena of De- velopment in Birds and Mammals : 750 Farther Development of the Brain in Man and Mam- mals é : 5 ONE Development of the Nerves . 760 Development of the Eye . . 762 Development of the Nose. . 772 DEVELOPMENT OF THE ALIMEN- TARY CANAL AND ORGANS ARISING FROM THE Hypo- BLAST . : eae Alimentary Canal . F : ioe The Liver. : P 5S. oie The Pancreas. 781 The Spleen, Lymphatic Glands, Thymus and oe roid Glands . : 782 INDEX TO VOLUME II. CONTENTS. PAGE DEVELOPMENT OF THE LUNGS AND TRACHEA : ec ae Oe Pleure . : : 7 9793 Pulmonary Vessels. : 783 DEVELOPMENT OF THE HEART AND BLOOD-VESSELS . oe: Development of the Heart . 784 Origin of the Heart . 21 784 Division into single Auricle, Ventricle, and Arterial Bulb . ‘ 787 Division of the Cavities : Ventricles . OST Division of the Auricles. . 788 Division ofthe Arterial Bulb 789 Formation of the Valves . 791 Development of the Blood- Vessels. Or The Principal Arteries : the Aorta . 7Q1 Aortic or Branchial Arches. 793 Development of the Great Veins. 796 Peculiarities of the Foetal Or- gans of Circulation . . 799 Course of the Blood in the Fetus 802 Changes in the ‘Circulation at Birth : 803 DEVELOPMENT OF THE GENITAL AND URINARY ORGANS . . 804 Primary Formation of the Uro- Genital System : . 804 Wolffian Bodies. 804 First Origin of the Wolffian Bodies . $06 Homologies of the Wolffian Body . : 809 The External Organs , OLE Further History of the Deve- lopment of the Uro-Genital Organs 5 tes The Urinar y Bladder and Urachus . - a) 3 Genital Cord . : OLA: Reproductive Organs. tora Reproductive Glands . . 814 Thewlesticle ar : OLS The Ovary . 5) 5 ae The Genital Passages : : 818 The Female Passages . . 819 The Male Passages . : 821 The Descent of the Testicles 823 Type of Development and Ab- normal Forms of the Genital Orcanseeaee 825 Table of Corresponding Parts of Genito-Urinary Organs, and their Relation to Formative Rudiments. : pk 520 827 GENERAL ANATOMY. GENERAL CONSIDERATIONS ON THE TEXTURES. Enumeration of the Textures.—The human body consists of solids and fluids. Only the solid parts can be reckoned as textures, properly so called ; still, as some of the fluids, viz. the blood, chyle, and lymph, contain in suspension solid organised corpuscles of deter- minate form and organic properties, and are not mere products or secretions of a particular organ, or confined to a particular part, the corpuscles of these fluids, though not coherent textures, are to be looked upon as organised constituents of the body, and as such may not improperly be considered along with the solid tissues. In con- formity with this view the textures and other organised constituents of the frame may be enumerated as follows :— The blood, chyle, and lymph. Epithelial tissue, including epithelium, cuticle, nails, and hairs. Pigment. Connective tissue, viz. Areolar tissue. Adipose tissue. Fibrous tissue. Elastic tissue. Cartilage and its varieties. Bone or osseous tissue. Muscle. Nerve. Blood-vessels. Lymphatic vessels and glands. Serous and synovial membranes. Mucous membrane. Skin. Secreting glands. Vascular or ductless glands. - Organic Systems.-—Every texture taken as a whole was viewed by Bichat as constituting a peculiar system, presenting throughout its whole extent in the body characters either the same, or modified only so far as its local connections and uses render necessary ; he accordingly used the term “ organic systems” to designate the textures taken in this point of view, and the term was very generally employed by succeeding writers. Of the tissues or organic systems enumerated VOL, II. B 2 GENERAL CONSIDERATIONS ON THE TEXTURES. some are found in nearly every organ ; such is the case with the con- nective tissue, which serves as a binding material to hold together the other tissues which go to form an organ; the vessels, which convey fluids for the nutrition of the other textures, and the nerves, which establish a mutual dependence among different organs, imparting to them sensibility, and governing their movements. These were named by Bichat the “ general systems.” Others again, as the cartilaginous and osseous, being confined to a limited number or to a particular class of organs, he named “ particular systems.” Lastly, there are some tissues of such limited occurrence that it has appeared more convenient to leave them out of the general enumeration altogether, and to defer the consideration of them until the particular organs in which they are found come to be treated of. Accordingly, the tissues peculiar to the crystalline lens, the teeth, and some other parts, though equally independent textures with those above enumerated, are for the reason assigned not to be described in this part of the work. Structural Elements.—It is further to be observed, that the anatomical constituents of the body above enumerated are by no means to be regarded as simple structural elements; on the contrary, many of them are complex in constitution, being made up of several more simple tissues. The blood-vessels, for instance, are composed of several coats of different structure, and some of these coats consist of more than one tissue. They are properly rather organs than textures, although they are here included with the latter in order that their general structure and properties may be considered apart from their local distri- bution ; but indeed it may be remarked, that the distinction between textures and organs has not in general been strictly attended to by anatomists. The same remark applies to mucous membrane and the tissue of the glands, which structures, as commonly understood, are highly complex. Were we to separate every tissue into the simplest parts which possess assignable form, we should resolve the whole into a very few constructive elements. 5 ad PHYSICAL PROPERTIES. The animal tissues, like other forms of matter, are endowed with various physical properties, such as consistency, density, colour, and the like. Of these the most interesting to the physiologist is the pro- perty of imbibing fluids, and of permitting fluids to pass through their substance, which is essentially connected with some of the most im- portant phenomena that occur in the living body, and seems indeed to be indispensable for the maintenance and manifestation of life. All the soft tissues contain water, some of them more than four-fifths of their weight ; this they lose by drying, and with it their softness and flexibility, and so shrink up into smaller bulk and become hard, brittle, and transparent: but when the dried tissue is placed in contact with water, it greedily imbibes the fluid again, and recovers its former size, weight, and mechanical properties. The imbibed water is no doubt partly contained mechanically in the interstices of the tissue, and retained there by capillary attraction, like water in moist sand- stone or other inorganic porous substances ; but the essential part of the process of imbibition by an animal tissue is not to be ascribed to mere porosity, for the fluid is not merely lodged between the fibres or laminz, or in the cavities of the texture ; a part, probably the chief part, is incorporated with the matter which CHEMICAL COMPOSITION OF THE TEXTURES, 3 forms the tissue, and is in a state of union with it, more intimate than could well be ascribed to the mere inclusion of a fluid in the pores of another substance. Be this as it may, it is clear that the tissues, even in their inmost substance, are permeable to fluids, and this property is indeed necessary, not only to maintain their due softness, pliancy, elasticity, and other mechanical qualities, but also to allow matters to be conveyed into and out of their substance in the process of nutrition. CHEMICAL COMPOSITION. Ultimate Constituents.—The human body is capable of being resolved by ultimate analysis into chemical elements, or simple consti- tuents, not differing in nature from those which compose mineral substances. Of the chemical elements known to exist in nature, the following have been discovered in the human body, though it must be remarked, that some of them occur only in exceedingly. minute quan- tity, if indeed they be constant : oxygen, hydrogen, carbon, nitrogen, phosphorus, sulphur, chlorine, fluorine, potassium, sodium, calcium, magnesium, iron, silicon, manganese, aluminium, copper. Proximate Constituents.—The ultimate elements do not directly form the textures or fluids of the body ; they first combine to form certain compounds, and these appear as the more immediate consti- tuents of the animal substance; at least the animal tissue or fluid yields these compounds, and they in their turn are decomposed into the ultimate elements. Of the immediate constituents some are found also in the mineral kingdom, as for example, water, chloride of sodium or common salt, and carbonate of lime; others, such as albumin, fibrin, and fat, are peculiar to organic bodies, and are accordingly named the proximate organic principles. The animal proximate principles have the following leading cha- racters. ‘They all contain carbon, oxygen, and hydrogen, and the ereater number also nitrogen ; they are all decomposed by a red heat; and, excepting the fatty and acid principles, they are, for the most part, extremely prone to putrefaction, or spontaneous decomposition, at least, when in a moist state ; the chief products to which their putrefaction gives rise being water, carbonic acid, ammonia, and sulphuretted, phos- phuretted, and carburetted hydrogen gases. The immediate compounds obtained from the solids and fluids of the human body are the following. I. Azotised Substances, or such as contain nitrogen, VizZ., albumin, blood-fibrin, myosin, syntonin, casein, globulin, ‘eelatin, ’ chondrin, salivin, kreatin, kreatinin, pepsin, mucin, horny matter or keratin, pig- ment, hemoglobin, urea, uric acid, hippuric acid, inosinic acid, s sarkin (or hy poxanthin), leucin, tyrosin, protagon and its components lecithin and neurin, azotised biliary compounds. II. Substances destitute of Nitrogen, viz., fatty matters, glycogen (or animal starch), grape sugar, sugar of milk, inosit, lactic, formic, and oxalic acids, certain principles of the bile. Some of the substances now enumerated require no further notice in a work devoted to anatomy. Of the rest, the greater number will be explained, as far as may be necessary for our purpose, in treating of the . particular solids or fluids in which they are chiefly found. it has been shown by Graham,* that chemical substances may be distinguished * Liquid Diffusion applied to Analysis,—Phil. Trans., 1861. t GENERAL CONSIDERATIONS ON THE TEXTURES. into two classes—the crystalloid and the colloid—which differ in several important characters. Crystalloid bodies, of which water, most salts and acids, and sugar, may be taken as examples. have a disposition to assume a crystalline state ; their solutions are usually sapid, diffluent, and free from viscosity ; they readily diffuse in liquids, and pass through moist organic membranes or artificial septa of organic matter, such as parchment-paper. Colloids, on the other hand, are characterised by low diffusibility and great indisposition to permeate organic septa, so that when they are associated with crystalloids, the latter may be easily separated by diffusion through a septum into another fluid ; i.e., by “ dialysis.” Colloids are, moreover, generally tasteless; they have little or no tendency to crystallize, and their solution, when concentrated, is always, in a certain degree, viscous or gummy. Among the colloids may be reckoned hydrated silicic acid, and various hydrated metallic peroxides, also albumin, gelatin, starch, gum, and vegetable and animal extractive matters. Several substances may exist either in the colloid or the crystalloid condition. In point of chemical activity the crystalloid appears to be the more energetic, and the colloidal the more inert form of matter; but the colloids possess an activity of their own, arising out of their physical properties, and especially their penetrability, by which they become a medium for liquid diffusion, like water itself. Another characteristic is their tendeney to change ; the solution of hydrated silicic acid, for instance, cannot be preserved ; after a time it congeals. In this respect a liquid colloid might be compared to liquid water at a temperature below freezing, or to a supersaturated saline solution. This dominant tendency of the particles of a colloid to cohere, ggregate, and contract, is obvious in the gradual thickening of the liquid and its conversion into a jelly ; and in the jelly itself the contraction still proceeds, causing separation of water, and division into a clot and serum. Their permea- bility to fluids, their ready capability of physical changes, and their comparative chemical inertness, are properties by which colloid bodies seem fitted to form organised structures, and to take part in the processes of the living economy. Graham further found that silicic acid may combine both in a dissolved and in a gelatinous state with a variety of very different fluids without undergoing alteration; and presuming that the organic colloids are invested with similar wide powers of combination, he remarks that the capacity of a mass of gelatinous silicic acid to assume alcohol, or even olein, without disintegration or alteration of form, and to yield it up again in favour of some other substituted fluid, may perhaps afford a clue to the penetration of the colloid matter of animal membrane by fatty and other bodies insoluble in water; and moreover, that the existence of fluid compounds of silicic acid of a like nature, suggests the possibility of the formation of a compound of colloid albumen with olein, soluble also and capable of circulating with the blood.* _ The important relation which this chemical doctrine bears to the constitu- tion and organic processes of the animal body, has appeared to justify the introduction of the present notice of it; for further information the reader is referred to the sources already cited. VITAL PROPERTIES OF THE TEXTURES. Of the phenomena exhibited by living bodies, there are some which, in the present state of knowledge, cannot be referred to the operation of any of the forces which manifest themselves in inorganic nature ; they are therefore ascribed to certain powers, endowments, or properties, which so far as known, are peculiar to living bodies, and are accord- ingly named “ vital properties.” These vital properties are called into play by various stimuli, external and internal, physical, chemical, and mental ; and the assemblage of actions thence resulting has been designated by the term “ life.” The words “life” and “vitality ” are * On the Properties of Silicie Acid and other Analogous Colloidal Substances, —Pro- ceedings of the Royal Society, June 16th, 1864. VITAL PROPERTIES OF THE TEXTURES. o) often also employed to signify a single principle, force, or agent, which has been regarded as the common source of all vital properties, and the common cause of all vital actions. As ordinary physical forces, such as mechanical motion, heat, electricity, chemical action, and the like, although differing from each other in specific character and mode of operation, are nevertheless shown to be mutually con- vertible and equivalent, and are held to be but different modifications of one and the same common force or “ energy.” so it may in like manner come to be shown that vital action is similarly related to the physical forces as they are related to each other, and is also a manifestation, under conditions special to the living economy, of the same common energy. 1. Assimilatory Property.—Of the vital properties, there is one which is universal in its existence among organised beings, namely, the property, with which all such beings are endowed, of converting into their own substance, or “ assimilating,” alimentary matter. The opera- tion of this power is seen in the continual renovation of the materials of the body by nutrition, and in the increase and extension of the organised substance, which necessarily takes place in growth and repro- duction ; it manifests itself, moreover, in individual textures as well as in the entire organism. It has been called the “assimilative force or property,” “ organising force,” “ plastic force,” and is known also by various other names. But in reality the process of assimilation pro- duces two different effects on the matter assimilated: first, the nutrient material, previously in a liquid or amorphous condition, acquires deter- minate form ; and secondly, it may, and commonly does, undergo more or less change in its chemical qualities. Such being the case, it seems reasonable, in the mean time, to refer these two changes to the opera- tion of two distinct agencies, and, with Schwann, to reserve the name of “ plastic” force for that which gives to matter a definite organic form ; the other, which he proposes to call “ metabolic,” being already generally named “ vital affinity.” Respecting the last-named agency, however, it has been long since remarked, that although the products of chemical changes in living bodies for the most part differ from those appearing in the inorganic world, the difference is nevertheless to be ascribed, not to a peculiar or exclusively vital affinity different from ordinary chemical affinity, but to common chemical affinity operating in circumstances or conditions which present themselves in living bodies only. 2. Vital Contractility. When a muscle, or a tissue containing muscular fibres, is exposed in an animal during life, or soon after death, and scratched with the point of a knife, it contracts or shortens itself ; and the property of thus visibly contracting on the application of a stimulus is named “ vital contractility,” or “ irritability,” in the restricted sense of this latter term. The property in question may be called into play by various’ other stimuli besides that of mechanical irritation—especially by electricity, the sudden application of heat or cold, salt, and various other chemical agents of an acrid character, and, in a large class of muscles, by the exercise of the will, or by involuntary mental stimuli. The evidence that a tissue possesses vital contractility is derived, of course, from the fact of its contracting on the application of a stimulus. 6 DEVELOPMENT OF THE TEXTURES. Mechanical irritation, as scratching with a sharp point, or slightly pinching with the forceps, electricity obtained from a piece of copper and a piece of zinc, or from a larger apparatus if necessary, and the sudden application of cold, are the stimuli most commonly applied. 3. Vis Nervosa..—The stimulus which excites contraction may be applied either directly to the muscle, or to the nerves entering 1t, which then communicate the effect to the muscular fibre, and it is in the latter mode that the voluntary or other mental stimuli are transmitted to muscles from the brain. Moreover, a muscle may be excited to con- tract by irritation of a nerve not directly connected with it. The stimulus, in this case, is first conducted by the nerve irritated, to the brain or spinal cord ; it is then, without participation of the will, and even without consciousness, transferred to another nerve, by which it is conveyed to the muscle, and thus at length excites muscular contrac- tion. The property of nerves by which they convey stimuli to muscles, whether directly, as In the case of muscular nerves, or circuitously, as in the case last instanced, is named the “ vis nervosa.” 4. Sensibility——We become conscious of impressions made on various parts of the body, both external and internal, by the faculty of sensation ; and the parts or textures, impressions on which are felt, are said to be sensible, or to possess the vital property of “sensibility.” This property manifests itself in very different degrees in different parts ; from the hairs and nails, which indeed are absolutely insensible, to the skin of the points of the fingers, the exquisite sensibility of which is well known. But sensibility is a property which really depends on the brain and nerves, and the different tissues owe what sensibility they possess to the sentient nerves which are distributed to them. Hence it is lost in parts severed from the body, and it may be imme- diately extinguished in a part, by dividing or tying the nerves so as to cut off its connection with the brain. It thus appears that the nerves serve to conduct impressions to the brain, which give rise to sensation, and also to convey stimuli to the muscles, which excite motion; and it is probable that, in both these cases, the conductive property exercised by the nervous cords may be the same ; the difference of effect depending on this, that in the one case the impression is carried upwards to the sensorial part of the brain, and in the other downwards to an irritable tissue, which it causes to contract ; the stimulus in the latter case either having origin- ated in the brain, as in the instance of voluntary motion, or having been first conducted upwards, by an afferent nerve, to the part of the cerebro-spinal centre devoted to excitation, and then transferred to an efferent or muscular nerve, along which it travels to the muscle. If this view be correct, the power by which the nerves conduct sensorial impressions and the before-mentioned ‘* vis nervosa ” are one and the same vital property ; the difference of the effects resulting from its exercise, and, consequently, the difference in function of sensorial and motorial nerves, being due partly to the different nature of the stimuli applied, but especially to a difference in the susceptibility and mode of reaction of the organs to which the stimuli are conveyed. DEVELOPMENT OF THE TEXTURES. The tissues of organised bodies, however diversified they may ultimately become, show a wonderful uniformity in their primordial condition. The results of modern researches have shown that the THE VEGETABLE CELL. 7 different organised structures found in plants and animals originate directly or indirectly by means of elementary corpuscles, which have been named “cells.” These so-called cells, remaining as separate cor- puscles in the fluids, and grouped together in the solids, persisting in some cases with but little change, in others undergoing a partial or thorough transformation, produce the varieties of form and structure met with in the animal and vegetable textures. Nay, the germ from which an animal originally springs, so far at least as it has been recognised under a distinct form, appears as a cell; and the embryo, in its earliest stages, is but a cluster of cells produced apparently from that primordial one; no distinction of texture being seen till the process of transformation of the cells has begun. No branch of knowledge can be said to be complete ; but, even now that between a quarter and half a century has elapsed since the pro- mulgation of the cell-doctrine, there is, perhaps, none which can be more justly regarded as in a state of progress than that which relates to the origin and development of the textures, and much of the current opinion on the subject is uncertain, and must be received with caution. THE VEGETABLE CELL. If we view under the microscope the early embryo of one of the higher plants (fig. 1.), we see that it is built up entirely of a number of closely adherent vesicles,—these are the elementary cells. Each of those cells Fig. 1. consists of an external membranous invest- ment (@), the cell-wall, containing in its interior a finely granular transparent sub- stance of semi-fluid consistence—the proto- plasm (b),—in this is imbedded at one part a more solid looking body of rounded form (the nucleus, c), which again itself con- tains generally one or two distinct strongly refracting particles (nucleoli). On closer ex- amination 1t may be observed that in many cells the protoplasm is not absolutely quies- cent as at first sight appears, but on the contrary exhibits slow streaming movements of its substance, indicating a certain amount of vital activity. This is more particularly the case in the more rapidly growing parts, Fig. 1—Ensryo or Drco- where also it is not uncommon to find two epee ea Mope- nuclei in a cell. This, as will be seen later vir ee on, is an indication of the commencing a, cell-envelope ; 0, proto- division of the cell into two: by the con- Plasm; ¢, nucleus. stant repetition of this process the growth of the plant is effected. In their early condition all plants are similarly composed of an agglomeration of cells, and some retain this primitive condition throughout life ; in all the higher classes, however, by changes in the form and in the contents of the cells, various modifi- cations occur, by means of which the different textures of the plant are produced. Some of these are shown in the accompanying figures S THE ANIMAL CELL. (fics, 2, and 38): it would however lead us too far to enter into a description of them here. Fig. 3. . 5 C535)! WAGES DES AAW === es! el i f VAY J i} fi Y | | | ~ AKA Fig. 2.—TrxturEs sEEN IN A Lonartuprnat Section of THE LEAF-STALK OF A FLOWERING PLANT. 1, 2, Polyhedral cells (from mutual pressure). 3, 4, 5, Elongated tubular and prismatic cells. 6, Pitted tissue. 7, Spiral vessels. | Fig. 3.—STELLATE VEGETABLE CELLS. THE ANIMAL CELL. Turning now our attention to the animal embryo, we find that it also is entirely made up of cells (fig. 4), rather smaller it is true than those composing the embryo plant, but, like them, consisting of a granular protoplasmic substance (0) enclosing a nucleus (c); this in its turn containing one or more nucleoli. And here, at the outset, we encounter a fundamental difference between the cells com- posing the animal and those composing the vegetable embryo. In the former there is no Fig. 4.—Tarre Crrrs membranous investment or cell-wall. In con- From EARLY Empryo sequence of this absence of a restraining en- or THE Car. Hicuty yelope the streaming movements of the proto- ee ak plasm, which are observable in every cell, whether 2, protoplasm ; ¢, mu- animal or vegetable, at an early stage of its cleus with nucleolus. The F = é y 5 lowermost cell has two ¢Xistence, and in some remain persistent through- nuclei. out life, are capable. as will hereafter be more fully explained, of effecting changes both in the form and also in the position of the animal cell.* Before proceeding to inquire into the changes which may occur in * The existence of animal cells destitute of envelope, although more insisted on of late years, has been all along recognised in the study of cell-development, and was expressly pointed out by Schwann himself (Microscopische Untersuchungen, &c., p. 209). It has appeared to some that another name should be used to designate bodies which thus exist in a naked non-vesicular form. Briicke proposed to call them ‘‘ elementary organisms,” a term too cumbrous for use. As the first ‘shaped ”’ products of organisation which appear in the development of all but the lowest organised beings, they might be named ‘“‘ proto- plasts,” or, as that name has been already used in a widely different sense—‘‘ mono- plasts,”’ but after all, seeing the universal currency of the term ‘‘cell,” it is probably most convenient and best to adhere to it, with the understanding that in many cases it is used in a conventional sense. PRODUCTION OF CELLS. 9 the embryo cells in order to the production of the various textures of which the animal body is composed, it will be convenient to consider the manner in which the cells themselves are produced, and the nature of the substance composing them. Production of Embryo Cells.—So far as is at present known, every cell in the animal body has been derived from a previously existing cell. In the case of the cells which compose the early embryo this parent cell is, as has been previously pointed out, the ovum itself, or at least its germinative part. The mammalian ovum differs indeed from the cells we have just been considering, both in its size, and in possessing a stout external membrane (fig. 5 a). Like them, however, it mainly consists of a protoplasmic substance (0), in which are embedded fatty granules (the yelk), and contains structures (the germinal vesicle (c) and germinal spot), which are comparable respectively to the nucleus and nucleolus. Fig. 5.—DiAcramMatic FicuURES TO ILLUSTRATE THE FoRMATION OF CELLS WITHIN THE MAMMALIAN Ovum BY SEGMENTATION OF THE YELK ; MAGNIFIED. a, external membrane ; 6, protoplasmic contents ; c, germinal vesicle containing the germinal spot. The embryonic cells are produced from the ovum by a process of cleavage or segmentation, of which the following is an outline :— The germinal vesicle disappears ; the contents of the ovum then shrink somewhat and separate into two equal parts (B); the first two segments divide each again into two (c), and the binary division thus goes on (D, E,) pretty regularly until the whole is transformed into a number of small segments, the embryonic cells, each consisting, as we have seen, of protoplasmic matter enclosing a nucleus. The latter is not always discoverable in the earlier segments, being perhaps hidden by the opaque granular mass, but it soon comes into view, and has been supposed to play an important part in the formation of the cells. At all events it may be observed, in those segments in which the nucleus is visible, that the division of this body precedes that of the protoplasmic substance. Whether the first nucleus is itself derived from the vanishing germinal vesicle and spot is unknown. 10 SUBSTANCE COMPOSING THE CELL. The formation of cells by segmentation may be traced with comparative ease in the ova of many invertebrata. The accompanying figure (fig. 6) represents the several stages of the process in small species of the ascaris worm. A, B, and care from the Ascaris nigrovenosa, as observed by Koélliker. He found that, after the germinal vesicle had disappeared, a new nucleus with nucleolus was formed in its place: the segmentation then goes on as in the mammalian ovum, but the nuclei are visible from the first. In many animals the segmentation process affects only a part of the contents of the ovum. Fig. 6.—Drviston or THE YELK or ASCARIS. A, B, © (from Kdélliker), ovum of Ascaris nigrovenosa; bp and x, that of Ascaris acuminata (from Bagge). The Protoplasm of the Cell.—The substance of which the embryonic cells, and all others which display similar vital contractility, chiefly consist, is in reality clear and hyaline, but commonly contains minute particles imbedded in the clear substance, which give it a granular appearance (fig. 4, 0). It is semi-fluid and viscid in con- sistence, and in chemical constitution closely agrees with the albumi- noid bodies, consisting, in fact, principally of a substance allied to myosin, the chief constituent of muscular tissue ; but in many animal cells it doubtless also includes other organic principles, especially fat, and glycogenous or amyloid matter. Protoplasm is characterised by properties which have been aptly termed “vital,” since upon their presence the life of the organism seems to depend. Chief among these properties are those of assimilation and of irritability : indeed, it is probable that the vital properties of the textures above enumerated depend, in great measure or wholly, upon the protoplasm which they contain. The Nucleus of the Cell.—The nucleus (fig. 4, c) is a round or ovoid, clear, and apparently vesicular body, commonly situate near the centre of the cell, and containing one or two strongly refracting granules—the nuc/eoliwhich are probably of a fatty nature. From the affinity which, in common with protoplasm, it possesses for certain colouring matters, the nucleus has been supposed by some eminent histologists (and notably by Beale, who has applied the term “ germinal matter” to both) to be identical in nature with that substance. Its behaviour, however, with many reagents is altogether different ; and in general it may be said that it offers greater resistance to their action than the substance which surrounds it. The fact that in the division of cells the segmentation of the nucleus appears to precede that of the protoplasm, has been held to be a strong argument in favour of the possession by the nucleus of a considerable amount of vital activity, but it is impossible to say whether this process may not be effected by means of the surrounding proto- plasm. At all events there are, it is believed, no recent observations which would tend to show the manifestation by the nucleus of any vital phenomena, unless when associated with protoplasm, whereas the converse fact is well established. CHANGES OF CELLS IN THE FORMATION OF TISSUES. 11 Changes which occur in Cells.— The changes which may occur in cells in relation to the production of the textures are of two prin- cipal kinds, according as the form of the cell, or the nature of the sub- stance composing it, undergoes alteration. These changes may occur at one and the same time-—indeed, this is commonly found to be the case ; it will, however, be more convenient here to consider them separately. 1. Chenucal and Plastic Changes occurring in Cells——The protoplasm originally composing the embryonic cell may become variously altered in chemical constitution, all such changes tending to diminish the original . activity of the cell and to fit it for a special function. An alteration com- monly met with in older cells is the conversion of the outer portion of the protoplasm into a comparatively dense layer, which constitutes an investment for the remainder, and in this way approximates the cell more to the vegetable type. Such a transformation is met with in a high degree in the stratified epithelia, in which the cells of the upper- most layers become almost entirely transformed into dense horny scales. Another change which is apt to occur is the deposition within the cell of various chemical principles, which are either derived directly from the plasma of the blood, in which in such cases they pre-exist, or are elaborated by the cell itself from some other constituent of that fluid. Examples of these changes are to be found in the deposit of fat and pigment, and of the peculiar constituents of certain secretions within the cells of the tissue or gland producing them. The deposition of fat occurs ordinarily and in its most characteristic form in the corpuscles of the connective tissue, transforming them into fat cells, although it may occasionally be found in other cells, such as those of the liver and of cartilage. Pigment on the other hand may be deposited both in connective tissue cells and in epithelium, and this to such an extent as to give an intensely black appearance to the part, as in the choroid coat of the eye and in the cuticle of the negro. Sometimes these chemical changes are accompanied by others of a plastic or organizing character, as in the fibrillation which is often found to occur in cells, and notably in those of the nervous aml muscular tissues, as well as in the formation of the spontaneously moving bodies called spermatozoa in the spermatic cells. Another example of such a change is to be found in the formation of red blood corpuscles within the cells of connective tissue. These plastic changes are equally unexplained with the other alterations of form and structure which accompany the production and metamorphoses of cells. As regards the changes in the quantity and chemical nature of the contained matter, it may be remarked that the introduction of new matter into a cell is to a great extent a phenomenon,of imbibition. In addition to this, many cells, by virtue of their amceboid movements to be presently described, are enabled to take into their substance minute solid particles, both inorganic and organic. But, while an alteration in the contents of a cell may be thus brought about by imbibition and intersusception of pre-existing material, the contained substance may also be changed in its qualities by a process of conversion or elaboration taking place within the cell. 2. Changes in Form—The changes of form which may occur in cells are of two kinds, the one being merely passive and mechanical, the other dependent upon the growth of the cell. Instances of the former are seen in those cases where, by mutual compression, the cells 12 MOVEMENTS OF CELLS. have acquired a more or less dodecahedral form (as is frequently the case in plants, see fig. 2), or where, by growth of young cells beneath them, they become flattened out and forced towards a free surface, as probably happens in the case of the stratified epithelia. Examples of the latter are observable in the ramification of the cells of the nervous and connective tissues, and in the elongation of cells to form muscular fibres. 3. Movements of Cells.—Many cells undergo spontaneous movements, leading to temporary changes in their form. If we watch carefully under a high power of the microscope any cell which is exhibiting these pheno- mena—a pale blood-corpuscle, for example—we observe, in the first place, at one point of its circumference, a protrusion of a portion of its proto- plasm, which is commonly at first clear and hyaline, but into which granules are soon seen to flow. After a short time this process may be retracted, and another similarly protruded at another point, and again withdrawn, and so on for a considerable time, the corpuscle remaining all the while perfectly stationary. Occasionally, however, especially if the corpuscle be maintained at the temperature of the body, the part protruded remains fixed, and the cell itself 1s drawn towards the extremity of the process. Should this occur a number of times in the same direction, a slow progressive motion of the whole cell is the result. In this way cells such as we are now considering may undergo very considerable changes of form and place within a relatively short time. Thus, under certain conditions, the pale blood-corpuscles may some of them make their way out of the blood-vessels and move freely in the surrounding tissues: hence the term “migratory cells” (Wanderzellen) applied to them. The movements which we have just been describing as occurring in cells are quite similar to those which are exhibited, but in a more vigorous manner, by the common fresh-water amoeba, and are hence designated “amoeboid.” They are more marked in cells in the young state, such as those of the embryo, but are not altogether absent in some which persist in the fully-developed tissues, as, for example, in the connective tissue corpuscles. The contractile property of the proto- plasm, to which its movements are due, would seem to be quite com- parable to the contractility of muscular substance ; for it is found that the substance of these protoplasmic cells contracts under the electric stimulus, whether this be directly applied, or, as observed by Kiihne in the cornea, indirectly through the medium of the nerves.* In the cells of the Vallisneria, Chara, and various other plants, when exposed under the microscope, the green coloured grains (of chlorophyll) and other small masses and corpuscles contained in the cavity, are seen to be moved along the inside of the cell-wall in a constant and determinate direction. This phenomenon appears to be of very general occurrence in the vegetable kingdom, although the movement does not always go on with the same regularity as in the instances cited. It is obviously due to a layer of protoplasm on the inner surface of the cell-wall, which enters into a peculiar flowing or undulating motion and trails the passive chlorophyll granules along with it; but how the motion of the pro- toplasm itself is produced is not at all understood. To the same class of phenomena are probably to be referred the remarkable movements observed in the pigment-cells of the frog’s skin, which were carefully investigated by Lister.t In these ramified cells the dark particles of pigment are * Untersuchungen iiber das Protoplasma und die Contractilitiit. 1864. t Phil. Trans., 1858. MULTIPLICATION OF CELLS. 13 at one time dispersed through the whole cell and its branches, but at another time they gather into a heap in the central part, leaving the rest of the branched cell vacant, but without alteration of its figure. In the former case the skin is of a dusky hue ; in the latter, pale. Like the movements of the protoplasm, the aggregation of the pigment molecules can be excited through the nerves, both mechanically and electrically. The fact above mentioned, that these movements of cells may be excited by stimulation of the nerves, is especially worthy of note, in as much as it proves that operations effected in and by cells are more or less under the governance of the nervous system. Moreover, the well known influence of mental states over the secretions, and the effects resulting from experimental stimulation of the nerves of secreting glands, although doubtless due in part to changes in the blood-vessels, seem to show that this subjection to the nervous system extends even to the chemical and physical operations which take place in secreting cells. A curious and interesting observation in proof of this is adduced by Kolliker. He found that the light of the firefly, Jampyris, is emitted from cells in which albuminoid matter is decomposed with production of urate of ammonia, and that the emission of light could be brought on or rendered more vivid by electrical and other stimuli operating through the nerves. The well-known tremulous movement which so often affects minute particles of matter, is not unfrequently observed in the molecular contents of cells; but this phenomenon depends simply upon physical conditions, and is of a totally different character from the motions of the protoplasm above referred to. Multiplication oz Cells by Division.—The amcboid movements of the protoplasm are directly concerned in the process of subdivision of a cell. This is more particularly to be observed in the division of a free cell—a white blood-corpuscle, for example—in which the process, as described by Klein and others, is, briefly, as follows (fig. 7) :—One Fig. 7.—Staces in tHe Division or A CoLourLess Corpuscte or Newr’s Broop (after Klein). of the processes of an amceboid corpuscle, the nuc.eus of which has previously undergone division, remains unretracted, and into this one of the nuclei from the body of the cell may pass. The protruded part then becomes more and more withdrawn from the rest of the cell, and, finally, by the rupture of the connecting neck of protoplasm, may become entirely detached, breaking away as an independent corpuscle. But the process is commonly of a more simple character, as is the case, for instance, with the process of cleavage, already mentioned in treating of the production of embryonic cells. The actual process of division has now heen observed in the ova of many of the lower animals. It is preceded by slow heaving movements of the proto- plasm ; a furrow then appears upon the surface, soon to disappear 14 INTERCELLULAR SUBSTANCE. again. This is repeated two or three times, but finally the furrow becomes permanent, and, deepening into a groove, gradually constricts the mass into two. In some cases, before Fig. 8. this process is complete, a second furrow appears at right angles to the first, and sometimes even a third, the division being thus into four or eight segments instead of into two only, as previously described in the case of the mammalian ovum. In the same manner the division of Fig. 8—Dracram or tan Divi- Other cells may take place, the nucleus SION OF A CELL. first becoming divided, and a portion of the protoplasm collecting around each half. The two cells thus produced may each undergo a similar change, and in this way cell-multiplication may be exceedingly rapid. The cells commonly become separated ; in some tissues, however, cartilage, for instance, they may remain in proximity, producing thus groups of two or four newly-formed cells, which, in the case of that tissue, are at first enclosed in a common cavity of the matrix: hence the process of multiplication has here been styled “endogenous.” It is, however, in all probability, essentially the same as in the less solid tissues. The division of cells is usually into two, as above described, but, as observed by Remak in the frog larva, it may occur into as many as five or six. Instances of the same kind are also observed in the development of pus corpuscles from connective tissue corpuscles, the cells becoming enlarged, and their nuclei multiplied previously to breaking up into pus cor- puscles. Sometimes, however, a multiplication -of nuclei within a cell would seem to occur without immediate Fig. 9.—MULTINUCLEATED Creuus. 400 DIAMETERS separation into new cells, as, ee: for instance, in the case of the large flattened multinucleated cells (fig. 9), which are found in the medullary cavities of bone, and in other situations, and which would seem, at least in bone, to fulfil a special function. Of cells in their relation to each other.—The cells which com- pose the early embryo have but little connection one with another, the intercellular substance being small in amount, or altogether absent. As growth proceeds, however, they come to present differences in their relations to each other. a. They may remain isolated, as in the instance of the pale corpus- cles of blood, chyle, and lymph. b. They may be united into a continuous tissue by means of a cementing substance : the epithelium and cuticle, the nails and hairs afford instances of this. c. Processes from neighbouring cells meet and become united, as is NUTRITION OF THE TEXTURES. 15 frequently the case with the corpuscles of connective tissue, and as is seen in the process of development of blood-vessels and nerves. Intercellular substance.—Of the matter which lies between cells —the intercellular substance—and its relation to them, it may be observed that sometimes it is in very small quantity, and seems merely to cement the cells together, as in epithelium ; at other times it is more abundant, and forms a sort of matrix, or ground substance, in which the cells are embedded, as in cartilage. It is homogeneous, translucent, and firm in most cartilages, and pervaded by fibres in yellow cartilage. In connective tissue it consists of fibres, with soft interstitial matter, which is scanty in the denser varieties, but abundant in the lax tissue of the umbilical cord ; in bone the intercellular sub- stance is calcified and mostly fibrous. As to the production of the intercellular substance, there can be little doubt that in cartilage it is derived from the cells. Formed as capsules round the cells by excre- tion from their surface, or by conversion of their proper substance, and being blended into a uniform mass, it accumulates while the cells multiply, and while fresh material is supplied to them from the blood, which they convert into chondrinous substance. The source of the intercellular substance is not, in every instance, so apparent, but it may be presumed that the cells have some influence in its nutrition and maintenance. From what has been said it will be obvious that cells play an important part in the growth of textures, and probably in nutrition. The former pro- cess is usually accompanied by a great multiplication of cells, the peculiar constituent of which—the protoplasm—seems to be specially endowed with the faculty of propagation by division, and of increase by appropriating and con- verting new matter. It is conceivable that in this way it may serve for the extension of growing tissue and the development of structural elements from the erude materials of growth. Again, in the nutrition of a mass of tissue the crude material may undergo preparation by the cells that lie in the interstices of the structure. The existence of this protoplasmic germinative substance is very general, perhaps indeed universal, in the animal and vegetable kingdoms. But whilst in the great majority of organic beings it assumes the form of a nucleated cell (protoplast, or monoplast), as the first condition of their organised structure, in simpler modes of life and organisation it is not subject to the same limitation of form and mass. In the mycctozoa (myaomycetes), a curious tribe, heretofore mostly reckoned among the fungi, but standing as it were on the debateable ground between the animal and vegetable kingdoms, the protoplasm is extended into reticular masses, or irregularly anastomosing trains ( plasmodia), spread over the surface of bark and other bodies to which it parasitically clings ; whilst in vibrios and some other infusorial animaleules of the simplest kind, it appears as fine molecular particles; but it is most probably derived from parents in all instances, however minute and apparently insignificant these may be. The intercellular or ground substance, possesses in a high degree the property of combining with and reducing the salts of silver when previously impregnated with them and exposed to the light. This method of staining, which was intro- duced by His and von Recklinghausen, has furnished us with a ready means of determining the position and form of delicate cellular elements in a tissue, since these, remaining unstained by the reagent, stand out white upon the dark ground :or in the case of an epithelioid tissue, appear as white polygonal areas bounded by fine dark lines (compare figs. 108 and 109, pp 166, 167). 16 NUTRITION OF THE TEXTURES. NUTRITION AND REGENERATION OF THE TEXTURES. Nutrition.—The tissues and organs of the animal body, when once employed in the exercise of their functions, are subject to continual loss of material, which is restored by nutrition. This waste or con- sumption of matter, with which, so to speak, the use of a part is attended, takes place in different modes and degrees in different struc- tures. In the cuticular textures the old substance simply wears away, or is thrown off at the surface, whilst fresh material is added from below. In muscular texture, on the other hand, the process is a chemical or chemico-vital one ; the functional action of muscle is attended with an expenditure of moving force, and a portion of matter derived in part from the muscle itself is consumed in the production of that force; that is, it undergoes a chemical change, and being by this alteration rendered unfit to serve again is removed by absorption. The amount of matter changed in a given time, or, in other words, the rapidity of the nutritive process, is much greater in those instances where there is a production and expenditure of force, than where the tissue serves merely passive mechanical purposes. Hence, the bones, tendons, and ligaments are much less wasted in exhausting diseases than the muscles, or than the fat, which is consumed in respiration, and generates heat. Up to a certain period, the addition of new matter exceeds the amount of waste, and the whole body, as well as its several parts, augments in size and weight: this is“ growth.” When maturity is attained, the supply of material merely balances the consumption ; and, after this, no steady increase takes place, although the quantity of some matters in the body, especially the fat, is subject to consider- able fluctuation at all periods of life. It would be foreign to our purpose to enter on the subject of nutrition in general; we may, however, briefly consider the mode in which the renovation of substance is conceived to be carried on in the tissues. The material of nutrition is immediately derived from the plasma of the blood, or liquor sanguinis, which is conveyed by the blood-vessels, and transudes through the coats of their capillary branches ; and it is in all cases a necessary condition that this matter should be brought within reach of the spot where nutrition goes on, although, as will immediately be explained, it is not essential for this purpose that the vessels should actually pass into the tissue. In certain instances, more- over, the pale corpuscles, which exist in the blood, pass through the coats of the vessels, and may become employed as elements of nutrition and reparation. In cuticle and epithelium, the nutritive change is effected by a continuance of the process to which these textures owe their origin. The tissues in question being devoid of vessels, nutrient matter is furnished by the vessels of the true skin, or subjacent vascular membrane, and is appropriated by young cells, derived most probably from pre-existing ones. These new cells enlarge, alter in figure, often also in chemical nature, and, after serving for a time as part of the tissue, are thrown off at its free surface. But it cannot in all cases be so clearly shown that nutrition takes place by a continual formation and decay of the structural elements of the tissue ; and it must not be forgotten, that there is another con- NUTRITION OF THE TEXTURES. 17 ceivable mode in which the renovation of matter might be brought about, namely, by a molecular change which renews the substance, particle by particle, without affecting the form or structure ; by a pro- cess, in short, which might be termed “ molecular renovation.” Still, although conclusive evidence is wanting on the point, it seems probable that the crude material of nutrition first undergoes a certain elaboration or preparation through the agency of cells disseminated in the tissue ; which may serve as centres of assimilation and increase, as already explained. Office of the vessels.—In the instance of cuticle and epithelium, no vessels enter the tissue, but the nutrient fluid which the subjacent vessels afford penetrates a certain way into the growing mass, and the cells continue to assimilate this fluid, and pass through their changes at a distance from, and independently of, the blood-vessels. In other non-vascular tissues, such as articular cartilage, the nutrient fluid is doubtless, in like manner, conveyed by imbibition through their mass, where it is then attracted and assimilated. ‘The mode of nutri- tion of these and other non-vascular masses of tissue may be compared, indeed, to that’ which takes place throughout the entire organism in cellular plants, as well as in polypes and some other simple kinds of animals, in which no vessels have been detected. But even in the vascular tissues the case is not absolutely different ; in these, it is true, the vessels traverse the tissue, but they do not penetrate into its structural elements. ‘Thus the capillary vessels of muscle pass between and around its fibres, but do not penetrate their inclosing sheaths ; still less do they penetrate the fibrillee within the fibre; these, indeed, are much smaller than the finest vessel. The nutrient fluid, on exuding from the vessels, has here, therefore, as well as in the non-vascular tissues, to permeate the adjoining mass by transudation, in order to reach these elements, and yield new substance at every point where renovation is going on. ‘The vessels of a tissue have, indeed, been not unaptly compared to the artificial channels of irrigation which distri- bute water over a field ; just as the water penetrates and pervades the soil which lies between the intersecting streamlets, and thus reaches the growing plants, so the nutritious fluid, escaping through the coats of the blood-vessels, must permeate the intermediate mass of tissue which lies in the meshes of even the finest vascular network. The quantity of fluid supplied, and the distance it has to penetrate beyond the vessels, will vary according to the proportion which the latter bear to the mass requiring to be nourished. We have seen that in the cuticle the decayed parts are thrown off at the free surface ; in the vascular tissues, on the other hand, the old or effete matter must be first reduced to a liquid state, then find its way into the blood-vessels, or lymphatics, along with the residual part of the nutritive plasma, and be by them carried off. From what has been said, it is clear that the vessels are not proved to perform any other part, in the series of changes above described, beyond that of conyey- ing matter to and from the scene of nutrition ; and that this, though a necessary condition, is not the essential part of the process. The several acts of assuming and assimilating new matter, of conferring on it organic structure and form, and of disorganising again that which is to be removed, which are so many manifes- tations of the metabolic and plastic properties already spoken of, are performed beyond the blood-vessels, It is plain, also, that a tissue, although devoid of vessels, VOL Il. c C. “9 18 THE BLOOD. and the elements of a vascular tissue, although placed at an appreciable distance from the vessels, may still be organised and living structures, and within the dominion of the nutritive process. How far the sphere of nutrition may, in certain cases, be limited, is a question that still needs further investigation ; in the cuticle, for example, and its appendages, the nails and hairs, which are placed on the surface of the body, we must suppose that the old and dry part, which is about to be thrown off or worn away, has passed out of the limits of nutritive influence ; but to what distance beyond the vascular surface of the skin the province of nutrition extends, has not been determined. Regeneration.—When part of a texture has been lost or removed, the loss may be repaired by regeneration of a new portion of tissue of the same kind ; but the extent to which this restoration is possible is very different in different textures. Thus, in muscle, a breach of con- tinuity may be repaired by a new growth of connective tissue ; but the lost muscular substance is not restored. Regeneration occurs in nerve; in bone it takes place readily and extensively, and still more so in fibrous, areolar, and epithelial tissues. The special circumstances of the regenerative process in each tissue will be considered hereafter; but we may here state generally, that, as far as is known, the reproduction of a texture is effected in the same manner as its original formation. In experimental inquiries respecting regeneration, we must bear in mind, that the extent to which reparation is possible, as well as the readiness with which it occurs, is much greater in many of the lower animals than in man. In newts, and some other cold-blooded verte- brata, indeed (not to mention still more wonderful instances of re- generation in animals lower in the scale), an entire organ, a limb, for example, is readily restored, complete in all its parts, and perfect in all its tissues. In concluding what it has been deemed advisable in the foregoing pages to state respecting the development of the textures, we may remark that, besides what is due to its intrinsic importance, the study of this subject derives great interest from the aid it promises to afford in its application to pathological inquiries. Researches which have been made within the last few years, and which are still zealously carried on, tend to show that the structures which con- stitute morbid growths are formed by a process analogous to that by which the natural or sound tissues are developed: some of these morbid productions, indeed, are in no way to be distinguished from areolar, fibrous, cartilaginous and other natural structures, and have, doubtless, a similar mode of origin; others, again, as far as yet appears, are peculiar, but still their production is with much probability to be referred to the same general process. The prosecution of this subject, however, does not fall within the scope of the present work. THE BLOOD. PHYSICAL AND ORGANIC CONSTITUTION. The most striking external character of the blood is its well-known colour, which is florid red in the arteries, but of a dark purple or modena tint in the veins. It is a somewhat clammy and consistent liquid, a little heavier than water, its specific gravity being 1:052 to 1°057; it has a saltish taste, a slight alkaline reaction, and a peculiar faint odour. To the naked eye the blood appears homogeneous; but, when examined with the microscope, either while within the minute vessels, or when spread out into a thin layer upon a piece of glass, it is seen to CORPUSCLES. 19 consist of a transparent colourless fluid, named the “lymph of the blood,” “ liquor sanguinis,” or “ plasma,” and minute solid particles or corpuscles immersed in it. These corpuscles are of two kinds, the coloured and the colourless : the former are by far the more abundant, and have been long known as “the red particles,” or “globules,” of the blood ; the “colourless,” “ white,” or “pale corpuscles,” on the other hand, being fewer in number and less conspicuous, were later in being generally recognised. When blood is drawn from the vessels, the liquor sanguinis separates into two parts ;—into fibrin, which becomes solid, and a pale yellowish liquid named serwm. The fibrin in solidify- ing involves the corpuscles and forms a red consistent mass, named the clot or crassamentum of the blood, from which the serum gradually separates. The relation between the above-mentioned constituents of the blood in the liquid and the coagulated states may be represented by the subjoined scheme :— Corpuscles ; : : 4 ) eel j Clot ey Buprine 8) l sy. Coagulated blood. Liquor sanguinis Serum Red Corpuscles.—These are not spherical, as the name “ globules,” by which they have been so gene- rally designated, would seem to imply, but flattened or disk- shaped. Those of the human blood (fig. 10 and fig. 12 A) have a nearly circular outline, like a piece of coin, and most of them also present a shallow cup-like depression or dimple on both sur- faces ; their usual figure is, there- fore, that of biconcave disks. Their magnitude differs somewhat even in the same drop of blood, and it has been variously assigned by authors; but the prevalent size may be stated at from ;,!,,th tO ss5ath of an inch in diame- ter, and about one-fourth of that in thickness, In mammiferous animals gene- rally, the red corpuscles are shaped as in man, except in the camel Fig. 10.—Human Buioop As sEEN ON THE tribe, in which they have an ellip- warm Stace. Maanirrep azour 1200 tical outline. In birds, reptiles, Dramerers. and most fishes, they are oval ¢, ¢, crenate red corpuscles; p, a finely disks with a central elevation on st@nular, y, a coarsely granular pale cor- both surfaces (fig. 12, B, from e a iacetaee vaible cea ese the frog), the height and ex- tent of which, as well as the proportionate length and breadth of c 2 20 THE BLOOD. the oval, vary in different instances, so that in some osseous fishes the elliptical form is almost shortened into a circle. The blood-corpuscles of invertebrata, although they (except in some of the redt-blooded annelides) want the red colour, are also, for the most part, flatened or disk-shaped ; being in some cases circular, in others oblong, as in the larvee of aquatic insects. Sometimes they appear granulated on the surface like a raspberry, but this is probably due to some alteration occurring in them. The size of the corpuscles differs greatlyin different kinds of animals; it is greater in birds than in mammalia, and largest of all in the naked amphibia. They are for themost part smaller in quadrupeds than in man; in the elephant, however, they are larger, being 5755th of an inch, which is the largest size yet observed in the blood-corpuscles of any mammiferous animal ; the goat was long supposed to have the smallest, viz., about s;5,5th of an inch; but Gulliver found them much smaller in the Meminna and Napu musk-deer, in which animals they are less than =;2,,th of aninch. In birds they do not vary in size so much; from Gulliver’s very elaborate tables of measurement it appears that they range in length from about 3355th to ~,)5oth of an inch; he states that their breadth is usually a little more than half the length, and their thickness about a third of the breadth or rather more. He found a remarkable exception in the corpuscles of the snowy owl, which measure ;=4,th of an inch in length; and are only about a third of this in breadth. In scaly reptiles they are from >,,th to 75oth of an inch in length; in the naked amphibia they are much larger: thus, in the frog they are =,,;th of an inch long, and ;,,,th broad; in the salamander they are larger still ; but the largest yet known are found in the protean reptiles. For example, in Proteus anguinus they are =} th of an inch in length, and >3-,th in breadth ; in the siren, which is so much allied to the proteus in other respects, they measure ,3,th of an inch in length, and >3,th in breadth, whilst in Amphiuma tridactylum they are as much as one-third larger than in the proteus. In the skate and shark tribe the corpuscles resemble those of the frog, in other fishes they are smaller. From what has been stated, it will be seen that the size of the blood- corpuscles in animals generally is not proportionate to the size of the body; at the same time, as Gulliver remarks, “if we compare the measurements made from a great number of different species of the same order, it will be found that there is a closer connection between the size of the animal and that of its blood-corpuscles than has been generally supposed ;” and he has pointed out at least one example of avery natural group of quadrupeds, the ruminants, in which there is ; cana of the size of the corpuscles in relation to that of the body. Structure.—The human red corpuscle is composed essentially of a soft colourless stroma (tegumentary frame of Gulliver) of the same shape and size as the corpuscle itself, throughout which is diffused a semi-fluid coloured matter which may be readily separated from the stroma by means of reagents. Some of these, such as water and acetic acid, appear to act simply by dissolving out the coloured part, leaving the stroma more or less swollen from imbibition of fluid. Others, such as ether and chloroform and the salts of the biliary acids, cause the discharge of the coloured matter into the surrounding fluid ; blood so CORPUSCLES 21 treated, when viewed in mass by transmitted light, is seen to have lost its opaque appearance and to have acquired a transparent laky tint. Such lake-coloured blood may also be produced by various other means, such as the action of heat (60° C.), the alternate freezing and thawing of a portion of blood, and the passage of electric shocks : the change in colour and translucency obviously depends upon the fact that the corpuscles, when deprived of their coloured part, interfere less with the transmission of light than before : such blood is often exceedingly prone to yield crystals of hemoglobin (to be afterwards described). The action of tannin is peculiar from the fact that under certain conditions the coloured part, instead of being diffused in the fluid, becomes collected into a minute, highly refracting, globular mass which remains attached to the exterior of the stroma (W. Roberts).* The corpuscles alter their shape on the slightest pressure, as is beautifully seen while they move within the vessels; they are also elastic, for they readily recover their original form again. It must be remarked that the blood-corpuscles when viewed singly appear very faintly coloured, and it is only when collected in considerable quantity that they produce a strong deep red. The human-blood corpuscles, as well as those of the lower animals, often present deviations from the natural shape, which are most probably due to causes acting after the blood has been drawn from the vessels, but in some instances depend upon abnormal conditions previously existing in the blood. Thus, it is not unusual for many of them to appear indented or jagged at the margin, when exposed under the microscope, (fig. 10, c, c) and the number of corpuscles so altered often appears to increase during the time of observation. This is, perhaps, the most common change ; it occurs whenever the density of the plasma is increased by the addition of a neutral salt, and is one of the first effects of the passage ofan electric shock. The corpuscles may become distorted in various other ways, and corrugated on the surface ; not unfrequently one of their concave sides is bent out, and they acquire a cup-like figure. Gulliver made the curious discovery Fig. 11. that the corpuscles of the Mexican deer and some allied species present very singular forms, doubtless in consequence of exposure; the figures they assume are various, but most of them become lengthened and pointed at the ends, and then often slightly bent, not unlike caraway-seeds. The red disks, when blood is drawn from the vessels, sink in the plasma ; they have a singular tendency to run 4», 11,Rep CorpuscuEs cob together, and to cohere by their broad sur- —‘Lucrep ryro Routs (after Henle). faces, so as to form by their aggregation cylindrical columns, like piles or rouleaus of money, and the rolls or piles themselves join together into an irregular network (figs. 10 and 11). Generally the corpuscles separate on a slight impulse, and they _™ Proceedings of the Royal Society, vol. xii. p. 481. For some interesting observa- tions by Dr. W. Addison, F.R.S., on the curious effects produced on red blood-corpuscles by immersion in sherry-wine, see Proceedings of the Royal Society, Dec. 8, 1859. 29 THE BLOOD. may then unite again. The phenomenon is probably of a physical kind: it will take place in blood that has stood for some hours after it has been drawn, and also when the globules are immersed in serum in place of liquor sanguinis.* By processes, which need not here be detailed, Vierordt and Welcker have esti- mated the number of red corpuscles in a cubic millimetre of human blood. The former assigns it at upwards of 5,000,000; the latter at 5,000,000 in the male, and 4,500,000 in the female. Fig. 12. AX B Fig. 12.—Human Rep Corpuscius (A) anp Buoop CorpusciEs or THE Frog (B) PLACED SIDE BY SIDE TO SHOW RELATIVE sIzE. 500 DiAMETERs. 1, shows their broad surface ; 2, one seen edgeways ; 3, shows the effect of dilute acetic acid ; the nucleus has become distinct (from Wagner). Like the mammalian blood-disks the large corpuscles of the frog and salamander may be described as consisting of coloured matter and stroma. They differ from them however in the possession of a more solid particle of an oval shape which lies imbedded in the stroma. This has been long known as the “nucleus,” it is rather more than one-third the length of the corpuscle. In the natural unaltered condition the nucleus is seldom visible; this is probably owing to the extreme smoothness of its outline and the fact that it possesses very nearly the same index of refraction as the rest of the corpuscle. For it may be rendered visible, even under such circumstances, by the combined action of watery vapour and carbonic acid upon the blood ; a precipitate (of paraglobulin) is thus produced upon the nucleus, and its outline comes into view ; on readmission of air the precipitate is re-dissolved, and the nucleus again disappears (Stricker), The effect of most reagents is similar to that produced on human blood. Water causes both stroma and nucleus to swell up by imbibition, the coloured part being extracted at the same time. A dilute solution of acetic acid in an indifferent fluid also removes the colouring matter, but the stroma and nucleus retain their shape, the last-mentioned body presenting a markedly granular appearance (fig. 12,3); if strong acetic acid be employed, the nucleus often acquires a reddish tint. Alkalies, on the other hand, even when very dilute, rapidly destroy both corpuscle and nucleus. Various reagents added to newt’s blood cause the coloured part of the corpuscles to become collected around the nucleus, and to be more or less withdrawn from the stroma; this is more especi- ally the case with a two per cent. solution of boracic acid (Briicke): the coloured matter and nucleus may subsequently be altogether extruded from the body of the corpuscle, * For possible explanations of this phenomenon the reader is referred to memoirs by Lister (Phil. Trans., 1858), and Norvis (Proc. Roy. Soc. 1869). CORPUSCLES. 23 Pale, white or colourless Corpuseles (figs. 10 and 13).—These are comparatively few in number, of a rounded and slightly flattened figure, rather larger in man and mammalia than the red disks, and varying much less than Fig. 13. the latter in size and aspect in different animals. In man (during health) the proportion of the & ie) white corpuscles to the red is about 2 or 3 to 2 1000. ‘This proportion is diminished by fasting (2) and increased after a meal, especially of albu- oy minous food. Their number compared with the red corpuscles is said to be greater in venous Fig. 13.— Pate Conpvs- than arterial blood, and much greater in the cLES OF Human Broop ; blood of the splenic and hepatic veins than in = ™AGNIFIED Apour 500 venous blood generally. They are destitute = ?“™™7*** of colour and specifically lighter than the red _ The upper two as seen corpuscles. In nature they are in many re- im the pena eee spects similar to the embryonic cells already free the ion of divs described (p. 8), and they possess in a high acetic acid, which brings degree the capability of undergoing amoeboid into view the single or movement; sending out processes (fig. 10, composite nucleus. g, p) into which their granules enter and re- tracting them again, and even occasionally performing extensive locomotion. The pale corpuscles possess one, two, or, commonly, three nuclei, which are frequently obscured by the granular character of the protoplasm, but may be brought into view by dilute acids (fig. 13). Minute, round, clear spaces may often be seen in the protoplasm (fig. 10) ; they are entirely free from granules, although probably filled with fluid, and have been named vacuoles. They are also met with in the embryonic as well as in other protoplasmic cells. The colourless blood- corpuscles are commonly distinguished into two kinds, according as the protoplasm composing them is finely granular throughout (fig. 10, »), or contains a greater or less number of coarser granules, strongly refracting the light (vy). Whether in the latter case the granules have been formed from fluid matter within the corpuscle, or whether they have not rather been taken in from the surround- ing fluid, by the same process as an amceba takes in its food, is at present uncertain: it is however an interesting fact that the pale blood-corpuscles are peculiarly apt to take into their interior minute solid particles that have been introduced into the blood; this pro- perty has served as a means of detecting escaped white corpuscles in tissues which are wholly extravascular, the cornea for example (Cohnheim). Albuminous granules, and molecules of a fatty nature occur in the blood in varying numbers ; sometimes very scantily, or not at all, but the latter sometimes very abundantly so as to give the serum a turbid, milky appearance. These are probably derived directly from the chyle, and they are especially seen in the blood of herbivora, in sucking animals, and in pregnant women. Granular masses occasionally occur in drawn blood, even when taken from a healthy person, but more especially in cachectic states of the system, which on minute examination are seen to be composed of excessively fine, colourless, discoid particles. The latter under favour- able conditions develope into vibrating filaments which break away 24 THE BLOOD. from the mass and move freely in the liquid (Osler).* Masses of pig- mentous matter are also occasionally found, especially in disease; and in the blood of the splenic vein cells enclosing red blood-corpuscles have been noticed (Ecker, Kélliker). Fine interlacing filaments are commonly to be seen in a preparation of blood under the microscope. These consist of fibrin, and are formed, after the blood has been drawn, in the manner to be presently noticed. Liquor Sanguinis, or Plasma.—This is the pale clear fluid in which the corpuscles are naturally immersed. Its great character is its strong tendency to coagulate when the blood is withdrawn from the circulating current, and on this account it is difficult to procure it free from the corpuscles. Nevertheless, by filtermg the slowly coagulable blood of the frog, as was first practised by J. Miiller, the large corpuscles are retained by the filter, while the liquor sanguinis comes through in perfectly clear and colourless drops, which, while yet clinging to the funnel, or after they have fallen into the recipient, separate into a pellucid glassy film of fibrin, and an equally transparent diffluent serum. When human blood is drawn in inflammatory diseases, as well as in some other conditions of the system, the red particles separate from the liquor sanguinis before coagulation, and leave the upper part of the liquid clear. In this case, however, the plasma is still mixed with the pale corpuscles, which, being light, accumulate at the top. On coagulation taking place in these circumstances, the upper part of the clot remains free from redness, and forms the well-known buffy coat so apt to appear in inflammatory blood. Horse’s blood ordinarily presents this condition when drawn. The readiest way to obtain the liquor sanguinis in quantity free from red corpuscles is to allow the blood of the horse to flow from the vessels into a receiver, kept cool by means of ice: the blood corpuscles sink to the bottom, leaving the upper part of the fluid clear and colourless. This may be drawn off into another vessel and is found readily to coagulate at a slight elevation of temperature. In the case of frog’s blood this artificial cooling is not always necessary ; for, if it be collected with as little disturbance as possible, c.g., if the heart be allowed to pump blood directly into a clean glass tube, little or no coagulation may take place, so that the corpuscles rapidly subside and leave the plasma perfectly clear and colourless.t In post mortem examinations the cavities of the heart are often found occupied by an almost completely colourless, gela- tinous coagulum, ‘This is due to the subsidence of the corpuscles after death. Coagulated plasma, whether obtained from buffy blood, or exuded on inflamed surfaces, presents, under the microscope, a multitude of fine filaments confusedly interwoven, as in a piece of felt ; but these are more or less obscured by the intermixture of corpuscles and fine granules, the former having all the characters of the pale corpuscles of the blood. The filaments are no doubt formed by the fibrin, as it solidifies in the coagulation of the liquor sanguinis. Sometimes, how- ever, fibrin presents when coagulated a gelatinous appearance under the microscope without any sign of filaments. Blood may be freed from fibrin by stirring it with a bundle of twigs, which entangle the fibrin as it concretes. * Centralblatt f. d. med. Wissensch. 1873. Proc. R. S., 1874. + Schafer. British Association Reports, 1872. CHEMICAL COMPOSITION. 2d CHEMICAL COMPOSITION OF THE BLOOD. The blood is slightly alkaline in reaction. Carbonic acid, oxygen, and nitrogen gases may be extracted from it by exhaustion by means of the Torricellian vacuum aided by gentle warmth. Carbonic acid is yielded in largest proportion, oxygen next, and nitrogen least. The nitrogen is simply retained by absorption, 7.e., in the same proportion as by water at the same pressure and temperature. The oxygen is held by the coloured matter of the red corpuscles ; it may be completely ex- pelled from this combination by means of carbonic oxide gas (Bernard). The carbonic acid, which is obtained in larger proportion from serum than from blood, is in great part combined with carbonate of soda in a bicarbonate ; from this combination it is set loose in vacuo if the colour- ing matter of the blood is present. Arterial blood yields more oxygen and less carbonic acid than venous blood. On being evaporated, 1000 parts of blood yie:d on an average, about 790 of water and 210 of solid residue. ‘This residue has nearly the same ultimate composition as flesh. A comparative examination of dried ox-blood and dried flesh (beef), by Playfair and Boeckmann gave the following mean result :— Flesh. Blood. Carbon ‘ : : : ; : : . 51°86 51:96 Hydrogen : : : : : : 2h ISS 7-25 Nitrogen. : : : . 2 ‘ me lta03 15:07 Oxygen . : E ; : - ; Pe 2130 21°30 Ashes . : i : : : : P | ge ae 4°42 Red Corpuscles.—The specific gravity of the red corpuscles in a moist state is calculated at 1:088. They consist, as already stated, of an insoluble colourless stroma, and a diffused red matter, which is soluble and separable by water. The stroma consists of various substances, chief among which are paraglobulin, cholesterin, and a phosphuretted fat which was named by O. Liebreich protayon, but which, as Hoppe-Seyler has shown, itself consists of two distinct substances—/lecithin and newrin. If blood be shaken up with ether, the fatty matters of the stroma are dissolved, and the colouring matter is in this way set free (Her- mann). Paraglobulin will be most conveniently described with the serum of the blood, in which it also occurs, and from which it is more readily obtainable ; and, for a similar reason, the consideration of the other two substances will be deferred until the nervous system has been treated of.* . The soluble coloured ingredient of the corpuscles has been named hemoglobin (cruorin of Stokes). This substance, although crystal- lizable, is indiffusible, and, according to Hoppe-Seyler, contains, when pure, in‘100 parts 54:2 of carbon, 21°5 of oxygen, 16:0 of nitrogen, 727 of hydrogen, 0:7 of sulphur, and 0°42 of iron; or ©, ,95; Ho6o, * The nucleus of the nucleated red corpuscle consists chiefly of mucin (Kiihne, L. Brunton). 6 THE BLOOD. N54) Fe, Sg, 0354. It may be obtained in quantity and tolerably pure by the following method (Preyer) : Blood (preferably from a dog) is drawn into a capsule, and the serum allowed to separate. The clot is then taken, and after being quickly minced, is thrown upon a filter, and washed with ice-cold distilled water until the washings yield but little precipitate with perchloride of mercury. By this process the serum, with the albumin it contains, is in great part removed, the cold water taking up but little of the hemoglobin. The latter is then dissolved out by warm water, and an amount of alcohol, just insufficient to cause its precipitation, is added to the solution. On placing this in a freezing mixture, a large part of the hemo- globin crystallizes out. The crystals of hemoglobin present various forms in different animals, but almost all (the hexagonal plates of the squirrel alone being excepted) belong to the Fig. 14. rhombic system. From human blood and that of most mam- mals, the crystals are elongated prisms (fig. 14, 1), but tetrahe- drons in the guinea-pig (2), and short rhombohedrons in the hamster (4). They are most readily obtained for mi- croscopical examination from the blood of the rat, where they appear merely on the addition of a little water. All hemoglobin crystals con- tain a certain amount of water of crystallization (Kiihne). They are doubly refracting (anisotropous), and the spec- irum of hemoglobin, whether in substance or in solution, may be always readily recog- nised by the double or single Fig. 14.—Brtoop-CrystaLs, MAGNIFIED. 1, from human blood ; 2, from the guinea- : : ‘ pig ; 3, squirrel ; 4, hamster. absorption bands, which are produced according as it is present in the oxidated or deoxidated condition.* Products of Decomposition of Hzemoglobin.—Hexemoglobin is an exceed- ingly unstable body. Even at the ordinary temperature the crystals cannot long be preserved without undergoing alteration, the substance of which they are composed readily decomposing into an exceedingly pure (ash-free) albuminoid substance, named by Preyer globin, and a brownish-red powder, very nearly allied to hemoglobin in chemical composition (hence termed methemoglobin), but differing from that body both in its general reactions and in the character of its spectrum. Another brownish-red substance, which contains all the iron of hemoglobin, and was long supposed to be the true colouring * For an account of the examination of the colouring matter of the blood by the prism, and of the differences in its absorptive effect on light, the reader is referred to an im- portant paper by Professor G. G. Stokes, in the Proceedings of the Royal Society for June 16, 1864, vol. xiii.-p. 355, as well as to an exhaustive treatise on the whole subject of hemoglobin, by W. Preyer (Die Blutkrystalle, Jena, 1871). CHEMICAL COMPOSITION. 27 matter of blood, is produced by the action of alkalies upon hemoglobin, and is termed hematin. When obtained pure ‘this body is insoluble in water, and also Fig. 15. in alcohol and ether, except in presence of an alkali. Like hemoglobin, its alka- 7 ONL line solutions produce a different effect sy & are upon the spectrum according as they are = a Ore \ oxidated or deoxidated ; the absorption by py Yee Nae 9 \ oy bands are, however, entirely different aK J Ee \ from those of hemoglobin. The effect of oa ahs, aS acids upon hematin is to separate the OO ee ae ise ee iron and to transform the substance into se \ te cos hematoin (acid-hematin), the spectrum / >» a ae of which is characterised by the presence / i zy i] u of four absorption bands. A compound lye Paty ~~ / aN; of hematin with hydrochloric acid (hemin, WKAR si Ce i Teichmann) is readily obtained from AX J wt hemoglobin by warming it with a little ya Px salt and glacial acetie acid. On cooling, t Ye = sat it crystallizes out in minute reddish-brown — acicular prisms (fig. 15), the demonstra- tion of which affords a positive proof Fig. 15.—H#min Crysrats, MAcyiriep of the presence of blood-colouring matter. (from Preyer). They may readily be obtained from dried blood without the addition of salt, merely by warming it with concentrated acetic acid.* Inorganic Constituents of the Red Corpuscles.—Desides the iron of the hemoglobin, the red corpuscles contain a certain propor- tion of salts, chiefly of potash and lime, combined with carbonic and phosphoric acids. It is, however, impossible to obtain the corpuscles in quantity, sufficiently isolated for exact analysis. Proportion of Red Corpuscles.—The red corpuscles form by far the largest part of the organic matter in the blood: their proportion may be approximately ascertained by filtering defibrinated blood mixed with solution of sulphate of soda; or by weighing the dried clot, and making allowance for the fibrin it contains. The latter method, how- ever, will serve only to give a rough estimate, as the very uncertain amount of serum remaining in the clot and affecting its weight cannot be determined. Prevost and Dumas made too large a deduction for the solid matter supposed to belong to the retained serum, and this reduced the estimate of the dried corpuscles too much, viz. to 129 parts per 1000 of blood. Lecanu also gives it at from 120 to 150: Becquerel and Rodier at from 131 to 152. Schmidt, from three modes of cal- culation, which it is needless here to explain, arrived at the conclusion that the proportion of moist red corpuscles in 1000 parts of blood is from 480 to 520; but there are reasons for regarding this as too high an estimate. Hoppe-Seyler estimates the proportion at 526 per 1000. Different observers agree that, as a general rule, the proportion of red particles is greater in the blood of the male sex than in that of the female. Lecanu gives the following mean result, derived from numerous analyses, exhibiting the pro- portion of dry crassamentum and water in the blood of the two sexes. No * For some interesting observations by A. Gamgee on the action of nitrites on hemo- globin, see Philosophical Transactions, 1868, p. 589. ; 23 THE BLOOD. deduction is made for the fibrin ; but, considering its small relative quantity, any possible variation in it cannot materially affect the general conclusion. Male. Female. Crassamentum, from. 1158 to 148 ’ : 68°3 to 129°9 Water 778 to 805 : : 790 to 853 As regards age, Denis found the proportion of crassamentum greatest between the ages of 30 and 40. Sudden loss of blood rapidly diminishes it. In two women who had suffered from uterine hemorrhage, the crassamentum amounted to only 70 parts in 1000. The same effect may be observed to follow ordinary venesection. In a person bled three times in one day, Lecanu found in the first drawn blood 139, and in the last only 76 parts of crassamentum in the 1000. This effect may be produced very suddenly after a bleeding. Prevost and Dumas bled a cat from the jugular vein, and found 116 parts of crassamentum in 1000, but in blood drawn five minutes afterwards, it was reduced to 93. The sudden loss of blood probably causes a rapid absorption of serous and watery fluid into the vessels, and thus diminishes the relative amount of the red particles. It is found that the blood of warm-blooded animals is richer in crassamentum than that of the cold-blooded ; and, among the former, the proportion is highest in the class of birds. Liquor Sanguinis, or Plasma.—The fluid part of the blood, as already described, separates spontaneously into fibrin and serum. The fibrin may be obtained by stirring the blood as soon as possible after it is drawn, or by washing the crassamentum with water, to free it from red matter. Procured in either of these ways, the fibrin contains pale corpuscles and a small proportion of fat. From dried fibrin of healthy human blood, Nasse obtained nearly five per cent. of fat, and still more from the fibrin of buffy blood. The proportion of fibrin in the blood does not exceed 24 parts in 1000; indeed, according to the greater number of observers, it is not more than 2}. Asa general rule, the quantity is somewhat greater in arterial than in venous blood, and it is increased in certain states of the body, especially in inflammatory diseases and in pregnancy. Origin of Fibrin. —It is now ascertained that the fibrin is not present, as such, in a liquid form, in the plasma, but is produced at the moment of consolidation by the co-operation or combination of two previously distinct substances. About thirty years ago, A. Buchanan* discovered that the fluid of hydrocele, which might in an unmixed state be kept for an indefinite time without coagulating, very speedily congealed and separated into clot and serum when mixed with a little blood. Ordinary blood-serum, blood-clot, especially washed clot, and buffy coat, even after being dried and long kept, when added in small proportion to the hydrocele-fluid, produced the same effect. From these facts Buchanan concluded that fibrin exists as a liquid both in hydrocele-fluid and in the liquor sanguinis, that liquid fibrin does not coagulate spontaneously, but requires for that end the influence of some “suitable reagents,” that such a reagent is naturally present in the blood, and brings about the solidification of its fibrin in the natural process of coagulation, and that it is absent from the hydrocele-fluid, but when supplied by the addition of blood, causes the fluid fibrin to solidify. On farther reasoning on the facts he had observed, Dr. Buchanan was led to believe that “coagulant power” * Proceedings of the Glasgow Philosophical Society, 1845. CHEMICAL COMPOSITION. =O was mainly seated in the pale corpuscles,* which abound in the washed clot and the buffy coat, and are present in the serum ; and that their efficacy depended on their organisation as elementary cells. In harmony with this latter view, he found on trial that the organised tissues, such as muscle, skin, and spinal marrow, possessed the same power, though in a less degree than the pale corpuscles, in which, as primary cells, the metabolic power is more energetic. The remarkable phenomenon described by Buchanan did not obtain the consideration it deserved, and the coagulation of hydrocele- fluid, under the conditions stated, was commonly ascribed to some catalytic action of the substance added, which induced liquid fibrin present in the fluid to solidify. Im 1861, however, A. Schmidt, ot Dorpat, apparently unaware of Buchanan’s observations, fell upon facts of the same kind, and pursuing the investigation by an elaborate series of experiments, not only with hydrocele-fluid, but with peri- cardial, peritoneal, and other serous fluids and effusions, which give a like result, has satisfactorily shown that fibrin has no existence in a liquid state, but that when it appears as a coagulum in a fluid, it is actually produced then and there by the union of two constituents present in solution, and forthwith shed out as a solid matter. One of these constituents which contributes in largest measure to the product, he names fibrinogenous substance, the other fibrinoplastic substance. In the coagulation of hydrocele-fluid, the former, or fibrinogen, is already there, while the fibrinoplastin is supplied from the blood. It is not that the latter converts albumin into fibrin, for, after a certain amount of fibrin has been coagulated from the serous fluid, no further addition will generate more, although abundance of albumin remains; and again, a given quantity of fibrinoplastin will not coagulate with equal rapidity and intensity any amount of fluid containing fibrinogen. In short, the fibrinoplastic substance seems to operate not by catalysis, but by combining with the other necessary ingredient. Now Schmidt has shown that the fibrinoplastic matter presents all the chemical characters of paraglobulin, and is, in fact, nothing else-than that substance. This paraglobulin is not restricted to the red corpuscles ; it is found in the serum after separation of the clot, and doubtless exists also in the pale corpuscles. Nor is it confined to the blood. From chyle and lymph, and from various organs and tissues of the body, a substance may be obtained having the same reactions and the same fibrino-plastic power. Fibrinogen may be obtained from hydro- cele-fluid in the same manner as paraglobulin from blood-serum (vide infra); it very closely resembles paraglobulin in its chemical relations, only it is less soluble in acids and alkalies, and less energetic in all its re-actions. Of course, it exists in blood-plasma, and in the process of coagulation of the blood combines with paraglobulin to form the fibrin of the clot.t * This idea or one similar, has been recently revived by Mantegazza, who conceives the fibrin to be derived from the pale corpuscles, or at least that their presence is necessary for coagulation to take place. Compare also Burdon Sanderson, Handbook for the Physio- logical Lahoratory, p. 173. + Schmidt, Alex., in Reichert & Du Bois Reymond’s Archiv fiir Anat. u. Physiol. 1861 and 1862. For a lucid account of this subject, founded on a confirmatory repeti- tion of Buchanan’s and of Schmidt’s fundamental experiments, see an article on ‘‘ the baie a the Blood,” [by Dr, Michael Foster], in the Natural-History Review-for Pin suave 30 THE BLOOD. Serum.—This is a thin and usually transparent liquid, of a pale yellowish hue ; it is, however, sometimes turbid, or milky, and this turbidity may depend upon different conditions, but most commonly on excess of fatty particles. The specific gravity of serum ranges from 1:025 to 1°030, but is most commonly between 1°027 and 1:028 (Nasse), and is more constant than that of the blood. The solid contents of the serum are not more than 8 or 9 in 100 parts; the proportion of water being, for males 90°88, and for females 91°71. It is always more or less alkaline. When heated, it coagulates, in consequence of the large quantity of albumin it contains; and after separation of the albumin, a thin saline liquid remains, sometimes named “serosity.” The following ingredients are found in the serum :— Albumin.—This principle is partly combined with soda as an albuminate ; its quantity may be determined (after previous removal of paraglobulin) by precipitating it in the solid form by means of heat or alcohol, washing with distilled water, drying, and weighing the mass. Its proportion is about 80 in 1000 of serum, or nearly 40 in 1000 of blood. Serum-albumin differs from albumin obtained from white of eco in the fact of its not being precipitated by ether; in other respects it closely resembles that substance. Albumin is coagulated and trans- formed into an insoluble variety by heat. Albumin is closely allied to paraglobulin, fibrinogen, myosin, and many other nitrogenized substances met with in the animal economy : they are therefore com- monly grouped together as albwminoid substances, protein bodies, or proteids. Albuminoids are characterised by their low diffusibility and their readiness, when in solution, to take on the solid condition, or to coagulate. They therefore belong to the colloid substances of Graham. They are precipitated from their solutions by alcohol, mineral acids, tannic acid, corrosive sublimate, and many other metallic salts. They are all coloured yellow by nitric acid, becoming red on subsequent addition of ammonia, Acid nitrate of mercury produces a red colour, and sulphate of copper and potash a violet colour in their solutions. The albu- minoids all consist of carbon, hydrogen, oxygen, and nitrogen, together with a small amount of sulphur. By the actioh of the gastric juice ordinary albuminoids are transformed into an exceedingly soluble, diffusible variety termed pepton. Albumin combines with both acids and alkalies forming respectively acid- albumin or syntonin, and alkali-albumin or casein. Paraglobulin.—When serum is diluted with about ten times its bulk of distilled water, and subjected to a stream of carbonic acid, the liquid becomes turbid, and paraglobulin is precipitated. It may also be obtained from the diluted serum by the cautious addition of acetic acid, but the least excess of acid will re-dissolve the precipitate. Para- globulin is a protein compound, agreeing very nearly with albumin in elementary composition, so far as this has been ascertained. Para- globulin is nearly insoluble in pure water, but readily dissolves on a very slight addition of either an alkali or an acid. Weak acids throw it down from its solution in alkali, but when added in slight excess re-dissolve it. In like manner it is precipitated by alkalies from its solutions in acids and re-dissolved by excess. From neither of these solutions is it thrown down by heat. It is dissolved by neutral salts, and from this solution heat throws it down in an insoluble precipitate. From its slightly alkaline solution in water it is thrown down by a stream of carbonic acid, and may be re-dissolved by passing air or CHEMICAL COMPOSITION. él oxygen through the liquid. Its precipitate is distinguished from that of other albuminoids by being always in form of fine granules or molecules. But the most important and distinctive character of para- elobulin is its fibrino-plastic property, already referred to, by which it co-operates with fibrinogen in producing solid fibrin; this property is destroyed by exposure of the solution to a boiling heat. Paraglobulin is almost identical in chemical nature and composition with the substance which composes the crystalline lens, and which was named by Berzelius globulin. The latter substance, however, besides exhibiting minor differences, does not possess the fibrino-plastic power ; they have therefore been separately distin- guished by Kithne. Like hemoglobin, paraglobulin is diffusible through animal membranes, not through vegetable parchment. Fibrinogen, on the other hand, is totally indiffusible. Both paraglobulin and fibrinogen may be precipitated from their solutions by the addition of common salt to saturation. A substance similar to myosin has also been described as occurring in blood- serum (Heynsius). Fatty Compounds.—A small amount of fat is contained in the serum, partly dissolved, and partly diffused in the liquid. It may be separated by gently agitating the serum with about a third of its bulk of ether, or by evaporating the serum and digesting the dry residue in ether, or in boiling alcohol. The turbid milky aspect which sernm often exhibits, is in most cases due to a redundance of fat, and may accordingly be removed by agitation with ether. Extractive Matters.—When the serum has been freed from albu- minous matter by coagulation, and from fat by ether, and is evaporated to dryness, a yellowish or brown mass remains, consisting of organic matters mixed with salts; the former belonging principally to the ill- defined class of substances denominated “ extractive matters.” These have now been more carefully sifted, and have yielded several definite and recognisable bodies, generated in the natural process of decomposi- tion of the tissues, or residual matters of nutrition formed in the blood itself, and on their way to be excreted by the kidneys. Several of the substances to be next mentioned belong to this class, and as they are obviously excrementitial and transitory ingredients, they are not allowed to gather in any notable quantity in the healthy state of the economy. Creatin and Creatinin—Products of the natural “wear” of the muscles, or derived from fleshy food. These compounds, which are found in muscular substances and in the urine, together with hypoz- anthin (also named sariin), obtainable from the same sources, have been stated to exist in excessively small quantities in the blood. Urea.—This substance, which accumulates in the blood of animals after extirpation of the kidneys or ligature of the renal arteries, as well as in certain diseases, has been found in very minute quantity in the healthy blood of the ox and of the calf, by Marchand and Simon, and in that of man, by Lehmann, Garrod, and others. It is, however, in such excessively small quantity, that its estimation is attended with great difficulty. Uric Acid has been shown to exist in healthy blood by Garrod, and in that of persons suffering from gout it is in such considerable quantity as to be readily detected. In health its proportion is extremely small. Hippuric Acid is found in the blood of herbivora, and, according to some observers, in that of man. ‘There is, however, much doubt upon this point. 32 THE BLOOD. Leucin and Tyrosin, which exist in almost all secretions and excre- tions, probably are present in minute quantity in the blood; but as yet they have only been detected in it in disease of the liver. Sugar has been found in the blood of dogs, oxen, and cats, also in that of diseased and healthy persons. The quantity is very small. The form of sugar is that known as glucose or grape sugar. Colouring and Odoriferous Matters.—The yellowish colour and peculiar faint odour which serum possesses are probably dependent upon the presence of certain definite principles. No one has, however, as yet succeeded in isolating them. ‘The odour of the blood is said to be of peculiar character in each species of animal, and to be heightened by the addition of sulphuric acid. Schmidt found, however, that the blood of only three animals yielded an odour distinctive of the species. Salts.—1. Having soda and potash as bases, combined with lactic, carbonic, phosphoric, sulphuric, and ‘fatty acids. Also chlorides of sodium and potassium, the former in large proportion. Schmidt has pointed out that the potash-salts exist almost exclusively in the blood- corpuscles and the soda salts principally in the serum. In the cor- puscles there are principally chloride of potassium and phosphate of potash : in the serum, chloride of sodium and phosphate of soda. The following table (giving the mean of eight experiments) exhibits the relative quantities of potassium and sodium, and of phosphoric acid and chlorine, in the blood-corpuscles and plasma. 100 parts of Inorganic Matters. \— —— é a -— Blood- Corpuseles. Plasma. Blood-Corpuscles. Plasma. | K. Na. Ki i ys. RO Cl. PO, Cl. 40°89 971 519 37-74 17°64 21:00 6:08 40°68 The table shows that the chlorides are, relatively to the phosphates, in much larger quantity in the plasma than in the blood-corpuscles ; and that the phos- phates are, relatively to the chlorides, in much larger proportion in the blood- corpuscles than in the plasma. 2. Lactate of ammonia. 3. Salts with earthy bases, viz., lime and magnesia, with phosphoric, carbonic, and sulphuric acids. The earthy salts are for the most part associated with the albumin, but partly with the crassamentum. As they are obtained by calcination, it has been sus- pected that the phosphoric and sulphuric acids may be in part formed by oxida- tion of the phosphorus and sulphur of the organic compounds. Nasse found in 1000 parts of blood 4 to 7 of alkaline, and 0°53 of earthy salts. The ashes of blood yield, according to Jarisch, 8°34 per cent. of oxide of iron, or about ‘0948 parts in 100 of blood. Mean Composition of Blood.—The following approximative state- ment of the mean composition of venous blood (horse) is furnished by Hoppe-Seyler :— In 1000 parts of blood— Corpuscles_ . ; : ; - ‘ . 3826:2 Plasma . E : " “ ; F . 6708 ARTERIAL AND VENOUS BLOOD. 33 In 1000 parts of corpuscles— Water . > , 4 2 - - - 565°0 Solids . 2 2 - : : A . 435°0 In 1000 parts of plasma— Water é : P ; ; . 908°4 Fibrin . Be! yy Albumin . 105 Solids. . . : P : . o16/ Fats. ee 0 ) Extractives . 3°6 | Soluble salts 5'8 Insoluble salts 1°5 Scherer and Otte give the following as the composition of human venous blood :— In 100 parts of blood— Water - : ; ‘ OD Fibrin . ‘ ; 0-2 Geena (with ~ Hemoglobin) . 19-44 [ Extractives ; “48 Solid matters . A ; . 20°95 Soluble salts, 7 83 The serum of the same blood yielded in 100 parts— Water . : ‘ : : : 2 . 90°66 Albumin F P 3 . ; : 2) 176 Extractives . é : F ; ; O61 Soluble salts. : g 5 ‘ g . O94 Difference between Arterial and Venous Blood.—By arterial blood is meant that which is contained in the aorta and its branches (systemic arteries), in the pulmonary veins and in the left cavities of the heart ; the venous blood is that of the veins generally, the pulmonary arteries, and right cavities of the heart. Their differences, apart from their functional effects in the living body, come under the heads of colour and composition. 1. Colour. Arterial blood, as already stated, is scarlet, venous blood dark, or purple. Venous blood assumes the scarlet colour on exposure to air, i.¢., to oxygen. This change is greatly promoted by the saline matter of the serum, and may be accelerated by adding salts or sugar to the blood, especially by car- bonate of potash, or of soda, and by nitre. Salts added to dark blood, without exposure to oxygen or air, cause it to assume a red colour, but not equal in brightness to that of arterial blood. On the other hand, the addition of a little water darkens the blood. According to Stokes, the corpuscles in the former case “ lose water by exosmosis, and become thereby highly refractive, in consequence of which a more copious reflexion takes place at the common sur- face of the corpuscles and surrounding fluid. In the latter case they gain water by endosmosis, which makes their refractive power more nearly equal to that of the fluid in which they are contained, and the reflexion is consequently diminished.” * But the presence of serum or of saline matter is not indispensable to the bright- ening, for although the clot when washed free from serum scarcely if at all reddens on exposure to oxygen, yet it is found that the red matter when squeezed out of the clot and dissolved in water, still becomes brighter and clearer on exposure to oxygen, whilst the colour is darkened (and the solution becomes turbid from deposition of paraglobulin), on being shaken with carbonic acid. As in this case the colouring matter is extracted from the corpuscles and is red- dened by oxygen without the presence of salts, it is plain that the difference of colour of arterial and venous blood essentially depends, not on a difference in the figure or density of the corpuscles, but on the alteration produced in the colour- * Proc. Royal Soc., vol. xiii. p. 362. VOL. If. D 34 THE BLOOD. ing substance by oxidation and deoxidation, which alters its absorptive effect on the light. Viewed in thin layers by transmitted light, venous blood appears green. It is, therefore, dichroitic. 2. Composition. The arterial blood, so far as is known, is uniform in nature throughout ; but in passing through the capillary vessels into the veins, whilst it generally acquires the common characters of venous blood, it undergoes special changes in its passage through particular organs, so that the blood of all veins is not alike in quality. Thus the blood of the hepatic veins differs from that of the portal vein, and both are in various respects different from what might be regarded as the common venous blood, which is conveyed by the veins of the limbs, and of the muscular and cutaneous parts of the body generally. Moreover, Bernard has shown that the blood of veins returning from secreting glands differs according to the state of functional activity of the organs. Whilst their function is in abeyance the blood in their veins is dark, as usual, but when secretion is active, the blood, which then also flows much more freely and abundantly, comes through from the arteries to the veins with very little, if any, reduction of its arterial brightness ; it also retains nearly the whole of its separable oxygen. Compared with blood from a cutaneous vein, arterial blood is found to contain a very little more water (about five parts in 1000) and to have a somewhat lower specific gravity. The arterial plasma yields more fibrin and coagulates more quickly ; the serum was said by Lehmann to contain less albumin and less fat, but more extractive and a little more saline matter. Arterial blood yields more oxygen gas, and less of both free and combined carbonic acid. Blood of the portal vein, compared with that of the jugular vein, was stated by Lehmann to contain more water in proportion to solid matter, less fibrin and albumin, more fat, extractive matter and salts. The pale corpuscles are vastly more numerous than in venous blood generally. The blood of the hepatic veins, according to Lehmann’s statement, is richer in both red and pale corpuscles, possibly from loss of water, and the proportion of pale corpuscles to the red is increased. The hepatic venous blood, moreover, yields sugar, derived from glycogen formed in the liver. The blood of the renal veins was stated by Bernard and Brown-Séquard not to coagulate in the normal state of the kidney and its function : on trial, however, we find that as regards coagulation it behaves like ordinary venous blood. COAGULATION OF THE BLOOD. In explaining the constitution of the plasma, we have been obliged so far to anticipate the account of the coagulation of the blood. The following are the phenomena which usher in and which accompany this remarkable change. Immediately after it is drawn the blood emits a sort of exhalation, the “halitus,” having a faint smell; in about three or four minutes a film appears on the surface, quickly spreading from the circumference to the middle ; a minute or two later the part of the blood in contact with the inside of the vessel becomes solid, then speedily the whole mass ; so that in about eight or nine minutes after being drawn, the blood is completely gelatinised. At about fifteen or twenty minutes, or it may be much later, the jelly-like mass begins to shrink away from the sides of the vessel, and the serum to exude from it. The clot continues to contract, and the serum to escape for several hours, the rapidity and degree of the contraction varying exceedingly in different cases ; and, if the serum be poured off, more eae usually continue to drain slowly from the clot for two or three ays. The nature of the change which takes place in the coagulation of the blood has been already spoken of: it is essentially owing to the coagulation of the COAGULATION. 35 liquor sanguinis, the fibrin being generated in that liquid by the concurrence of its two constituents in the way already explained, and separating in form of a solid mass, which involves the corpuscles but allows the serum to escape from it in greater or less quantity. But although the solidification of the fibrin and formation of a red clot would undoubtedly take place independently of any mechanical co-operation on the part of the corpuscles, still it must not be for- gotten that the red disks are not altogether indifferent while coagulation goes on : for they run together into rolls, as already described, and the circumstance of their doing so with greater or with less promptitude materially affects the result of the coagulating process. Thus there seems good reason to believe that, as H. Nasse pointed out, one of the causes—and in inflammatory blood probably the chief cause—of the production of the buffy coat, is an exaltation of the natural tendency of the red disks to run together, whereby being more promptly and more closely aggregated into compact masses, they more speedily subside through the liquid plasma, leaving the upper part of it colourless by the time coagulation sets in; and Wharton Jones has drawn attention to what he conceives to be another influential circumstance depending likewise on the corpuscles, in inflam- matory blood, namely, the more rapid and close shrinking of the network, or spongework as he terms it, into which the little rolls of corpuscles unite, and the consequent expulsion of the great part of the liquor sanguinis from its meshes before the fibrin solidifies, in which case the mass of aggregated corpuscles naturally tends to the lower part of the vessel, whilst the expressed plasma, being lighter, accumulates at the top. Of course it is not meant to deny that more tardy coagulation of the plasma would produce the same result as more speedy aggregation of the corpuscles ; it is well known, indeed, that blood may be made to show a buffy coat’ by delaying its coagulation, but buffed inflammatory blood is not necessarily slow in coagulating. Circumstances affecting Coagulation.— Various causes accelerate, retard, or entirely prevent the coagulation of the blood ; of these it will here suffice to indicate the more important and best ascertained. 1. Temperature.—Cold delays, and at or below 40 degrees Fahr. wholly suspends coagulation ; but even frozen blood, when thawed and heated again, will coagulate. Moderate elevation of temperature above that of the body promotes coagulation. 2. Coagulation is accelerated by contact of the blood with foreign matter, such as the sides of the basin or other vessel into which it is drawn. On the other hand, the maintenance of its fluidity is favoured by retention within its vessels or natural receptacles where it is in contact with the natural tissues of the body ; but when the coats of the vessels or other tissues, with which the blood is contiguous, lose their vitality and are altered in their properties, they become as foreign bodies, and coagulation is promoted. The usual exposure of drawn blood to the air promotes coagulation, but according to Lister, by no means so powerfully as was formerly believed. The effect of other gases is the same. Coagulation speedily takes place when blood is subjected to the air-pump, and has therefore been said to occur readily in vacuo, but Lister finds that this is owing to the agitation caused by the bubbling of the blood from the escape of liberated gases, whereby more and more of it is successively brought into contact with the sides of the vessel. 3. Arrest of the blood’s motion within the body is said to favour coagulation, probably by arresting those perpetual changes of material, both destructive and renovative, to which it is naturally subject in its rapid course through the system. The coagulation of the stagnant blood after death is also largely to be ascribed to the alteration then ensuing in the coats of the containing vessels. Lister found that, after D2 36 THE BLOOD. death, blood remains longer fluid in the small veins than in the heart and great vessels ; and even in these the coagulation is usually slow. Agitation of exposed bloed accelerates coagulation by increasing its ex- posure to foreign contact. 4, Water, in a proportion not exceeding twice the bulk of the blood, hastens coagulation ; a larger quantity retards it. Blood also coagu- lates more speedily when the serum is of low specific gravity, indicative of much water in proportion to the saline ingredients, 5. Almost every substance that has been tried, except the caustic alkalies, when added to the blood im minute proportion, hastens its coagulation ; although many of the same substances, when mixed with it in somewhat larger quantity, have an opposite effect. The salts of the alkalies and earths, added in the proportion of two or three per cent. and upwards, retard, and, when above a certain quantity, suspend or prevent coagulation ; but, though the process be thus suspended, it speedily ensues on diluting the mixture with water. Caustic potash and soda permanently destroy the coagulability of the blood. Acids delay or prevent coagulation. 6. Certain states of the system.—Faintness occasioned by loss of blood favours coagulation ; states of excitement are said to have, though not invariably, the opposite effect. Impeded aération of the blood in disease, or in suffocative modes of death, makes it slow to coagulate ; probably from retention of carbonic acid. In cold-blooded animals, with slow circulation and low respiration, the blood coagulates less rapidly than in the warm-blooded ; and, among the latter, the tendency of the blood to coagulate is strongest in birds, which have the greatest. amount of respiration, and highest temperature. 7. Coagulation commences earlier, and is sooner completed, in arterial than in venous blood. Nasse states that women’s blood begins ta coagulate sooner than that of the male sex. In general, when blood coagulates quickly, the clot is more bulky and less firm, and the serum is less effectually expressed from it ; so that causes which affect the rapidity of coagulation, will also occasion differences in the proportion of the moist clot to the exuded serum. There is no sufficient evidence of evolution of heat or of disengage- ment of carbonic acid from blood during~its coagulation, which some have supposed to occur. Theory of Coagulation.—Although it is certain that the coagulation of the blood consists in solidification of fibrin, and although it seems tolerably well established that this is the result of the combination of two primarily separate animal principles, it is by no means clearly understood how such combination and solidification do not naturally take place within the living body, and how the several conditions already mentioned as influencing the process operate in promoting or opposing coagulation. According to one view, which is fundamentally the same as that entertained by John Hunter and some other British physiologists, and which has been advo- cated by Briicke,* the blood has a natural tendency to coagulate ; or, if we may use the language suggested by later researches, the para-globulin and fibrinogen naturally tend to combine ; within the body this tendency is held in check by some inhibitory or restraining influence exercised by the coats of the vessels and the living tissues in contact with the blood ; but when blood is withdrawn from its natural receptacles, or if these lose their vitality, its intrinsic disposition to coagu- late being no longer opposed, is allowed to prevail. At the same time it is not * British and Foreign Medico-Chirurgical Review, vol. xix. 1857. THE LYMPH AND CHYLE. 37 inconsistent with this theory to admit the positive efficacy of contact with foreign or dead matter in promoting coagulation. Lister,* on the other hand, considers that the blood has no spontaneous tendency to coagulate, either within or without the vessels, but that the coagulation is brought about in drawn blood by contact with foreign matter. Accepting the conclusion of Schmidt, that para-globulin and fibrinogen are necessary to the evolution of fibrin, he thinks that, if these bodies unite in ordinary chemical combination, the action of foreign matter may determine their union, as spongy platinum promotes the combination of oxygen and hydrogen. He considers that the living vessels do not exert any action to prevent coagulation, but that their peculiarity, as distinguished from an ordinary solid, consists in the remarkable circumstance that their lining membrane, in a state of health, is wholly negative in its relation to coagulation, and does not cause that molecular disturbance, so to speak, which is produced in the blood by all ordinary matter. When the vessels lose their peculiar property by death, or become seriously altered by disease or injury, their contact with the blood in- duces coagulation like that of an extraneous body. More recently, Schmidt} has himself come to the conclusion that the union of para-globulin and fibrinogen to form fibrin is determined by the presence of a third substance, which, however, does not itself take part in the combination and which he has consequently named the fibrin-ferment. This substance he believes to be not preformed in the blood, but to become formed immediately after the withdrawal of that fluid from the body. Other substances also, according to Schmidt, possess the property of in- ducing the union of para-globulin and fibrinogen, amongst them being the colouring matter of the blood,t charcoal, spongy platinum, asbestos, animal ferments, &c. ; more especially those which are able to decompose peroxide of hydrogen. Schmidt considers the action of these substances to be purely one of contact; in this respect it will be seen he has adopted Lister’s view. Finally, it may be observed, - that in any attempted explanation of the coagulation of the blood, it is well to bear in mind that there is a purely physical or chemical phenomenon, which, as suggested by Graham, has a certain analogy to it, namely the change from the liquid to the insoluble state so easily induced in colloidal matter by slight external causes, THE LYMPH AND CHYLE. A transparent and nearly colourless fluid, named “lymph,” is con- veyed into the blood by a set of vessels distinct from those of the sanguiferous system, ‘These vessels, which are named “lymphatics,” from the nature of their contents, and “absorbents,” on account of their reputed office, take their rise in nearly all parts of the body, and, after a longer or shorter course, discharge themselves into the great veins of the neck; the greater number of them previously joining into a main trunk, named the thoracic duct,—a long narrow vessel which rises up in front of the vertebrae, and opens into the veins on the left side of the neck, at the angle of union of the subclavian and internal jugular; whilst the remaining lymphatics terminate in the correspond- ing veins of the right side. ‘The absorbents of the small intestine carry an opaque white liquid, named ‘‘ chyle,” which they absorb from the food as it passes along the alimentary canal; and, on account of the milky aspect of their contents, they have been called the “ lacteal vessels.” But in thus distinguishing these vessels by name, it must be remembered, that they differ from the rest of the absorbents only in the nature of the matters which they convey ; and that this difference holds * On the Coagulation of the Blood ; the Croonian Lecture for 1863.—Proceedings of the Royal Society, vol. xii. p. 580. + Pfliiger’s Archiv. vi. 1872. + In connection with this fact, it may be interesting to mention that, if blood which has been well whipped to remove the fibrin be frozen and thawed again (a process by which the red corpuscles become broken up), it yields a further coagulum, 38 THE LYMPH AND CHYLE. good only while digestion is going on; for at other times the lacteals contain a clear fluid, not to be distinguished from lymph. The lacteals enter the commencement*of the thoracic duct, and the chyle, mingling with the lymph derived from the lower part of the body, is conveyed along that canal into the blood. Both lacteals and lymphatics, in pro- ceeding to their destination, pass into and out of certain small, solid, and vascular bodies, named lymphatic glands, which have a special structure and internal arrangement, as will be afterwards described ; so that both the chyle and lymph are sent through these glands before being mixed with the blood. Thus much having been explained to render intelligible what follows, we may now consider the lymph and the chyle, which, as will be seen, are intimately related to the blood. The lymph may be procured free from admixture of chyle, and in quantity sufficient for examination, from the larger lymphatic vessels of the horse or ass. It may also be obtained by opening the thoracic duct of an animal that has fasted for some time before being killed. It is a thin fluid, transparent and colourless, or occasionally of a pale yellow hue; its taste is saline, its smell faint and scarcely perceptible, and its reaction alkaline. Sometimes the lymph has a decided red tint, of greater or less depth, which becomes brighter on exposure to the air. This redness is due to the presence of coloured corpuscles, like those of the blood: and it has been sometimes supposed, that such corpuscles exist naturally in the lymph, in greater or less quantity ; but they are more probably introduced into the lymphatic vessels accidentally. It can, in fact, be shown, that when an incision is made into a part, the blood very readily enters the lymphatics which are laid open, and passes along into larger trunks ; and in this way blood is conveyed into the thoracic duct, or any other large vessel, exposed as usual by incision immediately after the animal is killed. Indeed, mere rough handling of some organs, such as the liver and spleen, will rupture the fine vessels and cause the contents of the issuing lymphatics speedily to become red from admixture of blood. The lymph, when examined with the microscope, is seen to consist of a clear liquid, with corpuscles floating in it. These “ lymph-corpus- cles,” or lymph-globules, agree entirely in their characters with the pale corpuscles of the blood, which have been already described (page 23). It is alleged that some of the lymph corpuscles have a yellowish tint. Occasionally, smaller particles are found in the lymph ; also, but more rarely, a few oil globules of various sizes, as well as red blood-corpuscles, the presence of which has just been referred to. The liquid part (lymph-plasma) bears a strong resemblance in its physical and chemical constitution to the plasma of the blood; and accordingly, lymph fresh-drawn from the vessels coagulates after a few minutes’ exposure, and separates after a time into clot and serum. This change is owing to the combination of the constituents of the fibrin contained in the lymph-plasma, and in this process most of the cor- puscles are entangled in the coagulum. The serum, like the corre- sponding part of the blood, consists of water, albumin, extractive matters, fatty matters in very sparing quantity and salts. Sugar exists in small quantity in the lymph, and urea, in the proportion of from 0-01 to 0°02 per cent. ; leucin has also been found, at least in the lymphatic glands. FORMATION OF LYMPH-CORPUSCLES. 39 Human lymph has been obtained fresh from the living body in several instances, from lymphatic vessels, opened by wounds or other causes. It has been found to agree in all material points with the lymph of quadrupeds. The chyle of man and mammiferous animals is an opaque, white fluid, like milk, with a faint odour and saltish taste, slightly alkaline or altogether neutral in its reaction. It has often a decided red tint, especially when taken from the thoracic duct. This colour, which is heightened by exposure to air, is doubtless generally due to the presence of plood-corpuscles, and may be explained in the same way as the occasional red colour of lymph. Like blood and lymph, both of which fluids it greatly resembles in constitution, the chyle consists of a liquid holding small parti- cles in suspension. These particles are, 1. Corpuscles, precisely like the lymph and pale blood-corpuscles already described. 2. Molecules, of almost immeasurably minute but remarkably uniform size. These abound in the fluid, and form an opaque white molecular matter diffused in it, which was named by Gulliver the molecular base of the chyle. The addition of ether instantly dissolves this matter, and renders the chyle nearly, but not quite, transparent ; whence it may be inferred that the molecules are minute particles of fatty matter, and no doubt the chief cause of the opacity and whiteness of the chyle. According to the late H. Miiller, they are each coated with a fine film of albuminoid matter. They exhibit the usual tremulous movement com- mon to the molecules of many other substances. 3. Oz/-globules ; these are of various sizes, but much larger than the molecules above de- scribed, and are often found in the chyle in considerable numbers. 4. Minute spherules (Gulliver), from 33355 to gdoo of an inch in diameter; probably of an albuminous nature, and distinguished from the fatty molecules by their varying magnitude and their insolubility in ether. The plasma, or liquid part of the chyle, contains fibrin, so that chyle coagulates on being drawn from the vessels, and nearly all the corpuscles, with part of the molecular base, are involved in the clot. The serum which remains resembles in composition the serum of lymph ; the most notable difference between them being the larger pro- portion of fatty matter contained in the chyle-serum. The following analyses of lymph and chyle exhibit the proportions of ths different ingredients ; but it must be explained that the amount of the corpuscles cannot be separately given, the greater part of them being included in the clot and reckoned as fibrin. No. 1 is the mean of two analyses, by Gubler and Quevenne, of human lymph taken during life from the lymphatics of the thigh ; No. 2 the mean of three analyses by Gmelin of lymph from the thoracic duct of horses after privation of food; No. 3, by O. Rees, of chyle from the lacteals of an ass, after passing the mesenteric glands. if. ate III. Water ‘ . 4 SUBY RRP 939°70 902°37 Fibrin ; ; P 0°595 10°60 3°7 Albumin . F - 42-775 38°83 35°16 Fat. ; : ‘ 6°51 a little 36°01 Extractive matter . 5°05 10°87 29-76 Salts. ; : F U75 1000° 1000° 100°" 40 FORMATION OF BLOOD-CORPUSCLES, The extractive matters of the chyle and lymph probably vary with the nature of the food: they generally contain sugar and urea in appreciable quantities. The gas obtainable from lymph consists almost entirely of carbonic acid. From human lymph Hensen obtained 70 per cent. by volume, whilst in lymph from the dog, Ludwig and Hammarsten were unable to obtain more than about 40 per cent. FORMATION OF THE CORPUSCLES OF THE LYMPH AND CHYLE. The lymph-plasma appears to consist fundamentally of blood-plasma, which, having exuded from the capillary blood-vessels and yielded nutritive material to the tissues, is, with more or less admixture of waste products, returned by the lymphatics. Pale blood-corpuscles also, which have migrated from the vessels, may find their way into the beginning of the lymphatics. In this way the presence of corpuscles in the lymph even before it has passed through the lymphatic glands is accounted for. As to the further origin of the lymph and chyle corpuscles, it may, in the first place, be observed that the greatly increased proportion of these bodies in the vessels which issue from the lymphatic glands, and the vast store of corpuscles having the same characters contained in the interior recesses of these glands, are unmistakeable indications that the glands are at least a principal seat of their production. They are, most probably, pro- duced by division of parent corpuscles or cells contained in the glands, and in some measure also by further division of corpuscles thus produced, after they have made their way into the lymphatic vessels. The corpuscles found sparingly both in chyle and lymph before passing the mesenteric glands may be in part formed in the agminated and solitary follicular glands of the intestine—which, though differing much in form, yet in essential structure have much in common with the lymphatic glands—and may come partly also from the tracts of lymphoid tissue, which exist in the intestinal mucous membrane. Lymph- corpuscles are probably also produced in the spleen and in the thymus gland ; they may also be formed by proliferation of connective tissue corpuscles, or even of the flattened cells of which the commencing lymphatic vessels are composed. FORMATION OF THE BLOOD-CORPUSCLES. In the embryo of batrachians.—In the early embryo of the frog and newt (in which, perhaps, the steps of the process are best ascertained), at the time when the circulation of the blood commences, the corpuscles in that fluid appear as rounded cells, filled with granular matter, and of larger average size than the future blood-corpuscles. The bodies in question, although spoken of as cells and presenting a regularly defined outline, have no separable envelope. They contain, concealed in the midst of the granular mass, a pellucid globular nucleus, which usually presents one or two small clear specks, situated eccentvri- cally. The granular contents consist partly of fine molecules, exhibiting the usual molecular movements ; and partly of little angular plates, or tablets, of a solid substance, probably of a fatty nature. After a few days, most of the cells have assumed an oval figure, and are somewhat reduced in size ; and the granular matter is greatly diminished in quantity, so that the nucleus is conspicuous. Now, also, the blood-corpuscles, previously colourless, have acquired a yellowish or faintly red colour. In a further stage, the already oval cell is flattened, the granules entirely disappear, the colour is more decided, and, in short, the blood- corpuscle acquires its permanent characters. From this description it will be seen that the blood-cells which first appear agree in nature with the embryonic cells (described at page 8), and they are, in all probability, produced by the process of segmentation. The different parts of the embryo in its early condition, the heart, for example, are for a time entirely composed of cells of the same kind, and all have probably a common origin. : It is possible that some, at least, of the red corpuscles of batrachians, originate in a similar manner (endogenously) to that immediately to be described in the bird and in mammalia, for developing blood-vessels of the tadpole’s tail have been observed to contain blood-corpuscles before the establishment of a communication with the rest of the vascular system (Stricker), FORMATION OF BLOOD-CORPUSCLES. 41 In the bird.—In the egg of the bird, the first appearance of blood-corpuscles, as well as of blood-vessels, is seen in the blastoderma, or germinal membrane, a structure formed by the extension of the cicatricula, in the early stages of incu- bation. The commencing embryo, with its simple tubular heart, is seen in the middle of this circular membrane, and blood-vessels, containing blood-corpuscles, appear over a great part of its area. These first vessels, therefore, though con- nected with the heart, and intended to convey nutriment to the embryo, are formed in an exterior structure ; but, in a somewhat later stage, blood-vessels and corpuscles are developed in various textures and organs within the body. The formation of blood-corpuscles in the middle layer of the blastoderm has been recently carefully investigated by Klein.* He describes the blood-vessels of the embryo chick as originating in an endogenous manner in the interior of certain of the cells of the middle layer of the blastoderm. It would appear, first, that the nuclei of these cells become multiplied, and that then the protoplasm around each takes on a reddish colour, and, a cavity becoming formed within the mother-cell by the enlargement of a vacuole, the newly-formed, nucleated, red blood-corpuscles become free within the cavity thus produced (fig. 16). In other instances the cavity be- comes first formed within the Fig. 16 cell, which is considerably en- larged, and in the protoplasmic wall of which nuclei are em- bedded. From this wall, blood- corpuscles, both red and white, bud forth into the interior of the vesicle. The mother-cells send out processes which connect them with one another, and into these processes their cavities are eventually extended : in this way asystem of blood-vessels contain- ing blood is produced. According to Balfour f it is the nuclei them- selves which become the coloured corpuscles, whilst the nucleoli within them develop into the so- ealled “nuclei” of the blood- Fig. 16.—Varrovs Forms or MotTHeEr-CELis corpuscles, UNDERGOING DEVELOPMENT INTO BLoop- VESSELS It is uncertain whether any of (from the middle layer of the chick’s blastoderm. the primary red corpuscles are Klein.) formed by direct transformation d, d, blood-corpuscles. of embryonic cells, as described in the embryo of Batrachians. At the same time they agree with those cells in exhibiting amceboid movements. In man and mammalia.—In the embryo of man and mammalia the primitive red blood-corpuscles are nucleated spheroidal bodies, of much larger size than the future red disks. As to their origin nothing is certainly known : they are probably transformed embryonic cells. These large nucleated red and colourless corpuscles, continuing to increase in number, constitute the earliest, and, for a time, the only corpuscles in the embryo-vessels. But their multiplica- tion is soon arrested, and a new epoch in blood-formation begins with the development of the liver. The blood which returns to the embryo charged with fresh material of nutrition from the maternal system, has then to pass, at first entirely afterwards in great part, through the vessels of the liver; and it would seem that henceforth colourless nucleated corpuscles are produced in that organ and poured abundantly into the general mass of blood by the hepatic veins. It is probable that the liver continues its hemapoietic or blood-forming function throughout foetal life; but, in the meanwhile, the spleen and lymphatic system * Wiener Sitzungsberichte, Ixiii. 1871. + Quarterly Journal of Microscopic Science. July, 1873. 42 EPITHELIUM. haye also begun to produce pale corpuscles, and in after periods supersede the liver in that office. These corpuscles, either immediately or after fissiparous multiplication, acquire colour like the first—-those from the liver and spleen pro- bably in great part before they leave these organs--and are converted into nucleated red corpuscles. The nucleated red corpuscles thus produced are gradually converted into, or at least succeeded by, smaller disk-shaped red cor- puscles without nuclei, having all the characters of the blood-disks of the adult. This transition or substitution begins early, and proceeds gradually, until at length, long before the end of intrauterine life, the nucleated red corpuscles have altogether vanished. The disk-shaped red corpuscles are produced, in part at least, in the interior of connective tissue cells of the developing mammal in a manner somewhat similar to that described by Klein in the cells of the middle layer of the chick’s blasto- derm. The cell-nuclei, however, are not involved in the process, which seems to be rather of the nature of a deposit within the cells. The blood-corpuscles which are at first spheroidal eventually take on the flattened form and become free within a cavity which is hollowed out in the interior of the cell; the latter becomes united with neighbouring cells to form the blood-vessels of the part. This endogenous mode of cell formation commonly ceases before birth.* Throughout life the mass of blood is subject to continual change ; a portion of it is constantly expended, and its place taken by a fresh supply. It is certain that the corpuscles are not exempted from this general change, but it is not known in what manner they are consumed, nor has the process been fully traced by which new ones are continually formed to supply the place of the old. With regard to the latter question, it may be stated, that the explanation which has hitherto found most favour with physiologists is, that the corpuscles of the chyle and lymph, passing into the sanguiferous system, become the pale corpuscles of the blood ; and that these last are converted into red disks. Pale corpuscles are also generated in the spleen, and, after part of them have changed into red disks, pass directly into the blood, independently of those derived from the chyle and lymph. A production of blood-corpuscles is also said to take place in certain cells of the marrow of the bones, in which transitional forms to the red corpus- cles have been observed. (Neumann, Bizzozero.) As to the manner in which the pale corpuscles are transformed into the red, there is considerable difference of opinion. According to one view (adopted by Paget, Kolliker, Funke, and others), the pale corpuscles gradually become flattened, acquire coloured con- tents, lose their nuclei, and shrink somewhat in size, and thus acquire the characters of the red disks. Wharton Jones, on the other hand, arrived at the conclusion that, whilst in birds, reptiles, and fishes, the pale or lymph corpuscle, suffering merely some alteration of form and contents, becomes the red disk, its nucleus alone is developed into the red disk of mammalian blood. According to this view (supported by Busk, Huxley, and Gulliver), while the red corpuscle of oviparous vertebrata is the transformed pale corpuscle—its develop- ment not proceeding beyond this stage—the non-nucleated red disk of men and mammalia is, on the other hand, considered to be, not the homologue of the oval nucleated red disk of the oviparous vertebrata, but that of its nucleus. It is not within the scope of this work to enter upon a discussion of the relative merits of these opinions, and the reader is referred to physiological works for a consideration of these and other views adopted by various authors upon the point at issue. EPITHELIAL, EPIDERMIC, OR CUTICULAR TISSUE. General nature and situation.—It is well known, that when the skin is blistered, a thin, and nearly transparent membrane, named the cuticle or epidermis, is raised from its surface. In like manner, a transparent film may be raised from the lining membrane of the mouth, similar in nature to the epidermis, although it has in this situation * Schiifer, Proceedings of the Royal Society. 1874. VARIETIES OF EPITHELIUM. 43 received the name of “ epithelium ;” * and under the latter appellation, a coating of the same kind exists on nearly all free surfaces of the body. It is true that in many situations the epithelium cannot be actually raised from the adjacent surface as a coherent membrane, still its existence as a continuous coating can be demonstrated ; and, al- though in different parts it presents important differences, its several varieties are connected by certain common characters. The existence of a cuticular covering composed of cells has in one form or other been demonstrated in the following situations: viz.,1. On the surface of the skin. 2. On mucous membranes; a class of membranes to be afterwards described, which line those internal cavities and passages of the body that open exteriorly, viz., the alimentary canal, the lachrymal, nasal, tympanic, respiratory, urinary, and genital passages ; as well as the various glandular recesses and ducts of glands, which open into these passages or upon the surface of the skin. 3. On the inner or free surface of serous membranes, which line the walls of closed cavities in the head, chest, abdomen, and other parts. 4. On the inner surface of the heart, blood-vessels and lymphatics. Structure in general.—This tissue has no vessels, although nerves have been demonstrated in it in various situations ; apart from these, however, it possesses a decidedly organised structure. Wherever it may exist, it is formed essentially of nucleated cells united together by cohesive matter, often in too small quantity to be apparent. ‘The cells, where consisting of more than one layer, in whatever way they may be produced, make their appearance first in the deepest part of the structure, where they receive material for growth from the blood-vessels of the subjacent tissue ; then, usually undergoing considerable changes in size, figure, and consistency, they gradually rise to the surface, where, as shown at least in various important examples, they are thrown off and succeeded by others from beneath. In many situations the cells form several layers, in which they may be seen in different stages of progress, from their first appearance to their final desquamation. The layer or layers thus formed take the shape of the surface to which they are applied, following accurately all its eminences, depressions and inequalities. Epithelium when destroyed or cast off, is, for the most part, very readily regenerated. Varieties.—In accordance with the varied purposes which the epi- thelium is destined to fulfil, the cells of which it is composed come to differ in different situations, in figure and size, in their position in respect of each other, their degree of mutual cohesion, and in the nature of the matter they contain, as well as in the vital endowments which they manifest ; and, founded on these modifications of its con- * The term “epithelia,” which has passed into ‘‘ epithelium,’ was introduced by Ruysch to designate the cuticular covering on the red part of the lips. The word ‘‘epidermis”’ he considered inappropriate, as the subjacent surface is not skin (derma) ; but, as it is beset with papille, he named the covering layer ‘‘ epi-thelia,”’ trom em and @nAn, a nipple or papilla. The use of the term has, by a not unusual license, been ex- tended so as to signify the same kind of coating when it spreads over non-papillary surfaces, The word ‘‘endothelium,’’ recently applied by some German writers to dis- tinguish what has heretofore been spoken of as the epithelium lining the serous mem- branes, and the inner surface of blood-vessels and lymphatics, appears to me a needless innovation, and, considering the literal meaning of the word, not a happy one.—W. S. t The flattened cells which are enumerated under 3 and 4, and which have a close affinity with the ceils of the connective tissue to be afterwards described, may be con- veniently distinguished by the term ‘‘ epithelioid.” 44 EPITHELIUM. stituent cells, or, at any rate, those forming the superficial layer, four principal varieties of epithelium have been recognised, as follows :— 1. The cells may become flattened into plates or scales, and the variety of epithelial tissue thus constituted is termed scaly, or tessellated (pavement epitheium of German histologists). It might be well to employ the former term when the flattened cells overlap at their edges (as in fig. 17), the latter where the adjoining edges meet; in which case the lines of junction may be even (as in fig. 18), or more or less sinuous, as in various parts of the lymphatic system (fig. 19). Fig. 17. Fig. 18. TI rs $itir-> whi f Mul py, Fig. 17. EprrHeniuM-ScALES FROM THE INSIDE OF THE MovurTH; MAGNIFIED 260 3 DIAMETERS (Henle). Fig. 18. —EpirHeniorD CeLLs FRoM A SERouS MEMBRANE (PERITONEUM) ; MAGNIFIED 410 DIAMETERS. a, cell; 6, nucleus ; ¢, nucleoli (Henle). 2. In a second variety named colwmnar (cylinder-epithelinm of the Germans) the cells assume a prismatic figure, and are set upright on the surface which they cover (fig. 20). Fig. 19.—EprruEenior Criits or Commrnoina LyMpHatic ; MAGNIFIED 240 DIAMETERS (Auerbach), Fig. 20.—Cotumyar Ep1tHELIUM FROM INTESTINAL VILLUS OF A RABBIT; MAGNIFIED 300 DIAMETERS. a, Thick border (from Kolliker). 9 3. The cells may retain their primitive roundness, or, being flattened where they touch acquire a polyhedral or cubical figure, in which no one dimension remarkably predominates : in some places, however, the cells show a tendency to lengthen into columns and in others to flatten into tables, presenting thus transitional forms between the other varieties. This variety of epithelium has been named spheroidal and transitional. 4, Lastly the cells, which in this case are mostly prismatic in form, NUCLEUS OF EPITHELIUM-CELL. 45 bear on their basal or free ends spontaneously moving filaments, named cilia; on which account this variety of epithelium is termed ciliated (fig. 21). ine LN el ¢ Fig. 21.—Cotumwnar Cintatep Eprtarrium Cents rrom tHE Human Nasa MEMBRANE; MAGNIFIED 300 DIAMETERS. Fig. 22.—Dracram or Section or Srratirrep EprtHEeniumM, IN WHICH THE UNDER- MOST CELLS ARE OBLONG AND VERTICAL. When the cells of an epithelium are arranged in several superimposed layers instead of being in a simple layer, it is termed stratified: in Fig. 23. ie en o> Fig. 23.—HpmITHELIUM oF ConguNcTIVA OF CALF. 1, 2, 3, 4, 5, progressive flattening of the cells as they rise to the surface. The out- line figures represent single cells from different depths, viewed on their surface ; and at 4’ and 5’, edgeways. Magnified 410 diameters (chiefly after Henle). these cases it is commonly found that the lowermost Jayer is columnar in shape, and the uppermost scaly ; the intermediate strata presenting transitions between these forms (figs. 22, 23). The first three of the varieties here enumerated present local pecu- liarities which make it convenient to describe them with the tissues or organs with which they are associated. The ciliated epithelium, on the other hand, being of nearly uniform character as regards situation, vital properties and functional activity, can be most conveniently treated of under one general head, and will therefore be considered here. It may first be remarked, however, that amidst these changes the nucleus of the cell undergoes little alteration, and its characters are accordingly remarkably uniform throughout (see figs.). It is round or oval, and more or less flattened ; its diameter measures from ;,},,th to adooth of an inch, or more. Its substance is insoluble in acetic acid, 46 CILIATED EPITHELIUM. clear and colourless. It usually contains one or two nucleoli, distin- guished by their strong dark outline ; and a variable number of more faintly marked granules irregularly scattered. For the most part, the nucleus is persistent, but in some cases it disappears from the cell. CILIATED HPITHELIUM. In this form of epithelium, the particles, which are generally co- lumnar, bear at their free extremities little hair-like processes, which are agitated incessantly during life, and for some time after death, with a lashing or vibrating motion. ‘These minute and delicate moving organs are named cilia. They have now been discovered to exist very extensively throughout the animal kingdom ; and the movements which they produce are subservient to very varied purposes in the animal economy. Distribution and use.—In the human ody ciliated epithelium occurs in the following parts, viz.:—1. On the mucous membrane of the air passages and its prolongations. It commences at a little distance within the nostrils, covers the membrane of the nose (except the proper olfactory part) and of the adjoining bony sinuses, and extends up into the nasal duct and lachrymal sac. From the nose it spreads backwards a certain way on the upper surface of the soft palate, and over the upper or nasal region of the pharynx; thence along the Eustachian tube and lining membrane of the tympanum, of which it covers the greater part. The lower part of the pharynx is covered by scaly epithelium as already mentioned; but the ciliated epithelium begins again in the larynx a little above the glottis, and continues throughout the trachea and the bronchial tubes in the lungs to their smallest ramifications. 2. On the mucous lining and in the glands of the uterus, commencing at the middle of the cervix and extending along the Fallopian tubes, even to the peritoneal surface of the latter at their fimbriated extremities. 3. Lining the vasa efferentia, cont vasculosi, and first part of the excretory duct of the testicle. 4. To some extent on the parietes of the ventricles of the brain, and throughout the central canal of the spinal cord. 5. In the excretory ducts of certain small racemose glands of various parts (tongue, pharynx, &c.). In other mammiferous animals, as far as examined, cilia have been found in nearly the same parts. To see them in motion, a portion of ciliated mucous membrane may be taken from the body of a recently killed quadruped. The piece of membrane is to be folded with its free or ciliated surface outwards, placed on a slip of glass, with a little weak salt water or serum of blood, and covered with thin glass. When it is now viewed with a magnifying power of 200 diameters or upwards, a very obvious agitation will be perceived on the edge of the fold; this appearance is caused by the moving cilia, with which the surface of the membrane is covered. Being set close together, and moving simulta- neously or in quick succession, the cilia, when in brisk action, give rise to the appearance of a bright transparent fringe along the fold of the membrane, agitated by such a rapid and incessant motion, that the single threads which compose it cannot be perceived. ‘The motion here meant, is that of the cilia themselves; but they also set in motion the adjoining fluid, driving it along the ciliated surface, as is indicated by the agitation of any little particles that may accidentally float in it. STRUCTURE OF CILIATED EPITHELIUM. 47 The fact of the conveyance of fluids and other matters along the ciliated surface, as well as the direction in which they are impelled, may also be made manifest by immersing the membrane in fluid, and dropping on it some finely pulverised substance (such as charcoal in fine powder), which will be slowly but steadily carried along in a constant and deter- minate direction; and this may be seen with the naked eye, or with the aid of a lens of low power. The ciliary motion of the human mucous membrane is beautifully seen on the surface of recently extracted nasal polypi; and single ciliated particles, with their cilia still in motion, are sometimes sepa- rated accidentally from mucous surfaces in the living body, and may be discovered in the discharged mucus; or they may even be purposely detached by gentle abrasion. But the extent and limits of the ciliated epithelium of the human body have been determined chiefly from its anatomical characters. Cilia have now been shown to exist in almost every class of animals, from the highest to the lowest. The immediate purpose which they serve is, to impel matter, generally more or less fluid, along the surfaces on which they are attached ; or, to propel through a liquid medium the ciliated bodies of minute animals, or other small objects on the surface of which cilia are present ; as is the case with many infusorial animal- cules, in which the cilia serve as organs of locomotion like the fins of larger aquatic animals, and as happens, too, in the ova of many verte- brate as well -as invertebrate animals, where the yelk revolves in its surrounding fluid by the aid of cilia on its surface. In many of the lower tribes of aquatic animals, the cilia acquire a high degree of importance: producing the flow of water over the surface of their organs of respiration, indis- pensable to the exercise of that function ; enabling the animals to seize their prey, or swallow their food, and performing various other offices of greater or less importance in their economy. In man, and the warm-blooded animals, their use is apparently to impel secreted fluids or other mat- ters along the ciliated surface, as, for example, the mucus of the windpipe and nasal sinus- es, which they carry towards the outlet of these cavities. Structure.—The cells of the ciliated epithelium (fig. 24) contain clear oval nu- clei; their protoplasm is commonly granular, but the free border of the cell from Fig. 24.—Cinrarep EpirHriium CELLS FROM which the cilia appear to spring ~ ‘Tracnea or Cat; macnrriep azour 600 presents a bright appearance _ pramersrs (Klein). (fig. 21). They have most generally an elongated form, like the particles of the columnar 48 CILIATED EPITHELIUM. epithelium, which they resemble too in arrangement, but are often of greater length and more slender and pointed at their lower end, which is commonly branched. The cilia are attached to their broad or superficial end, each columnar particle bearing a tuft of these minute hair-like processes. In some cases, the cells are spheroidal in figure, the cilia being still, of course, confined to that portion of the cell which forms part of the general surface of the epithelial layer, as shown in fig. 25, whichre presents such cells from the epithelium of the frog’s mouth. In man Fig. 25. this form occurs in the ciliated epithelium of the cerebral ventricles and tympanum, where the cells form but a single stratum. The co- lumnar ciliated epithelium also may exist as a simple layer, as in the uterus and Fallopian tubes, the finest ramifications of the bronchia, and the central canal of the spinal cord ; but in various other parts—as the nose, pharynx, Eustachian tube, the trachea and its larger divi- Fis. 25.—Spuunorpan sions—there is a layer of elongated cells beneath CmIaTED CELLS FROM the superficial ciliated range, filling up the THE MovurH oF THE ° ane Frog; magxirrep 309 Spaces between the pointed extremities of the DIAMETERS. latter, and beneath this is an undermost layer, formed of small rounded cells. Probably the subjacent cells acquire cilia, and take the place of ciliated cells, which are cast off; but the mode of renovation of ciliated epithelium is not yet fully understood. The relation of the ciliated, as well as other epithelium-cells, to the connective tissue of the subjacent membrane, has much engaged attention since the importance of the connective-tissue-corpuscles has come to be recognised ; and a strong impression or belief prevails that such epithelium-cells are structurally connected by prolongations from their lower ends with these corpuscles, and genetically related to them. As a matter of observation, such anatomical con- nection is affirmed in reference to the columnar ciliated epithelium of the central canal of the spinal cord and the Sylvian aqueduct, (Lockhart Clarke, Gerlach). The cilia themselves differ widely in size in different animals, and they are not equal in all parts of the same animal. In. the human windpipe they measure ,54 th to 555th of an inch in length; but in many invertebrate animals, especially such as live in salt water, they are a great deal larger. In figure they have the aspect of slender, conical, or slightly flattened filaments ; broader at the base, and usually pointed at their free extremity. Their substance is transparent, soft, and flexible. It is to all appearance homogeneous, and no fibres, gran- ules, or other indications of definite internal structure, have been satis- factorily demonstrated in it. Motion of the cilia.—The manner in which the cilia move, is best seen when they are not acting very briskly. Most generally they seem to execute a sort of fanning or lashing movement ; and when a number of them perform this motion in regular succession, as is generally the case, they give rise to the appearance of a series of waves travelling along the range of cilia, like the waves caused by the wind in a field of corn. When they are in very rapid action the undulation is less obvious, and, as Henle remarks, their motion then conveys the idea of swiftly running CILIARY MOTION. 49 water. The undulating movement may be beautifully seen on the gills of amussel. The undulations, with some exceptions, seem always to travel in the same direction on the same parts. The impulsion, also, which the cilia communicate to the fluids or other matters in contact with them, maintains a constant direction ; unless in certain of the infusoria, in which the motion is often variable and arbitrary in direc- tion, and has even been supposed to be voluntary. Thus in the wind- pipe of mammalia, the mucus is conveyed upwards towards the larynx, and, if a portion of the membrane be detached, matters will still be conveyed along the surface of the separated fragment in the same direction relatively to that surface, as before its separation. The persistence of the ciliary motion for some time after death, and the regularity with which it goes on in parts separated from the rest of the body, sufficiently prove that, with the possible exceptions alluded to, it is not under the influence of the will of the animal nor dependent for its production on the nervous centres, and it does not appear to be influenced in any way by stimulation or sudden destruction of these centres. The time which it continues after death or separation differs in different kinds of animals, and is also materially influenced by tem- perature and by the nature of the fluid in contact with the surface. In warm-blooded animals the period varies from two or three hours to two days, or even more ; being longer in summer than in the cold of winter. In frogs the motion may continue four or five days after the destruction of the brain ; and it has been seen in the gullet of the tortoise fifteen days after decapitation, continuing seven days after the muscles had ceased to be irritable. With the view of throwing further light on the nature of this remarkable kind of motion, experiments have been made to ascertain the effect produced on it by different physical, chemical, and medicinal agents ; but, so far as these experiments have gone, it would seem that, with the exception of moderate heat and cold, alkaline solutions, chlo- roform vapour, and perhaps some other narcotics, these agents affect the action of the cilia only in so far as they act destructively on their tissue. The effect of change of temperature is different in warm and in cold-blooded animals. Inthe former the motion is stopped by a cold of 43° F., whereas in the frog and river-mussel it goes on unimpaired at 32° F, E. H. Weber made the interesting observation that, in ciliated epithelium particles detached from the human nasal membrane, the motion which has become languid or quiescent from the cold may be revived by warmth, such as that of the breath, and this several times in succession. A moderately elevated temperature, say 100° F., does not affect the motion in cold-blooded animals ; but, of course, a heat considerably higher than this and such as to alter the tissue, would put an end to it in all cases. Electric shocks, unless they cause abrasion of the ciliated surface (which is sometimes the case), produce no visible effect; and the same is true of galvanic currents. Fresh water arrests the motion in marine mollusca and in other salt-water animals; but it evidently acts by destroying both the form and substance of the cilia, which in these cases are adapted to a different medium. Most of the common acid and saline solutions, when concentrated, arrest the action of the cilia instantaneously in all animals ; but dilution delays this effect, and when carried farther, prevents it altogether ; and hence it is, probably, due to a chemical alteration of the tissue. Virchow has observed that a solution of either potash or soda will revive the movement of cilia after it has ceased. Nar- cotic substances, such as hydrocyanic acid, salts of morphia and strychnia, opium and belladonna, are said by Purkinje and Valentin to have no effect, though the VOL. II. E 50 CILIA. first-named agent has certainly appeared to us to arrest the motion in the river- mussel. In confirmation of an observation of Lister,* we find that exposure for a few moments to the vapour of chloroform arrests ciliary action, and that the motion revives again if the application of the vapour is discontinued. Bile stops the action of the cilia, while blood prolongs it in vertebrated animals ; but the blood or serum of the vertebrata has quite an opposite effect on the cilia of invertebrate animals, arresting their motion almost instantaneously. Whatever views may be entertained concerning the nature and source of the power by which the cilia act, it must be borne in mind that each ciliated cell is individually endowed with the faculty of producing motion, and that it possesses in itself whatever organic apparatus and whatever physical or vital property may be necessary for that end ; for single epithelium cells are seen to exhibit the phenomenon long after they have been completely insulated. It seems not unreasonable to consider the ciliary motion as a manifestation of that property on which the more conspicuous motions of animals are known to depend, namely, vital contractility; and this view has at least the advantage of referring the phenomenon to the operation of a vital property already recognised as a source of moving power in the animal body. But, assuming this view to be sound, so far as regards the nature of the motile property brought into play, it affords no explanation of the cause by which the contractility is excited and the cilia maintained in constant action. It is true that nothing resembling a muscular apparatus in the ordinary sense of the term, has been shown to be connected with the cilia, nor is it necessary to suppose the existence of any such; for it must be remembered that, while the organic substance on which vital contractility depends is probably uniformly the same in composition, it does not everywhere assume the same form and texture. The anatomical characters of human voluntary muscle differ widely from those of most involuntary muscular structures, and still more from the contractile tissues of some of the lowest invertebrate animals, although the movements must in all these cases be referred to the same principle. The heart of the embryo beats while yet but a mass of cells, united, to all appearance, by amorphous matter, in which no fibres are seen ; yet no one would doubt that its motions depend then on the same property as at a later period, when its structure is fully developed. In its persistence after systemic death and in parts separated from the rest of the body, the ciliary motion agrees with the motion of certain muscular organs, as the heart, for example ; and the agreement extends even to the regular or rhythmic character of the motion in these circumstances. It is true, the one endures much longer than the other; but the difference appears to be one only of degree, for similar differences are known to prevail among muscles themselves. No one, for instance, doubts that the auricle of the heart is mus- cular, because it beats longer after death than the ventricle ; nor, because a frog’s heart continues to act a much longer time than a quadruped’s, is it inferred that its motion depends on a power of a different nature. And the view here taken of the nature of the ciliary motion derives strength from the consideration that the phenomenon lasts longest in cold-blooded animals, in which vital contractility also is of longest endurance. In the effects of heat and cold, as far as observed, there is also an agreement between the movement of cilia and that of muscular parts ; while, on the other hand, it must be allowed that electricity does not appear to excite their activity. The effects of narcotics afford little room for inference, seeing that our knowledge of their local action on muscular irritability is by no means exact; but in one instance, at least, an agent, chloroform vapour, which stops the action of the freshly excised heart of a frog, arrests also * Phil. Trans. 1858, p. 690, where will be found other valuable observations on the effect of external agents on ciliary action. PIGMENT. 51 the ciliary motion. Something, moreover, may depend on the facility or difficulty with which the tissues permit the narcotic fluid to penetrate, which circumstance must needs influence the rapidity and extent of its operation. Again, we see differences in the mode in which the cilia themselves are affected by the same agent ; thus, fresh water instantly arrests their motion in certain cases, while it has no such effect in others. The existence of vibrating cilia on the spores and other parts of certain crypto- gamic vegetables may perhaps be considered to afford an argument on the opposite side ; but it is by no means proved that the sensible motions of plants (such, at least, as are not purely physical), and those of animals, do not depend on one common vital property. PIGMENT. The cells of the cuticle, and of other epithelial structures, sometimes contain a black or brown matter, which gives a dark colour to the parts over which the cells are spread. A well-marked example of such pigmented cells in the human body is afforded by the black coating which lines the choroid membrane of the eye, and covers the posterior surface of the iris. Pigment is also met with in certain cells of the investing membrane (pia mater) of the spinal cord, in the membranous labyrinth of the ear, and (with brownish yellow pigment) on the olfactory region of the nose. The pigment, strictly so called, which is contained within the cells, consists of black or brown granules or molecules of a round or oblong shape, and almost too small for exact measurement. These molecules are densely packed together in some cells ; in others they are more scat- tered, and then it may be seen that there is a certain amount of colour- less matter included along with them. When they escape from the ruptured cells, they exhibit very Fig. 26.—Picmentnp EpitHELIUM CELLS a aaa RRS oe strikingly the Brownian mole- FROM THE CHOROID; MAGNIFIED 370 cular movement ; and in conse- DIAMETERS (Henle). quence of this movement the ap- A, cells still cohering, seen on their parent figure of the particles is sub-surface ; a, nucleus indistinctly seen. ject to change. It is worthy of In the other cells the nucleus is con- remark, that when viewed singly ealed by the pigment granules. 5 4 Bhi B, two cells seen in profile; a, the with a very high magnifying power outer or posterior part containing scarcely they look transparent and almost any pigment. colourless, and it is only when they are heaped together that their blackness distinctly appears. The nucleus is colourless, but is very generally hidden from view by the black particles. The dark colour of the negro is known to have its seat in the cuticle, and chiefly in the deeper and softer part named the rete mucosum, ~ It is caused by dark-brown colouring matter within the cells, either diffused through their substance or in form of granules—usually more densely aggregated round the nucleus. The dark parts of the European skin owe their colour and its different shades to the presence of pigment granules in the cells in different proportions. Lastly, it cannot be E 2 52 CONNECTIVE TISSUE. doubted, that in both the coloured and white races, the colouring matter of the skin is the same in its essential nature as that of the choroid. In Albino individuals, both negro and European, in whom the black matter of the choroid is wanting, the cuticle and the hair are colourless also. In some situations the pigment is met with in enlarged and irregularly branched corpuscles which belong to the connective tissue. Such rami- fied cells are very common in many animals. In the human body cells of this description are found in the dark tissue on the outer surface of the choroid coat, lamina fusca (fig. 27, a a), and on the pia mater covering the upper part of the spinal cord. The condition of the pigment gy Rian Ours, 2 the ‘hairs will be afterwards noticed. FROM THE TIssuE or THE When the cuticle of the negro is removed by Cuororp Coar or tHe means of a blister, it is renewed again of its Be en core ot original dark hue ; but if the skin be destroyed ‘ “to any considerable depth, as by a severe burn, 5 eet eee oments the resulting scar remains long white, though it , colourless fusiform cells. ee = ; ? at length acquires a dark colour. Composition.—Examined chemically, the black matter is found to be in- soluble in cold and hot water, alcohol, ether, fixed and volatile oils, acetic and diluted mineral acids. The pigment of the bullock’s eye, when purified by boiling in alcohol and ether, was found by Scherer to consist of 58672 carbon, 5°962 hydrogen, 13°768 nitrogen, and 21°598 oxygen ; its proportion of carbon is thus very large. Preceding chemists had obtained from its ashes oxide of iron, chloride of sodium, lime, and phosphate of lime. Uses.—In the eye the black matter seems obviously intended to absorb re- dundant light, and accordingly its absence in Albinos is attended with a difficulty of bearing a light of considerable brightness. Its uses in other situations are not: so apparent. The pigment of the cuticle, it has been supposed, may screen the subjacent cutis from the pungency of the sun’s rays, but in many animals the pigment is not only employed to variegate the surface of the body, but attaches itself to deep-seated parts. Thus, in the frog the branches and twigs of the blood-vessels are speckled over with it, and in many fish it imparts a black colour to the peritoneum and other internal membranes. CONNECTIVE TISSUE. This substance consists of fibres of two kinds, more or less amorphous. matter, and peculiar corpuscles. By means of its fibres it serves in the animal body as a bond of connection of different parts; also as a covering or investment to different organs, not only protecting them outwardly, but, in many cases entering into their structure and con- necting and supporting their component parts. The corpuscles, on the other hand, are destined for other than mechanical purposes ; they appear to be essentially concerned in the nutrition and reparation of tissues. Three principal modifications or varieties of connective tissue have long been recognised, consisting of the same structural elements, but in widely different proportions, and thereby exhibiting a difference in their grosser or more Obvious characters and physical properties. ‘They are AREOLAR TISSUE. 53 known as the areolar (including the fat), the fibrous, and the elastic tissues, and will be now severally treated of. Without disregarding the alliance of cartilage and bone to the connective tissues, we shall not, in imitation of some respected authorities, include them in the same group ; but there remain certain forms of tissue, occurring locally, or ‘met with as constituents of other textures, which properly belong to this head, and will be briefly considered in a separate section as sub- ordinate varieties of connective tissue. Cartilage and bone are included in the group of connective tissues or connec- tive substances by several eminent German histologists, and present undoubted points of relationship with these tissues, both in their nature and the general purpose which they serve in the animal frame. Thus, yellow cartilage shows an unmistakable transition to elastic connective tissue, as fibro-cartilage does, even more decidedly, to white fibrous tissue. Moreover, the animal basis of bone agrees entirely in chemical composition, and in many points of structure, with the last-named tissue. Still, when it is considered that cartilage, in its typical form, consists of a quite different chemical substance, chondrin, and that bone is characterised by an impregnation of earthy salts, it seems more consistent with the purpose of histological description to recognise cartilage and bone as inde- pendent tissues. As to their community of origin, little stress need be laid on it as a basis of classification, seeing that the origin of blood-vessels, nerves, and muscles, may be traced up to protoplasm-cells, to all appearance similar to those that give rise to the connective tissues, and belonging to the same embryonic layer. THE AREOLAR TISSUE. Distribution and arrangement.—If we make a cut through the skin and proceed to raise it from the subjacent parts, we observe that it is loosely connected to them by a soft filamentous substance, of considerable tenacity and elasticity, and having, when free from fat, a white fleecy aspect ; this is the substance known by the names of “cellular,” “ areolar,” “ filamentous,” ‘ connective,” and “reticular ” tissue ; it used formerly to be commonly called “ cellular mem-. brane.” In like manner the areolar tissue is found underneath the serous and mucous membranes which are spread over various internal surfaces, and serves to attach those membranes to the parts which they line or invest; and as under the skin it is named “ sub- cutaneous,” so in the last-mentioned situations it is called “ sub- serous” and “submucous” areolar tissue. But on proceeding further we find this substance lying between the muscles, the blood-vessels, and other deep-seated parts, occupying, in short, the intervals between the different organs of the body where they are not otherwise insulated, and thence named “ intermediate ;” very generally, also, it becomes more consistent and membranous immediately around these organs, and, under the name of the “investing” areolar tissue, affords each of them a special sheath. It thus forms inclosing sheaths for the muscles, the nerves, the blood-vessels, and other parts. Whilst the areolar tissue might thus be said in some sense both to connect and to insulate entire organs, it also performs the same office in regard to the finer parts of which these organs are made up; for this end it enters between the fibres of the muscles, uniting them into bundles ; it connects the several membranous layers of the hollow viscera, and binds together the lobes and lobules of many compound glands ; it also accompanies the vessels and nerves within these organs, following their branches nearly to their finest divisions, and affording them support and protection. This portion 54 CONNECTIVE TISSUE. of the areolar tissue has been named the “ penetrating,” “ constituent,” or “ parenchymal.” It thus appears that the areolar is one of the most general and most extensively distributed of the tissues. It is, moreover, continuous throughout the body, and from one region it may be traced without interruption into any other, however distant; a fact not without interest in practical medicine, seeing that in this way dropsical waters, air, blood, and urine, effused into the areolar tissues, and even the matter of suppuration, when not confined in an abscess, may spread far from the spot where they were first introduced or deposited. On stretching out a portion of areolar tissue by drawing gently asunder the parts between which it lies, it presents an appearance to the naked eye of a multitude of fine, soft, and somewhat elastic threads, quite trans- parent and colourless, like spun glass ; these are intermixed with fine transparent films, or delicate membranous lamin, and both threads and laming cross one another irregularly and in all imaginable directions leaving open interstices or areole between them. These meshes are, of course, more apparent when the tissue is thus stretched out; it is plain also that they are not closed cells, as the term “cellular tissue” might seem to imply, but merely interspaces, which open freely into one another : many of them are occupied by the fat, which, however, does not lie loose in the areolar spaces, but is enclosed in its own vesicles. A small quantity of colourless transparent fluid is also present in the areolar tissue, but, in health, not more than is sufficient to moisten it. This fluid is generally said to be of the nature of serum ; but it is not improbable that, unless when unduly increased in quantity or altered in nature by disease, it may resemble more the liquor sanguinis, as is the case with the fluid of most of the serous membranes. On comparing the areolar tissue of different parts, it is observed in some to be more loose and open in texture, in others more dense and close, according as free movement or firm connection between parts is to be provided for. In some situations, too, the lamin are more numerous ; in others the filamentous structure predominates, or even prevails exclusively ; but it does not seem necessary to designate these varieties by particular names, as is sometimes done. Fibres.— When examined under the microscope, the areolar tissue is seen to be principally made up of exceedingly fine, transparent, and apparently homogeneous filaments, from about 553,5th to gs4poth of an inch in thickness, or even less (fig. 28). These are seldom single, being mostly united by means of a small and usually imperceptible quantity of a homogeneous connecting substance into bundles and filamentous laminee of various sizes, which to the naked eye, appear as simple threads and films. ‘Though the bundles may intersect in every direction, the filaments of the same bundle run nearly parallel to each other, and no one filament is ever seen to divide into branches or to unite with another. The associated filaments take an alternate bending or waving course as they proceed along the bundle, but still maintain their general parallelism. This wavy aspect, which is very characteristic of these filaments, disappears on stretching the bundle, but returns again when it is relaxed. The filaments just described, though transparent when seen with transmitted light under the microscope, appear white when col- lected in considerable quantity and seen with reflected light ; and they AREOLAR TISSUE. &5 not only occur in the areolar tissue strictly so called, but form the chief part of the tendons, ligaments, and other white fibrous connective tissues. They were long supposed to be the only fibrous con- stituent existing in the areolar tissue, but it is now well known that fibres of another kind are intermixed with them; _ these agree in all characters and are obviously identical with the fibres of the yellow elastic tissue, and have accordingly been named the yellow or elastic fibres, to dis- tinguish them from the white or waved filaments above de- scribed. In certain portions Fig. 28.—Fruamenrs of ARzoLAR TissuE, IN LARGER of the areolar tissue, AND SMALLER BUNDLES, AS SEEN UNDER A MAGNIFYING as for instance in that POWER OF 400 DIAMETERS, which lies under the serous and mucous membranes of particular regions, the yellow or elastic fibres are abundant and large, so that they cannot well be overlooked ; but in other parts they are few in number, and Fig, 29. small, and are then in a great measure hidden by the white filaments; in such cases, however, they can always be rendered conspicuous under the microscope by means of 2 aa as ee : Bey sans Q 2S) acetic acid, which causes b rAISS REO the white filaments to \ J al Ane =e swell up and become in- distinct, whilst the elastic fibres, not being affected by that re-agent, come then more clearly into view (fig. 29). More- over, they resist the pig 29,.—Muacnrrmp View or Argonan Tissue action of boiling alka- (rrom pIrFERENT PARTS) TREATED wiTH ACETIC line solutions of potash Acrp. and soda, of moderate The white filaments are no longer seen, and the strength, which very yellow or elastic fibres with the nuclei come into view. speedily destr oy the rest At c, a bundle of white fibres, which is swollen out by f the effect of the acid, and presents a number of con- of the tissue. Under the stricting bands as described in the text. 56 CONNECTIVE TISSUE. microscope the elastic fibres appear transparent and colourless, with a strong, well-defined, dark outline. They are further remarkable for their tendency to curl up, especially at their broken ends, which gives them a very peculiar aspect ; and in many parts of the areolar tissue they divide into branches and join or anastomose with one another, in the same manner as in the pure elastic tissue (a). They differ among themselves very widely in size, some being as fine as the white fila- ments, others many times larger. The elastic fibres lie, for the most part, without order, among the bundles of white filaments ; but here and there we see what appears to be an elastic fibre winding round one of these bundles, and encircling it with several spiral turns. When acetic acid is applied, the fasciculus swells out between the constricting turns of the winding fibre, and presents a highly characteristic appearance (¢). This remarkable disposition of the elastic fibres, which was pointed out by Henle, is not uncommon in certain parts of the areolar tissue ; it may be always seen in that which accompanies the arteries at the base of the brain. It must be observed, however, that the encircling fibre sometimes forms not a continuous spiral, but several separate rings; moreover, the whole appearance may be explained on the supposition that the bundles in question are naturally invested with a delicate sheath, which, like the elastic tissue, resists acetic acid, but, on the swelling up of the bundle under the operation of that agent, is rent into shreds or segments, mostly annular or spiral, which cause the constrictions. Indeed, some bundles have been shown to possess such a sheath, made up of flattened cells (Ranvier, Key and Retzius). Fig. 380. Moreover, the union of branches of the corpuscles (to be immediately noticed) around a bundle may, in some instances, be the cause of the appearance (Kolliker), A very different view of the struc- ture of areolar tissue from that here stated was taken by Reichert, and adopted by Virchow, Donders, and other distinguished histologists. According to this view the apparent bundles consist of a substance in reality amorphous or homogeneous, and its seeming fibrillation is partly artificial, the result of cleavage, and partly an optical illusion, arising from creasing or folding. In point of fact, however, the bundles readily separate into fibrils after exposure to dilute solutions of chromic acid, or to lime-water, or to baryta-water, by which the uniting matter is dis- solved; so that there can be no doubt of their truly fibrillar struc- ture. At the same time it is not Hig) 30'—-CELis ;ROM Oe ntaMt ROS mone denied that immature fasciculi may ‘Necrive Tissur or Young Gurnga-pre. Probably occur, in which the fibril- MAGNIFIED 350 DIAMETERS. lation is incomplete. d, branched corpuscle; e, flattened cor- puscle ; 4, ie corpuscle ; f, fibrillated Ground-substance and cell ; J, /, leucocytes or migratory cells. Corpuscles.— The fibrils are, as before said, united into the small bundles and laminee which are visible to the naked eye by means of a variable amount of homogeneous cementing matter or CELL ‘SPACES. 57 cround-substance, which also covers the surface of the bundles. In this substance lie the cellular elements of the tissue, the con- nective-lissue corpuscles (figs. 30, 31). These bodies, which Pig. 32, are of a protoplasmic nature, are commonly of a flattened form and not unfrequently have processes which ramify in the tissue and may anastomose with branches from neighbour- ing corpuscles (fig. 31). The cells have each a clear round or oval nucleus, containing one or more nucleoli: occa- sionally two nuclei are to be seen in a cell. Besides pre- senting considerable variations in size and shape the corpus- cles also exhibit differences in i Sa the character of their proto- ted plasm (see fig. 30), which in \ some is coarsely granular in appearance, in others finely ‘s granular, os even perfectly clear Fig. 31.—lRamiriep CoNNECTIVE-TISSUE Cor- and pellucid, with a few coarse ‘PUSCLES FROM Sanne ‘Mesindanw: 250 granules scattered in it here DIAMETERS. and there, whilst in others again there is a distinct appearance of striation or fibrillation within the cell; but these differences have hardly as yet been sufficiently investigated. The cells (with their pro- cesses) occupy spaces in the ground-substance which they more or less com- pletely fill, and which there- fore closely correspond to the corpuscles themselves in size and form, and in their branching and intercommu- nication. These cell-spaces (Saftcaniilchen, Reckline- hausen) are brought into ee Py ees we ore Fig. $2.—Crnu-Spaces or Suscurangous Con with a solution of nitrate of NECTIVE-TIssur, NreraTe oF SraveR PRepara- silver and subsequently ex- TION. 340 DIAMETERS. posing it to the light, by which the ground-substance and fibrils of the tissue are stained of a uniform brown tint, whereas the protoplasm of the cells remains unstained, and the cell-spaces consequently appear white (fig. 32).* * Tn the case of the pigment-cells of the frog’s skin previously noticed (pp. 12, 13), it is probable that the clear, branched figure which remains after the shrinking of the pig- mented matter, is the outline of the cel/-space, which was previously filled by the cell- substance, (Sharpey.) 58 CONNECTIVE TISSUE, In some parts of the tissue, and especially on the surface of the lamine, patches of cells are here and there to be found which present an epithelioid appearance in silver preparations, the cells being much flattened, and joined edge to edge, with but a small amount of intercellular or ground substance between them, like the layer on the inner surface of a serous membrane. The cells at the margin of such a patch, however, commonly have processes at their free border, and every transition is found between these epithelioid cells and the ordinary branched and irregular cells of the tissue. Corpuscles of a fusiform shape are not so common in the adult as was at one time supposed ; the appearance being generally produced by flattened cells seen edgewise. The connective-tissue corpuscles are for the most part considerably larger than the pale blood-corpuscles (which are also to be found in the tissue (fig. 30, 7), having probably escaped from the vessels), and do not, like these, exhibit active movements of locomotion, the motions which have been observed in them consisting merely of slow protrusion and retraction of processes or straining movements of the protoplasm composing them. Vessels and Nerves.—Numerous b/ood-vessels are seen in the areolar tissue after a minute injection. These for the most part only pass through it on their way to other more vascular textures, but a few seem to end in capillaries destined for the tissue itself, and dense clusters of vessels are distributed to the fat-lobules. Large /ymphatic vessels proceeding to distant parts also pass along this texture, and abundant lymphatic networks may be discovered in many parts of the subcutaneous, subserous, and submucous areolar tissue, having evident relation to the function of the membranes under which they lie. A close connection subsists between the cells of the areolar tissue and the commencements of the lymphatics ; for the flattened cells which form the walls of the latter vessels are in contact with, and pass into, the connective-tissue corpuscles of the tissue in which they lie. In this manner the cell-spaces of the connective tissue are brought into intimate relation with the lymphatics, and the latter vessels may, in a certain sense, be described as originating in the net-work of cell-spaces which the tissue commonly contains. Absorption readily takes place from the interstices of the texture, but that process may be effected through the agency of blood-vessels as well as of lymphatics. Larger and smaller branches of nerves also traverse this tissue on their way to other parts; but it has not been shown that any remain in it, and accordingly it may be cut in a living animal apparently with- out giving pain, except when the instrument meets with any of these traversing branches. It is not improbable, however, that nerves end in those parts of the areolar tissue, which, like that of the scrotum, contain contractile fibres ; but, if present in such cases, the nerves, like the vessels of the fat, are, after all, destined not to the areolar tissue but to another mixed with it. Composition and Properties.—The areolar tissue contains a con- siderable quantity of water, and consequently loses much of its weight by drying. It is almost wholly resolved into gelatin by boiling in water. Acetic acid causes it, that is, the bundles of white fibrils, to swell up into a soft, transparent, jelly-like mass; but the original condition may be restored by a solution of an alkaline carbonate. FAT. 59 The physical properties of this texture have been sufficiently indicated in the foregoing description ; also its want of sensibility. The vital contractility ascribed to certain portions of it is most probably due to the presence of muscular tissue. Regeneration.—With the exception of the epithelium, no tissue is so readily regenerated as the areolar. It is formed in the healing of wounds and in the adhesion of inflamed surfaces, It is produced also in many morbid growths. ADIPOSE TISSUE. The human body in the healthy state contains a considerable amount of fatty matter of different kinds. Fat, as has been already stated, is found in the blood and chyle, and in the lymph, but much more sparingly. It exists, too, in several of the secretions, in some consti- tuting the chief ingredient ; and in one or other of its modifications it enters into the composition of certain solid textures. But by far the greater part of the fat of the body is inclosed in small cells or vesicles, which, together with their contained matter, constitute the adipose tissue. Distribution.—This tissue is not confined to any one region or organ, but exists very generally throughout the body, accompanying the still more widely distributed areolar tissue in most though not in all parts in Fig. 33. which the latter is found. Still its dis- tribution is not uniform, and there are certain situations in which it is collected more abundantly. It forms a consider- able layer underneath the skin, and, together with the subcutaneous areolar tissue in which it is lodged, constitutes in this situation what has been called the panniculus adiposus. It is collected in large quantity round certain internal parts, especially the kidneys. It is seen fillmg up the furrows on the surface of the heart, and imbedding the vessels of that organ underneath its serous covering; and in various other situa- tions it is deposited beneath the serous membranes, or is collected between their folds, as in the mesentery and omentum, at first generally gathering along the course of the blood-vessels and at length accumulating very copiously. Collections of fat are also common round - the joints, lying on the outer surface of the synovial membrane, and filling ha Fig. 33.—Loosz AREOLAR TissuE inequalities ; in many cases lodged, like with Far-Cetis; or May. (Kél- the fat of the omentum, in folds of the liker.) ; membrane, which project into thearticular cavity. Lastly, the fat exists in large quantity in the marrow of bones. On the other hand, there are some parts in which fat is never found 60 CONNECTIVE TISSUE. in the healthy condition of the body. Thus it does not exist in the sub- cutaneous areolar tissue of the eyelids and penis, nor in the lungs, nor within the cavity of the cranium. Structure.—When subjected to the microscope, the adipose tissue (fig. 33) is seen to consist of small vesicles, filled with an oily matter, and for the most part lodged in the meshes of the areolar tissue. The vesicles are most commonly collected into little lobular clusters, and these again into the little lumps of fat which we see with the naked eye, and which in some parts are aggregated into round or irregular masses of considerable magnitude. Sometimes the vesicles, though grouped together, have less of a clustered arrangement ; as when they collect alongside of the minute blood-vessels of thin membranous parts. In well-nourished bodies the vesicles or fat-cells are round or oval, unless where packed closely together, in which case they acquire an angular figure, and bear a striking resemblance to the cells of vegetable tissues. The greater number of them are from =3,th to ;3,th of an inch in diameter, but many exceed or fall short of this measurement. Each one consists of a very delicate envelope, inclosing the oily matter, which, completely fillmg the enve- lope, appears as a single drop. A nucleus is commonly present (fig. 34), but is usually obscured by the fatty matter. The envelope is the remains of the original protoplasm of the embryonic cell: it is gen- Fig. 34.—Far CrLis FROM Raseits’ OMENTUM, SHOWING : Nucievs axp Provorrasurc erally quite transparent and apparently ENVELOPE, witn supporting Homogeneous in structure. According to Arrotar Tissuz beTwEEN some authorities it consists of two parts, THE CELLS (Klein). a delicate structureless external membrane, and a layer of finely granular protoplasm immediately surrounding the fat. Such is the normal condition, but in emaciated, dropsical, and old persons, the oily contents of the cells may become wholly or partially removed, in which case serous fluid may be found occupying its place,and then too the nucleus becomes apparent, The common fat of the human body consists essentially of palmitin, stearin and olein, which are the compounds of glycerine with palmitic, stearic and oleic acids respectively. These compounds, which are considered to be glycerine- ethers, contain three equivalents of the fatty acid to each equivalent of glyce- rine; they have hence been termed tri-palmitin, tri-stearin, and tri-olein. The tri-olein, or liquid fat, holds the other two in solution; and the varying consistency of animal fats depends on the relative proportion of the solid and liquid ingredients, During life the oily matter contained in the cells is liquid ; but the acicular crystalline spots which are sometimes seen after death indicate a partial solidification of one of its constituents. The fat being thus contained in closed cells, it will be readily understood why, though liquid or nearly so in the living body, it does not shift its place in obedience to pressure or gravitation, as happens with the water of dropsy and other fluids effused into the interstices of the areolar tissue ; such fluids, being unconfined, of course readily pass from one place to another through the open meshes, The areolar tissue connects and surrounds the larger lumps of fat, FAT, 6L but forms no special envelope to the smaller clusters ; and although fine fasciculi and filaments of that tissue pass irregularly over and through the clusters, yet it is probable that the vesicles are held together in these groups mainly by the fine network of capillary vessels distributed to them. In the marrow the connective tissue is very _ scanty ; indeed, the fat-cells in some parts of the bones are said to be altogether unaccompanied by connective filaments. The adipose tissue is copiously supplied with blood-vessels. The larger branches of these pass into the fat-lumps, where they run between the lobules and subdivide, till at length a little artery and vein are sent to each small lobule, dividing into a network of capillary vessels, which not only surrounds the cluster externally, but passes through between the vesicles in all directions, supporting and connecting them. The lymphatics of the fat are in close relation to the blood-vessels, accompanying and occasionally completely enclosing them, as they enter the lobule. No nerves have been seen to terminate in this tissue, although nerves destined for other textures may pass through it. Accordingly it has been observed that, unless when such traversing nervous twigs happen to be encountered, a puncturing instrument may be carried through the adipose tissue without occasioning pain. Uses and Amount.—As to the uses of the fatty tissue, it may be observed, in the first place, that it serves the merely mechanical purpose of a light, soft, and elastic packing material to fill vacuities in the body. Being thus deposited between and around different organs, it affords them support, facilitates motion, and protects them from the injurious effects of pressure. In this way, too, it gives to the exterior of the body its smooth, rounded contour, Further, being a bad conductor of heat, the subcutaneous fat must so far serve as a means of retaining the warmth of the body, especially in warm-blooded creatures exposed wo great external cold, as the whale and other cetaceous animals, in which it forms a very thick stratum. But the most important use of the fat is in the process of nutrition. Com- posed chiefly of carbon and hydrogen, it is absorbed into the blood and consumed in respiration, combining with oxygen to form carbonic acid and water, and thus contributing with other hydrocarbonous matters to,maintain the heat of the body ; and it is supposed that when the digestive process introduces into the system more carbon and hydrogen than is required for immediate consumption, the excess of those elements is stored up in the form of fat, to become available for use when the expenditure exceeds the immediate supply. According to this view, active muscular exercise, which increases the respiration, tends to prevent the accumulation of fat by increasing the consumption of the hydrocarbonous matter introduced into the body. Again, wheu the direct supply of calorific matter for respiration is diminished or cut off by withholding food, or by interruption of the digestive process, nature has recourse to that which has been reserved in the form of fat ; and in the wasting of the body caused by starvation, the fat is the part first consumed. The use of the fat in nutrition is well illustrated by what occurs in the hedge- hog and some other hybernating animals. In these the function of alimentation is suspended during their winter sleep ; and though their respiration is reduced to the lowest amount compatible with life, and their temperature falls, there is yet a considerable amount of hydrocarbonous material provided in the shape of fat, before their hybernation commences, to be slowly consumed during that period, or perhaps to afford an immediate supply on their respiration becoming again active in spring. It has been estimated that the mean quantity of fat in the human subject is about one-twentieth of the weight of the body, but from what has been said, it is plain that the amount must be subject to great fluctuation. The proportion 62 CONNECTIVE TISSUE. is usually largest about the middle period of life, and greatly diminishes in old age. High feeding, repose of mind and body, and much sleep, favour the pro- duction of fat. ‘To these causes must be added individual and perhaps hereditary predisposition. There isa greater tendency to fatness in females than males ; also, it is said, in eunuchs. The effect of castration in promoting the fattening of domestic animals is well known. In infaney and childhood the fat is confined chiefly to the subcutaneous tissue. In after-life it is more equally distributed through the body, and in proportion- ately greater quantity about the viscera. In Hottentot females fat accumulates over the gluteal muscles, forming a considerable prominence ; and. in a less degree, over the deltoid. A tendency to local accumulations of the subcutaneous fat is known to exist also in particular races of quadrupeds. Development.—