a^ UNIVERSITY m LIBRARY S7 59/ l?-)0 N Cornell University Library RB 27.S91 1870 v-1 . . ..._.^ and comoarative histojoa All books are subject to recall after two weeks Olin/Kroch Library DATE DUE .-Oiur^Ci uriELLssm »JU8lfflMW OAYLORO PRINTED IN U.S.A The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://archive.org/cletails/cu31924024543195 THE NEW SYDENHAM SOCIETY. INSTITUTED MDCCCLVIII. VOLUME XLVII. MANUAL OP HUMAN AND COMPARATIVE HISTOLOGY. EDITED BY S. STEICKER. ASSISTED BY J. ARNOLD, BABUCBIN, O. BEOKEB, BIESIADECKI, J. BOLL, B. BEUOKE, COHNHEIM, EBEBTH, TH. W. ENGELMANN, GEBLACH, IWANOPF, B. KLEIN, W. KUHNE, LANGBE, V. LA VALBTTB, LEBEB, LUDWIG, SIGMUND MAYEE, MEYNEET, W. MULLEE, OBEBSTEINEE, PFLUGEB, PEEYEE, V. EECKLINGHAUSEN, A. EOLLETT, EUDINGEE, MAX SCHULTZB, P. E. SCHtlLZE, SCHWALBE, SCHWEIGGEE-SEIDEL, LUDWIG STIEDA, C. TOLDT, E. VEESON, WALDEYEE, AND OTHBES. Volume I. THANSLATED BY HENRY POWER, M.B., Lond., F.R.C.S., OPHTHALMIO SURGEON TO ST. GEORGE'S HOSPITAL, EXAMINER IN PHYSIOLOGY AND COMPARATIVE ANATOMY IN THE UNIVERSITY OF LONDON. THE NEW SYDENHAM SOCIETY, LONDON. 1870. ^' OLIN C/V^ TEMSLATOE'S PEEFACE. The idea of translating Professor Strieker's " Manual of His- tology" originated from a consideration of the remarkable paucity of works on this subject in our language. The only complete treatises we possess are " KoUiker's Manual of Human Histology," translated in 1853-4 by Messrs. Busk and Huxley, and again in 1860 by Dr. George Buchanan; the "Physio- logical Anatomy " of Messrs. Todd and Bowman, 1843-57; and the "Introduction to Quain and Sharpey's Anatomy," 1864-67^ All of these works are extremely good ; but that they should constitute the only books of reference on the minute anatomy of the tissues is certainly surprising when we call to mind the great multitude of works that have been recently published on the kindred subjects of Anatomy and Physiology. No doubt a large amount of valuable information is contained in Dr. Carpenter's valuable physiological treatises, and the various papers of Dr. Beale ; but neither lay claim to constitute a complete exposition of histological knowledge ; and, with the exception of these, the student who is desirous of referring to any histological point must go back to the short work of Morel, published in 1861; the "Lectures" of Quekett, 1850; the " Microscopic Anatomy " of HassaU, 1849, or some of the stiU older works on general anatomy, all written at a time when the methods of investigation were far less perfect than at present. The translation of this treatise into English was commenced almost as soon as the &st part appeared in this country ; for it was felt at once nothing could give a stronger guarantee VI TRANSLATORS PREFACE. that the several parts as they were successively published would represent the most recent acquisitions to our knowledge of Histology than the high authority of Professor Strieker and the names of the distinguished workers who had con- sented to co-operate with him in its production ; especially as to the care of each of these writers was consigned the subject to which he had paid particular attention ; and the translator was glad to jSnd, after he had for some time been engaged upon it, that his own opinions respecting the merits of the treatise were concurred in by men who were so peculiarly qualified to judge as Professors Huxley and Turner. The translation occupied nearly seven months, and the print- ing four ; it is therefore only about one year behind the date of the original, and it is hoped that the second volume will be issued still more quickly after the appearance of the last part, which is promised in the autumn of the present year. The translator had accumulated some material which he thought might be advantageously added in the form of an appendix, to show the progress that had been made in the different subjects discussed in the text during the past twelve months ; but upon consideration it was thought better to omit them, and they will appear in a condensed form in the " Biennial Retrospect," to be published, as usual, at the begin- ning of 1871. In conclusion, the translator may be allowed to add that he has endeavoured to give as faithful a rendering of the original articles into English as possible; and though conscious of occasional obscurities in diction, he trusts that the inaccuracies that may be found will be neither numerous nor important. HENRY POWER. Seymour Street, London. July 5th, 1870. CONTENTS. INTRODUCTION. GENERAL METHODS OF INVESTIGATION. PAGE Microscopes ......... i. — vi. Mode of mounting objects ...... vii. Recklinghausen's Moist Chamber ..... vii. Strieker's Gas Chamber ....... viii. — x. Deville's arrangement ....... xi. Kiihne's arrangement ....... xi. Schultze's arrangement for warming the Stage . . . xii. Strieker's arrangement for warming the Stage . . . xiii. Briicke's arrangement for the application of Electricity . xx. Strieker's arrangement for the application of Electricity . xxi. Preparation of Tissues ....... xxv. By teasing with needles ..... xxvii. By section after hardening ..... xxvii. By staining ....... xxxii. By injection ....... xxxiv. By physiological injection ..... xxxvii. CHAPTER I. THE GENERAL CHARACTER OF CELLS. By S. STRICKER. Independence of Cells Ideal Type of a Cell Physiological peculiarities of Cells Phenomena of movement in Cells 1 4 10 11 Vlll CONTENTS. Changes of form occurring in Cells . a. Prom variation in temperature b. From mechanical influences . c. From electrical stimuli . d. From nervous excitation e. From chemical stimuli Metamorphosis of Cell substance Structure of Cells . Characters of the Nucleus of Cells Cell Genesis . Forms presented by Cells Modes of union of Cells . Classification of Cells Formative activity of Cells Changes of Cells in Death PAGE . 14 . 18 . 19 . 20 . 22 . 22 25 . 27 30 83 40 41 43 45 45 CHAPTER II. the connective tissues. By a. KOLLETT, pkopessob of physiology in graz. Theories of the nature of Connective Tissue Connective Tissue The Cells of Connective Tissue a. Amoeboid Cells b. Granular Cells c. Fusiform Cells d. Stellate Cells e. Pigment Cells Varieties of Connective Tissue Plexuses and Trabeoulse Retiform Connective Tissue Investing and supporting Connective Tissue Trabecular Connective Tissue . Intra-glandular Connective Tissue Fibrillar Connective Tissue Elastic Fibres Distribution of Fibrillar Connective Tissue Development of Connective Tissue . 47 52 58 54 55 60 61 61 63 63 65 65 68 69 70 81 84 84 CONTENTS. IX PAGE Fat Cells in Connective Tissue ..... 93 Cartilage . 95 Hyaline Cartilage .... 96 Fibro-Cartilage ...... 105 Elastic or reticular Cartilage .... 106 Cartilage with Connective Tissue 107 Parenchymatous or Cellular Cartilage . 108 Development of Cartilage ..... 109 Calcification of Cartilage ..... 114 Osseous Tissue ........ 115 Structure of Osseous Tissue 115 Development of Bone ....... 126 Intra-cartilaginous Ossification . 127 Intra-membranous Ossification .... 142 Contents of the Cavities of Bones 145 CHAPTER III. GENERAL CHARACTERS OF NERVOUS TISSUE. By max SCHULTZE. The Nerve Fibres . 147 Division of Nerve Fibres . 162 Peripheric Terminal Organs . 165 In the Olfactory Nerves 165 ,, Gustatory Nerves . . 166 „ Optic Nerves . 166 ,, Nerves of Common Sensation 167 ,, Pacinian Corpuscles . 167 ,, Muscles .... . 169 ,, Electrical Organs . 170 ,, Glands .... . 171 Mode of Origin of Nerve Fibres in Cerebro-spinal Nerve Centres. 172 ,, „ Sympathetic Gang lia . . 175 CHAPTER IV. THE TISSUE OF THE ORGANIC MUSCLES. By J. AENOLD. General characters of the Organic Muscles Structure of the Organic Muscles .... 188 190 ■^ CONTENTS. Nuclei of the Organic Muscles . Connection and arrangement of the Fasciculi Vessels ....... Nerves ....... Distribution ...... Mode of Investigation PAGE . 191 , 192 . 194 . 195 . 198 . 200 CHAPTER V. THE RELATION OF THE ULTIMATE FIBRES OF NERVES TO MUSCLE. By W. KtJHNE. General Description ........ 202 The Mode of Termination of Motor Nerves in the Invertebrata . 205 The Mode of Termination of Motor Nerves in the Vertebrata . 209 Amphibia 209 Eeptiles, Birds, and Mammals ..... 216 History and Literature ........ 227 CHAPTER VI. THE BEHAVIOUR OF MUSCULAR FIBRES WHEN EXAMINED WITH POLARIZED LIGHT. By E. BEUCKE. 235 CHAPTER VII. the heart. By F. SCHWEIGGEE-SEIDEL. Structure of the Muscular Tissue . 244 Connective Tissue of the Musculature . 251 Structure of the Endocardium . . 251 ,, Valves . . 253 ,, Pericardium . . 255 Bloodvessels . 255 Lymphatics . 255 Nerves ...•■• . 256 CONTENTS. CHAPTER VIII. THE BLOODVESSELS. By C. J. EBEETH, PEOPESSOE OF PATHOLOGICAL ANATOMY IN ZUBICH. General Structure of the Vessels .... . 264 Vasa Vasorum and Nerves ..... Arteries ......... . 266 . 267 Epithelial Layer . 267 Elastic Internal Coat. .... . 267 Internal Fibrous Coat .... . 268 Muscular Coat .... . 270 External Elastic Coat, or Tunica Adventitia . 274 Veins ......... . 275 Epithelial Layer ..... . 276 Elastic Internal Membrane . 276 Muscular Coat ...... . 277 Tunica Adventitia ..... . 278 Valves of the Veins ..... . 279 Capillaries ........ . 279 Cavernous Vessels — Lacunar Blood Paths — ^Vascular Plexuses . 279 Coccygeal Plexus . 292 CHAPTER IX. the lymphatic system. By PEOF. F. v. EECKLINGHAUSEN. Structure of the larger Lymphatics .... . 297 ,, Lymphatic Capillaries . 301 ,, Stomata. ..... . 307 ,, Serous Canals . 310 ,, Lymphatic Follicles . 326 ,, Lymphatic Glands .... . 329 „ Medullary Cords .... . 332 ,, Lymph Paths ..... • 334 „ Trabeculse of Connective Tissue . 834 The Chyle . 340 Xll CONTENTS. CHAPTER X. THE SPLEEN. By WILHELM MULLEE, OF JENA. General Structure .... „ in Eeptiles . ,, in other Vertebrata The Capsule of the Spleen Septa and Sheaths of the Veins Arterial Sheaths Bloodvessels . Lymphatics . Nerves . Development . 349 349 352 352 352 854 857 359 360 860 CHAPTER XI. THE THYMUS GLAND. By E. KLEIN. General Characters ........ 365 Capsule ......... 365 Follicles 367 Vessels 368 CHAPTER XII. THE THYROID GLAND. By E. VEESON. General Characters . 370 Vesicles . • 871 Framework . . 372 Vessels . Lymphatics . 372 . 372 CONTENTS. CHAPTEE XIII. THE BLOOD. By ALEXANDER ROLLETT. General Characters . . 874 Liquor Sanguinis ; . . 374 Red Blood Corpuscles . 375 Form and colour . 376 Size , . . 380 Number . . 383 Alterations in . . 884 1. From exposure to air . 884 2. From mechanical agents . 385 8. From drying . 387 3. From venffisection . 388 5. From electrical discharges . 388 6. From elevation of temperature . 392 7. From exposure to cold . . 398 8. From exposure to water — Saline solutions . , . . . 894 Sugar ..... . 396 Alkalies . 898 Acids ..... . 399 Urea . 402 Neutral solutions of carmine . 402 9. Gases and vapours . 403 Views respecting the Nature of the Red Corpuscles . . 406 Chemistry of the Red Corpuscles . . . . . . 411 Colourless Corpuscles . 414 Development of the Blood Corj )uscles . 419 CHAPTER XIV. THE SALIVARY GLANDS. By E. F. W. PFLUGER. General Plan of Structure Alveoli .... Cells of the Alveoli 423 423 426 XIV CONTENTS. PAGE Caudate Nuclei of Cells 426 Mucous and Albuminous Cells . . . ■ • 428 Crescent of Alveoli .....■• 428 Excretory Ducts ' • ■ 429 Distribution of the Nerves .....■• 433 Mode of Termination by Medullated Primitive Fibres . 438 Multipolar Cells . . .443 Mode of Kegeneration of the Glandular Epithelium . . . 448 Morphological Constituents of the Saliva ..... 453 Changes in the Glands consequent on functional activity . . 455 Stroma of the Salivary Glands ...... 460 Mode of Investigation 461 CHAPTEE XV. stiluctuee and development of the teeth. By W. WALDEYEE. General distribution of Teeth in the Vertebrata .... 468 Dentine . 466 Dentinal Fibres ....... 466 ,, Canals 466 Interglobular Spaces ....... 468 Enamel 471 Cuticula 474 Cementum 475 Odontoblasts . . . . . . . . . . 476 Gum 477 Development of the Teeth ....... 479 Enamel Organ 479 Dentine and Cement ....... 488 Recent Literature of the Teeth ...... 493 CHAPTER XVI. THE INTESTINAL CANAL. By E. KLEIN and E. VERSON. ORAL CAVITY, BY E. KLEIN. Structure of the Lips Gums 497 504 CONTENTS. XV PAGE Structure of the Hard Palate .... . 505 „ Soft Palate . 506 „ Tonsils . 513 TONGUE. Papillse ....... . 514 Septum Cartilagineum .... . 515 Mucous Glands . 516 Lymphatics ...... . 519 Muscles ....... . 519 PHARYNX. I^UlULJbUlO \J1 J.UD TVailO .... CESOPHAGUS. . o^'± Mucous Membrane 629 Muscular Layers . 530 Acinous Glands . 530 Lymphatics . 533 Structure of in Dog . 533 Rabbit . . 534 Horse . 535 Kat . 535 Birds . 535 Triton . . 537 Frog . 538 Transition of (Esophagus into Stomach . 539 STOIVTACH. Mucous Membrane of ..... . 544 Submucous Tissue . . 548 Lymphatics . 548 Nerves . 549 Muscular Coat . . 549 Structure of in Dog . 551 Rabbit . . 551 Rat. . 558 Birds . 554 XVI CONTENTS. SMALL INTESTINE, BY E. VERSON Muscular Coat of Small Intestine Mucous Membrane of Small Intestine Lymph FoUicles Glands Muscularis Mucossb Epithelium Nerves LARGE INTESTINE. Mucous Membrane of Glands of Muscularis Mucosae Submucous Layer Muscularis Externa Nerves 560 563 565 568 571 573 676 577 577 578 579 579 579 RECTUM. Muscular Coats of Mucous Membrane Lymph Follicles Epithelium Nerves 580 582 584 584 585 CHAPTER XVII. BLOODVESSELS OF THE ALIMENTARY CANAL. By C. TOLDT. Mucous Membrane of the Oral Cavity Mucous Membrane of the Tongue Saccular Glands of the Mouth and Pharynx and of the Tonsils Acinous Glands of the Alimentary Canal . Mucous Membrane of the Pharynx . Mucous Membrane of the (Esophagus Muscular Coat of the Alimentary Canal Mucous Membrane of the Stomach . Mucous Membrane of the Intestine . Solitary Glands and Peyer's Patches 587 589 590 591 592 593 593 594 596 599 INTEODUCTION. GENERAL METHODS OF rfTVESTIGATION. By S. STRICKEK. The microscope is a means of research. When objects are so small that at ordinary distances from the eye they no longer produce sufficiently large images on the retina, they require, for their examination, either a simple or a compound micro- scope. The domain of investigation embraced by this instru- ment, however, does not limit research. Microscopy defines no doctrine, but is simply a method of examination : yet it is the most delicate with which we are acquainted for terrestrial objects, because modem microscopes are the most perfect of all optical instruments. Up to the present time the microscope has been chiefly ap- plied to the investigation of the various organisms ; and our knowledge of the finer structure of plants and animals, and especially of the latter, has assumed the character of an inde- pendent science, which again presents important subdivisions. The observation of healthy tissues, and of those modified by, or originating in, disease, already constitutes the basis of two separate but closely allied departments of science, each of which can again be regarded from difierent points of view. We can for example, push our inquiry either into the morphology or into the biology of the tissues; or, as it may be otherwise expressed, into the normal or pathological anatomy and phy- siology of the tissues. At present, however, the morphology and physiology of the tissues are so intimately connected with each other that no line of demarcation can be drawn between them. The observation of the vital phenomena presented by B U INTRODUCTION. the tissues, and the experimental investigation of their proper- ties conducts us, in many instances, to a knowledge of the most delicate structural arrangements; whilst the converse always holds true, that a thorough knowledge of structure furnishes the key to many vital phenomena. The technical methods of research applicable to these two subjects are nevertheless different. When we desire to foUow, and ultimately to modify, the vital processes under the microscope, other means of research are required than when we merely wish to acquaint ourselves with the forms of the elementary parts. Moreover, experiments which are performed under the microscope diflfer according to whether they are con- ducted on living or on dead bodies. The sensitiveness of the former to external influences, makes — even in the microscopi- cally small compass of the instrument, and bearing in mind the management necessary for its use — experiments possible under circumstances which are not practicable in the case of dead tissue. Thus we find that changes can be induced in living tissue by slight variations in temperature, by feeble currents of electricity, and by weak solutions of acids ; whilst the operation of these agents must be much more energetic for the purpose of experiment on the dead body, and this is not always agreeable for the observer, nor suitable for the more delicately constructed instruments. The greater sensi- tiveness of the living organism demands proportionate delicacy in its treatment, but at the same time facilitates experiment; and to this we may ascribe the circumstance that experimen- tation on the living body has gained so much in value during the last few years, that is, during the period that the investi- gation of living tissues has been so extensively undertaken. The tissues may either be examined by the light which they reflect from their surface, or by that which passes through them — ^by direct or by transmitted light. Every object can be examined by direct light, provided that the degree of illumina- tion from without, and its own power of reflecting light, are sufficiently great, and that both the object and the instrument can be fixed. It is self-evident that the instrument must be capable of \)eing focussed, or it would be impossible for trustworthy reti- GENERAL METHODS OP INVESTIGATION, BY S. STRICKEE. iii nal images of various objects to be obtained. The examination of an object cannot be conducted by direct light with high powers, because the emplojnment of such powers necessitates the close approximation of the lens to the object, whereby the latter is covered, and its illumination prevented. It is, how- ever, possible to apply here the principle of the ophthalmoscope, and then this difficulty is overcome. Examinations conducted by means of direct light are greatly assisted by direct illumination, or, what is still better, by throw- ing a pencil of rays on the part of the object to be illuminated ; details then frequently become apparent which can scarcely be detected with the mere diffused light of day. If examinations by means of direct light are undertaken at greater distances — as when, for example, lower powers are em- ployed, or when the objects are examined or are prepared in a fluid — it is advantageous to use Brucke's doublet. This is placed in the arm of a Nachets' or Hartnack's stand, and the object is placed on the stage. The focussing can then be easUy accomplished with the unassisted hand by moving the lens. This combination is very serviceable for preparations that have been teased out with needles, as in the isolation of ganglion cells and the separation of fine fibres. The object is in every instance placed on an opaque ground : if it be dark, upon a dull grey; and if clear, upon an opaque black ground. The object requiring to be isolated should in all instances be laid on a slide of polished glass, beneath which again may be placed a piece of dull white or black paper, as may be most convenient. For the examination of larger portions of tissue in fluid, little shells may be used, resting on a plane base, and having a spherical hollow, resembling an ordinary glass salt-cellar. A duU opaque ground may easily be obtained by covering the surface of the glass with a thick layer of coloured wax or gutta- percha, which has the advantage of enabling the objects to be fixed in position by transfixion with needles. If it be required to bring the object into strong relief, in order to examine the details of the surface, the lenses of Stein- heil of Miinchen are especially to be recommended. It is advantageous, howeyer, to attach them to an arm moving on a baU and socket joint, which again plays, horizontally and ver- B 2 IV INTRODUCTION. ticalljr, on a fixed vertical support. When it is required to manipulate with forceps and scissors under still higher magni- fying powers, the little preparation cell should be fastened upon a blackened wooden block, several centimeters in height, and resting on the table. The arms being thus in a nearly hori- zontal position, and well supported, permit the observer to work with greater steadiness. In making preparations with strong lenses, the nose of the observer necessarily comes into close proximity with the object, and the bridge of the nose can be used as a point of support for the cutting instrument em- ployed. When sections are made with scissors and forceps under strong lenses, it is usually necessary that the object should be firmly fixed, and, at the same time, very steady movement on the part of the cutting instrument is required. It is in particular quite indispensable that some kind of sup- port should be given, if it be required, to make clean and thin sections of small and delicate objects. If the left eye be applied to the lens, the right hand can with great certainty direct a fine pair of scissors balanced on the bridge of the nose whilst the left hand fixes the object. For the fixation of very dehcate objects, substantial forceps, with very sharp, smooth points, will be found serviceable. If it be desired to work by means of direct light with a com- pound microscope, weak objectives, such as the No. 5 of Hart- nack's microscope, or those corresponding to them of other instruments, can alone be employed. Formerly weak com- pound microscopes, which gave erect images, were used for the preparation of objects. These so-called dissection micro- scopes are not, however, really necessary, since the opposite movement of the hand demanded for the inverted image is soon acquired by practice. The examination of objects can, in like manner, be under- taken with transmitted light, both with the aid of simple and of compound microscopes. In regard to the use of the former, there is little to be added to what has already been said. For the examination of objects with transmitted light, it is obvious that the support must be transparent, and the objects must themselves be illuminated by the reflected hght proceeding from either a mirror or a prism. Simple micro- GENERAL METHODS OF INVESTIGATION, BY S. STEICKER. V scopes, or the lower powers of compound microscopes, can only be used with transmitted light, when general views of the topographical relations of the tissues to one another are desired. The larger the object, the lower must be the mag- nifying power employed, in order that a general view of it may be obtained. With such large objects it is usual to examine them ia the first instance with a low power, and then to investigate the details of each part with a higher power. The very powerfiil lenses lately manufactured by Hartnack are extremely well adapted for the investigation of the living tissues, or of the well preserved and isolated elements of the tissues. In specimens which have been roughly treated and are consequently not in a very fit state for microscopic research, as in those that have been hardened with reagents, or stained with colouring matters, and repeatedly washed, very high powers are in the first instance less instructive than lower ones ; indeed, those who are not very expert in the use of the instrument can actually see less with a No. 15 than with a No. 8 Hartnack. However, the highest powers are even here very serviceable to the beginner, if he be engaged in the definition of the deeper lying tissues. It is only requisite to use the fine adjustment with extraordinary care, to turn the screw with great gentleness; so that a fresh field is obtained, which may remain for some time under observation prior to passing to a greater depth, or returning to a more superficial part. But if well isolated and well preserved morphological ele- ments are under observation, and if the tissues are examined whilst stiU fresh, and without the addition of any fluids, or only of those which occasion no change in them, the highest powers prove of the utmost value. The advances that have been made in our knowledge of cells and of the finer struc- ture of nerve fibres are the result of researches undertaken with the admirable instruments that have recently been constructed. The value of these high powers is strikingly illustrated by the investigations on the living cornea, conducted by Reckling- hausen and Kiihne. It is indeed true, that in the perfectly fresh state the structure of the cornea cannot be satisfac- torily ascertained, even with the best glasses. In this state VI INTEODUCTION. only those morphological elements are to be distinguished which refract light differently from the surroundiag parts, and thus it happens that when fibres or cells are imbedded in connective tissue, or in fluids, the refractive power of which is the same as their own, they cannot be perceived even with the best glasses, and artificial means must be resorted to in order to render them visible. These may either be mechanical, effecting the separation and isolation of the morphological elements, or chemical, which dissolve the connecting material, or act differently upon it than upon the morphological ele- ments. The best artificially prepared specimens, however, cannot supply the advantages of examination made on fresh preparations with magnifying powers of from 1,000 to 1,500 linear. Those outlines which can be distinguished in the living tissue, exhibit, besides sharpness, a certain softness, which renders their definition easy and pleasant. The natu- rally present cavities and fissures, in consequence of the different refractive power of their contents, differentiate themselves from the surrounding material with extraordinary sharp- ness. Lastly, outlines are distinguishable during life, which completely vanish after death. Even if these can be again rendered visible by the application of peculiar reagents, their fuU significance is only to be recognised by our knowing that they are naturally present. In the present condition of our instrumental means of re- search, it appears to be advantageous to commence histological studies by means of general topographical examination of the tissues with lenses of low powers ; then to proceed to the exami- nation of specimens that have been subjected to manipulation with lenses of moderate power, in such cases applying the stronger lenses only as a means of control for the penetrating powers of the weaker ones ; and finally to proceed to the exami- nation of the fresh tissues with the best means at our command. I can attribute no very high value to the binocular (double tubed) stereoscopic microscopes, so far as their use has at pre- sent extended. As yet they have only been employed with low powers. The relief of different parts of an object can be very well ascertaiued, even with a simple microscope, by merely varying the iuclination of the head. GENERAL METHODS OF INVESTIGATION, BY S. STEICKEE. vii The simplest, but at the same time the most certaia and elegant, mode of investigation with the compound microscope is to place the object in the centre of a smoothly polished slip of glass, covering it with a thin quadrangular and also perfectly clean glass plate. The little glass plate, called also the glass cover, should lie with its surface parallel to the glass slide, a position which can only be attained when the object to be examined has been greatly and equally extended. Irregularly shaped and thicker masses interfere with the examination, because they make the glass cover assume an oblique position. If the tissue to be examined is diffused through a fluid, a drop should be placed on the glass slide ; the cover should then be brought down to the upper surface of the drop, and cautiously allowed to fall by its own weight. By this means the inclu- sion of air bubbles is avoided. If the investigation is about to be continued for some time, or if it be desired that the medium in which the object lies should not become concen- trated by evaporation from the edges, a brush dipped in oil may be drawn round the margin of the covering glass, which will effectually prevent it. If, after the glass cover has been applied, a portion of the fluid about to be examined exudes from the edges, so that the cover slips with an unsteady move- ment over the surface, a little piece of filtering paper may be employed to remove the excess of fluid, and the oil may then be applied. By this means the simplest kind of moist chamber may be made. Kecklinghausen first introduced the use of the moist cham- ber. The guiding idea of this was, that the object should be placed in a space in which the air was saturated with moisture, and this appeared to be so much the more important when it was found desirable to examine objects without a cover- ing glass. In such cases the object is, of course, partially in contact with the air, and must necessarily give off watery vapour, unless the air be itself saturated with moisture. But if we consider, on the other hand, that the precipitation of watery vapour from an atmosphere saturated with it upon such an object is dependent on temperature, it is easy to understand how difficult it is to obtain the exactly interme- diate point in which water is neither given off nor taken up VlU INTEODUCTION. Any imperfections m this respect, however, will increase with the capacity of the space by which the object is surrounded. It should therefore be made as small as practicable, and, if pos- sible, altogether dispensed with ; ia other words, where practi- cable, only a covering glass should be used, the edges of which are oUed. The pressure which this exercises on the object is unimportant, and may, indeed, easily be avoided altogether ; for it is only requisite to form an outside wall with oil, and to place a small quantity of the fluid withia the space thus en- closed, before applying the covering glass, in order to protect it entirely from the weight of the latter. Circumstances may exist, however, which render it necessary that the preparation should be exposed to the air. It may, for instance, be requisite to ascertain the influence of various gases; in these cases a chamber must be used, of as small a size as possible, except where some special arrangements are made, enabling the amount of watery vapour present to be regulated. I employ for this purpose a ring of putty, varying ia thickness according to circumstances ; the object is then to be attached, as usual, to the lower surface of the covering glass ; this is now to be brought down upon the ring of putty, and to be gently pressed down on the object with the handle of the scalpel. A drop of water placed upon the slide is sufficient to saturate the space with aqueous vapour, and to prevent the object from drying. Great caution must, however, be used ; for it will be found that the dry, smooth, polished covering plate becomes immediately tarnished when it is placed on the wall of putty. The drop of fluid should therefore only have a small surface, in order that it may not evaporate to too great an extent, and, on the other hand, it should not be too small, lest the object dry with too great rapidity. It is obvious that small variations in the pro- portion of water in the object are unavoidable. A moist chamber formed in this fashion can easily be con- verted iato a so-called gas chamber. In that part of the soft wall of putty which corresponds to the middle hne of the glass slide, a small glass tube is to be introduced on each side, and to these caoutchouc tubes can be attached, which can be closed by buU-dog forceps when the passage of gas is not required. But when gases are to be transmitted, the necessary communi- GENERAL METHODS OF INVESTIGATION^ BY S. STRICKEE. ix cations can be made through the caoutchouc tubes, and the forceps removed. This temporary and easily deranged chamber will not prove satisfactory to those who are constantly working with gases ; by them it will be found better to cement the con- ducting tubules of glass once for aU into grooves cut in the shde. The spaces left can be filled up with putty. Fig. 1. Gas chamber, natural si2;e. A, bird's-eye view ; B, longitudinal section througb tbe middle line ; a a, wall ; 6 6, conducting tubes. A slide which is to be used for such investigations with gas must be attached to the stage of the microscope, because the con- ducting tubes pull upon it, and so render the object liable to be displaced. The gas should be transmitted from washing flasks fixed on the stage, so that there may be firm supports between them and the microscope, whilst they are themselves connected with gasometers at some distance from the stage. In my own investigations, in order to be able to dispense with the services of an assistant, and use both my hands at the stage for microscopic purposes, I have arranged my gas apparatus beneath the table in such a way that I can effect the passage of gas in one direction or the other by means of a treadle. If, for instance, I wish to transmit carbonic acid gas, I so arrange the apparatus, shown in fig. II., that the flask containing hydrochloric acid gas can be raised by a string attached to the treadle, and passing over puUeys. From the evolving flask M a caoutchouc tube leads to my fixed wash bottle w, and from this another tube passes to the microscope. The con.- X INTEODUCTION. duction of carbonic acid to an object under the microscope renders it requisite that we should be able to exchange it at ■wiU for atmospheric air. I introduce, therefore, between the wash bottle and the slide a T-shaped tube {a, fig. Ii.). The horizontal portion of this tube lies ia the axis of communica- tion between the wash bottle and the sMe ; whilst the cross- piece is directed towards the observer. A long caoutchouc tube is attached to the latter, the end of which is seized by the observer between his teeth. Fiar. ll. Between the T^tube and the wash flask w, a clip is intro- duced. When I open the clip,* and by means of the treadle f raise the flask containing acid, and thus cause carbonic acid to flow into the wash flask, and at the same time compress the caoutchouc tube between my teeth, the gas must pass over the slide ; but if I apply the clip, and inspire through the tube in the mouth, I then draw in free air from the opposite end of the chamber. By this arrangement common air can be exchanged * The use of the clip may be dispensed with if the column of water in the wash flask is high. GENERAL METHODS OF INVESTIGATION, BY S. STRICKER. XI at will for carbonic acid gas, without interfering with the ob- servation, and at the same time the hands are left free for any manipulation that may be requisite. A second apparatus, the so-called Deville's, is arranged for the preparation of hydrogen beneath my table in the same manner as that above described. I use this gas as an indifferent medium; and as it passes through a wash flask, mingle with it various vapours, as those of ammo- nia, chloroform, etc. The mixture is accomplished by the aid of a bag, which can be compressed with the foot, and from which a tube conducts into the wash flask. If the effect of pure hydrogen gas is desired to be seen, the above-mentioned gas chamber is insufScient. Kiihne, to whom we are indebted for making the first investigations with gas chambers, employs a mercurial valve. Adopting this principle, I take a slide made of hard caoutchouc, which is perforated in the middle, and to the surface of which a glass plate is cemented ; or, which comes to the same thing, I take a ring of hard caoutchouc, and cement it to a glass plate. A groove is now made round the perforation, which can be filled with mercury. The cover glass must then be cemented to a little ceU (fig. iii. b.) Fig. III. a, Gas chamber, -witli mercurial valve, natural size. A I, bird's- eye-view ; A II, longitudinal section through, the middle line; n n, groove ; n, clips ; gr, gas tubes ; r, object ; dd, covering glass in section. Fig. iii. b, covering glass. The object is placed on the inner surface of the cell thus formed, and the lateral walls of the cell are placed in the groove. XU INTRODUCTION. dipping, therefore, into the mercury. If the cover glass is now kept doAvn by clips, the gas chamber will be perfectly closed ; and no farther explanation is required to show how the gas, whose effect is to be examiaed, may be conducted over the object. There are certain difficulties accompanying the examination of objects in gas chambers ; taking the simplest case for ex- ample, a drop of blood is placed on the lower surface of the cover, which is then laid on the cell, and firmly luted to it. The first current of gas which passes over it dries up the edges of the blood spot, and this can scarcely be avoided. It becomes necessary, therefore, to experiment with great rapidity in the gas chambers, or to add some indifferent fluid to the prepara- tion, which may saturate the air contained in the little cell with aqueous vapour without essentially altering its character. But we are thus no longer working under the simplest con- ditions, and due allowance must be made for this in the conclusion at which we arrive. The employment of the moist chamber is rendered stiU more difficult, if it be desired to warm the object whilst under ob- servation with the microscope. Rollett was the first to in- troduce a means of varying the temperature in microscopic investigation. Max Schultze made improvements in this direction, and has constructed a stage capable of being heated, which can again be fitted to the stage of a microscope, is capable of being warmed throughout its whole extent, and can furnish the means by which the temperature of the object under examination can be varied at wiU. Yarious modes have since been suggested, by which the effects of elevation of tem- perature upon an object can be ascertained. In Max Schultze's stage, the mode of warming consists in the direct conduction of heat through metal plates. The attempt was subsequently made to conduct a warm fluid through the object stage, and still more recently, to employ warm vapour with the same object in view. A better method than any of these, and which demands attention as a means of heating the stage, consists in the conversion of a constant current of electricity into heat. In microscopical investigation, only a very small absolute quantity of heat is required, and indeed it is not necessary to GENEEAL METHODS OE INVESTIGATION, BY S. STEICKEK. XlU ■warm the stage in its whole extent, but only its centre ; or, what is still better, the glass cover placed on a slip of caout- chouc. An amount of heat so small as this we may reasonably expect to obtain from the interruption of even feeble currents of electricity. It is well known that the heating of a wire, introduced iuto the arc of a constant current, increases with the diminution in diameter of the wire ; and indeed, according to Eiess, in the proportion of the bi-quadrate of the diameter. For this purpose, therefore, we employ a proportionately thin wire, attached to the centre of a glass plate, the ends being in connection with the electrodes of a constant battery. When the current is closed, the temperature of the centre of the glass plate is raised. The attachment of the wire presents, however, certain iaconveniences ; and we possess in tia-foU a more appro- priate means at our disposal. I am accustomed to cut the tin-foil into the form represented by s in the adjoining figure, and then Pis'. IV. Slide adapted for being heated by means of electricity. Natural size. to glue it to a glass slide ; if now the extremities of the trn-foil are introduced iato the arc of a constant current, the end ia view is at once attained. A very convenient method of introduciug the slide into the current is to attach to one of Hartnack's microscopes a couple of brass springs, by which the preparation can be firmly clipped. These springs (d D, fig. v.), which are attached to holes in the stage by means of brass pins, are pro- vided also with india-rubber pins, by which means they are isolated from the microscope. When they firmly cKp the slide, they at the same time press on the broad end of the tin-foU s. It is then only requisite to attach a conducting wire at any XIV INTRODUCTION. point of each spring (e e, fig v.), and the circuit will be closed by the tin-foil. A second strip of tin-foil, of the same breadth as that attached to the slide (b, fig. iv.), is wound round the bulb of a thermometer, and introduced into the circuit at any con- venient point. This furnishes the means of correctly estimating Fig. V. Foot and stage of one of Hartnack's microscopes. the temperature attained by the centre of the slide, when all the secondary conditions are uniform. These latter can, however, be estimated by comparison, and the due employment of a thermometer, — a proceeding that is always requisite, whatever may be the mode of heating employed. In order to accomplish this, at the point where the object is situate, a fatty substance, the melting-point of which is known, should be placed, and the reading of the mercury should be taken at the moment that the fat begins to melt. The quantity of fat that is introduced should be very smaU, and should be in the field of the micro- scope. It wiU be found most expedient to cut a little disk out of the fat, to cover it dexterously, to watch it with a lens, and to calculate it accordingly. I also apply one of Meidinger's chains with amalgamated zinc plates. A chain of this kind works with very great GENERAL METHODS OF INVESTIGATION, BY S. STEICKEE. XV steadiness, if fed with regularity. It can be left closed for several days, and yet the temperature of the tin-foil kept to a definite degree, not varying with that of the room. It seldom requires water, but crystals of copper must be supplied at least once a day, so that the solution may be constantly and equally saturated. If we overlook, however, these slight drawbacks, and reflect that such precautionary measures are only requisite in cases where it is wished to maintain a particular prepara- tion at a uniform temperature for many days and nights, we shall feel that in the interest of such important investiga- tions it can scarcely be thought too great a trouble to attend at least once a day to the requirements of the machine. If the amount of work performed by the battery be but small, or if it be only occasionally applied, it will then long retain its activity without requiring other addition than that of a Httle water from time to time to supply the place of that which is lost by evaporation. Meidinger's arrangement gives off no injurious vapours, and may therefore be enclosed in a little box, and placed beneath or near the work-table. I transmit the conducting wires through holes bored in the table, and when required for use, fasten them to the points indicated by + and — in fig. v. Inasmuch as the temperature of a thin wire introduced into a thicker arc is inversely as the square of this wire, whilst its length, when small, is of no importance, it follows that the method of measurement formerly employed is justified. But it is also clear that the active force present can be accurately accommodated on the basis of this law. For if the temperature diminishes as the square of the strength of the current, this decrease can, to a certain extent, be covered by diminishing the transverse section of the tin-foil, so that if a weak current be in use, the strip of tin-foil must be made proportionably narrow. As these strips are easily torn, I am accustomed to glue the tin-foil upon thin paper, and then cut out a very long strip with its central window. The larger portion of the strip I twine round the bulb of a thermometer in such a way that after making several coils, the two ends hang free. I then, cover the whole bulb with a layer of shellac or glass cement, and pass it through a cork into an empty vessel, so that the ends of XVI INTRODUCTION. the tin-foil project. No special expertness is then required on the part of the experimenter to introduce these into the arc of the current. The bulb can also be so placed in front that its readings can be readily taken. The shorter end of the strip of tin-foil, with the window, I place as is shown in fig. vi. In my arrangement, the temperature of the strip of tin-foil rises in almost arithmetical proportion to the number of elements used,* when these are so arranged that each zinc is connected with a copper pole. With one element, and the arrangement just described, I obtain an elevation of temperature amounting to about 5° C (9" Fahr.), and with six elements rather more than 30° C (54° Fahr.). If great accuracy is required, the regu- lation of the temperature must be accomplished by means of a rheostat. In order to exercise a direct control over the temperature of the glass cover, I attach a thermometer to the slide itself. In Fisr. VI. All. Gas chamber, -with thermometer, capable of being heated by means of a constant current. fig. VI., a represents the flattened bulb of the thermometer, whilst the dotted line b indicates the direction of the tube. Both the * It must be expressly understood that the ratio here given corresponds only to a certain definite arrangement. It follows from Ohm's law that the resistance of the introduced strip governs this ratio. The strength of the battery req^nired must be ascertained by experiment. GENERAL METHODS OF INVESTIGATION, BY S. STEICKEE. xvii tubes and the bulb lie in a groove made in an india-rubber slide. A coil of very fine copper or platinum wire is wound round the mercurial bulb a, and the ends are made to lie on the broad metal plate pp. The springs which conduct the current through the instrument press upon these plates. Fig. VI. A II. is a longitudinal section of the stage in full work- ing order ■,ggi& the little glass cover, upon or to the under sur- face of which the object to be examined is attached. The cover is in contact, not only with the surface of the slide, but also with the coil of wire surrounding the bulb of the thermometer, the transverse section of which is seen at a a. When the circuit is closed, the wire becomes heated, and acts on the one hand upon the mercury, and on the other upon the cover. The hard caoutchouc is a bad conductor of heat, and hence the cover receives the greater part of the heat. The figure renders it apparent, also, how the slide can be at the same time used as a gas chamber. Where only the centre of the slide, or the cover, is desired to be heated, the flame of a candle or gas jet may be con- veniently employed as a source of heat. For this purpose a copper ring and rod of the form kkkh fig.vii. are so inserted into the glass slide o o, that they do not pro- ject beyond its surface; when it is required to be heated, the rod q, with its coil, is slipped over the free end K K, and to the extremity q the flame, which should be as small as possible, is applied. If the rod is of about the thickness of a large knitting-needle, it can be made of sufiicient length to obviate any inconvenience to the observer from the flame. The centre c of the slide must be accurately arranged for a par- ticular object glass, flame and focus. If a very small one be employed, we may reckon upon tolerable uniformity of tem- perature being maintained, though of course this mode has no pretensions to scientific accuracy. If, however, the general effect of an increase of temperature within certain limits is all that is required, it is sufficiently useful. The facility with which it can be made renders it valuable for large laboratories. I have constructed another slide with a thermometer at- tached, on the same principle of heating. The thermometer is fashioned, as in fig. vi.; in the form of an arch, and is imbedded in C XVlll INTRODUCTION. a plate of caoutchouc. The bulb, however, is not surrounded by a spiral, but by a metal shell, which resembles h h h in fig. VII., and to this the projecting rod h' is fastened. If the apparatus represented in fig. vii. is imagined to be made of ebonite, and perforated in the centre, the dotted line will re- present the position of the tube of the thermometer. Inas- much as the object must in every case be placed on a covering glass, two clips (e e, fig. vii.) are added to fix the glass. If the Fig. VII. Slide capable of being heated, represented of natural size, khkk, copper ring and rim imbedded in the plate oo; qq, heating rod ; e e, dps. plate is to be used as a gas cell capable of being heated, the object must be placed on the lower surface of the cover ; but if only as a slide capable of being heated, it must be placed on the upper surface, and requires then its own cover. In the latter case the lower cover (g g, fig. vi. A ii.) is equivalent to the ordinary slide, and only possesses the advantage of being a thin plate, the temperature of which can be easily raised.* The disadvantages of an ordinary gas cell appear prominently in the cell capable of being heated. In no arrangement with which we are at present acquainted does an equipoise between the preparation and the atmosphere surrounding it occur. The • The mechanician, Heinitz, in Vienna, has constructed a gas cell capable of being heated on the model of that just described, with a degree of ele- gance that leaves scarcely anything to be desired. GENERAL METHODS OF INVESTIGATION, BY S. STRICKEE. xix temperature of each part of the cover changes as the object glass sweeps over it, and must necessarily vary within certain Hmits, even with the best means of regulating the temperature. Each time that it is cooled, a precipitation of the watery vapour from the atmosphere that is saturated with it must occur. Recklinghausen and Kiihne have endeavoured to obviate this inconvenience by the construction of a more complicated appa- ratus for supplying heat. Whilst the results of these ex- periments are still unknown, it is advisable to postpone the iavestigations on the effects of heat in the gas cells. The reason that has induced me to describe the construction of the beatable gas cell at so great a length is, that it affords excellent results iu quite another line of inqviiry. If the floor of the cell be covered with a drop of water, and the preparation is attached to the under surface of the cover over the water, all increase of temperature will cause the atmosphere within the ceU to contain more watery vapour, of which a part wiU con- dense on the object. If a delicate test object be examined, such, for example, as the blood corpuscles constitute for a practised observer, it wiU be remarked that every addition to the temperature produces a perceptible alteration in the object, attributable to the increased proportion of water in the serum. We thus possess the power of supplying water, in very precise proportions, to preparations enclosed within a cell. It has been further ascertained that the action of gases on blood is different in accordance with the amount of water that it contains. The results of the experiments that have been hitherto made will be detailed in the chapter on the blood. A single example may, however, here be given to show the advantage that gas cells capable of being heated can afford. It may, in some cases, be very desirable to be able to vary the temperature within certain limits with rapidity. I have, in- deed, had occasion to perform some experiments in which it was requisite to pass, alternately, iced water and steam through the cell. For this purpose I have constructed a metal slide, in which a central perforation (c, fig. vill.) permits the passage of light ; and the preparation may agaiu either be placed upon a glass cover cemented down, or may be so arranged that the hole in the slide serves as a cell. The plate itself must consist c2 XX INTRODUCTION. of t-wo leaves, so separated as to allow an evenly enclosed space to exist between them. Then, at opposite points of the space, two small tubes are inserted (a, fig. ix.) To one of these an india-rubber tube b is attached, which leads to the vessel for generating steam F. This consists of a flask, through the cork of which a rectangularly bent glass tube is transmitted. The free end of this tube must now be brought into connection with the slide ; in this communication a T-shaped tube is again intro- duced. A lamp with a small flame is placed beneath the flask. Fiff. VIII. «Ez: Metal slide for the conduction of water and steam, a a, conduoting tubes ; t, thermometer. which is half filled with water, so as to keep up gentle ebullition. The steam escapes through the perpendicular limb of the T-shaped tube, because it here meets with the least resistance. When, however, this is prevented, which is easily accomplished by means of a caoutchouc tube and a clip, the steam passes through the slide, and heats it. If the lamp is now removed, the cooliag flask exerts a suction power on the vapour in the space between the two leaves of the slide, and atmospheric air consequently enters ; or if a receiver containing iced water be already prepared, this also may be sucked up, and rapid cooling efiected. The temperature is ascertained by the thermometer which occupies the position shown in the figure. Electricity is also an agent of considerable importance in mici-oscopical investigations. Brucke, in his physiological inquiry into the tissues, employed a slide covered with tin- foil, as shown in fig. x. The sUde s s was placed on two GENERAL METHODS OF INVESTIGATION, BY S. STRICKEE. XXI copper supports K, which were attached to the stage P. The electrodes were fastened to the supports, and the object was brought between the points of the lamina of tin-foil. - The mode al- ready described of obtaining and transmitting a current for the pur- pose of observing the effects of heat, will also, of course, serve for observ- ing those of electricity. When this is the object in view, the slide should only be covered on its surface with tin-foil, in the form represented in fig. X. The springs resting on ebonite rods wiU. serve as conduct- ors. The distance of the laminse of tia-foil from one another is of im- portance in regard to the trans- mission of the current. As a general rule they should not be separated from one another to a greater ex- tent than a few millimeters. I pre- fer to see the two electrodes at the sides of the field, because then the position of the object in regard to them, and to the middle line, is simultaneously visible. It is a matter of very great moment to observe and distinguish between the effects of the current in the immediate neighbourhood of the poles, and at some distance from them ; for the effects of electrolysis are produced on breaking the cur- rent in the vicinity of the elec- trodes, and the tissues become al- tered as they would be were they £iubjected to the action of weak acids or alkalies. At parts more remote from the electrodes changes also occur, xxu INTRODUCTION. which, however, are not so remarkable as those which are induced by the chemical processes above alluded to. The eflfects which may be trusted as being really due to electricity should occur quickly after the passage of the current, and not be limited to the part in the immediate neighbourhood of the electrodes. If the current be allowed to pass for some time, that is to say, for more than a few seconds, through the tissue, Vis. X. (£ 1 V S .£3 i ■^ -^ 1 H +^ - o "^ ft !> -r; m 1 ! 51 S .S 1 l-^'-^ 1 11 (BOO 1 p-'-^ >S 2 o =1 ! 1 ll Tl P< t< vl '■) c3 r? ^ HI s- E-i CI i W o a H^ b STRUCTURE OF NERVE FIBRES. 155 of turpentine. Transverse sections of the spinal cord are admirably adapted to exhibit the extraordinary variations that occur in the thickness of the axis cylinder, and the methods of Pfliiger and Waldeyer are those which are best adapted to bring the axis cylinder speedily into view in fresh nerves. Pfliiger's plan consists in adding a drop of coUodion, Waldeyer's in adding a drop of chloroform, to the preparation, in as dry a state as possible, and covering with a thin glass. The medullary sheath will then be found to have lost its brilliancy, and in the greater number of nerve fibres the axis cylinder appears very distinctly as a finely granular central fibre. We are in possession of extended observations by Bidder and Volkmann,* in reference to the difference in thickness existing amongst the peripheric medullated fibres, and espe- cially between the cerebro-spinal and sympathetic fibres, which is very considerable. A fourth form of nerve fibre may be added to those already described, which also occurs in the peripheric nerves, but is distinguished from the foregoing by the absence of the medullary sheath, and is on this account usually described as the peripheric non-meduUated nerve fibre. These consist of fibres composed of a thicker or thinner bundle of primi- tive nerve fibrils, according to the kind of axis cylinder present, united together by a nucleated sheath of Schwann. All the branches of the olfactory nerve in the mucous mem- brane of the nose of aU Vertebrates consist of such non- meduUated nerve fibres. They are also of frequent occurrence in the sympathetic, the branches of which, distributed to the intestines, are often entirely composed of them ; as, for example, the thick splenic nerves of Ruminants, which are often more than a millimeter in diameter. It was here that Remak first observed them,-f and hence the non-medullated sympathetic fibres bear the name of Remak's fibres. Remak himself sub- sequently called them ganglionic fibres.j Some fibres show the fibrillar structure much more distinctly than others, as was * Die Selbstandigheit des Sympathischen Nervensy stems. Leipzig, 1842. f Ohservationes Anatomicce et Microscopicee de Systematis Nervosi Struc- tura. Berol., 1838. X Monatsberichte der Berliner Akademie, 1853, 12th May. O 156 STEUCTDRE OF THE NERVOUS SYSTEM, BY MAX SCHULTZE. remarked by Pfliiger * in the course of his investigations on the nerves of the salivary glands, on -which account he divided them into two varieties. It is this kind of nerve fibre which, with few exceptions, is present amongst the Invertebrata. Nerve cords, which consist of such fibres, do not possess the bright Fig. 22. Fig. 22. MeduUated nerve fibres, u, from tlie olfactory nerve of the Pike ; b, from the olfactory nerve of Man ; c, from the sympathetic (splenic nerve) of the Ox ; d, from the nerve passing to the organ of Jacobson in the Sheep. In this specimen are two meduUated fibres. glancing appearance of ordinary nerves, but are semi-trans- parent grey, gelatinous, and resemble embryonic tendinous tissue. If they are freed from the denser connective tissue which invests them, they can be broken up into their con- stituent fibres as easily as other nerves, which is a consequence * Die Endigungen der Absonderungsnerven in den Speicheldrusen, " On the Mode of Termination of the Secretory Nerves in. the Salivary Glands." Bonn., 1866, p. 31. STRUCTURE OF NERVE FIBRES. 157 of the firm consistence of the sheath of Schwann surrounding each fibre. The diameter of these non-meduUated nerve fibres varies very considerably. In the sympathetic they scarcely exceed that of the medium-sized medullated fibres, but in the olfactory nerves of many animals fibres may be found at least three or four times thicker than the largest meduUated fibres. Such thick fibres are shown in fig. 22, a, taken from the nasal fossa of a pike, consisting, when fresh, of a very soft, almost fluid, finely granular mass, with parallel strise, contained in a transparent and structureless sharply defined sheath, in which, on the addition of acetic acid, nuclei make their appearance. By carefully hardening the specimen the fibrillar structure becomes very distinct, whilst at the same time the whole contents of the sheath may be broken up into fibriUse of the nature of primitive nerve fibrils, between which the fine granules and molecules are interspersed to constitute an inter- fibrOlar mass. In Man and most other vertebrate animals the fibres of the olfactory nerve are of less diameter than in fish, and resemble rather those of the sjTnpathetic nerve, except that they are arranged in bundles within a common nucleated sheath, so that funiculi are formed similar to those shown ia the subjoined fig. b, taken from man. Here, as in the sympathetic nerve c, the substance of the individual fibres is fibrillar, and finely punctated, and probably consists of primitive fibrillse and an interfibrillar substance. According to the preceding account of the structure of the nerve fibres, the following kinds may be distinguished : — 1. Primitive fibrils. 2. Fasciculi of primitive fibrils. 3. Primitive fibrils with medullary sheath. 4. Fasciculi of primitive fibrils with medullary sheath. 5. Fasciculi of primitive fibrils, invested by the sheath of Schwann (as in the non-meduUated nerve fibres of the sym- pathetic, the olfactory nerve, and the nerves of the greater number of invertebrate animals). 6. Fasciculi of primitive fibrils, with medullary sheath and the sheath of Schwann (as the fibres of most of the cerebro- spinal nerves). 1 and 2 may be distinguished as naked axis cylinders ; and o 2 158 STaUCTUBE OF THE NERVOUS SYSTEM, BY MAX SCHULTZE. where they are invested by a sheath, as simply axis cylinders. It remains undecided whether nerve fibres exist, possessing a medullary sheath and the sheath of Schwann, the axis cylinder of which is formed by a single primitive nerve fibril. If the nerve fibres be divided into two groups, according to the presence or absence of the medullary sheath, they may be further subdivided into I. Non-meduUated fibres. 1. Primitive fibrils. 2. Fasciculi of primitive fibrils. 3. These last, with a sheath of Schwann. II. MeduUated fibres. 1. Primitive fibrils with medullary sheath. 2. Fasciculi of primitive fibrils with medullary sheath. 3. These last with a sheath of Schwann. We see then that the primitive fibril forms the elementary constituent of aU. nerve fibres. The variations that are ob- served are dependent on the number of the fibrils united together to form one cord, and upon the absence or presence of the medullary sheath and the sheath of Schwann. It is at once obvious how complicated a structure one of the so-called meduUated primitive nerve fibres is when it is found to be composed of a bundle of primitive fibrils united by inter- fibrillar material constituting the axis cylinder, and of two investing sheaths. The foregoing description differs from tliat generally received in tlie acceptance of the primitive fibrils, as the ultimate structural elements of the nerve fibres. I have already elsewhere* shown the probability of the existence of a fibrillar structure in the non-medul- lated fibres of the olfactory and sympathetic nerves, which the greater number of observers have regarded as purely granular rather than fibrous ; and my views have been supported by later observers, as Waldeyer,f Pfluger,J and others. We must here also take into con- sideration the similarity of the nerve fibres of the greater number of * Untersuchungen iiber den Bau der NasenscTileimhaut, p. 63. t Zeitschrift fur rationelle Medicin, Band xx., 1863, p. 202. X Die Endigungen der Ahsonderungsnerven in die Speicheldriisen, 1866, p. 31. STRUCTURE OF NERVE FIBRES. 159 invertebrate animals, which all recent observers agree in describing as consisting of fasciculi of fibrils with interfibrillar granular substance.* Many Crustacea make exceptions to this, but only in so far that in them a structure analogous to the medullary sheath is present, in the interior of which fasciculi of fibrUs lie enclosed, forming a kind of axis cylinder.! Since their first discovery by Eemak, the axis cylinders of the medul- lated nerve fibres of man and other vertebrates have repeatedly been held to exhibit a fibrillar structure. Eemak himself described the axis cylinder, or as he termed it, believing it to be hollow, the axis tube, as marked by parallel lines, and regarded this as an indication of its fibrous nature. J His followers, however, became more and more convinced that the axis cylinder was a homogeneous structure, and this has recently been maintained by Waldeyer, to whom we are indebted for a laborious work on the subject. § Waldeyer admits the probability of the origin of the axis cylinder from isolated fibrils in the nerve centres, just as he acknowledges that it splits peripherically into fibrils, but he holds that in its course it is a homogeneous structure. KoUiker has arrived at the same result, since after adducing nu- merous arguments in favour of the fibrillar nature of the axis cylinder, he concludes with these words : " There is no absolute and decisive proof of fibrillation in the axis cylinder. "|| I am very far from denying that the axis cylinder, as it is ordinarily brought into view, gives the impression rather of a homogeneous than of a fibrillated cord. There is no doubt that when examined with moderate powers, and when hardened by the ordinary methods, its substance does appear homogeneous, or presents only a linear arrange- ment of fine molecules. But in proportion as the process of har- dening is avoided in the prosecution of the investigation, and the structures are maintained, both as regards their consistence and refractive powers, in a state analogous to the fresh condition, es- pecially when high magnifying powers are employed, so much the more clearly am I able to recognise a parallel striation and a substance of a finely granular nature between the striffi, which are appearances that I can only refer to the axis cylinder being constructed of fibrils, and * Cf. especially Leydig, Lehrhuch der Hislologie des Menschen iind der Thiere, 1857. f Bemak and Hackel, the last in Miiller's Archiv, 1857, p. 469. X Observationes Anatomicte, etc., 1838, p. 2, note 2. § Zeitschrift fur rationelle Medicin, Band xx., 1863, p. 193. II Gewebelehre. fifth Aufl., 1867, p. 244. 160 STEUCTUEE OF THE NERVOUS SYSTEM, BY MAX SCHULTZE. an interfibrillar substance. For this investigation I especially em- ploy the lateral columns of the spinal cord with their thick medul- lated fibres, from which, on account of the absence of the sheath of Schwann, it is easy to isolate the axis cylinder, not only when quite fresh, with the addition only of a little serum, but still better after twenty-four hours' or more maceration in solution of iodine in serum,' in which the axis cylinder becomes slightly hardened without shrink- ing or otherwise materially altering in appearance. Perosmic acid is also here of great service, solutions of which, varying in strength from one-half to one-eighth per cent., acting for a short time on the axis cylinder, harden it without materially changing its volume, and without producing a trace of granular coagulation. Axis cylinders thus freed from the medullary sheath show with remarkable distinct- ness the characters of parallel striation. But even whilst still con- tained within the medullary sheath, the fibrous and granular structure of the axis cylinder may be observed, as I was first convinced from - observations made on the thick fibres of the brain of the torpedo, which possesses a proportionately thin medullary sheath.* A decisive argument in favour of the fibrillar structure of the axis cylinder is derived from the observation of its origin from the great nerve cells of the spinal cord or of the brain. In regard to this point I must refer to the following account, and to the essay I have just cited, in which the particular observations are given, and will only mention here that the fibrils which emerge in a convergent direction from the cell substance, in order to form the axis cylinder pro- cess of the cells, unite, and are often far removed from one another by interfibrillar material (see figs. 18, 29, and 80, at a.) The forma- tion of the proper axis cylinder results from a diminution in the quantity of the interfibrillar material, whilst the fibrils become more closely approximated in their parallel course, so that ultimately only a very small quantity of interfibrUlar substance remains. In the periphery also it is not difficult to see the fibrillar character of soli- tary axis cylinders, as, for example, in the corpuscles of Vater and Pacini, as was shown to me by Dr. Grandry, providing the specimens are examined in the perfectly fresh state, without other addition than that of serum, and with sufficiently high powers. I consider it, indeed, to be possible that, notwithstanding these * See my Essay, entitled Observatwnes de cellularum, fihrarumque nervcarum Structura, Bonner Universitats Programm, 1868, fig. 5, and the preceding woodcut, 21, p. 154. STRUCTURE OP NERVE FIBRES. 161 observatioHS, axis cylinders exist in which the original fibrillar nature is entirely lost by fusion of the fibrils with each other, and which have thus become homogeneous ; but I regard the principle as correct, that the thicker axis cylinders are composed of several primitive fibrils, since these converge at the centric, and for the most part separate from one another at the peripheric extremity. On physiological grounds also I maintain the possibility of isolated conduction in these con- stituent fibrils, even when no trace of interfibrillar substance is present. I may just add that my views on these points differ essentially from those of Stilling,* who indeed regards the axis cylinder as a complicated fibrous structure, but distributes his elementary fibrils generally on the surface, and considers that they unite with consti- tuents of the nerve and medulla, which also again consists, accord- ing to him, of fine fibres or tubules. StilHng, as is well known, has not been able to distinguish the preformed structure from the pro- ducts of coagulation that occur in nerve fibres hardened in chromic acid. Both naked axis cylinders, and those enclosed in a medullary sheath, offer some remarkable and unexplained peculiarities when they are satu- rated with dilute solutions of nitrate of silver in the dark, and are then exposed to light. After Frommann,! who made the first ob- servations on the point, the best subsequent investigations have been made by Dr. Grandry.J As a result of this treatment there occurs in the axis cylinder a fine transverse striation, caused by the partial deposition of brownish-black silver compounds, which is here and there so regular as to remind the observer of the structure of striated muscular tissue, though in other parts it exhibits great irregularity. When the action of light has been more protracted, the appearance in question gradually disappears, and the whole becomes equably tinted of a brownish black. As Grandry remarks, however, not only the axis cylinder, but also the branched processes of the ganglion cells, and frequently the cells themselves, exhibit this striation in a very surprising manner. No one has hitherto succeeded in showing any relation between these appearances and the finer structure of the parts. * Neue Untersuchungen iiber den Bau des Siitkenmarkes, 1859, p. 708. t Vhchow't, Archiv, Band xxxi., Taf. 6, figs. 11 to 16. ^ Recherches sur la Structure intime du cylindre de I'axe et des cellules nerveuses, Bulletin de I'Academie Moyale du Belgique, 3Iars, 1868. 162 STEUCTURE OF THE NERVOUS SYSTEM, BY MAX SCH0LTZE. 1. Division of the Nerve Fibres. A peculiar feature presented by the nerve fibres in their course is their division. This frequently occurs near their peripheric extremity, but is also to be observed in the nerve centres, and occasionally in the nerve trunks. It may take place in aU kinds of nerve fibres, with the exception of the primitive fibrils. Branched and ramified fascicu?L of primitive fibrils are composed of the processes of many multipolar gan- glion cells. In the olfactory nerve may be seen the repeated subdivisions, quickly following each other, of non-medullated fibres provided with a sheath of Schwann, with the sheath prolonged upon the branches.* The mode of division, how- ever, that has been most frequently described is that of the meduUated fibres, such as is seen, for example, in the nerves distributed to muscle, f This mode of division is usually dichotomous, and affects all the constituents of the nerve fibre. The division of the fibrillar axis cylinder probably consists only in a 'gradual process of isolation of the associated primitive fibrils. The meduUary sheath is con- tinued at the point of division over the branches, and is finally lost at their extremities. It is very remarkable that at the point of division, in consequence of a sudden diminution in the quantity of the nerve medulla, an attenuation of the nerve fibre occurs, whilst beyond this point, when the division is completed, the medulla is again found in its ordinary propor- tion. The sheath of Schwann divides in precisely the same manner. As the branches after division are much thicker when taken collectively than the trunk from which they proceed. * This may be particularly well observed in the thin plates of the nasal fossse of rays and of sharks. Max Sehultze, Bau der Nasenschleinhaut, Taf. 4, fig. 8, V. 9. t See in particular Reichert and Miiller's ^rcAiV, 1851, p. 29. E. Briicke and Joh. Miiller were the first who observed the divisions of medullated nerve fibres in muscle. See the last mentioned author's Handbuch der Physiologie, fourth edition, Band i., p. 524. Paul Savi was the iirst who saw the primary divisions of medullated nerve fibres in the electric organs of the Torpedo, in 1844. DIVISION OF NERVE FIBRES. 163 ■whilst the axis cylinders diminish, it is obvious that the sheaths must augment in thickness. This holds in particular for the medullary sheath, the thickness of which is proportionately Fig. 23. Fig. 23. MeduUated nerve fibre, from the electric organ of tlie Tor- pedo, at the point of division, presenting a very thick sheath of Schwann, a, trunk fibre ; h, sheath ; c, nucleus of the sheath ; d, point of division ; e, branches. After R. Wagner. much greater when the axis cylinder is thin than when it is thick. Instead of the dichotomous division, three, four, or more, even up to five and twenty branches may suddenly arise 164 STRUCTURE OF THE NERVOUS SYSTEM, BY MAX SCHULTZE. from a single trunk fibre, as was first observed by Rud. Wagner in the nerves of the electric organ of the Torpedo* By far the most remarkable example of nerve division occurs, however, in the electric eel (Malapterurus electricus). Here, according to Bilharz, each of the two electric organs which lie like masses of bacon-fat beneath the skin, receives a nerve from the medulla oblongata, consisting of only a single meduUated fibre, having a diameter of 0025 miUimeters,f which, in order that it may give a peripheric terminal fibre to each electrical plate, must divide millions of times. The sheath of Schwann disappears sooner or later in the process of division, and is consequently absent in the ultimate fibrils, as may be seen, for example, in the nerves of the cornea. Here the meduUa also sooner or later disappears from the sur- face of the axis cylinder. Coincidently, or somewhat later, the sheath of Schwann can no longer be distinguished, the axis cylinder, which alone remains, repeatedly divides, and the fine primitive fibrillse, as first demonstrated by Hoyer:|: and Cohn- heim,§ ultimately project from the sub-epithelial tissue between the cells of the tesselated epithelial layer of the conjunctiva cornese, and terminate by free extremities at the surface. The same appearance may be seen in many other nerves, as in the acoustic and optic, in the nerves of the tongue, in those dis- tributed to the glands and elsewhere, though in these instances each primitive fibril is connected with a peculiar terminal apparatus, which will be hereafter described. In many parts, however, the division into primitive fibrils does not take place ; that is to say, an axis cylinder of appreciable diameter termi- nates, so far as we at present know, without previously breaking up into the finest nerve filaments. The above-mentioned examples, the nerves distributed to many electrical organs, to the transversely striated muscles, the Vater's (Pacini's) cor- * Feiner Sau der Ulekt. Organes im, Zitterrochen, "Minute Anatomy of tte Electric Organs of the Torpedo," 1847, p. 17. t According to Bilharz, he. cit., p. 22—^90"'. J Uber die JEndigungen der sensibeln Nerven in der Sornhaut, Virchow's Archiv, Band xxxviii., 1867, p. 343. § Reichert and Du Bois Reymonds' Archiv, 1866, p. 180. PEEIPHEEIC TERMINAL ORGANS OF THE NERVES. 165 puscles, exhibit, in part at least, when carefully examined, no exception to this rule. 2. Of the Peripheric Terminal Organs. The peripheric division into primitive fibrils appears to occur in aU the nerves of special sense, but especially in those cases where perception of a great variety of impressions occurs within a very limited space. Peculiar terminal organs are found in such instances in connection with each fibre, of which a more detailed description will be given in the consideration of the different senses, but which will be here only regarded from a general point of view. In the nasal mucous membrane, fusi- form easily alterable cells are found occupying interspaces between the pallisade-like cells of the olfactory region. These possess a centric and a peripheric process, of which the former exactly resembles the primitive nerve fibrils of the olfactory nerves,* whilst the latter either ends at the level of the free surface of the epithelial cells, as in man, mammals, and fishes, or extends beyond this surface in the form of a long stiff hair, or of several finer hairs, analogous to ciha, but incapable of movement. I have named these cells olfactory cells, and the hairs ol- factory hairs. The general relations are the same in the mucous membrane of the tongue as Axel Keyf has shown in the papillse fungiformes of the frog, and Schwalbe:]: and Loven§ in the gustatory cells of the papillse circumvallatse, and of some of the fungiformes in man and mammals. These terminal organs corresponding to the olfactory cells may be termed gustatory * The existence of these cells was first recognised by Eckliard in the frog. See his Beitrdge zur Anatomie u. Physiologie, Bind i., 1855, p. lY, Taf. 5, figs. 3, 4 c ; and a discussion on their relation to the Nervous System will be found in Schultze's Essay in the Monatsberichte der Berliner Akade- mie, 1856, November, p. 504, and at still greater length in Max Schultze's Untersuchungen uber den Bau der Nasenschleimhaut, Halle, 1862, with five plates. t Miiller's Archiv, 1861, p. 329. J Archiv flir Mikroshojp. Anatomie, Bandiii.,p. 154; Bandiv.,p. 154. § Idem, Band iv., p. 96. 166 STRUCTURE OF THE NERVOUS SYSTEM, BY MAX SCHULTZE. cells. Similar conditions are found in the auditory organs, since in those parts where the nerve terminations are simple, the terminal branches of t'he meduUated acoustic fibres, after losing their medullary sheath, penetrate between the epithelial cells, especially between those of the otolith sacs and of the ampullae of the semi-circular canals, and after breaking up into primitive fibrils become continuous with peculiar ciliated auditory cells * The mode of termination of the nerves in the cochlea is of greater complexity, especially because a portion of the non-nervous cells of the epithelial investment of the cochlear canal develops into the several structures forming the organ of Corti. But even here the terminal nerve struc- tures appear to consist of cells supporting hairs, which are continuous with extraordinarily delicate non-meduUated nerve filaments (primitive fibrils). The terminal nerve apparatus of the optic nerve in the retina presents quite peculiar features. Here are found the layer of rods and cones, and the nucleated external granules, which last, like the terminal apparatus of the olfactory nerve, appear as fusiform cells, with a centric and a peripheric process. The centric process of the rods is a single primitive fibril, but that of the cones is a fasciculus of primitive fibrLls."f- The peripheric process terminates in the case of the so-called rods and cones in an essentially similar manner, the extremity in each consisting of a pale inner segment resembling ganglionic cell substance, and a bright highly refractile external segment, which is separated from the former by & sharply defined line, and which in the * See Max Sohultze's Ueher die Endigungsweise des Hornerveti im Labyrinth, Miiller's Archiv, 1858, p. 343; Franz Eilh. Schulze in idem, 1862, p. 381 J Odenius, Archiv fiir Mikroskopische Anatomie, Band iii., p. 115. Hasse so far gives a diflferent account, in that he has not been able to observe the division of the axis cylinder into finer filaments (primitive fibrils). See others in Zeits. fur wissens. Zool., Bd. xvii., p. 638 ; Bd. xviii., p. 89. I must, however, maintain the correctness of my assei'tions respecting and illustrations of the above-described objects. The consideration of the auditory organ of invertebrate animals is of great importance in regard to the relations in (question. See Hensen, Zeitschrift filr wissenschaftliche Zoologie, Band xiii., p. 319, " On the Auditory Organs of the Crab." I Max Schultze, Archiv filr Mikroskopische Anatomie, Band ii., Taf. 10. PERIPHEEIC TERMINAL ORGANS OF THE NERVES. 167 rods is of cylindrical, and in the cones of conical form. The structure of the outer segments, which, in all probability, con- stitute the proper terminal structures, upon the excitation of which perception depends, differs from that of any other nervous organ, especially in its consisting of a series of thin plates superimposed on one another in the direction of its long axis * The tactile nerves of the skin, lastly, terminate in the so-called tactile corpuscles, which are oval or spherical, very soft, and easily alterable bodies, occupying the interior of many tactile papillae of the skin,-f- each of which is continuous with one or more medullated nerve fibres that divide in their interior, though up to the present time the precise mode of termination of the primitive fibrils in them has not been completely elucidated. In immediate relation to the sense of touch stand also in all pro- bahility the nerve hairs found on the surface of young fish and naked amphibia, which have been ascribed by F. E. Schulze,J and the arrangement of which in the form of pencils or brushes calls to mind the nerve hairs in the ampullsB of the auditory organ. These appear to be well adapted for the perception of movements of the water in which the animals live. In fishes also is found the lateral canal sj'stem, with the nerve bulbs described by Leydig. I have also observed a very similar disposition of the nerves in regard to hair-bearing epithelial cells in the vesicles of Savi present in the torpedo. § According to recent investigations by Franz Boll, the highly nervous ampullae of the so-called mucous canals of the head of rays and sharks are covered with cell-supporting hairs. We may also regard the corpuscles of Voter or Pacini as * Max Schultze, Archivfiir Mikroshopische Anatomie, Band iii., p. 215. A reference may also be made to the differentiation of one or several axial fibres in the outer segment, first observed by Ritter. See especially Hen sen, Virchow's Archiv, Band xxxix., p. 475, Taf. 12. t We owe the discovery of these structures to Meissner and Rud. Wagner. See Gottinger, Nachrichten, 1852, No. 2 ; or in more detail Meissner, Beitrdge zur Anatomie und PJiysiohgie derHaut. Leipzig, 1853. X Miiller's Archiv, 1861, p. 759. § Untersuchungen iiher den Bau der Nasenschhimhaut, 1862, p. 11. In this essay will be found a more detailed account of the relations at present known to exist between nerves and epithelial investments. 168 STRUCTURE OF THE NERVOUS SYSTEM, BY MAX SCHULTZE. constituting terminal organs of the sensory nerves. These are most commonly found in man in the subcutaneous connective tissue of the sides of the lingers and toes, seated on the volar and plantar nerves; also on the nerves supplying joints, and in the nerves coursing between various muscles of the trunk and extremities ; * in animals, however, they are found in many other parts of the body, and may be most easily obtained for examination from the mesentery of the cat. Each of these corpuscles receives a meduUated nerve fibre, which does not again emerge from it. The corpuscle itself consists of many concentrically arranged layers of connective tissue, becoming always more closely packed near the centre, and surrounding a cavity filled with soft abundantly nucleated and very easily alterable material, which undergoes coagulation after death, and into the interior of which the nerve fibres penetrate. These, after they have lost the medullary sheath and the sheath of Schwann, which becomes continuous with the laminated sheaths of connective tissue investing the corpuscle, consist only of the axis cylinder, which terminates in a little bulb.-f- Dr. Grandry, who has examined the Pacinian corpuscles with higher magni- fying powers than appear to have been previously employed, observed a very distinct fibrous structure in the axis cylinder in their interior, and also that the terminal bulbs consist of finely granular substance, from which the diverging terminal fibrils may be clearly distinguished. Closely allied to the foregoing are the numerous terminal nerve corpuscles described and depicted by Krause as existing in the conjunctiva, the genitals, and other parts of the body, which difier from the Pacinian corpuscles only in the absence of a thick laminated investment.! * See Rauber, Untersuchungen uber das Yorlcommen und die Bedeutung der Vater'schen Korper, " Researches on the Distribution and Function of the Corpuscles of Vater," 1867. f See the numerous illustrations of these corpuscles and their minute microscopic anatomy in Henle and Kolliker's Essay, Ueber die Pacini'schen Korper an den Nerven des Menschen und der Sailgethiere, Zurich, 1844, which -was followed by the work of Herbst, entitled Die Pacini'sche Korper und Hire Pedeutung,G6ttingen, 1848. There are numerous recent investigations on the point, amongst others, those of Leydig, Krause, Kolliker, and Rauber. J See W. Krause, Die terminalen Korperchen, 1860 ; Anatomische PEEIPHEEIC TERMINAL ORGANS OF THE NERVES. 169 The mode of termination of the nerves in the transversely- striated muscles has been the subject of numerous researches, and we now know through those of Kiihne, Engelmann, and others that. axis cylinders of moderate thickness penetrate the sarcolemma of the muscular fibres, and either branch out to form the so-called terminal nerve plate, or, as in the frog, break up into primitive fibrils in the interior of the contractile sub- Fig. 24. Fig. 24. a, Vater-Pacinian corpuscle from the mesentery of the Cat, examined with, a low power — after E. Ecker; b, the end of the nerve fibre, consisting of a fibrillated axis cylinder, the fibrils of which are lost in a finely granular mass, magnified 1,000 linear — after Grandry. stance, and therefore probably in the interfibriUar substance. Frankenhausen has recently maintained that in the smooth muscular fibres there is a connection between the primitive nerve fibrils and the nucleoli of the fibre cells, on which point, however, the reader is referred, as in regard to the nerves of muscles generally, to the section on muscles. A peculiar and remarkable mode of nerve termination is Untersuchungen, 1861 ; Bense, JJi'e Nervcnendigungen in der Oeschlechts Organen, in der Zeitschrift fiir rationelle Medicin, 1868, Band xxxiii., p. 1. 170 STRUCTURE OF THE NERVOUS SYSTEM, BY MAX SCHULTZB. found in the electrical organs of those fish that are provided either with true or the so-called pseudo-electric organs (as the Torpedo, Malapterurus, arid Gymnotus amongst the former, and the Eaja and Mormyrus amongst the latter). The axis cylinders Piff. 25, A. From the electric organ of Mormyrus oxyrhyncus, and also as in the M. longipinnis and cypiinoides. v anterior, h posterior connective tissue septum ; a a, electric plates ; 5 6, nerves penetrating into their interior. B. From the electric organ of Mormyrus dorsalis, and also as in the M. anguilloides. Lettering as in A. of the nerve fibres, which pass to these organs from the nerve centres, here terminate in the so-called electrical plates, which are direct expansions of the nerve fibres in the form of remark- able discs, each of which lies in a small chamber of the organ formed by septa of connective tissue. Fig. 25, after Ecker PERIPHERIC TERMINAL ORGANS OF THE NERVES. I7l taken from the Mormyrus, shows the electrical plates forming direct expansions of the nerve-fibre substance, from which it appears that the nerve fibres penetrate foramina in the plates (as in some species of Mormyrus and Malapterurus) before they break up in its substance. The point of entrance always occurs on one only of the two surfaces of the disk, and, indeed, on the same or corre- sponding surface of aU the plates of the same animal ; thus, for example, in the torpedo, in which the plates have a dorsal and ventral surface, the nerves are always applied to the ventral surface, the dorsal remaining smooth ; consequently all these electric plates have a smooth free, and a rough surface to which the nerve fibres are attached, and these all look in the same direction. At the moment of the discharge in all the electric fishes hitherto examined, that side of the animal to which the rough surfaces of the electrical plates are turned is negative as compared with the opposite. In Malapterurus only a single primitive nerve fibre, which has just previously lost its medullary sheath, penetrates each plate ; but in all other animals many fibres enter. The structure of these electric plates, composed of albuminous material, difiers in two points from the former. The plates of the true electric organs are homogeneous disks, slightly uneven on their free surface, in the interior of which oval or spherical nuclei, surrounded here and there with a little finely granular substance, lie scattered at definite distances. The plates of the so-called pseudo-electric organs, on the other hand, exhibit similar nuclei, but their sub- stance is not homogeneous, being marked by delicate, meandering, and looped systems of lines, which result from their complicated structure, composed of a number of layers of very thia curved plates. The tissue in some measure calls to mind that of the transversely striated muscles.* * A. Ecker, Untersuchungen zur Ichthyoloffie,'Freihwcg, 1857; Berichte der Naturf. Gesellschaft zu Freiburg, 1858, No. 28. Max Sohultze, Vber Pseudo-electrik. Organ, Sitzungsberichte der Naturf. Gesellschaft in Salle, 1857, p. 17;andiiiMuller's^rcte, 1838, p. 193. AlsoBilharz, Das Elektrik. Organ des Zitierwelses, 1857; and Max Schultze, Zur Kenntniss der Ulek- trik. Organ der Fische, 2 Abtheilungen. Halle, 1858 and 1859. P 172 STRUCTURE OF THE NERVOUS SYSTEM, BY MAX SCHULTZE. In regard to the mode of termination of the nerves in glands, the investigations of Pfliiger* on the salivary glands may here be mentioned, in which he showed that the extremities of the nerves formed such a connection with gland cells, that either the cells themselves or their nuclei constituted the terminal organ, as will be more explicitly described in the article on Glands. Hensen has described the cutaneous nerves of the frog as terminating periphericaUy in the nucleoli of the cells of the epidermis."!" Tbey form extraordinarily fine fibres, which penetrate both the cells and nuclei, and in consequence of the frequent division of the nuclei are also themselves frequently bifurcated. 3. On the mode of origin of the Nerve Fibres in the Nerve Centres. The transition from the foregoing to the consideration of the central source or origin of the nerve fibres is to be found in the description of those nerve or ganglion cells which are intercalated in the course of the nerve fibres, and of the so-caUed ganglia. The microscopic examina- tion of the ganglia of the brain and spinal cord, as well as of the sympathetic nerves, alike shows that the cells are to be regarded as an essential part of these structures, and that they exhibit a nucleus and nucleoli lying in a rela- tively considerable quantity of a dense finely granular and fibrillated cell substance, which is often tinged of a yellow colour. The greater number of these cells, when isolated in the perfectly fresh state in serum, are spheroidal ; yet they are often also very irregular in outline, destitute of any doubly con- toured investing membrane, and become broken up and dis- appear with the greatest facility. In sections made through fresh or hardened ganglia such cells appear to be arranged in layers surrounded by fibrous connective tissue, in which large numbers of both meduUated and non-medullated nerve fibres * Du Endigungen der Absonderungsnerven in die Speicheldriisen. Bonn., 1866. ■j- Vircliow's Archiv, Band xxxi., p. 63, Taf. 2, fig. 14; Archiv fur Mikroshopisehe Anatomie, Band iv., p. 121. MODE OF ORIGIN OF NEEVE FIBRES IN NERVE CENTRES. 173 commonly lie imbedded. Each cell, however, occupies a kind of capsule composed of nucleated connective tissue, from the inner surface of which it retracts when acte i upon by strongly hardening fluids. Fig-. 26. Fig. 26, A. Three bipolar ganglion cells, from the Ganglion Gasserii of the Pike — after/ Bidder. B. Three bipolar ganglion cells, from the auditory nerve of the Pike, a, still contained in the medullary sheath ; h, entirely ; c, partially exposed, in order to show that these ganglion cells are only nucleated dilatations of the axis cylinder. p 2 174 STRUCTURE OF THE NERVOUS SYSTEM, BY MAX SCHULTZE. The majority, perhaps it may even be said all, of these cells possess processes, which, however, in the fresh state can be torn off with a facility proportionate to the difference in the consistence of the cell substance and the investing capsule of connective tissue. These processes are nerve fibres, as was first observed by Remak in the Vertebrata,* and by Helmholtzf amongst the Invertebrata. If only one be present, causing the cell to look like a berry attached to its stalk, it is termed unipolar ; if there are two which are often connected with the opposite extremities of the cell, this is termed bipolar, and when there are several, it is multipolar. That these processes are nerve fibres is most clearly evident in certain bipolar gan- glion cells, which are introduced in the course of those medul- lated nerve fibres that may easily be obtained from the perfectly fresh spinal ganglia of sharks and rays, where they were first noticed by Robin and Rudolph WagnerJ in 1847 ; or from the Gasserian ganglion of the same animals, where I have been able to demonstrate their presence with great ease ; or from the same ganglion of the osseous fishes (pike, accordiag to Bidder) ; § or lastly, from the auditory nerve before its entrance into the sacculi of the labyrinth.|| The cell substance is here a con- tinuation of the substance of the axis cylinder ; it includes a nucleus and nucleoli; the medullary sheath usually ceases at the point of transition of the fibre into the nucleated enlarge- ment of the axis cylinder, and reappears at the corresponding point on the opposite side ; though it occasionally invests the entire cell, the cytoid enlargement of the axis cylinder in that case occasioning no interruption to the medullary sheath. It is obvious that such a ganglion cell is only a nucleated swelling of the axis cylinder. The fibrillated structure of the latter may be followed in the cell substance, although it is there in * Froriep's Noiizen, 1837, Nos. 47, 56, 58 ; Ohservationes Anat. et Microscop. de Systematis Nervosi Structura. Berol, 1838. f Defabrica Systematis Nervosi Evertehratorum, Diss, inaixg., 1842. X R. Wagner, NeurologiscJie Untersuchungen, p. 7. § Zur Lehre von dem Verhdltniss der Oanglionhorper zu die Nerven- fasern, " On the relations of tlie Ganglia to the Nerve Fibres." Leipzig, "l847. II Max Sckultze, De Retincs structura penitiori. Bonn., 1859, fig. 7. MODE OF ORIGIN OF NERVE FIBRES IN NERVE CENTRES. 175 part concealed by the presence of a considerable quantity of the interfibrillar substance. And just as the medullary sheath is not essential to our conception of a nerve fibre, so we can only regard it as forming an accessory sheath to the ganglion cell, to which, indeed, it rarely constitutes a continuous invest- ment. The sheath of Schwann, if present, is continued over the ganglion cell, and forms the above-mentioned capsule of nucleated connective tissue. It is, however, absent in the bipolar ganglion cells of the auditory nerve. The structure of the spinal ganglia of other vertebrata and of man is more complex. It has been frequently observed, and has very recently been corroborated by the researches of Schwalbe,* that the cells of these ganglia each possesses for the most part only a single non-meduUated process which runs towards the periphery, and which, according to Kolliker, subse- quently becomes the axis cylinder of a meduUated nerve fibre. Like the substance of the ganglion cells, it presents a fibriUated structure. From some of the cells, on the other hand, instead of a single process, several are given off, which, however, do not arise, as in fishes, from the opposite poles of the cells, and with the further course of which we are still unacquainted. Observations similar to these were made by Kolliker on the cells of the Gasserian ganglion.-f Like those of the spinal ganglia, the cells of the sympathetic ganglia are invested by dense connective tissue, and each pos- sesses a proper nucleated capsule, proceeding from and con- tinuous with the sheath of Schwann, covering the nerve fibres with which it is in connection. The number of these last here also varies to a considerable extent. In the sympathetic of the frog, which has been most frequently examined, there occur, besides such unipolar cells as have just been described, others from which two processes spring in close proximity, of which one winds spirally round the other. The minuter details respecting the mode of connection of these spiral fibres, which were first described by L. Beale| with the ganglion cells, is still * Archivfiir Miltroshopische Anatomie, Band iv., p. 45. t Handbuch der Gewehelehre, 5. Aufiage, p. 319. X Philosophical Transactions, 1863, Vol. cliii., p. 539. 176 STEUCTURE CiF THE NERVOUS SYSTEM, BY MAX SCHULTZE. a subject of dispute, as is evident from the conflicting state- ments of J. Arnold,* Courvoisier,f K6lliker,J and others. The existence of multipolar cells in the large ganglia of the sym- pathetic, though contested by many, is certain, as I have myself found such cells both in children and in adults (fig, 27). Un- Fig. 27. Fig. 27. Nerve cells fi om a lumtar sympathetic ganglion of an adult Man. a, -without a sheatli ; b, -with a sheath. The cell substance con- tains pigment of a vivid yellow tint, and is consequently darkly granular. fortunately, on account of the surrounding fibrous connective tissue, it is impossible to isolate the processes for any consider- able portion of their length. The processes in connection with the ganglion cells of the spinal cord which furnish axis cylinders to the spinal nerves, those in the anterior horns of the grey matter proceeding to the motor, and those in the posterior horns to the sensory nerves, are much more accurately known. The researches of Deiters in particular have demonstrated that from every gan- * V rchow's Archiv, Bande xxviii. and xxxii. t Archw filr 3rikros7copische Anatomie, Band ii., p. 13, and Band iii. J Ilandbiich der Gewehelehre, 5. Auflage, p. 254. 3 to' g n so OQ ^\^ P rr' rt pi tJ- P' P^ li 'S, f^l^*- / trq' ^ 00 ^ .. . -.-'^ ■^'t 178 STRUCTURE OF THE NEEVOUS SYSTEM, BY MAX SCHULTZB. glion cell, however numerous its processes may be, only one periphericaUy coursing axis cylinder arises. This runs without branching, obtains, sooner or later, a medullary sheath, and passes into one of the roots of the nerves. It possesses a fibrillar structure, as I have myself most distinctly seen, both in sensory and motor and ganglion cells. The other processes of these ganglion cells, the number of which is greater in the large cells of the anterior horns than in those of the posterior, branch in an arborescent manner very soon after their origin. Their stmcture is also distinctly fibrillar ; but the quantity of interfibrillar granular substance they contain is greater than in the axis-cylinder process. The fine filaments (primitive fibrils), which result from their ramification, soon evade observation, and their ultimate destination is unknown. Deiters believes that in some few instances he has observed them to become invested with a delicate medullary sheath. The fibrils of both kinds of processes arise from the gan- glion cell substance itself, which exhibits a fibrillar structure throughout, though a finely granular substance, often contain- ing yellowish or yellowish-brown pigment, also exists be- tween the fibrils ; this may extend into the branched processes, or after being interrupted for a greater or less extent, may again make its appearance in them. The fibrillar structure may be most distinctly perceived in the cortical portion of the ganglion cells, though it unquestionably extends into the interior. In many cases, and especially in young rather than in more fully developed ganglion cells, a considerable quantity of finely granular material appears to occupy the interior of the cell, and to surround the nucleus. The course of the fibrils within the ganglion cells is very- complicated ; they may be seen passing from the processes into the cell substance in a divergent manner in every direction, and are there lost in the confused whorl of decussating filaments. This structure exists in the perfectly fresh state, as may be seen in the large cells of the fresh spinal cord which have been isolated after the addi- tion of serum, and is very distinct in preparations macerated in perosmic acid and other hardening agents, which either check the natural conversion of the fibrils after death into a granular mass, or which do not produce any granular coagulation. tp 2 g 3 CD B tr" O O b3 2 CO CD S « H r+ O S. >> g- i CPJ ft p c' -: B 1 K tn o >-i CD ^ p O o- l-t3 3 P ^5 Q c+ P '^ c/ _J. ►1 CD o o K p 2 ht- a CD PJ / I ■ 3 o- B P o re- I - ■ ■ « 180 STEUCTUEE OF THE NEEVOUS SYSTEM, BY MAX SCHULTZE. Remak* first called attention to this fibrillar structure, and it -was subsequently further investigated in the ganglion cells of various parts by Leydig, Beale, Frommann, Arnold, K61- liker, and myself,f although up to the present time there has not been complete agreement between the different observers in regard to its nature. In consideration of the great difficulty experienced in isolat- ing fresh ganglion cells, and in determining their distribution, it appeared to me worth while to subject to severe scrutiny, in the fresh state, those parts of the brain of the Torpedo in which, as has long been known, large ganglion cells, similar to the motor cells of the spinal cord, are accumulated in great numbers.^ It was most convincingly shown here that the large cells removed from the living animal, and prepared in serum, in which they were capable of being easily isolated, possess, both in their processes and in their proper substance, an exquisitely delicate fibrillar structure. In large specimens the interfibrOlar substance is strongly tinged of a yellow colour, and is in some parts coarsely granular. These circumstances render the investi- gation of the direction of the fibres difficult, so that young specimens are to be preferred for examination. Each of the numerous processes of these ganglion cells receives a compound fibril from the cell substance, giving the impression that the whole mass of fibrils given off by ganglion cells only traverse it. The nucleus of these cells is seen with a sharply defined outline lying imbedded in the finely granular fibrOlated mate- rial, but does not appear to stand in any direct connection with the fibrils which cover its external surface. Its substance is homogeneous, and it contains in its interior a large nucleolus which stands out in strong relief as a highly refractive sphe- rical body, and conceals one, or more rarely several, vacuolse. We may regard such a ganglion cell, from which a peripheric- ally directed nerve fibre proceeds, as representing the source * Monatsberichte der Akademie der Wissenscliaften zu Berlin, 1853. t See Kblliker, Handbuch der Oewehelehre, 5. Auflage, p. 251, and the woodcut on p. 275. J Ohservationes de Structura cellularum fibrarumque nervearum. Bonner Uaicersitats Programm, Aug., 1868. Fig. 30. •\^ V ^ \ \ U I. / Fig. 30. Ganglion cells from the electric lobes of the hrain of the Torpedo, medium-sized specimen, x 600. a, axis-cylinder process ; the remainder, arborescent processes, recent. After short maceration in sermn containing a little iodine. 182 STEUCTURE OF THE NEEVOUS SYSTEM, BY MAX SCHULTZE. and origin of this axis cylinder, but only in the sense that the fibrils which compose the axis cylinder are collected into a group from the arborescent processes of the cell ; and thus the fibrils which are seen traversing the substance of the ganglion cell do not originate in the cell, but only undergo a kind of arrangement in. it, and then pass to the axis-cylinder process, or extend into the other branched processes. The researches of Deiters have rendered it probable that at the origins of the cerebral nerves the groups of ganglion cells which were described by Stilling under the term nerve nuclei, contain ganglion cells which closely resemble those of the an- terior and posterior comua of the spinal cord, especially in the circumstance that they give off" only one periphericaUy directed axis-cylinder process, the remaining processes breaking up into a ramification of primitive fibrils. It is well known that a considerable number of ganglion cells are found distributed through the brain, which do not directly give origin to periphericaUy coursing fibres ; as, for example, the retort-shaped ganglion cells of the cortex of the cerebellum, and the peculiarly shaped cells of the grey cortical layer of the cerebrvim, for the exact description of which we are indebted to the recent investigations of Rudolph Amdt* and Meynert.f In the former, according to Deiters,| the a2ygous process directed towards the white substance of the cerebellum corre- sponds to the axis-cylinder process ; and it is known that the periphericaUy coursing processes of these cells branch in an arborescent manner. Other microscopists, as Gerlach,§ have observed ramifications occur in the centricaUy directed process. It is therefore scarcely justifiable, in the present state of our ' knowledge, to institute a precise comparison between these cells and those which are found in the spinal cord. On the other hand, I have myself seen a fibrillar structure in these ganglion cells of the cerebeUum and their peripheric processes with the utmost distinctness, as, indeed, had previously been observed * Archivfiir Mihroskopische Anatomic, Band iii., p. 441. f Vierteljahrsehriftfiir Psychiatrie, Bande i. and ii. \ Loc. cit., p. 72. § Mikroskop. Studien, p. 11. MODE OF ORIGIN OF NERVE FIBRES IN NERVE CENTRES. 183 by Kolliker in their processes * so that in this respect there does not appear to be any diiFerence between the two sets of cells. The same holds good for the cells of the grey cortex of the cerebrum. As Meynert and Amdt state, these possess a thicker peripheric process and a large number of branched processes, which are directed towards the white substance. The ganglion cells have a more or less conical form, the base of the cone being directed to the white substance, and sending forth a number of processes which quickly ramify, whilst the apex of the cone is contiuuous with a single, longer, thicker, and at first unbranched process. In accordance with the observations of Mejniert, however, I have seen this process, which has been compared to the axis-cylinder process, divide, sooner or later, in a dichoto- mous manner, and undergo further subdivision in cells which had been completely isolated by maceration in iodized serum. I have witnessed a similar division in the pedunculated ganglion cells of the Pes huffocampi major, respecting which Deitersf was of opinion that the thicker process, constituting the stalk of the cell, was an axis-cylinder process. Nevertheless, I am unable to admit that either these cells or those of the grey cortex of the brain can, without further investigation, be classified with the multipolar cells of the spinal cord. Still it is quite true that the cells of the cerebrum, as I have already observed, possess an exquisite fibrillar structure, and rather appear as a point of junction and intersection for nerve fibrils that are already developed, than as a point of origin for those which have not hitherto been in existence. In addition to the larger cells of the cerebrum which have just been mentioned, an enormous number of smaller cells are found in that organ, the nuclei of which are invested by only a small quantity of cell substance. It has been demonstrated that some of these give off processes, of which the ultimate destination is certainly not known, but which are, nevertheless, sufficient to characterise the cells as nerve cells, and to distin- guish them from the connective tissue cells that are undoubtedly present in the spongy connective tissue of the central organs * Handhuch der Oewehelehre, 5. Auflage, 1867, p. 243. t Loc. cit., p. 66. 184 STRUCTURE OP THE NERVOUS SYSTEM, BY MAX SCHULTZE. ot the nervous system. Amongst these small cells, some are multipolar, some bipolar, and some unipolar. They form thick layers in the cerebellum, and both Gerlach* and more recently Franz Schulzef have shown that their processes consist of im- measurably fine fibrils. If we therefore venture to inquire into the central origin of the primitive fibrils in the brain and spinal cord, which appear to exist already completely formed in the larger ganglion cells, we may suppose that it is from these extremely small and, in part at least, unipolar nerve cells, though it must be admitted that this is pure hypothesis. In the present state of our knowledge, however well we may be acquainted with the peripheric mode of termination of a great number of nerve fibrils, it cannot be said that the mode of central origin of any single fibril has hitherto been proved. We may, however, conclude from analogy that the central ex- tremity is to be sought either in the cell substance of the nerve cells, or iu the nucleus, or in the nucleolus. Observations have been made which render aU these three modes of central termi- nation of the nerve fibrils probable ; but no perfectly satisfac- tory conclusion can be said to have been as yet attained on this point ; and it is even conceivable, according to my observations, that there is no actual termiuation of the fibrils in the brain or spinal cord ; in other words, that aU fibrils originate at the periphery, and thus only traverse the ganglion cells. The question of the relation of the nerve fibres to the ganglion cells appears, from what has been stated above, to be still an open one on certain points. If the view long ago entertained, especially by Valentin, that the nerve fibres only coil roand the ganglion cells, and do not enter into more direct connection with them, is opposed by the brilliant investigations of Eemak and Helmholtz, still the question of the centric mode of origin of the nerve fibres has not yet been thoroughly solved. It is obvious that the mere interruption of a nerve fibre in some part of its course by a bipolar ganglion cell, as was so beauti- fully described and delineated by Bidder in 1847, afi'ords no informa- tion respecting its centric origin. Such a ganglion cell is to be regarded * Mikroshop. Studien, Taf. 2. t Ueher der feineren Sau der Rinde des hleinen Gehirns, " On tlie Minute Anatomy of the Cortex of the Cerebellum." Rostock, 1863, flg. 11. MODE OF ORIGIN OF NERVE FIBRES IN NERVE CENTRES. 18^ as composed essentially of only a nucleated enlargement of the axis cylinder. If we pass to a more central portion of the nervous system, we meet with the multipolar ganglion cells of the spinal cord, or of the medulla oblongata, from which, according to the important dis- covery of Deiters, the axis cylinder of the fibre in question proceeds as an undivided process. The numerous other processes of the cell connect it, and by its means the axis cylinder, with more distant regions of the central organs, and probably also of the peri- phery of the body, but clearly do not entitle us to regard the ganglion cell as the exclusive origin of the nerve fibre. If we compare the axis-cylinder process with the stem of a plant and its divisions, and the peripheric terminal organs with the branches, leaves, and flowers, the ganglion cell is equivalent to the root stock, and the branched processes to the subterranean root fibres. It is requisite to follow these out in order to arrive at the extremity opposite to the peripheric termination. In consequence of the evidence I have adduced, of the exquisitely delicate fibrillar structure of the ganglion cell substance, and of all its processes, a path is opened by which we may investigate the true central terminations of the fibrils entering into the composition of the axis cylinder. Unfortunately, the indi- vidual fibrils within the substance of the cells escape all accurate observation. The above comparison of the ganglion cells and their processes with the root stock, stem, and root fibres of a plant, is, after all, like most comparisons, only an imperfect one. The branched processes of a multipolar ganglion cell, such, for instance, as may be found in the anterior horn of the spinal cord, have certainly not all been satisfactorily ascertained to pass as primitive fibrils to the axis-cylinder process ; but rather this receives only a single group, the remainder extending as branched processes in other directions. Thus the ganglion cell con- stitutes a common point of union of numerous separate fibrils proceed- ing from widely different regions of the nervous system ; and whilst one of these associated bundles becomes the axis cylinder of a fibre, and after becoming invested by a medullary sheath, immediately runs peripherically, the others pass in unknown directions. It remains to consider whether, admitting that a large number of the fibrils are abeady formed, and only traverse the ganglion cells, there may not be some which do actually originate in these. In regard to this point, the interfibrillar granular substance is first to be noticed, which is probably a residue of the embryonia protoplasm, by the agency of which the fibrils are differentiated ; a substance which pos- sibly remains in greater abundance in the immediate vicinity of the 186 STBTICTURE OF THE NERVOUS SYSTEM, BY MAX SCHULTZE. nucleus, and there retains a power allied to that which it possessed when in the embryonic state. Yet, however probable it may appear that the several fibres arise in and from this substance, no observations have as yet been made which establish it with perfect certainty. An- other mode of origin of new fibrils or thicker fibres from the ganglion cells has, on the contrary, been suggested by various observers. Since Harless* stated that the nuclei and the nucleoli of the large cells of the brain of the torpedo were the points of origin of the nerve fibres, the same view has been entertained by many others in regard to other ganglion cells, and especially for those of the sympathetic of the frog, as in the first instance by Axmann, Lieberkiihn, and Wagner, and subsequently by Beale, Arnold, Frommann, Jolly, and Courvoisier. But it was noticed by Frommann and Arnoldt as occurring also in the cells of the spinal cord and in those of the brain ; and Meynert stated that the nuclei and the nucleoli were centres for fibres, the fineness and deli- cacy of which render them comparable to our primitive fibrils. I agree with Kolliker and others, however, in the statement that this, at least, is not the ordinary condition, and I have not been more success- ful than Kolliker in obtaining any positive evidence of such a mode of origin of the fibres in question. Although anastomoses occur between adjoining ganglion cells, it is a matter of much difl&culty to acquire any certain information respect- ing the constancy or frequency of their occurrence. As there are ganglion cells with two nuclei, like those, for example, that, according to Guye and Schwalbe, are constantly met with in the sympathetic, and occasionally in the brain of the rabbit, so we may refer one form of the anastomoses occurring between ganglion cells to the type of bi-nucleated cells ; those, namely, in which a short thick bridge unites two nucleated corpuscles with one another. Such anastomoses have recently been described by Meynert, E. Arndt, and Besser, as they are seen in the cortex of the cerebrum. They appear, however, to occur but rarely. The numerous anastomoses supposed to take place between the large ganglion cells in the nuclei of origin of various nerves in the spinal cord and medulla oblongata, and depicted amongst others by Schroder v. der Kolk and Lenhossek, have long been recognised as illusions. Other anastomoses between the ganglion cells of the vari- ous cortical layers of the brain, which are stated to occur by Meynert, require further corroboration. It is quite a matter of doubt whether * Mviller's ArMv, 1846, p. 317, Taf. 10. f Arnold, in Virchow's Archiv, Band xli., Taf. 4. ORIGIN OF NERVE FIBRES IN NERVE CENTRES. 187 we shall ever be able to observe tbose anastomoses between ganglion cells which result from the union of the finest outrunners of the branched processes, since the most carefully conducted methods of isolation adopted by Deiters have only led to negative results. Nor have my own numerous researches on the ganglion cells of the electric lobes of the torpedo, which are admirably adapted for this investiga- tion, been more fortunate ; for although Kud. Wagner long ago stated that anastomoses could here be distinctly seen, I, notwithstanding the employment of better modes of isolation, have been unable to discover a single instance of their occurrence. Lastly, an interesting accession to our knowledge of the terminations of the nerves may here be noted, with which I have become acquainted whilst these sheets were passing through the press. Paul Langerhans found, as he has described in Yirchow's Archiv, Bandxliv., p. 325, and depicted in the twelfth plate of that volume, that processes of the non-meduUated fibres of the cutis in man penetrate between the cells of the rete Malpighii, exactly in the same way as has been described (p. 164) by Hoyer and Cohnheim as the mode of termination of the nerves in the cornea. These nerve fibrils, however, do not terminate by free extremities ; but enter, as is rendered highly probable by Langerhans, in all instances, into small cells lying between the deeper cells of the rete mucosum, which again give off several fine fibrous outrunners into the upper layers ; and these finally terminate with slightly clubbed extremities just beneath the horny layer. These nerve fibres have no connection with the tactile corpuscles. By means of these observations, which supple- ment those of Tomsa and others respecting the mode of termination of the nerves in the corium in several important particulars, the inti- mate connection between the terminations of the nerves and the epithelial layers in the skin of man has been demonstrated, which, since the year 1856, has been gradually shown to occur in all the other , organs of sense, although it was in the first instance received with so much mistrust. Thus one more argument in favour of nerve plexuses representing the terminal structure falls to the ground. CHAPTER IV. THE TISSUE OF THE ORGANIC MUSCLES. By J, AKNOLD. The constituents of this tissue are fusiform contractile fibres, connective tissue, and cement, with vessels and nerves. FOEM AND GENERAL CHARACTERISTICS. — Fusiform fibres of this tissue are sometimes designated as smooth muscular fibres, or as contractile or muscular fibre cells ; and when examined in an isolated and uncontracted condition, appear as sub-cylindrical fibres, generally with two or more flattened sides, and occasion- ally in the form of flattened oval plates. They for the most part resemble a spindle, being slightly swollen near the centre, and pointed towards each extremity (fig. 31, a); but the thickest part is frequently not quite centrally situated, being nearer to one end than to the other (fig. 31, b). In many instances the extremities of the fibres are not single, but more or less divided, so that processes are given ofl" from one or both poles ; and in accordance with the depth to which the division extends, the length, form, and relative position of these processes vary (fig. 31, c). Thus, when the depth is slight, they are small, short, and more or less parallel to one another ; when, on the other hand, it is considerable, they are long, broad, and diverge from each other almost at right angles. This fork- ing of the muscular fibres occurs especially in those places where the fasciculi are arranged in the form of a network, and may properly be regarded as peculiar to this variety of the tissue. Such fibres, at aU events, occur very frequently in the urinary bladder of the frog, at the points of intersection of the fasciculi. STR0CTUEE OF ORGANIC MUSCULAR TISSUE. 189 The surfaces of the muscular fibres, as well as their borders, are generally smooth; the latter are, however, occasionally Fiff. 31. Pig. 31. a, Muscular fibres treated with, serum; 6, muscular fibres fi-om tbe muscular tissue of the intestine, isolated by means of nitric acid ; c, dichotomously divided miiscular fibres from a pleuritic mem- brane. Q 2 190 THE TISSUE OF THE OKGANIC MUSCLES, BY J. AENOLD. slightly serrated, and the former are sometimes uneven, — appearances which, like the curving of the ends, must be regarded as consequences either of manipulation in the prepara- tion of the specimen, or as post-mortem changes. Another explanation must, however, he given of the trans- verse striae, which occur in considerable numbers, and at regu- lar distances, on one or both sides of the fibres. These, from the concordant results of the observations of Meissner* and Heidenhain,-f- are probably to be regarded as phenomena of contraction. The length of the fibres varies from 0045 — 0"230 milli- meters ; the mean length is from 0048 — 0089 millimeters ; the breadth 0004— O'Ol millimeters. Structure of the smooth Muscular Fibres. The substance of the muscular fibre cells examined in serum whilst perfectly fresh has a dull appearance, except at the edges, which are frequently somewhat clearer. In many speci- mens no further indications of structure are perceptible, but in others there is a more or less distinct longitudinal striation, which is often particularly obvious near the extremities, and is rendered still clearer by the addition of a few drops of a O^Ol per cent, solution of chromic acid, or of solution of gold con- taining O'l per cent. (fig. 31, a). In many fibres, dark, highly refractile granules are imbedded in various parts, apparently without any definite arrangement. These, which disappear on the addition of alcohol, are not to be confounded with the granules that are commonly found at the two ends of the nucleus. The latter form pyramidal rows extending for a greater or less distance from the poles of the nucleus to which their bases are applied towards the ends of the fibres to which their apices point. These granules are imbedded in a substance which has likewise the form of a pyramid, and is difierentiated from the adjoining material by its greater transparency when examined by transmitted light. In many fibres a second line is to be observed, which lies at some distance from, and not * Zeitschrift fiir rationelle Medicin, Band ii., 1858, t S'tudkn des Physiologischen Instituts, 1861. STRUCTURE OF ORGANIC MUSCULAR TISSUE. 191 quite parallel to, the margiii. This forms the line of demarcation between an external darker and an internal clearer and brighter layer. A similar differentiation of parts may be discerned on examining the transverse section of a fibre in which the cortical layer appears as a dark ring investing the remaining brighter portion. The outer contour of this is always distinctly marked, but its inner is never very sharply defined. The thickness of the cortical layer varies, and in many fibres it is altogether absent. Margo* gave a description of certain small points arranged serially in the interior of the fibre cells, and separated from each other by minute intervals ; whilst Wagenerf first described the distinct longitudinal striation that gives the impression of a fibrillar arrangement near the extremities of the fibres. The rows of granules extending from the poles of the nucleus were first mentioned by Klebs,J and subse- quently by Franlienhauser§ and Wagener.|| Nucleus. — General form and sizi. — The nucleus of the fibre cells is generally single, very rarely multiple, always dis- tinctly rod-shaped, and either rounded at the ends or pointed. It is occasionally curved or spirally convoluted. On transverse section the nucleus appears either round or subangular. It invariably occupies the fusiform enlargement of the fibre, but its position in regard to the transverse diameter is less constant, since on section it is sometimes seen to lie in the middle of the ring formed by the transverse section of the fibre, and sometimes near the margin. Moreover, the nucleus some- times lies obliquely in relation to the axis of the fibre cell. The length of the nucleus varies from 0015 — 0'022 millimeters, and its diameter from 0002 — 0003 millimeters. * Neue Untersuchungen iiber die Entwickelung, das Wachsthum und den Bau der Muskelfasern, " Recent Investigations on the Development, Growth, and Structure of Muscular Fibres," 1859. f Sitzungsherichte der Gesellschaft zur Beforderung der gesammten Naturwissenschaften, No. 10, 1859. X Virchow's Archiv, Band xxxii., 1865. § Die Nerven der Geb'drmutter und ihre Endigungen in den Glatten Mus- kelfasern, " The Nerves of the Uterus, and their Mode of Termination in smooth Muscular Fibres," 1867. II Loc. cit. 192 THE TISSUE OF THE OEGANIC MUSCLES, BY J. ARNOLD. Structure of the Nucleus. — In perfectly fresh mus- cular fibres treated -with serum the nucleus may indeed be perceived, but its contour is not very well defined ; on the addition, however, either of chromic acid (O'Ol per cent.), acetic acid (1 per cent.), or solution of chloride of gold (O'l per cent.), the contours become sharp and dark, whilst the previously homogeneous contents appear finely granular. In the substance of many nuclei, especially when treated with serum and chloride of gold, but less distinctly with acetic acid, there may be observed from two to four large (from O'OOl — 0'002 millimeters) highly refractile round granules (fig. 31, a). If one only be present, it lies near the centre, or frequently somewhat nearer to one of the poles of the nucleus. If, on the other hand, two are present, they are situated at the two ends of the nucleus. These granules are most distinct in transverse sections of the nucleus, and are then seldom absent. They may also be per- ceived in association with isolated nuclei, and in such cases they either lie close to the surface of the latter, or project more or less from its margin. Frankenhauser* has paid particular attention to the structure of the nucleus ; and although Hesslingt had previously noted the exist- ence of a nucleolus in the interior of the nucleus, Frankenhauser first stated that it was an essential and a never-failing constituent. Piso-Borme| also observed the presence of nucleoli. Connection and Arrangement. — The contractile fibre cells are united into fasciculi or membranes of various size, through the intervention of a connecting material. The fibres are so arranged that the ends of two or more are inserted between the diverging extremities of two which touch at their dilated middle portion, an arrangement by which an intimate union of the several structures is efiected. In cases where the greater number of the fibres are superimposed by their flat sur- faces, a membrane is formed, consisting of one or many layers, the fibres for the most part preserving the same direction in * Zoc. cit. f Gewebehhre, 1866. X Moleschott's Untersuchungen, Band ix., 1860. STRUCTURE OF ORGANIC MUSCULAR TISSUE. 193 each layer, thougli they may pursue very different directions if several layers be present. Where the fibres are united, not in one, but in several directions, fasciculi of fibres are produced. These vary in length and thickness, and either run parallel to each other, or cross at a more or less acute angle, or, lastly, pre- sent a plexiform arrangement, and frequently anastomose . It is from these differences in the directions taken by the fibres, and iu their mode of union, that the irregularities observed in sec- tion result. For if the section be carried transversely through a portion of the tissue ia which the muscular fibres run parallel, round or subangular rings, lying in close proximity, are met with, presenting a central or laterally situated transversely divided nucleus ; whilst if the bundles of fibres run in various Fig. 32. v/. V.,-, -'*tV. ^-'^^■^ I ^ y. i Fig. 32. o, Transverse section of the longitudinal fibrous layer of the intestine of a Frog ; b, transverse section of muscular bundles from the uterus of a Sheep ; c, muscular trabeculse from the urinary bladder of a Frog, treated with acetic acid. 194 THE TISSUE OF THE ORGANIC MUSCLES, BY J. AKNOLD. directions, transverse and oblique sections of the fibres and nuclei appear (fig. 32, a and h). The quantity of connecting sub- stance is sometimes very sparing, so that the surfaces of the fibres are in almost direct contact, or are separated only by very thiu layers or columns of the connecting substance. Occasion- ally, however, it is more abundant. In the former case the muscular fibres appear, on transverse section, as closely com- pressed polygonal areas; in the latter, as roundish spaces, between which are more or less broad laminae of the connecting sub- stance. This material is homogeneous, except that it contains numerous pale branched cells, the processes of which inter- communicate, and also a moderate number of dark, highly refractile granules, O'OOl to 0-002 millimeters ia diameter, which are always visible. They sometimes lie in the centre of the connecting material, sometimes close to the borders of the spindle-like expansion of the fibre cells. They closely resemble the granules of the nucleus. In specimens treated with solu- tions of chloride of gold they present a dark violet tint, and are always much darker than other parts of the connecting substance (fig. 32, c). Both the muscular fasciculi and the membranous expansions are invested both externally and internally by connective tissue, which, for the most part, is distinctly fibrillar, and contains loose fibres of connective and elastic tissue. By means of this the several laminae are united into a membrane, and the fibres into fascicidi. The latter are sometimes so combined as to form a tough, dense, fiattened or roundish mass, which, as Treitz* has shown, fulfils the office of a tendon. Vessels. — The layers of the connective tissue investing the fasciculi and membranes of organic muscular tissue, are traversed by numerous arteries of various size, which break up into a network of capillaries, firom which again the veins take origin. These, like the arteries, run in the investing connective tissue ; but the capillaries penetrate the muscular layers. The meshes of the capillary plexus are of moderate width, and are Prager Vierteljahresschrift, Band i., 1852. NERVES OF ORGANIC MUSCLE. sometimes elongated, and at others round or rhomboidal. The vessels themselves present no important peculiarities. Nerves. — In aU organs or parts of organs, in the composition of which the organic muscidar tissue plays an important r61e, and apart from diflferences occurring in particular instances, a similar arrangement of the nerves is to be found. The different nerve fibres contain a variable number of dark-edged and pale nerve tubules. Of these, the former present the features character- istic of the medullated fibres, vary in size, and are usually the most abundant. There are, however, a few fasciculi, which chiefiy consist of the pale fibres, and contain but a small number of the dark-edged variety. The former appear as fine glistening filaments, of from O'OOIS to 0'0023 millimeters m breadth, with here and there a nuclear enlargement of O'OOS to 0005 milli- meters ia diameter, a peculiarity which at once enables them to be distinguished from even the finest doubly contoured fibre. The fasciculi thus composed of pale and dark-edged fibres, lie in the connective tissue surrounding the muscle bands or mem- branes, and form wide-meshed flat plexuses, in which the ad- joining fibres cross and interchange from one plexiform layer into another. In the plexus formed by the larger nerves {prin- cipal or fundamental plexus) ganglion cells lie scattered, which are often collected iato microscopic ganglia; and from the same plexus fibres are given oflf, which are at first dark edged, but subsequently assume the form of broad pale bands. These pre- sent a fine longitudinal striation, with nuclei at various dis- tances, which are sometimes smaller than the fibres, and at others cause their edges to project. The pale fibres are from 0'004 to 0-005 millimeters in breadth, and their nuclei have about the same diameter. After running for a certain distance they rapidly diminish in size, and split into finer glistening fibres, which have nuclear enlargements and a diameter of from O'OOIS to 0'0023 millimeters, and are similar to those contaiaed ia the fasciculi. These fibres form plexuses with meshes of moderate size, and of rhomboidal or elongated shape. Bodies resembling nerve cells or nuclei with distinct nucleoli occupy the points of junction. Pale fibres, proceeding directly from the main or ftmdamental plexus, enter into this plexus. The 196 THE TISSUE OF THE ORGANIC MUSCLES, BY J. ARNOLD. network of pale fibres, just described, lies immediately upon or beneath the muscular laminse, embraces the muscular bundles, and probably intercommunicates freely with thefibres proceeding from the fundamental plexus to form an intermediate plexus (fig. 33, 6). In the larger muscular fasciculi, portions of the inter- mediate plexus are sometimes found withia the layers ; but in general the arrangement above described is that which obtains. Fine fibres are given off from the intermediate plexus, which penetrate between the muscular fibres, and at the points of division still present nuclear enlargements, though these are subsequently absent, the fibres at the same time becoming rapidly attenuated (fig. 33, a). After they have undergone re- peated division, they appear as fine, cylindrical, dark filaments, of from 0-0003 to 0-0005 millimeters in diameter. These con- tain, both in their course and at their points of division, dark granules of round, elliptical, or polygonal form, which, by their somewhat larger size (O'OOl to 0-0018 millimeters) and brighter appearance, serve to indicate the course of the fibres (fig. 33, a and V). They are tolerably distinct in preparations moistened with serum; but, as has already been stated in the description of the connecting substance, the delicate plexus formed by the fibres is not very perceptible without the addition of other reagents. The delicate fibres bearing nuclei, which have just been described, unite with one another to form very delicate networks, which traverse the connecting substance occupying the interstices of the muscular fibres, and are seen winding round the fibres in the form of delicate dark lines, interrupted •with nuclear enlargements, and constitute the intra-muscular plexits. Transverse sections of frozen portions of muscle treated with serum_and chloride of gold permit these fine nuclei-bearing fibres, with their relations to the connecting substance on the one hand, and with the muscular fibres on the other, to be rea- dily perceived (fig. 33, c). From the intra-muscular plexus, and chiefiy iu the vicinity of the spiadle-Hke enlargements of the muscular fibres, dark peculiarly stiff filaments proceed, having a diameter of 0-00015 to 00002 milHmeters. These penetrate into the interior of the fibres, and extend towards the nucleus. Several of these filaments, or one only, in accordance ■with the number of granules in the nucleus, may penetrate NEEVES OF ORGANIC MUSCLE. a Fig. 33. 197 Fig. 33. Nerve ramifications and terminations in a muscular fasci- culus taken from the urinary bladder of the Frog (prepared in chloride of gold solution) ; J, nerve ramification in the muscular coat of a small artery (prepared in acetic acid, 1 per cent., and chromic acid, 1-lOOth per cent. ; c, ramification of the nerve, as shown on a transverse section of muscular fasciculi from the uterus of a Sheep. (The section was made from a portion of frozen muscle which had afterwards been treated with 0-01 per cent, of chromic acid.) 198 THE TISSUE OF THE ORGANIC MUSCLES, BY J. ARNOLD. the muscular fibre from different sides ; but, whatever may be their number, they all pass towards the granules of the nucleus, which might therefore be regarded as the extremities of the fibres, were it not that in many cases they again give ofi" fila- ments, which, traversing the substance of the nucleus and of the muscular fibre ia the opposite direction, enter the intra-mus- culai: plexus. Consequently these granules are not the free ends of the smallest nerve fibres, but only the nodal points of the finest nerve plexus lying within the nucleus. The best demonstration of these relations also is to be obtained from transverse sections (fig. 33, c). After Klebs* liad in the first instance recognised that an intimate relation existed between the finest nerve filaments and the substance of the muscular fibres, it was shown by Frankenhauserf that the former penetrated into the interior of the latter, and proceeded to the granules of the nucleus, to which he appHed the name of nuclear cor- puscles (Nucleoli, Kernkdrperchen). The statements above made are the result of careful investigations which I have elsewhere more fully reported. As regards the relations of the finest nerve filaments to the substance of the muscular fibre and its nucleus, as well as to the intra-nuclear granules, I coincide with Frankenhauser. On the other hand, I was unable to recognise the actual extremities of the nerve fibres in the granules of the nucleus ; they rather appear to me as nodal points of the finest nerve plexus lying in the interior of the nucleus. Distribution. — Smooth muscular fibres are widely distri- buted through the body. In the organs of respiration they are seen to form layers of circular fibres in the posterior wall of the trachea, and in the bronchi. Their presence in the walls of the alveoli of the lungs in man and mammals is still doubtful, being admitted by some observers, whilst it is denied by others. Muscular fibres are, however, certainly present in the alveoli of the lungs in infants, and in the lungsacs of the frog, sala- mander, and triton. * Loc. cit. f Die Nerven der Gebarmutter und ihre Endigungen in den Glatten Mushelfasern, " The Nerves of the Uterus, and their Mode of Termination in smooth Muscular Fibres," 1867. DISTRIBUTION OF ORGANIC MUSCLE. 199 In the alimentary canal, smooth muscular fibres form mem- branes, which are to be found from the lower part of the oeso- phagus to the extremity of the large intestine. They also form a proper layer in the mucous membrane, the so-caUed tuuscu- laris mvxosa, and in the small intestine extend from thence into the villi. The excretory ducts of many glands possess a proper muscular layer, as may be seen in the pancreatic duct of the Ox, Cat, Pigeon, and Carp. According to Tobien, the ducts of all the salivary glands contain muscular fibres ; but Kolliker only saw a few in Wharton's duct, and Henle but a few in Steno's duct ; whilst, according to Ebertb, they are not present in the ducts of the salivary glands generally. Smooth muscular fibres are also found in the lymphatic glands, and in the spleen. Opinions are, however, divided in regard to the distribution of the muscular tissue in the latter. In man, muscular fibres are contained in the capsule of the spleen ; and some also maintain that they are present in the trabeculse. The quantity of smooth muscular fibres in the cap- sule of the spleen in various animals differs to a considerable extent. They are very abundant in the porpoise, hedgehog, dog, cat, pig, mole, rat, and rabbit, but exist only in small quantity in the ruminants and in apes. In the pig, dog, ass, sheep, rab- bit, horse, hedgehog, guinea-pig, peccary, bat, and cat, again, nearly all the trabeculse contara muscular fibres ; but in some, as the ox, these fibres are only present in the more delicate tra- beculse. Smooth muscular fibres are also found in the walls of the gall bladder, in the cystic duct, and in the ductus communis choledochus. They constitute an essential portion of the middle coat of the vessels ; they form connected laminae and membranes in the parietes of the calyces and pelvis of the kid- ney, and of the ureters and urinary bladder. They are found beneath the mucous membrane of the prostatic and mem- branous portions of the urethra, both in the male and female. Smooth muscular fibres are widely distributed in the male sex- ual apparatus, entering into the composition of the vas deferens, the vesicula seminalis, the prostate, the corpora cavernosa, Cowper's glands, and parepididymis ; between the tunica vagi- nalis communis, and propria, and in the dartos. In the female 200 THE TISSUE OF THE OEGANIC MUSCLES, BY J. ARNOLD. sexual organs it occurs in the oviducts, in the broad and round aud in the anterior and posterior ligaments of the uterus. It is by far the most important constituent of the uterus. In the vagina it forms an actual muscular membrane. Its presence in the ovaries, whilst admitted by some, is denied by others. Numerous smooth muscular fibres are found in the nipple and in the surrounding areola, also near the hair follicles, where they have received the name of arrectores pih ; and in the sebaceous and sweat foUicles. Finally, the presence of smooth muscular fibres in the ciliary muscle, efiecting the con- traction and dilatation of the iris, is to be noted, and I may also refer to the discovery of smooth muscular fibres in the membranes of the egg. Methods of Investigation. — The more delicate points in the structure of organic muscular fibre are best demon- strated in preparations that have been treated with serum, chromic acid (001 per cent.), and solution of gold (O'l per cent). The urinary bladder, lungs, and smaller arterial vessels of the frog may be particularly recommended as forming good mate- rial for examination ; but for the isolation of the individual fibres without the application of any reagents, the muscular tunics of the intestine are most appropriate. The means usually employed to effect the separation of the elementary fibres are acetic acid diluted with from 3 to 5 per cent, of water, nitric acid (20 per cent.) and solutions of potash (32 per cent.), all of which act in the same way by dissolving the connecting substance, and thus enabling the muscular fibres to be isolated. Maceration in iodized serum, and in dilute chromic acid (O'Ol to 005 per cent.), is in some cases very effective. For the pre- paration of transverse sections, alcohol, chromate of potash, and chromic acid — the last two being employed alternately — consti- tute excellent hardening agents. If it be desired to examine the muscular fibre in as fresh a state as possible, transverse sec- tions may be prepared from frozen portions of muscle, which have then been placed in serum. Such sections are, moreover, well adapted for being treated with gold, silver, and dilute chromic acid solutions. The course and termination of the nerves are distinctly seen in preparations macerated for from two METHODS OF INVESTIGATING ORGANIC MUSCLE. 201 to four minutes in 4 cub. centim. of a solution of acetic acid, con- taining from 0"5 to 1 per cent., and then for half an hour or more in 4 cub. centim. of a O'Ol per cent, of chrondc acid. Besides this combined action of acetic and chromic acids, I can also recom- mend acetic acid and alcohol both for the investigation of gold preparations and of sections treated with solutions of gold and chromic acid. The best materials are the urinary bladder and the smaller arteries of the frog. For treating the sections, carmine, anilin, chloride of palladium (F. E. Schubie), and picric acid (Schwarz) may be employed. CHAPTER V. THE MODE OF TERMINATION OF NERVE FIBRE IN MUSCLE. By W. KtfHNE. We exercise control over our muscles through the agency of the nerves, and it is through the nerve paths alone that the wiU excites them to contract. The question therefore naturally arises. In what way do nerves terminate in muscle ? Inquiries were made on this point long before instruments and modes of investigation could furnish any answer, and these led to ever new and ever unsatisfactory researches. We now believe that we are able to perceive the direct con- tinuity of the contractile with the nervous substance. Yet it may stiU happen that, in consequence of further improve- ments in our means of observation, that which we regard as certain may be shown to be illusory. Nevertheless, work is indispensable, and we must press on till we reach the point in the domaiQ of morphology, in which order and law become the last expression of our knowledge. Up to the year 1840 all attempts to give a satisfactory account of the ultimate termi- nation of the motor nerves failed. The admission of loop-like extremities in the muscle can only be regarded as an expression of ignorance, and of the impossibility of following the course of the nerves in muscle with clearness. But suddenly and accidentally an unprejudiced observer, in investigatiag the interesting small Tardigrada, recognised nearly aU that we know at the present time regarding the ends of the motor neives. In 1840, Doyfere discovered that the nerve ap- plied itself to the muscular fibre by means of a conical enlarge- ment. Both of these structures are destitute of sheaths or THE MODE OF TERMINATION OF MOTOR NERVES. 203 investing membranes in the Tardigrada(or bear animalcules), and the nervous and muscular tissues thus come into direct contact. The observation of Doyfere long remained misunderstood, and passed into oblivion in consequence of the general acceptance of the view of Ernst Briicke and Joh. MiiUer, to the effect that the primitive nerve fibres undergo division between the muscular fibres. It was, indeed, completely forgotten when R. Wagner recognised with much discrimination the value of that mode of nerve termination which Savi first discovered in the electrical organs of the Torpedo, and applied it as a fact of general significance to all peripherically distributed nerves. It then first became intelligible how so small a number of nerve fibres as those which are ordinarily contained in a motor nerve can influence such a much larger number of muscular fibres. In a care- fully written essay, Reichert showed that the pectoral cutaneous muscle of the Frog, which is composed of about 160 muscular fibres, receives only about six or seven primitive nerve fibres ; but the proportion was no longer unintelligible when far more, in fact nearly 300, terminal fibres, proceeding from the division of the latter, could be proved to be present. Of these investiga- tions, however, few or none were directed to the solution of the question respecting the proper termination of the nerves, but rather to their mode of division between the muscular fasci- culi. The latter point lies beyond the limits of the present paper, and we shall therefore content ourselves vsdth the descrip- tion of what is of most importance in regard to it. When thin transparent muscles or thin sections of muscles are examined, nerves of varying degrees of fineness may be seen, the course of which is seldom parallel, but frequently at right angles, to the direction of the fibres of the muscle. This is especially noticeable in regard to isolated nerve fibres, and to the terminal portions of such fibres. The muscles of different animals, and even the several muscles of the same animal, are very unequally supplied with nerves. In a few of the lower animals, as in Bowerbankia, the muscles appear to possess as many nerve as muscular fibres ; in others, especially in Fishes, there are sur- prisingly few, whilst amongst the warm-blooded Vertebrata the muscles of the eye, as a general rule, contain but few more muscular fibres than primitive nerve fibres. If we start with R 204 MODE OF TERMINATION OF MOTOE NERVES, BY W. KUHNE. the assumption that every muscular fibre must be supplied with at least one nerve fibre, even if this be the result of division, it is obvious that the muscular apparatus of Fishes, divided as it is to so great an extent by tendinous intersections, and which as a consequence of the shortness of these fibres, contains in an equal volume many more individual muscular fibres to be sup- plied with nerves, than the long-fibred muscles of other classes, can receive only a smaller number of primitive nerve fibres. The Fish would indeed have to carry a weighty mass of nerves, were the relation between the two tissues the same as in Mam- mals. Hence, nowhere are so many divisions of the primitive nerve fibres to be so easily found as in the muscles of this class. The large relative number of nerves distributed to the ocular muscles, and generally present in aU the muscles of Mammals, but as it would appear especially in the muscles of Man, is very suggestive in regard to the exact regulation of their movements, for the uncommonly fine adjustment of the ocular muscles would be unattainable if the excitation of one nerve fibre had as a con- sequence the excitation of as great a number of muscle fibres as in. the Frog, and still more as in the Fish. In regard to the general distribution of nerves, allusion may here be made to the well-known fact that considerable segments of every muscle may be met with in which no nerves are to be found, and that in particular the extremities of the muscles appear to be desti- tute of nerves for a considerable space. The muscles that are best adapted for the study of the mode of division of the nerves supplying them, are the musculus cutaneus pectoris of the Frog, and also the sartorius, the ocular and digital muscles, and the hyoglossus of the same animal ; the ocular muscles of the Fish, and amongst mammals those of the Cat, and, above aU, the thin muscles which extend from the vertebral column to the skin in the Snake. These may be examined almost whilst yet stiU. living, and merely flattened by a covering glass, or after being rendered transparent by means of a 1 per cent, solution of hydrochloric acid. After the discovery of Doyfere had shown the mode of con- nection of nerves without sheaths, with similarly naked muscular bands, the question naturally arose from a purely morphological point of view, whether transversely striated muscle, which TEEMINATION OF MOTOR NERVES IN INVERTEBRATA. 205 is invested by a sarcolemma, and to "which only nerves provided with sheaths are distributed, does not at some point allow the passage of these through the membrane. Still more strongly was the hypothesis respecting the continuity of the sheath of Schwann with the sarcolemma, or in other words, of the passage of the nerve fibre directly into the contractile substance, advanced by physiologists, thus leading the way to the establishment of all that has been discovered respectiag the termiaation of motor nerves since the time of Doy^re. We shall commence with the transversely striated muscles, proceeding from the lower to the higher groups of animals, and leaving on one side, for the present, the relations existing in the unstriated fibres, and the still very incompletely known but apparently smooth muscular fibres of the worm, and other stiU more lowly organised Invertebrata. The Mode of Termination of the Nerves in Invertebrata. The striated muscles of the Articulata consist of completely closed cylindrical tubes of sarcolemma, the contents of which present the well-known appearance of a stage or ladder-like arrangement of superimposed disks of muscle prisms* The muscle prisms are separated from each other in the transverse direction by a considerable amount, and in the longitudinal by a small amount, of homogeneous fluid material. All muscles, moreover, contain, besides those constituents which form the really contractile substance of the muscle, still another material that has some, though a less important, influence on the develop- ment of force. It is generally regarded as the remains of the original formative cells of the muscle, and is composed of nuclei with a distinctly double-contoured membrane, and transparent contents, often with nucleoli ; of vesicles of various form, without definite investment ; of granules ; and lastly, of a finely granular pappy mass. These masses may be very variously distributed in * The term " disks" was introduced into the description of muscle hy Mr. Bowman. The same parts were designated by Rollett "chief-substance disks." The muscle prisms have been also, after Mr. Bowman, termed " sarcous elements." E 2 206 MODE OF TERMINATION. OF MOTOR NERVES, BY W. KUHNE. the interior of muscles, sometimes appearing in the form of a few short striae, scattered through all parts of the fibre ; sometimes as long bands lying between the contractile substance and the sar- colemma ; and often, also, fillin g the interior of a canal miming through the whole length of the fibre. In many instances the muscles of Crustacea present these masses in the form of a com- plete cylindrical tunic lying between the sarcolemma and the muscular substance. The masses may again be entirely isolated, or may communicate through the entire muscular fibre ; those which lie in the central canals sending oflT radial processes which run towards the surface to joia with the superficial portions, whilst in those which lie immediately beneath the sarcolemma, the processes extend towards the extremities of the fibres, and thus come into contact with others. The most appropriate objects for the examination of the mode in which nerves termiaate, appear to be the muscles of insects, and amongst these the best are the muscles of the great black water beetle (HydrophUus piceus), which is to be preferred to the nearly allied Dytiscus marginahs. Instead of the muscles of the legs, it is better to employ the large colourless fasciculi lying in the thorax, which are attached by broad processes to the internal wing-like apodemata of the coxae. If the muscle be suddenly separated from both its attachments by scissors, we obtain a preparation which, either without any addition, or merely with the addition of a little of the blood of the beetle, or a drop of 0"5 per cent, solution of chloride of sodium, will pre- sent, after gentle manipulation with needles, many beautifully isolated muscular fibres. These fibres are quite free from con- nective tissue, and are only bound together by nerves and tracheae, both of which can be torn across with the greatest facility. Amongst the nerves many extraordinarily thick pri- mitive fibres are to be found, invested by a distinct mem- brane, beneath which are very pale vesicular, and in parts also very finely granular medullary sheaths, whilst the axial portions present a fibrillar structure. The thick nerve fibres undergo repeated division, rivalling in this respect the ramifi- cations of the bloodvessels of higher animals, and send off finer and still finer branches to the muscular fibres, each of which contains an extraordinary number of ultimate terminations. It MODE OF TEEMINATION OF MOTOE NEEVES IN AETICULATA. 207 may then be observed that the middle portions of the muscular fibres, at all points of their circumference, present rows of fun- nel-shaped processes forming little eminences of various size, the apices of which correspond to the points of entrance of the several branches of nerves. The latter appear in aU instances to consist only of 0. single axial fibril or axis cylinder; but this may usually be seen to divide into two strongly diverging branches immediately beneath the apex of the nerve cone or eminence, and it may also be followed for a short distance into the interior of the eminence. Fig. 34. Fig. 34. Muscular fibre, -witli the extremities of two nerves, from tlie HydropHlus piceus. At the termination of the nerve the medullary layer, which has previously become extremely pale, entirely disappears; the image of the sheath of the nerve, therefore, where it joias the muscle, is not in the slightest degree obscured. It is impossible for the observer who sees this to doubt that the nerve sheath becomes continuous with the sarcolemma, and that the contour of the latter, as it rises towards the cone, or extends over the eminence, is directly continuous with the nerve sheath; or, in other words, that the nerve sheath and the sarcolemma form two communicating tubes. In whatever mode the nerve terminations may be presented to the eye, whether in a transverse section of the muscular fibre, or in the optic transverse section which is seen if a bent muscular fibre pre- sents its convexity to the observer, he wiU stOl be constantly 208 MODE OP TERMINATION OF MOTOR NERVES, BY W. KUHNE. led to the same conclusion. The forms that the nerve emi- nence may assume are very various, sometimes constituting a pointed cone, at others a low rounded elevation, whilst in others, again, it is almost flat, — varieties that are doubtless attributable to the traction which has been exerted in the nerve in the preparation of the specimen. Nevertheless we may sometimes see, if not the pointed limpet-like cones, yet elevations of considerable height on muscular fibres, whose nerves have not been disturbed, as well as in flat portions of muscles which have been removed from the surface with scissors. We may therefore apply the general term of nerve eminence to the whole nervous expansion at this point, and honour its discoverer by naming it the Doy^rian emiuence. Wherever a nerve terminates, it will be found that the con- tractile substance is covered beneath the nerve eminence with the secondary constituents of the mass ; that is, with nuclei, granules, molecules, and the like. This relation is perfectly intelligible in the case of those muscular fibres which possess an entire investment of this substance ; but it is also found where the chief strige of it do not lie immediately beneath the sarcolemma, but are present as a central axis only, in which case the latter forms a conical projection, that passes transversely through the contractile substance, and nearly reaches the apex of the Doyferian eminence. In other cases, where elongated small masses are found immediately beneath the sarcolemma, these lose their otherwise straight form, and bulge upwards towards the nerve eminence. The eminence has in some instances only a single process, running in a longi- tudinal direction from its basis, but more frequently there are two, which pass in opposite directions. The termination of the axis cylinder in the eminence, and its usually forked divi- sion, does not appear to have been clearly recognised by the greater number of observers. Rouget considers that it termi- nates in the Crustacea in a blunt point at the line of junction of the granular nucleated mass with the contractile substance ; whilst in Beetles, after a somewhat longer course, it terminates at the same point. It will not be possible, without further investigation, to decide the question in regard to the final dis- position of the axis cylinder ; for, however probable Rouget's MODE OF TERMINATION OF MOTOR NERVES IN VEETEBRATA. 209 statements respecting the form that the process of the axis cyliader possesses may be, the position which he ascribes to it is, upon grounds that will hereafter be discussed, certainly sur- prising. The method of staining with solutions of gold and silver, which has been found so advantageous in other depart- ments of the minute anatomy of the nerves, has up to the present, so far as this question is concerned at least, yielded no decisive results. From what has already been stated it may, however, be maintained, in regard to the Arthropoda, that each of their muscular fibres receives a great number of nerve ends ; that the nerve sheath is continuous with the sarcolemma ; that the proper conducting nervous fibre, that is to say, the axis cylin- der, traverses the point of union of the two tubes, and divides in the nerve eminence ; and that all nerve eminences possess at their base a layer of protoplasmic muscle substance, that may stretch to a variable extent into the contractile part of the fibre. These results have been obtained from an examination of the tissues in Hydrophilus piceus, Dytiscus marginalis, Carabus auratus, Silpha obscura, Melolontha vulgaris, Geotrupes stercorarius, Trichodes apiarius and alvearius, Musca domes- tica, Tabanus bovinus, Bombus, Tegenaria, Argyroneta aquatica and Astacus fluviatilis, and consequently in all three classes of the Arthropoda. The Mode of Termination of the Nerves in the Vertebrata. A. Amphibia. — The knowledge of the mode of termination of the nerves in Amphibia, and especially in the Frog, is of great interest, because these animals have for so long a period been employed by physiologists as the subject of investigation in regard to the relations existing between motor nerves and muscles. The different muscles of the Frog which have been particularly examined are the sartorius, the muscles of the eye, the short fibres of the penniform gastrocnemius, and the small muscles of the foot that lie between the toes. The uncontractile protoplasmic substance, or the remains of it, in the muscles of Frogs, occupies as is well known, a very 210 MODE OF TERMIJSTATION OF MOTOR NERVES, BY W. KUHNE. inconsiderable space, as compared with the transversely striated contractile material. The muscle fibres are, indeed, dotted with nuclei, which are found not only immediately beneath the sarcolemma, but in all parts of the transverse section ; yet the protoplasmic portion is very small in quantity, and exists only in the form of a few molecules at the poles of the nuclei, or may even be altogether absent. Without methodical investi- gation it is almost impossible to strike upon the precise point in the fibres of the muscles of a frog which displays the mode of attachment of the nerve. This is sufficiently shown by the fruitless results of the observations repeatedly made antece- dently to the last ten years. After the experience that had been obtained respecting the connection of the nerves with the transversely striated muscu- lar fibres invested with sarcolemma of the Invertebrata, it was somewhat more than an hypothesis when it was maintained that the conditions must be essentially similar in aU animals in which nerves induce the act of contraction, and conse- quently in tlie Vertebrata. In order to decide whether every muscular fibre is connected with at least one nerve fibre, it was requisite to isolate the former in its whole length, and to exam!ine its entire superficies. This was effected by the mode of isolating the fibres, suggested by Budge, through the agency of a mixture of chlorate of potash and nitric acid, — a plan that was advantageously modified by V. Wittich, who recom- mended that the muscle should be warmed with a very diluted solution of the same mixture. It is still better to soften the intermuscular connective tissue by maceration for twenty -four hours, in an extremely dilute solution of sulphuric acid, and subsequently to convert it into gelatine and effect its solu- tion by warming it for a few hours at 104° Fahr. The isolation of the muscular fibres may then be accomplished by vigorous agitation vsdth water in a test tube. By this method any muscle can be completely broken up into its individual fibres. The capillaries, which still often remain attached, must be re- moved by pencilling with a camel-hair brush. On carefully examining such isolated muscular fibres throughout their whole length, one spot at least may always be found to which a nerve fibre, usually more or less ramified, cleaves. In long MODE OF TERMINATION OF MOTOR NERVES IN AMPHIBIA. 211 muscles — as, for example, the sarfcorius — many fibres may be found which present several such spots, whilst in the shorter fibres of the gastrocnemius, as a rule, only one nerve eminence is visible. In specimens prepared in this way the contiauity of the nerve sheath of Schwann with the sarcolemma may be observed in profile, without any further manipulation. In order to bring the termination of the nerves in the fresh, still living, and contractile muscle into view — as in the Arthro- poda — the fibres of the gastrocnemius are to be isolated. In the broken-up and separated muscle the course of the finest nerve twigs, as they cross the fibres at right angles, may be followed without difficulty by the pigmented vessels that ac- company them. In this region the terminal branches are given off; and if a few muscular fibres are raised with the forceps, after the tendinous fasciculi to which they are attached have been divided at both extremities, in all probability the desired appearances wiU be presented to the eye. The specimen so obtained may be examined, either without any addition or in a 0'5 per cent, solution of chloride of sodium, in which the muscle long retains its excitability. The aqueous humour and the serum of the blood of the frog may also be employed. Just before the nerve traverses the sarcolemma it usually undergoes division, forming the so-called terminal brush (leash or pencil) of the nerve, the extremely short branches of which seldom exceed in length the transverse diameter of the mus- cular fibre, and may lie in all conceivable directions to its axis. The number of branches of the first order rarely exceeds five ; those of the second order may amount to ten or twelve. The medullary investment and the sheath of Schwann accompany the nerves up to the very point of their attachment to the muscular fibre, but here the medullary sheath terminates abruptly, and without marked attenuation. In profile views no kind of distinction is to be perceived between the contour of the sarcolemma and that of the membranous sheath ; indeed, the flat and granulated nuclei of the latter can not unfre- quently be followed into that part which aU would acknow- ledge to be true sarcolemma, and which, as is well known, is in the frog destitute of nuclei. No better evidence than this can be offered in regard to the continuity of the two tubes. 212 MODE OF TEEMINATION OF MOTOR NERVES, BY W. KUHNE. At the point where the terminal nerve branches are abruptly- given off, no elevation occurs in the frog, and only very rarely, Fig. 35. Fig. 35. Motor nerve terminations from the Frog. To avoid confusion, the transverse striae of the muscular fibres are not indicated. At a, the passage of the nerve through the sai-oolemma is seen in profile. The re- maining portion of the intra-muscular cylinder axis expansion is more or less out of focus ; b b, terminal nerve-bulbs ; ccc, nuclei of the sheath of Schwann ; e, nuclei of the muscle. MODE OF TERMINATION OF MOTOR NERVES IN AMPHIBIA. 213 if the nerve has been forcibly stretched at the point where it appears to be most easily torn, does the medullary portion re- tract, so that a small empty funnel hangs over the border of the muscular fibre. Beneath the sarcolemma the nerves, now destitute of medullary sheaths, may be recognised in the form of small, moderately broad fibres, extending in a direction parallel to the muscular fibres, and often somewhat exceeding the breadth of the finest medullated branches. These fibres form a delicate pattern between the contractile substance and the sarcolemma, dividing and giving oS branches of nearly equal breadth, from which again others course in a nearly parallel direction. The whole system which they form is usually three or four times longer than the transverse diameter of the muscular fibre. It never invests the whole circumference of the contractile substance, and the branches never penetrate far into the interior of it. There can be no question that we have here an intra-muscu- lar branched expansion of the axis cylinder, and that it is the axial portion of the doubly contoured nerves which alone pene- trates the sarcolemma, and forms beneath it a wide-meshed and in part fibriUated plexus. The fibres of the plexus appear to be in part round and partly flattened ; they are very trans- parent, with delicate and for the most part smooth, though here and there finely serrated, contours. Good instruments show with sufficient sharpness that the intra-muscular axis cylinders are not diffusely troubled or granular at their terminations. The actual extremity is always a distinctly rounded point. Here and there the axis cylinders are somewhat enlarged, and in such places small strongly granular corpuscles may usually be observed, the size of which is intermediate between those of the nuclei in the sheath of Schwann and the weU-knovsra muscle nuclei. They are pear-shaped, with the pointed extremity directed towards the end of the axis cylinder, and are found not only in the expanded portions of the latter, but occasionally in other parts, though always lying close to the axis cylinder. The finer structure of these terminal nerve bulbs may be well seen even with ordinary microscopic powers, but stUl better with a very strong objective and a low ocular. A fine tortuous fibre may then be observed to separate from the axis cylinder, which in 214 MODE OF TERMINATION OF MOTOR NERVES, BY W. KUHNE." some places attains a considerable length, and, runniag along the bulb, terminates at its pointed end in a small swelling. This is all that has been ascertained up to the present time re- specting the termination of the nerves in the Amphibia; the muscles of Tritons, Toads, the Proteus, and Salamanders present- ing the same characters as those of the Frog. In these animals none of the granular and nucleated matrix is to be found which exists in the muscles of Arthropoda. A muscle nucleus with a small amount of protoplasm around it may, indeed, lie near the intra-muscular axis cylinder, but we never find at this point any special or peculiar disposition of this portion of the mus- cular contents. As regards the position of the terminal bulbs, as from their form these structures are named, they appear either to lie close to the nerves and on the same plane, or, as in the majority of instances, upon the latter and between them and the sarcolemma. Occasionally the author believes he has observed them to be absent. No physiological or morpho- logical explanation has been advanced in respect to the sig- nificance of the nerve bulb ; but it appears highly probable that the nuclei represent the earlier formative cells of the nerve and muscle, and consequently may be compared in some measiu'e in their structure to the nuclei of the cells connected with nerves in the cutis of the tadpole that have been de- scribed by Hensen. According to this observer, the embryonic nerve fibres terminate in the nucleoli of these nucleated cells ; the small pear-shaped knob at the end of the central fibre in the nerve bulbs would therefore correspond to the nucleoli. Although there can be thus no doubt that in the Amphibia the nerve sheath is continuous with the sarcolemma, from whence it obviously follows that the contents of the former, if it ex- tend beyond this point, must lie beneath the sarcolemma ; yet this doctrine has received much opposition. The accuracy of the statements that have here been made may, however, be irrefra- gably proved by careful inquiry. The whole contents of the freshly isolated muscular fibre can be rendered fluid by hydro- chloric acid of 1 per cent., whilst not only the primarily coagu- lated muscle plasma, but also the greater part of the muscle prisms, can be converted into a solution of syntonine. The entire contents of the muscle then, as is well known, move MODE OP TERMINATION OF MOTOR NERVES IN AMPHIBIA. 215 easily hither and thither in the sarcolemma, if care be taken that the lumen of the latter remains open, and all pressure be avoided. The intra-muscular axis cylinders of muscular fibres thus treated dissolve first at the points, then separate along their whole extent from the sarcolemma, and fall towards the centre of the tube, so that on shaking they float to and fro iu the fluid. And there is yet another experiment which has led Cohnheim to the same result. He dipped fresh muscular fibres for a short time in acid, treated them with a weak solution of nitrate of sUver, washed them with water, and allowed them to blacken in the light. A fine precipitate of silver occurred in the form of thin membranes between the muscle cyHnder and the sarco- lemma, which, after exposure to Hght, surrounded the muscular substance with a black layer beneath the sarcolemma. In this layer, staiued with silver, the whole intra-muscular nervous apparatus appears as a white silhouette, iadicating that some- thing is here intercalated between the sarcolemma and the con- tractile substance, and this indeed is the intra-muscular axis cylinder. This experiment is interesting on several other accounts ; for, in the first place, previous to the blackening taking place, the form of the nerve termination appears with surprising clearness, because the fine layer, composed of the sUver precipitate, surrounds in the first instance everything that is of nervous nature with very distinct limiting lines ; and, secondly, a means is obtained which is unfortunately the only one at present known, by which preparations of muscles ex- hibiting the mode of terminations of the nerves can, for a few months at least, be preserved. Lastly, it shows that there is pre- sent between the sarcolemma and the axis cylinder on the one hand, and between this and th6 contractile substance on the other, a capillary layer not capable of precipitation with a silver solution under the conditions which the experiment accidentally realizes, a something which is difierent from that which sur- rounds the whole contractile substance beneath the sarcolemma. The experiment of making the nerves float by treating the muscular tubes with diluted hydrochloric acid renders the for- mer indeed probable ; for it is then seen that the axis cylinder, beginning at the point, only gradually separates from the sar- colemma, to which it appears to be very firmly adherent ; the 216 MODE OF TERMINATION OF MOTOR NERVES, BY W. KUHNE. second method must at the same time appear still more im- portant, because it indicates a more intimate connection be- tween nerve and contractile substance than between this and the sarcolemma. As regards the methods of investigation, it may here be added, that the greatest possible -delicacy in manipulation is required, for the subject is one of the most difficult in the whole range of microscopic art, and is one also on which his- tologists are not, as yet, by any means unanimous, as the short historical sketch at the end of this article sufficiently shows. It is not sufficient to take the muscular fibre from still living and contractile muscles, but care must also be taken that, whilst still under the scrutiny of the observer, they retain their contractility, the covering glass being prevented by supports from exercising any pressure upon them. Fibres affected with rigor mortis are totally unserviceable, and also those which have had their axes rotated, or which have been in any way damaged. Maceration in acids that are at all concen- trated leaves no vestige of the intra-muscular nerves beyond a few interrupted and broken striae. Extremely dilute acids, as acetic acid of 05 per cent., or hydrochloric acid of 01 per cent., do not, indeed, render the image any clearer, but they do not destroy it; the terminal bulbs, however, soften under their influence in quite a peculiar manner, breaking up into a brush- like set of fibres ; a change that stands in strong contrast to the well-known shrinking of the muscle nuclei and of the sheath of Schwann, and most distinctly proves the difierence of the cor- puscles of the axis cylinder from those structures. The mode of termination of the nerves in Fishes has been hitherto but little investigated; by the application of some of the methods already adopted for the muscles of Amphibia, however, evidence has been obtained that here also the nerves penetrate the sarcolemma, and, at the point of entrance, lose their medullary sheath. The few extended investigations which have been instituted upon the mode of termination of the nerves in the Torpedo ocellata will be mentioned in the following paragraph. B. Reptiles, Birds, Mammals. — In these animals also the mode of isolating the fibres by means of Budge's solution per- MODE OF TERMINATION OF MOTOR NERVES IN REPTILES. 217 mits the intimate union of the nerves with the muscular fibres to be proved ; for, if the vascular network which contains the acid mixture have been removed with a brush, a short and frequently divided nerve stump often remaius obstinately ad- herent to the fibre. An iuvestigation by Rouget first led to exact conclusions iu regard to the mode of termination of the nerves ; since it demonstrated the existence of the Doyferian eminence, in the first instance in lizards, and subsequently in warm-blooded animals. Rouget corroborated the statement he had already made, of the passage of the nerve through the sarcolemma, of the fusion of this with the sheath of Schwann, and added the important observation from his iavestigation of fresh muscle, such as can easily be obtained from Reptiles, that just beneath the poiut of entrance of the nerve, a mass of nuclei and granular substance, constituting a Doyferian eminence, may be found exactly similar to that found in Ar- thropoda. And thus, although in the muscles of these animals there exists no such abundance of nucleated and protoplasmic formative material as in Arthropoda, yet this material is ac- cumulated in greatest quantity immediately beneath the ends of the nerves. According to Rouget, the grumous mass, with the nuclei imbedded in it, constitutes the proper termination of the nerves, with which the axis cylinder becomes continuous, and thus modified, rests with a circular or elliptical flat basis on the contractile substance, the cylindrical mass of which it embraces for a certain distance, but never entirely surrounds. The rows of nuclei and of gTanular material that in Arthropoda extend for some distance along the muscle, are entirely absent in lizards and the warm-blooded vertebrates. The observation of Rouget soon received confirmation, and Krause appears to have been the first who correctly described and represented the nuclei of the nerve eminence, stating them to appear in the fresh muscle as small delicately contoured vesicles, with rela- tively large nucleoli ; whUst, after the death of the muscle, and the addition of even very dilute acids, they become wrinkled and filled with granules. Rouget had only seen, and at a later period depicted them, when thus altered. The nuclei which are seen at the extremity of the nerve are, moreover, not all alike ; one portion belonging to the eminence, and another to the 218 MODE OF TERMINATION OF MOTOE NERVES, BY W. KUHNE. membrane which covers it; the latter being considerably smaller and flatter, rarely exhibiting a distinct nucleolus, and being always finely punctated or granular. As Krause has shown, they lie in the membrane, and may be regarded as the nuclei of the sheath of Schwann, where the latter, expanded over the eminence, is about to pass into the sarcolemma. Nuclei presenting these characters are consequently only found upon the upper part of the eminence, so that their position alone renders it impossible to mistake them for the vesicular nuclei which are present only at the base of the eminence, or that portion of it which is directed towards the muscle. The small, hazy nuclei are distributed in far smaller number and irregularly in the membrane, of the eminence, whilst the vesi- cular nuclei are arranged more or less definitely around the margin of the base. Finally, these small ellipsoids are placed with their long axis radially to the axis of the muscular fibre. They vary but shghtly in size ; in the lizards they are very little larger than the muscle nuclei, from which they are dis- tinguished by their somewhat less elongated form, and by their presenting more rarely two nucleoli in their interior. In the warm-blooded animals, on the other hand, their size con- siderably exceeds that of the muscle nuclei. The form of the nerve eminence in the muscles of Reptilia presents aU conceivable varieties, being sometimes higher, and sometimes lower; sometimes having a long, eUiptical, or even very extended basis ; at others being nearly circular, or pre- senting the shape of a parallelogram with rounded angles. Those that are the most elongated are always the least promi- nent, forming, when the nerve end is seen in profile, scarcely any projection from the muscular fibre. In the warm-blooded animals, in which the nerve eminence is nearly circular, the eminence is likewise very flat, — relations which are here only aUuded to, since they appear to be of subordinate importance. The muscles of warm-blooded animals, as is well known, alter with great rapidity after death, and it is not surprising, there- fore, that organs so delicate as the extremities of the nerves should likewise undergo cadaveric changes. Researches on the minute anatomy of these parts ought therefore to be com- menced on Reptiles, whose muscles, especially at a low tempera- TERMINATION OF MOTOR NERVES IN VERTEBRATA. 219 ture, remain, like those of Amphibia, excitable for an astonish- ingly long period. It is, in truth, not difficult to recognise in lizards, as in Lacerta agUis and L. viridis, the mode ia which the nerve terminates in the Doyerian eminence. The granular mass, together with its nuclei, forms only the base or floor of the , nerve end, whilst this is itself composed of a transparent non- . granular plate, the terminal nerve plate,OT the motor nerve plate. At whatever period after death the muscles may be examined Fig. 36. A. B. c. Fig. 36. Muscular fibres with nerve ends, from Lacerta viridis. A. Seen in profile -tpp, the terminal nerve plate ; s s, tlie base or sup- port of tlie plate, consisting of a granular mass with nuclei. B. The same as seen in a perfectly fresh muscular fibre, whose nerve ends are still probably excitable ; the delicate and pale contours which the frequently branched plate naturally possesses are not expressed in the woodcut. 0. The same as it appears after the death of the nerve end, as, for instance, two hours after poisoning with large doses of woorara. there will always be found a third element in addition to those above named; namely, vesicles of various form, which are clear and transparent, pale contoured, and free from nucleoli; and these are to be found also in the nerve eminences of the warm-blooded animals. They are products of the very easily alterable nerve plate, probably acted on by the post-mortem formation of acid in the muscle. Completely isolated muscular fibres removed from the still irritable thigh of a lizard, show characters which are almost s 220 MODE OF TERMINATION OF MOTOR NERVES, BY W. KUHNE. precisely similar to those of the frog ; for though the muscular fibres are thicker, the nerve fasciculi are quite as much branched and divided. It is a matter of no difficulty, moreover, to find branches so placed that the point of entrance may be seen in profile; so that here also, from observations made on the per- fectly fresh and living object, no doubt can exist in regard to the relations that exist between the nerve and muscle. The nerve plates can, on the other hand, be better surveyed and ex- amined in face, enabling the nuclei to be well seen. A structure of beautiful form appears between these in pale bands, consisting of a delicate pattern of parallel lines, which sometimes form longer cords, sometimes sinuous plates, which are again perfo- rated. If the muscle be tetanicaUy contracted, the plates appear folded like the crop of a bird, their softly sinuous edges being angular and serrated. There may also be found at the periphery small delicate processes with club-like ends. Careful focussing with the microscope, with a profile view, shows that the terminal plate lies immediately beneath the membrane of the nerve emi- nence, and just above the granular mass; for it will be found that the greater number of bright nuclei first make their appearance on effecting the adjustment for depth. A few of the latter do, however, lie on the same plane as particular parts of the plate, where, for instance, they, with the granular mass surrounding them, occupy cavities in, or lie between, its folded borders. The above-described image is extraordinarily pale and delicate, and only a practised eye can recognise it in quite fresh and stiU contracting muscle. It is seen, for example, in the very thin cuticular muscles of the Coluber matrix, which can be placed under the microscope without preparation, and which present a few nerve ends supplying some of the fibres on their surface. Now inasmuch as these muscles contract through their whole extent when their nerves are irritated, and whilst still under observation, we may conclude with certainty that the pale and delicate image of the terminal plate represents truly the living condition, not only of the muscle, but of the nerve, whose termination it forms. In those cases where the muscular fibre dies whilst in a state of rest, this image becomes continually clearer and sharper; whilst the contour of the plate, in the first instance, simply TERMINATION OP MOTOR NERVES IN VERTEBRATA. 221 becomes more clearly defined, without undergoing any essential change of form. But since portions of muscle thus excised rarely die in the condition of physiological rest, hut become tetanically contracted before the occurrence of rigor mortis, and are then fixed in this condition by coagulation, it is compara- tively rare to meet with the earliest stage in which the image is best shown. It is advantageous, therefore, to permit the muscles to die out in the dead body, and to examine them before they are so much stifiened as to become cloudy and opaque It appears, therefore, that the most distinct definition of the plates occurs previously to the death of the muscle, and especially at the time of the death of the nerve in the stage known to physiologists as that ia which the muscle can no longer be excited to contract through the nerves, but is still capable of responding to direct stimulation. This condition, in which the muscle long retains its irritability, may, as is well known, be in- duced by poisoning with woorara, if the poison be given in large quantities, and be allowed to act for a sufiiciently long period to produce evident paralysis of the terminal extremities of the motor nerves. Muscles that have thus been poisoned present in a distinctly marked manner an increased sharpness of contour of the terminal nerve plate — an appearance which may consequently be regarded as the outward and visible sign o commencing paralysis. This may perhaps be the result of a slight contraction of the plate, or of an inappreciable retraction of the granulated basis from the borders of the plate, which is nevertheless sufficient to induce the alteration in the image that we observe. In the perfectly stiffened muscle, when its reaction has be- come acid, the contours of the plates change their form ; the terminal nerve organ becoming continuously more and more folded and notched, and at length divided ofi" into spherical masses, vesicles, or other forms, which are sometimes most re- markable. The whole of these changes may also be quickly induced by the action of very dilute acids ; so that, in point of fact, no diflference is observable from the ordinary cadaveric appearances, especially if, in order to dilute the acids, serum instead of water be employed, which prevents imbibition from taking place. This is, perhaps, a proof that the later cadaveric 62 222 MODE OF TERMINATION OF MOTOR NERVES, BY W. KUfiNE. changes of the terminal plate of the nerve depend on the posti mortem acidification of the muscle. > What has been already stated in reference to the muscles of Lizards and Snakes is equally applicable to those of warm-blooded animals, and also to those of Man. It is, indeed, scarcely pos- sible to break up human muscles under the microscope in so fresh a condition that they may still be excited by irritation of their nerves, but they may be obtained so weU preserved from amputated limbs that the terminal plate can be demonstrated ■with its nerve eminence but little altered, or, at all events, not separated into distinct masses by a process of constriction. The plates can be immediately seen in the muscles of Mammals and Birds, only these should be prevented from becoming too rapidly stiifened; and this may easily be accomplished by lowering the temperature of the preparation to 32° Fahr., and the addition of serum at the same temperature on cooled slides. With the rigidity which here always supervenes on the tetanic condition, the object ceases to be available for investigation, chiefly on account of the deeper-lying fibres of the muscle becomiag too opaque ; and as the terminations of the motor nerves in these animals become paralysed instantaneously after the cessation of the cir- culation of the blood through them, it follows that, even in the freshest condition of preparations taken from warm-blooded animals, the plates do not present very sharp outlines. The determination of the thickness of the terminal plate and its relations to the adjoining parts, are points that demand methodical investigation. In the small nerve eminences of slender muscular fibres it presents itself when examined in profile as a thin mass projecting externally into the meduUated nerve fibre somewhat in the form of a cone, with a sinuous inferior border, which is turned twards the basal substance or matrix on which it rests throughout its whole extent, and by which, as by a layer equal to itself in thickness, it is separated from the contractile substance. In accurately made transverse sections of the frozen muscles of Lizards, it appears, on the other hand, in the form of an irregularly reniform mass which, at some points at least, gives the impression of being directly superimposed upon the muscular prisms. Such preparations remove every doubt respecting the relative portion of th^ TERMIITATION OF MOTOR NERVES IN VERTEBRATA. 223 contractile substance, the granular substance of the nerve eminence, the nerve plates, and the sarcolemma, which un- doubtedly lie in that order from within outwards. Moreover, transverse sections of frozen muscles with their nerve eminences afford an insight into the thickness of the nerve plates. They show that this, as a whole, is not inconsiderable; that in the central part it is nearly as large as the short diameter of a nucleus of the basis substance, though at the edges and irregu- lar processes it is far smaller; so that were it not for their transparency the transverse sections of these parts might be mistaken for gra^nules of the basis. Preparations made with osmic acid stain the nerves as far as the apex of the nerve eminence of a bluish black colour, whilst the contractile substance, the nerve plate, and the basis sub stance assume a clear yellow tint, and fat molecules in the muscle become brown, — reactions which prove that the whole iutra-muscular nerve termination loses the characteristic consti- tuents of the nerve medulla. The termiaal nerve plate can be brought into view in an isolated condition, though certaialy not situated externally to the muscle, without other addition than clear muscle serum. Isolated muscular fibres from the lizard, fixed under a covering glass, frequently exhibit, when they are in a complete state of rigor mortis, such contractions of the muscle coagulum, that large balls of this material accumulate in swollen portions of the sarcolemma, between other smaller spaces, filled only with muscle serum. If the last- mentioned empty spaces happen to occur at the place of the nerve entrance, the plate hangs free in the lumen of the sarco- lemma, and it is deserving of notice that it even then still adheres to the protoplasmic substance and nuclei which consti- tute the basal substance of the nerve eminence. It appears, therefore, that further investigation is requisite to enable a positive statement to be made in. regard to the union that exists between the two constituents of the nerve eminence. From what has been now advanced, we may conclude, then, that the appearances presented by the extremities of the motor nerves are so various that scarcely any scheme can at present be con- structed that shall give a representation, the morphological and physiological features of which shall be applicable to aU animals. 224 MODE OF TERMINATION OF MOTOE NERVES, BY W. KUHNE. According to Doybre, the pale, transparent, and non-granular nerve of Milnesium tardigradum becomes converted at the peri- phery into a finely granular eminence, which partly surrounds the equally pale, untroubled, and non-striated muscular fibre, and may extend a little distance along its border. These state- ments have been completely corroborated by renewed and very careful investigation of the Tardigrada (bear animalcules) by V. Greeff. This observer readily found the appearances so long known from Doy^re's drawings, but also observed a small spherical nucleus to be constantly present in the little nerve eminence, with a few sparsely scattered somewhat larger nuclei, very sparingly surrounded by punctated protoplasm, adherent to the muscle, and which for the most part lie at a consider- Eig. 37. Fig- 37. Termination of a nerve in Milnesium tardigradum (one of the sloth or bear animalcules), according to Greeff. m, muscular fibre ; K, nucleus of muscle ; D, eminence of DoySre j n, nerve. able distance from the termination of the nerve. V. Greeff was unable to find, either on the nerve or on the muscle, anjrthing corresponding to the sheath of Schwann or to the sarcolemma. Of those points which have been described by a few observers in respect to the termination of the nerves in the non-striated muscles of the lower animals, and in the smooth muscular tis- sue of the Vertebrata, mention has already been made under their appropriate heading. Trinchese has given some details respecting the termination of the nerves in the muscles, that TERMINATION OP MOTOE NERVES IN VERTEBEATA. 225 have hitherto been regarded as unstriated, of Helix pomatia and of Bowerbankia. According to him, a fine nerve fibril enters the large muscular fibre cells of the muscular apparatus of the foot of HeUx pomatia near their centre, divides immediately in their interior into two branches, which extend to the two pointed ends of the muscular fibre in the form of two elon- gated, and towards their extremities spirally twisted, threads. In the centre, and just subjacent to the point of division, an ellipsoidal accumulation of finely granular substance exists. In Bowerbankia, whose muscles Trinchese likewise describes as smooth bands, only a low conical process of the somewhat broader nerve fibre is present, in which cone, and at its base where it touches the muscle, is the granular material with a spherical nucleus and nucleoli. The question now arises, what is the essential nature of the termination of the motor nerve ? The author cannot doubt that this is at present most imperfectly known in the Arthro- poda. Rouget, indeed, states that he succeeded in perceiving a prolongation of the axis cyUnder in the nerve eminence in the form of a system of branched fibres ; and we must probably admit that this system does exist : but the further statement of Rouget, who attributes nervous properties to this part alone, as was generally previously admitted in Germany, and that this ramified system of fibres lies beneath the nucleated substratum, appears to the author to be very much ia need of confirmation. Engehnann, who also examiaed the muscles of the Arthro- poda, depicted a transparent homogeneous and quite vesicular mass at the apex of his nerve eminence, which appears to be the analogue of the terminal nerve plate found in ReptUes and Mammals, and, like these, to be bounded throughout the greater part of the surface turned towards the contractile substance by a granulated substratum. If this supposition be established — ^namely, that in the Arthropoda also a non-granular plate, or even a structure similar to the iutra-muscular axis-cylinder system of the Amphibia is present, covering the granular nucleated substratum, to which Rouget's statements appear to point — we should have obtained the much-desired uniformity of structure; and there would then be OTie mode of nerve termiaation, in which the nerve ends with a motor plate ia a 226 MODE OF TEEMINATION OF MOTOR NERVES^ BY W. KUHNE. nerve eminence, resting on a nucleated bed of protoplasm or a matrix; and a second mode, in which, as in Amphibia, the matrix is absent, and the nerve ends in an elongated and branched fibre-like plate. Only the Amphibia possess terminal bulbs, the analogue of which Cohnheim stands alone in con- sidering to be found in the plates of Lizards ; that is to say, in the small granular sessile and more conical corpuscles that are found in these animals, respecting which further investigations are needed. GreefiF first advanced the view that the mode of nerve termination in Milnesium may be assimilated to an ex- panded flat ganglion cell adherent to the muscular fibre ; and were we to transfer this idea to the higher animals we shotdd have to regard their nerves as terminating in a collection of ganglion cells, corresponding in number to the nuclei pre- sent, or in a ganglion cell containing many nuclei, or perhaps in a series of ganglion cells which have become fiised together ; that is to say, which have formed a ganglionic nerve plate. This view does not, however, materially advance our knowledge; for, even if it be correct, we shall have to seek for the minute anatomy of these terminal ganglion cells just as has been done for those of the nervous centres and others ; and if we have already acquired a considerable amount of information respect- ing these, we yet know still more in regard to the nerves terminating in muscle, since we are acquainted vsdth the plates, and their subjacent protoplasm, from which they are rarely sharply differentiated. We need not despair of discovering their analogue in aU nerve eminences, even in the minute ones of Milnesium, though perhaps better instruments and improved methods of investigation vsdll be required to discover the finer points of their structure than those we at present possess. As long as the granular contents of the nerve eminence were regarded as the proper continuation of the axis cylinder, as it now is by Eouget, in the case of Mammals and Reptiles — ^though he does not perceive that this involves a contradiction to his former very decisive and explicit statements that in the Arthro- poda his system of fibres was the only part of a truly nervous nature, the remaining structures, i. e. the granular mass and the nuclei, being accessory — so long could the view be main- tained that the nerve becomes directly continuous with the TERMINATION OF MOTOB NERVES IN VERTEBEATA. 227 contractile substance. This last idea is, however, opposed, from a morphological point of view, by a consideration of the mode of nerve termiaation in the frog ; since, if there be a fact in the whole range of this inquiry capable of being easily ascertained, it is the invariably sharply defined and distinct termination of the intra-muscular axis cylinder in the Amphibia. That view is also, and has long been, opposed by physiological considerations ; for it is demonstrable that the muscle does not act upon the nerve fibre, but that, on the contrary, all stimuli are conducted from the nerve to the muscle, and never in the inverse direction ; and for this purpose the nerve termination forms, as we now know, the visible structure. It may indeed be that a finer series of radiating processes from the nerve plate may penetrate between the granules of the substratum than we are at present disposed to admit ; and many circum- stances may be adduced in favour of this supposition, as, for example, the intimate adhesion of the two parts to one another, even when the contents of the eminence no longer rest upon the muscle. It is obvious, then, that it remains to be shown that the substratum constitutes a direct transition to the con- tractile, since there are muscles, especially amongst the Am- phibia, ia which this structural characteristic is entirely absent, The present state of our information upon these points may be shortly expressed as follows : — In all • transversely striated muscles the nerves terminate beneath the sarcolemma, the sheath of Schwann becoming continuous with the latter. Up to this point the axis cylinder is accompanied by the medullary sheath. The extremity of the axis cyhnder always corresponds to a remarkably broad expansion, which constantly forms a flat branching mass. This terminal nerve plate sometimes presents the character of a membrane, and at others resembles a system of fibres. In the greater number of cases the plate rests upon a substratum of nuclei and finely granular protoplasm, whilst in others this material is absent, and the nerve plates possess the so-called terminal nerve bulbs. The extremity of the nerve never penetrates into the interior of the contractile cylinder, and, on the other hand, never entirely invests it. Short muscular fibres usually receive only one nerve ; but long fibres have several. 228 MODE OF TERMINATION OF MOTOR NERVES, BY W. KUHNE. ' We may add, hypothetically, that the substratum represents the remains of a formative material important in the develop- ment of both the muscular and nervous tissue, and that a similar explanation may be offered of the nature of the terminal nerve bulbs in respect to the nervous tissue. HiSTOKT AND LiTEBATTJKB. — The preceding observations have been so ordered as to give the historical development of the principal facts with which we are at present acquainted respecting the modes in which nerves terminate in muscle. Those observers, therefore, that have contributed any essentially new information on the subject, have already been mentioned. A few remarks may, however, stUl be added, since the questions involved have given occasion to hvely con- troversy during the last ten years. In few departments of histology has methodically prosecuted inves- tigation, proceeding always from hypothesis, proved more fruitful in results than in relation to the question of the connection existing between nerve and muscle. The modern science of morphology has undoubtedly reaped the value of that experience that has been obtained in all other branches of knowledge, in having become a special sub- ject ; and the example before us will serve, perhaps, to point out the advantages that ^histology, which inohnes as much towards mor- phology as towards physiology, has to anticipate from hjrpotheses borrowed from both departments. We shall here leave unnoticed the older works, so far, at least, as they bear upon the unsatisfactory view of nerve loops. In the same year that Savi (2) communicated his important obser- vations of the division of the primitive nerve fibres in the electric organs of the Torpedo to a scientific congress at Florence, Doyere (1) discovered the termination of the motor nerves iu Milnesium tardi- gradum. Eemak (3) then incidentally stated that in mammals the nerves appeared to him to end in a plexus of pale fibres, winding around the external surface of the sarcolemma. Quatrefages (4) verified the discovery of Doyere in the case of Eolidina. In 1844, E. Briicke and Job. Miiller first observed the division of primitive nerve fibres in the muscles of the eye of the pike, and E. Wagner (6) observed the same thing in the musculus hyoideus of the frog. Kolli- ker (7) soon after established the Doyerian mode of termination of the nerves in the larva of Chironomus, and Eeichert (8) demonstrated the division in the cutaneous muscle of the thorax in the frog, where he found by direct counting that a few nerve fibres furnish more branches than the number of the muscular fibres to be supphed. The TERMINATION OF MOTOR NERVES IN VERTEBRATA. 229 Doyerian mode of termination was again corroborated by Meissner (9), in Mermis and Ascaris, and by Wedl (10), Walther (11), and Munk (12), in several Nematodes. At a somewhat later period, Schaafhausen ex- pressed himself in terms similar to those of Kemak, and believed that he had seen a fine network of fibres, tinted with carmine, investing the whole muscular fibre. At this date the above-described mode of ter- mination of the nerves in the muscles of insects was discovered (14, 15), and inasmuch as the nerves were here proved to terminate beneath the sarcolemma in muscles possessing this membrane, the view entertained by Schaaf hausen respecting the similarly constructed muscles of vertebrate animals was rendered improbable. Neverthe- less, a similar conclusion was arrived at by Beale (16, 17), an ener- getic inquirer who maintained that in the frog in particular the nerves gave off relatively broad nucleated fibres. Since, however, he did not adopt the method of isolation, but coloured his preparations deeply with carmine, it is possible he may have been deceived by the confusion of fibres traversing the accessory structures associated with muscle. Investigations undertaken upon isolated muscular fibres from the frog (18, 20) now led to the discovery of the intra-muscular axis cylinder and its terminal bulbs. The penetration of the nerve through the sarcolemma, now for the first time demonstrated, was established by Margo (19), who considered the axis cylinder terminated in a system of nucleated and granulated fibres which penetrated the contractile substance to aU depths. The views of Margo, which he subsequently extended to the Arthropoda (27), have never found adherents, since they clearly rested on illusory appearances caused by the well-known serially arranged interstitial granules which are present in so many muscles. In the meanwhile Kolliker reverted to the views of Beale, but with the addition that he regarded the nerves as frequently ex- hibiting free extremities, and did not, as Beale thought, form a com- pletely closed plexus. Besting on this assumption, Kolliker, who undoubtedly first rediscovered the intra-muscular axis cylinder of the frog (25, 26), maintained that the terminal bulbs there seen were really nuclei of the sheath of Schwann. Krause (24) and Kouget (29) agreed with him in all points, and now, whilst Beale (28) retained his first opinion as being applicable to all classes of animals, Eouget (29) came forward with his discovery of the nerve eminence in reptiles and warm-blooded animals, and was corroborated in all essential particulars by Krause (31), Engelmann (34, 38), and the author (39, 40) ; by the latter, indeed, with special emphasis, because Krause had given quite a different signification to the nerve eminence ; had 230 MODE OF TERMINATION OF MOTOR NERVES, BT W. KUHNE. placed it external to the sarcolemma ; had described the nuclei as being situated in the membrane, and the whole structure as being an organ more analogous to the nerve bulbs invested by the sac-like sheath of the nerve. The opposite vlevrs that Krause took on these points to the descriptions given by Rouget, Waldeyer (35), Letzerich (37), and Engelmann, were based on the application of uncertain methods of investigation, especially in the attempt to establish the presence of a sharply defined line belonging to the sarcolemma between the contractile substance and the substratum of the nerve plate which he obtaiued by the coagulation of the muscle in bichromate of potash, or by the examination of the transverse sections of dried muscle. The lines thus produced do, indeed, lie subjacent to the sarcolemma. It is conceivable that Krause, and perhaps also Letzerich, if the author rightly comprehends the latter, perceived in the nerve eminence the first indications of the nerve plate ; that which Krause described as a pale terminal fibre ending in a bulb being a portion or an optical longitudinal section of the nerve plate, whilst that which Letzerich compared to fluid wax was the plate itself. Thus, in the first inves- tigation on the muscles of Reptiles in Germany, the nerve plate was recognised (47) as the immediate and proper terminal organ of the axis cylinder, whilst it was at the same time established that the granulated and nucleated mass previously taken for it was only the substratum of the plate. That which Rouget, Engelmann, Waldeyer, and Krause regarded as the nerve plate, advantageously exchanged its name for that of nerve eminence (Doyere's cone), in order to preserve the otherwise very appropriate term of terminal plate for the true ex- tremity of the nerve, which expresses well the peculiar form that it presents. The nerve plate was soon recognised as an essential con- stituent of the nerve eminence in the muscles of warm-blooded animals and of man (48). In the meantime Rouget (43) and Krause (41), in the case of the frog, pursuing the method suggested by Wal- deyer, who also believed he had seen a nerve eminence in that animal, adopted another view, Krause describing in the muscles of the frog extremely minute nerve eminences which he believed to be situated externally to the sarcolemna, and to which long, pale, and delicate nerve fibres ran, whilst Rouget considered that the nerves ended by a blunt extremity at the sarcolemma, which was itself continuous vnth the sheath of Schwann. Neither a nerve eminence, nor any simUar prolongation of the axis cylinder is present, according to Rouget, in the muscles of the frog. The true intra-muscular termination of the nerve again apparently escaped the observation of both observers ; for TERMINATION OF MOTOE NERVES IN VERTEBRATA. 231 Krause, in preparations where the nerves had undergone much stretch-, ing, and had on that account become attenuated, mistook the point of attachment of the nerve which had thus been rendered conical with the ultimate nuclei of the sheath of Schwann for the nerve eminence ; whilst Kouget obviously overlooked the entire expansion of the now no longer meduUated nerve, after he had been accustomed to the in- finitely more sharply defined images of the same parts in the muscles of lizards. In the meanwhile Engelmann (38) had been successful in discovering the elongated expansion of the axis cylinder in the frog, with the exception only that he denied the minute anatomy of the terminal bulbs, aiid believed a granular substratum to be here present, constituting an intermediate structure between nervous and contractile tissue, and continuous with both. The objections to this view, extended by Engelmann to the muscles of aU animals, have been already ad- duced, and it need here only be added that his description of the granular mass in the frog is decidedly erroneous. The most satisfac- tory demonstration of the accuracy of the mode of termination of the nerves described in the text results from the application of the silver mode of preparation, and has been furnished by Cohnheim (46, 60) ; this mode is equally well adapted to display the terminal nerve plate in the Doyerian eminence which comes into view in muscles blackened with silver, in the form of a beautiful white pattern. The same author has pointed out that the isolation of the nerves from the remains of the nerve eminence adherent to them, accomplished by Kranse with the aid of moderately strong hydrochloric acid, is not to be regarded as a proof of the eminence being situated on the outer surface of the sar- colemma, because the acid under the conditions maintained by Krause, to wit, degree of concentration and duration of action, effects the solu- tion of the sarcolemma, and consequently lays bare the muscle, and breaks down the continuity of the nerve with the muscular fibre. The existence of the terminal plate has still more recently been vigorously contested by Kouget (56) and ICrause, who explain the whole appear- ance as a hitherto undescribed post-mortem phenomenon of coagula- tion, in contradiction to which, again, Eouget stated that the true termination of the axis cylinder in the nerve eminence consists in its metamorphosis into a granular mass with interspersed nuclei. Eouget soon again retracted this view for the muscles of Arthropoda, and especially for those of Crustacea, in which he discovered an analogue to the plate, or at least to the more fibrous mode of the termination of nerve fibres that occurs in the frog. It is reserved. for further. research to decide whether Eouget's statements are correct, to the effect that 232 MODE OF TERMINATION OF MOTOR NERVES, BY W. KUHNE. this fibre system, in opposition to all analogy derived from the Verte- brata, penetrates the granulated substratum, and comes into direct contact with the contractile substance. Engelmann's observations (67), at all events, expressly establish the latter point. To all appearance, the general results of inquiry upon the important question of the mode of termination of the motor nerves seem to show that the views of Remak, Beale, and Kolliker must generally be given up, whilst Eouget admits that in the case of Crustacea, at least, the axis cylinder does not terminate in a band-like and granular manner. It appears, lastly, from the very recent brief essay of Krause (64), that this author also has given up his two former views in respect to the muscles of Amphibia, and has now actually seen the fibre system of the intra-muscular axis cylinder, and also, by the application of the colouring method with solutions of gold, the exceedingly beautiful form of the nerve plate in the muscles of Lizards. The next step that has now to be taken in advance, is to interpret the relations of the lower surface of the plate to the granulated substratum. The author is unable to express an opinion upon the statements of Trinchese (63), which relate to the nerve eminence of the Torpedo. According to this observer, the nerves of this fish possess duplicate sheaths at their extremity, of which only the perineurium is continuous with the sar- colemma, whilst the nucleated sheath of Schwann accompanies the axis cylinder where it penetrates into the nerve eminence, and every- where loosely invests the flat plexus formed by the division of the axis cylinder. Trinchese describes peculiar ganglionic enlargements on the thus modified axis cylinder, and true terminal ganglion cells, with nucleus and nucleoli, on the projecting extremities of the network ; other nuclei distributed through the nerve eminence he refers to the sheath of Schwann contained in the muscle. The drawings of Trin- chese, although taken from preparations materially modified by diluted hydrochloric acid, and undoubtedly deprived of their best qualities, show what excellent materials were at his disposal, and render it ex- tremely probable that these animals present the most magnificent motor terminal plates in existence, though the deUcacy and beauty of their form are lost in all but physiologically fresh specimens. Literature. 1. DoYEKE, Memoire sur les Tardigrades. Ann. des sciences nat., 2"»« Serie. 1840. PI. xvii., Fig. 1 — 4. LITERATURE OF THE TERMINATION OF MOTOR NERVES. 233 2. Savi, Etudes anat. sur le syst. nerv. et sur I'org. electr. de la TorpiUe. 1844. 3. Eemak, Arch. f. Anat. u. Physiol., S. 189. 1843. 4. QuATEEFAGES, Aud. d. Sc. nat., 2^' Serie. 1843. T. xix., p. 299, PI. ii., Fig. 12. 5. E. BsucKB u. JoH. MuLLEB, JoH. MiJLLER, Handbuch der Physiologie, 4. Aufl. 1844. Bd. i., S. 524. 6. K. Wagner, Handworterbuch der Physiol., Bd. iii., S. 888. 7. KoLLiKEB, Mikroskop. Anat., Bd. ii., 1. Halfte, S. 238. 8. Reicheet, Arch. f. Anat. u. Physiol., S. 29. 1851. 9. Meissneb, Zeitschr. f. wiss. Zool., Bd. v., 1854, S. 234, u. Bd. vii., 1856, S. 26. 10. Wedl, Wiener Sitzungsberichte, Bd. viii., S. 298. 11. Waltheb, Zeitschr. f. wiss. Zool., Bd. viii., S. 163. 12. MuNK, Gottinger Nachrichten. 1858. Nr. 1, S. 11. 18. Sohaathausen, Amtl. Bar. d. Naturforscher-Vers. zu Bonn, S. 198. 1859. 14. W. KuHNE, Monatsschr. d. Berl. Akad., S. 395, 493. 1859. 15. W. KuHNE, Arch. f. Anat. u. Physiol., S. 564. 1859, auoh Myolog. Untersuch. 1860. 16. Beale, Proc. of the Eoyal Society, London, Vol. x., S. 519. 1860. 17. Beale, Philos. Transact., pp. 611 — 619, PI. xxiii., rec. 19 Jun. 1860. 18. W. KuHNE, Compt. rend., S. 316. 18 Fev. 1861. 19. Maego, Sitzung. d. Ungar. Akad. d. Wiss. 14 Oct. 1861. 20. W. KiJHNE, Ueber die periph. Endorgane der mot. Nerven. Leipzig, 1862. 21. KoLLiKEB, Wiirzb. naturwiss. Zeitschr., Bd. iii., S. 1, 8. u. 22, Marz, 1862. 22. W. KiJHNE, ViECHow's Arch., Bd. xxiv., S. 462. 1862. 28. Natjnyn, Arch. f. Anat. u. Physiol., S. 481. 1862. 24. Keatjsb, Zeitschr. f. rat. Med., Bd. xv., S. 189. 1862. 25. KoLLiKBB, Zeitschr. f. wiss. Zool., Bd. xii., S. 149. 26. KoLLiKEB, Zeitschr. f. wiss. Zool., Bd. xii., S. 268. 27. Maego, Ueber die Endigung der Nerven in der quergestr. Muskel- subst. Pest, 1862. 28. Beale, Arch, of Med., Vol. iii., p. 257. 1862. 29. RoDGET, Note sur la terminaison des nerfs moteurs dans les muscles chez les Reptiles, les Oiseaux et les Mammiferes. Compt. rend. T. Iv., pp. 548—551. Seance 29 Sept. 1862. '234 MODE OF TERMINATION OP MOTOR NERVES, BT W. KUHNE. 30. Beaie, Pliilo3. Trans., June 19, 1862. 81. Kkause, Gottinger Nackr., Nr. 2. u. 3. 1863. 32. Beale, Proc. of the Koy. Soc, June, 1863. 33. Beaie, Quart. Joum. of Microsc. Sc, p. 97. 1863. 34. Engelmann, Centralbl. f. d. mad. Wiss., Nr. 19. 1863. 35. Waideyeb, Centralbl. f. d. med. Wiss., Nr. 24. 1863. 36. Kbaijsb, Zeitschr. f. rat. Med., Bd. xviii., S. 136. 1863. 87. Letzebich, Med. Centralzeit., Nr. 37. 1863. 38. Engelmann, Unters. lib. d. Zusammenh. v. Nerven. u. Muskel- fasern. Leipzig, 1863. 39. W. KuHNE, YiRCHOw's Arch., Bd. xxvii., S. 508. 1863. 40. W. KxJHNE, ViBCHow's Aroh., Bd. xxviii., S. 528. 41. Kbause, Zeitschr. f. rat. Med., Bd. xx., S. 1. 1863. 42. Keause, Gottinger Nachr., Nr. 18. 1863. 43. KouGET, Joum. de la Physiol., Nr. 20, S. 574. 44. Beale, Quart. Joum. of Microsc. Sc, p. 302. 1863. 45. Waldeyee, Zeitschr. f. rat. Med., Bd. xx., S. 242. 46. CoHNHEiM, Centralbl. f. d. med. Wiss., Nr. 55. 1863. 47. W. KuHNE, ViEOHOw's Arch., Bd. xxix., S. 207. 48. W. KiiHNB, "ViBOHOw's Arch., Bd. xxix., S. 433. 49. Ebause, Zeitschr. f. rat. Med., Bd. xxi., S. 77. 50. W. KuHNE, Centralbl. f. d. med. Wiss., Nr. 24. 1864. 51. W. KuHNB, ViECH. Arch., Bd. xxx., S. 187. 1864. 52. Beale, Arch, of Med., Vol. iv., p. 161. 1864. 53. Beale, Transact, of the Microsc. Sc. Oct. 1864. 54. ScHONN, Anat. Unters. im Bereiche d. Muskel- u. Nervenge- webes. Stettin. 55. Engelmann, Jenai'sche Zeitschr. f. Med. etc., i. 3, S. 322. 1864. 56.- EouGET, Compt. rend, lix., p. 809. 57. EouGBT, Compt. rend. Hx., p. 851. 58. Kbause, Zeitschr. f. rat. Med., Bd. xxiii., S. 157. 59. ScHONN, Jenai'sche Zeitschr. ii. S. 26. 60. CoHNHEiM, ViRCH. Arch., Bd. xxxiv., S. 194. 61. W. KiJHNE, Compt. rend. 1864. 62. W. KuHNE, ViBOH. Arch., Bd. xxxiv., S. 412. 63. Geeefp, Archiv f. mikrosk. Anat. von M. Schultze, Bd. i., S. 101. 64. Bbalb, Croonian lecture for 1865. 65. MoxoN, Quart. Joum. of Microsc. Sc. Oct. 1866, p. 235. 66. Teinchese, Joum. de I'Anat. et de la Physiol. 1867, p. 485. 67. Engelmann, Jenai'sche Zeitschr., Bd. iv., S. 807. 68. Keause, Arch. f. Anat. u. Physiol., Heft v., S. 646. 1868. CHAPTER VI. THE BEHAVIOUR OF MUSCULAR FIBRES WHEN EXAMINED BY POLARISED LIGHT. By E. BRUCKE. When muscular fibres are examined with a microscope to which a polarising apparatus is attached, remarkable and instructive phenomena are observed. If the field be darkened by crossing the planes of polarisation of the Nieol's prisms, those fibres only disappear which lie parallel to the plane of polari- sation of one or other of the prisms ; the rest, which cut those planes at various angles between 0° and 90°, appear of a grey colour upon a black ground, the most distinct being those w'hich cut them at an angle of 45°. In those parts where the muscu- lar fibres ruiming parallel with one another are arranged in several layers, the colour assumes a whitish tint, passing into yellow. The tint varies with the thickness of the layers, precisely as the succession of colours in Newton's rings, from the centre towards the circumference. If one of the Nieol's prisms be turned to the extent of 90°, so that the field becomes clear, and attains its maximum brightness, the complementary tints make their appearance. These phenomena, with others that will presently be described, are equally apparent when the muscular fibres are thoroughly impregnated with, and sur- rounded by, strongly refracting fluids, as glycerine, turpentine, and Canada balsam. This is essentially owing to the circum- stance that the muscle substance is doubly refractUe, two systems of undulations propagating themselves according to. different laws, and interfering the one with the other. This explanation had already been given in 1839 by 236 MTJSCULAR FIBRES IN POLARISED LIGHT, BY E. BRUCKE. Prof. C. Boecb * of Christiaoiia, who was the first that applied the polarising microscope to the investigation of animal and vegetable tissues; and no other intelligible explanation has since this period been advanced of the phenomena observed. The next question to determine is, whether the entire sub- stance of the muscular fibres possesses an equal power of double refraction, or whether it is possible to distinguish doubly refracting from isotropal parts. If sufficiently high magnifying powers are employed, and the observations be made on animals which have large sarcous elements, amongst which our large water-beetle, the Hydrophilus piceus, is the best, it will be immediately seen that only the sarcous elements are doubly refracting, and that the intervening material which separates them from one another is isotropal; for it remains dark in the dark field of the crossed Nicol's prisms, in what- ever azimuth the muscular fibre to which it forms a part may be placed ; it is just as dark in those muscular fibres which form an angle of 45° with the polarising planes of the prisms, as in those which make an angle of 0° or of 90° with those planes. This becomes still more evident if a water-beetle be killed by immersion in strong alcohol, and after a few days' maceration the muscles of one of its thighs be placed in oil of turpentine, and finally in Canada balsam. Owing to the high refracting index of the balsam the muscular fibres appear in ordinary light very pale and transparent, and aU the stronger shadows vanish ; but on this very account aU the phenomena caused by double refraction appear with corresponding distinctness under the polarising microscope. But in what way are the sarcous elements doubly refractile ? Are they positive or negative ? Are they uniaxial or biaxial ? If a transverse section of the muscle hardened in spirit be thoroughly impregnated with Canada balsam, and examined with the polarising apparatus, .it will be found that as it is turned round the axis of the instrument a portion of the cut * Transactions of the Scandinavian Society of Naturalists in GStheborg in 1839, and in Copenhagen in 1840. Report on the progress of Anatomy and Physiology in Scandinavian Literature in the years 1840 — 1843, by Ad. Hannover, in J. Miiller's ArchivfUr Anatomie u. Physiologic, 1844. BEHAVIOUR OF MUSCULAR FIBRES IN POLARISED LIGHT. 237 surface remains constantly dark in the dark field of the crossed Nicol's prism, whilst the remainder, in the effective azimuths — that ia, in those in which they make angles between 0° and 45° with the planes of polarisation — become clear. It soon appears that such as always remain dark are those which lie exactly parallel to the axis of the instrument, whilst this is not the case with the rest. There is thus an optic axis precisely corre- sponding with the longitudinal direction of the muscular fibres. Now, inasmuch as this coincides with the longitudinal dimen- sions of the straight prisms represented by the sarcous elements, and since we are unable to discover a second optic axis, or Fig. 38. any indication of its existence, we must regard the sarcous elements as uniaxial. Are they positively or negatively doubly refractUe? In order to determine this I have constructed the instrument shown in the accompanying figure. The blackened brass plate a a, perforated in the centre, and connected to the object plate of the microscope, possesses two slides, which can be moved over one another ; the lower c c by means of the micrometer screw b, the upper e e with the unassisted hand by means of the handle d on the parallelogram g g. Both slides carry prisms of quartz, the upper one movable t2 38 MUSCULAR FIBRES IN POLARISED LIGHT, BY E. BEUCKE. in. the direction of its length in a groove li h ; the lower one fixed, and only movable together with the slide by means of the micrometer screw. The prisms rest upon their thin edges, and the stage is perforated immediately beneath them, so that the light is freely transmitted. They have both a corresponding angle of 1° 6' 54", and are so cut that one of the inclined planes ia each is parallel to the crystaUographic principal axis, so placed that the light reflected from the mirror of the microscope passes perpendicularly to this axis in each, and so arranged that the two principal axes cross each other at right angles, each of them makiag an angle of 45° with the polarising plane of the sub- jacent Nicol's prism. Since the two prisms act in a contrary sense, so that the ray which is ordinary in the first becomes extra- ordinary in the second, there are obtained, if the Nicol's prism situated above the ocular be made to cross that which lies below the quartz, a few black striae, where equal thicknesses of the latter lie over one another, whilst on both sides colours appear ia the sequence of the Newtonian system of rings for reflected light. The prisms, moreover, by sliding can be so arranged that the black stria which is present when the differences of velocity of the rays = 0, or the colour corresponding to some determinate difference of theray,canbe made to occupy the middle of the fleld. I now make the upper of the two quartz crystals an object stage, and distribute the muscular fibres of Hydrophilus piceus upon it in such a mode that, whilst some lie parallel to the principal axis, others are arranged perpendicularly to it. K the micrometer screw is now turned so that an increasingly thick portion of the lower prism is gradually brought into the field, it will be remarked that each colour is first assumed by those muscular fibres which are arranged at right angles to the axis of the upper prism, then by the ground, and lastly by the muscular fibres which lie parallel to the axis of the upper prism. If the screw be turned in the opposite direction, these colours are first shown by those muscular fibres which lie parallel to the axis of the upper prism, then by the ground, and then by the fibres which stand perpendicularly to the axis of the upper prism. Every muscular fibre therefore acts optically like a thickening of the prism to the axis of which it is parallel, or, which is the same thing, as an attenuation of the BEHAVIOUR OF MUSCULAR FIBRES IN POLARISED LIGHT. 239 prism to the axis of which it is perpendicular. The sarcous elements are consequently positive like rock crystal. The proof of this is obvious. Since the light passes through the first prism at right angles to its principal axis, the plane of vibration of the extraordinary ray is perpendicular to the principal axis, that of the ordinary ray parallel to the principal axis, or at an azimuth of 90° from the former- The extraordinary ray precedes the ordinary, and interference phenomena exhibit differences of shade, which are dependent on the thickness of the prism, and the wave-lengths of the ordinary and extraordinary ray. The two rays emerge from the first prism with this difference of shade, and as they pene- trate into the second, which crosses the first at 90°, the ordinary ray can only produce vibrations parallel to the axis, the extraordinary only those which are at right angles to the principal section. Thus the vibrations which constitute the ordinary rays of the first prism form the extraordinary in the second, and vice versa. Since now in the second prism the extraordinary ray is propagated with as much increase of rapidity as in the first, it is clear that the difference of velocity must diminish until equal thicknesses of the two prisms are traversed ; that it is then = ; and if the passage through the second prism is longer than through the first, it increases with opposite signs. If now a doubly refracting body be placed on the upper prism, the optic axis of which is parallel with the principal axis of the crystal, the ordinary ray of this upper prism will be propagated as an ordinary ray in it ; and the extraordinary as an extraordinary ray. It acts thus upon the difference of shade as a thickening, if the ordinary in it, as in the prism itself, is propagated less rapidly than the extraordinary ; but if the opposite occur, it must operate in the same manner as a thinning of the prism with the principal axis of which its optic axis is parallel. An important question still remains, which can be solved by the help of the polarising microscope : Are the sarcous ele- ments to be regarded as single and individual elementary bodies, or as groups of solid bodies capable of being variously disposed? If the muscles contract, the fibres are seen to 240 2m:uscular fibres in polarised light, by e. brucke. become thicker, and the transverse striae to approximate. Each sarcous element must consequently change its form, and be- come shorter and thicker. If such a change of form result from any force acting in an elementary solid body, the opera- tion of that force must extend as far as the individual mole- cules, the optic constants must be changed, and it is not conceivable that they should be so changed that the ordinary and extraordinary ray, after they have traversed equal thick- nesses in the same direction, should present again the same difference in velocity that they offered under similar circum- stances before the change of form. But it is quite a different matter if the sarcous elements are groups of solid doubly refracting bodies, of which each indi- vidual remains unchanged in form in the act of contraction. The form of the whole group — that is, of the sarcous element — is here changed by an alteration in the arrangement of the several corpuscles, just as in a company of soldiers groups of various breadths and depths are produced by changes in the position of the several individuals. In the latter case the optic constants are not altered in the act of contraction, and the rays on this account, if they have traversed equal thick- nesses in the same direction, must constantly exhibit the same differences in velocity, whether the muscle be in the relaxed or in the contracted condition. Siace we have a measure of the difference of velocity in the colours which appear under the polarising microscope, we are enabled to answer the question experimentally, whether the optic constants of the contractile substance change during contraction to any considerable extent or not. AH the investi- gations I have directed to this point have had a negative result; i.e., I have never seen any alteration of colour that could not be entirely referred either to changes in the thickness of the layer traversed, or in the angle which the rays under- going interference make with the optic axis. As, therefore, I have in vain sought after a change of the optic constants, I must maintain that the sarcous elements are not elementary and simple solid bodies, but groups of smaller doubly refractUe bodies. These doubly refracting bodies I have called Disdia- clasts, after the phrase employed by Erasmus Bartholin, the BEHAVIOUR OF MTTSCULAE FIBRES IN POLARISED LIGHT. 241 discoverer of double refraction in calc spar, in the title to his "weU-known treatise* The composite nature of the sarcous elements furnishes an explanation of the various appearances presented fey muscles in a state of rigor mortis. In my re- searches on the structure of muscular fiferes with polarised light,-f I have constructed nine different schemes, and we may not unfrequently see one and the same muscular fibre iu dif- ferent parts representiag two different schemata, which is at- tributable to the circumstance that, in the several sections of the fibre, the sarcous elements have divided with great regularity into smaller groups of disdiaclasts, so that much narrower systems of transverse striae appear in these sections- than in others, though they are neither shortened nor thickened by contraction. Margo,J who found that the sarcous elements exist also in the fibres of the adductor muscle of bivalves, frequently saw the muscles in Anodonta only partially striated.§ In this case the sarcous elements of the transversely striated parts lie next, one another in regulai- rows ; but in those parts that, with weak powers, appeared homogeneous, he found, with higher powers, instead of numerous small irregularly distributed granules, small groups of disdiaclasts. If the living muscular fibres of frogs or beetles be immersed in water, they, as is well known, die rapidly ; the ends swell up strongly, and the contractile contents ooze out of the sarcolemma. If such termiaal portions of fibres be observed under the polarising microscope, with the prisms crossed, no sarcous elements are observed in them, but they present the appearance of fine sUvery-grey clouds distributed in the dark * Experimenta Crystalli Islandici Disdiaclastia quihus mira et insolita Refractio detegitur. Hayn, 1869. t Denkschriften der Wiener Ahademie der Wissenschaften, Band xv., Separatauflage Wien. hei Qerold. % XJher der Muskelfasem dm Mollusken, SitzungsbericMe der Wiener Ahademie, Band xxxix., s. 566. § The fibres of the adductor muscle were originally erroneously regarded as smooth muscular fibres ; that is to say, the substance of -which is doubly refracting, but in -vyhich neither sarcous elements nor isotropal intervening substance can be distinguished. 24a MUSCULAR FIBRES IN POLARISED LIGHT, BT E. BEUCKE. field. Here the sarcous elements have become disturbed, whilst the absorbed -water has shifted the several disdiaclasts from their position. This state, resulting from the imbibition of water, is essentially different from that induced by the action of dilute acids, which effect a change ia the substance of the disdiaclasts themselves, and take away their power of doubly refracting light. In conclusion, I will add a few remarks on the external and internal aids to the study of muscular fibres in polarised light. To whomsoever the foregoing details and the ordinary works on physical science are insufficient, Aug. Beer's Introduction to the Higher Optics* will prove of service. In the choice of an instrument it is in the next place to be noted that the upper Nicol's prism should be placed over the ocular, and not between the objective (in the more restricted sense of the word) and the so-called collective. Amongst instruments constructed with the latter arrangement I have found nothing better adapted than this for minute and difficult investigation. Bottger, of Berlin, originally furnished the best Nicol's prisms for these purposes; more recently, however, Hartnack, in Paris, has constructed an admirably perfect instrument, arranged accord- ing to a method described by him and Prazmowski in the " Aonales de Chdmie et de Physique," 4° sdrie, T. vii. The microscopic image can be rendered still more beautiful by distributing the muscular fibres upon a plate of gypsum or mica, attached to the stage by means of Canada balsam. Dam- mar resin, or Jefirey's solution of mastic and caoutchouc in chloroform. By appropriate inclination of the gypsum or mica plate a coloured field is obtained, from which the muscles are projected, tinted with different colours, varying in proportion as their inclination on the plate increases or diminishes the differ- ence of the paths which the rays respectively pursue. This experiment has the additional advantage, that the isotropal portions do not entirely vanish as in the dark field, but remain apparent, tinted with the colour of the ground. The most beautiful effects are obtained when the thickness of the little plate is so proportioned that when the prisms are parallel to • Brunswick, 1853, 800. EEHAVIOUE OF MUSCULAR riBEES IN POLARISED LIGHT. 243 one another or crossed, it presents a beautiful purple colour ; the muscular fibres then appear blue or yeUow, according to their inclination. Amongst the different purple tints which can be obtained, that is the best which first appears in increasing divergence of the rays with crossed prisms, and which corre- sponds to the purple which is exhibited by Newton's colour glass in reflected light at the limit between the first and the second system of rings. It furnishes in particular the most sensitive field; that is to say, small difierences in the divergence of the rays occasioned by doubly refracting bodies lying upon the plate are rendered manifest by relatively great changes of colour. From preliminary investigation with the polarising microscope it is easy to discover, out of a series of gypsum or mica plates of various thickness, those that are best adapted for this purpose, jittention being paid not only to the colours themselves, but to the amount of change of colour occasioned by small accidental variations in the thickness of the sections. If the little plates which are used for preserving the prepara- tion contain air between their lamellse, which collects into bub- bles in the preliminary immersion in oil of turpentine, this can be expelled by boiling in turpentine, and allowing it to remain in it till cold. It may then be transferred to the balsam or varnish, with which it and the muscular fibres lying upon it are to be enclosed. CHAPTER VII. the heart. By F. SCHWEIGGER-SEIDEL. The muscular tissue of the heart presents certain peculiarities which connect it with the structure of those muscles that are subject to the will, whilst, on the other hand, in certain not unes- sential points it presents characters that are perfectly unique. The structure is apparently fibrous, although the slightest examination shows that it is impossible to exhibit fibres corre- Fior, Fig. 39. Small portion of a transverse section through the muscolar tissue of the heart, c, capillaries. spending to the elements of the ordinary muscles. When it is broken up, we for the most part obtain only portions of thin fibrous-Hke structure, because the fine muscular fibres, dividing frequently and anastomosing with one another, form a close and continuous network.* The contractile substance is transversely * Th3 anastomosing muscular fibres of the heart, which had already been depicted by Leeuwenhoek, were rediscovered by KoUiker. See his Mikro- skopische Anatomie, Band ii., pp. 209 and 483. Remak also described the peculiar characters of the muscular tissue of the heart in Muller's Arehiv for 1850. MINUTE ANATOMY OF THE HEAET. 245 striated, sometimes contains fat drops even when apparently- healthy, and presents nuclei that are arranged at tolerahly regular distances from one another. In the several round or oval disks which are found in sections perpendicular to the direction of the fibres, the nucleus is always in the centre,* excepting in those cases where, on account of the thinness of the section, disks without nuclei happen to be exhibited (fig. 39). The more or less wide fusiform spaces of the contractile substance in which the nuclei lie are filled in the larger speci- mens with a granular mass, which sometimes (in man) is of a yeUow colour (fig. 40, A). Fin-. 40. Fig. 40, A. Muscular fibres from the heart of Man, divided by trans- verse septa into separate nuo'eated portions. From a preparation pre- served in alcohol after having- been macerated in a 1 per cent, solution of potash, and in glycerine. B. Two laterally adherent muscle cells from the Guinea-pig. From a specimen that had been treated with acetic acid and solution of common salt. The interpretation of the nature of the so-called muscular fibres of the heart is difierent from that applicable to those of the vo- * Bonder's Physiologie des Menschen, 1859, p. 23. 246 THE HEART, BY F. SCHWEIGGER-SEIDEL. luntary muscles. Weismarm* first established, from extended re- searches in comparative anatomy, that the relations in question are not the same for aU the Vertebrata. In Lizards, Amphibia, and Fishes he found the several segments of the cardiac muscula- ture to be formed of closely approximated elongated and fusiform ceUs, the substance of which presented transverse strias (fig. 43). In Mammals, Birds, and Eeptiles, on the other hand, although an analogous cellular structure could be demonstrated during the embryonic period, yet the anastomosing fibres of the heart must always, he thought, be regarded as formed from the coalescence of isolated ceUs. KoUiker and Aebyf opposed this view, and the latter observer even found the muscular fibres of adults to be divided into separate portions by transverse septa. But EberthJ has recently made an important step in advance, by showing that in two of the above-named groups of Vertebrata a separation of the several cells from one another occurs iu the fully developed condition of the muscular tissue of the heart ; so that what was commonly regarded as a single fibre turns out to be a complex structure composed of one or many nu- cleated transversely striated muscle ceUs.§ Here, therefore, iu opposition to the term fibres, applied to the structural elements of the ordinary muscles of the trunk, we may speak of chains of muscle cells or muscle-ceU trabeculse. The difference above referred to between the several groups of animals amounts only to a dissimilar mode of arrangement of the muscle cells, the independency of which in the heart stiU remains certain. As a proof of this statement, it happens that especially in Mammals we are able to render the limits of the several cells apparent, and to obtain these in an isolated state. The best means for • Archiv fur Anatomie und Physiologie, 1861, p. 42. t Zeitschriftfur rationelle Medicin, 3 R., Band xvii., p. 195. X Virchow's Archiv, Band xxxvii., p. 100. § As long as a division of the cells from one another can he generally demonstrated we can ohtain no correct estimate of the degree of coalescence that has taken place j hence it is not easy to discover the difference that exists between the statements made by KoUiker in the fifth edition of his Sandbuch der Gewehelehre, and those advanced by Ebeith. Kolliker now admits that the coalescence of the cells is somewhat less intimate than he had stated it to be. MINUTE ANATOMY OF THE HEART. 247 this purpose is the nitrate of silver, with subsequent applica- tion of caustic potass, by the employment of which Eberth was able to split up the muscular substance of the heart into sepa- rate prismatic portions, corresponding with the black lines that come into view after treatment with silver, and result from the staining of the connecting substance between the cellular ele- ments. But we may also convince ourselves that, by the ap- plication of other means which render the tissue transparent, the muscular fibres are separated into distinct portions by highly refractive transverse lines, and that each of these divi- sions contains a nucleus. The want of transparency of the contractile substance usually prevents the delicate boundary lines of the cells from being discerned. But in all experiments in which isolation of the fibres is effected it is possible to obtain small nucleated portions of muscle, presenting similar appearances to those seen in fig. 40, B, the single septal fine a being easily distinguishable fi:om a fissure (i/) produced by the previous manipulation. The limiting surfaces of the several muscle cells are not plane. The transverse lines crossing the bundle frequently appear like a fiight of steps. Eberth found the borders of the ceUs more or less regularly dentated. I have, however, ob- served them to be smooth, and believe the difference to be occasioned by the circumstance that the muscle substance sometimes comes under observation in the contracted, coagulated condition, as after treatment with nitrate of silver, and some- times in the swollen, distended condition, as after treatment with acetic acid. Other irregularities of form appear to be due to the pressure which the muscle cells exercise upon one another. Every muscle cell contains a nucleus, occupjdng a central position, or two or more rarely several nuclei may be found, which sometimes lie in close relation to one another, and are of smaller size, thus appearing to proceed from- the division of a single one. If the nuclei be widely separated from one another, the question arises, which it is not necessary here to consider, whether the several nucleated cells represent stages of development, or whether there is a disappearance of the cell wall, or, in other words, that it has become incapable of recognition. In adults the solitary nuclei 248 THE HEART, BY F. SCHWEIGGEE-SEIDEL. have a length of about 0014, and a breadth of about 0007 mil- limeters ; whilst the muscle ceUs themselves measure, on the average, 0050 to 0070 miUimeters in length, and 0015 to 0-023 millimeters in breadth. The cellular elements are, for the most part, united to one another in the longitudinal direction, but in various parts they send off short lateral processes, which coalesce with those of neighbouring cells, and in this way form the anastomoses that occur between the longitudinal fibres. The cells are only placed in direct apposition to one another, in a transverse direction, in those parts where the stronger muscular Fig. 41. Ij.f' B' 'ti ' 1 .111' ' \ ■^ I 'I- ■ ■ ■' A f' JT""^ ' ■■•'J ' ■.,M?" 'l' ^' I' >f\ Fig. 41. Anastomosing muscular fibre of the heart, seen in a longi- tudinal section. On the right, the limits of the separate cells -with their nuclei are exhibited somewhat diagrammatically. trabeculse are formed. If, however, we consider the abundance of capillaries which, together with nerves and connective tissue, tra- verse the muscle substance in Mammals, we shall arrive at the conviction that it is impossible for any material to be of a more compact nature. Sections in various directions establish this most satisfactorily, and transverse sections, made from weU-hard- ened hearts (fig. 39), are admirably adapted for the purpose. But in fine longitudinal sections, numerous larger or smaller fissures, arranged in a stellate manner, may also be seen, and so fine that they have been described by some observers as fissures or MINUTE ANATOMY OF THE HEART. 249 spaces within the muscular fibres* Varying conditions of contraction of the musculature naturally produce variations ia the appearances presented. The fissures between the muscle cells are filled, not only by the capillaries, but by a very deli- cate connective tissue, which, in the form of a perimysium, constitutes sheath-like investments, and appears to consist of isolated branched cells. I have not been able to discover a proper sarcolemma, i.e., a special delicate investing membrane capable of isolation, around the muscle cells, and therefore, in common with other observers, wholly deny the existence of such a membrane investing the muscular fibres of the heart, or, at least, maintain that, if present, it can be demonstrated only with the greatest difficulty .f Nevertheless the cells of muscle, like all other naked cells, must possess a peripherical investment. Independently of the above-mentioned element- ary division into fibre cells, the muscular tissue of the heart splits up into coarse subdivisions. By means of septa proceed- ing from the perimysium, thick fasciculi or bundles are some- times formed, which, as the well-known columnse camese, are particularly well marked ia the auricles. In the walls of the ventricles, on the other hand, the arrangement is rather of a lamellar character, several thin expansions of muscle being so applied to each other as to form a thicker plate, which is visible even to the naked eye.j The thinner lamellse are either connected with one another by extremely delicate connective tissue, or there exists between them certain smooth-edged * Eemak, he. cit., Rindfldsch Lehrhuch der Pathologisehen Gewebelehre, 1866, p. 73. Eberth, in accordance with this view, represents longitudinal fissures as existing in the muscle cells ; but it may be seen in his fig. 13, that these really indicate the line of union of two adjacent cells. Moreover, Eberth does not appear to attribute sufficient importance to my view of the natural Assuring of the muscle ; at least, at p. 121, he observes that the muscular network of the mammalian heart does not exist to the extent attributed to it ; but that the appearances seen may frequently be produced by manipulation. + As to Winkler, who maintains the presence of a sarcolemma in the ArcMvfur Anatomie und Physiologie for 1867, it is obvious from his ac- count of the appearances presented on transverse section, that he reaUy treats of the sheaths of the perimysium. \ See Henle, Sandbuch der Systematisehe Anatomie, Band iii., Ahth. 1 ; Oefdssekhre, p. 54, figs. 40 and 44. 250 THE HEART, BY F. SCHWEIGGER-SEIDEL. fissures, wliich may be followed for some distance, both in regard to length and depth. These fissures, to which Henle has drawn attention, are in my opinion deserving of particular notice. I find that they are lined by a very delicate mem- brane, composed of flat cells, the contour lines of which, after treatment with nitrate of silver, appear in the form of a black pattern. Moreover, it is possible to raise up and isolate this membrane after short maceration, which has confirmed me in the opinion that many observers have considered it to repre- sent the sarcolemma. The fissures, in fact, occur ia the con- nective tissue, as may be seen at their angles, and have in rabbits, where, I think, they can best be seen, a length of from 0'06 to 0.25 millimeters. We shall return, however, to this subject hereafter. The arrangement of the muscular bands in the wall of the heart — ^the so-called lamination of the cardiac musculature — cannot be folly treated of ia this work, since it possesses no histological interest. The careful investigations of C. Ludwig, Pettigrew, Winkler, and others, have, however, shown how complex these arrangements are ; and, according to Henle, in addition to all these there must still be added the varieties due to individual differences. The results of accurate exami- nation seem to show that the musculature of the auricles, speaking generally, is divisible into two layers, arranged at right angles to each other, of which the external is circular, but in the case of the ventricles the arrangement of the fibres cannot be described in so simple a manner. We must pro- bably seek for the immediate cause of the spiral arrangement of the muscular bands that here exist in the history of its de- velopment, as it is well known that at an early period the cardiac tube forms not only a loop, but a spiral curve, through which necessarily a deviation in the course of both the longi- tudinal and transverse fibres will be occasioned. Sections made through the wall of the ventricle, in a direction perpen- dicular to the surface and parallel to the longitudinal axis, exhibit, both externally and internally, longitudinally running bands, whilst the median portion presents transverse sections of the fibres ; consequently we can here, though only quite generally, distinguish the two chief directions they pursue. MINUTE ANATOMY OF THE HEART. 251 The connective tissue is closely connected with the mus- cular substance of the heart, and presents at some spots a remark- able condensation ; it is arranged in well-marked layers — this is particularly the case in the so-called fibrous rings at the car- diac orifices, and in a lesser degree at the apices of the papillary muscles, both beiag points which constitute the origin, or perhaps the termination, of muscular fasciculi. The fibrous rings are composed of very strong fibrous tissue, traversed by exceedingly fine elastic fibres, and sometimes assume to some extent the character of cartilage, the appearances presented resembling those found in true cartilage, at its point of tran- sition into perichondrium. To these differences, which are by no means essential, the somewhat discordant statements and descriptions made by various authors may be ascribed. At the cardiac orifices the fibrous tissue enters into the formation of the valves, and in the papillary muscles it passes immediately into the tissue of the chordae tendinese, though always sharply separated from the tissue of the endocardium. The endocardium forms a membranous lining to the cavities of the heart, but is not everywhere of equal thickness. It par- ticipates in the construction of the valves, and is composed of several layers. Its proper basis is formed of an elastic layer, which contains networks of elastic fibres developed to a variable extent, with a corresponding variation in the quantity of con- nective tissue. The external layer is the loosest in texture. Its internal surface is lined by a layer of nucleated polygonal cells, resting upon a peculiar close-textured lamella of elastic fibres, which constitutes the endothelium of the cardiac cavities. It may be added that the' simple elastic lamina usually adheres closely to the muscular wall itself by means of a layer of connective tissue, whilst the muscular tissue aids in the formation of the endocardium by giving off to it both smooth and transversely striated fibres. The smooth muscle cells are introduced between the elastic lamellse, but do not form a continuous layer, being arranged in separate bands, which vary in size, and sometimes attain a thick- ness of O'lO millimeters. The several layers of the muscle cells in these fasciculi do not all pursue the same direction, though they generally appear to be divided transversely whentthe section U 252 THE HEAET, BY F. SCHWEIGGER-SEIDEL. has been made perpendicularly to the axis of the heart. These statements are true at least in regard to the endocardium of the septum ventriculorum of man, in which smooth muscular tissue is very distiactly visible. * Moreover, the more exter- nally situated transversely striated muscular tissue of the endocardium does not form a continuous or uniform layer, on which account it may easily be overlooked, or may be regarded as belonging to the muscular layers in general. That the latter is not the case, however, is obvious from the circum- stance that the muscular elements in part possess special peculiarities, and also that the endocardial layer is separated from the general musculature of the heart by connective tissue, lymph vessels, and networks of nerves. Moreover, we. find in the endocardium per se all the usual layers entering into the composition of the vascular walls, and may therefore very correctly, with Luschka,t identify the endo- cardium with the whole vessel, and not simply with its tunica intima. It remains to be remarked that the above statements are not applicable to the auricles, since their endocardium, although it possesses considerable thickness, anods remarkably rich in elastic tissue, does not present any proper muscular layers, though here and there a few smooth muscle cells are discoverable. The transversely striated muscle of the endocardium of the ventricle occurs in two forms, either as the well-known Purkinje's fibres, or as a wide-meshed network of muscular bundles, the elenients of which are distinguished from those of the heart by their proportionate size, being broader and shorter. As regards the grey gelatinous-like fibres recog- nisable by the naked eye, which Purkinje described in 1845 as being situated under the endocardium of the calf, they must partly be considered as a peculiar motor apparatus, and partly as an embryonic form of the muscular tissue * K.611iker denies positively the presence of smooth, muscular tissue in the endocardium {Mikroskopische Anatomie, Band ii., p. 493). Nevertheless, in regard to the localities referred to, no doubt can exist of the correctness of my statement. t Virchow's Arohiv, Band iv., p. 171 ; and Anatomie, Band i., Abth. 2, p. 380. , MINUTE ANATOMY OF THE HEART. 253 of the heart* The fibres are united to one another in the form of networks, and are composed of more or less prismatic segments (granules), having a diameter of from 0'05 to O'lO millimeters, each of which consists of a cortical layer of transversely striated fibrillar muscle substance, and a hyahne axile material con- taining one or two clear nuclei. Some observers regard the transversely striated mass as an intermediate substance, within which are deposited transparent isolated cells; whilst others, with whom I agree, regard each granule as a muscle cell, in which (as in a certain stage of development) only the peripheric layers have undergone conversion into contractile substance. In what relations these segments of the fibres of Purkinje stand to the cardiac muscle in its fully developed condition, is a subject that can only be elucidated by a knowledge of the history of development; but it may here be remarked that various observations have been made, which agree in showing that the fibres of Purkinje pass directly into ordinary muscular bands, and that in some animals their place can be supplied by ordinary muscular tissue. The controversy whether this or that animal possesses the fibres of Purkinje is therefore of small importance, because the differences depend merely upon the various forms presented by the endocardial muscle. A division of the stronger fibres, as we have already seen, does not occur here, whilst they are for the most part surrounded by a well-marked sheath of connective tissue. These sheaths, when penetrated by an injection pipe, sometimes become fiUed with injection, and then form a wide-meshed network which it is impossible to mistake for the vessels of the lymphatic system (Eberth). As already indicated in discussing the internal membrane of the heart, we have to consider the valves. These indeed are usually considered to be duplicatures of the endocardium, but this expression is not absolutely correct. The substance * Besides the work of Purkinje (Miiller's Archw, 1845, p. 294), reference may be made to the statements of Kolliker, Hessling, Reichert, Remak, Aeby, Obermaier, and Lehnert. More exact and extended references to the literature of the subject will be found in the last-named authors. Obermaier, Archiv fur Anatomie u. Phymlogie, 1867, pp. 245 u. 358 ; Lehnert, Max Schultze's Archiv fur Mikroskopisehe Anatomie, 1868, p. 26. U2 254 THE HEART, BY F. SCHWEIGGEK-SEIDEL. of these valves consists essentially of two lamellee, a fibrous and an elastic ; the former is directly continuous with the fibrous rings, the latter in the case of the venous valves is a prolonga- tion of the endocardium of the auricle, but iu the arterial valves it is a prolongation of the membrane lining the ventricular chambers. The free surface of the fibrous layer is invested by a thiQ membrane composed of cells which do not rest upon any special elastic substratum, except that perhapsthe elastic element of the fibrous layer itself undergoes a slight thickening at the margin. In the semi-lunar valves the elastic layer is considerably thickened, whilst at the attached border of the venous valves the two layers disappear towards their apices, their place being supplied by the tolerably abundantly nucleated tendinous tissue of the chordae tendinese. The latter near the musculi papillares possess an external elastic layer with a delicate investing membrane composed of cells, which constitutes a prolongation of the endocardium.* At the apices of the valves muscular bundles pass directly into the endocardium of the auricle, and extend to a greater or less distance downwards, but in all instances are limited to the upper portion.f According to the statements of Oehl,I small isolated muscles are pre- sent in the larger tendinous cords of the left auriculo-ventricular valves. The fibres of Purkinje are continuous with the chordss tendinese. Villous processes or outgrowths are sometimes found attached to the valves (Luschka, Lambl.). In regard to the endocardium in general, it should be mentioned that the microscopic appearances which are found in various animals differ chiefly in the greater or less development of the elastic network of fibres. The foregoing description is chiefly taken from observations made on the heart of man. • Analogous observations were formerly made by Bonders, in regard to the structure of the valves. I cannot agree with the statement of Luschka, that the valves are the direct continuation of the arterial wall, Archiv fiir Physioloaische Heilkunde, 1856, p. 537; compare also Henle. t Amongst the most recent investigations on the musculature of the auriculo-ventricular valves are to be enumerated those of Gussenbauer, Sitzungsherichte der Wiener Ahidemie der Wissenschaften, Band Ivii., Abth. 1. f Mem. d. Acad. d. Scienze d. Torino, Vol. xx., 1861. MINUTE ANATOMY OF THE HEART. 255 The pencardium, in opposition to the endocardium, is a serous membrane, and possesses the general characteristic peculiarities of such membranes. The subserous tissue is occasionally marked by the presence of a large number of fat cells. The bloodvessels are branches of the coronary arteries, and are distributed in the muscular substance, as well as to the pericar- dium and endocardium. The vessels of the last-named membrane extend, according to Luschka, into the valves. The capillary ves- sels distributed through the muscular substance of the heart are very numerous, the muscle cells themselves being enclosed in a network of vessels. The rootlets of the veins are formed by several capillary vessels uniting directly to form a thicker trunk ; an arrangement by which, we may conclude, the dis- charge of the blood is facilitated. In reference to the lymphatics of the heart, we possess recent investigations byEberth and Belajeff;* and, as they have pointed out, a network of lymph capillaries of the ordinary kind may be distinguished both in the pericardium as well as in the endocar- dium, the meshes of which are sometimes large and sometimes small, and are usually arranged in a single layer, but occasionally, where the thickness of the membrane is considerable, in several layers. The endocardial lymphatic network of the auricle is con- tinued bymeans of afewfiner tubesupon the auriculo-ventricular valves, and reaches nearly to their middle. In the same way a few lymph tubes may be traced as prolongations of the network of the endocardium of the ventricle into the semi-lunar valves. In the muscular substance of the heart itself the above-named observers found, in opposition to Luschka, that the lymph vessels were " not so numerous,'' whilst I conclude, from my own re- searches, that the muscular substance of the heart stands in still closer relation to the lymphatics than appears from their statement, because I am of opinion that the formerly described fissures of Henle found in the muscular substance must be re- garded as a portion and continuation of the lymphatic system. But since these fissures are connected at many points with one another, they form a canal system, permeating the muscular substance to an extent which certainly cannot be termed sparing. * Virohow's Archiv, Band xxxvii., p. 124. 256 THE HEART, BY F. SCHWEIGGER-SEIDEL. It has already been mentioned that the smooth fissures are covered with a delicate membrane analogous to the endothelium of the lymphatics, to which it must also be added, that it is easy to follow sub-pericardial lymph vessels and their prolonga- tions into the lacunar system. That this system cannot be in- jected through the vessels constitutes no objection to our view, On sticking an injection pipe into the muscular substance of the heart, the fluid penetrates between the several elements of the muscles into the perimysium, and may become widely dif- fused, so that with slight pressure we may even see the injec- tion penetrating into the lymph vessels of the pericardium without any evident rupture or extravasation. A complete injection of the lacunae cannot be obtained in this manner. It is observable that the lymphatics of the muscular substance are not always in the form of fissures, but sometimes assume a tubular form, dependent upon the amount of injection forced in, and upon the degree of contraction of the muscular substance. In regard to the finer distribution of the cardiac nerves, which is of peculiar physiological importance, little is at present known, and our knowledge is particularly defective in reference to the more intimate histological relations of the fibres spring- ing from various sources and distributed to the difierent tissues. The nerve fibres proceeding from the plexus cardiacus lie in mammals beneath the pericardium, but in part also they are found in the septum ventriculorum, where they run in the substance of the muscular mass and in the spaces between the two ventricles. Their distribution under the pericardium is independent of the vessels, and it even appears in some animals that the nerves cross the superficial muscular fasciculi and the vessels at right angles, as is clearly shovra. in the illustrations given by Lee.* The isolated, somewhat flattened fibres, which intercommuni- cate by means of delicate fasciculi, consist chiefiy of non-medul- lated nerve fibres. The double-contoured fibres vary in relative proportion, but are usually only sparingly present. The nerves * R. Lee, Philosophical Transactions, London, 1849, Plaies ii. and iii. MINUTE ANATOMY OF THE HEAET. 257 enter into communication with ganglion cells. These, united into groups, lie on the external surface of the fasciculi of fibres, and sometimes form small detached ganglia, which are con- nected with the nerve by a peduncle. Accumulations of cells of materially larger size do not occur, whilst in particular the enlargements of the nerves perceptible to the eye are occasioned simply by the penetration into their substance of connective tissue, accompanied by large vessels. The relation of the fibres to the ganglion cells can be better studied in the cardiac nerves of the frog than in the sub-peri- cardial nerves of mammals, as the former spread out in the thin interauricular septum, and are very well known in regard to their course of distribution, in consequence of several special works having been devoted to them (C. Ludwig, Bidder). The greater number of ganglion cells exhibit the structure peculiar to the cells of the sympathetic, in which from one and the same pole, besides the so-called straight fibre, there originates also the spiral fibre of Arnold and Beale, which has elsewhere been fully described. Besides these, however, as has been shown by various observers, true bipolar cells are present, and, lastly, also ganglion cells, characterised by the peculiar mode of their arrangement, which, if we accept the view of Auerbach,* are found " in opposition," — that is to say, two pear-shaped cells lie in a common sheath with their flat sides applied to one another, whilst the nerve fibres issuing from their pointed ex- tremities course in opposite directions. The approxiination of such binary cells being very close, especially when they are exa- mined in the fresh condition, they may easily be mistaken for simple bipolar cells. No spiral fibre is here present. Auerbach found this form of ganglion cell in the plexus myenteri- cus, Bidder in the auricular septum, and I myself in other sympathetic ganglia. According to my views, those cells from which two straight fibres can be seen to issue, belong to the same category, since as many even as three small ganglion bodies may be found invested by a common capsule. Since the influence of the nerves on the activity of the heart has been more accurately investigated, the view has generally been ad- * Virchow's .ear bouiidetl by sinuous outlines that are often crenulatcd and lobed ; as, for example, in the pulmonary Fig. 50. Fig. 50. a, Small capillaries with fusiform cells, taken from the me- sentery of Leucisous ; h, capUlaries of the pecten of the eye of the Bird, exhibiting polygonal cells ; V, hyaloid membrane investing the capillaries; c, capillaries from the intestine of the Snail, showing irregularly lobed cells. capillaries of the frog and of mammals, in the capillary veins of the choroid of the rabbit, and in the capillaries of cepha- MINUTE ANATOMY OF THE CAPILLARIES. 283 lopods. The dark contour lines often exhibit larger or smaller knot-Hke swellings. Many of these are composed of less deeply- tinted substance, surrounded by the intensely brown cementiag material, and perhaps consist of some modification of the latter, which is feebly acted on by nitrate of silver. The slighter stauiing may, however, also depend on dimi- nished thickness of the cement, whilst the deeper tints of other parts may proceed from the presence of particles of albumen, belonging to the original contents of the vessel, being retained in small indentations of the cell membrane, and be- coming of a deep brown colour by the action of the silver. That the dark lines winding round the nuclei in the silvered Fi-. 51. Fig. 51. Capillaries of the lungs of the Frog, with irregularly den- tated cells, a, vascular meshes. wall of the vessel are not due merely to albuminous preci- pitates occurring in the small furrows surrounding the several cells, as Auerbach* appears willing to admit, seems to be suffi- ciently refuted by the reactions of the cement in other mem- branes composed of cells, to which no application of nitrate of silver has been made. Besides the above-described dark inter- * Virchow's Archiv, Band xxxiii., 1865, p. 380. 284 THE BLOODVESSELS, BY C. J. EBEETH. vening portions, clear areas of various size are also observable, interposed between the plexuses of lines. The margins of these are, for the most part, similarly dentated to those of the adjoining cells, but they are always of smaller size, and destitute of nuclei. These appearances are not so frequently met with in the capillaries of mammals, but are common in the large arteries and veins, and also in the vessels of lower animals ; as, for example, in the Cephalopods. Many of these non-nucleated areas (intercalated areas, as Auerbach calls them), may fairly be regarded as portions of the vascular cells which have been pinched oif. Small, irregularly shaped, dark, sharply defined spaces may, after treatment with nitrate of silver, be met with within as well as between the cells. The number of the dark and clear intermediate areas varies much ia difiierent individuals, and more in the arteries and veins than in the capillaries. It has not been clearly proved that they are actually spaces in the waU (Stomata of Cohnheim). To enable us to understand the passage of blood corpuscles through the vascular walls, it is not requisite that coarse spaces or openings should exist, provided we may regard the vessel as composed, not of a stiff, but of a soft material, forming an elastic and permeable membrane. If the openings were reaUy coarse, colouring particles of large size would pass through the vascular wall in various regions. But this never occurs. We do indeed see that fine colouring particles* escape through the vascular wall, but this does not occur easily with those possess- ing the diameter of the colourless blood corpuscles. These, on the other hand, by reason of their softness and elasticity, accommodate themselves to the fine invisible pores of the vascular membrane, and having traversed these, regain their original form. Their escape must not, however, be regarded as a simply passive process, like the filtration of a colloid substance, to which it was likened in the first instance by Hering ;f for it * W. Reitz, Sitzungsherichte der Wiener Akademie, Band Ivii., ] i t Wiener SitzungshericMe, Band lyii., 1868. MINUTE ANATOMY OF THE CAPILLARIES. 285 can be influenced in the most various modes by the con- tractility of the cells. Everything, in fact, which favours or checks their active motility influences their extravasation (Hering). The finer capillaries consist only of a tube composed of cells or of a cylindrical layer of protoplasm. As the capillaries Fiff. 52. Fig. 52. Capillaries from tlie hyaloid membrane of the Frog, a, capillary wall ; b, nucleus of the same ; c, cells of the tunica adven- titia ; d, processes of these cells clasping the capillary wall ; e, stellate cells anastomosing with the cells of the tunica adventitia. become larger, a delicate tunica adventitia is superadded, which, ia the hyaloid membrane of the frog (a membrane well adapted for this investigation), is formed, according to the Y 2 286 THE BLOODVESSELS, BY C. J. EBERTH. researches of Iwaiioff* and myself, of a delicate network of fine fibrils, composed of the processes of stellate cells lying directly upon the vascular wall. Each of these cells consists of a large elongated nucleus, invested by an extremely delicate layer of protoplasm. CHEONSczczEwsKYt obsetved, in capUlaries which had been treated with nitrate of silver, the cells detached from their connections, and at the same time the external wall of the capillary prolonged over the hiatus. However little evidence there may be against the presence of a tunica adventitia in the capillaries of other organs, I must still remark that such observations as the above, for reasons that I cannot here discuss, are not always conclusive. Between the capillaries of the hyaloid of the Frog isolated stellate cells occur, with round nuclei and delicate protoplasm, branching ofi" into many processes which often anastomose with the processes of the cells of the tunica adventitia. Towards the small arteries and veins the pericapiUary plexus becomes con- stantly closer, and soon in its stead there appears a delicate transversely folded and nucleated membrane, which is sometimes elevated in the form of small vesicles. The general structure of these parts renders it scarcely probable that, as Iwanoff admits, the capillary sheath con- stitutes a lymph space. J Numerous examinations of the tunica adventitia of the larger hyaloid vessels, treated with nitrate of silver, and undertaken with the view of detecting the indications of cells in it, have led, in all instances, only to negative results. A similar nucleated membrane forms the outermost covering of the larger-sized capillaries, and of the arteries and veins of * Medizinisches Centralhlatt, No. 9, 1868. t Virchow's Archiv, Bandxv., p. 172, 1866. X In my first treatise I described the capillaries of the pecten in the eye of the bird as possessing- a delicate double-contoured tunica adventitia re- sembling the structureless membrane of certain gland tubes. More recently I have satisfied myself, from transverse sections of the pecten, that the apparent tunica adventitia is only the hyaloid membrane -which invests the ■whole of the pecten, and from its exactly following the course of the vessels, gives, vrhen seen on the flat, the illusory appearance of a complete tunica adventitia. MINUTE ANATOMY OF TUB CAPILLARIES. 287 the brain, spinal cord, and retina of man. The action of nitrate of silver frequently brings into view irregular flat cells in their substance, which are often fused into one another. By careful treatment they may be obtained in the isolated condition. Fig. 53. Fig. 53. A rather large capillary from the hyaloid of the Frog, pre- senting a membranous and nucleated tunica adventitia. This layer may be distinguished as the external vascular epithelium, or still better as the vascular perithelium. The number of cells seen on a transverse section of a capil- lary tube is, Tyith few exceptions, dependent less on their size than on their form, because the size of the cells in the capil- laries corresponds with the calibre of the vessels. In the 288 THE BLOODVESSELS, BY C. J. EBERTH. simplest examples, a fusiform spiral cell presents itself, the lateral surfaces of which are in contact, whilst the extremities occupy the spaces between the ends of adjoining cells. The capillaries in the pecten of the bird, even when extremely delicate, possess small polygonal cells, the breadth and length of which are nearly equal. It is only occasionally, and in the larger vessels especially, that the cells are distinctly fusiform. As concerns the substance of which the cells are composed, it is always more abundantly and distinctly granular towards the centre and around the nucleus, whilst near the margin it is quite clear, and thins off to a delicate border. The capillary cells of the pecten of the bird, on the other hand, are, even in profile, only indistinctly fusiform, are of nearly equal thickness at the centre and at the margins, and consist of finely granu- lar protoplasm, with a simple or divided nucleus, the contents of which frequently separate from the investing membrane of the nucleus, in the form of a roundish spherule, resembling a large nucleolus. Only a few vascular regions form an exception to these statements ; namely, the capillaries of the liver of Mammals and Amphibia, the chorio-capillaries of the former class, the hyaloid of frogs, and the young capillaries of the tadpole, and of patho- logical products of recent formation. After repeated observations, I have only been able to discover the presence of cells in the capillaries in these in- stances, in a few isolated points ; but in their stead I found fusiform or branched nucleated areas on the walls, bounded by finely punctated or interrupted hues. In the chorio-capillaris and the hyaloid membrane of the frog I found fusiform or polygonal cells in some only of the coarser capillaries, whilst in others no trace of them was discernible. As regards the significance of these facts, three possibilities exist, either the capillary wall does not consist of cells at all, or, if this be the case, they have disappeared in consequence of fiision with one another, or the capillary wall has become only imperfectly diflferentiated into cells. Now if, after repeated examination, a cellular structure is only demonstrable in the stronger and older capillaries, and but rarely in the younger, the conclusion is admissible, that CAVERNOUS VESSELS. VASCULAR PLEXUSES. 289 all capillaries are not constructed alike, and that they are not altogether intercellular tubes. Supposing that a nu- cleated or a non-nucleated, and in the first instance solid, process elevates itself from a capillary wall, gradually becomes elongated and hollow, its cavity communicating with the lumen of the capillary, — this may, in favourable cases, be regarded as a funnel-shaped outgrowth from a cell, but it is not an intercellular passage. In many instances, as in tad- poles, such outgrowths from capillaries are discoverable, which present no trace of cellular structure when treated with nitrate of silver, although in older vessels they can be readily brought into view. Must we not consequently conclude that the capillary wall thus beset with processes, is similarly composed to the funnel-like projections, and that, as Strieker says, they are composed of protoplasm, which has assumed a tubular form? The capillary wall is contractile both ia young and in adult animals. Strieker* saw the capillaries, not only of tadpoles, but of the nictitating membrane of frogs, contract to such an extent, that not even a single file of blood corpuscles could traverse them. Lastly, he observed small loop-like projections raise themselves from the wall of the capillaries of the nicti- tating membrane, and again become retracted. It is not im- probable that it is by means of such contractions the corpuscles are pressed into the capillary wall, and ultimately made to traverse them. Cavernous Vessels, Lacunar Blood Paths, Vascular Plexuses. Cavernous vessels result from the unravelling of the vas- cular wall, which becomes converted into a spongy tissue ; or from its becoming fibrous and membranous towards the lumen of the vessel, giving off processes that intercommunicate with each other, and which either form a spongy layer on the inner surface of the vascular wall, or a plexus traversing its entire calibre. A similar result is obtaiaed from the occurrence of quickly consecutive anastomoses of vessels of various size. The * Wiener Sitzungsberichte, Bande li. and lii. 290 THE BLOODVESSELS, BY C. J. EBEBTH. primary vascular wall becomes teased out into thin trabeculse and plates, varying in thickness, which are sometimes formed of simple cellular threads, and sometimes of all the tissues entering into its composition. Structures of this kind are rarely met with in the arteries. The so-called carotid gland of the frog is, however, an ex- ample of it. In this instance, the strong muscular wall of the carotid artery forms internally a network of trabeculse, enclos- ing spaces of variable size, which communicate freely with one another and with the lumen of the vessel. These trabeculse are simple outgrowths of the vascular waU, containing mus- cle cells, which chiefly run in the oblique and longitudinal direction. I cannot corroborate the statement of Leydig, that these are transversely striated, but they are certainly much stronger than other muscles entering into the formation of vessels. A similar structure has been found by Retzius to occur in the pulmonary arteries and aoita of the turtle. The structure of cavernous veins consists, in some instances, of simple trabeculse of connective tissue, as in the cavernous sinus, whilst in others it contains, in addition to the connective tissue, bloodvessels and muscular bundles running longitudi- nally, and anastomosing with one another, as in the corpora cavernosa of the generative organs. The endothelium of the vessels forms the innermost layer of these blood cavities. The cavernous capillaries repeat, on a small scale, the rela- tions of the cavernous veins. In the pulmonary organs of the snail the blood cavities are traversed by delicate nucleated trabeculse, composed of fine homogeneous connective tissue. There is here as complete an absence of a cellular investment as in the great vessels of the lungs and heart.* In the branchise of Crustacea the framework of the blood spaces is, on the contrary, composed of cells, the external ex- panded extremities of which rest immediately against the cuticle forming the so-caUed chitinogen layer, whilst the pyriform or clavate bodies of the cells which conceal the nucleus are applied * Semper, ZeMschrift fur wissensehaftUche Zoologie, 1856. Eberth, Blut- gefasse der Wirlellosen, " Bloodvessels of Invertebrates." CAVERNOUS VESSELS. VASCULAR PLEXUSES. 291 to the axes of the. gill laminae, and adhere to the wall of the larger branchial vessels. Between the cells are roundish spaces intercommunicating with one another, through which the blood courses. There is no special membrane lining or limiting these blood passages.* Fig. 54. Fig. 54. Gill lamina of the Hiver Crab, a, cuticula ; 6, clavate cells ; c, lacunar passages for the blood in the interspaces of the cells. Surface view. « Cavities similar to these, through which the blood courses, are also found, according to WUhelm Miiller, in the spleen of mammals. * Hackel, Muller's Arcliiv, 1857. Leydig, Lehrbuch, 1857, p. 385. Eberth, he. tit. 292 THE BLOODVESSELS, BY C. J. EBERTH. In the process of reparation of a wound ttere also originate finer or coarser intercellular blood paths, destitute of definite walls, which occupy the interspaces of the granulation ceUs. Originally they form an intermediary plexus of plasmatic canals which are supplied by the arteries, — the blood issuing through spaces in the unravelled vascular wall, and being similarly discharged into the veins. A portion of these plas- matic canals subsequently expand into true bloodvessels, the walls of which are formed by the fiision of the cells lining the blood canals ; the greater number, however, disappear altogether* Certain vascular plexuses are closely allied to the cavernous tissues, and, indeed, not unfrequently, as in the case of the papillse of the comb of the cock, develop into actual cavernous .spaces. Amongst these vascular plexuses there is one which lies in front of the coccjrx in man, and deserves special notice, from the peculiarities of structure it presents, and to which it owes the names it has received from its discoverer, Luschka,-f- of coccygeal gland, and nervous gland. This plexus forms a round or slightly oval, pale red, compact body, of at most 2' 5 millimeters in diameter, the surface of which is either smooth or slightly tuberculated. Sometimes, instead of this single body, there may be found from three to six poppy or millet-seed sized masses, connected together by loose con- nective tissue, and seated on fine branches of the middle sacral artery. According to their discoverer, these bodies consist of fibrillar connective tissue, with numerous oblong nuclei, con- taining closed roundish vesicles, and simple or branched slightly varicose tubes, which are composed of a delicate structureless basement membrane, lined by an epithelium-like layer of * Thiersch., Artihel Wundheilung , " Reparation of Wounds," in Pitha's and BUkoth's Handhueh. der Chirurgie, pp. 553 and 555. f Steissheindruse oder Nervendriise des Beckens, " Coccygeal Gland or Nervous Gland of the Pelvis," Archivfur Pathologische Anatomie und Physi- ologie, Band xviii., p. 106, 1860. JDer Hirnanhang und die Steissdriise des Menschen, " The Pituitary Body and Coccygeal Gland of Man." Berlin, 1860. Anatomie des Menschlichens Beckens, " Anatomy of the Human Pelvis." Tiihingen, 1864, p. 187. CAVERNOUS VESSELS. VASCULAR PLEXUSES. 293 round or slightly polygonal cells, replaced in recently bom animals by true ciliated epithelium. The rich supply of nerves to these supposed glands, and especially of sympathetic fibres, and their position near the lower extremity of the great sympathetic, appears to justiiy the view that whilst the hypo- physis is the cerebral pole of the sympathetic, this gland con- stitutes the anal pole, and is to be regarded as a nervous gland. Luschka's statements, so far as regards the presence of gland vesicles and tubes, have recently been corroborated by Krause.* Amold,-|- however, calls the glandular structure of this organ in question, pointing out that the glandular bodies of the mid- dle sacral arteries are capable of being injected, and that they only represent ampullar and fusiform dilatations of the lateral and terminal branches of that artery ; in other words, a true plexus arteriosi coccygei. These vascular sacculi, which may already be found as small, partial, but true aneurisms in the course of the middle sacral artery, and in larger number enter into the composition of the coccygeal gland, consist, according to Arnold, of an investment of connective tissue, which covers a layer of concentrically arranged and obliquely coursing muscular fibres, within which again is a delicate structureless coat, resembling the elastic fenestrated membrane. The innermost layer, the epithelial- like coat of the gland vesicles and tubes of Luschka, is com- posed of fusiform and polygonal cells, which frequently overlap each other at their edges. The connective intervening sub- stance of this is rich in muscles, which run in the most diverse directions, and form a continuous layer on the surface. At a later period Arnold discovered the existence of similar structures, consisting partly of vascular sacs, and partly of retia mirabilia, in the course of the middle sacral artery in the dog, cat, otter, squirrel, rabbit, rat, horse, ox, and pig. Krause and MeyerJ have therefore corroborated the princi- * Zeitschriftfilr rationelle Medicin, Band x., 3 R., p. 293. Anatomische TJntersuchurujen. Hannover, 1860, p. 98. t Archwfiir Pathologische Anatomie, xxxii., p. 293, 1865; xxxv.,p. 454, 1866 ; xxxix., p. 220, 1867. X Zeitschrift fur rationelle Medicin, xxviii. 294 THE BLOODVESSELS, BY C. J. EBEETH. pal statements of Arnold, but, at the same time, have esta- blished the occurrence of a laminated epithelium lining the interior of the vascular sacs, and have pointed out the analogy of these with the carotid glands of the frog, and termed them caudal hearts. The subject has again been taken up very recently by Sertoli * and the results of his inquiries are not in accordance Fig. 55. ** r 1 ' J ■> ! «• Fig. 55. Section of a naturally injected coccygeal gland, a, vessels ; 6, collection of cells. * Archivfiij- Pathologische Anatomie, Band xliii., p. 380. COCCYGEAL VASCULAR PLEXUS. 295 ■with those of the previous observers. He finds that the stroma of the so-called coccygeal glands is formed of a tough, fibrous, richly nucleated connective tissue, traversed by bundles of smooth muscles, and containing rounded and elongated tubes, the walls of which are principally composed of fibres of connective tissue, running in a longitudinal direction, with, at most, a few isolated muscle cells distributed amongst them. These tubes become fiUed with polygonal cells, which, in con- centric series of several layers, surround one or more centrally situated capillaries, or, less frequently, fine arteries or veins. These vessels are for the most part of normal calibre, and are rarely dilated ; but when they are so, it is probably the result of manipulation. My own view is that the coccygeal gland is a plexus of Fi?. 56. Fig. 56, A. Cellular -vascular sheath, from the coccygeal plexus, a connective tissue with scattered cells and nuclei ; h, round and polygOT nal cells lying immediately upon the capillary wall c. B. A capillary from the coccygeal plexus, with a vascular sheath very rich in cells. References as in A. vessels which are sometimes of equal width, and sometimes slightly dilated, or varicose, with lateral dilatations, which lie in a stroma of connective tissue, the numerous round, oval and fusiform cells of which are certainly only in very small proportion muscular. The greater number of these vascular sacs are found in the capillaries and veins, and seldom in the 296 THE BLOODVESSELS, BY C. J. EBERTH. arteries. Their number and size is often so considerable that true cavernous spaces are formed, and the intervening sub- stance is reduced to a thin framework. Around these vessels, and immediately external to their delicate cellular internal membrane, which is identical with that of the ordinary capillaries, lie rounded and elongated heaps of slightly polygonal cells, which are never invested by a definite structureless membrane, but have onlya layer of connective tissue with longitudinal fibres on their outer surface. Many capillaries are invested, and frequently for considerable tracts, with a single layer of these ceUs, which are covered by a fibrous tunica adventitia containing numerous nuclei. Small groups of similar cells lie also more remote from the vessels in the matrix or intervening substance. The larger ceU masses must therefore be regarded as richer collections of these scattered through cellular vascular sheaths. The size of these cell masses diminishes in proportion to the development of the vascular sacculi. On one occasion I found in the cell masses laminated struc- tures similar to those found in the granules of the thymus. The intervascular tissue of the coccygeal gland is very rich in nerves. As regards the ganglion cells, which Luschka stated he had observed, neither Arnold, Krause, nor myself have been able to satisfy ourselves of their presence. Nor have I been more fortunate in obtaining a view of the club-shaped termi- nations of the nerves resembling Pacini's corpuscles, or terminal bulbs, described by Luschka. They are said to be 0'8 milli- meters broad, and to possess a thick membranous and fibrous investing sheath containing numerous longitudinal nuclei. Inasmuch as a glandular structure is not demonstrable in the so-called coccygeal gland, which rather appears to consist of a rich plexus of for the most part capillary vessels, invested by a cellular sheath, some of which are normal, whilst others are dilated in a fusiform or sacciform manner, it is clear that for the future it should be named the plexus vasculosus coccy- geus, and that it should be classed with the carotidean vascular plexus of the so-called carotid gland, at the upper extremity of the common carotid of man and mammals. CHAPTER IX. THE LYMPHATIC SYSTEM. By PEOFESSOE F. v. RECKLINGHAUSEN. In consequence of the pressure under which the blood courses through the vessels of the several organs of the body, the tis- sues are constantly permeated with serous fluid, which partly furnishes the materials requisite for their nutrition, and is in part also subservient to the preparation of the secretions. This serous or tissue fluid requires constant renewal, a rapid ex- change of material, without which it quickly alters the compo- sition of the various tissue elements around which it plays. The passage of fresh fluid from the blood iato the tissues would, however, cease as soon as the pressure of the latter ap- proximated that under which the blood moves in the vessels, were not a constant escape of the fluid provided for by means of a canal system, which is so far separate from the bloodves- sels supplying the tissues, that the pressure of the blood is not transmitted directly into the canal system — that is to say, not with its. full force. These canals, the lymph vessels, form therefore a peculiar system, the rootlets of which are distri- buted through the tissues, and which only so far stands in connection with the bloodvessels, that it, 1st, indirectly with- draws from them the fluid they contain, and, 2nd, that it ulti- mately returns that fluid to the bloodvessels by its terminal trunks. The origin of the lymphatic system is in relation with the capillary vessels in which the blood moves under a con- siderable pressure; its termination, on the other hand, commu- nicates with the chief venous trunks, and consequently with those parts of the vascular system in which the blood pres- sure descends to its minimum amount, and is in fact almost reduced to zero, 298 THE LYMPHATIC SYSTEM, BY F. v. RECKLINGHAUSEN. The difference in tlie amount of these two pressures consti- tutes an essential factor in the production of the movement of the lymph; so that the greater the difference, the more rapid is the movement. The lymphatic vascular system borrows its contents, as well as the impulsive force under which they move, from the blood vascular system ; and in so far it may be re- garded as an appendage of, or as an accessory closed system to, the blood vascular apparatus. The dependency of the lymphatic system on the bloodves- sels is indicated by the circumstance that, as a general rule, the lymphatic system in any organ is so much the more strongly developed in proportion as its supply of bloodvessels (mucous and serous membranes, skin, glands) is more abundant; but there are also organs characterised by a peculiar richness in lymphatic vessels, which are at the same time especially adapted for ab- sorption (gastric and intestinal mucous membrane, central ten- don of the diaphragm). The entire lymphatic system may be divided into two sec- tions ; the first containing the fluid which, immediately after its escape from the bloodvessels, circulates around the several elements of the organs, the interstitial serous spaces ; and, secondly, the system of the efferent canals, the proper lympha- tic vessels. This second section will be here first described, because its structure is much more accurately known. The efferent canals, or lymphatic vessels, ordinarily agree in their form, arrangement, and in the structure of their walls with the bloodvessels. In the greater number of organs they form plexuses, which are so much the more close, the more abundantly the tissues are supplied with bloodvessels : more- over they only occur in association with bloodvessels ; and those tissues which are destitute of bloodvessels, like the cor- nea, vitreous humour, and epithelial tissues, possess also no proper lymphatics. Like the bloodvessels, they generally form cylindrical tubes, and only in certain regions, hereafter to be described, present the characters of fissures or lacunas, under which condition, however, they not unfrequently form investing sheaths for different organs. The Ijonph vessels may be dis- tinguished for the purposes of description into the smallest branches, the capillaries which are intercalated between the MINUTE ANATOMY OF THE LARGER LYMPHATICS. 299 system of the blood capillaries, and the larger lymph vessels which issue from the several organs, and ultimately unite to form the main trunks. The larger lymphatics of Mammals and Birds are always tubes, the walls of which agree with those of the bloodvessels in their structure, and hence present a tunica intima very rich in elastic fibres, and lined by a single layer of tesselated epithelium; a tunica media, consisting exclusively of muscular elements; and a tunica adventitia, composed as usual of loose connective tissue. The tunica media does not attain the thickness of that in the arteries, but its fibres pursue a similar transverse direction. Upon the whole, the lymphatics are not so thick-walled as the arteries, but, in the relation between the thickness of the wall and the calibre of the vessel, assimilate much more closely to the veins. The form of the lymphatics of Birds and Mammals is peculiar, and so far differs from that of the bloodvessels, that they are provided with very numerous valves, resembling gene- rally the valves of the veins. Immediately above each valve the vessel is somewhat wider than just below, and not 'unfrequently there is a distiuct saccular dilatation at this point. As a conse- quence of this arrangement, the lymphatics only preserve their cylindrical form for short distances in those parts which are destitute of valves, whilst in thosa parts where the valves are numerous they assume a varicose or moniliform appearance. The valves, like those of the veins, are simply duplicatures of the tunica intima. The structure and arrangement of the larger lymphatics present essentially different features in the Amphibia. They ■ do not here form even approximatively cylindrical tubes, but lacunce, which occupy the interspaces between the several or- gans. If, in consequence of an arrest of the flow of the lymph, or by artificial injection, they become more completely, filled than is natural to them, they swell out in the form of large sacs, which, however, possess no constant or definite form, since they only represent interstitial spaces. As a general rule they do not possess an independent thick wall, capable of being detached from the surrounding parts, but their limits or boun- daries are formed by the fasciae and such condensed layers of connective tissue as are found on the surface of the different 2 300 THE LYMPHATIC SYSTEM, BY F. v. EECKLINGHAUSEN. organs, the surface which is turned towards the interior of the cavity being covered with a single layer of tesselated epi- thelium. Only such septa as divide the several lymph spaces from each other, and are composed of pure connective tissue, can be regarded as properly belonging to them. The lymph sacs in thesa animals therefore resemble the peritoneal and pleural sacs, with this difference, that the lymph sacs commu- nicate with one another by means of microscopic openings in their septa, and consequently form a continuous system of cavities. Inasmuch as the lymph sacs are almost entirely destitute of proper waUs, the muscular elements, the function of which is to aid in the propulsion of the lymph, also fail ; but in their stead special contractile organs, acting rhythmically, appear in certain parts of the lymphatic system of Amphibia. These constitute the lymph hearts discovered by J. MiiUer, and one of them lying posteriorly near the sacrum propels the lymph into the sciatic vein, whilst the anterior pumps it into a branch of the jugular. They are chiefly composed of trans- versely striated short muscular laminae. These peculiarities in the structure and arrangement of the large lymphatics of Amphibia in contrast with those of other Vertebrata, are of great interest. They prove clearly that great variability occurs in the lymphatic system, much greater even than in the blood vascular system ; and, in truth, this variability occurs not only in different classes of animals, but in one and the same species, and not onlyin the larger trunks, but in the smaller vessels. The number and size of the principal trunks of any organ, as, for example, of one of the extremities of man, pre- sents as little constancy as the mode of their division. Even in one and the same organ the results of injection are often quite different, and it frequently happens that injections of the same organs in nearly allied animals present such remarkable differences, that only the most general statements can be made in reference to the arrangement of the lymphatics of any par- ticular locality.* It is obvious, therefore, that those typical modes of arrangement which occur in the arterial and capillary blood vascular systems of the different organs can only be im- * See the illustrations in. L. Teichmann's Saugadersystem. Leipzig, 1861. MINUTE ANATOMY OF THE CAPILLARY LYMPHATICS. 301 perfectly demonstrated in the lymphatics, and that only the general relations existing between the structure of any organ and its lymphatics present characteristic features. The varieties that occur in the arrangement of the lymphatics exhibit many pecu- liarities in certain regions of the smaller lymph vessels. Thus we see, in parts where they are very numerous and closely arranged, there are not unfrequently lacunar spaces even in Mammals, as if they had coalesced to form a flat and wide vessel; we meet also with a pair of lymph tubes accompanying a bloodvessel, and not unfrequently with regular sheaths, which partiaUy or en- tirely surround them, as, for example, in the case of the chyle vessels in the mesentery of the Mouse (Briicke). In such in- stances as these we recognise in Mammals arrangements essen- tially similar to the lymph sacs of Amphibia. There is stiU another circumstance that becomes intelligible from this comparison if we remember that certaiu sections of the lyruphatic system of the Amphibia do not possess a tubular form, but represent ensheathing or lacunar spaces. They are thus analogous, as we have already seen, to serous sacs, and it wUl be understood how the latter stand in. immediate relation with the lymphatic system, are in direct communication with it, and possess similar contents (see vnfrcC). This variability of form recurs in the narrowest section of the lymphatic system, that is to say, in the lymphatic capillanes. For even amongst Mammals we meet iu certain organs with lacunse, representing the roots of the lymphatics ; whUst in. Am- phibia the great majority of the lymph capillaries are tubular. The lacunse correspond in form with the spaces between the parts of the organs they invest, such as the ducts of glands, etc. The capillary tubes, even in their finest branches, are provided with varicose enlargements, and these are often situated at the points of junction of the vessels, and occur so suddenly that trans- verse processes project into the lumen of the vessel, which are again so placed that they form a kind of valve. Such dila- tations often succeed one another at very short intervals, especially in those lymphatics which immediately follow the capillaries, giving the impression of tubes constructed of a series of Florence flasks, of which each is inserted by its neck into the base of the one preceding it (see fig. 57). It is easy to z 2 302 THE LYMPHATIC SYSTEM, BY F. v. RECKLINGHAUSEN. recognise, from the position of these processes, what direction the lymph current pursues in any particular vessel, since they are so arranged that, Kke the valves of the larger lymph vessels, they prevent any regurgitation of the fluid. The arrangement of the capillary lymphatics in reference to the bloodvessels is a subject of special interest. The larger Ijrmphatics run sometimes in immediate proximity to the arteries and veins, and sometimes separately, or, at all events, present no constant relation to them. But for the smaller and capillary lymphatics, the general statement may be made that they hold their course at as great a distance as possible from the blood capillaries. This characteristic feature may be most easily recognised in membranous expansions, in which the blood and lymphatic capOlaries are distributed upon one plane : in such cases the points of junction of the lymphatic plexus al- ways occupy the middle points of the meshes of the blood capillaries, and the converse. It is evident that this arrange- ment is most advantageous for the purpose of drainage. All fluid escaping from the blood capillaries must traverse the tisssue to reach the capillaries ; and so long as this transudation occurs, a continuous play of fluid around all the tissues must take place. If, on the other hand, the lymphatic efferent canals lay in immediate contiguity to the blood capillaries ; if the whole were not, so to speak, intercalated between the tubes of the IjTnphatic system and of the bloodvessels, the fluids might easily stagnate in those parts which were more remote from both, and a constant interchange of material would cease to take place. There is yet another point that is deserving of notice. In those membranes which present a free surface covered with an epithelium, as in the mucous and serous mem- branes and the skin, the lymph capillaries are found constantly to occupy a deeper plane than the bloodvessels. Whilst the latter ascend tiU they lie just beneath the epithelium, the lymphatic capillaries do not reach the uppermost stratum of connective tissue. These relations are most easily recognised in the membrane forming the web of the foot in the Frog, which is a duplication of the external skin ; the lymphatics here exclusively lie in the middle connective tissue layer, whilst the bloodvessels course in the thin cutaneous laminae MINUTE ANATOMY OF THE CAPILLARY LYMPHATICS. 303 on either side. A similar arrangement of the two sets of ves- sels is strikingly shown in the case of the villi of the small in- testine, in which the proper tissue of the villi forms a peripheric layer traversed by a close iietwork of capillary bloodvessels, whilst the chyle vessel lies quite in the interior, near the axis, and is generally single and unbranched, as in the rabbit, ox, sheep, and man, though occasionally it has been observed to form a set of anastomosing capillaries, as in the dog, sheep, and ox. Again, if the results obtained from the injection of the cutaneous lymphatics by Teichmann, in a case of ele- phantiasis,* be considered to represent the normal distribution of the lymphatics, the capillaries of this system lie exactly in the- centre of the papillae of the cutis, whilst the blood capil- laries traverse their periphery. At first sight it appears remarkable that the lymphatics should He so deeply in organs destined for absorption, as, for example, in the viUi ; this relation, however, is in itself a suffi- cient indication that the connective and other tissues of the villi play a most important part in the act of intestinal ab- sorption, and that here also the central chyle vessel only acts as an efferent or drainage pipe. The function performed by the roots of plants is probably similar to that of the epithe- lium and the parenchyma of the villi. The chyle vessels, on the other hand, appear to be analogous to the vessels and fibro- vascular tissue of the plant ; if these were able to absorb, a more superficial position would be more appropriate to the discharge of their function. Having now learnt the form and arrangement of the capillary lymphatics, we turn to the consideration of their structure, a question which has recently received particular attention, and has met with various answers. Are they, like the bloodvessels, provided with a proper wall, or are they destitute of a limiting membrane, constituting only lacunae, or spaces in the tissues amongst which they lie ? The decision of this question is particularly interesting in the case of the chyle vessels of the villi. The chyle formed after the ingestion of food containing abundance of fat owes its white colour to the * Untersuchungen iiber das Saugadersystem, Taf. 6, fig. 4. 304 THE LYMPHATIC SYSTEM, BY F. v. EECKLINGHAUSEN. presence of numerous extremely fine molecules, which are pro- bably oil globules. Particles of a similar nature are met with during the process of absorption, both in the parenchyma of the viUi and in the epithelial ceUs. In aU probabihty, there- fore, they press through the epithehal layer as undissolved Fiff. 57 Fig. 57. Central tendon of the diaphragm of a Rabbit, treated with silver, and examined from the thoracic side, a, lymphatic capillaries with the contours of the epithelial cells ; 6, first appearance of the cells ; c, connective tissue with serous canals; d, flask-shaped dilatations. Magnified 60 diameters. molecules into the substance of the villi, and beyond this into the central lacteal. It would hence appear that the paths traversed by these minute oil drops in the periphery of the viUi open directly into the central chyle vessel; and the sim- MINUTE ANATOMY OF THE CAPILLARY LYMPHATICS. 305 plest view is, that no special limitiDg meml)rane exists (Briicke). On the other hand, microscopic examination shows that there is really a double, and not a mere single, outline to be seen in the central lacteal and in the finest capillaries in the tail of the Tadpole, from which the conclusion has been drawn that a homogeneous investing membrane is present (KoUiker). It was found also that in injected preparations the injection tightly filled the capillaries of the chyle and lymphatic vessels, without the escape of any of it into the surrounding tissues ; and hence it was considered that the assumption was perfectly justified, that these vessels were as completely enclosed by an investing membrane as the bloodvessels themselves (Teichmann, Frey). In point of fact, the presence of a special membrane in the lacteals and lymphatics may be most easily proved by the application of the silver method of staining the tissues adopted by Recklinghausen. If a solution of silver be injected into the lymphatics as far as the capillaries, or if the tissues be generally impregnated with a solution of this salt, fine dark lines appear in the Ijrmphatic capillaries (fig. 57), which are usually strongly looped or sinuous, including polygonal, or not unirequently rhombic, areas, in all their peculiarities identical with the silvered lines of the most various epithelial tissues. The networks of silvered lines become visible as early as in the rather larger vessels succeeding the capillaries, where the en- closed areas are fusiform, and agree with those brought into view by the agency of silver on the inner surface of the large lymph and blood vessels. In the case of these last-named vessels, it may easily be proved that the lines in question de- pend on the presence of a single layer of flat epithelial cells lining the timica intima ; but, inasmuch as the same markings may be traced continuously into the lymphatic capillaries, it follows that these also possess a similar layer of tesselated epithelium. In fact, even in the capillary lymphatics, subsequent treat- ment with carmine not unirequently brings into view an oval nucleus in each area. Moreover, if the intestinal villi be torn off a few hours after death, we may sometimes meet with one from the centre of which a wide tube projects, consisting of flattened epithelial cells. It is no longer, therefore, a matter of doubt that the capil- 306 THE LYMPHATIC SYSTEM, BY F. v. SEeKLINGHAUSEN. lary lymphatics — at least, in those organs in which they have been investigated with special reference to this point, as the serous membranes, the walls of the intestine, the diaphragm, both in its muscular and tendinous portion, and the membrana nictitans of the Frog — are lined by a single layer of flattened epithelium. They also possess a special membrane, though not completely homogeneous and structureless, as was formerly maintained, nor entirely closed, as we shall hereafter have oc- casion to see. I was formerly of opinion, after I had satisfied myself of the pre- sence of an epithelium in the lymphatic capillaries, that I had by this means discovered an essential distinction between them and the blood capillaries ; but, as subsequently it has been shown by experiments with silver that the wall of the capillary bloodvessels, in some organs at least, consists of epithelial cells, the distinction faUs. The lymphatic capillaries are, in fact, constructed on the same type as the blood capillaries (see the section on the bloodvessels). The ex- istence of such an analogy has been contested, because the blood capil- laries can be easily isolated in portions of considerable length in some organs, as the brain, whilst it is very difficult to exhibit such de- tached portions of the capillary walls of the lymphatics. Very re- cently Frey has been led to the conclusion* that, "whilst in the blood capillaries the walls maintain a perfect independence in regard to surrounding tissues, in the lymphatics they fuse with them." I be- lieve that we must beware of admitting that the blood capillaries are so completely isolable in all organs, or form such independent tubes, as in the hrain. In many glands — as the liver, for example, not to mention the spleen — the wall of the capillary bloodvessels is not capable of being isolated. And now arises the question, do the lymphatic capillaries possess a special wall or not ? Admitting an answer in the affirmative, are the above-mentioned phenomena taking place in the resorption of chyle consonant with it ? They would appear to demand that the lumen of the chyle capillaries should not be closed towards the free surface of the mucous membrane. But these a;ppearances can be equally well ex- plained, if we suppose that the wall is not everywhere formed of a continuous solid layer, or, in other words, that it possesses ' Handbuch, p. 427. STOMATA OF THE CAPILLARY LYMPHATICS. 307 foramina. Up to a recent period it has been generally accepted that epithelial investments, except in the case of glandular epithelium, serve as a protection to the subjacent tissues, and therefore, by the intimate union of the cells with each other, form a firm, close tissue, permeable only for fluids. Since, however, the terminal apparatus of the sensory nerves has been discovered in the epithelial strata, and very recently also cup-shaped organs, both of which seem to be but ill adapted for protection, the epithelial tissues have gradually attracted more and more attention from histologists, and it is not sur- prising that further inquiries should be undertaken with the view of discovering other and peculiar arrangements. It is reasonable, therefore, on d priori grounds, to concede that the epithelial coating of chyle and lymphatic capillaries may pre- sent special peculiarities which stand in relation to the absorp- tion of material from the surrounding tissues, and may, at any rate, at certain times, facilitate their passage. In some lym- phatics, openings of appreciable size are already known to occur, through which, even during life, small bodies may be absorbed into the interior of the tube. They were first demonstrated by Recklinghausen, in the central tendon of the diaphragm. If we inject into the peritoneal cavity of mammals mUk, blood, or fluids which have insoluble substances (consequently not carmine) in suspension, a beautiful injection of the net- work of lymphatics of the central tendon of the diaphragm may be obtained. If we press a cork ring against the central tendon from the thoracic side, attach a portion to it with needles, and then excise it, we are enabled to procure the surface of the tendon in an absolutely uninjured state. If now we place a drop of mOk upon this, the absorption of milk globules into the lymphatic vessels may be directly observed under the microscope. The milk globules run towards certain points at which small vortices occur whilst they are penetrating into the subjacent lymphatics. The openings through which they gain entrance are only wide enough to admit two or three milk globules abreast, are roundish, sometimes even quite roimd, and represent, as is clearly shown by subsequent staining with nitrate of silver, spaces between the epithelial cells. They usually lead perpendicularly into the lymphatic vessels, over which they 308 THE LYMPHATIC SYSTEM, BY F. v. RECKLINGHAUSEN. are immediately placed, but sometimes they are situated some- what obliquely, towards the margin of the vessel, or they may even be as far distant as a semi-diameter of the vessel, in which case there is an oblique canal leading to the latter. The openings (stomata) never exceed the size of an epithelial cell. The rich lymphatic plexus of the central tendon with these large stomata is obviously subservient to the absorption of the fluids of the peritoneal cavity, which, like the lymph, contains contractile cells, capable, from their size, of passing through the stomata. In the frog, which has no diaphragm, Schweigger-Seidel and Dogiel found that openings of a similar nature exist in that surface of the wall of the cistema lym- phatica magna that is turned towards the abdominal cavity. Dybskowskyalso was able, by causing the absorption of coloured fluids from the pleural caVity of dogs into the lymphatic plexus of the pleura, to demonstrate the existence of similar openings between the epithelial cells. From these experiments we may now reasonably expect that analogous formations will be found in the pericardium and in the arachnoid membrane of the brain, and that, consequently, we may conclude all serous cavities to possess a very intimate connection with the lymphatic system. Further, it has been shown, in regard to many epithelial layers, even in parts where the lymphatics certainly do not approximate the surface, that when they have been treated with nitrate of silver, sharply defined spaces exist between the epithelial cells which may be placed in the same category with the stomata above described. Oedmansson first described them in the epi- thelia of serous membranes. He drew attention to their occur- rence in the epithelial stratum of the chyle vessels and of the follicles of Peyer ; Ludwig, Schweigger-Seidel, and Dybskowsky demonstrated their presence in the pleura and peritoneum, and further showed that they were especially abundant in the small-celled epithelium which lies directly over the lymph vessels on the peritoneal surface of the central tendon of the diaphragm. They are distinguished from the proper stomata by their much smaller size, the largest only attaining the diameter of a red blood corpuscle, and they are principally found at the points of jimction of several epithelial cells. I recognised these spaces when I first began to employ silver as STOMATA OF THE CAPILLAET LYMPHATICS. 809 a means of staining the tissues; but have met with them under so many diflerent conditions, that I am not at present satisfied of their nature. In perfectly fresh silvered prepara- tions, preserved as carefully as possible in their natural condi- tion, we frequently meet with areas of considerable extent in which scarcely any openings are present, whilst in others, agaiQ, they are very numerous ; the difference being in no way attributable to the mode of preparation. At the same time, it cannot be denied that within a few hours after death, or as a consequence of mechanical violence, or careless prepara- tion, they always appear more numerous, clearly on account of the epithelial cells becoming detached from each other. The variability iu the appearances presented by perfectly fresh specimens may be explained on the supposition that at certain times, or under certain conditions, connected with the imbibi- tion of fluids, the substratum of the epithelium opens, whilst under other conditions it closes up. At present no absolute proof has been adduced to show that they are really openings, nor has any one shown that solid particles can traverse them. I must express myself in exactly the same terms in regard to the very regular and interesting appearances of a similar nature, situated for the most part at the points of junction of several epithelial cells, which are frequently exhibited in the lymph vessels of silvered preparations, but which are some- times undiscoverable even when the greatest care has been taken in the preparation of the specimen. I endeavoured to obtain them constantly, and hoped, in accordance with what has been above stated, to accomplish this by permitting the central tendon to lie for several hours iu diluted pericardial fluid, thus rendering its tissues as moist as possible with an indifferent fluid, yet without being able to observe the spaces occur with such constancy and regularity as, after the foregoing exposition and the observations I have stiU to make, was to be desired. The present condition of our knowledge may there- fore be expressed in these terms, that stomata can be certainly proved to exist in certain lymphatic capillaries ; that openings, at least of an occasional character, must also exist in other lymphatics, especially iu absorbiug membranes, though this stiU remains to be satisfactorily demonstrated, notwithstanding that 310 THE LYMPHATIC SYSTEM, BY F. v. RECKLINGHAUSEN. Oedmansson, His, and others have described foramina present- ing features analogous to such stomata. We come noAV to the essential point of the whole inquiry, the nature, namely, of the relation borne by the lymphatics to the surrounding tissues. And we must first ask whether definite channels exist by which the fluids transuded from the blood are conducted to the commencement of the lympha- tics, or whether the surrounding tissues behave like Descemet's membrane, ia which pores and canals are present of sufficient magnitude to enable them to be readily seen by means of the microscope ? If we consider the phenomena of the absorp- tion of fat, it appears absolutely requisite to assume, not only that there are foramina in the walls of the capillary lym- phatics, but that there are channels in the surrounding substance of the parenchyma in the case of the viUi, though in regard to the other rootlets of the Ijonphatic vessels, their existence appears less requisite, since their contents, apart from the lymph corpuscles which are probably formed in their Ulterior, ordiaarily consist of a fluid destitute of any undis- solved particles, or oil drops. In the parenchyma of the villi, a plexiform disposition of the chyle constituents hasbeen observed to be situated immediately beneath the epithelium, forcibly suggesting that special arrangements are here present, by means of which the vessels containing the chyle are brought into direct communication with the cavity of the intestine. Very recently it has been maintaiaed by Letzerich that a special system of canals, commencing with cup-shaped organs, in the epithelium, conducts the chyle into the central lacteal; but, even in the event of this statement proving correct, there must still be apertures or canals analogous to those above described, which lead from the abdominal cavity to the lym- phatic vessels of the central tendon of the diaphragm. A lively discussion is still maintained, as to whether the lym- phatics are closed channels, or whether they stand in communi- cation with interspaces of the tissue, from which, indeed, they may be supposed to be developed. The former view has be- come more definite since Virchow and Uonders advanced their doctrines respecting the stellate connective tissue corpuscles ; the corpuscles, in consequence of the fusion of their membranes. MODE OF ORIGIN OF THE CAPILLARY LYMPHATICS. 311 are supposed to form a continuous system of tubes, a plasmatic vascular system, or, as it was called by KoUiker, a system of serous tubules, easily suggesting what was said in precise terms by Leydig, that this system of tubules was intercalated between the blood capillaries on the one hand, and the lym- phatic capillaries on the other, and constituted the direct path between them. This statement was mainly supported by ob- servations made on the tail of the tadpole, in which KoUiker found a distribution of lymphatic vessels with dentated out- lines in connection with stellate, angular bodies, the connective tissue corpuscles. Whilst all such stellate and angular bodies require the existence of a membrane to be admitted, both this plas- matic system and the lymphatic system were regarded as closed. Physiologists, however, and particularly Briicke and Ludwig, maintained the view that the roots of the lymphatics, them- selves destitute of a membrane, commenced simply from the interstices of the tissues, or from the so-called lacunae. Foh- mann, and before him Mascagni, had already, by injecting the lymphatics with mercury, obtained, when sufficient pressure was employed, such complete injections as to arrive at the conclusion that the tissues were entirely composed of a close plexus of lymphatics, and that the solid tissues constituted only small trabeculse and septa between them. Briicke, in support of this view, argues from the known fact " that when injections of the bloodvessels are performed shortly after death, and therefore whilst the fluids permeating the tissues, as the lymph and blood, still remain uncoagulated, in not a few cases either the entire mass of injection, or the fluid portion of it, returns by the lymphatic vessels, which thus become even more completely filled than can be effected after the employment of much care and trouble." Ludwig and Tomsa have, moreover, in their injections, driven gelatinous fluids into the ultimate lymph canals of the testes in man and in dogs, and the injection was found to fill almost all the intervals between the tubuli seminiferi, following their course, and thus occupying spaces which formed continuous lacuniform sheaths around the ducts. The contiguous lacunae were divided from one another by very thin septa of connective tissue, in which the bloodvessels ran. On a small scale, therefore, the arrangements were similar to 312 THE LYMPHATIC SYSTEM, BY F. v. EECKLINGHATJSEN. those met with in the lymph sacs of Amphibia. The idea was consequently not far fetched, that these appearances originated from the manipulation of the specimen, and the extravasation of the fluid ; and, in fact, this objection was raised by the opponents of the \dew held by Briicke and Ludwig; and Langer even pointed out that ia the testes of the frog the lymphatic vessels do not form sheaths of this nature, but tubu- lar plexuses, as is usual in the lymphatic capillaries of other parts. Nevertheless it cannot be doubted that in the testes of many Mammals the lymphatic tubes ultimately terminate ia lacunar channels. Ludwig and Tomsa have further attempted to prove the existence of such interstitial lacunae in other organs, as in the tongue and kidneys, and to demonstrate their connection with the lymphatic vessels. From this exposition of the two opposite views it is obvious that they difier from one another in one point, which is deserving of especial notice. In the one view, the anastomosing connective tissue corpuscles form a plexus, the nodal points of which are represented by the body of each corpuscle; the fibres of the plexus are hollow cylinders, and their disposition, upon the whole, similar to that of the lymphatics. On the other view, the interstitial spaces depend for their form on that of the morphological elements of the tissues (ducts, fibres, etc.) between which they he. They vary in their form and size, but in general, because by far the greater number of tis- sues consist of cylindrical or spherical elements with more or less convex surfaces, they constitute fissures (that is to say, spaces the transverse section of which is not circular, as in. tubes, but elongated, presenting in some instances a very small, and in others a relatively large diameter). Special importance has been attached to this lacuniform character of the channels by Ludwig. At the point of transition of these into the proper lym- phatics, the lymph path undergoes a. sudden alteration of form. In opposition to these two views, I have stiU a third to propose, which is in accordance with all the facts that have hitherto been observed. The essential feature of this is, that the masses of connective tissue, whether they form the exclu- sive structure of an organ, or are intercalated between the proper morphological elements of some other tissue, are tra- MODE OF ORIGIN OF THE CAPILLARY LYMPHATICS. 313 versed by fine canals, the serous canaliculi, which are directly- continuous with the Ijrmphatic vessels. These canals, in many organs, form plexuses, so that portions of them appear to be branched in a stellate manner exactly resembling the connec- tive tissue corpuscles. These last however, are not, as Virchow, KoUiker, and Leydig supposed, fused with the walls of the lymphatic vessels, but occupy the interior of the serous canali- culi, so that from this poiut they may extend into the lumen of the lymphatic vessels. Moreover, the serous canaliculi are not provided with a special wall, and are consequently not tubes, on which account they are to be distinguished from the serous canals of KoUiker, but are rather to be regarded as excavations in the remaining substance of the connective tis- sue. They do not, however, represent — and on this account my view is to be distiaguished from that of Briicke and Ludwig — mere fissures between the specific components of the connective tissue, but are the interstices of the fibrous fasciculi and la- mellae of connective tissue, cemented to one another by a tenacious, homogeneous, firm material in which the serous canalicidi are buried. Their form and arrangement, whUst it is not independent of the form of the interstices, is yet not altogether identical with it, but peculiar, and one not entirely determined by the arrangement of the several morphological elements of the organ. On my view, therefore, it cannot be admitted that the commencement of the lymphatics are, as Ludwig imagines, simply lacunse, whilst, on the other hand, it is equally opposed to the view that they constitute closed mem- branous tubes, as is maintained by the adherents of the doctrine that they owe their origin to the connective tissue corpuscles. When organs composed of connective tissue, and recently removed from the body, are treated with solution of nitrate of silver, the solid parts alone become stained, whilst spaces and channels in the tissue remain uncoloured ; the lymph and bloodvessels coming into sharp relief as colourless tracks. In the connective tissue itself, stellate, unstained figures make their appearance, which are consequently spaces, though not altogether empty, since, by this mode of treatment, connective tissue cells become dimly visible in their interior. His main- tained that the silvered tracings of the cornea agree with the SI 4 THE LYMPHATIC SYSTEM, BY F. v. RECKLINGHAUSEN. form of the cells ; in other words, that the soUd substance presents cavities which precisely correspond to the cells and their processes. In the meanwhile, if we allow the corpuscles of the cornea, with all their processes, to come into strong relief, by exposure for several hours in the moist chamber (which is the best method of rendering them distinct), the ramifications of their processes are always found to be few in number, and the communications between their finest branches to be dis- covered only with difficulty, whilst the silvered lines form a close plexus ; the stellate corpuscles of the cornea, however, do not be- come covered with the tracings. But further, we see the actively moving cells of the cornea traverse its substance in all direc- tions, without, as a rule, attaching themselves to the processes of the stellate, immovable corneal corpuscles, though they sometimes do so with great distinctness ; with the spaces in which the latter lie, channels must therefore stUl be in com- munication, which are not occupied by the protoplasm of the cells. Moreover, W. Engelmann, since the migrations take place in every possible direction, has drawn the conclusion that the cells run without obstruction between the fibrils of connective tissue, pressing in from one to the other ; various circumstances, however, are in opposition to this view. By careful observa- tion it may be seen that the movements of the migrating cells do not take place with equal facility in aU directions. They become constricted at certain points, and these constrictions remain unaltered in position, whilst the several corpuscles force themselves through ; again they appear to meet with an ob- stacle, and must pass round it, though the constricting and obstructing substance may be so delicate as not to be visible. But further, if the cornea, or other variety of connective tissue (independently of the cells) consists only of fibrils with intervening fluid, in cases where the injection of an insoluble mass has been effected by means of simple pene- tration, the whole tissue can be split up into fibrils, or, in the case of the cornea, into lamellae, and we may then obtain the sub-cylindrical canals (Bowman's corneal tubes), which often form very distinct plexuses. It is true that the latter, as they appear after injection, present a very unnatural form, being dilated to an enormous extent, on which account, however, they SEROUS CANALS. 315 must not be at once cast aside as " artificial products," but they rather show, since their forms cannot be referred to the arrange- ment of the fibrils, that the interfibrillar and interlamellar sub- stance does not possess, in aU directions, an equal density, but must consist of a soft fluid mass, and a firmer and more resistant material. From microscopical investigation we learn that the corneal corpuscles are situated in the channels which contain the injection; this must consequently correspond with their natural position, and it foUows that these spaces are, at least in. certain directions, immensely dilatable, and can Scarcely there- fore possess a proper investing membrane. If we take all these facts into consideration, we must, I think, come unavoid- ably to the conclusion, first, that, in the denser organs com- posed of connective tissue, a^ the cornea, tendons, fascise, and cutis, the lacunae between the fibres or fasciculi are not filled with fluid alone, but in great part contain a more solid cement- ing substance ; and, secondly, that in this more solid substance there are no cavities constituting matrices for cells, although plexiform canals destitute of walls are present, which are partly fiUed with ceUs, and partly with a variable quantity of fluid consisting of the juice of the tissues. Since the nitrate of silver, when properly applied, only colours the solid tissues, the serous canals appear as colourless bands, re- sembling the lymph and blood vessels, which can be followed to their finest branches withafacilityproportionate to their breadth, or as they happen to be filled more strongly with fluid at the time when they were stained with the silver. We must attribute the ■ incomplete appearance of the plexuses in some cases to the ab- sence of fluid, especially where the wider parts only, in which the connective tissue corpuscles He, make their appearance. The serous canals have, however, very different forms in the various organs. They appear as distinct plexuses of subcyUndrical ca- nals in the dense organs composed of connective tissue, to which reference has above been made, the form of the networks being in accordance with the stratification of the organ ; so that in the tendons and fibrous organs the meshes are considerably elongated in the direction of the fibres, whUst in the cornea they are expanded into layers between the lamellae, and are in communication with one another by comparatively few branches, ,; .. A A 316 THE LYMPHATIC SYSTEM, BY F. y. RECKLINGHAUSEN. that perforate the lamellae in an oblique direction. In soft interstitial and investing connective tissue, Kk« the peri- mysium, the canals appear extraordinarily wide, the dilatations in particular being in close proximity with each other, and the solid tissue, in which the canals are imbedded, being much diminished in quantity. Lastly, in all soft organs lying imme- diately upon the surface, in the most supei-ficial layers of the capsules of the joints, in the serous membranes, and in the mucous membrane of the intestine, the solid portions are reduced to thin septa, which very incompletely separate the closely approximated spaces lined with cells. All these varieties con- stitute gradations of one and the same type, the terminal members of which present, on the ^one hand, the form of a cylindrical tube, and on the other, that of a lacuna ; neither of them, however, represent the typical form, and it is conse- quently most appropriate to employ the term canal, since it expresses nothing definite with regard to their form. " In opposition to the importance which I attribute to the silvered preparations, various objections have been adduced, with all of which I am acquainted, since I have myself formerly had to meet them ; but from my numerous researches I draw the conclusion that all the indis- tinct appearances obtained by those who oppose my method, proceed from injuries, accidental rents, and alteration of chemical composition ; and I. still believe that no method is more suitable than mine. All ob- jections to. it may be disposed of in the words of Schweigger-Seidel : " The regularity of the figures, the constancy with which the same forms recur in certain localities, and the presence of nuclei, which however are not always equally distinct, in their interior, furnish satis- factory proof that they are not accidental formations." Schweigger- Seidel niakes the above statement only in regard to the lines showing the presence of an epithelium, and maintains that the indications of the presence of serous canals, after the removal of the epithelium, originate in an albuminous layer, subjacent to the epithelium, and con- sequently upon the surface, and not in the interior of the connective- tissue lamina. I do not, however, quite comprehend why Schweig- ger-Seidel leaves quite out of consideration the markings produced by silver in the cornea ; for in the cornea it is quite easy to demon- strate that the layer on which the silver acts is not equivalent to the anterior surface of the cornea, which first comes into contact with the' solution of silver, but not unfrequently rather lies in close approxima- SEEOUS CANALS. 317 tion to the membrane of Descemet. From the consideration of this one point, the doubt which he has expressed could be overthrown, and the proposition above advanced be also maintained in regard to the silvered markings of connective tissue. The serous canals represent spaces which are continuous with the lymphatic vessels, and it may even be said that they Fiff. 58. Fig. 58. Central tendon of the diaphragm of a RabbH treated with silver, a, lymphatic capillaries with epithelium ; b, commencement of the same; c, serous canals; c?, transition of serous canals into lymphatic vessels most abundant at the border D. Magnified 300 diameters. constitute the roots, so frequently sought after, of the lymphatics. As a proof of this, the foUowing facts may be adduced : 1 . In A A 2 318 THE LYMPHATIC SYSTEM, BY F. v. RECKLINGHAUSEN. silvered preparations, a direct transition of the colourless pas- sages of the serous canals into the smaller lymphatics may be observed. Successful preparations of the central tendon of the diaphragm show in the most distinct maimer the transition of the small cylindrical serous canals (see fig. 58) into the lymphatic capillaries. The latter, at their very commencement, frequently present dentated contours, and at the bottom of Fig. 59. Fig. 59. Central tendon of the Rabbit, treated -with, solution of nitrate of silver, the most superficial serous layer immediately adjoin- ing the pericardium being shown, a, lymphatic capillaries ; h, their origin ; c, serous canals -with communications ; d, seroiis canals equal in •width to the origin of the lymphatic vessels ; e, bloodvessel with epi- thelial cells. Magnified 300 diameters. these depressions the limits of the lymphatic vessels very fre- quently become insensibly lost in the serous canal system. This disappearance of the boundaries of the lymph vessels it is very easy to understand is so much the more obvious in pro- RELATION OF SEROUS CANALS TO CAPILLARY LYMPHATICS. 319 portion as the canal system is wider, and is consequently par- ticularly well marked in the serous membranes and other analogous structures (fig. 59). In preparations of this kind it is important to avoid everything that may produce alterations in the structures under examination ; for if the contours of the lymphatic vessels and serous canals are in the smallest degree rendered indistinct and hazy, it is impossible to determine accurately the nature of their connection. But such blurred images are always obtained if the epithelium has not been carefully removed previous to the impregnation of the preparation with the solution of silver. His appears to have had only such indistinct specimens before him, as he believed that an unskilled observer might remain in doubt as to the continuity of the contours.* 2. If the lyraphatic vessels be injected towards their rootletS) it is very easy, even with an insoluble injection, to produce extravasation into the tissue, by which it becomes more or less stained. Under the microscope we may then see in the softer tissues only a dense mass of colouring matter, without any of the ordinary canals being visible ; harder tissues must consequently be selected, if we desire in this way to ascertain the path fol- lowed by the injection. In the fascia of the thigh of the frog, forming the wall of a lymph sac, I have succeeded in fill- ing canals contaiaing connective tissue cells with granular colouring material, by injecting the sac ; and we may also force very fine injections through the lymphatic vessels of the cutis into the subcutaneous connective tissue, the fluid passing di- rectly into channels that precisely agree in their form with the plexuses containing healthy pigment, i.e., the ramifications of the so-called pigment cells ; indeed, the injection may sometimes be propelled into the plexus of pigment cells itself. We can- not, therefore, entertain any doubt that the injection, if it escape from the capillary lymphatics, enters into channel-like spaces of the tissue, which are nothing else than the serous canals themselves, since they here contain the pigmented connective tissue cells. Moreover in all soft tissues, as, for instance, in the villi of the small intestine, plexuses first make their appearance ; and then, when the injection has been driven with great force, the * Zeitschrift filr wissenschaftliche Zoologie, Band xiii.. Heft. 3, 1863. 320 THE LYMPHATIC SYSTEM, BY F. v. EECKLINGHAUSEN. diffused tense infiltration is produced, in -which no determinate figures are discoverable. Against these results it has been objected, and to a certain extent justly, that such appearances are due to over distension, and originate in extravasation or rupture of the tissues ; and it is certain that they do not appear "with the above-named injections, unless very considerable pressure has been applied. In the meanwhile, the injection of the substance of the villi occurs even when only very slight pres- sure has been employed ; and we here possess a very good means of control by a comparison of the results obtained with the natural injection that takes place with the chyle. The same appearances are presented in both instances, of a plexiform arrangement of chyle drops around the central lacteal in the first instance, and ultimately of chylous infiltration of the whole parenchyma of the villus. Can it be possible that such a plexi- form appearance of the chyle masses has given rise to the belief that the lacteals in the villi form a dense network still closer and more compact than that of the bloodvessels ? The open communication existing between the serous canals and the capillary lymphatic vessels enables the latter to receive substances from the former ; and the facts that have already been adduced, in regard to the behaviour of the villi during chymification, afford sufficient evidence of the passage of a lymph current through the interstices of the tissues (serous canals) into the rootlets of the lymphatic vessels. Moreover, the passage of the cellular elements of the connective tissue from the serous canals into the lymphatics, although not as yet directly witnessed, is in the highest degree probable, since they migrate from place to place within the lumen of the former. Judging from silvered preparations, the communication be- tween the rootlets of the lymphatic vessels and the serous canals is often so free as to render it difficult to determine the limits between them ; this can, indeed, only be accomplished by determining the existence of an epithelium, and consider- ing that the lymphatic vessels commence where the epithelium first makes its appearance. The conclusions that have been here stated have by no means obtained general acceptance, and it must be acknowledged that further evidence is still required. We should endeavour to effect the physiologi- ORIGINS OF THE LYMPHATIC VESSELS. 321 cal impregnation of the tissues ■with insoluble colouring or other par- ticles, and subsequently to stain them with silver, in order to establish the fact that the absorbed material passes from the serous canals into the lymphatic capillaries ; the evidence would be perfectly satisfactory, were it possible to propel the particles, whilst the preparation is under observation with the microscope, directly from the serous canals into the lymphatics. I, however, venture to hold that the theory as above stated affords an explanation of all the facts at present known, whilst others are not equally comprehensive. In order to render this evident, let us consider the facts on which the supporters of other views rely. Ludwig and Tomsa, for instance, regard the fissures they have dis- covered between the canaliculi of the testis as the origins of the lym- phatic vessels, and they undoubtedly lie so close between the paren- chyma, — not nnfrequently investing the bloodvessels, — and the con- nective tissue is withal so small in quantity, that it is scarcely possible to look in this organ for other roots of the lymphatic vessels, that is, for a serous canal system. Ludwig and Zawarykin injected similar lacuuEe in the kidneys surrounding the tubuli uriniferi. Tomsa made injeotionrs of the nose of thedog, and sawplexuses suddenly proceed from the injected capillaries, which he regarded as transverse sections of lacunae intervening between the muscles, or fasciculi of connective tissue. At the same time, their fissure-like form was not demonstrated by him, and both his illustrations and descriptions agree equally well with my explanation, especially as it appears from them that fusiform cells (connective tissue corpuscles) are found at the borders of the injected canals. In the case of the kidneys, I have not been able to convince myself that the laounre in the tissue, serving as origins for the lymphatic vessels, are fissure-like in form. In regard to the lymph lacunae of the testis, whether they exist to the extent described by Ludwig and Tomsa, or are less developed, they can afford no evidence on the mode of origin of lymphatics in other organs ; for His and Tommasi have demonstrated that they are lined by the cha- racteristic epithelium of the lymphatic capillaries, and hentie are most probably analogous to these rather than to serous canals.- The other theory, which refers the rootlets of the lymphatic system t6 the con- nective tissue corpuscles, rests on a fact which is also in full accordance with my view ; namely, on the connection of the cells of the tissue with the dentated rootlets of the lymphatic vessels (Kdlliker)'.. I cer- tainly do not participate in the doubts entertained by many respecting the lymphatic nature of these rootlets. It is true, indeed, that we cannot ordinarily perceive any current traversing them, since the fluid is as clear as water ; but in one instance I was able, after pro- 322 THE LYMPHATIC SYSTEM, BY F. v. RECKLINGHAUSEN. tracted observation, to see a cell projecting from the terminal angular extremity of one of these rootlets gradually become absorbed into it ; and which, in its brightness, its refractile power, and its size, com- pletely corresponded with those tissue cells which are in contact with the lymphatic vessels ; as it was entirely absorbed, it was immediately conducted, with moderate rapidity, but apparently passively, to one of the main trunks. I have not as yet been able to observe one of the stellate or fusiform connective tissue cells, which join with these lymphatic vessels, or lie quite on their exterior, to be pushed onward in a similar manner into the lumen of the vessel ; yet I regard it as probable that this may sometimes occur. The above observation renders it more than probable that the tissue cells are not strongly adherent to the vascular wall, but lie in cavities which are continuous with the lumina of the lymphatic vessels. Large granular cells may also be seen in the interior of the larger-sized vessels of this descrip- tion, lying near the wall, and at moderate distances from each other. These are considered by Kolliker to be collections of fat molecules constituting the remains of the primary formative cells ; they usually present pale but well-deiined outlines, possess numerous small teeth and projections on their surface, some of which enter the cavity of the vessel, whilst others penetrate the surrounding tissues. These cells do not give the impression that they are undergoing disintegration, but rather appear to me to be simply the connective tissue cells which hang from the interior of the larger vessels, and still remain attached to their walls. It might, indeed, be considered that these lymph passages or rootlets simply constitute expansions of the serous canals, leading to others by means of their closely proximated pointed processes, and an endeavour be thus made to prove that the serous canals and lymph passages are continuous. The question may be asked, do these persistent connective tissue cells under any circumstances de- velop into epithelial cells ? I confess that I am unable to give a positive answer, and shall only here remark that, like Kolliker, I have been unable to obtain any evidence of the presence of an epithelial investment in these vessels by the action of nitrate of silver. After being injected with this fluid, the largest branches near the spine exhibited only con- fused lines which might be regarded as indications of an epithelium, whilst in the smaller vessels branched cells became coloured, around which were a number of fine lines resembling coiled fibres. Whether, as from this account appears probable, the peripherical portions of the lymph canals are destitute of an epithelium, or whether such an epithelium may yet be demonstrated by further investigations, all the peculiarities of these vessels agree in a most remarkable way with the COMPARISON OF THE LYMPHATIC AND SEROUS SYSTEMS. 323 view of the origin of the lymphatic vessels from serous canals. It is not difficult, from these considerations, to obtain additional evidence in favour of my theory ; nevertheless I do not venture to do so, since we are treating of peculiar and, so to speak, embryonal tissues of lymph capillaries that are, perhaps, as yet destitute of epithelium, and in a very early stage of development ; connections and communi- cations may therefore exist at this period, which at a later stage are in some way or other modified or altogether abolished. If now we may consider the system of serous canals as the origin of the lymphatic capillaries, the former system of tubes appears to be adapted for the conduction of the proper fluids of the tissues, whilst the latter constitutes the collecting tubes which carry off the superfluous fluid. Regarded from this point of view the comparison of the structural character of the two systems is of great interest. Both are only sparingly pre- sent in the denser tissues that are permeated by only moderate quantities of nutritive fluid,as in the case of tendons; on the other hand, in tissues like the central tendon of the diaphragm and the mucous membrane of the intestine, in which the current of the nutritious fluid of the tissue is extraordinarily rapid, the lym- phatic vessels are very abundant and vsdde in relation to the total sectional area of the serous canals ; lastly, the serous canal system may have a great extension in relation to the entire efferent system of the lymph path, in which case the tissues are very soft and juicy, and the fluid in their interior undergoes only slow interchange, and is, perhaps, on this account, especi- ally adapted to the formation of new cells. To the last category probably belong the looser masses of connective tissue which invest the several organs, and unite the interstitial connective tissue layers, on the one hand, with the serous and synovial membranes on the other. In point of fact, the outer layers of these tissues are very defective in continuity, whilst the serous canals are extraordinarily wide ; the solid structures being only present in the form of thin membranes and trabeculge, and we know from pathological processes how quickly a cellular infil- tration occurs in them. In the tunica adventitia of the blood- vessels such cellular infiltrations have frequently been regarded as lymphatic vessels in a state of distension. In certain parts of the body this unusually wide serous canal system appears to S24 THE LYMPHATIC SYSTEM, BY F. v. EECKLINGHAUSEN. coalesce, and form larger cavities, ■which then become invested with an epithelium : of this the serous cavities may be taken as an example in a physiological point of view, and the so- called serous cysts in a pathological. Where spaces of this kind form in or upon the tunica adventitia of the blood- vessels, we obtain sheath-like investments resembling the lymph sheaths of the tubuli seminiferi. To these belong the perivascular lymphatics described by His as existing partly in the membrane, and partly in the substance of the brain and spinal cord; these are reaUy interstitial spacesbetween the bloodvessels and the substance of the brain, continuous with a wide " epicerebral cavity " situated beneath the pia mater. That this last does not constitute a mere interstitial space may be maintained on the ground that it can be filled from the true lymphatic vessels of the pia mater. His has demonstrated the existence of an epithelium in the larger of these perivascular canals and sheaths, and they therefore repre- sent the same grade of organization as the lymphatic capillaries. , Macgillavry also found, in injected preparations of tiie liver, lymphatic sheaths around the bloodvessels, but it has not been satisfactorily ascertained whether they are or are not lined with an epithelium. Strieker has, moreover, described a similar ar- rangement of sheaths around the blood capillaries of the lower eyelid of the Frog ; whilst Langer has shown that in this region only two lateral lymph tubes are present, which lie close to the bloodvessel, and occasionally unite by transverse anastomoses which cross the vessel like a bridge. It further appears from Langer's carefal investigations in the Frog, where the large bloodvessels are ensheathed by lymph sacs, or by processes of the lymph sacs, that from the point of their entrance into the different organs an "invagination of the bloodvessels by the lym- phatic tubes is no longer to be distinguished " ; in the serous and mucous membranes two lymph vessels, but in the interior of the parenchymatous structures only a single lymphatic vessel accompanies each artery. These investigations afford an im- portant caution against too hastily admitting the existence of lymphatic sheaths around the bloodvessels. Many authors were formerly inclined to ascribe a perivascular system of canals to the bloodvessels of other organs, or at least to seek for EELATION OF THE SEROUS CANALS TO THE BLOODVESSELS. 325 lymphatic sheaths generally within the tunica adventitia of the bloodvessels. But this only is certain, that in the latter situa- tion the serous canal system presents an extraordinary expansion, and is on this account predisposed to cellular infiltration. The fluid contents of the serous canals, as well as of the lymphatic vessels, that is to say, the lymph itself, primarily comes from the blood ; it is therefore a question of peculiar im- portance to determine what relation the serous canal system bears to the bloodvessels, and especially to the blood capillaries. At jGbrst sight it appears most natural to consider that the serous canals stand in the same communication with them as with the lymphatic capillaries. This was the relation which the authors of the last century understood by their vasa serosa, vessels which, on account of their small calibre, only permitted the pas- sage of the colourless serum, and arrested that of the corpuscles. Leydig has translated this view into modern language, in stating that the connective tissue corpuscles are continuous not only with the lymphatic vessels but also with the bloodvessels. Fiihrer, and before him Lessing, had already maintained the view that "the vasa serosa formed a plasmatic system con- necting together the blood and lymphatic capillaries," in the interior of which the cells were situated. I formerly held it to be improbable that the serous canals were continuous with the bloodvessels, since I had not then given up the old view that the wall of the bloodvessels consists of a homo- geneous substance. Since, however, it has been demonstrated by Aeby, Auerbach, and Eberth, by means of solutions of nitrate of silver, that the walls of the capillaries were composed of an epithelium, at all events in such organs as they had examined ; since, moreover, the permeability of the vascular wall for the red blood corpuscles (Virchow, Strieker), and also for the colourless corpuscles (Cohnheim), has been noted under circum- tances which, though certainly not normal, yet can never- theless be so rapidly brought about that it is impossible to admit the occurrence of a qualitative change in the nature of the capillary wall, I consider it to be very possible that the serous canals may stand in the same open continuity with the blood- vessels as with the lymphatics. That such communications do actually exist under normal conditions is also rendered highly 326 THE LYMPHATIC SYSTEM, BY F. v. EECKLINGHAUSEN. probable by the well-known fact that in the lymph, and espe- cially in the chyle, not only colourless, but also red corpuscles may be discovered. Herbst instituted a series of experiments in which he augmented the total volume of the blood by slowly introducing blood, in the greater number of instances, but frequently also other fluids, as milk, into the jugular vein ; and in these he constantly observed the presence of red blood cor- puscles in the abundant contents of the thoracic duct, and, where that fluid was employed, milk corpuscles also. Lastly, Dr. Rud. Bohm has very recently seen in silvered preparations of the synovial membranes the serous canals become continuous with the blood capillaries in a manner very similar to that noted above as occurring in the lymphatic capillaries. The Lymphatic Follicles. In various parts of the digestive organs there are to be found, situated within the mucous and submucous tissues, and also in the spleen and the lymphatic glands either projecting from their surface or appearing on section, small spherical bodies of the size of a miUet seed — the so-caUed Follicles (see the article devoted to the digestive tract and the spleen). From the description given by Briicke, it was already known that the solitary follicles of the intestine and of Peyer's patches stood in inti- mate relation to the vessels of the lymphatic system. And this has been fully borne out by the more accurate modes of investi- gation recently adopted, but it has been further proved that the lymphatic foUicles of the pharynx, tonsils, and lingual glands are also much richer in lymphatics than the remaining portions of the mucous membrane ; that all these structures consist of tissues which recur in the lymphatic glands, and they may there- fore truly be accounted a portion of the Ij^inphatic apparatus. We must commence with the description of the follicles on this account also, that they represent a very simple type of the lymphatic gland. The follicular tissue (adenoid substance of His, cytogenic tissue of KoUiker) is characterised, first, by its reticulum, and secondly, by the lymph corpuscle-like cells which are adherent to the reticulum. MINUTE ANATOMY OF THE LYMPHATIC FOLLICLES. 327 The Reticulum, first demonstrated by Billroth, consists of very fine fibrils varying in their thickness, which for the most part pursue a straight course, and form a close network, the meshes of which are only sufficiently large to contain a few lymph corpuscles in each. The fibrils when fresh are extra- ordinarily pale, present a homogeneous appearance, and are distinguished from elastic fibres, to which, after the hardening of the gland, they present some similarity, by their lustre, and especially also by their chemical characters ; acetic acid and soda making them swell up so strongly that they can no longer be perceived. The nodal points of this plexus are usually very small, and exhibit nuclei, but whether these are simply adhe- rent to or are contained within peculiar cells occupying the interior of the substance of the fibrils remains to be ascertained. The lymph corpuscle-like cells, which constitute by far the greatest part of the follicular tissue, become isolated with extra- ordinary facility. They are contained in the milky fluid which flows when sections are made, and diflfer in some respects, and especially in their size, from one another (see lymph). The fibrils of the reticulum, situated at the periphery of the follicle, are in direct connection with the intercellular substance of the surrounding connective tissue ; they attach themselves also to the bloodvessels, and especially to the capillaries, which tra- verse the follicle in the form of a wide-meshed plexus. The vessels are thus supported by a framework of fibrils, and hang freely ia the spaces of the meshes. The relations of the lymphatic vessels are of special interest. It has been a subject of dispute whether the follicles are rich or poor in lymphatics ; the presence of lymphatic vessels in the follicles has even been altogether denied, and the conclusion drawn that the follicles are of no special importance in the lymphatic system. It is true that lymphatic vessels are not present in the interior of each individual follicle ; for even the most complete injection of the lymphatic vessels of the intestinal canal, as was pointed out by Teichmann, leaves the interior of the foUicles free, whilst Frey's injections of the tonsils have shown that here also, however, abundantly lymphatics are distributed through the whole organ, none are present in the individual follicles. These injections have, however, shown 328 THE LYMPHATIC SYSTEM, BY F. v. RECKLINGHAtrSEKT. that the surface of each follicle is invested by an extraordi- narily close network of lymphatic vessels, the several branches of which are widely separated from those of the neigh- bouring follicles. The results of the investigations of His and Recklinghausen have further shown, and the same thing may be recognised in the illustrations accompanying Teichmann's work, that it is common for the foUicles of the intestine to be surrounded by a lymph lacuna, and for the lymphatic plexuses to have become so close that the several tubes coalesce with one another to form a single spheroidal fissure. These lacunse or lymph sinuses (according to His) in some instances surround nearly the whole surface of the follicle, leaving only that extremity or pole uncovered which is directed towards the surface of the mucous membrane ; the follicle therefore hangs freely in the lymph path, or in what we may consider as an enormously dilated portion of it. That we are here dealing with lymphatic lacunse, analogous to the lymph sacs of the Amphibia, and not with simple interstices or spaces between the tissues, is obvious from the action of solu- tions of silver, which bring into view a distinct epithelium immediately contiauous with that lining the efferent or larger tubes of the lymphatics. The follicles of the digestive tract must therefore undoubt- edly be regarded as belonging to the lymphatic system ; they probably form lymph cells in their interior, which pass into the lymph lacunse, and then constitute ordinary lymph corpuscles. The relations of the epithelium investing the follicle on the sur- face directed towards the lymph lacuna, and the presence or absence of persistent openings for the passage of lymph cor- puscles, are points that still remain to be elucidated. Relations to the lymphatic system, of so intimate a nature as this, have, up to the present time, only been demonstrated in the above-mentioned follicles, whilst really nothing is known respecting the lymphatics of the well-known Malpighian cor- puscles of the spleen, though they otherwise agree in structure with the folKcles of the intestine ; and we are equally ignorant of the lymphatics of the rest of the splenic tissue. The rela- tions of the Thymus, again, which essentially consists of follicu- lar tissue, to the lymphatic vessels, has also not hitherto been demonstrated. MINUTE ANATOMY OF THE LYMPHATIC GLANDS. 329 Lastly, there are also found in certain organs composed of connective tissue, as the peritoneum and pleura of Mam- mals, and the mesentery and urinary bladder of the Frog, such large accumulations of lymph corpuscle-like cells in the interior of very vascular regions, as to cause them to present the great- est similarity to the foUi-cular tissues, though here, again, no intimate relation to the lymphatic vessels is capable of be- ing demonstrated. It is noticeable, however, that, in regard to the chief division of the bloodvessels, these structures differ from those of the lymphatic follicles proper ; for whilst in the latter the main trunks are distributed upon the surface, the artery occupies a central position in each follicle of the spleen, so that these appear to represent a dilatation of the tunica ad- ventitia : on the other hand, veins are altogether absent in the interior of the splenic follicles. All these differences in the arrangements of the vascular system are, however, insufficient to justify us in attributing to these structures a function different from that of the lymphatic follicles of the digestive tract ; they, too, probably constitute centres of development for the lympha- tic cells which are carried away from the splenic follicles, not indeed by the agency of lymphatic vessels, but by other pas- sages, as by the veins which form a very dense investing plexus around them (Easier), and by the analogous structures of the serous membranes consequent upon their communication with the above-described cavities. The Lymph Glands, GLANDXiLiE Lymphatics. Up to a very recent period, the structure of the lymphatic glands was classed with those in which no efferent duct could be discovered. The lymphatic vessels were seen to penetrate the surface of the gland at numerous points, as the vasa affe- rentia, and to emerge from the hilus of the gland as vasa efferentia; but in the interior of these organs the lymph path, especially in its relation to the glandular structure, was in the highest degree obscure. His, in the first instance, and subse- quently Frey and Teichmann, have famished intelligible ac- counts of their structure ; and although their descriptions cer- tainly differ in some few points, it nevertheless appears to me 330 THE LYMPHATIC SYSTEM, BY F. v. RECKLINGHAUSEN. that these differences are of a subordinate nature, and that we may now consider a perfectly clear description can be given of all the structural arrangements presented by these glands. The lymphatic glands exhibit, not only in different species of animals,but also in one and the same individual, a varying struc- ture which is undoubtedly difficult to define ; the first exami- nation of preparations of the lymphatic glands produces a very confused impression, as may best be understood if it be borne in mind that the variability which in general characterises the lymphatic system manifests itself especially in the structure of these organs. The lymph paths in particular exhibit the greatest variations in form, sometimes being tubular and at others fissure-like or lacuniform, both constantly and for the most part very suddenly passing into each other. In the larger and generally also in the smaller lymphatic glands, two substances are distinguishable (Fig. 60), which may be designated the cortical (a), and medullary (b). It is true that these names cannot be taken in a strict sense, since if the medullary substance be regarded as occupying a central position surrounded by the cortical substance, we not unfrequently find, on the contrary, considerable portions pre- senting themselves at the surface of the glands, and this else- where than at the bottom of the depression which represents the so-caUed hilus of the gland, and is occupied with connective tissue, the tissue of the hilus. In the subcutaneous lymphatic glands of the dog, for example, the meduUary substance con- stantly appears at the surface, forming spots which may be easily recognised with the naked eye by their white colour, and are frequently separated from the remaining portions of the gland by a yellowish pigmentary border. In these glands no true hilus is present. It cannot be maintained that a sharp distinction exists between the two substances, and we shall hereafter see that there is no essential difference of structure; but that the follicles of the cortex, which are usually regarded as characteristic of it, find their complete analogy in the me- dullary substance. Nevertheless it is advantageous, in the first instance, to dis- tinguish between the two substances, since in many animals the difference between them is even macroscopically very per- MINUTE ANATOMY OF THE LYMPHATIC GLANDS. 331 ceptible, as in the ox and horse, in both of which the medul- lary substance presents an iatensely brown colour. The finer points of structure are best defined and most clearly visible in the ox, and it was therefore very fortunate that His chose the glands of this animal for his investigations. If sections be made from fresh glands, especially with high powers, we usually see only a homogeneous tissue, in which small lymph cor- Fig. 60. Pig. 60. Vertical section of a lymphatic gland from the Ox. a, cor- tical substance ; B, medullary substance, o, capsule ; a', trabeculae ; 6, follicles ; V, follicular cords (medullary cords) ; >i, lymph path, designated in the follicles lymph sinus or investing sinus; the fine fibres traversing this are omitted. Preparation macerated in alcohol, and magnified 25 diameters. puscles, and iadeed successive layers of cells, are arranged so closely that an intermediate substance is only apparent at the very thinnest parts of the sections. For the purpose of demon- strating the different structures, it is expedient in the first instance to harden the glands ; and this can best be accom- plished by maceration in alcohol, after which extremely fine sections must be washed, or still better, gently pencilled out. When this has been done, sections of the medullary substance are found to present a dotted character ; these, however, are B B 332 THE LYMPHATIC SYSTEM, BY F. V. EECKLINGHAUSEN. not complete perforations, but are distinguished from the denser tissue in consequence of their much greater transparency, and also by the circumstance that they contain the pigment, and this in the most marked manner in the ox ; with still higher powers (see fig. 61), we see that they are traversed by fine fibres which are frequently arranged in a steUate manner, and often con- tain nuclei or cells to which granular masses of pigment cleave. Fig. 61. Section of the medullary substance of a lymptatic gland from the Ox. a, follicular cords ; 6, trabeculse ; c, lymph path. Mag- nified 120 diameters. These fibrils unite to form thicker fasciculi of connective tissue, the traheculcB, which are not unfrequently flattened ; they lie always in. the centre of the above-mentioned spaces, and con- stitute the main trunk from the sides of which the fine fibrils of the reticulum are frequently given ofi" nearly at right angles; the latter are then attached on the other side to the cords of the compact substance (medullary cords of Kolliker; medullary tubes of His ; lyrnph tubes of Frey). These medullary cords (fig. 61) have the same structure as the tissue of the lymphatic follicles (see above), consisting MINUTE ANATOMT OF THE LYMPHATIC GLANDS. 333 consequently of a reticulum of fibres enclosing l3nnph cor- puscle-like cells, and may -correctly be termed follicular struc- tures, or follicular cords. The reticulum is distinguished froni the fibrous tissue of the light spaces by the circumstance that the fibrils are individually finer, and the meshes of the plexus, especially in the peripheric layers, are much smaller. For their most remarkable peculiarity — namely, their want of transparency, as compared with the light spots — ^the follicular cords are iadebted to the large number of these cells. It must be admitted, however, that this most obvious difference be- tween the cords and the lighter spots is but slightly marked in fine sections of the recent or in thicker sections of the hardened gland substance, before they have been brushed and washed, since ia the latter also the lighter spaces are fully occupied with lymph corpuscles. And, on the other hand, the differences may again disappear if the brush has been too freely used, since then the reticulum alone remains in the follicular cords. From this it follows that the lymph corpuscles are by some means firmly retained by the latter, whilst in the more trans- parent portions of the lymph path they lie loose and unat- tached. It may be asked, how are the corpuscles fixed in the reticulum of the follicular cords ? It is probably effected by the great compactness of the reticulum and the smalhiess of its meshes which retain any lymph corpuscles that are traversing it either by a natural or artificial current, and it is also possible that the lymph cells adhere more loosely to the trabeculae since they only touch by a few points of their surface. The mode of fixation of the lymph corpuscles is a matter of considerable importance. If, by plunging the point of an injection syringe into its tissue, we propel various solutions through the substance of a lymphatic gland, or inject the organ through its afferent vessels, we shall find that we are able to clear the more transparent parts of corpuscles as effec- tually as by brushing, whilst the follicular cords preserve their cellular contents almost intact. Only a very small amount of pressure is required to accomplish this — no more, in fact, than that at which the lymph current ordinarily traverses the gland. It may be fairly maintained, therefore, that the natural lymph current is powerful enough to wash away the lymph corpusclies B B 2 334 THE LYMPHATIC SYSTEM, BY F. v. EECKLINGHAUSEN. contained in the light spaces ; and we may further draw the conclusion that each separate lymph corpuscle only temporarily occupies this tissue. In other words, these light spaces only constitute a path by which the corpuscles can be conducted away, whilst the reticulum of the follicular cords constitutes their proper domicile. Injections of the lymph and blood vessels of the lymphatic glands furnish evidence, however, of stUl other and more im- portant differences between the lighter spots and the follicular cords (see fig. 62). The distribution of the bloodvessels, properly speaking, only occurs in the latter ; they alone contain capillary networks, whilst the lighter spaces contain only the larger bloodvessels, which, proceeding from the trabeculse, traverse them in order to reach the follicular cords. On the other hand, injections, whether made by puncture of the gland substance or through the afferent ducts, prove to us that the light spaces represent the trae paths pursued by the lymph. They, for the most part, fill with great facility, and the injecting fluid, if composed of thick solutions of gelatiue and some coarsely granjilar colouring material, remains confined and limited to their interior. If, however, the fluid is more watery, and the colouring material very finely divided, it penetrates into the foDicnlar tissue, in all instances clearly entering from the peri- phery. In cases where a very tense natural injection of the mesenteric glands has occurred with chyle, it is easy to demon- strate the presence of chyle granules in the peripheric portions of the follicular tissue ; from whence it follows that the folli- cular cords are not completely excluded from the Ijrmph path. Thus it appears that although the reticulum is very compact near their surface, it wiU stiU permit solid corpuscles to pene- trate from the lymph path into the iaterior of the follicle, and therefore conversely it is probable that material particles — ^lymph cells, for example — may pass from them into the Ijrmph path. We are thus able to differentiate three separate parts in the tissue of the lymphatic glands : (1) the follicxilar tissue ; (2) the trabeculse ; and (3) the lymph path. And we must now follow the form and arrangement of these into further detail. The trabeculse are direct processes from the sheath of the lymphatic glands (see fig. 60), and, like this, consist of connective tissue, MINUTE ANATOMY OF THE LYMPHATIC GLANDS. 385 together with, in many animals — as the horse, sheep, and ox — a considerable quantity of smooth muscular fibre (0. Heyfelder). The processes which the sheaths give off towards the interior of the lymphatic glands are at first flat septa, which, near the centre, break up into cylindrical or subcylindrical cords, the trabeculse, which ultimately become contiuuous with the con- Fig. 62. J&& ^&r*JjK Fig. 62. Section of the medullary substance of a lympliatic gland from the Ox. a, follicular cord ; b, trabeculse ; c, path pursued by the lymph ; d, bloodvessels. Magnified 300 diameters. nective tissue of the hUus. At the surface of the gland* the trabeculse are situated at a distance from one another, . and usually, in conjunction with the external sheath, enclose alveolar-like spaces, iu such a way that the latter are only uninvested on the part looking towards the hilus. As they divide into rounded cords, the trabecule come into much closer approximation ; the spaces which they invest are consequently smaller than the alveoli, and at the same time are ia much more 336 THE LYMPHATIC SYSTEM, BY F. v. RECKLINGHAUSEN. free communication with each other. The follicular tissue, as a general rule, forms rounded cord-like masses, connected with one another in a plexiform manner ; these are not usually perfectly cyhndrical, but present projections, and are some- times even quite moniliform. Near the surface of the lym- phatic glands the follicular cords give off particularly well- marked dilatations of perfectly globular form, constituting the granules that, both on the surface and also on section, are clearly perceptible to the naked eye, and are commonly de- scribed as follicles. The corticaUy situated foUicles of the lymphatic glands are thus nothing but the club-shaped dilata- tions of the follicular cords of the medullary substance, and may be the more easily identified with the latter, since not unfrequently large globular follicles are to be found deeply situated in the medullary substance. The follicular framework is so intercalated in the meshes of the trabecular system, that the superficies of the follicular tissue never comes into imme- diate contact with the superficies of the trabeculse, and the spaces which intervene between the two are the Ijrmph paths. The form of the latter consequently agrees with the form of the two above-mentioned tissues, so that at the superficies of the alveolar trunks they present an approxiijiation to the form of concave spherical shells (lymph sinuses, His ; investing spaces, Frey) ; whilst in the interior of the gland they simply assume the form of the spaces left by the trabeculse of the follicular network. It is easy to demonstrate, from injected prepara- tions, that the vasa afferentia, which, as is well known, are distributed on the surface of the gland, directly open into these ' concave areas, or lymph sinuses, and thus suddenly become converted from cylindrical tubes into lacuniform spaces. With injections of solutions of silver it is particularly easy to recog- nise the immediate transition from one to the other, on account of the facility with which the epithelium of the afferent lymphatic vessels can be followed on the outer wall of the lymph sinus. It is, however, unquestionably a matter of greater difficulty to establish the origin of the roots of the vasa efferentia from the internal lymph paths. This is not in any measure due to any difficulty of filling the vasa efferentia with injection in the direction of the current. On the con- AREANGEMENT OF THE LYMPH PATHS. 337 trary, if the injection is sufficiently fluid, this may be accom- plished with extraordinaiy facility, especially when the mode of injection by puncture is adopted. In such cases it will be found that the vessels of origiu of the vasa efFerentia have such a remarkably moniliform character, and communicate so frequently with one another, that they form quite a cavernous structure. The several canals in this cavernous plexus are so short that their union with the lymph paths of the medul- lary substance are far more difficult to recognise than if they were continuous with a few elongated canals. A general view of the relations existing iu these parts may be best obtained from injections with solutions of silver (see fig. 63), and from these it can be established that the branches of the plexus, which up to this point have presented an approximatively circular section, suddenly undergo enormous dilatation, and into the lumen of these dilatations the several segments of the medullary substance imbedded in the hilus substance project, whUst the connective tissue walls of the cavernous plexus be- come continuous with the trabeculse of the medullary sub- stance. The indications of an epithelium may be easily traced from the lymphatic tubes to the trabeculse, and may further be followed on them through the medullary substance. But the trabeculse and septa at the periphery of the glands exhibit also, in silvered preparations, the same characteristic indications of an epithelium ; and I have so frequently been able to satisfy myself of the presence of this, that I may venture to say that they are invested by an epithelium throughout the whole gland. The characters of the lymph path at its entrance into and at its exit from the gland are essentially similar. The re- lations of the several parts may be most simply represented by considering a rete mirabile to be introduced between them, the several branches of which suddenly diverge from the extremity of the afferent vessel, and then proceed to divide and sub- divide, becomuig consequently more attenuated. These fijier branches perforate the intervening layers of tissue in all direc- tions, freely anastomosing with one another, and finally sud- denly reunite in the extremity of the contiauous and tubular efierent vessel. The folHcular substance is chiefly developed in the dilatations near the point at which the vasa efferentia 338 THE LYMPHATIC SYSTEM, BY F. v. RECKLINGHAUSEN. axe attached, and from this point becomes gradually more and more attenuated, till it loses itself on the lymph path at the borders of the medullary substance. This schematic representation of the arrangement of the lymph path corresponds to a fact of no small importance. Teichmann has shown that at certain points, in man especially, near the knee, retia mirabilia frequently occur in the place of Fi?. 63 Fig. 63. Section from the medullary substance of a mesenteric gland of a Dog, after injection with silver, a, rootlets of the vas efferens, with a lining of epithelium in their interior ; 6, dilatations of the channels, also lined by epithelium, and containing in their interior some gland substance with a follicular cordc; ci, fibrils traversing the lymph path, upon which, again, as at d', an epithelium may be distinguished ; e, fibrous intervening substance, which at e' forms trabecxilse. Magnified 200 diameters. true lymphatic glands, differing from the latter in the circum- stance that the lumen of the several branches is clear and free from follicular tissue. Teichmann maintains that the lymphatic glands originate from these by accumulations of lymph cor- puscles, which attach themselves to the interior of the vessels, and here form knots or clumps composed of follicular tissue. AEEANGEMENT OF THE LYMPH PATHS. 339 This view of the mode of origin of the lymphatic glands, which is similar to that formerly proposed by Engel and others, agrees but little with the recent observations of Sertoli, who found that lymph canals lined with epithelium first made their appearance ; around these the connective tissue increased ; and in this, and consequently external to the origiual lymph path, accumulations of cells occurred to form the follicular glandular substance. Tlie structural arrangements here described as existing in the lym- phatic glands can be most easily recognised in the glands of the ox and sheep. The glands of other mammals, and of man, present difficulties which are easily set aside if the fundamental structure of the lymphatic glands, as we now understand it, proves to be correct. In the lympha- tic glands of oxen, the lymph path and follicular tissue may be dis- tinguished with precision, (1) because the fibrous framework of the lymph path is beset with pigment both in the medullary and the cortical substance, whilst the follicular tissue is colourless ; (2) because the follicular tissue through the entire medullary substance forms continuous uninterrupted cords, which for the most part exceed the lymph paths in breadth. In the lymphatic glands of man and the dog the relations of the medullary tissue are somewhat different, the lymph path here occupying relatively a much greater space than the folhcular substance. Moreover, the trabecular system is much less completely developed, and it is not every section of the lymph path which, as in the lymph glands of the ox, is traversed throughout its whole length by a trabecula ; for sometimes the position of the tra- becula is not distinguishable, so that between two neighbouring follicular cords there appears only a homogeneous framework of fibrils ; whilst sometimes closer plexuses are formed by these fibres, which present nodal points analogous to the trabeculse. Lastly, the follicular cords, especially in the lyniphatic glands of man, present less sharply defined surfaces towards the lymph path than in the ox, the reticulum is of looser structure, and the lymph corpuscles adhere less firmly; and thus, by the too firm use of the brush, appearances are easily obtained, of which it is much more difficult to give a satisfac- tory explanation than in preparations obtained from the ox. Lastly, it is to be remarked that the proper lymph tubes penetrate far deeper into the medullary substance. The lymphatic glands of man and the dog, again, differ essentially inter se in this point, that in man a highly developed hilus substance is present, giving a correspondingly distinct reniform shape to the glands, and only absent or sparingly developed 340 THE LTMPHATIC SYSTEM, BY F. v. EECKLINGHAUSEN. in those of the mesentery, whilst it is usually altogether absent in the lymphatic glands of the dog, whilst the medullary substance and the efferent vessels, as already mentioned, are much more visible upon the surface. The lymphatic glands of the pig exhibit peculiarities of quite an opposite character ; here the folhcular structure preponde- rates in extent over the lymph path, and nodal dilatations appear throughout the entire medullary substance on the follicular cords ; that is to say, true follicles are formed, which make their appearance on section when examined with the naked eye, and the lymph path is so narrow that its injection can only here be effected with the greatest difficulty. According to Franz Schmidt, in other parts of the body of the pig, as in the pharynx, exceedingly strongly developed follicles are found; but it requires still further investigation to determine whether this is a consequence of the fattening of these animals, as Schmidt thinks, or whether it results from some peculiarity of this genus. A more exact investigation is still required in order to determine the relations of the epithelia to the several tissues of the lymphatic glands. I have been unable to discover any epithelial layer on the • follicular cords. The mode of connection of the fibrous framework with the epithelium is of special interest. I have frequently distinctly seen that epithelial cells are continued from the surface of the trabeculse upon the thicker fibrils (see fig. 68, d ) ; these consequently possess an epithelial investment of the same kind as the nerves which traverse the lymph sacs of the frog. It still remains to be ascertained whether this relation is generally present or is only partial, and whether the follicular cords, as has hitherto- appeared to me, are destitute of epithe- lial cells, and thus lie naked in the lymph path. The Chyle, or milk-wMte fluid formed during digestion, and contained in the lymphatics of the intestine, and the Lymph, ■which is the colourless, slightly opalescent fluid contained in the rema inin g portions of the lymphatic system, coagulate like the blood, and then separate into an albuminous serum, and a clot, which last contains the morphological elements — the lymph corpuscles or cells. In addition to these there are found, though in very variable proportion, small granules of rather high refractive index, which were formerly termed elementary granules, and are in all probability minute drops of oil. In the chyle there are also extremely small points like- wise consisting of oil, and termed the molecular base of the chyle ; these are present in such enormous numbers as to ORIGIN OF THE LYMPH COEPUSCLES. 341 impart to the chyle its opacity and dense white appearance ; lastly, there are red blood corpuscles. The lymph corpuscles are now universally admitted to be identical ia aU their characters with the colourless corpuscles of the blood. They show m particular the same constantly varying form and the same phenomena of contractility, as long as they are living ; whilst they assume the spheroidal form, which was formerly considered to be their natural shape, as soon as they die. The manipulations that up to a recent period were adopted for microscopical examination very easily kiU them, and thus a fatal effect is produced by evaporation, by the addition of water, or of saline solutions containing more than 2 per cent, of salt. Even mechanical agencies, as the weight of the covering glass, are sufficient to rapidly extinguish all indications of life. Whilst the substance of the lymph cells during life is highly refractile, and even possesses a peculiar brilliancy, it becomes paler and dull after death ; coincidently there appear small points (perhaps fat drops) in its interior, and in their centre a nucleils which is usually strongly gra- nular. The corpuscles of the lymph, like the colourless cor- puscles of the blood, are not aU exactly alike; thus there are some which present a granular character, whilst others present the form of very large cells with multiple nuclei, and others, again, are very small, and were formerly not recognised as true cells, but were described as free nuclei. Undoubtedly in the latter by far the greatest part of the body is occupied by the nucleus, so that this is often only invested by an extremely thin layer of extraordinarily pale cell substance, which very easily under- goes disintegration. Lastly, we also sometimes find ia Mammals and Amphibia large lymph corpuscles with brown granules in their interior, thus constituting pigment cells. In the various sections of the lymphatic vascular system the quantity of these elements varies, and they especially differ in their number ac- cording to whether the organs from which the lymph vessels proceed are in a state of rest or activity. From whence now do these various morphological elements flow ? Where is their place of origin ? Formerly it was believed that they only originated in the lymph path, and the element- ary granules were regarded as representing the very commence- 342 THE LYMPHATIC SYSTEM, BY F. v. EECKLINGHAUSEN. ment of organization ; and even within a very recent period it has been sought to estabKsh the view that the lymph follicles and the lymphatic glands are the only seats of origin of the Ijonph corpuscles, and that these continue to increase by fission after their entrance into the lymph path ; but such processes of division have not been observed in any trustworthy manner, and I have only once had an opportunity of directly observing under the microscope how out of a Ijrmph cell a young lymph corpuscle situated near the nucleus was suddenly ejected; Iwas not, however, able to ascertain how it originated. The forma- tion of lymph cells in the follicles of the lymphatic glands, on the other hand, can at least indirectly be demonstrated ; for the lymph which is carried by the vasa eflferentia from the glands is always far richer in cells than that which is flowing towards them, and moreover the lymphatic vessels which come from the intestinal follicles, and especially from the Peyer's patches, furnish a lymph containing a far greater number of cells than the rest of the lacteals (KoUiker). The foUicular substance of the lymphatic glands is probably to be regarded as the chief formative centre for the lymph cells ; it would, however, be going too far to say that the lymph corpuscles proceed exclusively from the lymphatic glands. The very pre- cise observations of Herbst and Teiehmann show that cells are already contained in the lymph of man and mammals before it has traversed the lymphatic glands. In all probability such corpuscles proceed from the connective tissue in which the lym- phatic capillaries are distributed, and in the form of contractile connective tissue corpuscles may easily have migrated from the serous canals into these capillaries. It is impossible to as- cribe the office of the formation of lymph corpuscles exclusively to the follicular apparatus, or even to the lymphatic glands, because, so far as we at present know, true lymphatic glands are absent' in the Amphibia, notwithstanding the abundance of cells in their lymph. According to this, the question of the arrival of the lymph corpuscles in the peripheric plexuses of the lymphatics is con- nected with the question of the origin of the migrating con- nective tissue cells. In obtaining a reply to these inquiries, the researches very recently made by Cohnheim, and subse- ORIGIN OF THE LYMPH COEPUSCLES. 343 quently by F. A. Hoffinann, under my direction, ia regard to the genesis of the pus corpuscles, are of great importance, since the characters of the latter agree in all respects with the lymph corpuscles, migrating connective tissue corpuscles, and colourless blood corpuscles. Insoluble colouring matters are, it is well known, rapidly absorbed by all these contractile cells when brought into contact with them. If, now, some such colouring matter, capable of being easily recognised (for which purpose vermilion is best adapted), be introduced into the bloodvessels of a living animal, the colourless corpuscles take up the particles into their interior ; if, at the same time, an inflammatory process be excited in some organ, as in the cornea, pus corpuscles containing this colouring matter may be met with in the inflamed connective tissue, and even in the healthy cornea, but it is especially in the loose interstitial con- nective tissue that some migrating corpuscles containing the pigment may be discovered. We can only draw the conclusion from this, that such corpuscles must have been sufiiciently ap- proximated to the circulating blood to be able to withdraw the pigment from the blood. The simplest view is that they have entered in the blood itself, and thus, previous to their migration into the tissues, were colourless blood corpuscles. On this ground Cohnheim is opposed to the theory of Virchow, according to which the pus corpuscles originate in the connective tissue itself, and maintains that pus corpuscles are nothing but vagrant colourless corpuscles, and consequently are formed in those organs to which we refer the origin of the latter ; that is to say, in the spleen and lymphatic glands. The immediate consequence of this doctrine is that the healthy migrating con- nective tissue corpuscles, as well as the lymph corpuscles of the peripheric lymphatics, must be brought to the tissues with the blood, and that both originate in the spleen and lymphatic glands ; the latter, however, in the circuit of the blood through them, would certainly furnish similar cells to those which are brought to them in the vasa afierentia, which would also pass out by the vasa eflerentia. There are still some additional grounds of support to be adduced for this doctrine of the mi- gration of the colourless blood corpuscles. Cohnheim in par- ticular rests upon direct observation of the first stages of 344! THE LYMPHATIC SYSTEM, BY F. v. RECKLINGHAUSEN. inflammation in the exposed mesentery of the frog, where he saw the colourless corpuscles, which, as usual whenever the blood current is retarded, accumulate in the lateral quiescent layer, and traverse the vascular walls, especially those of the veins, m order to migrate in the well-known mode ; and thus the observation formerly made by Waller* in 1846, but again for- gotten, except ia England, under the predominant influeilce of Virchow's teaching, has reassumed its proper position. Hering has moreover observed in the mesentery, when spread out under the microscope, that the escaped colourless blood cor- puscles enter into the lymphatic vessels ensheathing the blood- vessels, in order to be transported to other parts as lymph corpuscles. On these grounds we shall certainly be inclined to regard this doctrine as well founded ; nevertheless, in spite of considerable attention to this question, I have been unable to arrive at any very positive conclusion, and cannot avoid making a few observations. In the first place it is certainly not easy to foUow a particular corpuscle through its whole course from the blood current through the venous wall into the surrounding tissue, or to exclude the suspicion that the escaped cells proceed, not from the vascular wall, but from the adjoining connective tissue layers; secondly, the migration does not occur immediately after the exposure of the mesentery, but only after the lapse of some hours, when the most serious retardations and disturbances of the circulation have occurred. It is true I have been able to observe the migration of colour- less blood corpuscles under much more favourable circumstances, and without remarkable alterations of the blood current, in the tail of narcotised tadpoles, not only in the capillaries, but in the smaU veins and arteries, and on these grounds I should not object to accept the doctrine that the migrating cells of the connective tissue proceed from the blood current, were it not that, (1) in consequence of the narcotisation, a certain retardation of the circulation was present ; (2) that it was embryonal tissue that was under examination ; and (3) that other observations are adducible, admonishing us that, with such movable elements, and structures so disposed to wander, we must exercise extreme * S. Eosioski, Wiener Med. Woclienschrift, 1868, Nos. 56 and 57. ORIGIN OF THE LYMPH CORPUSCLES. S45 caution. I have especially observed that not only colourless ceUs escape from the blood path, but that migi'ating corpuscles of the connective tissue penetrate into its interior. After their entrance they creep along with long processes applied to the wall, in order again to escape at another point. What should we say if, in the above observations upon the mesentery, the escaping cells prove to be only such penetrating cells, which have entered either at a neighbouring point of the vascular waU (either of a vein or a capillary), or perhaps have crept on to a more distant point in the arteries, or have originally been formed in the sur- rounding tissue ? Whether the lymph corpuscles and the migrating connective tissue cells originate in the place where they are met with, and become converted into immovable connective tissue cor- puscles, as I have already stated is not impossible, or whether they are brought to the tissues from some distant point ia the blood current, the above experiments so far afford evidence that they must move in spaces which stand in direct com- munication with the interior of the bloodvessels. The larger the quantity of vermOion that is introduced into the blood current, so much the more abundant are the corpuscles contain- ing pigment discoverable in the lymph sacs of the frog. Heriag found that in narcotisation with opium lasting for some hours, the lymph vessels of the liver became extraordinarily rich in lymph corpuscles, together with red corpuscles ; and Toldt observed that if iasoluble anilin was simultaneously introduced into the blood current, the lymph paths in the medullary sub- stance of the lymphatic glands of the liver became tightly packed with blue-tinted cells (admittedly without the presence of free pigment granules), between which were heaps of red blood corpuscles. The red blood corpuscles constantly present in the lymph, and especially abundant in the chyle, were some- times formerly regarded as being developed in the lymph path from lymph corpuscles, but more recently they have been con- sidered to enter the lymph path by rupture of the vessels. According to still more recent experiments, however, show- ing the permeability of the walls of the bloodvessels (see the section on the bloodvessels), and the connection of the blood capillaries with the serous canals, the presence of red blood 346 THE LYMPHATIC SYSTEM, BY F. v. RECKLINGHAUSEN. corpuscles is no longer remarkable. The serous exudations found in the larger cavities of the body exhibit in aU their characters, in their capability of coagulation, as well as in the number and nature of their cellular elements, in their normal condition at least, the most complete coincidence with the lymph ; it may, however, be remarked that it is not uncommon to meet in them with the large so-called granule spheres, which, when freshly examined, possess numerous contractile, constantly varying, extraordinarily fine fibrils or pseudopodia on their surface, and probably have swallowed the granules which are imbedded in their substance. Recent Liteeatuee. Barthol, Panizza, Sopra il sistema linfatico dei EettUi Pavia, 1833 ; und JosEPHUs Meybk. Systema Amphibiormn lymph. Berolini, 1845. H. MuLLEE. Zur Morphologie des Chylus und Eiters. Wiirzburg, 1855. F. Noll, Henlb's Zeitschrift, Bd. ix. Eemak, Mulleb's Aich., 1850, pp. 79 and 183. A. KoLLiKBR, Wiirzburg Verhandlung, iv. ; and Ann ales des Sciences naturelles, 1846 ; and Handbuch der Gewebelehre, 5. Auflage, 1867. 0. Heyfeldbb, Ueber den Ban der Lympbdriisen. Breslau, 1851. E. BBtfcKE, Sitzungsberichte und Denkschriften der "Wiener Akademie, 1852—1855. DoNDEES, Nederland. Lancet, 1852. Cnoop Koopmans, Nederland. Lancet, 1855. A. Zenkbb, Zeitscbrift f. wissensch. Zoologie, vi. ; Funkb in idem ; EuD. Heidenhain, Symbola ad Anat. Gland Peyeri, Breslau, 1859 ; and Molbschott's Untersucbungen, iv. Th. Billeoth, Beitrage zur patbol. Histologie. Berlin, 1858. Zeit- scbrift f. wissencbaft. Zoologie, Bd. xi. Vibchow's Arch., Bd. xxi. W. His, Zeitscbr. f. wissenscb. Zoologie, Bande xi., xii., xiii., u. xv. H. Fbey, Vierteljabrscbr. d. naturf. Gesellsch. in Ziiricb, 1860 u. 1862 ; Untersucbungen iiber den Bau der Lympbdriisen. Leipzig, 1861. Also, Handbucb der Histologie u. Histocbemie, 2. Auflage. Leipzig, 1867. L. Tbiohmann, Das Saugadersystem, vom anatomiscben Standpuncte. Leipzig, 1861. W. Keause, Anatom. Untersucbungen, 1860. BIBLIOGRAPHY OF THE LYMPHATIC SYSTEM. 847 PiEES Walter, Unters. iiber die Textur d. Lymphdrusen. Dorpat, 1860. Ad. Kjelberg, studier i Laran om lymplikarlens ursprung. Upsala, 1861. F. V. RECKLiNGHAtrsEN, Die Lymphgefasse und ihre Beziehung zum Bindegewebe. Berlin, 1862. Zur Fettresorption. Virohow's Arch., Band xxvi. Ueber Eiter- und Bindegewebskorperchen, idem, Band xxviii. W. MuLiiEB, Zeitscbr. f. rationelle Medicin, Band xx. C. Ltjdwig u. W. Tomsa, Sitzungsber. d. Wien. Akademie, Band xliii., 1861 ; und Band xlvi., 1862. C. LuDwiG, Ursprung der Lympbe, Wiener med. Jabrbiicber, 1862. W. Tomsa, idem, 1862. LuDwiG u. Zawaeykin, Zur Anatomie der Niere, idem. Band xlviii., 1863; u. Zeitscbr. f. rat. Med., Band xx. E. Oedmanssen, Vibchow's Arch., Band xxviii. C. Langee, Ueber das Lympbgefasssyst. d. Frosobes., Berichte d.Wien. Akadem., Bande liii. u. Iv., 1866 u. 1867. Franz Th. Schmidt, Det foUicnlaere Kjertelvaev. Kopenhagen, 1862. N. Kowalewsky, Sitzungsber. d. Wien. Akademie, Band xlviii. C. HuETER, Medic. Centralblatt, 1865. L. AuEEBACH, ViRCHOw's Arcb., Band xxxiii. C. LuDwiG, Schweiggek-Seidel, Dogiel, u. Dtbkowsky, Berichte d. Kon. Sachs. Gesell. Leipzig, 1866, 1867. Enr. Sertoli, Sitzungsber. d. Wien. Akadem., Band liv., 1866. Gust. Heebst, Das Lympbgefasssystem u. seine Verricbtung, Got- tingen, 1844. A. Waller, The Philosoph. Magazine and Journal of Science, xxix., 1846. Jul. Cohnhbim, Virohow's Arcb. Bande xl. u. xH. Friede. Alb. Hoffmann u. F. v. Recklinghausen, Centralblatt, 1867 ; u. Hoffmann, Viechow's Arcb., Band xlii. Ew. Heeing, Sitzungsber. d. Wien. Akad., Band Ivi., 1867. C. Toldt, idem, Ivii., 1868. W. Engelmann, Ueber die Hornhaut des Auges. Leipzig, 1867. S. Chrzonszczewsky, Virohow's Arch., Band xxxv. N. Aponasiew, Virohow's Arch., Band xUv. F. LdscH, idem. C C CHAPTER X. the spleen. Bt WILHELM muller, OP JENA. The structure of the spleen is. intimately associated -with that of the lymphatic glands. In both organs numerous trabeculse proceeding from the capsule divide and subdivide, containing in many animals muscular tissue, the contraction of which effects a shortening of certain, vascular channels and the eva- cuation of the fluids contained in the parenchyma. In both organs the cytogenous or adenoid tissue is employed to invest at least a portion of the bloodvessels with sheaths containing numerous cells, the rounded appendices of which, rich in capil- laries, constitute the follicles of the lymphatic glands and the so-called Malpighian corpuscles of the spleen. In both organs the wall of certain vessels undergoes a peculiar modification, characterised by the breaking up of the tissue into a plexus of embryonal cells, the interstices of which are permeated by the fluids contaiued in their respective vessels ; in. the one case by lynj.ph, in the other by blood. It is a consequence of this agree- ment in structure that certain causes of disease produce similar pathological effects in. both organs, as is seen in typhus, leucae- mia, and certain forms of glandular sarcoma (Hodgkin's disease). The spleen is not present in all Vertebrata. In the Lepto- cardia and Myxinoids, for instance, it has not as yet been demonstrated. In the remaining Vertebrata, which possess the organ, it is constantly included between the laminae of the peritoneum. Its position, however, is various; according to whether it is developed in the meso-gastrium, the mesentery proper, or the peritoneal investment of the pancreas. The structure, again, presents varieties in the different classes of the STRUCTURE OF THE SPLEEN IN REPTILES. 349 animal kingdom ; in the OpMdia and ia the Saurians, the con- stituent -which in all other Vertebrata is chiefly developed, is here rudimentary, whilst that which in the latter is an acces- sory apparatus, agreeing with the cytogenous vascular sheaths of the lymphatic and lymphoid glands, attains in the former its greatest development. In consequence of this mode of develop- ment, the spleen of these animals forms the Hnk connecting the lymphatic and lymphoid glands to the spleen of other verte- brates. These peculiarities of structure justify us in proceed- ing to describe the spleen of Ophidia and Saurians separately from the remaining vertebrates. The Spleen of Reptiles. — In Ophidia the spleen appears to the naked eye as a granular mass, situated at the upper Fig. 64. Pig. 64. From the spleen of the Tropidonotus natrix. a, follicle, with its capillary plexus ; h, septum with venous plexus. extremity of the pancreas ; but in Mammals it lies on the left side of the stomach, and presents a more homogeneous struc- ture. It possesses a capsule composed of fibrillar connective tissue and fine elastic fibres. The interstices of the fibrils of the connective tissue contain, especially in the middle layers of the capsule, numerous lymph corpuscle-like ceUs. The deeper layers exhibit, in preparations that have not been injected, regularly c 2 850 THE SPLEEN, BY WILHELM MXTLLEE. arranged bands of smooth muscular tissue. In injected pre- parations a rich plexus of veins comes into view at this part, to the walls of which most, if not all, of the smooth muscles must be attributed. The interior of the organ is traversed by septa given off at tolerably regular intervals from the internal surface of the capsule. The structure of these processes agrees with that of the capsule, and they intercommunicate with one another in the interior of the organ. They form stellate expansions ; their connective tissue becoming infiltrated with lymph corpuscles, which in this modified form occupies aU the interspaces of the proper parenchyma of the organ. This last appears in the form of spheroidal masses (globi or follicles), the diameter of which, in the ordinary domestic animals, varies from 05 to 0'75 milli- meter. The follicles themselves are composed of cells and a retiform intermediate substance. The cells agree with the lymph corpuscles of the animals in question, consisting of a mass of protoplasm containing a nucleus, but destitute of a cell wall. Larger morphological elements are constantly found intermingled with them, con- taining two or three nuclei which may be regarded as the result of a process of multipKcation. At the periphery of each follicle the cells lie more closely packed together than near the centre, and in the fresh state they are connected together by a pale finely granular tenacious intermediate sub- stance. In preparations that have been hardened by diluted solutions of chromic acid, a plexus of delicate fibres may be recognised. This plexus is more distinctly fibrillar, and its meshes are more elongated near the periphery of the follicle than elsewhere, and the interspaces are here also filled with closely compressed lymph corpuscle-like cells. This more com- pact plexus extends beyond the limits of the follicles, so that neither in the fresh nor in the hardened state can a continuous investing membrane be demonstrated around them. The bloodvessels of the spleen of Reptiles consist of arteries, capillaries, and veins. The artery enters the spleen of Ophi- dians at the part opposite the pancreas, which is sometimes hollowed out in the form of a hilus, and runs towards the centre, enclosed in a membrane-like investment of connective STRUCTUEE OP THE SPLEEN IN REPTILES. 351 tissue containing numerous lymph corpuscles. At this part it divides into fine branches, which run towards the centre of the several foUicles, where the smallest arterioles break up into a very characteristic capillary plexus. This forms meshes of 0015 — 003 millimeter in width, which contain the paren- chyma. The meshes are polygonal in form, strongly re- sembling the capillary plexuses of the foetus ; the calibre of the vessels exhibits, within a short space, variations of con- siderable extent, and the wall, whUst it in part corresponds precisely to that of ordinary capillaries, is in part constituted of distinct nucleated cells, which are with difficulty, and only through their somewhat more elongated form, distinguishable from those of the adjacent parenchyma. Near the periphery of the follicles the meshes of the capillary plexus diminish, whilst the diameter of the vessels increases in size, and they at length become continuous with a very close plexus of thin-walled veins, which wind around the follicles. These veins, which in some parts consist only of a thin connective-tissue layer con- taining numerous cells, transmit their blood into larger branches, lined with epithelium, and provided with layers of muscular tissue, which partly run along the septa in the in- terior of the organ, and partly in the deeper layers of the capsule, to reach the point of entrance of the artery, by the side of which they emerge from the organ as the splenic veins. The fact that the walls of a portion of the capillaries in the spleen of Ophidians very frequently present features reminding the observer of their embryonic structure, naturally suggests that besides a continuous new formation of lymph corpuscles, a similar neoplastic formation of capillaries may also take place, but what relation this process bears to the function of the organ is not at present known. The plexus of thin-waUed veins which wind around the periphery of the follicles resemble the lymph spaces that siorround the periphery of the follicles of the lymphatic glands. They repre- sent at the same time the rudiment of a splenic pulp. If we imagine the elements of the walls of these canals to become developed into a plexiform tissue traversing the lumen of the vessel, we shall obtain a tissue presenting the essential charac- teristics of the splenic pulp, as it occurs in other vertebrate 352 THE SPLEEN, BT WILHELM MDLLEE. animals. No observations have hitherto been made on the lymphatics or on the nerves of the spleen in Reptiles. The Spleen of Fishes, Amphibia, Chelonians, Birds, AND Mammals. — However various may be the structural arrangements of the spleen in these several divisions of the animal kingdom, the essential features of construction are the same in all. The organ is constantly invested by a capsule which sends off processes into the interior. These either hold some determinate relation to the venous system of the organ, forming venous sheaths, septa, and trabeculse, or to the arterial system in the form of arterial sheaths. The interspaces of these tissues are filled with the peculiar parenchyma termed the splenic pulp. The Capsule of the Spleen. — The thickness of the splenic capsule appears to bear a direct proportion to the whole volume of the organ. In the embryo it is invested by a short form of cylinder epithelium, resembling the ordinary epithelium of the peritoneum. As the organ grows this be- comes flattBued, and in adults forms delicate, partly square, partly rhomboidal plates. In all Vertebrata fibrillar connective tissue, with which elastic fibres are abundantly intermixed, enters into the composition of the capsule. In Fishes and Amphibia, so far as observation has at present extended, these elements form the entire capsule. In the higher Vertebrata, from the Chelonians upwards, a variable proportion of smooth muscular fibres, which are always situated in the deeper layers of the capsule, is likewise present. In Camivora, in the Rumi- nants, and in the Pig, these are so largely developed, that the physiological experiment of merely dipping the spleen into warm water furnishes evidence of their presence, whilst in the Rodentia and Cheiroptera they are much less abundant. Muscular fibres, even if they are constantly present, are only sparingly distributed in the splenic capsule of Man. Septa and Sheaths of the Veins. The association of these two constituents is justified by the constancy of the relation which they bear to one another. STRUCTURE OF THE SPLEEN. VENOUS SHEATHS. 353 From the deeper layers of the splenic capsule fibrous bands are given oif at regular distances, which are recognisable with the naked eye, and become continuous with cylindrical cords, the so-caUed trabeculse of the spleen that penetrate its substance. They communicate with one another by lateral branches, and form a network traversing the entire organ. Their structure is identical with that of the deeper layers of the capsule, except that they for the most part contain bands of smooth muscular fibres. A certain number of these trabeculse extend constantly between the ramifications of the veins, and become attached to their walls either at acute or at right angles. The structure of the latter is thus rendered more complex, as the splenic veins have already at their point. of entrance into the organ received an annular investment from the capsule which soon coalesces with the vascular walls. The latter thus acquire remarkable firmness, and from the increased strength afforded by the at- tachment of the numerous trabeculiE are prevented from collaps- ing, presenting in consequence, in this respect, a certain simi- larity to the sinuses of the dura mater. This modified venous wall sooner or later becomes incomplete, whilst the connective tissue layers containing muscular fibres split into small bands, between which the lumen of the vessel is only limited by the epithelium layer and by a delicate layer of connective tissue containing numerous cells, and representing the tunica intima. This assumption of a fibrous character by the external vascular layers may even commence in the trunks of the splenic vein, as occurs in the Eimiinants ; but more frequently, as in Man, it is first observable in the smaller branches. The slender bands containing muscular fibres, into which the sinus-like venous wall divides,- run. for a greater or less distance along the branches,- ultimately becoming detached and uniting .with the trabecular network of the organ (W. Miiller). The object fulfilled by the connection of the trabecular network of the spleen with the walls of the veins is sufficiently obvious. The longitudinal bundles of muscles. belonging to the latter tend to shorten the canals, whilst the trabeculse which are laterally at- tached to them widen them, and thus conditions favouring .the discharge of fluid from them are established (Tomsa). A coin- cident contraction of the muscles of the capsule and of the 354 THE SPLEEN, BY WILHELM MULLEE. trabeculse must, moreover, exert pressure upon the intervening parenchyma which compels the movement of such of the con- stituents of the latter as are capable of changing their position to those parts where the tension is least (W. MiiUer). Arterial Sheaths. — At their entrance into the hilus of the organ the arteries receive a sheath from the capsule with which the proper vascular wall is loosely connected. This sheath con- sists of fibrillar connective tissue with numerous elastic fibres, and a moderate proportion of cell elements lying between the fas- ciculi, the latter appearing partly as rounded lymph corpuscle- like bodies, and partlyas elliptical nuclei which only presentsmall masses of protoplasm at their poles. The sheaths accompany the arterial branches, without essential modification in their structure, to the points at which the arteries and veins previ- ously running together separate from one another, which usually occurs in the arterial branches, of from 03 to 0-2 millimeter in diameter. From this point onwards the arterial sheaths pre- sent a remarkable modification in their structure, which consists in the conversion of their connective tissue into a cytogenous tissue, whilst at the same time it becomes much looser in tex- ture. The connective tissue bundles throughout the whole thickness of the sheath become coincidentally much looser ; their fibrils become more delicate, and lymph corpuscle-Hke cells are abundantly found in their interstices. A cylindrical sheath, rich in cells, is thus formed, which accompanies the arterial branches either to their entrance into the blood pas- sages of the pulp, as in Fishes, Amphibia and Chelonia, or to their passage into the capillaries, as in Birds and Mammals. In the first-named animals it is only seldom that any further development of these sheaths occurs ; in Birds and Mammals, on the other hand, rounded or ellipsoidal sharply circumscribed bodies, varying from 03 to 1 millimeter in diameter, appear with great regularity, termed the Malpighian bodies of the spleen, which are easily recognisable with the naked eye, on account of their whitish colour. They represent, as is now generally ad- mitted, local hyperplasise of the cytogenous connective tissue of the arterial sheaths. Their disposition upon th% arterial branches to which they belong varies to some extent, according STRUCTURE OF THE SPLEEN. ARTERIAL SHEATHS. 355 to whether they are developed from the entire circumference of the arterial sheath, or from only a definite point of it ; in the former case, surrounding the artery to which they belong like a ring ; in the latter, being situated eccentrically, or being only laterally attached. The parenchyma of the Malpighian bodies is formed of cells and a retiform intermediate substance ; the cells agree ia their characters with the lymph corpuscles of the several animals, and they are constantly found iu various stages of development, some beiag smaller, with a single nucleus, and others larger, with several nuclei. Like those of the splenic pulp, they are capa- ble of executing amoeboid movements, and are usually more densely crowded at the periphery of the Malpighian bodies than at their centre. When treated with solution of carmiae, cceteris paribus, they become more intensely tinted than those of the pulp, though it has not been hitherto determined whether the deeper hue is the consequence of the presence of a larger proportion of protoplasm capable of imbibing the colour, or to a difference in the fluid by which the protoplasm is per- meated. Associated with the cells is a delicate intermediate substance, the periplast of Huxley. This forms a network around the several cells or groups of cells, and when examined in the recent state, consists of a pale, extremely finely granular, tenacious material, which presents the form of delicate fibrils in pre- parations hardened in chromic acid. At the periphery of the Malpighian bodies the network becomes closer, the individual fibrils present a greater similarity to ordinary connective tissue fibrils, and the meshes become more elongated and narrow, though without actually forming a continuous membrane, as was first correctly demonstrated by Henle. Pulp. — The tissue of the splenic pulp is composed of cells and of an intercellular substance. The former resemble the lymph corpuscles of the animal, and constantly appear as small uni-nucleated and larger multi-nucleated cells, famishing evi- dence of the occurrence of continuous processes of new forma- tion. These become less deeply tinted with carmine than those of the Malpighian bodies, which they, however, resemble in 356 THE SPLEEN, BY WILHELM MULLEE. exhibiting amoeboid movements (Cobnheim). There may be frequently found in the splenic pulp, especially in adult animals, large cells which either contain granular pigment presenting the characters of Hsematoidin, or rounded bodies resembling coloured blood corpuscles. We may presume that the greater number of these cells containing blood corpuscles are occasioned by the migration of coloured blood corpuscles into the proto- plasm of the adjoining pulp cells. The cells of the pulp are connected with one another by means of an intercellular substance. This was first observed by Tigri, and was more minutely described by Billroth. When examined in the fresh state, this appears as a pale, feebly refract- ing, very finely granular, tenacious substance, forming a deli- cate network between the protoplasm of the several cells.. In chromic acid preparations it assumes the character of a; tisane composed of homogeneous iutercommunicatiag fibres. At the periphery of the Malpighian corpuscles it becomes continuous, without any sharply defined line of demarcation, Fig. 65. Fig. 65. From the spleen of tlie Hedgehog, a, a Malpighian cor- puscle, -with its vascular apparatus ; b, splenic pulp, with the interme- diary hlood passages ; c, the rootlets of the veins. with the intercellular substance of the cortical layer. Near the capsule of the spleen, and also near the terminations of the capillaries and the origins of the veins, the intermediate sub- stance becomes more strongly refractile as regards light, and more distiactly fibrillar. It here becomes continuous on the STBUCTURE OF THE SPLEEN. BLOODVESSELS. 357 one hand by numerous processes witli the connective tissue of the capsule, and on the other hand with the tunica adventitia enveloping the capillaries and rootlets of the veins. The cells and intercellular substance of the pulp are not so closely compressed as are those of the Malpighian bodies ; on the contrary, they frequently leave rounded or lacuniform spaces between them, in which, in spleens recently removed from the animal after ligation of the vessels and exposure to the action of chromic acid at 0° Cent., coloured blood corpuscles constantly occur. Bloodvessels of the Spleen. — Several arterial and venous trunks usually penetrate into the interior of the spleen at the hilus. Both sets of vessels, invested with their sheaths, run for some distance in proximity to each other, branching like a tree as they proceed. When they have diminished to a diameter varying from 0'3 to 02 miUimeter, the arteries separate from the veins. Their mode of branching continues to be tree-like without the occurrence of anastomoses between the branches. In this course the arteries give branches to their investing sheaths which break up into a capillary network, presenting few and wide meshes. This capillary plexus is richer in the Malpighian corpuscles, the meshes being particularly small near the periphery. The calibre of these capillaries, as a rule, is moderately small, but frequently unequal, and the structure of the wall also exhibits varieties, sometimes presenting the characters of fully developed and sometimes of embryonic capUlaries (Huxley, W. Miiller). At the surface of the Malpi- ghian corpuscles the capUlaries either open into the intermediate blood passages or into the rootlets of the veins. No proper veins accompany the arterial sheaths from the point at which they become cytogenous. The arteries, as is usual amongst the Mammalia, quickly divide into numerous capillaries, that run a long course, and are invested by a delicate tunica adventitia composed of con- nective tissue. Generally speaking they exhibit the structure of frilly developed capillaries, but in some places they present for a considerable distance, walls composed of separate cells rich in protoplasm, constituting the transitional vessels of 358 THE SPLEEN, BY WILHELM MTJLLER. Schweigger-Seidel. After a longer or shorter course the capil- lary waU becomes much attenuated and finely granular, the nuclei surrounded with a distinct mass of protoplasm, their continuity interrupted, and finally the homogeneous wall breaks up into small striae, to which the cells are attached, and which are continuous with the cellular and fibrous plexus of the pulp. Through the spaces thus produced in the primary capillary wall the blood escapes into the cavities formed by the cellular and fibrous plexuses of the pulp, that is to say, into the intermediate blood passages. From the latter the blood is collected into the rootlets of the veins. These com- mence as cribriform, interrupted canals, the boundaries of which are essentially formed of lymph corpuscle-like cells and a delicate iutercellular substance, constituting a plexus with numerous lacunae. After a short or, as in man and rabbits, a somewhat longer course, the vein obtains a continuous in- ternal investment, consisting of a layer of fusiform epitheUal cells with spheroidal nuclei, which not unfrequently project into the lumen of the vessel, the superjacent connective tissue layer becoming at the same time condensed, causing the lymph corpuscle-like cells to crowd more closely together, and the fibrillar intercellular substance to become more distinct, whilst it piirsues a transverse direction, and forms a tolerably close plexus (Henle). The smaller venous branches unite like the branches of trees to form larger trunks, investing which a tunica adventitia, consisting of longitudinal connective tissue fibrils with interspersed cellular elements, soon makes its ap- pearance. The cylindrical muscular fasciculi belonging to the adjoining trabeculse attach themselves longitudinally to these branches, and immediately become firmly adherent to their walls. As this occurs every now and then at difierent points, the gradually enlarging venous ramuscules obtain their already described compact walls, resembling those of the sinuses of the dura mater, and which they retain up to their point of exit from the organ. The foregoing description of the arrangements of the circulating apparatus in the spleen rests (1) on the observation that, in recently hardened spleens still containing blood, both in the embryo (Pere- meschko) and in the adult (W. Miiller), the tissue of the pulp is con- STRUCTURE OF THE SPLEEN. LYMPHATICS. 359 stantly traversed by blood corpuscles ; (2) upon the observation that artificial injections of the spleen constantly fill the same spaces which naturally contain blood corpuscles (W. Miiller) ; (3) on the observa- tion that, after the injection of the very fine seeds of the lycopodium, their presence in the pulp may be constantly demonstrated with the aid of the tests exhibiting the reactions of starch (Tigri). In opposition to this view is a second, which, originally advanced by Billroth, Grohe, Sasse, and Gray, has recently been supported by KoHiker. Accord- ing to this view, the spleen, like other organs of the body, possesses a completely closed vascular system of ordinary structure, the veins everywhere forming plexiform anastomoses between which the paren- chyma, traversed by capillaries, is contained in the form of cords, constituting the intervascular tissue cords of Billroth, or the bulbs of Grobe and Sasse. I have already, in my work on the spleen, ex- plained why I cannot adopt this view. Moreover, in a series of the injected spleens of rabbits, and in the spleen of a monkey which was placed at my disposal by C. Thiersch, and more recently in examinations made upon the amyloid spleen of man, I have been unable to dis- cover any facts favourable to the view maintained by Billroth and Sasse. KoUiker adduces in its favour, besides the points already mentioned, (1) that the current of blood would experience too much obstruction were it to freely traverse the pulp ; (2) that the fresh spleen constantly presents an acid reaction ; (3) that since the appearance of my work, no one has expressed himself in favour of the views therein contained ; (4) that this view would constitute a novelty. The first objection is opposed by comparison of the blood pressure in the arteria lienalis with the pressure of the lymph in the vas afierens of any group of lymphatic glands. The second is easUy confuted by applying the best neutral litmus paper ; the third is over- thrown by the work of Peremeschko, who is the only author that has thoroughly entered into the consideration of the question. Lymphatics of the Spleen. — It is highly probable that the spleens of all vertebrate animals possess lymphatic vessels. They are divided into a superficial and a deep set. The former run in the capsule, and constitute a close plexus, from v^hich trunks arise that pass with the trabeculse into the interior of the organ, in order to anastomose there with the deeper set (Tomsa). The latter, as usual, accompany and form open net- works between the arteries and their sheaths, and extend to near their terminations. According to the observations of 360 THE SPLEEN, BT WILHELM MULLEH. Tomsa, they penetrate the cytogenous sheaths of the vessels and their circumscribed enlargements, forming a plexus which, near the periphery of these structures, is only incompletely surrounded by the cavities of the adjoining pulp. Nerves of the Spleen. — The nerves of the spleen also accompany the arteries in their course. They consist chiefly of Remak's fibres. They appear, in part at least, to terminate in peculiar organs that invest the capillary terminations of the vessels (W. MiiUer). These organs form ellipsoids, in the long axis of which a single capillary vessel runs. The substance of the ellipsoid consists of a pale, very finely granular substance in which oblong nuclei are imbedded (Schweigger-Seidel and W. Miiller). These are highly developed in the spleens of Birds and carnivorous animals, but are only rudimentary in those of Rodents and of Man. In the interior of their granu- lar mass fine fibres of Remak occur, the mode of termination of which has not as yet been actually determined. They require fiirther investigation. Development of the Spleen. — In all Vertebrata the spleen proceeds from a segment of the peritoneum. The situation of this segment differs in the several classes. In Ophidia it is the peritoneal investment of the upper extremity of the pancreas ; in Fishes, Frogs, and Chelonia, it is the mesentery of the small or large intestine ; in the Salamanders, Lizards, Birds, and Mam- mals, it is a prolongation of the mesogastrium from which the organ is developed. Its first appearance occurs in the form of a homogeneous thickening of the peritoneum, caused by in- crease of the embryonic formative cells of which it is composed. This thickening occurs very early in Man ; it is already demon- strable at the period when the first budding out of the pancreas has made its appearance. At this time bloodvessels may be fol- lowed to the seat of the rudiment of the spleen (W. Miiller).* At this period there may be observed in chromic acid preparations a very delicate pale network intervening between the embryonic * Their relation to the first appearance of the spleen requires further investigation. DEVELOPMENT OF THE SPLEEN. 361 cells ; but whether this proceeds from the outgrowth of a few cells, as Peremeschko raaintains, or from the detachment of the peripheric protoplasm of numerous cells,l am not able to decide. The further development of the organ occurs tolerably rapidly, so that in the human foetus of eight centimeters in length the various constituents are already differentiated. The cells lying beneath the peritoneal epithelium become elongated, and form fusiform nucleated bodies, and similar ones at an early period invest the larger vessels. From both small processes are given off, which grow towards one another, and represent the commencement of the trabecular system. Along the arterial branches, denser accumulations of small nucleated cells may already be discerned, which are conspicuous in tinted prepara- tions by their deep colour, and these form by far the chief consti- tuent of the pulp. This consists of cells with from one to three nuclei and a delicate intercellular substance, forming plexuses, the interstices of which are constantlyfilled with blood corpuscles. According to Peremeschko, there are now developed larger pro- toplasmic corpuscles in the tissue of the pulp containiug from two to six nuclei, that are capable of performing amoeboid move- ments, and which, towards the end of embryomc life, atrophy. In the further course of development the several constituents increase in volume, and a part of the fusiform cells of the capsule and the vascular sheaths develop into smooth muscular tissue. The arterial sheaths, containing numerous cells, are clearly distinguishable from the pulp, and from the middle of embryonic life the Malpighian corpuscles are recognisable. The cavities of the pulp may, about this time, be artificially injected (Peremeschko). From the commencement of differentiation of the several constituents of the organs, as this author has pointed out, the cells of the pulp appear paler and more delicate than those of the arterial sheaths. To explain this it must be borne in mind that both of these morpholo- gical elements develop from different textural formations, the pulp developing from the walls of the rootlets of the veins, the arterial sheaths with their Malpighian bodies from the connective tissue investing the arteries. It is of importance to establish this difference, because it famishes the key to a series of comparative anatomical and pathological observa- 362 THE SPLEEN, BY WILHELM MULLER. tions. Up to the present time, no facts have been ascertained in regard to the development of the lymph passages, or of the nerves of the spleen. LiTEEATUEE. 1. Maecelli Malpighii opera. Londini, 1686. ' 2. Fbedbkici Etjtschii, opera. Amstelodani, 1737. 3. JoH. Theod. Elleb, De liene in Hallee's Dissert, anat., Vol. iii. 4. Christ. Ludw. Kolopf, De fabrica et functione lienis. Halae, 1750. 5. De la Lone, Snr la rate, Histoire de I'Academie. 1754. 6. J. F. LoBSTEiN, De liene. Argentor. 1784. 7. GuLiBLMi Hewsonii, Opus posthumum. Lugd. Bat. 1785. 8. J. P. AssoLANT, Eecherches sur la rate. Paris, 1800. 9. A. MoRESCHi, Del verso e primario uso della milza. Milano, 1803. De vasorum splenioorum constitutione. Mediol. 1817. 10. JoH. MuLLEE, Ueber die Structur der eigenth. Korperchen in der Milz. Archiv fiir Anat. und Physiol. 1834. 11. J. Henle, Allgemeine Anatomie. Leipzig, 1841. Zeitschrift fiir ration. Medizin, 3. Eeihe, Bd. viii. 12. Sohwager-Baedeleben, Disquisit. microscop. de glandul. ductu carentium structura. Berolini, 1841. 18. Kbause, Handbuch der menschlichen Anatomie. Hannover, 1842. 14. Oesteelen, Beitrage zur Physiologie des gesunden und kranken Organismus. Jena, 1843. 15. Atto Tigbi, Nuova disposizione dell' aparecchio vascolare san- guigno della milza umana Bologna, 1847. II Progresso, 1849. Gazetta medica italiana, Tom. iii. 1853. 16. A. KoLLiKEE, Art. Spleen in Todd's Cyclopaedia. London, 1849. Handbuch der Gewebelehre. Leipzig, 1867. 5. Auflage. 17. A. EcKEE, Art. Blutgefassdriisen in Kud. Wagner's Handwor- terbuch der Physiologie. Braunschweig, 1849. 18. ScHAPPNEE, Zur Kenntniss der Malpigh. Korperchen der MHz. Zeitschrift fiir rationeUe Medizin, Bd. vii. 1849. 19. William Sandees, On the structure of the Spleen. London, 1850. 20. E. Eemak, Ueber runde Blutgerinsel und pigmenthaltige Zellen. Archiv fiir Anat. und Physiol. 1852. BIBLIOGEAPHT OF THE SPLEEN. 363 21. Hughes Bennett, On the function of the Spleen. Monthly Journal of medical Science. Edinb. 1852. 22. Fkanz Leydig, Beitrage zur mikrosk. Anatomie der Eochen und Haie. Leipzig, 1852. Anatomisch-histologische Untersuch- ungen iiber Fische und Reptilian. Berlin, 1853. 23. Rudolph Vibchow, Zur patholog. Physiologie desBlutes. Archiv fiir pathol. Anatomie, Bd. v. 1853. 24. Thomas Huxley, On the ultimate Structure and Relations of the Malpighian bodies. Quat. Journal of micr. Science, ii. London, 1854. 25. Henry Geay, On the Structure and Use of the Spleen. London, 1854. 26. GoETHius Stinstra, Commentatio physiologica de funct. lienis. Groningen, 1854. 27. F. FiJHEEE, Ueber die Milz und einige Besonderheiten ihrea Capillarsystems. Archiv fiir physiol. Heilkunde. 13. Jahr- gang, 1854. 28. A. Sasse, De Milt. Amsterdam, 1855. 29. Edwards Crisp, A treatise on the Structure and Use of the Spleen. London, 1857. 80. Theodor Billroth, Beitrage zur vergleichenden Histologie der Milz. Archiv. fiir Anat. und Physiol. 1857. Zur normalen und pathol. Anat. der Milz. Archiv. fiir pathol. Anat., Bd. xx. und xxiii. Neue Beitrage zur vergleichenden Anatomie der Milz. Zeitschrift fiir wissenschaftl. Zoologie, Bd. xi. 31. 0. Meissnee, Zeitschrift fiir rat. Medicin. 8. Reihe, Bd. ii. 32. L. FicK, Zur Mechanik der Blutbewegung in der Milz. Archiv fiir Anat. und Physiol. 18S9. 33. Sappey, Trait. d'Anatomie, 1859. 34. Hbinrich Frey, Histologie und Histochemie des Menschen. 2. Auflage. Das Mikroskop. Leipzig, 1867. 35. NicoLAUs KowALEwsKY, Ueber die EpitheHalzellen der Milzvenen und die Malpigh. Korper der Milz. Archiv fiir pathol. Anat. Bande xix., xx. 36. F. Grohb, Beitrage zur pathol. Anat. und Physiol. Archiv fiir pathol. Anat., Bd. xx. 37. Lddwig Teichmann, das Saugadersystem. Leipzig, 1861. 88. Axel Key, Zur Anatomie der MOz. Archiv fiir pathol. Anat., Bd. xxi. 39. E. Siven, Om mjeltens anatomi och fysiologi. Dissert, inaug. Helsingfors, 1861. D D 364 THE SPLEEN, BY WILHELM MULLEE. 40. Fk. Schwbigger-Seidbl, Untersuchungen iiber die Milz. Archiv fiir pathol. Anat., Biinde xxiii. und xxvii. 41. LuDwiG Stieda, Zur Histologie der Milz. Ajchiv fiir pathol. Anat., Bd. xxiv. Ueber das Capillargefasssystem der Milz. Dorpat, 1862. 42. A. TiMM, Zeitsehr. fiir rat. Medicin. 3. Eeibe, Bd. xix. 43. W. Baslek, Einiges iiber das Verhalten der Milzgefasse. Wiirz- burger med. Zeitscbrift, Bd. iv. 44. W. ToMSA, Ueber die Lympbgefiisse der Milz. Sitzungsbericbte der k. k. Akademie zu Wien. -ISBS. 45. WiLH. MiJLLEE, Ueber den feineren Ban der Milz. Leipzig und Heidelberg, 1865. 46. Perbmeschko, Beitrage zur Anatomie der MUz und Ueber die Entwicklung der Milz. Sitzungsbericbte der k. k. Akademie zu Wien. 1867. CHAPTEE XI. THE THYMUS GLAND. By E. KLEIN. In Man and Mammals, at an early period of tHeir existence, a placentiform lobulated body, called the thymns gland, which in point of structure must be associated with the peripheric lymphatic glands, lies behind the upper part of the sternum, and partly occupies the Incisura jugularis at the lower part of the neck. It is invested by a capsule rather loosely con- nected with the organ by means of vessels and fasciculi of con- nective tissue, the thickness of which increases with the size of the organ. The number and size of the lobes vary to a considerable extent. In dogs, in the pig, and in the cat, there are usually only two closely connected lobes of unequal size, which present an acute edge externally and below, but are remark- ably thick at their surfaces of contact. In the calf, on the other hand, the organ consists of two oval placentiform iobes not pre- senting acute edges, and of nearly equal size, united together by a short cylindrical intermediate portion. The thymus of the new-bom infant exhibits two or three lobes ; when there are three, these are so arranged that a central thicker lobe has some- times a larger and sometimes a smaller lobule on each side. The several lobules of the thymus in man, as well as in the dog, the cat, and the pig, may possess small appendices ; and the fissures by which the lobes are produced are sometimes deep, and sometimes less strongly marked. Each lobe is divided into several lobules by fissures uniting at various angles, and these again are subdivisible into the ultimate divisions termed acini, alveoli, granules, or more correctly, foUicles. The capsule exhibits the usual structure of membranous con- nective tissue ; its elements are, wavy connective tissue fibres D D 2 366 THE THYMUS GLAND, BY E. KLEIN. united into fasciculi of various sizes, which decussate in all direc- tions, and thus form a tolerably resistant membrane ; fine elastic fibrils, which are partly united in a plexiform manner, and partly form large arches running in an irregular manner between the fibres of the connective tissue ; a few lustrous, broad, strongly refracting bands, characterised by their looped course and resistance to the action of acids ; and, lastly, cellular ele- ments. These either resemble colourless blood corpuscles, or are provided with processes like the so-called stellate cells, or they may appear as large, finely granular, irregularly shaped bodies, usually containing a single small, spheroidal, highly re- frad-ing nucleus. On the outer surface of the capsule, or that which is directed towards the thoracic cavity, a single layer of pavement epithelium, resembling in form and character that of the, peritoneum, may easily be demonstrated. The cells of this layer are polyhedral, and slightly elongated or rhombic in form, containing a vesicular spheroidal or elliptical nucleus. If a portion of the capsule, carefully detached from the re- cently removed thymus of a dog, be spread out upon the slide with the aid of some indifierent fluid, and examined with a high power, besides the tissues and structures above mentioned we may discern also the deeply situated delicate ramifications of the bloodvessels, together with the sparingly distributed trunks of medullated nerve fibres ; and lastly, certain peculiar cavities. At the points where two or more strong fasciculi of connective tissue decussate we meet with such large usually elongated spaces, which have somewhat sinuous margins bounded by a single layer of fusiform disproportionately large cells ; the tissue immediately external to these, and forming a kind of wall to the cavity, is but little condensed. It is clear that we have here to deal with the cavities belonging to the lym- phatic system, respecting which it is difficult to state decisively whether they are simple lymph sacs, or are wide thin-waUed lymphatic vessels. It is worthy of remark, that the quantity of lymph corpuscles they contain is extremely small, and bears no proportion to the size of the space. The tissue bounding the several foUicles of the thymus, and dipping into the interior of the organ from the surface of the several lobules, consists of a network of connective tissue. STRUCTURE OF THE THYMUS GLAND. 867 which, as may be particularly well seen in the thymus of the dog, is usually composed of fine fibres, arranged in the form of delicate rhombic meshes. These are generally filled with more or less closely packed large ceUs; but near the free surface of the foUi cles, where they are not confluent with one another, the cells are smaller and more crowded, whilst the tissue becomes so con- densed as to form a kind of capsule. The individual follicles are either entirely thus encapsuled and isolated, as frequently occurs in the calf, or several may be united at their centric portion, as in the dog and man. On the whole, their structural characters are comparable with those of the Peyer's patches of the small intestine. The form of the several follicles is elongated, spheroidal, or polyhedral, and those situated near the surface are always larger than those more deeply seated ; those of the dog and calf are usually elliptical in form. The finer structure of the follicles displays the same mor- phological elements, with the same relative disposition, as the ordinary lymph follicles. According to His,* fine capillary bloodvessels, proceeding from the vessels running in the septa, penetrate the follicles at numerous points of their surface, and in consequence of these frequent anastomoses, form a very close-meshed plexus. Between the vessels, and attached to them, as well as to the connective tissue of the septa, an exceedingly compact, but very delicate, network is extended, chiefly formed by the anastomosing branches of multipolar cells, in the interstices of which are numerous lymph cells ; in addition a narrow-meshed network may be distinguished, resembling the above, except in the absence of cells, and in the greater breadth of the trabeculse, especially at their nodal points. These narrow-meshed networks are the pro- longations of the interalveolar or interfoUicular lymphatic vessels. Lastly, there occurs a third kind of trabecular structure La the form of strong elongated fibres, which are stretched between adjoining vessels, or between these * Beitrdge zur Kenntniss der zum Lymphsysteme gehSrigen Driisen, Siebold and Kolliker's Zeitschrift fur wissenschaftUche Zoologie, Band x., p. 333. 368 THE THYMUS GLAND, BY E. KLEIN. and the septa of connective tissue. These are not much branched, and are attached by means of conical longitudi- nally striated beises to the vessels. The contents of the follicles, that is to say, of the trabecular structures, consist of cells, which, according to their size, may be arranged in three categories- Of these the first, and by far the most numerous, are ordinary lymph corpuscles; the second are larger coarsely granular spheroidal bodies, composed of protoplasm, and containing one or several nuclei ; and the third are Hassall's concentric corpuscles, of which Ecker * re- cognises two forms, one simple and the other compound. The former are spheroidal vesicles, varying from 00075 to 0009 millimeter in diameter, containing in the interior of their con- centrically striated sheath sometimes only a homogeneous mass with fatty lustre, but sometimes a nucleus and granular material. These last are as much as 0027 millimeter in diameter, and are composed of several simple vesicles that are collectively invested and imited together by a concentrically striated membrane. Both species of the concentric bodies occur, according to Ecker, at every stage of development ; yet with increasing abundance as the gland gradually advances to complete maturity. Vessels. — In the calf and in man the larger branches run- ning in the folHcular septa divide into numerous branches that everywhere surround the follicles, "f" The arteries give ofi" capillaries that penetrate into their interior, and after communi- cating by transverse branches^ run in a radial direction, and terminate in circular vessels. As a rule the latter do not quite reach the centre of the follicles, but become continuous with veins which accompany the arteries. The distribution of the vessels in the thymus of the dog pre- sents some difference from that which has just been described. Here the larger trunks situated in the septa give off branches that penetrate into the interior of the follicles, and then break up at the outer part into a capUlary network, by which they * Blutgefdssdrusen in R. Wagner's EandwSrterbuch, Band i., p. 115. t Ecker, he. cit., and His, he. cit. STRUCTURE OF THE THYMUS GLASD. 369 are completely filled* The very wide spaces charged with lymph cells, which immediately invest the foUicles, are in com- munication, by means of finer vessels, with the central parts of the follicles. M. His regards these spaces as lymphatics ; but, according to my observations, it must still remain doubtfiil whether they are lymphatic vessels or sinuses investing the foUicles. According to the older views,f the follicles are hollow vesicles invested externally by a structureless membrane, and internally by a layer of connective tissue, their cavities aU communi- cating with a common central canal. Jendrassik I has demonstrated that the elementary parts of the thymus gland are solid lymph follicles, in the central part of which a cavity is formed by softening. I find that these cavities only occur in the follicles of the thymus in man and the calf, and not always even there. The central part of the foUicle, which, both in man and the calf, consists of a network of cells with interspersed lymph corpuscles, after prolonged hardening, easily becomes detached during manipulation. In regard to the physiological atrophy of the thymus, it con- sists, according to His, of a gradual breaking-down and infiltra- tion of the glandular tissue with fat, which extends gradually from the septa and the surface of the follicles towards their interior ; but even in the earliest period, when there can be no question of atrophy, smaU isolated groups of fat cells may be found in the investing sheaths of the follicles. * Kolliker, Gewehelehre, p. 485. t J. Simon, A Physiological Essay on the Thymus Gland. London, 1845. 4to. Gerlach, Gewehelehre Mainz, 8vo, Lieferung, 2 and 3. Ecker, loc. 'cit. X AnatomiseJie Untersuchungen uber den Sau der Thymusdrilse, Sitzungs- herichte der k. Akad. zu Wien., 1856, Juli-heft. CHAPTER XII. THE THYROID GLAND. By E. VEESON. The term thyroid gland is applied to an organ composed of a framework of connective tissue condensed externally to a more or less thick investing membrane, and traversing the in- terior of the organ in the form of strong trabeculse ; and, se- condly, of gland vesicles, sustained by the framework, which, as their name implies, constitute structures similar to the acini of a gland, but completely closed and vesicular. The vesicles of the thyroid gland are composed of a thin transparent hyaline membrane, lined by epithelium, the cells of which are arranged in. a single layer, and in fresh, uninjured specimens appear longer than broad, and are provided with a spheroidal nucleus, which may itself include one or several nucleoU. In this condition, however, the epithelium of the vesiculse is only encountered in quite young animals when examined with the microscope immediateljr after having been taken from the living animal. In a very short time, even under the eye of the observer, the free surface of the cell waU may be seen to project irregularly, and spheroidal tenacious and hyaline drops, which after some time coalesce in the centre of the vesicle, gradually develop from the bodies of the epi- thelial cells. Usually, however, delicate lines of demarcation may be recognised between them, giving a facetted appearance to the clump of escaped and coalesced cell contents. Before these drops become intimately fused with each other in the centre they frequently indicate the path they are about to pursue by pseudopodial processes which partly adhere to the cell wall. These contents, at a more advanced age, and under pathological conditions, are converted into coUoid, though STEUCTUEE OF THE THYEOID GLAND. 371 they originally represent only the product of a physiological process. The several gland vesicles present great variation in size, and even in adults some may be found which are of much smaller diameter than the largest of those discoverable in the infant. It appears that in extra-uterine life the progressive increase of the several gland vesicles, if any, is usually very smaU. On the other hand, in a human embryo of the fifth or sixth month, I have found their diameter to be 00252 — 0'0336 millimeter, whilst their diameter in the newly bom already amounts to 01 — 01 6 millimeter, and may in adults exceed 0'2 millimeter. The gland vesicles of the tortoise are particularly well adapted for investigation, since they measure from 0-14 — 0'27 millimeter. Mammals possess in general very small vesicles, which sometimes, by their further growth, so press upon one another that the space required for the capil- laries is only obtained by an inflexion of their opposite walls. Such conditions I found to occur frequently iu the dog, where the walls of the vesicles form projections internally, in which the epithelial cells are seated like the voussoirs of an arch. It is deserving of notice that the larger vesicles occupy the centre of the several lobules, or, where these are not present, the centre of the entire gland, whilst at the periphery they appear much smaller and are compressed and flattened in form. The epithelial cells, as already mentioned, are always some- what higher than broad, and do not vary remarkably either with age or with the species of animal. Thus, for example, iu an embryo of the fifth or the sixth month they were from 0006— 00095 mihimeter long, and from 0004— O'OOS milli- meter broad; in adults they attain the length of O'Ol — 0'16 millimeter; in the dog, from O'OOS — 0-0126 millimeter; in the calf, of about 0-0105; in the tortoise, from 0-0168 milli- meter, etc. The framework of the thyroid gland is a direct continuation of the external investing membrane, and, like this, consists of fasciculi of connective tissue, with numerous elastic fibres and connective tissue corpuscles, which for the most part appear fusiform or branched. The organ is partially traversed by S72 THE THYROID GLAND, BY E. VEESON. stronger bands which, on the one hand, are connected with the investing sheath, and on the other, isolate large groups of gland vesicles. In this way the thyroid gland of man is divided into primary and secondary segments, the line of division between which is recognisable by slight furrows. In other cases, however, these strong septa may fail, and the whole glandular organ represent a continuous mass. The connective tissue lying between the several gland vesicles of the individual segments is very sparing in quantity, and sometimes even it is difficult to discover between the walls of contiguous vesicles a few fibres accompanying the capillaries. Near the investing membrane, and between the peripheral vesicles, it is more abundant. If the fresh vesicles of the tor- toise be isolated by means of needles, we find them invested by a fine network of fibres, which frequently bear branched cells. The Arteries are large branches of the "thyroid artery, and penetrate into the interior of the gland, following the course of the fibrous septa, dividing the organ into segments or lobules. Their branches accompany the secondary septa, and these again break up into large capillaries having a diameter of O'OOG- — 001 millimeter, that form a network around the several gland vesicles from which again the veins take their origin. These, externally to the fibrous sheath, are character- ised by the width of their lumen and the proportionate thin- ness of their walls. The lymphatics, according to Frey, commence with csecal extremities between the gland vesicles, and unite to form meshes surrounding the lobules, finally emerging from the sur- face of the organ as vessels of considerable size. The nerves appear as thick trunks of dark-edged fibres which adhere firmly to the vessels. In man the thyroid gland appears to be composed of a me- dian and two lateral lobules united by means of connective tissue. Other mammals, as the dog, calf, horse, etc., possess a thyroid gland consisting of two separated lobules lyiag on either side of the trachea. A single median lobe occurs in Amphibia and Birds, which descends into the thoracic cavity. BIBLIOGEAPHT OF THE THYROID GLAND. 373 Bibliography. Panagiotides and Wageneb in Froriep's Notizen, Band xl. Panagioiides, De Glandulee Thyreoideae striictura penitiori. Berolin, 1847. Diss. EcKER, Versuch einer Anatomie der prim. Formen des Kropfes, etc., in Henlb and Pfeupfee's Zeits. f. rationelle Medicin, Band vi. ScHAFFNEB, Zur Histologie der Schilddriise und Thymusdriise, idem, Band vii. EoKiTANSKY, in Zeitsckrift der Wiener Aerzte, 1847, undDenkseliriften der Kais. Akad. d. wiss. zu Wien., Band i., 1850. KoHLBAuscH, Beitrago zur Kenntniss d. Schilddruse in Mxjller's Arch., 1853. EuLBNBEEG, Untersuoh. iiber die SchUddriise in Arch. d. vers. f. gem. Arbeit, Band iv. Fbest, im. viii. Bde., d. Vierteljahr, d. naturforsch, G-esellschaft in Zurich. CHAPTER XIII. THE BLOOD. By ALEXANDER ROLLETT. The red blood of vertebrate animals consists in part of a solu- tion of various substances^the blood plasma — and in part of very small corpuscular structures of peculiar form. The corpuscles are so abundant and so equally distributed through the fluid medium, that their interspaces are of micro- scopic dimensions, and fresh blood consequently presents to the naked eye the appearance of a homogeneous red fluid. The individual corpuscles do not aU agree with one another in their characters, and hence several different kinds may be distin- guished amongst them. In the first place, we may distinguish between the coloured and the colourless forms, the number of the former predomi- nating in healthy blood. The coloured corpuscles are more \uiiform than the colourless, amongst which several subdivisions must be made. The Blood Plasma. — The blood plasma, or Liguor Sangui- nis, when examined in the fresh state and in microscopically thin layers, is destitute of colour. If a drop of blood be re- moved for a short time from the liviug body of an animal, fibrin separates from it in a solid form. But in reference to the coagulation of the blood,* we shall here only discuss the micro- scopic phenomena presented by the fibrinous clot. The fibrin, when in small quantities, separates itself in the form of delicate fibres decussating at vaiious angles, though when in large only * Compare Kuhne, Lehrluch der Physiologischen Chemie. Leipzig, 1866, pp. 162 to 174. RED COBPUSCLES OF THE BLOOD. 675 very gradually, as often occurs in the blood of cold-blooded iEinimals ; or if larger quantities of fibrin quickly separate, the whole drop of blood solidities, without any alteration of the microscopic appearances being perceptible. In this case the change that has occurred only becomes evident on moving or breaking up the mass when it has undergone coagulation. • If, on the other hand, we leave a few drops of blood for a little while to themselves, which may be best effected by at- taching them to the under side of a glass cover in a moist cell, we shall observe that the coagulum embracing the corpuscles retracts from the borders of the drop, and that a zone of clear serum is exuded, which gradually increases in breadth. Here also striae and bands of coagulated fibrin may be iso- lated by breaking up the coagulum and thorough elutriation with water. The fibrinous coagulum appears doubly refractile under the polarising microscope. We shaU hereafter revert to the behaviour of "the blood cor- puscles in the fibriuous coagulum. The Red Blood Corpuscles. — A knowledge of the general structure of these bodies cannot here be discussed, but will be taken for granted in the course of the following observations. After the blood corpuscles had once been seen by Swammer- dam in the Frog in 1658, by Malpighi in the Hedgehog in 1661, and by Leeuwenhoek in Man in 1673, numerous observa- tions were accumulated respecting them, perhaps even to a greater extent than upon any other* morphological element of the animal body. Up to the present time, however, no struc- tural arrangements have been discovered in them with the microscope that can enable us to furnish an explanation of all or even of the greater number of the phenomena they display. Compared with other morphological elements of the tissues, the red blood corpuscles appear so peculiar, and are so readily and permanently alterable by the action of numerous and often not obvious external influences, and present so many remark- * For the older literature, see Mibie Edwards, Lemons sur la Physiologie et I'Anatomie comparee. Paris, 1857, T. i., p. 41. S76 THE BLOOD, BT ALEXANDER ROLLETT. able appearances, that statements based upon mere analogy can only be received with the most profound distrust. The results that have been obtained by direct observation and inquiry wiU therefore here first be given, in order that we may not become confused with theories that have been incon- siderately advanced ; the views of various histologists, founded on their own investigations, will, however, be subsequently noticed. Form and Colour. — Throughout the whole series of ver- tebrate animals two typical forms are presented by the red blood corpuscles. They form thin disks, the contour of which is either circular or elliptical. The circular disks occur in Man and Mammals, with the exception of the Camel and Auchenia. The two last-named genera have, like all Birds, Amphibia, and most Fishes, elliptical blood corpuscles. Amongst the Fishes only a few Cyclostomata (Petromyzon, Ammoccetes) are known to possess circular disks. A smaU drop of human blood, brought as quickly as possible under the microscope in the form of a thin layer, exhibits densely crowded coloured corpuscles. Their colour depends upon haemoglobin.* The individual corpuscles, however, do not appear red like pure hsemoglobin, or its concentrated solutions, but of a yellowish or green tint, per- haps on account of its small thickness, just as the same colour may be obtained if thin layers of concentrated watery solu- tions, or thick layers of diluted solutions, of haemoglobin are examined, and this whether it be oxyhsemoglobin or reduced haemoglobin, or a definite mixture of both. The red colour of the blood is only exhibited under the microscope when large numbers of blood corpuscles are examined superimposed on one another. Where a number of the corpuscles thus lie upon one another, as may occur by chance in every small drop of blood, there may also be seen, as F. Hoppe, f Preyer, | and Strieker § * Compare Kuhne, Lehvhuch der Physolog. Chemie. Leipzig, 1866, p. 196. \ Vircliow's Archiv, Band xxiii., p. 446. X Max Sohultze's Archiv, Band ii., p. 92. § Pfluger's Archiv, 1868, p. 651. RED CORPUSCLES OF THE BLOOD. S77 have shown, the characteristic absorption bands of haemoglo- bin, providing that a spectrum apparatus of appropriate con- struction is connected with the microscope. Strieker has also demonstrated in the microscopic spectrum the conversion of the oxyhsemoglobin bands into those of reduced hsemoglobia on alternate exposure to and COj. The circumstance of the red blood corpuscles being the car- riers of the colouring matter of the blood, confers upon them their obviously great importance in the organism at large, on account of the part which the haemoglobin plays in the ex- change of the respiratory gases. As regards the form of the blood corpuscles when examined microscopically in fresh blood, the greater number of the iso- lated corpuscles will be found to present perfectly circular con- tours, and to be of nearly equal size (fig- 66, a). The description that must be given of this form may be best Fig. 66. Fig. 66. Red blood corpuscles. understood by making the corpuscles float by gentle taps on the covering glass. They then offer alternately the circular form and another completely different one, that, namely, of short rods with rounded poles and slightly hoUowed surfaces, and resemble a finger biscuit, or a section carried through the axis of a bi-concave lens (fig. 66, h). Such a corpuscle, as it again revolves, places itself upon its edge again, and, in short. S78 THE BLOOD, BT ALEXANDEE EOLLETT. gives the impression of a rotating disc, with a thinner central portion, caused by a fossa-like indentation of the surfaces and a thickened border. A solid model of the blood corpuscle may- be represented by the revolution of the curve c c c (fig. 67) around the axis a h. This form of blood corpuscle has also been termed the saucer- shaped. If the observer has convinced himself of the varying form of one and the same blood corpuscle, he wiU understand Fig. 67. i Fig. 67. Diagrammatic section of one half of a blood corpuscle. how in every blood drop there are presented to his eye numbers of such corpuscles standing on their edge. Nevertheless, the number of those which are lying on their flat surfaces is always much greater. Lateral views of the blood corpuscles are also very commonly obtained on account of the adherence of the corpuscles in groups to one another by their broad surfaces. Chain-like forms are thus produced, which, when viewed laterally, resemble rouleaux of coin (fig. 66, c). The cause of this formation of rouleaux, which is frequent in fresh blood, has not as yet been discovered. It does not occur within the vessels. It is seen not only in freshly drawn blood, but also in blood which has been immediately whipped, and thus freed from fibrin, though it may afterwards have remained for some time at rest.* Besides the corpuscles just described, which are by far the most abundant, M. Schultzef constantly found in the blood of * See EoUett, Wiener Ahadem. Berichte, Band i., Abth. ii., p. 183. t Archwfur MikrQskop. Ahatomie, Band i., p. 35. EED CORPUSCLES OF THE BLOOD. 379 himself and of a few other persons a small number, varying with the period of the day, of minute bodies, differing from the ordinary corpuscles in their spheroidal form and in some other peculiarities, together with transitional forms between them and the ordinary corpuscles. Further, ia accordance with the frequently cited observation, though standing much iu need of confirmation, of Lehmann,* the blood of the hepatic veia con- tains corpuscles of smaller size and more spheroidal form than usual, whilst those of the portal veia are of the ordinary kind. The surface of the common form of corpuscle appears smooth, and the substance of the disk exhibits in its interior no indi- cation of any difference iu the index of refraction of its several parts. In passing from the centre to the circumference, however, there is a distinct change in the colour and transparency. In that position of the corpuscle in which the disk appears broadest and its edge most sharply defined, the centre is trans- parent, and the lateral portions are darker, whilst the extreme edge again presents a clearer ring. The latter is occasioned by the refraction which transmitted Ught experiences in the focal plane of the microscope when it traverses objects bounded by circular contours.-f- The appearance presented by human blood corpuscles is dif- ferent from that of the corpuscles of animals with elliptical corpuscles. External to the eUiptical border of the flat surface of the disk there may be observed, at least in Birds, Amphibia, * Physiologische Chemie, Band ii., pp. 85 and 232. t Nageli and Schwendener, Das Mikroshop, Theil i., p. 184, et seq. Halting, Das Mikroskop. Braunschweig, 1866, Band ii., p. 26, et seq. E £ 380 THE BLOOD, BY ALEXANDER EOLLETT. and Fishes, a different structure when the disk stands on its edge. The optical section of the long axis appears here also slender, elongated, and rounded at the extremities. The long sides, however, have a projection at their centre (fig. 68, b). This prominence corresponds with an area situated near the centre of the disk, which, in comparison with the remaining coloured mass of the corpuscle, appears whiter than the rest. This is sometimes more or less circular as in the Bird, or ellip- tical as in the Frog, Triton, and land Salamander ; it is often quite smooth, but also frequently presents fine indications of dark points or strise. This spot corresponds to a structure which possesses no ana- logue in the fuUy developed blood corpuscles of Man and Mammals, but behaves itself quite difierently from the remain- ing substance of the corpuscle, and shows at least as gTeat an amount of agreement with the structure termed the nucleus in other animal cells, as do the nuclei of the different cells with one another. In common with most histologists, we shall designate this structure as the nucleus of the blood corpuscles. The fuUy developed elliptical corpuscles of the camel* and Auchenia are as destitute of a nucleus as the circular corpuscles of Man and other Mammals. It thus appears that we may divide the blood corpuscles of animals into two classes, the nucleated and the non-nucleated. It must, however, be mentioned at once, that nucleated blood corpuscles occur at an early period of the development of the blood both in Man and Mammals. Size of the Red Blood Coepuscles.^ — There is a large amount of literature bearing on the subject of the micrometric investigation of the blood. The considerably differing results of the measurements that have been recorded have, for the most part, only a relative value. The micrometer employed has not, as a rule, been reduced to a definite standard. Exact comparison with a standard, it is well known, is no easy matter even for macro- * Donne, Cours de Microseopie, etc., Paris, 1843, p. 70 ; Comptes Rendia, T. xiv., p. 367. SIZE OF THE RED CORPUSCLES. 381 Bcopic measurement. But it is still more difficult in the case of the micrometer. Harting* and Welckerf- have, on this account, detailed special methods by which the measurement of blood corpuscles may be accomplished. As a rule, only the size of those blood corpuscles should be compared, which have been obtained by the same observer with the same instrument. It is self-evident also, when aU the foregoing remarks are fully taken into consideration, that only those measurements are serviceable for comparison, in which an exact statement is made of the conditions under which they have been made. Hence we must be on our guard respecting the inconsiderate emplajj^ment of the various tables that have been published on the size of the blood corpuscles in different animals.J The absolute dimensions obtained by Welcker§ with a micrometer, are — For man on an average expressed in millimeters : — Miu Max. Diameter of disk . . . 0-00774 (0-00640 0-00860) Greatest thickness of the disk 0-00190 In six males and three females a miniinum was observed of 0-0045 millimeter, and a maximum of 00097, all occurring be- tween the terminal values, the smallest excepted, being very nearly of equal size. The measurements were made on the corpuscles of fresh blood, or of blood dried in thin layers on glass. The measurements given by Welcker for the small red corpus- cles, described by Max Schultze, are 0-005— 0006 millimeter ; and from these, gradual transitional forms may, according to Max Schultze, be traced up to those of ordinary diameter, from 0008 to 0010 millimeter. We are indebted to Welcker for exact measurements of the • Das Mikroskop, etc., Band ii., p. 288, et seq. t Zeitschrift fiir rationelle Medicine 3 R., Band xx., p. 259. % The most extensive tables on this subject are to be found in Milne Edwards, loc. cit., p. 84. § Loc. dt., p. 263. E E 2 382 THE BLOOD, BY ALEXANDER KOLLETT. corpuscles in various animals, and a few of his mean values will be found in the suhjoined note* The smallest corpuscles are those of the Moschus Javanicus. Amongst the largest are those possessed by the perennibran- chiate Proteus anguinus, and the Siren lacertina (the long diameter of which amounts to g mm. and the short to ^ mm.).-f" The largest knovm, according to Eiddei,J are those of the Amphiuma tridactylum, which are one-third larger than those of the Proteus. Welcker§ employed a very short cylinder of plaster of Paris, * Loc. cit, p. 279. I. ClRCULAK CORPITSCLES. Dog . Cat . . 0-0073 . 0-0065 Rabbit . 0-0069 Sheep . Goat (old) . Goat (8th day) Mosehns Javanicus . 0-0050 . 0-0041 . 0-0054 . 0-0025 Petromyzon mari. Ammocoet branch. -, . 0-0150 . 0-0117 II. Elliptical Corpuscles. a, Long diameter j h, short diameter. a. h. Lama 0-0080 0-0040 Pigeon (old) 0-0147 00065 Pigeon (fledged) . 0-0137 0-0078 Pigeon (fledged) . 0-0126 0-0078 Duck . 0-0129 0-0080 Fowl . -,0-0121 00072 Rana temporaria .0-0223 0-0157 Rana temp, (dry) 0-0214 0-0156 Triton Cristatus . 00293 0-0195 Proteus (1 and 2) f '0-0582 • ( 0-0579 0-0337 0-0356 Sturgeon 0-0134 0-0104 Cyprinus Alburn. 0-0131 00080 Lepidosiren Annectena . 0-0410 0-0290 ae Edwards, he. cit, p. 89. nal de la Physiologie , Band ii. Paris, 1859, p. 159. § Loc. cit, pp. 265—275. NUMBER OF THE EED CORPUSCLES. 383 the proportion of the radius to the height of which was estimated to correspond with the dimensions of the blood cor- puscles; and by scooping out the surface, and rounding off the edge, he obtained a curvature of the surface, which, to the eye (!) was similar to that of the blood corpuscles (compare fig. 67). He thus determined the mean volume of human blood cor- puscles to be 0-000,000,072,217 of a cubic millimeter. Welcker, moreover, carefuUy Hned the iuterior of this model, which was 5,000 times larger than the corpuscles, with paper of uniform thickness, then weighed the paper used, and compared this with the weight of a known superficial measure of the same paper. From the data thus obtained he estimated that the superficies presented by a blood corpuscle amounts to 00,001,280 square millimeter. It is sufficiently obvious that these num- bers have only a coarsely approximative value. Number of the Red Corpuscles. Estimates of the number of the corpuscles have also been undertaken with the microscope. This method was suggested by Vierordt, and has been modifiled by Welcker.* Their direct enumeration may be accomplished in the following way : — A measured volume of blood is diffused as equably as possible in a thousand times its volume of an iadifferent fluid (six grammes of Na. CI. in one litre of water, according to Welcker), a small quantity of the mixture is taken up iu a capillary tube of known calibre, and the length of the thread of fluid is estimated under the microscope by means of a micrometer. When the contents of the tubule have thus been ascertained, they are quickly distributed with a little solution of gum upon a slide, and the whole is allowed to dry. The prepara- tion is covered with a micrometer divided iato squares, and the corpuscles in the several squares can then be successively counted. In one experiment Vierordt used 0-0005 — 00008 cubic * Yieiorit, ArcMv fur Physiol. Eeilkunde,'Biinix.i.,-p^. 26, 327, 854; xiii., p. 259 ; Grundriss der Physiol, 3. Auflage, 1824, pp. 8, 9. Welcker^ Prager Vierteljahreschrift, Band xliv., p. 60 ; und Zeitschrift fUr rationeUe Medicin, 3 K., Band xx., p. 280. 384 THE BLOOD, BY ALEXANDER EOLLETT. millimeter of blood, in which about from 2,000 to 3,000 cor- puscles were counted in the space of an hour. Comparative enumerations, with test specimens of blood diluted to various extents, and measured in capillary tubes of various widths, gave a difference of two to three per cent, in the numbers, and seldom amounted to five per cent. In a cubic millimeter of the healthy blood of a man, 5,000,000 red blood corpuscles were estimated to be present. From this, and from the above-stated dimensions respecting the volume and surface of the corpuscles, there appear to be in a hundred volumes of blood thirty -six volumes of corpuscles and sixty-four volumes of plasma. The surface of the corpuscles in one cubic millimeter may be estimated to amount to 643 square nlillimeters. Vierordt, Welcker, and Stolzing have also counted the blood corpuscles of various animals. Alterations of the Red Blood Corpuscles. We shall now pursue another line of inquiry. Up to the pre- sent time, independently of the above-given enumerations, we have, as far as possible, considered the blood corpuscles in their normal condition. We are, however, indebted for much im- portant information to the observation of certain changes which the corpuscles undergo vmder various circumstances, as well as to the results obtained from experimental histology. For the purposes of inquiry into the nature of the red cor- puscles, mechanical agents, the discharge of the Leyden fiask, the application of induced and constant currents, exposure to heat and cold, and lastly, the addition of various chemical agents have been employed. 1. In freshly prepared specimens of human blood it may fre- quently be seen, after the lapse of a variable space of time, that the borders and surfaces of the corpuscles have lost their smooth aspect. The borders appear dentated ; the surfaces, as may best be seen when the corpuscles are rolling over, are beset with little eminences. At the same time the corpuscles become smaller and more spherical (fig. 69). A few such cor- puscles are often visible in fresh blood, immediately after it has ALTERATIONS OF THE BED C0EPUSCLE3. 385 been drawn, so that it is difficult to determine whether they are pre-existent in it, whilst it is still circulating, or not. It is certain that, in blood abstracted from healthy persons, in many Fig. 69. instances, nearly all the corpuscles undergo this alteration, and this is stated (by Max Schultze)* to occur with stUl greater rapidity in those suffering from febrile diseases. The corpuscles thus altered have been described as mulberry-shaped, and the phenomenon regarded as a stellate contraction of the corpuscle. It was well known, long ago, to Hewson.-f The evaporation of water, and perhaps the cooling of the blood, are conditions favourable to these changes. But they may also occur, as wUl hereafter be shown, even when such conditions are not present. The appearances are presented by the corpuscles of Mammals, as well as by those of Man. And analogous phenomena are occasionally, though rarely, presented by the elliptical and nucleated corpuscles. The blood corpuscles of Salamandra maculata, and of Triton cristatus and tseniatus easily assume a mulberry -like form under the microscope. In the blood of the Frog the phenomena first make their appearance as a consequence of the operation of external agents, and the corpuscles then become exactly similar to those of Mammals. 2. From the action of mechanical agents on the blood corpuscles we learn that their substance is composed of an extremely extensible and, within wide limits, completely elastic material. That the blood corpuscles become elongated in their passage through the vessels, and that they also become curved in tra.- * Loc. cit. t Oj>usposthumum,-py. \^,20. 386 THE BLOOD, BY ALEXANDER EOLLETT. versing the angles of division of the vessels, were facts well known to the older observers. Lindwurm,* in thick solutions of mucilage; HassaU,f in micro- scopic coagula ; and Henle,| in thick semi-fluid jelly, all saw the blood corpuscles assume a distorted or elongated and some- times an extremely elongated fusiform shape. The greatest variety of such forms is obtained when defibri- nated blood is imbedded in pure solution of gelatine, melting at 35°to 36° 0.(95° to 97° F.); from which, again, when it has become stiff, fine sections can be prepared, and placed under a covering glass; we may here particularly observe in such sections through the clefts of the gelatine, how the parts of the corpuscles drawn out into various forms, and often much attenuated, are always pale, and often even without perceptible colour; whilst the swollen parts appear, on the other hand, more deeply tinted. Long processes extend from some of the corpuscles, which ulti- mately divide without coalescing with others. The nuclei of the elliptical blood corpuscles are somewhat less yielding, and they are frequently found to be completely detached from the substance of the blood corpuscles ; these, however, in many instances, as is deserving of special mention, do not in consequence suffer any notable change, either in their diameter or in their capabilities of resistance.§ Instances of the mechanical influences inducing change in the form of the red corpuscles occur, as already pointed out, in the movement of the blood while circulatiag. E. H. Weber,|| in 1830, adduced his own observations upon this point, and referred to the numerous ones made previously to the time of Leeuwenhoek. The phenomena may be well seen in examining the circulation in the membrane of the foot, and in the tongue or mesentery of the frog. Accordiag to RoUett, in the circulating blood of Mammals, as, for instance, of guinea-pigs, that have been narcotised with • Zeitschrift fur rationelle Medicin, Band y\., p. 266. ■f Microscopic Anatomy, p. 31, et seq., plate ii., fig. 6. J Canstatt's Jahresberichte, 1850, Band i., p. 32. § Kollett, Sitzungsberichte der Wiener Akademie, 1862, Band xl., vol. i., pp. 65—71. II Handbuch der Anatomie, Band i. Braunschweig, 1830, p. 159. CHANGES IN THE RED CORPUSCLES BY DESICCATION. 387 opium, the red corpuscles of the blood do not retain their ordi- nary average form in the mesenteric vessels, when driven forward with the stream; but become, during their flow, more or less irregular in outline* If the current be re- tarded or altogether arrested, or if the blood corpuscles are compressed against each other or against the interior of the vascular wall, they assume the same appearance as that which we have above described as characteristic of the fresh blood corpuscles. Moreover in diapaidesis, as it has been described from direct observation by Stricker,-f- Prussak,J and others, the phenomena we are now considering may be observed ia the red corpuscles during their transit through the vascular waU. Lastly, it is to be observed that the blood corpuscles, not- Anthstanding their great extensibility, may be broken up by mechanical means. § This may easily be accomplished if a drop of fresh blood be quickly expanded into a thin layer by the pressure of a glass cover, which after the lapse of a few seconds is raised, and again firmly pressed down ; there may then be seen coloured spheroidal or discoidal fragments. In nucleated corpuscles, as in those of the frog and triton, isolated nuclei are often visible, which are usually round, frequently distorted, and always granular. The number of the coloured fragments is always small in comparison with these, proving that the substance of the blood corpuscles becomes to some extent finely distributed through, or actually dissolved in, the surrounding fluid, which in point of fact appears slightly tinted. In anti- cipation of observations hereafter to be mentioned, it must be specially remarked that in these researches no shrivelled colourless shreds were noticed representing remains of the broken-down corpuscles. 3. The characters presented by the blood corpuscles on drying also deserve mention. C. Schmidt |1 has observed that when a thin layer of blood corpuscles is dried upon glass, * Sitzungsherichte der Wiener Ahademie, Band 1., p. 196. t Loc. cit., Band lii., p. 386. X Loc. cit., Band Ivi., p. 13. § Hensen, Zeitschrift fiir loissenschaftliche Zoologie, Band xi., p. 260. Vintschgau, AttidelV Instituto Veneto. Extr. dalyol. vii., ser. iii., pp. 3 — 6. II Die Diagnostih verddchtiger Flecke. Mitau and Leipzig, 1848, p. 3, et teg. 888 THE BLOOD, BY ALEXAOTJEE ROLLBTT. they remain extended, and do not undergo any remarkable change in the dimensions of their larger diameter. Welcker* and others have corroborated this statement. The clear spot of the non-nucleated corpuscles, to which alone the above statement is strictly applicable, comes, under these circum- stances, very distinctly into view, but passes without sharp definition into the surrounding darker parts. The nucleated corpuscles do not remain quite unaltered in the dimensions of their surfaces ; the variation is, however, of smaU amount. Many retain their form and smoothness ; others become curved or sinuous. The clear spot correspond- ing to the nucleus, and its delicate markings, come more distinctly into view. In some corpuscles the nucleus, after drying, always appears very sharply defined, and separated from the remaining substance of the blood corpuscles by a clear reddish refractile border investing it like a wall, and making it appear as if lying in a cavity. In blood dried in masses the blood corpuscles are found to present manifold changes of form and to become ultimately attached to one another, so that it is difficult to recognise them in fragments of dried crust. 4. In the coagula which originate in the lymph sacs of frogs or salamanders after bleeding, according to Rindfleisch -f- and Preyer, if coloured or colourless processes are protruded from the substance of the corpuscles, which are at first smooth, but afterwards resemble a string of pearls. According to Preyer, these can be again withdrawn, or may become completely isolated, or may separate into a few spheroidal masses. Beale § saw similar changes occur in the red corpuscles on a slide, in consequence of evaporation (? coagulation) and warming. 5. In order to observe the effect of electrical discharges || and of induction currents upon the blood corpuscles, the arrangement exhibited in pp. 21, 22, of this manual may be employed, except • Loc. cii., p. 261. t Experimental Studien iiber die Histologie des T.lUtes. Leipzig, 1863, p. 8. X Virchow's Archiv, Band x.^x., p. 417. § Quarterly Journal of Microscopical Science, No. 13, 1864. II Rollett, Sitzungsberichte der Wiener Aka .emie, Band xlvi., pp. 92 — 97 j Band xlviL pp. 356—390 ; Baad 1., pp. 178—202. , CHANGES IN THE RED CORPUSCLES BY ELECTKICITT. 389 that it is better to provide the copper pole with clips than with hooks. In these the ends of the induction coil or the ends of a transversely divided discharging rod of a Leyden flask are re- ceived, so that the tia-foil electrodes make a complete arc of union with the blood found between them and the wires. In order to enter more minutely into the phenomena which can be observed under the microscope, it is necessary in the first instance to bear in mind the results of microscopic experiments. K the blood of a mammal be introduced into the arc of discharge of a Leyden phial, and a series of shocks be passed through it, it becomes altered, losing its opacity, and assumiag a transparent lake-like tint. Microscopic examination shows that the blood corpuscles become altered, ultimately presenting only extremely delicate, pale, and feebly refracting particles. If in a consecutive series of examinations the number of the discharges requisite to produce the most complete transparency possible be taken as a measure of comparison for the clarifying power Of the dis- charging current, we arrive at the following conclusions : — The action of each successive shock is superadded to those which precede it. The transparency of each element of the conductor formed by the blood is dependent on the intensity (density) of the current acting upon the unit of its transverse section with which it proportionally increases ; it is also dependent upon the amount of what may be termed the specific resistance of the blood corpuscles, which differs in different kinds of blood, and with the increase of which, though not in a hitherto clearly ascertained ratio, the clarifying influence diminishes. With a given specific resistance of the blood corpuscles, and with given size and specific conductivity of the blood, the course of the phenomena can be varied according to the quantity and mean intensity of the electricity in the phial. The most advantageous distance of the tin-foU electrodes from one another for microscopic investigations is six mil- limeters; between these a thin layer of blood, covered with a thin plate of glass, should be introduced, and a Leyden flask employed, presenting a surface of about five hundred square centimeters, with a striking distance of one millimeter. Striking distances of greater extent cannot be \ised, as the 390 THE BLOOD, BY ALEXANDER EOLLETT. blood with the glass cover may be easily displaced, the sparks then passing directly from one electrode to another. Moreover, the surface of the flask must not materially exceed the above, or the discharging shock will occasion electrolysis (scarcely per- ceptible in the above-mentioned arrangement) to occur to an extent which may seriously interfere with the result. When these conditions are preserved, and the discharges are made to succeed each other at intervals of from three to five minutes, the following consecutive changes may be observed in the blood corpuscles : — The circular disk-like corpuscles (fig. 70, a) in the first in- stance present one or two projections at their borders, and these gradually increase in number to three, five, or more. Fig. 70. I have named this form the rosette form (fig. 70, h) ; it passes gradually into the mulberry form (fig. 70, c), which can always be produced at will by the discharge. To this succeeds a stage in which the processes become pointed, so that the corpuscles assume more the form of a paradise apple (horse chestnut) (fig. 70, d). Lastly, aU the spikes are withdrawn, and a coloured cor- puscle results (fig. 70, e),which then loses its colour, and a smooth colourless body is left (fig. 70, /), that long remains in the fiuid in an unaltered condition. In the case of the frog the blood corpuscles first assume a spotted appearance. Local thickenings then occur in the direc- tion of the shortest diameter, which for the most part proceed radially from the nucleus (fig. 71, a and h). This, however, is not always the case ; for it sometimes happens that the thick- enings are nearly perpendicular to the longest diameter of the corpuscle, and cross it in the form of transverse bands. The lat- ter is of most frequent occurrence in the blood of tritons. Upon this stage, which is obviously analogous to the first (fig 70, b) and to the second (fig. 70, c) stage in the blood corpuscles of CHAITGES IN THE RED COEPUSCLES BY ELECTEICITT. 391 Mammals, there follows a stage in which the corpuscles again become smooth ; their substance is then equably thickened, but the two other diameters have become somewhat smaller, whilst the mass either on one or both sides of the nucleus becomes swollen, so that the latter as it were closes a communication between the halves of a double funnel. At length the walls of Fig. 71. these funnels coalesce, and the corpuscles become egg-shaped or round. In the latter condition they are at first still coloured, but at a later period they gradually lose their colouring material, and there then only remains a duU colourless mass surrounding the nucleus. The nuclei appear somewhat rounded and more clearly visible in their interior. Just as the coalescence of corpuscles may be observed to occur at the points where they are accidentally in contact, so it frequently happens that two or more blood corpuscles, when they have become coloured spheroids, completely coalesce with each other. The larger spheroids with numerous nuclei then lose their colouring matter just in the same manner as the individual corpuscles. Another highly remarkable phenomenon is that the nucleus may escape suddenly or gradually from the corpuscles. Non-nucleated coloured spheroids thus originate, which again gradually lose their colour. Neumaim also has subjected the operation of induction currents upon the blood corpuscles to examination, and the phenomena he has observed' agree in all essential particulars with those that have been above described. On the other hand, the constant electric current does not produce these effects. It only produces alterations in the blood 392 THE BLOOD, BY ALEXANDER EOLLETT. corpuscles in the immediate neighbourhood of the metallic electrodes ; those observed at the positive pole being similar to those effected by acids, and those of the opposite pole .to those of the alkali which is there set free * We shall hereafter enter more fully into the action exerted by acids and alkalies on the corpuscles. 6. After Klebs.f RoUett,J and Beale§ had originally de- scribed the influence of increased temperature on the red blood corpuscles, Max Schultze || first applied a more exact and methodic mode of investigation by means of the slide he has constructed, which is capable of being heated to a definite degree. At about 52° C. (125° F.) the red corpuscles of man present first shallow and then deep fissures, which ultimately lead to the detachment of spherical masses. Some blood corpuscles assume various shapes, or thrust forth moniliform fibres. The latter forms immediately remind one of those found by Rind- fleisch and Preyer in extravasated blood. Finally, spheroidal coloured drops are always found, so that the middle part of the original corpuscles corresponds to one of the larger of such fragments, which, varying iu magnitude from this to an almost molecular fineness, are beset with smaller particles at their margin, or are surrounded by a series of them in a free state. The alterations described by Klebs as occurring at a tempera- ture of 38°C. (100° F.) were not observed by Max Schultze. From observations made in a water bath, EoUett ascertained the temperature at which the blood corpuscles became spheroidal to be between 4.0° and 50° C. (104°— 122° F.) The changes iu the corpuscles, however, do not occur suddenly, but only after long exposure, and without the segmentation observed at 52° C. (125° F.) Lake-coloured blood, according to Max Schultze, is first ob- tained when the temperature is raised to 60° C. (140° F.) * Rollett, loc. cit., Band xlyii., p. 359 ; Band lii., p. 257. A. Schmidt, Virchow's Archiv, Band xxix., p. 29 ; Sdmatologische Studien. Dorpat, 1865, p. 116. Neumann, Reichert mi 'D-a'Bois' Archiv, 1865, pp.682— 690. t CentraTblatt fur die medicin. Wissenschaften, X^&i, ^. %5l. \ Loc. cit., Band 1., p. 192. § Loc. cit. [I Loc. cit., p. 1 . CHANGES IN THE EED COEPUSCLES BT HEAT AND COLD. 393 At about 53° to 54° C. (127" to 129° F.),Max Schultze observed the same changes in the blood corpuscles of the fowl as those that have been already described. The corpuscles of the blood of the frog at about 45° C. (130° F.) become partially maculated and to some extent tuberculated on their surface, others assume the form of a finger-biscuit or of a dumb-bell, whilst a few become oval or spherical. 7. If blood, contained in a platinum vessel, be alternately frozen and thawed several times in succession, it likewise as- sumes a carmine colour. The non-nucleated blood disks are deprived of colour without becoming materially diminished in size, or they will be found to have become spherical, or of smaller diameter, or only their feebly refracting colourless remains can be discovered. In the corpuscles of the blood of the frog the nucleus is seen to be surrounded by a pale elliptical or circular area, or the colour of the blood corpuscle appears to be to some extent re- tained. Various forms are also found which appear indented or chipped off; finally here also the blood corpuscles lose their colour. The extensibility and elasticity of the uncoloured remains of the blood corpuscles are similar to those of the intact blood corpuscles.* In frozen blood the nuclei either still resemble unaltered nuclei, only somewhat more sharply defined, or they are sphe- roidal, enlarged, and appear as if composed of a delicate frame- work of highly refractile substance, in the meshes of which a less strongly refractile substance is contained. These spaces are often but few ia number. Frequently only a single space is present, in the form of a large vacuole surrounded by a ring of refractile material. These characters of the nucleus deserve attention in regard to facts that will hereafter have to be mentioned. 8. In reference to the phenomena that are occasioned by the addition of fluids to the blood corpuscles, three different conditions under which they may occur must be clearly distia- guished. The reagent may be intimately commingled with the • Rollett, loc. cit., Band xlvi., pp. 74, 75. 394 THE BLOOD, ET ALEXANDER EOLLETT. blood by mechanical means, in which case it is only possible to observe the final changes efiected in the corpuscles by the re- agent under the microscope ; or the plasma or serum of the blood corpuscle may be washed away with the reagent, under the microscope, in the manner described at p. xx. of the introduc- tion to this work, in which case, in order to prevent the cor- puscles from floating off, it will be found advantageous to spread upon the slide a thiu layer of a felt-like mass of fine clean asbestos, or of scraped Swedish filtering paper, and to place the blood drop on this ; or, lastly, the blood and the reagent may be placed in close proximity with each other, and allowed to diffuse slowly. It is only when, in the process of washing by the first method, the several blood corpuscles exhibit differences in their behaviour with the reagent that we are justified in concluding that an internal and original difference exists between them. It is not permissible to draw this conclusion when the second and third methods are employed, or at least only providing that very great caution has been exercised ; for if the uni- formity of the mixture has not been constantly maintained, some of the corpuscles will necessarily be first and more ener- getically acted on by the reagent, and the amount of change in any instance will be proportionate to the duration of the ex- posure to its influence. We may very easily satisfy ourselves that the changes effected by one and the same reagent are very different during the first period of its action, and lead to other results than at later periods. The many difficulties that encompass the study of the opera- tion of reagents on the blood have not, as a rule, received sufficient attention ; and less, perhaps, has been accomplished by this mode of experiment than might otherwise have been the case. a. The addition of water renders the surface of the cor- puscles smooth, and so changes their various diameters that they become spherical,* and thus acquire that form which with a given surface can contain the largest amount of material. This effect is commonly indicated as a process of imbibition, a * Hewson, Opus posthumum, p. 25. ACTION OF WATEE ON THE RED CORPUSCLES. 395 swelling up, although the diameter of the spheroid may be actually smaller than the long diameter of the corresponding disk (fig. 72). The spheroids are at first strongly coloured. On the cautious addition of -water it may be frequently observed that the alteration of the primary form of the blood corpuscle to a spheroid does not occur with perfect uniformity in aU the several and corresponding diameters, so that variable and Piff. 72. transitory unsymmetrical intervening forms are met with. In the nucleated ellipsoids it frequently happens that the nucleus changes its position in the corpuscle with a jerk,* whilst the corpuscle itself, as though in consequence of a recoil, is pro- jected in the opposite direction. The nucleus then lies eccen- trically in the corpuscle. When water has continued its action on the corpuscles for a longer period, the spheroids become discoloured, and frequently produce the impression that their colouring matter is being gradually extracted ; frequently also the colour disappears very rapidly, just as a hue of colour vanishes from a white surface when a coloured source of light by which it was previously illuminated is suddenly removed. The impressions thus given are precisely similar to those decolorations which have been formerly mentioned as the result of electrical discharges. Smooth colourless bodies with feebly defined but smooth contour lines then remain (fig. 72, b h h). The nucleus which at the commencement of the action of * See also the statements respecting the movements of the nucleus by C. H. Schultz. Preyer, he. cii., p. 437. F F 396 THE BLOOD, BY ALEXANDER EOLLETT. water, -when the corpuscles have acquired a spherical form, comes more prominently into view, and remains so as long as these still retain their colour, but subsequently becomes less con- spicuous, and after the long operation of large excess of water appears smooth, distended, and less highly refractile. Especial attention should be directed to a structure which can be easily demonstrated in the elliptical corpuscles after the cautious addition of water (fig. 73). The still ellipsoidal cor- puscle is bounded by a perfectly smooth contour line, but the place of the nucleus sometimes cappears to be occupied by a Fig. 73. coloured spheroid; whilst in other cases numerous processes radiate from this ball towards the contour line, becoming pointed peripherically. The parts lying between the latter and the coloured portion are homogeneous and colourless. According to Kneuttinger,* these forms are obtained when fresh frog's blood, from which the fibrin has not been removed is mingled with three or four times its volume of water, and an examination shortly afterwards made of the gelatinous mass. If larger quantities of water be added and thoroughly com- mingled with the blood, some of the corpuscles remain much longer in the condition of coloured spheroids than others ; and the inference has been not unreasonably drawn, that an essen- tial difference exists amongst such corpuscles. b. Salts act very differently, according to their chemical nature and their degree of concentration. Many metallic salts occasion precipitates in the blood corpuscles similar to the acids * Zur Histologie des Blutes. Wiirzburg, 1866, p. 21. ACTION OF SALTS ON THE RED CORPUSCLES. 397 hereafter to be mentioned. The action of those salts which produce no precipitate (common salt, Glauber's salt, sal am- moniac, borax, magnesium chloride, and others) has been repeatedly described, in contrast to the action of water, as a shrivelling or contraction. Solutions of this nature cause the blood corpuscles to become less glutinous and extensible, their outline more distinct, their form curved, their surface wrinkled, and their border dentated. Such are the effects of moderately strong solutions of these salts. Very strong solu- tions of some of these salts, or the addition of the salts them- selves, in powder, to the blood (common salt, Glauber's salt, magnesium chloride), only cause the blood corpuscles to shrink in the first instance, but soon they become round and pale, so that only colourless bodies remain.* In dilute solutions of some of these salts, the concentration of which is about equal to that of the blood serum, the corpuscles retain their characters for some time without alteration. Solutions of this kind are therefore frequently applied instead of serum for the purposes of dilution. With still greater degrees of dilution effects are produced similar to those that are observed when water is added in quantity to the blood. A successive series of forms may frequently be observed to occur in the nucleated elliptical blood disks, on the addition of saline solutions of medium degrees of concentration, though they cannot be certainly caused to appear. Hiihnefeldt and Hensenf have obtained and represented forms similar to those above mentioned, by the agency of ammonia and sal ammoniac. They may also be observed on the applications of other saline solutions. They are almost identical with those that have been already described as re- sulting from the action of water (fig. 73). The blood corpuscles, however, appear equably maculated, coloured and colourless areas alternating with regularity ; or, as frequently occurs in * KoUiker, Zeitschrift fur wissenschaftliche Zoologie, Band vii., p. 184. Botkin, Virchow's Archiv, Band xv., p. 176. Barsy, Ueber den Einfiuss einiger Sake aufdie Krjfstallisation. des Blutes, " On ths Influence of some Salts on the Crystallization of the Blood." Ihaug. Diss. Dorpat, 1863. t Zeitschrift fur wissenschaftliche Zoologie, Band ix., p. 261. F F 2 398 THE BLOOD, BY ALEXANDER ROLLETT. the blood corpuscles of Tritons, on the addition of three or four per cent, solutions of common salt, projections may form on the flat surface at right angles to the long axis, with paler or colourless spaces intervening between them. The alkaline salts of the biliary acids, and the bile itself, according to the older observations of Plattner (1844), which Kiihne* has corroborated by more recent researches, dissolve the red corpuscles of most animals, with phenomena in those of man which are similar to the effects that, according to L. Hermann, result from the action of chloroform or ether on the corpuscles. This subject, however, will be more fully discussed hereafter. c. The action of sugar under the microscope is similar to that of the above-named salts. Its solutions, in moderate degrees of concentration, harden the corpuscles by the withdrawal of water, and forms are produced analogous to those that are met with after the action of moderately strong alkaline solutions. d. Alkalies.^f as a general rule, when in a state of moderate concentration, exert a solvent action on aU the constituents of the blood corpuscles, including the nuclei. The following may be particularly mentioned amongst the many forms that are met with : — In the case Of potash and soda lyes, and of solutions of lime, baryta, and strontian, containing O'l gramme, in 100 cubic cen- timeters of water, a remarkable difference occurs, as compared with the action of pure water ; for the corpuscles first change into coloured spheroids, but soon disappear without leaving a trace. In the nucleated blood corpuscles, on the other hand, after they have become converted into coloured spheroids, the nucleus may still be indistinctly seen, and appears to be ex- panded in its interior, though the diameter of the coloured spheroid is not itself materially altered. The corpuscle soon gives the impression of undergoing flattening, and immediately the whole spheroid, with the nucleus, entirely disappears. As already stated, the impression of the flattening occurs only in the nucleated blood corpuscle, but is visible both in the • Virchow's Archiv, Band xiv., p. 333. t Kneuttinger, loc. cit., p. 39. ACTION OF ACIDS ON THE RED COEPUSCLES. 399 elliptical corpuscles and in the nucleated round corpuscles of the embryoes of Mammals. If the action of the reagent pene- trating into the blood be rendered less energetic, the flattening stUl often occurs ; and when all the rest of the corpuscle has quietly dissolved, the nucleus remains behind, enormously en- larged, and usually of a somewhat angular fortn, though homo- geneous in its substance. This phenomenon, however, may be more frequently observed after the application of the alkaline earths, than after that of the pure alkalies. In regard to lime water, it deserves especial mention that, in many instances, after the coloured spheroids have been produced, and the cor- puscles are about to flatten, the previously enlarged nucleus contained in the interior of the spheroid contracts suddenly to a strongly refracting body. The corpuscle then becomes pale, and this centrally situated body remains surrounded by a clear colourless area. This peculiar appearance occurs usually only at the commencement of the action of Ume water. e. Acids* readily occasion precipitates in the blood cor- puscles. The precipitate either appears distributed through a clear transparent substance, surrounded by the circular or ellip- tical contour line of the corpuscle, which frequently expands suddenly with a jerk (acetic acid) ;-|- and coincidently the nucleus, which has become more highly refractile, and fre- quently somewhat angular or inflated, and darkly granular, comes more distinctly into view (acetic acid, diluted tincture of iodine), whilst it appears distinct from the colourless substance of the blood corpuscles, in consequence of being strongly tinted with heematin; or the precipitate occurs in the thoroughly granular or cloudy corpuscle, which appears as if hardened and usually somewhat shortened in its long dia- meter. When the acids act in this manner, the nucleus fre- quently appears to be not very sharply defined, but frequently shrivelled and surrounded by an empty space, as though lying in a cavity of the substance of the blood corpuscles (chromic acid, hydrochloric acid, nitric acid, picric acid, tannic acid, and concentrated tincture of iodine). When the acids are much * Kneuttinger, loc. cit., p. 28. f Idem. 400 THE BLOOD, BY ALEXANDER EOLLETT. diluted, the second of the above-mentioned modes of operation frequently passes into the first, because in very diluted acids the action of the acid is complicated with that of the water. The former of the above-mentioned efiects is best exhibited by means of acetic acid, in solutions containing twenty grammes of pure acetic acid in 100 cubic centimeters of water, and upwards. The beautiful staining of the nucleus, with the colouring matter of the blood which then occurs, was first mentioned by Henle,* and has been corroborated by Kneut- tinger ;f it is e^xhibited in the most beautiful and convincing manner if the blood of a frog or triton is allowed to float into acetic acid : the blood sinks in the acid, and the dregs of the vessel can then be examined. The non-nucleated corpuscles of Man and Mammals are first rendered spherical by the action of acetic acid, and then lose their colour, in which condition they remain for a considerable period. Briickej has subjected to a special investigation the changes that are eflected on corpuscles of the fresh blood of the Triton by the action of a two per cent, solution of boracic acid, and we shaU now proceed to describe them. Soon after the addition of the solution the corpuscles seem to be converted into ellip- soids, as after the action of certain proportions of water, the nuclei being often eccentrically situated ; they ultimately, to a: greater or less extent, become spherical. Forms are also obtained similar to those that have already been mentioned as occurring after the addition of water or saline solutions (fig. 73). In other corpuscles the nucleus alone appears of a deep colour, the remaining substance of the corpuscle being pale or completely colourless, and separated by a smooth con- tour line from the surrounding fluid, as after the action of many other acids in certain degrees of dilution. Direct obser- vation of the action of boracic acid under the microscope renders it evident that the latter form does not necessarily pro- ceed from any of the foregoing. In the gi-eater number of * Allgemeine Anatomie, p. 431. ■j- Zoc. cit., pp. 28, 29. J Sitzunffslerichte der Wiener Akademie, Band lyi., p. 79. ACTION OF ACIDS 'ON THE RED COEPUSCLES. 401 instances the nucleus gradually becomes coloured, -without the colour being discharged from the border of the corpuscle, although the substance of the corpuscle becomes proportion- ately colourless. A similar coloration of the nucleus occurs also with a two per cent, solution of boracic acid, when applied to the corpuscles dried on a sHde. If the corpuscles are so modi- fied by freezing, by shocks of electricity, or by ether or chloroform (the changes efiected by which will be subse- quently considered) that they have yielded up their colouring matter completely to the serum, and they are then treated with a two per cent, solution of boracic acid, the nuclei stiU. acquire their deep tint from the colouring matter contained in the sur- roundiag fluid. Briicke also observed the corpuscles discharge their nuclei from the action of boracic acid. /. If it be desired to ascertain what alterations are efiected in the blood corpuscles by small variations in the degree of acidity or alkalinity of the reagent, it is requisite, as has been shown by W. Addison,* in order to avoid the action of the water of the solution, to give a certain degree of concentration to the fluid by the addition of a smaU proportion of sugar or of salt. In such investigations it wiU be found, as he has correctly stated, that on the addition of an acid fluid, as of a solution of cane sugar weakly acidified with hydrochloric acid, the blood corpuscles possess, in aU instances, smooth contours, and exhibit an increased degree of refraction ; whereas on the addition of an alkaline fluid, as of a solution of common salt rendered feebly alkaline with liquor potassee, the blood corpuscles become granulated and rough. Appearances essentially similar are produced with still greater clearness by passing weak currents of electricity through the blood. That the corpuscles quickly become tuberculated and spinous in the vicinity of the alkaline pole was observed by Neumann,-|- who also saw the formation of the fibres described by Addison. The change of form corresponding to the action of weak * Quarterly Journal of Microscopical Science, 1861; Jan., Transact., p. 20 ; April. Journal, p. 81. t Zoc. cit., pp. 679—681. 402 THE BLOOD, BY ALEXANDER KOLLETT. alkalies can, according to Addison, be changed by acid solu- tions into the form they induce, and vice versd. g. Urea,* in the state of fine powder, or in solution in water, in the proportion of from twenty-five to thirty grammes or less in 100 cubic centimeters of water, powerfully afiects the form of the corpuscles, though they are not all affected in the same way. In the blood of Amphibia some of the corpuscles always assume a curved form, and then small drops and spherical fragments become detached from them. Others become spheri- cal without undergoing any further alteration in shape ; but both large and small spheroids ultimately become colourless. During the assumption of the spheroidal form some of the corpuscles discharge their nuclei. The latter become slightly enlarged in the Frog, but much augmented in volume in the Triton, and then assume the remarkable appearance of a trabecular framework with large meshes. The nuclei which do not escape undergo similar changes if once the spheroid become colourless, so that the pale clear remains of the sub- stance of the blood corpuscles appear as a kind of appendage to the enlarged nucleus. To regard these structures as nucleated albuminous spheroids escaped from adjoining coloured corpuscles is due to a misconception of the phenomena observed.f If we now consider the action of less concentrated solutions of urea, we find that the incurvation of the corpuscles and detachment of drops is of rarer occurrence, and that the majority of corpuscles immediately become spherical, and at a subsequent period, together with the nucleus, entirely vanish. The incurvation of the border and the formation of drops is also exhibited by the non-nucleated blood corpuscles of Mam- mals when treated with urea. h. Neutral solutions of carmine in pure ammonia (one gramme of carmine in 200 cubic centimeters of solution) produce on the * Hulinefeldt, Chemismus in der thier. Natur., 1840, p. 60. Kolliker, Zeitschrift fur wissensclwftliche Zoologie, Band vii., pp. 184, 253. Botkin Virchow's Archiv, Bandxx., p. 37. Hensen, he. cit., p. 264. Viutschgau, loc. cit., p. 13. Preyer, he. cit., p. 432. Kneuttinger, he. cit, p. 56. t Kneuttinger, he. cit., p. 58, fig. 9 b. ACTION OF AMMONIA ON THE RED CORPUSCLES. 403 corpuscles the same effect as water. In the blood of Amphibia the inflated nuclei become, after a short time, tinged of a red colour. The blood corpuscles behave differently in the above- mentioned solutions of carmine in ammonia if from one-half to one per cent, of common salt be added, since they then remain apparently unaltered, and take up none of the carmine into their interior. On the other hand, the nucleus immediately becomes stained. If a mixture of blood and this coloured saline solution be allowed to freeze or be acted on by discharges of electricity, a series of remarkable phenomena may then be observed, upon the investigation of which I am now engaged. If the blood of frogs or newts be allowed to flow into such saline solutions of carmine, there may always be found, besides the ordinary red and white blood corpuscles with nuclei, which long remain unstained, a few isolated free nuclei of an intense red colour. It thus appears that when unaltered the blood corpuscles do not absorb any colouring matter. Eindfleisch* has described a remarkable alteration efi'ected in the blood corpuscles of the frog by the addition of soluble aniHn blue. They are then found to become nucleated spheroids, which quickly assume a blue colour, but it is only in solutions containing about a haff-gTamme to 100 cubic centi- meters that the remarkable phenomenon of the discharge of the nucleus from the now spherical corpuscles occurs. It is especially remarkable that any part of the nucleus which once projects beyond the contour line of the corpuscle immediately swells up to a considerable extent, so that at this period the form of the nucleus resembles a short nail with a large head, which seems to have been driven into the substance of the corpuscle. When the nucleus has become altogether detached from the corpuscle, it sweUs up uniformly, becomes stained, and undergoes further changes, to be hereafter investigated. i. Gases and vapours have lately, since the employment of gas cells, been likewise applied directly to preparations of blood under the microscope. a. Strickerf has been especially engaged in investigating the * Loc. cit., pp. 10, 11. t Pflugei's Archiv, 1868, p. 590. 404 THE BLOOD, BY ALEXANDER EOLLETT. action produced by the exposure of the blood corpuscles of the newt and frog alternately to carbonic acid and air. So long as the blood remained unchanged he observed only the already-mentioned phenomena in the micro-spectrum, and was thus enabled to correct the older inexact statements* Blood corpuscles changed by the action of water, however behaved themselves differently. Strieker applied water in the form of vapour, by which means very fine gradations in the amount supplied can be attained. On transmitting carbonic acid he then observed the occur- rence of precipitates both in the nucleus and in the substance of the corpuscle ; these precipitates vanished with oxygen, and returned with carbonic acid, and so on. Strieker considers these appearances, as had already been held by A. Schmidt and Schweigger-Seidel in the case of the precipitate obtained by the action of carbonic acid in the substance of the blood corpuscles of the frog, to be caused by the separation of para- globulin; in order, however, to obtain such precipitates the addition of water must be carried almost to the extent of rendering the blood corpuscles colourless. If smaller quantities of water be added, these precipitates do not occur. Under certain conditions the remarkable form appears that we have already described (fig. 73, a). This form, as an easily repeated experiment of Strieker shows, vanishes with an excess of carbonic acid. The blood corpuscles then appear once more equably tinted, and on the admission of air revert again to their original form. With the addition of a certain amount of water the nucleus alone becomes tuberculated, and more sharply defined when carbonic acid is transmitted, whilst upon the passage of air it again becomes smooth. If this stage be exactly attained, the whole blood corpuscle may be seen to become spherical with carbonic acid, and again to assume its smooth form on the admission of air. Moreover, the thorn-apple form of the mammalian blood corpuscles can be made to disappear by car- X 'S.axVess, Monographie iiber den Einfluss derOase aufdieForm. Erlangen' 1846. " Monograph on the influence of gases on form." ACTION OF VAPOURS ON THE RED CORPUSCLES. 405 bonic acid, but can again be produced on the accession of air ; the experiment, however, as Strieker has remarked, cannot be very frequently repeated, as the thorn-apple form ultimately remaias persistent. A. Schmidt* showed that ozone gave a carmine tint to the blood by destruction of the blood corpuscles. b. Ether,-j- chloroform,| bisulphide of carbon,§ and alcohol, || conducted in the form of vapour over the blood, also render it of a carmine colour. If the appearances exhibited by the blood corpuscles are closely observed, it may be seen that in the circiilar disks the border becomes thickened, IT and in place of the central depression a navel-Hke fossa appears. The funnel so formed becomes narrower and closes, and the corpuscles now appear as a coloured spheroid. Chloride of methyl vapour acts in a similar manner.** The above-mentioned vapours, but not the last, finally render the corpuscles colourless. When ether and chloroform vapours act on the blood of the Amphibia, they render the corpuscles, in the first instance, spotty, though the colour subsequently becomes equably diffused, whilst the blood corpuscles appear to be somewhat diminished in size. On the other hand, the thickness of the border is increased, so that the nucleus lies in a depression. A few only of the blood corpuscles become spherical. The majority, when in the condition of a disc with thickened borders, lose their colour, and the nuclei then become more sharply defined. The blood corpuscles of the Amphibia also behave themselves simi- larly when air impregnated with ether or chloroform vapour is persistently transmitted over the preparation, and the phe- * Virchow's Archiv, Band xxix., p. 14. t V. Wittich, Journal fur praktische Chemie, Band Ixi., p. 11; and Konigsberger Medic. Jahrbiicher, Band iii.,p. 332. L. Hermann, Reichert and Du Bois' Archiv, 1866, p. 27. X Chaumont, Monthly Journal of Medicine. Edinburgli, 1851, p. 470. Bottclier, Vircliow's ^rc/wu, Band xxxii., p. 126; Band xxxvi., p. 342. ICneuttinger, loc. cit., p. 48. A. Schmidt and Sch weigger- Seidel, Berichte der Konig. Sachs. Gesellschaft der Wissenschaften, 1867, p. 190. § Hermann, loc. cit. II Hermann, loc. cit. Kneuttinger, he, cit., p. 44. % Hermann, loe. cit., p. 31. A. Schmidt and Schweigger- Seidel, foe. cit., p. 196. ** Hermann, loc. cit. 406 THE BLOOD, BY ALEXANDER ROLLETT. nomena do not essentially vary if the air thus charged with vapour is exchanged at definite periods for pure air. If these reagents be added to the blood in a fluid condition, it will be found that ether and chloroform eifect similar changes, except that a large number of blood corpuscles become spheroidal. Alcohol readily produces precipitates and irregular shrivelling. Opinions respecting the Structure of the Red Blood Corpuscles. — In the exposition of these we need only go back to the time when the view which, though it had been advanced indeed before Schwann, yet was generally adopted only in consequence of his doctrine of the structure of animal cells, namely, that the red corpuscles are vesicles consisting, of a membrane with fluid contents, began to be doubted. The opponents of this view, after Max Schultze had, in 1861, demonstrated that a cell membrane is not a constant constituent of a cell, directed their attacks against the presence of a mem- brane in the red blood corpuscles. The presence or absence of a membrane must necessarily influence the conception of the nature of those constituents of the blood corpuscles which were formerly regarded as the coloured contents. In the criticism directed by Max Schultze against the ceU theory of Schwann, the red blood corpuscles played a part, since in the discussion respecting the necessity of a nucleus to complete our idea of a cell, those of Man and Mammals were adduced as being destitute of a nucleus. This was for a considerable time almost universally taught, and of late has been opposed by Bottcher* alone. After what has already been stated in refer- ence to the question of the nucleus, however, I do not consider it requisite to enter more fally into that subject, but shall refer to the communications of Bottcher, Klebs,t A. Schmidt, and Schweigger-Seidel.l We must deal difierently with the ques- tion, whether the red blood corpuscles do, or do not, possess a membrane. * Virchow's Archiv, Bande xxxvi. aad xxxix. t Virchow's Archiv, Band xxxviii. X Konig. Sachs. OeselUchaft, etc., Math. Phys. Classe, 1867, p. 190. STRUCTURE OF THE RED BLOOD CORPUSCLES. 407 It must, I think, in reference to this point, be admitted that important evidence, based on the form of the corpuscles, can be adduced against the view that they consist of vesicles in the sense held by a large number of histologists after the time of Schwann. A vesicle filled with fluid, the parietes of which are yielding, and which again floats freely in another liquid, might be con- ceived to assume almost any form rather than of a body with two concave surfaces, as in Mammals, or with two convex sur- faces, surrounded by a circular or elliptical zone of a certain thickness, as in Birds, Amphibia, and Fishes. Schwann* adduced the assumption of a spheroidal form by the blood corpuscles on the addition of water, as a proof of their vesicular nature, maintaining that if they were not so they might indeed swell up and become colourless, but that they would retain their form like a sponge on the imbibition of fluid. The explanation of the action of water producing tension of the membrane, in consequence of the fluid contents of the vesicle increasing by endosmose,was at this time very generally accepted, just as the shrivelling of the surface, on the addition of saline solutions, was regarded as a consequence of a diflusion current setting from the interior. Briicke,t however, showed that neither the phenomena presented by the imbibition of water, nor after the addition of saline solutions, furnished conclusive evidence of the vesicular nature of the corpuscles. If we base our opinion on the experiments performed on the red blood corpuscles by means of mechanical agents, we may exhaust aU the various methods, without once meeting with a form which can be indisputably regarded as the torn and empty investing membrane, and the occurrence of which is in no other way capable of being explained ; so again, whatever may be the changes that induction currents and electrical discharges, as weU. as freezing, induce in the corpuscles, no condition can at any time be seen directly proving the pre- sence of a membrane. * Ueber die Uebereinstimmung in Structur und Wachsthum der thieris- che nund PJlanzlichen Organismen. Berlin, 1839, p. 74. f Berichte der Wiener Akademie, Band xliv., p. 389. 408 THE BLOOD, BY ALEXANDER KOLLETT. On the contrary, the escape of the nucleus, the coalescence of the coloured spheroids, the physical character of the colour- less remains after the discharge of the colouring matter, are all opposed to the existence of such an investment. The results of these inquiries are much more in favour of the view main- tained by Rollett,* that a stroma or matrix enters into the structure of the coloured elastic extensible substance of the red blood corpuscles, which exhibits so remarkable a similarity in all animals, and that to this the form and the peculiar physical properties of the corpuscles are due. Hence the conclusion, that, however complicated the chemical constitution of the sub- stance of the blood corpuscles may be, yet, by the action of a series of agents, the colouring matter can be separated from the stroma, without causing the latter to lose its essential characters. The phenomena induced in the red blood corpuscles by vari- ous reagents, as urea, chloroform, and ether, and also the pheno- mena described by Max Schiiltze as resulting from the action of heat, fairly agree with this simple view. No doubt it may be urged that the membrane is highly extensible, and that it is reasonable to suppose that by the action of the above- mentioned agents it would be rapidly destroyedjrendering the phenomena observed consistent with its original presence around the tenacious semi-solid gelatinous contents of the blood corpuscles. But the theory that under these circumstances the membrane is really destroyed can only be based on the proof of its existence. We cannot hold the latter as ascer- tained if we regard the forms which a series of reagents (acids) occasion in the blood corpuscles ; in the latter case we have much more ground for believing in the formation of arti- ficial products, than they who hold the opposite view have reason in the previously adduced cases to admit the destruction of a naturally present membrane. The proof of the pre- existence of a membrane must here again, in the first instance, be furnished. A circumstance bearing upon the question of a membrane is met with in the peculiar structures already frequently mentioned as occurring in the blood corpuscles of the Amphibia (fig. 73, • Loc. cit., Band zlvi., pp. 73, 94, 95, and 98. STRUCTURE OF THE RED BLOOD CORPUSCLES. 409 a b). A retraction of the cell contents from the membrane has here been considered to occur, and we may associate with this the forms which Remak* and more recently Preyerf have described in regard to the fission of blood corpuscles, in which a gradually deepening furrow detaches a coloured por- tion of the blood corpuscle, whilst a glass-clear substance (the empty membrane) becomes apparent between the separating part and the investing contour line of the rest of the corpuscle. Hensen,J who has devoted considerable attention to the first- mentioned forms, sought to explain the retraction of the con- tents from the membrane, the existence of which he believed, from his observations of these forms, to be proved, by ascribing a protoplasm to the red blood corpuscles, which invests the nucleus and lines the inner surface of the membrane (primordial utricle), these two portions being connected by delicate radially coursing fibres, in the spaces of which the closed cell fluid is ocontained ; he supported this view especially upon the existenc of colourless fibres running in a radial direction from the nucleus, and it is well known that similar observations have been made by other histologists. But, independently of these fibres, which certainly do not represent any constant structure in the blood corpuscles, since they only appear to be met with under exceptionally favourable circumstances, the protoplasm distributed throughout the whole corpuscle must, according to the view of Hensen, form a considerable portion of their substance. The term protoplasm is now frequently so em- ployed as to render it very desirable that its appHcation should be restricted to a definite idea ; but if we pay attention to the appearance and the most striking peculiarities of the protoplasmic masses described by Max. Schultze§ and by Kiihne ; || and if also, as will be subsequently discussed, we consider that in their development the red blood corpuscles are formed at the expense of the cells composed of contractile * Miiller's Archiv, 1858, p. 178, Taf. viii. t Virchow's Archiv, Bandxsx., p. 417, Taf. xv., figs. 26 and 27. X Zeitschrift fur mssenschaftliche Zoologie, Band xi., p. 260, etc. § JDnsProtoplasmader RhizopodenuudderPJlanzenzellen. Leipzig, 1863. II Untersuchungen uber das Protoplasma und die Contractilitdt. Leipzig, 1864. 410 THE BLOOD, BT ALEXANDER BOLLETT. protoplasm, in which metamorphosis the essential characters of the latter are lost, it is impossible to avoid expressing our opposition to the theory of Hensen. In fact, the forms which led Hensen to the above-mentioned view are susceptible of quite a different interpretation. Briicke,* who observed such forms to be produced by the action of a two per cent, solution of boracic acid, considers that there is a porous structure composed of a non-contractile, very soft, colourless, perfectly transparent substance, which he further represents as the body of an animal, whose central part forms the nucleus of a nucleated corpuscle, and is free from haemoglobin, whilst the remaining portion of the mass contains the whole of the hsemogoblin. Briicke considers that this latter portion accurately fills the intermediate spaces of the porous mass, and thus in combination with the parts free from pigment makes one continuous whole. To the colourless porous sub- stance he has applied the term " oekoid," whilst he calls the contained substance the " zooid ;" and he is of opinion that the retraction of the zooid either completely or partially from the oekoidexplains the formation of the above-mentioned forms. Stricker-f- agrees with Briicke in considering the oekoid to be the part enclosing the colouring matter, and as that which under certaia conditions can retract towards the nucleus. He terms it the " body," at the same time attributing a greater amount of independence to the nucleus, and drawing attention to the analogy between the blood corpuscles of Amphibia and Mammals. The question now arises, are the red blood corpuscles con- tractile as a whole, or is that part only contractile which is called the zooid by Briicke, or the body by Strieker ? Klebs]: regarded the blood corpuscles of Mammals as contrac- tile bodies, iu consequence of his observations on the influence of temperature, though these have since been opposed by Max Schultze. The mulberry form he considered to correspond to the mobile condition, the curved-disk form to the quiescent * TFiener JBerichte, Band Ivi., p. 79. t Pfluger's Archivfiir Phydologie, 1868, p. 591. \ Centralhlatt fur die medicin. Wissenschaften, 1863, p. 851. CHEMICAL CONSTITUTION OF THE BED COEPUSCLES. 411 condition, and the spherical form to the state of death. Eollett,* in consequence of his investigations upon the effects produced by electrical discharges on the blood corpuscles, is opposed to the view that they are contractile. He relies upon the facts that we always see the corpuscles in the interior of the vessels of the living animal in a state of merely passive movement ; that blood corpuscles preserved outside the body for many months, or placed in blood destitute of oxygen but impreg- nated with carbonic acid, or in blood impregnated with carbonic oxide, behave themselves, when acted on by electrical shocks, in a manner essentially similar to those that have been recently taken from the living animal. Max Schultzef also, from his experiments on the influence of warmth on the non-nucleated corpuscles of Man and Mammals, arrived at the conclusion that these at least were not contractile ; and Kiihnej expresses him- self in similar terms. We arrive h^re, however, at a point at which it appears ne- cessary to determine what signification must be applied to the term contractility; Briicke, in the treatise above alluded to, justifying himself in speaking of the contraction of the zooid as of a living being, remarks that it would profit us nothing were we to refer the separation of the zooid from the oikoid, not to a contraction of the former, but to a process resembUng coagulation, and that we have no guarantee that we have arrived nearer to the' truth. A movement which we may designate by the term contraction certainly occurs ; for the coloured ma- terial unquestionably retreats from all sides towards the- nucleus. What may be the causes of this contraction, and whether it may be compared in its essence with the contraction of a dying amoeba, vsdU probably long remain a subject of uncertainty; to the illumination of this darkness we may, however, soon attain. Outline of the Chemistry of the Eed Corpuscles. — The best-known constituent of the red blood corpuscles is hse- t Wiener Akad. Berichte, Band 1., pp. 190—200. * Archivfiir Mikroskop. Anatomie, Band i., pp.- 33, 34^. J Physiolog^ Chemie. Leipzig,, 1866, p. 191. G G 412 THE BLOOD, BY ALEXANDER ROLLETT. moglobin ; this can easily be obtained in tbe crystalline condi- tion. Hsemoglobin crystals have long been known as blood crystals, and have been subjected to microscopical scrutiny. In the first instance they were recognised accidentally, Rei- chert* having observed them in a preparation from the guinea- pig preserved in alcohol, in the form of tetrahedra. Fiinke,t Kunde,| Schwann,§ at a later period obtained the crystals me- thodically from blood treated with water, and found that the crystals of colouring matter from the blood of different animals presented different crystalline forms, whilst those from the same animal were for the most part identical. Those from dif- ferent animals were at first considered to belong to very different crystalline systems. It has been more recently ascertained that blood crystals can not only be obtained by destroying the blood corpuscles with water, but that an entire series of conditions which render the blood carmine in colour by destruction of the corpuscles also lead to the production of haemoglobin crystals. Thus, for in- stance, RoUett has shown that freezing and subsequent thawing of the blood, as well as the discharges of voltaic electricity ; RoUett and A. Schmidt, that the alteration which the cor- puscles undergo at the positive pole of a constant current ; Max Schultze, that the elevation of the temperature of the blood by means of a water bath at 60° C. (140° Fahr.) ; Bursy, that the addition of powdered salt ; V. Wittich, that the addition of ether, or transmission of ether vapour ; Bottcher, that the ac- tion of chloroform ; and Kiihne, that the alkahne salts of the biliary acids, produce the same effect. From each drop of such lake-coloured blood a large number of beautiful crystals may be obtained on the object slide of a microscope. Such crystals, obtained in constantly increasing numbers from different species of animals, and examined with still increasing care, are now proved to belong to two different * MuUer's Archiv, Jahrgang, 1849, p. 197. t Zeitschrift fiir rationelle Medicin, N. F., Band i., p. 172 ; Band ii., p. 199. X Idem, Band ii., p. 27L § Handhuch der Physiol. Chemie, Band i., p. 365 ; Band ii., p. 161. CHEMICAL CONSTITUTION OF THE RED CORPUSCLES. 413 crystalline systems. Lang* was the first to show that what were regarded as regular tetrahedra from the blood of the guinea-pig, when examined with a Nicol's prism ia a polarising microscope, appeared clear in four azimuths, and dark in four azimuths, and therefore that from their optical characters they belonged to the rhombic system : and further, that when com- pared with the prismatic crystals of human blood belong- ing to the same system, the following results were obtained. The lengths of the axes of the prisms of human blood present, according to measurements of the acute angle of the rhombic terminal plane (54° 1'), the proportion of 1 : 1,96 = 1 : 2-0,98; if then the second axis-length be divided by 2, the two axes would be of nearly equal length, which agrees well with the crystals from the blood of the guinea-pig. The crystals of by far the greatest number of animals, how- ever, occur either in the form of simple tetrahedra, or of tetra- hedra with truncated angles and edges ; or, like those of man, they form rhombic prisms, respecting which the recent treatise of Preyerf may be consulted. The blood crystals of squirrels alone, formerly described as six-sided plates, appear, as shown by Von Lang,f to be six-sided plates belonging to the hexagonal system. Von Lang also first demonstrated that crystals of hsemoglobin, examined in two azimuths, with only one Nicol's prism over or under the object, exhibited colours different from those in the two intervening ones, and that they therefore present absorption phenomena in regard to light, in accordance with their crystal- line form (Pleochroismus). Besides hsemoglobiu, a series of other substances have been ascribed to the blood corpuscles, constituting their colourless portion, which nevertheless appear to exist in very variable quantities in difierent animals. To these belong the albuminous bodies. The globulin, or paraglobulin of Kiihne may be pre- cipitated by means of carbonic acid from blood corpuscles mo- * Sitzungsheriehte der Wiener Akademie, Band xlvi., p. 85, et seq. t Pfliiger's ArcMv, Jahrgang, 1868, p. 365. t Loc. cit., p. 89. G G 2 414 THE BLOOD, BY ALEXANDER EOLLETT. dified to a certain degree by the action of water (Kiihne, A. Schmidt, Strieker). Moreover, an albuminous body, which still requires investi- gation, has been termed fibrinoid by Hoppe, and fibrin by Heynsius. L. Hermann and Hoppe have demonstrated the presence of protagon, and Hoppe the presence of lecithin in the stroma of the blood corpuscles. As a consequence of the presence of hsemoglobin they contain a variable quantity of oxygen, and A. Schmidt has demonstrated the presence of carbonic acid in them. In addition to these substances there still occurs a cer- tain proportion of salts differing qualitatively from the mineral matters of the plasma. The Coloueless Moephological Constituents of the Blood. — Amongst these the white corpuscles of the blood de- serve to be first mentioned. These were distinguished by Hewson from the coloured, and the great majority are characterised by the lively movements they are capable of performing.* Max Schultze,-f who has lately carefully investigated these forms, distinguishes several kinds in human blood. First, round cells, not attaining the size of the red blood corpuscles, com- posed of a thin layer of ceU substance, investing one or two nuclei, which last are either spheroidal or flattened by mutual compression. With these maybe associated other forms, equalling in size the ordinary red blood corpuscles, and, hke the former, possessing nuclei. Lastly, finely and coarsely granular amoeboid cells are met with, and various intermediate forms between them. In freshly drawn blood these last appear as more or less rounded or irregularly shaped forms. At a temperature of from 85° to 40° C. (95° to 104° Fahr.) lively movements, resembling the creeping motions of an amoeba, occur. When the tempera- ture, however, is raised above 40° C, the movements cease, and the cells harden. * Wharton Jones, Philosophical Transactions, 1846. Davaine, Memoire de la Societe de Biologic, 1850, Tom. ii., p. 103. Lieberkiihn, Muller's Archiv, 1854, p. 11, et seq. t Archiv fur Mikroskop. Anatomic, Band i., p. 9. COLOURLESS CORPUSCLES OF THE BLOOD. 415 As long as they are in active movement they are capable of absorbing small particles of colouring matter, as of carmine and arulia blue, and also milk globules, iato the interior of their bodies. In reference to the further peculiarities of these true protoplasmic masses, I must refer to the first chapter of this manual. Besides the white corpuscles of the blood, Max Schultze admits, as constant constituents of human blood, irregularly formed masses of colourless globules, which he regards as fragments of ceU substance. There is a statement frequently met with in books, that, under certain circumstances, fat drops are met with in the blood, often iu such quantity that the serum acquires a milky appearance, as in sucking animals,* and after the use of olea- giuous food.f Oily matters, which have entered the blood, seem however to disappear with great rapidity. In the remarks made upon Schlemm's observations on kittens, Joh. Miiller;]: states that he only found milky serum when the animal had shortly before iugested milk. Yet another morphological constituent occurs in the so- called elementary corpuscles of Zimmerman. § These have been held to be generators of the blood corpuscles. The greater number of them, obtained iu the mode adopted by Zimmerman, from blood treated with salt, can be easily recognised as arti- ficial products ; that is to say, as the colourless remains of dis- torted red corpuscles (Hensen). It is not a matter of surprise that similar forms should also be frequently found in freshly prepared blood (Kneuttiuger). Lastly, Max Schultze has demonstrated that the smallest elementary corpuscles of Zim- merman agree with his before-mentioned granules. As regards the number of the white blood corpuscles, they are much less abundant in normal blood than in the red, and their relative number is subject to much greater variation * ScUemin and Joh. Miiller, Froriep's Notizen, Band xxv., 1829, p. 121. t Kiihne, Physiolog. Chemie, p. 181. KoUiker, Oewehelehre, 1867, p. 620. X Loc. eit, § Rust's Magazine, Band Ixvi., p. 171 ; Virch.ow's Archiv, Band xviii., p. 221 ; Zeitsehrift fiir wlssenschaftliche Zoologie, Band xi., p. 344. Hensen, loc. cit., p. 259. Max Schultze, loc. cit., p. 39. Kneuttiuger, loc. cit., p. 5. 416 THE BLOOD, BY ALEXANDER EOLLETT. The variations depend upon tlie age, sex, period after food, and the vascular territory from which the blood examined has been taken. Under all these different circumstances the number of the ■white blood corpuscles has been counted, according to the methods adopted for the enumeration of the red* On the average there is, according to Welcker, one white corpuscle to 335 red, and according to Moleschott, one to 357. Boys have one colourless to 226 coloured. Men, one to 346. Old men, one to 381. Girls, one to 389. Young women who are menstruating, one to 247. The same women, when not menstru- ating, one to 405. Pregnant women, one to 281 (Moleschott). Hirt found in the early morning, and in the fasting condi- tion, that the proportion was one white corpuscle to 716 red; half an hour after breakfast, 1 : 347 ; two to three hours later. Fig. 74. 1 : 1,514 ; ten minuted after a midday dinner, 1 : 1,592 ; half an hour after the same, 1: 429; two to three hours after the same, 1 : 1,481 ; half an hour after tea, 1 : 544 ; two to three hours after tea, 1 : 1,227. In the splenic vein, Hirt found the proportion to be 1 : 60 ; • Welcker, Prager, Virteljahrschrift, loc. cit. Moleschott, Wiener medi- cin. Wochenschrift, 1854, No. 8. Hirt, De Copia relativa Corpuseulorum Sanguinis Alborum. Diss, inaug. Lips., 1855. E. de Purg,Virchow's Archiv, Band ■viii., p. 301. Marfels, Moleschott's Untersuchungen zur NaturUhre, etc., Band 1., p. 61. Lorange, Quomodo ratio Cellularum alb. et rub, mutetur, etc., Diss, inaug. Regiomont, 1856. COLOURLESS CORPUSCLES OF THE BLOOD. 417 in the splenic artery, 1: 2,260; in the hepatic vein, 1: 170; and in the portal vein, 1 : 740. Several kinds of colourless morphological constituents can Kkewise be distinguished in the blood of the Frog* (fig. 74, a) ; namely, the ordinary amoeboid cells, and the so-called granule cells, filled with highly refractile granules. The former (fig. 74) exhibit more, the latter less lively changes of form, associated in freshly drawn blood with locomotive move- ments, and likewise take up into their interior mUk globules and particles, of colouring ma,tter.-|- Preyerj saw por- tions of the red blood corpuscles- of extravasated blood in Amphibia taken up by white blood corpuscles, and thus explained the nature and mode of occurrence of the bodies that were previously called blood-corpuscle4ioIding cells. When acted upon by induced currents, and the discharges of voltaic electricty, these cells become round, § just as occurs, according to Kiihne, in amoebae when irritated. Golubew showed that the cells of the frog, after having been made to contract by the application of a stimulus, recommence their movements. The character of these movements, however, is no longer the same as before the irritation ; for, whilst the pro- cesses are ia the first instance conical and finely pointed, on the recommencement of the movement after excitation they are more rounded, as well as shorter and broader, are quickly protruded, and are again withdrawn, to reappear in the imme- diate proximity ; so that a kind of undulation runs round the corpuscle (fig. 74, 6). After a short time, either the origiaal character of the movement reappears, or the corpuscles expand on the recurrence of movements, into a flat disk. When in either of these phases, increased strength of excitation imme- diately causes the corpuscle to reassume the spheroidal form (fig. 74, c). • Eindfleiseh, he. cit., p. 21. Kneuttinger, he. cit., p.. 10, et seq. Golu- bew, Sitzungsberichte der Wiener Ahademie, Band Ivii., p. 555. t Recklinghausen, Vircliow's Archiv, Band xxviii., p. 185 ; Die Lymph- gefdsse und ihre heziehung zum Bindegewehe. Berlin, 1862, p. 22. X Loe. eit., p. 423. § Neumann, Reichert and Du Bois' Archiv, 1867, p. 31. Golubew, he. eit., p. 555. 418 THE BLOOD, BY ALEXANDER EOLLETT. After the continuous application of strong shocks the white corpuscles become destroyed, molecular movements occur in the swollen ceLs, or they are ultimately reduced to disks, and discharge their granules. A great number of these cells can be observed in an isolated condition if a drop of blood, recently obtaiued from a Newt or Frog, be brought upon a glass cover placed over a moist ceU, and the drop, whilst freely dependent, allowed to coagulate. It is soon observable, when the zone of serum extends beyond the limits of the clot, that in this zone, in consequence of an active migration from the coagulum, numerous amoeboid cells are present, and that they have accumulated on the surface of the coagulum. Sclarewsky* has discussed this phenomenon of the migration of the white blood corpuscles from the coagulum at consider- able length, as it may be observed in blood coagulated in capillary tubes. The above-mentioned simple experiment is far better adapted for the isolation of the cells for microscopical observation, and the investigations which can thus be made into the details of the migration of the individual cells renders it clear that the individual movement of the cells is the chief, if not the exclusive, cause of their emigration. The causes which must be admitted for the movements leading to this migration are stiU to be ascertained. Besides these migrating cells a few small colourless structures, presenting the appearance of free nuclei, occur in the blood of the Frog at all periods of the year ; lastly, we meet, in the blood of the frog, with the fusiform cells, first exactly described by Von Kecklinghausen,-f- which, however, vary in number with the period of the year, being especially abundant in spring. They possess a bright homogeneous cell substance, and a granular oval nucleus. Von Eecklinghausen, who has acquainted us with the remark- able fact that if the freshly drawn blood of the Frog be pre- served in moist air, after a short time an active process of cell formation takes place in it, which ultimately leads to the formation of red blood corpuscles, has also famished some * Pfliiger's Archw, 1868, p. 660. t Max Schultze's Archiv, Band ii., p. 137. DEVELOPMENT OF THE BLOOD COKPXJSCLES. 419 description of the intermediate forms that may be observed. Sclarewsky* and Golubewf have also been lately occupied with the investigation of the intermediate forms between the white and red blood corpuscles. From the statement of these authors it is to be concluded that the pale cells, which otherwise resemble red blood corpuscles, occurring in the blood of the Frog, and described by earlier observers, are to be regarded as amongst these intermediate forms. From the facts just mentioned, we are directly conducted to the difficult questions of the origin and regeneration of the organised constituents of the blood. Development of the Blood Coepuscles. The first coloured blood corpuscles in the fowl originate con- temporaneously with the formation of the first vessels in the germinal area,§ or in the vascular area and area opaca,\\ and they either detach themselves from the walls of the vascular spaces (AfanasieflT), hanging together in isolated groups (blood islands. Wolf and Pander), or they may originate, according to the view of His, ia the form of groups, from large masses of protoplasm in the walls of the vessels, and at a later period burst iato their Imnen. Soon after the coalescence of the vessels with the heart, these primordial blood corpuscles, which are lying ready to be borne onwards by the current, are floated off either separately or in groups (His). The primordial blood cells exhibit numerous processes and outgrowths (His). More- over, the coloured blood corpuscles circulating during the later periods of intra-oval life exhibit numerous forms attributable to fission, which have been described and depicted by Remak.lT ^ * Centralblatt fur die medicin. Wissenschaften, 1867, p. 865. t Loc. cit., p. 566. X Wharton Jones, Philosophical Transactions, 1846. Hensen, loc. cit., p. 263. § Afanasiefif, Sitzungsberichte der Wiener Akademie, Band liii., p. 560. II His, Untersuchungen uher die erste Anlage des Wirhelthierleibes. Leipzig, 1868, p. 95. 1[ Untersuchungen Uher die Entwickelung der Wirhelthiere, Berlin, 1855. p. 164 ; MuUer's Arehiv, 1858, p. 178. 420 THE BLOOD, BY ALEXANDER EOLLETT. In the tail of young tadpoles the newly formed vessels are found to be fiUed with peculiar, short, compressed, fusiform bodies, flattened on two of their sides, which present a very light yellow tint, and contain numerous yolk granules, but are otherwise homogeneous. In addition to these primary cells there appear, it would seem, concomitantly with the progressive development of the intestinal tract, a constantly increasing number of white cor- puscles. The number of the cells filled with yolk granules, on the other hand, gradually diminishes.. We soon after meet with the intermediate forms already described as existing in adult animals, together with coloured blood corpuscles of thp form ordinarily present in the blood of the Frog. In Mammals there may be observed in the blood of the embryo, at an early stage, nucleated coloured blood corpuscles in process of fission. At a later period these forms are less abundant, in accordance with the progressive development of the embryo and of the spleen in particular (KoUiker), and we meet with numerous white corpuscles in the blood of the liver, which become metamorphosed into coloured nucle- ated blood corpuscles. Up to a certain period of embryonic life only nucleated red blood corpuscles are present in the blood (KoUiker). The non-nucleated first appear at a later period, their relative number then undergoing a constant increase. According to KoUiker, non-nucleated corpuscles are not present in the blood of foetal sheep measuring three and a half inches in length ; in those of nine inches long they are but seldom found, whilst they constitute the majority in fcstuses that are thirteen inches in length. According to Robin,-f- in human embryoes measuring thirty millimeters, about one half of the total num- ber of blood corpuscles are destitute of nuclei ; a few nucleated corpuscles are stiU discoverable in embryoes of the fourth month, and even at stUl later periods. As has already been mentioned, the red blood corpuscles can * K.611iker, Zeitschrift fur rationelle Medkin, Band iv., p. 112 ; Gewe- belehre. Leipzig, 1867, p. 637. E. H. Weber and Kolliker, Zeitschrift fur rationelle Medicin, Band iv., p. 160. f Journal de la Physiologie. Pari?, 1858, p. 288. DEVELOPMENT OF THE BLOOD CORPUSCLES. 421 be regenerated in large numbers in the blood of adult animals, and this is accomplished at the expense of the white corpuscles, as was demonstrated in the case of the frog by V. Reckling- hausen, and still more recently again by Golubew. Fission of the red blood corpuscles ia adult animals has only been observed in a few rare instances. Whether the colourless corpuscles always undergo multipli- cation within the blood itself, and by what mode of cell genesis they multiply, are stiU open questions. It is certain that a large number of white corpuscles are added to the blood, not only during the period of development and of growth of the animal organism, but also throughout life, by the agency of the lymph current, the corpuscles of this, current originating in localized germ-producing organs, situated external to the blood (lymphatic glands). If the continual addition of such young ceUs had only as an object the supply of material for the regeneration of the red blood corpuscles, it would demonstrate that the latter are very unstable structures, structures in which rapid metamorphoses take place. Independently, however, of the circumstance that it is possible the white corpuscles themselves undergo disinte- gration in the blood, we know as a fact that they migrate from the interior of the vessels into the tissues, and that they par- ticipate in effecting certain plastic processes in these tissues ; on the other hand, up to the present time we are acquainted with only two regularly recurring processes, in one of which — menstruation — there certainly occurs, whilst in the other — the preparation of bile* — there very probably occurs the destruction of a large number of red blood corpuscles. Moreover, the observations on the disintegration of the red blood corpuscles may here be alluded to, that have been de- scribed as taking place in the formation of pigment in the spleen, in the blood-corpuscle-holding cells of the spleen (vide spleen), and of the meduUa of the bones ; but in regard to the period of the occurrence of which during life nothing is at present known. Kiilme, Physiologische Chemie, p. 88. 422 THE BLOOD, BY ALEXANDER ROLLETT. Forms that may be supposed to be transitional between the white and the red corpuscles contained ia the general mass of the blood of Mammals have however been described by Erb* under the term of " granular blood corpuscles," appearing in particular after artificial losses of blood. KoUikerf adverts to the fact that he long ago found similar forms in the blood of the young sucking mouse. The mode ia which they originate from the nucleated white corpuscles, and the stages of their conversion into the ordinary form of the red blood corpuscles, stiU require to be systematically followed out. In the blood of leucsemic patients nucleated red blood corpus- cles are frequently to be found presenting the appearance of the nucleated embryonic blood corpuscles of Mammals and of Man. Reference may here also be made to the statements advanced respecting the presence of red corpuscles in process of development in the pulp of the spleen. (See the chapter on the Spleen.) In the last place, attention has very recently been directed by NeumannJ to the nucleated red corpuscles constantly pre- sent in the medulla, and especially in the red medulla of bones (Man, Eabbit) ; and Bizzozero§ has corroborated the obser- vations of Neumann in the case of Man, the Eabbit, and the Mouse. Both inquirers describe a complete series of transitional forms existing between the white nucleated and the non- nucleated red blood corpuscles, and associate the marrow of the bones consequently with the development of the blood. Still farther communications on this function of the bony marrow have just been made by Hoyer.|| * Virch.ow's Archiv, Band xxxiv.,p. 138, Taf. iv. t Gewehelehre. X Centralblatt far die medicin. Wissenschaft. Jahr,, 1868, p. 689 ; and Archiv fiir Heilkunde, 1869, p. 640. § CentralhlaU, 1868, p. 881 ; and 1869, p. 149. y Centralblatt, 1869, pp. 244 and 257. CHAPTER XIV. THE SALIVAET GLANDS, By E. F. W. PFLiJGER. § 1. General Plan of Steuctuee. — The salivary glands represented by the parotid, submaxillary and sublingual glands, when examined with the naked eye, appear to be rounded or polygonal yeUowish-white masses, flattened by mutual pressure, and opening by hoUow peduncles into a common excretory duct. The gland, in each instance, consists of a tube branching frequently in a tree-like manner, and lined throughout by a layer of epithehal cells. The numerous ter- minal branches, named alveoli, are lined by large tesselated epithelium, whilst the other portions are invested either with columnar or small tesselated epithelium, and present a clavate form, being arranged like grapes on the principal ex- cretory duct. The salivary glands consequently belong to the group of acinous glands. The alveoli, however, with their secondary and tertiary processes, must not always be regarded as possessing the form of a berry, since they not seldom appear to be quite cylindrical, or only slightly contracted, where they spring from the trunk. The number of alveoli belonging to one of the smallest excretory ducts is so large that they lie tightly compressed and flattened in a polygonal manner against one another, leaving only a very small space for interstitial tissue. The Alveoli. — If a section of the tubes measuring 0030 millimeter in diameter be made, a canal and a wall may be distinguished. Even in glands hardened in alcohol it may easily be perceived that in the somewhat larger alveoli the 424 THE SALIVARY GLANDS, BY E. F. W. PFLUGEE. cavity is of very variable calibre, and may attain the mean diameter of a salivary cell, but may be also both extraordinarily fine (1 — 2 fi) and several in number in one and the same alveo- lus. The central canal gives off, as I have found, in conjunction with Mr. Anton Ewald, student in medicine, extremely fine tubuli (salivary capillaries), which penetrate between the sali- vary cells and also between the tunica propria and the epithe- lial cells ; so that these, like the cells of the liver, are surrounded by tubuli that can be iajegted with Prussian blue, and appear to proceed from one alveolus to another. The parietes of the tubes, composed in general of a single layer of cells, are invested externally by an extremely fine, and when fresh, completely structureless membrane, called the membrana propria. The existence of this may be demonstrated by macerating the fresh submaxillary gland with distilled water, when the membrane becomes raised from the epithelium, often to a considerable dis- tance, in the form of a hyaline vesicle. Eecently the presence of a membrana propria in glands generally has been called into question, and especially by Schliiter,* in the case of the salivary glands. In order to exhibit it I would recom- mend the pancreas of the rabbit to lie for four days ia iodized serum of a light sherry colour, and subsequently for two days in five cubic centimeters of diluted chromic acid, containing one- fiftieth per cent. By an action that is clearly of a digestive nature, the epithelial cells are in part detached, and obviously lie ia a wide hyaline sac which they by no means fiU. This appearance will incontestably demonstrate the existence of a membrana propria, forming a closed and continuous membrane. A question of a totally different nature is whether this membrane may be regarded as being composed of flat cells fused or coalesced together. According to Boll^f and Kolliker, it is composed of anastomosing connective-tissue cells that form a reticulum in which the alveolus lies as in a cavity of trellis or wicker-work. However plausible this view may appear on a priori grounds, there are facts which can scarcely * Disqisit. Mic. et Phys. de Gland. Salivar. Vratisl, 1865 ; Inaug. Diss. t Pranz Boll, Ueber den Bau der Thrdnendriise im Arcliiv f. Mikroskop. Anatomie, Band iv., 1868, p. 146. ALVEOLI OF THE SALIVARY GLANDS. 425 be brought into unison witL. it. Thus, (1) on examination of the membrana propria in fresh preparations, I have never been able to distinguish a nucleus, although I tested for it with dilute chromic acid, which causes the nuclei of the epithelial cells to come iuto prominent relief, and although the quadri- polar flattened cells regarded by Boll and KoUiker as consti- tuents of the membrana propria frequently contain a very brniiant large nucleus, which, according to Boll, may be round and very thick. (2) The vesicular elevation of the membrana propria from the salivary cells, consequent upon diffusion, pre- supposes a continuous membrane, which in fact comes into view, whilst it is impossible to see any reticulum. (3) The small quadripolar cells of the reticulum so rarely occur in rabbits that they are by no means sufficient to furnish an La vestment to all the alveoh. (4) The quadripolar cells are unquestionably connected with the epithelial cells by means of processes, and cannot consequently be regarded as connective tissue cells, a point, into the consideration of which it will be hereafter necessary to enter. The view entertained by Boll and KoUiker has not, consequently, at present received adequate confir- mation. In the next place, as regards the contents of the alveoli. These consist of cells fiUed with numerous granules, so that the gland substance appears black by transmitted light, ren- dering it impossible to distinguish either the cell contour lines or the nuclei. Such are the appearances presented by perfectly fresh preparations made from the gland whilst still warm and almost living, if moistened with the aqueous humour. In diluted chromic acid, containing one-fiftieth per cent., the greater part of the granules quickly dissolve, whilst the alveolus becomes transparent, and presents the most beautiful mosaic of cells. For this experiment the submaxillary glands of the rabbit are admirably adapted. Every cell is rendered polygonal by mutual compression, and presents sharply defined bright double contours. For the most part they only form a single layer, which lines the central canal of the gland, and is diffe- rentiated from this by a sharp contour line. In most animals the membrana propria is easily elevated. The cells adhere very strongly to one another, so that after being detached from the 426 THE SALIVARY GLANDS, BY E. F. W. PFLUGEB. membrana propria they still hang together in small groups. It is noteworthy in regard to the size of the epithelial cells, that as a general rule those contained in the same alveolus are of nearly the same size. But if we compare those belonging to different alveoli, they are found to be of very different dimensions. It is possible that the small epithelial cells may belong to alveoli of smaller diameter. There may, however, be found aU the transitional forms between the two, so that we are here dealing only with the same gland substance in different stages of development. This remark applies also to adult animals. If we now proceed to examine with more minuteness the salivary cells of the alveoli, I must in the first place observe that they appear to be invested by a membrane both towards the lumen of the tube and where they are ia apposition with each other. It is important to observe that the double con- tours of two salivary cells in contact with one another, are not always perfectly distinct, as though at some points there existed a stiU more intimate union between them. The proto- plasm of the salivary cells is tenacious, finely granular, and frequently striated. A ceU of this kind may give rise to the impression that its protoplasm is composed, of innumerable extremely fine fibrils. The average size of the salivary cells is 0'014 millimeter in diameter. The largest epithelia of this kind with which I am acquainted, I have found in certain alveoli of the salivary glands of the Ox. An extremely pale spherical nucleus is to be found in the in- terior of the protoplasm in all fresh specimens, and even in those that have been moistened with diluted acids. After the action of the acid has been long continued, it becomes highly refractUe, and presents a dark and sometimes double contour line. It then gradually shrinks, and applies itself as a flat disk to the wall of the cell, which frequently renders its recognition a matter of difficulty. The cell nucleus lies eccentrically to the salivary cell and alveolus, and immediately beneath the mem- brana propria. Its average size in the fresh condition, after being brought into view by dilute acids, amounts to 0'306 miUimeter. The most remarkable peculiarity presented by the nuclei of the cells, when fresh, is that they give off an extremely delicate fibre (fig. 75), which often penetrates that surface of the salivary cell ALVEOLI OF THE SALIVARY GLANDS. 427 which is in contact with the membrana propria. I have seen these caudate nuclei in perfectly fresh specimens. The sub- maxillary gland of the rabbit or pig is best adapted for their demonstration. The existence of the processes of the nuclei has been corroborated by G. Otto Weber, as weU as by Boll, whilst by KoUiker and Heidenhain, though undoubtedly in- correctly, it is denied. The latter,* it is remarkable, has him- self drawn a thick process, attached with such remarkable distinctness to the nucleus of an isolated salivary ceU, receiving as it leaves this a sheath of the cell membrane, that, uponthe Pig. 75. jrc-v v'^ GJv, •, • qR Fig. 75. Isolated. alveoli of the Rabbit, exhibiting processes. Magni- fied 480 diameters. ground of this positive ■ observation alone, I should draw the conclusion that the process is frequently not seen in connection with the cell, because it is destroyed in putting up the prepa- ration. The nuclear process appears to be hoUow, since it often discharges a large quantity of tenacious material, which: clearly proceeds from 'the nucleus. In consequence of the nuclear process leaving the cell, it gives the latter the appearance of being stalked, as has been seen by Schliiter, myself, Gianuzzd, Boll, and KoUiker. According to the descriptions given by Schliiter and myself, the ceU processes are often of great length, branch, coalesce (Schliiter), and support the alveolar cells Hke berries. There is never more than one nucleus in each salivary cell. * K. Heidenhain, Studien des physiologischen Instituts zu Breslau, 1858, Taf. iv., fig. 13 X. H H 428 THE SALIVARY GLANDS, BY E. F. W. PFLUGEE. Occasionally, indeed, there appear to be more, but in such cases there is always a doubt whether the line of division between two adjoining cells is perceptible. According to Heidenhain, there are two kinds of salivary cells, of which one contains mucus, but no albumen ; the other albumen, but no mucus. The former he denominates " mucous- cells,'' the latter "albuminous-cells." Both are glassy, trans- parent, and delicately striated ; the latter are, in addition, finely granular. Where mucous cells predominate, as in the sub- maxillary gland of the dog, cat, ox, and sheep, they may perhaps represent the young condition of the albuminous cells. In the rabbit, at least in the submaxillary gland,* no mucous cells are, according to this observer, to be found. Besides the points already described, there still remains to be noticed a structure, first mentioned by Gianuzzi, and to which he has applied the term semi-lunar body.-f- When sections are made of hardened salivary glands, there appears here and there a concavo-convex lenticular lamina, usually of very small thickness, which adheres intimately to the alveolus surrounding the salivary cells that lie in its cavity, and presents, on section, a semi-lunar form But in- asmuch as, on investigation of fresh glands, I was never able to see the semi-lunar body, and found that even in rab- bits it eluded my observation, I was inchned, since this structure is only demonstrable in those animals which have mucous cells, to regard the semi-lunar body as an artificial pro- duct, and as originating in the post-mortem formation of a mucous vesicle, compressing the cell protoplasm towards the wall. And it is remarkable that, according to the recent in- vestigations of Heidenhain, the submaxilltoy gland of the dog, when the mucus is withdrawn from it, no longer presents the demi-lune, but resembles the same gland in the rabbit.J The elimination of the mucus is efiected by exciting the gland to " See Heidetiliain, he. cit., p. 6. t S. Gianuzzi, "On the effects of acceleration of the blood currents on the secretion of Saliva ; " Ber. d. K. Sachs Oes. d. wiss. Math. Phys. Classe, Sitzung vom Nov. 27, 1865. J Heidenhain, he. 'eit., Taf. ii., fig. 5. STRUCTURE OF THE EXCRETORY DUCTS. 429 react through the nerves for many hours, whereby the mucus and the mucus-forming materials axe consumed. Later inquirers do not agree with me in my opinion regard- ing the demi-lune; nevertheless, they completely justify it, by each one giving a different interpretation of its nature. C Ludwig and Gianuzzi ascribed to it a laminated structure, and described the blackening it underwent from the action of perosmic acid, and the reddening with carmine. They were un- able to see nuclei distinctly. Boll and Kolliker described the " half-moon " as composed of connective tissue, which, firmly adherent to the alveolus, represents the cells constituting the reticulum already referred to. Heidenhain maintained that the demi-lune was formed by a layer of young epithelial cells, destined to supply the place of those salivary cells which were undergoing distintegration. I beHeve this view to be not an unreasonable one, for inasmuch as in the submaxillary gland of the dog the protoplasm of the mucous cells is scarcely, if at all, tinted with solutions of carmine, whilst the small nuclei lying at the periphery, as well as the numerous superimposed long cell processes running outward, are deeply stained, we have a suf&cient explanation of the occurrence of a complete mar- ginal zone in the alveolus. But since the term " demi-lune " can possess such difierent significations, it is better to avoid its use entirely. § 3. The Excretory Ducts. — In the interior of the gland, besides the structures already described, are tubes often of con- siderable size, and lined with cylindrical epithelium, to which the name of excretory ducts is applied. Close investigation shows that they must possess great functional importance. As evidence of this, I would first remark that if a dog be kiUed as rapidly as possible, and fine sections be prepared from the sub- maxillary gland, transparent drops may be seen exuding from the columnar cells lining the excretory ducts, and some of these having already become detached, lie in the lumen of the tube, appearing in the form of round, sharply defined, clear spherules. These unquestionably proceed from the cylindrical epithelium. But inasmuch as drops, presenting precisely the same appearances, are found in freshly secreted saliva, that has H H 2 430 THE SALIVARY GLANDS, BY E. F. W. PFLUGER. been caused to flow by irritation of the gland, it would appear highly probable that these cylindrical epithelial cells also belong to the secretory apparatus. Anatomical examination tells stiU more strongly in favour of the importance of these structures, since it then appears that the thickness of the wall of the duct, as we advanc3 towards its peripherical distribution, instead of, as might be expected, diminishing, undergoes material increase. The thickening of the wall is, in general, occasioned by the elongation of the cylindric al cells, which, however, never form more than a single layer. Besides this, the wider ducts exhibit more or less strongly marked outgrowths, lined with the same epithelium. If the ramifications of the ducts be traced in a peripherical direction, fine passages are at length met with, having a diameter of O'OIO millimeter, possessing the same epithelial lining as the larger ones, and, if I am not mistaken, terminating in blind extremities ; these are the secretory tubules — -that is, the capillaries of the salivary ducts having the same tenuity as the biliary capillaries, and leading to the alveoli. In a word, these excretory ducts, or salivary tubes, possess diverticula of various form. Not unfrequently they form loops or bend suddenly. If we now proceed to the study of the characters of the Fig. 76. Transverse section of a fresli salivary tube in diluted chromic acid of one-fiftieth per cent. Magnified 480 diameters. columnar epithelium, the cells will be found to possess an average diameter of 0004 millimeter, and to be of very variable length. The cylindrical epithelial cells are so well defined at their points of contact with each other, and on their free surfaces directed towards the interior of the tube, that they appear to possess a membranous wall; and these walls, towards STEUCTTJEE OF THE EXCRETORY DUCTS. 431 the lumen of the tube, are united into a highly refractile con- tinuous layer, the cells being here intimately adherent. They are, however, strongly adherent elsewhere — to so great an ex- tent, indeed, that when in the fresh condition it is impossible to isolate them. If the surface of the tube be examined, a beautiful mosaic of cells comes into view, the transverse section of the cells being for the most part completely filled by a well- defined nucleus. The ceU contents, when a freshly made transverse section of the salivary duct of a dog is examined, appears to be perfectly hyaline. This animal is well adapted for the purpose, because the toughness of the gland (submaxil- lary) permits fine sections to be made of it whilst still warm, after removal from the body. The most remarkable feature of these cylindrical epitheUal ceUs is presented by the surface turned from the canal, and which is immediately in contact with the membrana propria. From this spring a large number of ex- tremely fine varicose hairs, quite a bunch or pencil of such hairs proceeding from each cell. The surface of the tube composed of these cylindrical cells, always easily capable of de- tachment from the membrana propria, appears, on account of the equality in length of the several hairs, like a thick brush. These extraordinarily fine fibrils may be observed in any of the fluids in which the fresh gland can be properly examined. There may also be constantly seen, on focussing the surface of the salivary duct, fine points, which represent the optic trans- verse section of these varicose fibrils. For these reasons I am not disposed to regard these brushes as artificial products, which have originated by a splitting of the peripheric portion of the cells. Whilst in most cells the fibres commence immediately below the nucleus, it may be observed in some preparations, in which the cells have been isolated in iodized serum, that a few fibrils take origin from a higher point in the interior of the cell. In many of these cylinders the body of the cell very constantly presents the appearance of being delicately transversely striated. In the greater number of instances, however, that portion of the cell which is next to the canal remains transparent. From preparations made with iodized serum, it can be shown that some of these cylindrical cells, in consequence of the smallness 432 THE SALIVAEY GLANDS, BY E. F. W. PFLUGEE. or disappearance of their processes, and the assumption of a polygonal form, approximate closely to the flattened epithelium found in the alveoli. This similarity also extends to the cell contents and to the nucleus. Besides these extremely fine processes of the columnar ' cylinder cells, resembling the fibrils proceeding from the axis cylinder of a nerve, others of greater thickness, and of high refractive power, may be observed to be given off from their sides. The significance of all these processes will be hereafter discussed at greater length. Lastly, as regards the dimensions of the calibre of the tubes, it is found that they vary from a diameter of 0"030 millimeter or less to a size easily recognisable with the naked eye. The enlargement is essentially efiected by increased diameter of the lumen, and to a less extent by increased length of the columnar epithelium. I have met with such canals in the interior of the glands of the dog, the lumen of which had a diameter of O'l millimeter or more. Besides the salivary tubes, other tubes are found in the salivary glands, varying considerably in diameter, and lined by a small description of tesselated epithelium, that generally diminishes vidth the bore of the tube. These may be injected through the ordinary excretory ducts, as well as, through the salivary tubes, and ultimately form by their ramifications passages which have only a diameter of O'OO? millimeter or less, and are lined by a very small-celled pavement epithelium. These passages constitute without doubt, excretory ducts pro- ceeding from the alveoli, and form a stage in that developmental metamorphosis of the gland which exists even in the adult. Whether the salivary tubes, which are continuous vsdth these excretory ducts lined by pavement epithelium, communicate with the alveoli, and in what way this communication, if pre- sent, is efiected, demands further investigation. I know for a fact that a mosaic of salivary cells may lie in immediate juxta- position to columnar epithelium; but it is very rare for the canal of a salivary tube to be directly continuous with a canal which is lined with salivary cells. I am of opinion that the communication between the salivary tubes and the alveoli is efiected by means of very fine passages (salivary capillaries). DISTRIBUTION OF THE NERVES IN THE SALIVARY GLANDS. 433 The proper excretory ducts (Ductus Whartonianus, Stenordanus, etc.) are generally admitted to be lined by an epithelium, con- sisting of a single layer of short cyliadrical cells. Boll, how- ever, describes the epithelium as composed of tesselated cells. The wall is strengthened by fibres of connective tissue, with numerous elastic fibres and membranes, as weL. as by smooth muscular fibre ceUs. § 4. Distribution of Nerves in the Salivary Gland. — The nerve tissue of the salivary glands consists of ganglion cells and fibres. The latter are composed both of medullated, which constitute the greater number, and of pale nerves. Three difierent kinds of pale nerves may be distinguished. a. Fasciculi of extremely delicate transparent fibres, pre- senting the characters of axis cylinders, and invested with a sheath of connective tissue, containing nuclei. Were it re- quisite to adduce any proofs of the nervous nature of these fasciculi, it might be pointed out that these pale fibres form from time to time large fusiform varicosities, consisting of nerve medulla, characterised by its double dark contour. The pale fibre between two such varicosities differs in no respect from that lying in their immediate proximity. The above feature, however, renders it probable that these pale fibres conceal a thin layer of nerve medulla between the axis cylinder and the sheath. At the same time, neither a special investing sheath nor nuclei can be demonstrated around the individual primitive fibres, as indeed follows from what has been above stated, and these consequently, in the fresh condition, possess the appear- ance of naked axis cylinders. b. A second kind of pale nerve fibre found in the salivary glands I shall denominate gelatinous fibres. They consist ap- parently of bands of finely granular protoplasm, lying in a sheath of connective tissue, in which are nuclei, and presenting exactly the same appearance and behaviour as the protoplasm of the large ganglionic cells of the glands. Such gelatinous fibres may be observed to leave the ganglion cells, and hence are unquestionably of a nervous nature. They are probably composed of fasciculi of extremely fine varicose fibrillse, which, lying in close apposition, give the impression of a finely granular, 434 THE SALIVAEY GLANDS, BY E. F. W. PFLUGEE. somewhat striated protoplasm. These fibres present the same appearance as the so-called protoplasmic processes of the nerve cells of the cerebrospinal organs. . c. A third kind of pale fibre is composed of bundles of some- what tougher, more highly refractile, very fine (0"0005 milli- meter) fibrils, which likewise lie in a tube of connective tissue containing oval nuclei. These are liable to aU the objections that have been raised on various sides against the nervous nature of the fibres of Remak. Fig. 77. The preparation was taken from the submaxillary gland of the Ox, and was blackened with perosmic acid. Magnified 590 diameters. The medulkted fibres, which are present in extraordinary numbers in aU parts of the salivary glands, and of all sizes down to those of only 00015 millimeter in diameter, present DISTRIBUTION OF THE NERVES IN THE SALIVARY GLANDS. 435 a series of very remarkable peculiarities. In the first place . they have such delicate and pliable sheaths, that they some- times appear to be destitute of them. In accordance with this, varicosities form in the coarser trunks, as ia the fi.bres of the brain or spinal cord (see fig. 77), where, however, they become still larger, and form more easily than amongst these. On account of the extraordinary delicacy of the sheath these fibres tear with remarkable facility, and pour forth their contents in the form of myelin drops, which rapidly become stained of a blue-black colour by osmic add, like these nerves themselves. A second peculiarity of the medullated glandular nerves is exhibited in their mode of division, the division occurring so frequently as to have been seen by almost all observers. Accord- ing to my own observation, the number of divisions increases in. a most unusual manner towards the periphery, so that almost feathery medullated primitive fibres U« between the alveoli, and give off branches in all directions. If we now proceed to the consideration of the terminal organs of the nerve fibres, we must first discuss the relations these bear to the proper tissue of the gland. The salivary tubes, with which we shall best commence our description, are accom- panied by numerous bands of medullated nerve fibres of very various size. Many are in the most intimate relation with the tubes, as is shown in the accompanying figures. In one instance the specimen was fresh (fig. 78), in another it was stained by maceration in perosnaic acid (fig. 79). These nerves, as seen in figs. 78 and 79, perforate the mem- brana propria, and then break up into a number of fibres, which become finer by further subdivision, and wind around the out- side of the columnar epithelial cells, to form a sub-epithelial plexus, which demands still closer examination. The fibrils lying on the membrana propria are pale and soft, and give the impression of naked axis cylinders. But that they are accom- panied for some distance by the nerve medulla is recognised by the blackening of the osmic acid preparations around the termi- nation of the thicker primitive fibres. The axis cylinders run- ning on the membrana propria branch ultimately into the finest possible varicose fibrils, which have precisely the same characters Fig. 78. Fig. 79. Fig. 78. Fresh specimen. From the Ox, exhibiting a meduUated nerve which penetrates the membrana propria. The axis cylinder divides into branches upon the- membrana propria to form the sub-epithelial plexus. Magnified 590 diameters. Fig. 79. From the Ox, showing the termination of one of the thickest nerve fibres at a thick salivary tube blackened by perosmic acid. Magnified 590 diameters. Fig. 81. Fig. 80. V ;*■*{■ . A. Il Fig. 80. Showing an axis cylinder breaking up into fibrils which are continuous with the fibrils of the colximnar epithehmn. Magnified S90 diameters. Fig. 81. From the Ox, showing medullated and in part varicose nerves blackened by perosmic acid, which branch in the sub-epithelial plexus, and one of which (re), can be distinctly traced into the processes of the columnar epithelial cells. The preparation exhibits a marginal portion of the surface of a salivary tube. Magnified 800 diameters. DISTRIBUTION OF THE NERVES IN THE SALIVARY GLANDS. 437 as the fibrils which emerge and join them from the columnar epithehal cells. It is frequently observable that the last rami- fications of the axis cylinder are continuous with these fibrils ; and that the columnar cells thus represent the continuations of the fitner and the fitnest meduUated nerves with the sub-epithelial plexus is frequently capable of direct proof, as appears from an examination of fig. 80. We may even succeed, though rarely (fig. 82), in effecting the complete isolation of all parts, and in thus showing the continuity of the medullated nerves with the processes of the columnar cells. It may thus be rendered evident that these fine processes are in direct continuity with the axis cylinder, from which they do not in any respect differ. At the same time it may be remarked that the axis cylinder of the Fig. 82. Fig. 82. From the Rabbit, exbibiting a medullated nerve, becoming continuous with an axis cylinder which passes directly into the pro- cess of a cylinder cell, and directly opens into the columnar cell. Magnified 590 diameters. afferent nerves appears to be thicker than the fibrillar processes of the columnar cells, which must consequently be regarded as continuations of the fibrillse of the axis cylinder. After the nerve has penetrated the membrana propria of the salivary tube, the axis cylinder either immediately terminates, or does so after it has first run for some distance Upon the membrana propria ; in 438 THE, SALIVARY GLANDS, BY E. F. W. PFLUGER. the latter case it runs between this and the fibrillar processes of the columnar epithelial cells. When we consider the incredibly large supply of nervous fibrils that lies beneath the membrana propria, the question of the object of this abundance naturally suggests itself. After studying with greater exactitude the laws of the growth of glandular epithelium, we shall find that a completely satisfac- tory solution of this question may be attained. I shall treat of this point, however, at a later period. I would only mention here that numerous young salivary cells develop from every columnar ceU, with its fibrillar processes, and that each of these must again have its proper nerves. This is true also in the case of the adult animal. From the almost imperceptibly fine fibrils of the columnar cells the fibres of the epithelium cells of the alveoli proceed, which we shall now subject to a carefal consideration. Two kinds of nerve termination are to be distinguished in the alveoH : — I. The most important is that of the meduUated primitive Fig. 83. Fig. 83. From the Ox. An alveolus with the terminations of medullated nerves which have been blackened by perosmic acid. Magnified 590 diameters. fibres. These branch very frequently between the alveoli, apply themselves to the membrana propria, and usually give ofi" at the point where they penetrate it several branches, which nm for DISTRIBUTION OF THE NERVES IN THE SALIVARY GLANDS. 439 some distance on its outer surface to the nearest epithelial ceUs, in order to penetrate over these into the alveolus (fig. 83). The nerve becomes blackened by perosmic acid up to the point where it perforates the membrana propria; at this point the Pig. 8i. Fig. 84. Prom the Rabbit. Medullated fibre blackened by perosmic acid. Magnified 500 diameters. medulla appears to cease (figs 84 and 87). That the membrana propria is perforated is shown in the most striking manner by the circumstance that the continuity of the meduUated and Pig. 85. Fig. 85. From the Rabbit, after maceration ia iodised sermn, stow- ing the termination of a medullated nerve in an alveolus. From the submaxillary gland. Magnified 590 diameters. frequently very thick primitive fibres with the salivary cells may often be easily demonstrated. I have seen this occur in a great variety of modes, and in the clearest manner in the 440 THE SALIVAEY GLANDS, BY E. E. W. PFLUGEE. salivary glands of the ox and rabbit (submaxillary and parotid glands) (figs. 87 and 88). Pig. 86, Fig. 86. Termination of a branching fine medullated fibre in the salivary cells of an alveolus. From the submaxillary gland of the Ox, the nerve blackened by perosmic acid. Magnified 490 diameters. In completely isolated preparations (Figs. 86 and 88, A b) it may be observed that the white substance of Schwann ceases V.li: Pig. 87. ','.* Fig. 87. Termination of a medullated fibre of average thickness in the large salivary cells of an alveolus. Prom the submaxillary gland of the Ox. The nerve has been blackened by perosmic acid. Magnified 500 diameters. as though suddenly cut off at a short distance from the salivary cells, and that the nerve appears as if adherent to the soft protoplasm of the epithelial cell. DISTRIBUTION OF THE NERVES IN THE SALIVARY GLANDS. 441 If the point of attachment be examined with very high magnifying powers, it will be seen that immeasurably fine fibrils proceed from the nerve, which pass directly and without interruption into the fibrils of the protoplasm of the salivary cells. This appearance is most beautifully presented if the meduUated fibre be deprived of its medulla by pressure. There then remains a pale fibre composed of extraordinarily fine Fi-. Fig. 88. Termination of medullated fibres treated with perosmic acid in isolated salivary cells, a, thick branched fibres distributed to large salivary cells ; B, fine nerves distributed to smaller salivary cells. Fi'om the submaxillary gland of the Rabbit. Magnified 590 diameters. fibrils, which are directly continuous with the fibrillated sub- stance of the epithelial cells. This character is especiaUjr important, because it constitutes a clear evidence of the abso- lute continuity and fusion of the axis cylinder and epithelial cell. As I have not seen any fibres blackened by perosmic acid upon the membrana propria, though both the blacken- ing and the medulla may constantly be seen extending to epithelial' cells in well-isolated preparations, I must conclude that ordinarily the mode of termination in the alveoli is that the nerve perforates the membrana propria, and enters directly into the superjacent salivary cells. The^ nerve me- dulla consequently terminates at the cell. That point of the salivary cell where the nerve enters is marked by a slight in- 442 THE SALIVARY GLANDS, BY E. F. W. PFLTJGEE. crease in the transparency of the protoplasm, and this portion occupies a segment made up of from one-fourth to one-third of the spherical volume of the cell (fig. 88). I have not seen the nucleus in this segment, but in the remaining more darkly- granular portion. The nerve tears across with remarkable facility at the point of its insertion, which appears to be ex- tremely soft, and hence leaves no trace of the point at which it was attached to the ceU. This may be reasonably attributed to the fact that the connection is only effected by means of the axis cylinder, which, whilst it is continuous with the semi- fluid protoplasm of the cell, undergoes no sudden interrup- tion at this point. It is on this account impossible, without appropriate, though necessarily very slight, hardening with reagents, to bring into view the isolated fresh salivary cells, with their associated nerve fibres. It is not surprising that the meduUated primitive fibres are sometimes very fine, some- times very thick, when we know that the epithelial cells gradually increase to substantial structures, from minute no- dules on extremely fine axis-cylinder fibrils. With their increase the size of the nerve also augments ; it acquires a medulla, and becomes progressively thicker. It is this circum- stance in part, and partly the fact already mentioned, that, on the application of pressure or other form of mechanical vio- lence, the medulla separates from the dark-edged primitive fibres, whilst the axis cylinder breaks up into fibrils pene- trating the protoplasm of the salivary cells, that forbids us any longer to regard the latter mode of nerve termination as peculiar. Whether this holds for all pale nerve terminations found in the alveoli appears to me, from the stand-point obtained in the physiological experiment demonstrating that two kinds of nerves exert an action upon the gland, to be doubtfal. There may in particular be found well-preserved long tubes, ap- parently composed of connective tissue, the wall beset with nuclei, continuous with the membrana propria of the aveoH, and containing one or more fine fibrils, that are lost in the gland vesicles. They rarely occur in comparison with the meduUated fibres, but are more stable on account of their sheath, so that they alone can be seen in some of the modes BISTEIBUTION OF THE NERVES IN THE SALIVARY GLANDS. 443 of preparation, on account of the fluidity of the meduUated fihres. II. On the mode of Nerve Termination effected by Multipolar Cells. — I have elsewhere described small pale cells (fig. 89) possessing numerous processes adherent to the alveoli, and for the most part smaller than the salivary cells. I re- gard these as nerve cells, and consider them as entering into communication, not only with the salivary cells, but also with the nerve fibres. All later inquirers (KoUiker, Boll, Heidenhaui) have with remarkable unanimity and with great precision described these multipolar cells as indifferent structures forming a reticulum,. Fig. 89. Fig. 89. Multipolar nerve cell. From the Rabbit. Magnified 80 diameters. and properly to be regarded as belonging to the connective tissue. According to KoUiker and BoU, these cells constitute the membrana propria, which I have already described. The above-named inquirers silently assume that the opinion I hold of the direct continuity of these multipolar cells with the glandular epithelium by means of thick and anastomosing fibres is erroneous. Boll was unable to discover these com- munications, but refers to apparent connections, and is of opinion that the multipolar cells, with their intercommunica- l I 444 THE SALIVARY GLANDS, BY E. F. W. PFLUGEB. tionSj in some instances closely resemble salivary cells, so that the possibility of a false impression is conceivable. But as I am satisfied that I have seen the connection of the multipolar cells with salivary cells, I hold it to be my duty, especially on account of the importance of all that depends upon it, to prove this point with the most rigorous scientific accu- racy. As I have more recently on many occasions observed such connection, I may remark that we are here engaged with the examination of completely isolatable cells, which communicate with one another by means of a thick anastomosis, and the two points of attachment of which may be seen in perfect profile (fig. 90, A B c). One of these cells is pale, striated, with many radiating processes, and with the body almost entirely filled with the nucleus (fig. 90, b). The other is round or slightly poly- gonal, with abundant granular protoplasm and a relatively small nucleus. Fig. 90. Fig. 90, A, B. Multipolar cells in connection -with salivary cells. Magnified, A, 480, B, 590 diameters. c. Peculiar cells with, round tHck processes, and containing refrac- tile fat particles. Magnified 590 diameters. As the observations were made upon rabbits, the fully deve- loped salivary cells of which have so stereotyped an appear- ance, I regard it as absolutely impossible that I should have mistaken any other cell for a salivary cell. Moreover, I have actually seen the connection whilst the salivary cells in question were stiU adherent to others, and forming part of the characteristic mosaic (fig. 90, A and c). It follows therefore that the multipolar cells cannot be con- nective tissue cells, as maintained by KoUiker, Heidenhain, and BoU ; for the true salivary cell is an enlargement of a medul- DISTRIBUTION OF THE NERVES IN THE SALIVARY GLANDS. 445 lated nerve. It cannot, consequently, give off any process which is a connective tissue iibre, or which is continuous with connective tissue cells; for between animal tissue and con- nective tissue substance there cannot be any continuity of substance. Inasmuch as I am now satisfied that the multipolar cells are continuous through their processes with nerve fibres (fig. 89), it follows that they must either be modified epithelial cells or ganglion cells. Their continuity with nerve fibres does not decide the question, since the salivary ceUs also present this character under the most various modifications ia common with true nerve cells. There consequently remain, as means for determining the point, only analogy and anatomical structure. To whatever degree the multipolar cells may differ amongst themselves in their size and form, and ia the characters of the nucleus and of the protoplasm, as indeed was observed by Boll, they neverthe- less resemble nerve cells more closely than epithelium, as is shown by the fact that small ganglion cells have been admitted to occur amongst them by various observers, as by Henle and Krause. In the next place, in regard to the great variation that they present, it is important to remember that if the alveoli, as we have decisively proved, undergo continuous regeneration and disintegration, the nervous tissue must be subject to similar metamorphoses. The are broad at the end, directed to- wards the dentine, but as the processes pass on they gradually diminish to form dentinal fibres. The odontoblasts are inti- mately connected with each other by means of the fine short teeth which the lateral processes of all dentinal cells form. The short pulp process usually springs from ihe cell with a moderately broad base, and is constantly connected with one of the cells lying immediately beneath the membrana eboris, which last are usually somewhat larger and more darkly granular than those more deeply seated.. We are indebted to Boll (59) for first furnishing us ■with precise information in regard to the nerves of the teeth. He observed in the incisor teeth of the Rodents, after the pulp had been macerated for an hour in a solution of chromic acid containing 32 per cent., a very large number of non-medullated extremely fine nerve fibres, which exhibited a sUky lustre, and were gradually but directly con- tinuous with the meduUated fibres. If the observer is so fortunate as to preserve the membrana eboris in its natural connection with the pulp, which Boll sometimes accomplished by introducing a fine knife between the pulp and the dentine, after treatment with chromic acid, the extraordinary richness of these non-medullated fibres in the peri- pheric portions of the pulp becomes apparent; Preparations that have been teased out with needles show that the nerve fibres pass outwards between the odontoblasts in considerable numbers, and accompany the dentinal processes to which they are subjacent in the form of fine hairs. Boll was, however, unable to see the actual penetration of the nerve fibres into the dentinal tubuli, although their length and the direction they pursued rendered this probable. The gvrni is distinguished from the other portions of the oral cavity by its vascularity and its large papiUse, which L L 2 478 STRUCTUEE AND DEVELOPMENT OF TEETH, W. WALDEYEE. again, like the papilte fungiformes, are beset with small pro- jections (Kolliker, 58). No glands appear to be present in them. Here and there small round heaps of pavement epi- thelium, frequently presenting the appearance of concentric lamellse of horn, are met with, either imbedded ia the sub- stance of the gum, or occupying fossae on its surface (Serres, 8 ; Kolliker, 58). The periosteum of the alveoli, which fulfils the office of periosteum, not only to the internal surface of the alveolus, but also to the cement, termed the Periodontiunj, is characterised by its softness. It contains but few elastic fibres, though I, with Kolliker (58), have found its nervous supply abundant. Dentinal structures occur in large numbers, and present a great variety Of form, amongst the Invertebrata. The teeth of the mastica- tory -apparatus of the Echraus most closely resemble those of the Vertebrata. H. Meyer* states that they are composed of enamel fibres; this, however, is not quite accurate. The teeth of the EchinidsB are long, slender, slightly curved plates, which present a well-marked longitudinal ridge on their inner surface. The greater part of each tooth is formed by a radial lamina attached vertically to the surface of this ridge or keel. The radial lamina is moderately soft, and can be easily broken up into thin leaflets, which are again composed of elongated prisms somewhat curved at their extremities. The peri- pheric plate is considerably harder, and its prisms are much smaller and softer than those of the keel. Between these prisms, which in part run parallel to one another, and partly decussate ia each plate, lie thin lustrous calcareous plates which often exhibit an extremely delica,te plexus of fine anastomosing canaliculi. When treated with hydrochloric acid, the prisms dissolve with the disengagement of a large quantity of gas, and leave no organic residue. They appear, therefore, to be entirely composed of carbonate of lime. In their degree of hardness, in their size and chemical characters, they con- sequently , differ remarkably from true enamel, and they do not possess the regular four or six-sided form, characteristic of the fibres of the latter substance. In MoUusks^ Worms, and Arthropods the oral or gastric teeth, are composed of .chitine, which is sometimes impregnated ■with lime or silica. It may he said generally that the teeth amongst the Invertebrata are to be regarded as pure mineral * MiiUer's Archiv, 1849, p. 191, et seq. DEVELOPMENT OF THE TEETH. 479 or epithelial structures (and are therefore analogous to the enamel), whilst in the lower Vertehrata they are chiefly composed of peculiarly modified and ossified connective tissue ; in the higher classes of animals, which present the most complicated form of dentinal struc- tures, an epithelial structure (the enamel) is again included in their structure. Development of the Teeth. — The genesis of the teeth in the human embryo commences, according to the observations of Robin and Magitot (46), at about the fiftieth to the sixty- fifth day. The margins of the jaw at the beginning of the third month form a slightly raised rounded ridge, the " 'maxil- lary ridge,'' which is most prominent in the lower jaw, and consists of a thickening of the embryonic connective tissue and epithelium of the mucous membrane of the mouth. This epithelium, with its vascular substratum resembling mucous tissue, constitutes therefore the matrix of the several constitu- ents of the teeth, the epithelium forming the enamel, and the mucoids tissue the dentine and cement. The " erlamel organ " is formed by a peculiar structure re- sulting from the growth and multiplication of the epithelial cells, which dip down into the mucous tissue. In a direction con- trary to this there is then developed a papilliform process of the mucous tissue, the origin of the pulp and of the dentine. The two parts together constitute- the rudiment of the tooth. When at a later period the connection of the enamel organ with the oral epithelium is interrupted, the rudiment of the tooth is enclosed in the alveolar border of the jaw on all sides, as in a capsule, by the sub-epithelial connective tissue. That portion of the coimective tissue which immediately in- vests the rudiment of the tooth is usually termed the " dental sac" and at a later period forms the cement* Enamel Organ and Enamel. — Near the end of the second month of foetal life the margin of the jaw exhibits a slight * KoUiker (58) calls the entire rudiment of the tooth enamel organ, papilla dentis, and the connective tissue investment of both, " dental sac- culus," and distinguishes the latter again as "proper dental sacculus,'' a nomenclature which has little to recommend it. 480 STETJCTUEE AND DEVELOPMENT OF TEETH, W. WALDETEB. longitudinal furro-w, with rounded borders, termed the " dental groove." The epithelium of the oral cavity completely covers it, so that it is scarcely perceptible when the surface alone is examined. The two projectiag borders of the groove are termed the " dental ridges " (Marcusen, 31), or " lips of the dental groove" (Dursy, 67). Soon, from the bottom of the dental groove, a narrow process of the oral epithelium dips into the subjacent mucous tissue, presenting on section the form of a short tubular gland, but in point of fact constituting an epithelial fold along the whole length of the jaw — the Fig. 100. *? i^ F%. 100. Upper jaw of a foetal sheep three centimeters ia length. Vertical section, magnified 50 diameters, showing the enamel germ, with the semi-lunar rudiment of the dentine germ and dental sac in transverse section. 1. Dentinal groove. 2. Palatal process. e,n(Mnel germ of Kolliker (47). The primary dental groove, especially of the upper jaw, increases in size, and becomes entirely filled with oral epithelium. The epithelium also becomes extraordinarily increased in thickness on the two dental ridges, and in the deep groove between the lips and the margin of the jaw, especially in Ruminants (KoUiker, 47). At some points the enamel germ appears to descend perpen- dicularly from the base of the furrow into the subjacent tissue, but in other regions, especially in the neighbourhood of the incisors, it extends obliquely towards the median line, and consequently forms a larger or smaller angle with the dental groove. DEVELOPMENT OF THE TEETH. 481 The above account differs from that which I formerly gave, in recognising a dental groove in the vicinity of the subsequently appearing dental rudiment, and in not regarding this groove as a secondary formation caused by an hypertrophy of the epithelium. Kolliker (58) also describes a groove of this nature, and figures it with the enamel germ proceeding from its deepest part.* The state- ments of Marcusen (31) on the development of the teeth, which I -J. Pig. 101. Vertical section of the inferior maxilla of a human foetus, measuring eleven centimeters from the vertex to the coccyx. Magnified 25 diameters. 1. Dental groove. 2. Remains of the enamel germ. 3. Enamel organ presenting externally epithelium, as also where it forms the enamel germ of the papillae of the dental sacoulus. 4. Secon- dary enamel germ ; rudiment of the permanent tooth. 5. Dental germ. 6. Lower jaw. 7. Meckel's cartilage. have already indicated as being the first that were accurate (49), require still to be followed out in further detail. Dursy (67) has very recently entered minutely into the description of the first occurrence of the dental groove, and has accompanied his statements with nu- merous illustrations. He considers it to be formed by an inequality in the growth of the margin of the jaw. He regards the enamel germ as resulting from the progressive development of the dental furrow and its epithelium, which, however, does not penetrate more deeply * Loc. A, fig. 260. 482 STRUCTURE AND DEVELOPMENT OF TEETH. W. WALDETER. into the margin of the jaw, but is rendered deeper by the increased elevation of the margins. I believe, however, that we must draw a distinction between the small primary dental groove with its epithe- lium and the true enamel germ. The latter is a secondary formation which, although proceeding from the epithelium of the primary dental groove, is yet distinguished from this, both by its sudden attenuation, by the difference in its direction, especially in the case of the incisor teeth, and by its microscopic characters. The epithelium of the den- tal groove, with the exception of the deepest layer, consists of large spherical or flattened transparent cells. The cells of the deepest layer are columnar, and are immediately continuous with the similarly formed cells situated at the periphery of the enamel germ, whilst the cells at the centre of the enamel germ are dark, granular, and round. Even at a later period we must still distinguish between the con tinuously enlarging dental groove and the enamel germ (see fig. 101.) Whether the enamel germ penetrates by its own growth into the blastema of the jaw, as I have described (49), or becomes more deeply imbedded in consequence of an increase in height of the dental walls, it will perhaps be difficult to decide. The small primary dental groove superjacent to this, which is not always present, may however be identified with the dental groove of Arnold (12) and the primitive dental groove of Goodsir. Both overlooked the enamel germ, and imagined the teeth to be developed from isolated papDlse in their dental groove. A series of remarkable changes soon take place in the more deeply seated portions .of the enamel germ, especially at the several circumscribed spots corresponding to the later developed milk teeth. The spheroidal cells forming the central part of the enamel germ begin to increase with rapidity, so that the germ becomes conically elongated, assuming the form of a club, "which is continuous by means of a relatively narrow neck with the epithelial cone of the dental groove. Coincidently the dentine germ increases in a contrary direction, forming a club-shaped mass, and projects upwards into its base, so that the enamel germ comes to invest the dental papilla like a cap. The connection between the several portions of the enamel germ then become dissolved, probably in consequence of an increase of the connective tissue of the dental ridges, so that now a special division of the enamel germ, which since the time of Purkynd (14) has been called the enamel organ, cor- DEVELOPMENT OF THE TEETH. 483 res ponds to eachof the dentinal germs. Each enamel organ is thus composed of a strongly developed portion that surmounts the dentine germ like a cap, and a narrow cord of cells extend- ing to the epithelium of the mouth — the neck of the enamel organ, which represents the remains of the primitive enamel germ (see fig. 101). The neck of the enamel organ disappears at a later period, whilst the two dental ridges coalesce with one another above. The rudiments of the teeth are thus sur- rounded on all sides by the loose connective tissue of the wall of the jaw. Histological changes of a very remarkable character occur in the enamel organ, coincidently with the morphological changes that have been described above. The marginal cylindrical cells, where they are in immediate contact with the dentine, appearing as an epithelium covering it, become remarkably elon- gated, and form very regular six-sided prismatic bodies — in fact, the most beautiful and regular columnar epithelium found in any part of the animal body (see figs. 102 and 103). The sides of the cells present a distinct limiting membrane; but the protoplasm has no investment at the two extremities. At the base of the dentine germ, where it becomes continuous with the lateral walls of the enamel club, the cells become pro- gressively shorter, until at last they assume a cubical form, and thus coat the portion of the internal surface of the enamel organ, or rather of the dental sacculus, which is turned away from the dentine germ. In accordance with Kolliker (47), we desig- nate the elongated cylinder cells as the internal or enamel epithelium, and the remaining marginal cells as the external epithelium of the enamel organ. As far as the external epithe- lium reaches, the adjoining connective tissue exhibits tolerably regularly formed conical and vascular papiUse, which project into the epitheUum, and correspond to the papillse found in the remaining portions of the oral mucous membrane (see %. 101.) The complete continuity and concatenation of all these structures is most satisfactorily proved by a recent statement made by Dursy (67), which I am able to corroborate, that especially towards the neck of the enamel germ, similar papillary structures are present, which here pass without interruption into the papillse of the gum. It is only 484 STEXJCTURE AND DEVELOPMENT OF TEETH, W. WALDEYEE. requisite to remark that they are much stronger, and developed at an earlier period, in the enamel organ than in the gum. The small roimd cells of the enamel organ between the external and internal epithelium undergo at the same time a peculiar transformation. They acquire a stellate form, and Unite with each other by their processes in the same manner as the cells of ordinary mucous tissue, which this part of the enamel organ so strikingly resembles that up to the time of Huxley (37) and Kolliker (47) they were always regarded as gelatinous connective tissue. The cells, however, lying in Fig. 102. Fig. 102. Longitudinal section of a milk tooth from the foetal sheep, carried through the margin of the dentine pulp and adjoining portion of the enamel organ. Magnified 200 diameters. 1. Dental sacculus. 2. External epithelium and stratum intermediiun here united to the internal epithelium or enamel cells 3. after the disappearance of the enamel pulp. 4. Young layer of enamel detached from the enamel cells. 5. Dentiue. 6. Odontoblasts. 7. Part of the dentine pulp. immediate contact with the epithelium (stratum intermedium of Hannover, 39) retain their original form, and from these a continuous development of enamel cells, as well as of gelatinous epithelial tissue, appears to proceed. The enamel cells may be frequently seen to be in connection at their lower extremities with the cells of the stratum intermedium, so that a multipli- cation of the enamel cells from the cells of this stratum in DEVELOPMENT OF THE TEETH. 485 the direction of their length may be admitted to occur (see fig. 103, 2). The jelly of the enamel organ (enamel pulp) possesses only a transitory and mechanical significance, occupy- ing the space subsequently required by the growing tooth. Nevertheless, before the formation of the enamel is completed, both the epithelial and gelatinous tissue and the stratum inter- medium undergo atrophy. The outer and inner epitheUa consequently again come into close apposition (see fig. 102) ; the latter is entirely used up in the formation of the enamel, and iu teeth examined just at the period of eruption we can only detach from the enamel a membrane composed of one or more layers of very flat epithelial ceUs, which clearly represent the outer epithelium with a larger or smaller amount of the stratum intermedium. As soon as the eruption of the tooth is effected, these cells become homy, and form the cuticula dentis. This conversion so remarkable in a histological poiut of view, of a portion of the epithelial cells of the enamel organ into stellate gelatinous tissue, finds an analogy, according to KoUiker (58), only in the cells of the external investment of the egg of the Perch. I have myself occasionally met with a similar metamorphosis of the epithelial cells in the Graffian follicles, but never occurring in so regular a manner. Renewed investigations, notwithstanding the objections raised by KoUiker (58) and KoUmann (67 a), compel me to adhere to the view I have above expressed of the nature of the cuticula dentis. Its tenuity cannot be considered as an objection, especially if, as I am now inclined to believe with Hertz (52), the external epithehum is alone to be regarded as the basis of the cuticula. The formation of the enamel is purely and exclusively refer- rible to the enamel epithelium, the enamel prisms resulting from the direct calcification of the long cylindrical cells. The intimate connection of enamel cells with small portions of the enamel prisms, which remain adherent to the cells in the form of processes, is in the first place in favour of this view (see fig. 103, 3). Again, the limit to which the calcification extends is not boimded by a straight line, but is very irregular, a circumstance that is opposed to the idea of a calcification of any secretion formed by the enamel cells. If young enamel be treated with diluted acids, the enamel prisms sweU up to some extent, and 486 STRUCTURE AND DEVELOPMENT OF TEETH, W. WALDEYER. reassume the form of the original columnar cells, and the dis- tinct membranous investment of the longer sides «omes iato view. The disappearance of the nucleus in such calcifications and metamorphoses of cells is so common, that there is nothing remarkable in its absence in those of the enamel. Fig. 103. Fig. 103. Highly magnified. 1. Various forms of odontoblasts. 2. Three enamel cells, with, a few cells of the stratum intermedium at- tached ; two enamel cells exhibit Tomes' processes. 3. An enamel cell, with a small portion of enamel. 4. Fragments of enamel fibres from young and still soft enamel (acicula). 5. Old enamel fibres with transverse strise. KoUiker (58) has recently so far inclined towards the view pro- pounded above, that he appears inclined to explain the formation of enamel in the same sense as Schwann (23), who held that the enamel cells continued to grow at their free extremities, and that the new growth underwent continuous calcification, Hertz (52) and myself (49) transfer the growth of the cells to the nucleated extremity directed towards the stratum intermedium, which is more in accordance with the facts observed, and with the general mode of increase of cells ; for the nucleus, with the immediately surrounding protoplasm, is DEVELOPMENT OF THE TEETH. 487 always that of part of the cell from ■which the phenomena of life radiate with the greatest activity, whilst the peripheric portions con- stantly, on the other hand, have a tendency to death or to transforma- tion into intercellular substance, etc. In favour of the same view also is the remarkable circumstance, that in all elongated columnar cells, with one nucleus in their interior, the latter is constantly found to occupy the attached and never the free extremity. From the foregoing remarks, then, it appears that enamel is to be regarded as the petrified dental epithelium, and that its essential part corresponds to the mucous layer of the oral epithelium, whilst the cuticle, though perhaps by a secondary metamorphosis, is associated with the horny structures. The dehcate membrane described by Huxley (37), in his account of the structure of the teeth, which can be raised with tolerable facility from the surface of the developing enamel after it has been sub- jected to the action of hydrochloric acid, is the youngest layer of the enamel as yet but slightly impregnated with mineral constituents (Tomes, 29). The foraminated appearance of the membrane is in favour of this view. The enamel cells first undergo petrifaction in their investing (external) zone, the axial portion of the protoplasm retaining its softness for a time, and in isolated cells forming a kind of process (Tomes' Process of the Enamel Cells (49), (see fig. 103, No. 2). As a consequence of this the youngest layer of enamel must necessarily exhibit a number of foramina, corresponding to the " Processes " of Tomes. Huxley correctly identifies this membrane with the membrana prceformativa of Easchkow, but erroneously con- siders the cuticula dentis to proceed from it. Easchkow described a thin homogeneous membrane investing the dentine germ, which was regarded by Todd and Bowman, and by Kolhker, as a basement membrane of the dental papilla covering the surface invested by epithelium (enamel cells). Huxley (37) and EoUiker also describe a basement membrane between the mucous membrane and the external epithelium. Such a membrane is, however, only discoverable when the enamel cells have attained a certain stage of development, and have already begun to be calcified. If this membrane, which ex- hibits the characteristic foramina of Huxley's membrane, be raised by the action of hydrochloric acid, no other homogeneous basement membrane can be demonstrated on the dentine germ. The papillary projections of the dental sacculus directed towards 488 STRUCTURE AND DEVELOPMENT OF TEETH, W. WALDEYEE. the enamel organ afford an explanation of many of the peculiarities in the course of the enamel fibres which have been mentioned above. In the first place, the fine transverse striae which run in a circular direction around the external surface of the enamel are directly refer- rible to the papUlse. For if, towards the end of the formation of the enamel, the enamel pulp disappears, and the external and internal epithelial cells again come into contact with each other, the papillary processes make their mark on the enamel membrane, and naturally also on the product of its calcification, the enamel. The transverse ele- vations of the latter are thus of precisely the same nature as the well- known fine striae of the nails. Moreover, since the greater part of the enamel is formed before the enamel jelly has disappeared, and therefore at a time when the enamel membrane already exhibits the impressions of the papillae, we may reasonably refer many peculiarities in the course of the enamel prisms, especially their decussations, spiral course, and undulations, as well as their optical characteristics, to the same cause. Dentine and Cement. — As Dursy (67) maintained, the first germ of the dentine appears in the dental sacculus as a dark semi-lunar area at the bottom of the dental groove — that is to say, of the enamel germ — coetaneously and continu- ously with which it is developed along each half of the jaw (see fig. 100). At certain points corresponding to the position of the subsequent teeth the young structure develops in the form of papillse projecting against the enamel germ, whilst the remainder atrophies. The two horns of the semi-lunar mass (seen in section) extend, from the base of the dental papilla, some distance upwards, and embrace the dentine germ and the enamel organ. This constitutes the first trace of the dental sacculws, which at this period consists of tissue somewhat richer in cells and vessels than the mucous tissue of the dental groove. The dental sacculi are only well defined at the earlier periods of the formation of the tooth. AVben the process of development is more advanced, it is impossible any longer to distinguish a capsule-like layer of connective tissue around it. Moreover the dentine germ is only a special division of the mucous tissue of the dental groove, unusually rich in vessels and cells. After it has attained a certain size, the odontoblasts above described develop from the cells lying at the periphery, DEVELOPMENT OF THE TEETH. 489 and we soon recognise a solid shell of dentinal bone superim- posed on the dentine germ, like a cap. The histological forma- tion of the dentine is precisely similar to the ordinary process of ossification. Whilst the peripheric portions of the odontoblasts constantly undergo metamorphosis, with disappearance of their nuclei, into a gelatigenous matrix which subsequently undergoes calcification, their centric portions penetrate the hardened mass in the form of longer or shorter threads, and represent the first rudiments of the dental fibres. The lateral processes of the odontoblasts occasion the numerous anastomoses of the dental fibres, or of the dental tubuli. Every odontoblast communi- cates with the more deeply situated and successively enlarging cells of the young pulp by means of its pulp process, so that when an odontoblast is calcified up to the base of the fibre, another occurs in its place without any interruption to the continuity of the fibre. Hence every dental fibre, with its anastomoses, must be regarded as formed of several continuous odontoblasts. The layers of matrix immediately surroimding the fibres undergo conversion, as appears from their chemical characters, into elastic tissue, and form the dental sheaths of Neumann. It has not yet been ascertained whether they also undergo calcification. Thiis it appears that the dentine, with all its constituents, proceeds from odontoblasts that have become metamorphosed in their form and chemical com- position. No further detail respectiBg tlie process of dentinification need here be entered upon, since, so far as regards the osteoblasts, it presents the most complete analogy to that of ossification (see p. 135). This analogy is still more close in regard to the formation of the cement, in which the histological processes are identical with those of intra-membranous ossification. The matrix of the cement is the loose myxomatous connective tissue of the dental alveoli which immediately surrounds the teeth, and so far we may thus consider the dental sacculus to be the matrix of the cement. A special cement germ, such as has been described by Kobin and Magitot (46), in certain species of 490 STRUCTURE AND DEVELOPMENT OF TEETH, W. WALDEYER. animals, as in the Ruminants, Pachydermata, etc., does not, according to my observations, exist. In animals with successive teeth, as Kolliker (47) has de- monstrated, a process is found, even at the period of the first appearance of the enamel organ at its median side, which is either given oif from the neck of the enamel germ or from a still deeper part, and becomes the enamel organ of the per- sistent teeth (see fig. 101). On the other hand, no trace of a dentine germ for these latter teeth is at this period visible. Hertz (52) mentions the occurrence in several preparations of a second inflection of the oral epithelium superjacent to the enamel germ of the milk teeth, which he is inclined to regard as the enamel germ of the persistent teeth. Nevertheless there is much here that requires elucidation, especially in respect to the formation of the three molars of man, which, as is well known, are not preceded by milk teeth. The processes occurring in second dentition have been very recently minutely investigated by Kehrer (56) and Lieberkiihn (57). As the persistent tooth projects, the alveolar wall dividing it from the milk tooth sacculus undergoes absorption, and with this there immediately occurs a process of cell proliferation in the sacculus of the mUk tooth, under the influence of which the fang, with the formation of the so- called Howship's lacunae, is absorbed as far as the crown. The young granulations in the meanwhile take the place of the fang of the milk tooth. The remains of the pulp of the nulk tooth unite with the granulations now causing erosion, which, however, are themselves compressed by the growing tooth, that pushes the remains of the milk tooth so far forward that it falls out. No obhteration of the vessels of the milk tooth occur. The true mode in which absorption is effected, the formation of the lacunae of Howship, is no better understood here than in the case of the absorption of bone. Kehrer believes, from finding chalk granules in the protoplasm of young cells, that the amoeboid cells of the granulations destroy the dental tissue by a kind of mining process, effected by their pseudopodia. The Gubernaculum of the second set of teeth, aheady described by the older anatomists, consists, according to the observations of Lieber- kiihn, only of a cord of connective tissue, which traverses the alveolus in order to conduct the nerves and bloodvessels to the dental sacculus. It has no relation to the process of dentition itself. Our knowledge of the development of simple teeth consisting DEVELOPMENT OF THE TEETH. 491 only of cement, dentine, and probably also always of cuticle, requires revision. According to the statements of Owen (25), these neither possess an enamel organ, nor form a closed dental sacculus.* We possess no accurate information of the relations of the oral epithelium. Probably there is here, as Leydig (36) describes in several species, as, for example, in the Anguis fragilis, a thia covering to the freely projecting dental papilla, which subsequently becomes the homy cuticle. In accordance with a more recent investigation of Leydig (62), the crowns of the teeth, which, however, have no investing enamel, originate in Salamandra maculosa, in several dental sacculi which lie at the bottom of the " epithelium of the jaw." The fangs are de- veloped from the subjacent connective tissue. Leydig considers the substance of the dental crowns to be a cuticular formation. The simple horny teeth do not differ in their formation from the ordinary papillffi of the oral mucous membrane possessing a strong horny investment. Nothing is at present known of the mode of de- velopment of the more compound forms occurring in Ornithorhyncus and others. Accurate knowledge of the dental tissues, and of their de- velopment, commences with the works of Purkynd and his scholars, Frankel (13) and Raschkow (14). Leeuwenhoek (2) had indeed previously seen the dental canaliculi, and, like J. Hunter (4), had recognised the cement as a distinct substance, the discovery of which is ordinarily attributed to Blake (5) and Tenon (6) ; stiU it is only from the time of Purkyn^ that the knowledge of this subject has become common property. The enamel fibres have been described by many from the time of Malpighi. Retzius (19) and Hannover (39) gave the most accurate description of the structure of the dentine and enamel, especially with regard to the various lines and markings upon and in them, and the course of the canaliculi and enamel fibres. Nasmyth (22) and Erdl (27) first described the cuticle, and Czermak (33) the interglobular substance. We are indebted to E. Neumann (48) for the demonstration of the dental sheaths, * Owen, moreover, claims enamel for many animals, in which it does to exist, as, for instance, the frog. M M 492 STRUCTURE AND DEVELOPMENT OF TEETH, W. WALDETER. and to F. Boll (59) for following out the dental nerves in their further course. In recenlj times. Tomes (29, 40) has most suc- cessfully worked at the finer points of dental structure, and by demonstrating the dental fibres first opened the way to a cor- rect iaterpretation of the nature of the dentine ; previously to him, as by J. Miiller (16) and Lessing (28), the dental canali- culi were regarded in reference to their contents precisely in the same light as the lacunae of bone. Tomes also famished numerous and valuable contributions to the comparative ana- tomy of the teeth. On the latter subject, however, the im- portant work of Owen (25) constitutes the principal authority, but those of Erdl, Hannover, Huxley (37), Agassiz (15), F. Miiller, and Henle (20) may also be enumerated. Amongst the points in the histology of the teeth still requiring elucidation the structure of the enamel and the final terminations of the dental nerves deserve to be mentioned. If we except the works of Arnold (12) and Goodsir (21) (who however con- sidered that the teeth originate from free papiUse at the bottom of an open dental groove) as constituting the first com- prehensive investigations towards the elucidation of the genesis of these structures, those of Marcusen (31), Huxley (37), and Kolliker (47, 58), have proved of the highest value. Marcusen gave the minute details of the primary origin of the teeth quite correctly, and referred the enamel to the oral epithelium, as Huxley also has always maintained ; and Kolliker's accurate investigations have placed the fact beyond doubt. Purkyne and Kaschkow had already demonstrated the enamel organ, Schwann (23) the enamel cells and odontoblasts, andLent(38)and KoUiker (58) the dentinal processes of the latter. The external epithe- lium has likewise been correctly described and explained by Marcusen. All later observers, Nasmyth, Huxley, Natalis, Guillot (44), Todd and Bowman (35),\ Robin and Magitot (46), notwithstanding that they described this epithelium with great minuteness, have furnished us with no new information respecting it. Dursy (67) has followed the papillary pro- cesses of the dental sacculus, together with the intervening depressions of the external epithelium which frequently appear as glandular structures belonging to the latter, as far as the enamel germ, and from thence on to the papiUse of BIBLIOGRAPHY OF THE TEETH. 493 the maxillary mucous membrane. To judge from his de- scription and illustrations, H^rissant (3) must have already seen the papillae, which he considered to be glands for the secretion of enamel. Their importance in the formation of enamel has not been sufficiently estimated. Most of the contested points await their elucidation from an accurate knowledge of the histogenesis of the dentine and of the enamel. Kolliker (58),with whom Hertz (52) is in accordance, so far as regards the dentine, and KoUmann (67a), in regard to the enamel, still considers both substances as a hardened excretion of the odontoblasts or enamel cells ; whilst Tomes, Hertz, and Wenzel (66) (in the continuously growing incisors of Rodents), in regard to the enamel, and Boll recently in regard to the dentine, agree with the view given in the text. KoUmann admits also a membranous investment to the free ends of the enamel cells ; this continuous layer forms the membrana prsefor- mativa, and at a later period, when calcified, the cuticula dentis. In the following account of the literature of the subject, besides the most recent works, only those are mentioned which have given either extended and complete descriptions, or have furnished some new facts. References to the older literature are well given in Hdrissant, Henle (26) and Robin, and Magitot. Literature. 1. Malpighi, Anatome plantarum. Lugd. Batav., 1687. 2. Leeuwbnhoek, Philos. Transact., 1678. Opera omnia. Lugd. Batav., 1722, T. i. 3. He'eissant, Nouvelles rechercltes sur la formation de I'email des dents at sur celle des gencives. Mem de I'Aoad. de Paris, 1754. 4. J. HuNTEK, The natural history of the teeth. London, 1778. Deutsch, Leipzig, 1780. 5. Blake, De dentium formatione at structura. Edinburgh, 1798. 6. Tenon, Mem. de I'institut national. An vi. 7. SoHBEGEE, Isenflamm's und Eosenmtjllee's Beitrage, 1800. 8. Seeees, Essai sur I'anatomie at la physiologie des dents. Paris, 1817. 9. Heusingee, Histologie, 1822. (Hornzahne.) 10. F. CuviEE, Des dents des Mammiferes considerees comme cha- racteres zoologiijues. Paris, 1825. M M 2 494 STRUCTURE AND DEVELOPMENT OF TEETH, W. WALDETER. 11. E. EoTjssEAtT, Anatomie comparee du systeme dentaire, etc. Paris, 1827. 12. Arnold, Salzburger med. Zeitung, 1831. 13. Feankel, Depenitiori dentium humanorum struotura observ. Diss. inaug. Vratisl., 1835. 14. Kaschkow, Meletemata circa mammalium dentium evolutionem. Diss, inaug. Vratisl., 1835. 15. Agassiz, Kecherches sur las poissons fossiles, 1832 ff. 16. J. MiJLLBB, Arch., 1836, p. iii.; und Poggendoeff's Annal., xxxviii. 19. Ebtzius, Mullee's Arch., 1837. 20. Henle und J. MtfLLEE, Systemat. Beschreibung der Plagiosto- men, 1838. 21. GooDSiR, On the Origin and Development of the Pulp and Sacs of the Human Teeth. Edinb. Med. and Surg. Joum., 1838. 22. Nasmyth, Med. Chirurg. Transact., Vol. 22, 1839. 23. Schwann, Mikrosk. Untersuch, etc. Berlin, 1889. 24. Geebee, Handbuch der allg. Anatomie, 1840. 25. Owen, Odontography. London, 1840 — 1845. 26. Henle, Allgemeine Anatomie, 1841. 27. Ekdl, Abhdlgn. der Kgl. bayr. Akad. der Wissenschaften, Math. natw. Klasse. Miinchen, 1848. (Zahne der Nagethiere.) 28. Lessing, Verhandl. der naturw. Gesellschaft in Hamburg, 1845. 29. Tomes, A Course of Lectures on Dental Physiology and Surgery. London, 1848. Also a System of Dentistry, translated by zxjE Nedden. Niirnberg, 1862. f Also London Phil. Transact., 1849 (Marsupials) : ibid., 1850 (Eodents). 30. Krukenbeeg, Mullee's Arch., 1849 (Anastomosen der Zahn- kanalchen). 81. Maecusen, Ueber die Entwicklung der Zahne der Saugethiere. Bullet, de la cl. phys.-math. de I'Acad. imper. de St. Peters- bourg, 1849. 32. Hassall, Microscopic Anatomy of the Human Body. Lond., 1849. 83. CzERMAK, Beitrage zur mikrosk. Anatomie d. menschl. Zahne. Zeitschrift f. wiss. Zool., 1850. 34. Todd, Cyclopaed. of Anat. and Physiol., art. Teeth, Vol. iv., (Owen), 1852. 35. ToDD-BowMAN, Physiological Anatomy, Vol. ii. 36. Leydig, Ueber die Verknocherung der Schleimhaut der Mund- und Eachenhohle des Polypterus. Zeitschr. f. wissensch. Zool., 1854, und Lebrbuch der Histologie, 1857. BIBLIOGRAPHY OF THE TEETH. 495 37. Huxley in Quarterly Journ. of Microseop. Sc, 1854, 1855, 1857. 38. Lent, Beitrage zur Entwicklung des Schmelzes und Zahnbeins., Zeitschr. f. ■wiss. ZooL, 1854, vi. 39. Hannover, Die Entwicklung und der Bau des Saugethierzalms. Nova acta Acad. Caes. Leop. Natur. Curios. Breslau und Bonn, 1856. 40. Tomes, On the Presence of Fibrils of Soft Tissue in the Dentinal Tubes. Lond. Philos. Transact., 1846, p. ii. 41. Welckek, Bemerkungen zur Mikrographie. Ztschr. f. rat. Med. N. Folge., Band viii. 42. KoLLiKEE, Mikroskopische Anatomie. 43. riiBSTBNBEKG, Ueber einige Zellen mit verdickten Wanden im Thierkorper. Mulleb's Arch., 1857. 44. Natalis G-tjillot, Ann. des sc. nat. (Zoologie), iv. Serie, 1858, T. ix. 45. KoLLiKEB, Ueber verschiedene Typen in der mikrosk. Structnr des Skeletts der Knochenfische. Wiirzburger Vhdlg., 1859, ix. 46. EoBiN et Magitot, Journ. de la Physiol. Paris, 1860, T. ui. et iv., 1861. (A very complete treatise.) 47. KoLLiKEE, Die Entwicklung der Zahnsackchen der Wiederkauer. Zeitschr. f. wiss. ZooL, 1863. Gewebelehre, 4. Aufl. 48. E. Neumann, Beitrage zur Kenntniss des normalen Zahn- und Knochengewebes. Leipzig, 1863. 49. Waideyeb, Unters. iiber die Entwicklung 'der Zahne, Abth. i., Konigsberger med. Jahrbiicher, Band iv., 1864, Abth. ii. Zeitschr. f. rat. Med., R. iii., Bd. xxiv. 1865. 50. Bbigel, Ueber eine neue Untersuchungsmethode der anatom Zahnverhaltnisse. Berl. klin. Wochenschrift, 1865, Nr. 47 51. Saitee, Arch, of Dentistry, 1865. 52. H. Heetz, UntersuchuDgen iiber den feineren Bau und die Ent wicklung der Zahne. Vibch. Arch., 1866, Bd. xxxvii. Id Bin Fall von geheilter Zahnfractur mit nachfolgender Schmelz bildung., ViKCH. Arch., 1866, Bd. xxxviii. 53. HoHL, Ejiochenkdrperchen mit eigenthiimlichen Kapseln in der Zahnpulpa. Arch. f. mikrosk. Anat., 1866. 54. Beuch, Untersuch. iiber die Entwicklung der Gewebe, etc. Frankfurt, 1867, Lief. 2. 55. Ray Lankesteb, Quart. Journ. of Microseop. Sc, 1867. Teeth of Mikropteron with excessive formation of cement. 56. Keheee, Ueber die Vorgange beim Zahnwechsel. Centralbl. f. d. med. Wissensch. Berlin, 1867, Nr. 47. 496 STRUCTURE AND DEVELOPMENT OF TEETH, W. WALDEYER. 57. LiEBEBKiiflN, Ueber Wachsthum und Eesorption der Knochen. Marburger Univers. Programm., 1867. 58. KoLLiKEE, Gewebelekre, 5. Aufl., 1868. 59. F. Boll, TJntersucbungen iiber die Zahnpulpa. Arch. f. mikrosk. Anat., iv., 1868. 60. HoHL, Die Befestigung des Zahnes in der Alveole. Deutsche Vierteljahrsschr. f. Zahnheilkunde, 1867, p. 15. 61. Pfltjgbe, M. (Hamburg), Entwicklungsgesch. d. Zahne. Deutsche Vierteljahrsschr. f. Zahnheilkunde, 1867. 62. Lbydig, Ueber die Molche der Wiirtembergischen Fauna. Teos- chel's Arch. f. Naturgesch., 1867, p. 163. (Entwicklung der Zahne der Salamandrinen.) 63. CuTLEE, S. in "Dental Cosmos," 1867, September. See also Deutsche Viertljahrsschr. f. Zahnheilkunde, Januar, 1869, pp. 65 u. 69. 64. MiJHLEEiTEE, Bcitragc zur Kenntniss der Anordnung der Dentin- zellen. Deutsche Viert. f. Zahnhlkde., Juli, 1868, p. 168. 65. Inzahi, Giov. Ueber die Nerven der Cornea und der Zahne. Eiv. clin., vii., p. 109, 1868. 66. Wenzbl, Untersuchungen iiber das Sohmelzorgan und den Schmelz, etc.. Arch. d. Hlkde., 1868, p. 97. 67. E. DuESY, Zur Entwicklungsgeschichte des Kopfes (mit Atlas). Tiibingen, 1869, p. 211. 67a. KoLLMANN, Ueber das Schmelzoberhautchen und die Membrana praeformativa. Sitzungsberichte der Miinchener Akademie. Math. phys. CI. 1, 2, 1869. 6, Februar. In regard to the chemical characters of Dentine see especially : 68. V. BiBEA, Chemische Untersuchungen iiber die Knochen und Zahne. Schweinfnrt, 1844. 69. Hoppe-Seylee, Vieohow's Arch., Bd. v. und Bd xxiv. (Zaha- schmelz). 70. Zaiesky, Ueber die Zusammensetzung der Knochen des Menschen, etc., in Hoppe-Seylee's Med. Chem. Untersuchungen. Hft. i., 1866. CHAPTER XVI. THE INTESTINAL CANAL* By E. KLEIN AND E. YEESON. A. Okal CAViTy, BY E. Klein; The mucous membrane of the oral cavity in man begins at the lips as a direct continuation of the outer integument. Three anatomically different partsf can be distinguished in it : a cutaneous, a transitional, and a muco-membranous portion. The transitional portion is marked off from the cutaneous portion by the outer border of the red lips, and from the muco- membranous portion by the most prominent part of the con- vexity of the Hps, so that when the mouth is closed the red visible portion of the lips represents the transitional portion. The cutaneous portion is covered by a thin epidermis con- sisting of one or two layers of flattened epithelium, intimately fused with one another ; subjacent to this is a thinner mucous layer, in which are small rounded cells containing relatively large nuclei. The cutis internal to this is composed of fasciculi; of fibres, which decussate with one another, the principal ones being directed towards the free border of the lips. The fibres which form these fasciculi consist, for the most part, of fine connective * The account given in this section rests on investigations which the authors have undertaken in my laboratory for this work. — S. Stricker. t E. Klein, Zur Kenntniss des Baues der [Mundlippen des neugebornen Kindes, " On the Structure of the Oral Lips of the newly born Child ;" Sitzungsherichte der k. k. Akadem. der Wissenschaften in Wien, December Heft, 1868. 498 THE INTESTINAL CANAL, BY E. KLEIN AND E. VERSON. tissue fibres, between which isolated or plexiform fibres of elastic tissue run. The surface of the cutis directed towards the epidermis pre- sents rows of cylindrical or conical small vascular papiUse stand- ing in tolerably close proximity with one another, and project- ing iuto the rete mucosum to about half its thickness. The nervous and vascular trunks proceeding from the subcutaneous tissue, or from the muco-membranous and transitional portions, make their way between the muscular fasciculi, and curve at nearly right angles in the cutis. Hairs and sebaceous follicles are distributed in moderate number at nearly equal distances, and at various depths in the tissue. The hair follicles of the upper lip are directed obliquely downwards at their base, those of the lower lip upwards. The points of distinction between the transitional and the cutaneous portions of the lips are the absence of hair follicles and sebaceous glands in the former ; the presence of wedge-like fasciculi of the orbicularis oris m it, which reach nearly to the epithelium ; the .much greater trans- parency of its superficial cells ; the arrangement of its morpho- logical elements generally ; and, lastly, its far more abundant supply of bloodvessels. The epitheUuni, as a whole, remains at a short distance from the last hair follicles, as deep as at the cutaneous portion, but beyond this rapidly increases in thickness. The super- ficial cells are much flattened, intimately fused with one another, and without apparent nuclei; but those which are rather deeper, though still tabular, become somewhat elon- gated, and possess a weU-defined and usually elongated nucleus. The ceUs of the middle layers increase as they are .more deeply situa,ted in their vertical diameter, and become proportionately narrower, with round nuclei ; the deepest cells •are round, wdth relatively large spheroidal or irregularly shaped nuclei. The chief fibrous layer of this transitional portion is com- posed of broad highly refractile fibres, capable of resistiag the action of acetic acid, and united into plexiform fasciculi. The fasciculi separate from each other at many points to permit the passage of the horizontally coursing vascular trunks, which are here very numerous. A. ORAL CAVITY, BT E. KLEIK. 499 The thickness of this layer is least where the hair follicles cease ; from this point it gradually increases, and is thickest at the commencement of the muco-membranous portion. Its surface is beset with very numerous thin and elongated papillEe, which are frequently clavate, oblique in direction, and vascular. Between the fibrous layer and the submucous tissue of the muco-membranous portion, and near the commencement of the latter, are situated the coronary artery and vein. These give off larger and smaller branches to form a plexus beneath the epithe- lium from which the vessels for the supply of the papiUse arise. The third part of the lip, the muco-membranous portion, possesses an epithelium that far exceeds in thickness that of the two above-named portions ; but if this be followed over the fold of the lip, it will be found again quickly to diminish. It presents the several layers characteristic of laminated flattened epitheHum ; the most superficial layers consisting of flattened tubidar cells, with a flattened and for the most part elongated, though occasionally spheroidal, nucleus; subjacent to these are cells that at first are of greater breadth than depth, but become in the deeper layers more and more polyhedric, till they are finally succeeded in the deepest layers by cells which are arranged in the form of palisades. Many of these cells are ribbed, or exhibit thom-Hke pro- jections, by virtue of which they are connected with each other by a dentated suture. The tissue of the mucous layer is composed of finer and coarser fibres. The former are either united into fasciculi, or run, in the form of fine isolated or paired elastic fibres, sinuously between or in many spiral coils around the decus- sating and plexiform fasciculi. Besides these, broad, highly refractile, strongly looped fibres occur. Wherever the fibres of the membrana mucosa pursue any definite general direction, it is horizontal, and directed from one side of the lip to the other. Moreover, numerous fasciculi pierce the muscular layers to reach the subcutaneoiis tissue of the transitional portion. Near the muscular fasciculi the tis- sue undergoes alteration, becoming less dense, and the mucous membrane passes into submucous tissue. The membrana mucosa is beset with conical, usually un- 500 THE INTESTINAL CANAL, BT E. KLEIN AND E. VERSON. divided, but occasionally bifid or trifid papillse, which often, coming into contact at their -wide bases, project into the epithe- lium; the longest of these (0-525 — 0-63 of a millimeter in length) are situated at the commencement of the muco-membranous portion posteriorly; coincidently with the diminution in the thickness of the epithelium they likewise become shorter, and do not exceed half the depth of the epithelium. The epithelial cells covering the papiUse are arranged iu an imbricated manner, and are much flatter than the cells situated on the same level between the papillse. Corresponding to the first two or three rows of papillse situated at the commence- ment of the muco-membranous portion, the epithelial surface presents a small elevation; and in newly bom children the papiUse of this part of the lip, and those at the angles of the mouth, project as much as one millimeter beyond the lower plane of the epithelium. The glands that are situated in the submucous tissue of the muco-membranous portion make their first appearance behind the most prominent portion of the convexity of the lip, and, indeed, at that point where the epithelium begins to be con- stant in thickness. They constitute acinous glands that are essentially similar to the salivary glands. Our knowledge, however, is not sufiiciently advanced to enable us to state that they present those charac- teristics of the salivary glands which have been the subject of recent investigation. They open on the surface of the mucous membrane or epithelium by means of small excretory ducts. Each of these is a canal bounded by a structureless membrane, in which the laminae of tesselated epithelium only extend to the depth of the epithelial layer generally ; beyond this it is Hned by a single layer of cylindrical epithelium. After pursuing a spiral course obliquely through the membrana mucosa it gives off numerous branches, which frequently divide and terminate in the individual acini. The acini belonging to a large branch are united into a lobule by the fasciculi of the submucous con- nective tissue, and these again are formed into lobes. The fasciculi and fibres which limit a lobulus or a lobe, and in the meshes of which the several acini are imbedded, are continued as a sheath to the excretory duct iu its passage A. ORAL CAVITY, BY E. KLEIN. 501 through the mucous membrane. The plexiform tissue com- posed of fasciculi of fine connective tissue fibres belonging to the submucous layer, and which, together with delicate fre- quently coiled elastic fibres, forms the framework of the gland, is at the same time the support of small nerves, and of a close system of capillaries which surround the acini. In this tissue there lie, partly isolated amongst the fine fibres of the connective tissue fasciculi, partly accumulated in larger numbers near and around the acini, lymph corpuscle-like cells, as well as large, coarsely granular, irregularly shaped masses of protoplasm, which usually contain a small nucleus. Sebastian* counted fifty-seven glands in the lower lip alone ; in other cases there were thirteen and twenty-one of these glands. Their diameter amounts from ^ to 1^ millimeter, or more ; and as a rule their size increases in proportion to th© smallness of their numbers ; they are largest in children, and diminish as age advances. In the lower lip of the childf they are arranged in four or five consecutive rows. Their number rarely exceeds three in the upper lip, and they are altogether absent at the angles of the mouth.J I find that in the child they are larger in the lower than in the upper lip. Besides the glands, large vessels and nerves are also found in the submucous tissue of the muco-membranous portion, the latter for the most part running in a vertical direction, giving ofi" smaller branches to the mucous membrane, which again subdivide, and may be followed to the immediate vicinity of the epithelium. The nerves of the papillae have not been accurately investigated. According to W. KJrause, the so-called terminal bulbs — structures respecting the nature of which there is still some doubt — are found in the lips of many Mammals. § Kolliker|| has observed in the papillae of the lips, but only of that part which is visible when the mouth is closed, 'tactile corpuscles, and * Sebastian, Hecherches anatomiques, physiologiques, pathologiques, et semeiologiques stir les Glands Lahiales. Groningen und Bremen, 1842, 4to. t E. Klein, he. cit. % Henle, Splanohnologie, p. 138 § W. Krause, Die terminalen Korperchen. Hanover, 1860. i| Zeitsehrift fiir wissenschaflliche Zoologie, Band iv., Heft i. p. 43. 602 THE INTESTINAL CANAL, BY E. KLEIN AND E. VEESON. in one instance lie found nerve coils in the small papillae, and at the bases of the larger. Gerlach* also ascribes tactile corpuscles to the papillae of the borders of the lips. The fasciciili of the musculus sphincter oris are intercalated between the submucous tissue of the muco-membranous por- tion and the subcutaneous tissue of the cutaneous portion. According to C. Langer,f the muscular fibres of each side have three points from which they radiate towards the median Une, namely, the angle of the mouth, and the two musculi incisivi ; from the angles of the mouth the fibres arranged in a laminated manner pass to the lips, one portion terminating without crossing the median line in the cutis of its own side, another passing beyond this to terminate in the skin of the lip on the other side, and, finally, a portion of the fibres attaching them- selves to the incisor processes of the bones on the same side. Moreover, according to Langer, the fibres of the sphincter penetrating the cutis lose themselves amongst its plexiform fibres. Woodham Webb J has likewise, some time ago, demon- strated the presence of transversely striated muscles in the lips of Man, from which extremely delicate fasciculi extend iato the papillae of the cutis, and are there lost. It may be shown by carefully made sections that a portion of the muscular fibres which Langer and Woodham Webb considered to penetrate the cutis belongs to a peculiar system of muscular fibres (compressor labii) which arise in the spaces intervening between the first 5 — 7 consecutive rows of hair follicles, arrange themselves in the subcutaneous tissue in four or five fasciculi, traverse, forming slight curves, the fasciculi of the sphincter, and at their entrance into the rtiuco-membranous portion, that is to say, into the submucous layer of this portion, every two or three fasciculi decussate alternately, in order finally to penetrate * Handhuch der allgemeine und speciallen Qewehelehre des menschlieh.es Korpers. Mainz, 2 Aufl. t Ueber den Musculus orbicularis oris, Wiener Medicinische Jahrbiieher, Heft ii. ; und Zeitschrift der Gesellschaft der Aerzte. Wien, 1861. X " On Striated Muscular Fibres in the Skin of the Hiunan Lip," Quar- terly Journal of Medical Science. London, 1857, January, Vol. v., p. 89, plate vii., fig. 16. A. ORAL CAVITY, BY E. KLEIN. 503 the mucous membrane itself in a fan-like manner, or, more rarely, to enter its transitional portion. The several muscular fibres, both of the muco-membranous portion as well as of the cuticular portion, may be followed into close proximity with the epithelium, or to the base of the papillae. The sarcolemma is continued for a short distance between the fibres of the membrana mucosa, or of the cutis, in the form of delicate fibres. In the cutaneous portions the muscular fibres partially decussate at the base of a hair fol- licle, whilst elsewhere they may be followed on the wall of the hair follicle to near the rete mucosum. This muscle in the lower lip is more strongly developed near the middle line than at the sides; but ia the upper lip, in which it is usually more feebly marked, the opposite obtains. Laterally the fibres are directed radially towards the oral opening, and the area embraced by its origin and insertion is larger. At the angles of the mouth the mucous membrane rests upon the inner surface of the buccinator, and extends, as the mucous membrane of the cheeks, as far back as to the anterior border of the vertical ramus of the lower jaw, without presenting any important variation in. its structure. Its epithelium is of the same thickness and structure as that already described as covering the muco-membranous portion, except that the number of ribbed cells in the middle layers of the mucous membrane of the cheeks is much greater than in that of the lips. The form of the papiUse which project from the Memb. mucosa into the epithelium is irregular ; they are often conical, with elongated apices, or with their points prolonged in a filiform manner. At their bases they are relatively broad. Their height varies, sometimes amounting to half the depth of the epithelium, sometimes scarcely exceeding its lower boundary line, The Memb. mucosa is most dense beneath the epithelium, and ia it the same arrangement of the elements may be recog- nised as in that of the lips. Towards the buccinator muscle it becomes more loose. Its fasciculi stand in the same connection with those of the subcutaneous tissue as in the case of the lips. The glands of the mucous membrane of the cheeks (Glandulae buccales) are thinly scattered, and are only to be found at con- siderable distances from each other; near the point where 504 THE INTESTINAL CANAL, BY E. KLEIN AND E. VERSON. Steno's duct opens they also form a series of glands known as the glandulse molares * According to Ward, they are from two to four in number, are situated between the masseter and bucci- nator muscles, and are larger and composed of more lobules than the remaining glands of the oral mucous membrane. At the point where the lips are reflected upon the anterior surface of the jaws, the mucous membrane at the middle line, boih above and below, forms a small duplicature, termed the frcenwm. The epithelium of the mucous membrane is here thinner than elsewhere ; the papiU.se are also smaller and less numerous ; the mucosa itself is not' distinguishable. The vessels are relatively numerous, and it contains a considerable number of fine irre- gularly coursing elastic fibres. That portion of the mucous membrane which covers the alveolar processes of the jaw, and surrounds the necks of the teeth, passing anteriorly into the mucous membrane of the lips, posteriorly at the root of the oral cavity into that of the hard palate, and below into that of the floor of the mouth, is named the gum (Gingiva). The gum, on account of the abundance of tendinous fasciculi it contains, is denser and tougher than the mucous membrane of any other part of the mouth ; it is intimately adherent to the bone in consequence of the direct prolongation of the ten- dinous fasciculi of the periosteum into the mucosa. The epithelium of the gum is composed of laminae of tesse- lated cells, amongst which are exceedingly well-marked ribbed cells. The superflcial cells are strongly flattened ; those more deeply situated become thicker, and possess strongly defined ribs. The deepest cells are cylindrical, with conical external extremities. The papillce of the mucosa of the gum are aU relatively broad at their bases, of unequal height, with conical or rounded external extremities, which are sometimes simple and sometimes divided. The tissue of the mucosa is tough, and is composed of broad * N. Ward, art. " Salivary Glands," in Todd's Cyclopcedia of Anatomy and Physiology, Vol. ii., p. 422. A. ORAL CAVITY, BY E. KLEIN. 505 fasciculi of connective tissue, the fibres of which run in a straight direction. It also contains a not inconsiderable number of finer or coarser closely coiled elastic fibres. In the mucous membrane of the gum, three separate fibrous layers may be dis- tinguished : a. Fasciculi of fibres which run in a horizontal direc- tion from right to left parallel to the surface, and then break up into smaller fasciculi that, after frequently decussating, reunite into coarser bundles ; these predominate on the anterior surface of the alveolar process over the two following sets of fibres. h. Fasciculi which, proceeding from the periosteum of the al- veolus, cohere in large bundles, and immediately again break up iu a fan-like manner whilst coursing towards the epithelium, either from before backwards or from behind forwards. On ap- proximating the epithelium, the smaller fasciculi break up into isolated fibres, which, running apparently between the cells, penetrate the deepest epithelial layers, c. Lastly, there are fasciculi which run in a vertical direction from above down- wards, or from below upwards, and in other respects resemble those described under a. At the posterior part of the gum of the upper jaw, where this passes into the mucous membrane of the hard palate, all three sets of fibres frequently, decussate. The nerves of the mucous layer of the gum are not numerous. The mucous membrane of the hard •palate presents many difierences in structure from that of the gum. The laminated pavement epithelium, which at first is thinner than that on the gum, gradually increases in depth posteriorly. The num- ber of ribbed cells contained in its middle layers varies at difierent points. The papiUse of the mucous membrane pro- jecting into the epithelium are not nearly so munerous at the commencement of the hard palate as on the gums. The me- dian papOlee, especially near the foramen incisivum, are fre- quently observed, through tracts of considerable extent, to be indicated only by sparingly distributed slight depressions of the deep surface of the epithelium. Posteriorly the papUlse increase somewhat in number and height, although even in some parts of the posterior third of the hard palate they are not much larger than quite anteriorly. The mucous layer subjacent to the epithelium is thinnest 506 THE INTESTINAL CANAL, BY E. KLEIN AND E. VEESON. over the anterior third of the median line ; more externally it is generally thicker, attaining its maximum posteriorly. The fasciculi, as a general rule, run as if they radiated from the arch of the alveolus of the upper jaw towards the median line of the hard palate. In the anterior part of the mucous membrane, consequently, they run from before backwards, but more posteriorly from side to side. Their constituent elements consist anteriorly, for the most part, of broad fibres, which form a close plexus beneath the epithelium ; but at a plane somewhat deeper there is a loose network of connective tissue, constituting a submucous layer, the fibres of which are more densely matted as they approach the bone, and finally become continuous with the periosteum. In the middle and posterior thirds the mucous membrane beneath the epithelium is looser in texture, but at a deeper level the fasciculi of connective tissue are woven into a compact felt, and separate in the submucous tissue from one another to form meshes of variable size. Laterally the submucous tissue con- tains fat cells which are most abundant in the middle third. The vessels and nerves run in the submucous tissue of the middle line and lateral portions of the anterior third, the former pursuing for the most part a longitudinal, the latter a transverse direction. The more externally the part examined is situated, the more numerous are the nerves, the small branches of which form arches in the mucosa. In the middle part of the hard palate, and in the first instance laterally, acinous glands occur in the submucous tissue, which are isolated in front, but subsequently grouped either into a single or (towards the pos- terior and external portion of the middle third) into two longitu- dinal rows. Szontagh counted 250 glands in the hard palate.* After the mucous membrane of the oral cavity has covered the hard palate, it forms posteriorly a muscular fold, the velum palati, or soft palate, which presents in man a conical median prolongation, the uvula, and is also continuous with the mu- * Szontagh, Beitrdge zur feineren Anatomie des menschlicken Gau- mens, " Essays on the Minute Anatomy of the Hard Palate in Man ;" Sitzungshericlite der k. k. Akademie der Wissenschafi. zu Wien. Marz Heft, 1866. A. OEAL CAVITY, BY E. KLEIN. 607 cous membrane of the nasal passages. The mucous membrane of the soft palate is continued laterally and downwards as the arcus palato-glossus into that of the root of the tongue, and as the arcus palato-pharyngeus into that of the pharynx. In newly bom children the apex of the uvula and the im- mediately adjoining parts are covered with tesselated epithe- lium, whilst the posterior or upper surface is invested with a laminated cylindrical and ciliated epithelium. The most superficial ceUs are here beset with short hair-like processes, present a conical form, with the apices directed away from the surface, and contain rounded or laterally flattened nuclei; subjacent to these are fusiform or elongated oval cells, and still deeper he others that are flattened at the sides by mutual pressure. The transition of laminated pavement epithelium into lami- nated cyliadrical and ciliated epitheUum is efiected by a diminution in the number of the middle layers of the cells, which are not arranged as before, with their shortest diameter perpendicular, but parallel to the surface ; and by the dis- appearance of the most superficial flattened cells, which are replaced by cylinder cells, that increase in number in propor- tion to their distance from the apex of the uvula. On the posterior surface of the uvula and of the soft palate of the new-bom infant there may moreover be found nume- rous isolated areas, presenting well-developed pavement epi- thelium, as well as transitional forms between the laminated cylinder and pavement epitheUum. In adults* a laminated pavement epithelium exists both on the anterior and on the posterior or superior surfaces of the uvula and soft palate, and this may be divided into two layers, of which the cells forming the deeper are smaller than those of the superficial. The tissue of the mucous membrane contains fasciculi of connective tissue, and a considerable quantity of coiled elastic fibres of various size united into plexuses. The part situated immediately beneath the- epithelium, is much closer * E. Klein, Tiber das Epithel des Weichen Oaumes, etc., "On the-Epi- thelimn of tlie Soft Palate," etc. ; Wiener Sitzungsherichte der h. h. Akade- mie der Wissensehaft. zu Wien, Januar heft, 1868. N N 508 THE INTESTINAL CANAL, BY E. KLEIN AND E. VEESON. in. texture than that which is deeper, and forms the sub- mucous tissue in which the glands and muscles are found. The fasciculi of connective tissue found in the velum palati and uvula may be considered to run in three directions ; the first of these, for the most part lying externally, run hori^ion- tally and from side to side ; the second longitudinally ; and these two sets form the felt of the mucosa ; lastly, there is a third set, which, emanating from the first two, runs from the mucosa in an obliquely divergent manner into the deeper parts, in order to enter the mucosa of the opposite side. These last- mentioned fibres form, by their decussation, the loose network of the submucous tissue of the soft palate and uvula, which, as usual, contains a variable quantity of fine elastic fibres, small Ijrmph cqrpuscles, and large connective tissue corpuscles, with numerous vessels and nerves. In the soft palate and uvula of the adult there project from the surface of the mucous mem- brane into the epithelial layer conical or cylindrical papillae with rounded extremities. These papillae are much larger and more numerous on the uvula than on the soft palate. (In one transverse section of the uvula of an adult I counted 130 in a single plane.) In the velum palati of the new-bom infant the relations of these parts are somewhat different. In such I find no papiUse on the upper surface, but the vessels advance as far as the epithelium, and there loop back, or course for some distance immediately beneath the epithelium. On the inferior surface again we find similarly looped vessels forming broad and flat -arcades, especially in longitudinal sections, im- mediately subjacent to the deeper surface of the epitheUum, or a bloodvessel with a little mucous tissue may project into the inferior layer of the epithelial ceUs. These appearances may be remarkably weU seen at the borders of the folds. Two or three branches may there be seen to be given off from a larger vessel, and, accompanied by a little fibrous tissue, to penetrate between the epithelial cells. At the most prominent portion of the folds two or three poiated papiUae appear of equal breadth but variable length. The mucous membrane of the velum palati is extraordinarily rich in vessels. Just be- neath the epithelium, as well as in the deeper layers of the A. ORAL CAVITY, BY E. KLEIN. 509 mucosa, besides numerous extremely thin-walled bloodvessels, there are numerous lymph channels, both in. the form of larger lymphatic lacunae and of lymphatic vessels. The larger nerve trunks lying externally to the first rows of glands, the num- ber of which is much more considerable at the anterior than at the posterior surface, give off fine branches, which run both internally into the submucous tissue as well as externally into the mucosa, where they may be followed in the former instance between the glands and the muscles, in the latter as far as the epithelium. The thickness of the mucosa is variable, and depends on the size and number of the glands. In general the thickness of the mucous membrane increases from the commencement of the hard palate towards the point of the uvula, and it is always somewhat thicker on the upper surface than on the lower. The acinous mucous glands of the soft palate are situated, as has been noted above, in the submucous tissue. Their size varies, and the largest are found in the uvula. Szontagh* counted one hundred of them on the anterior surface of the soft palate, forty on the posterior surface, and twelve on the uvula. In the last-named situation they become larger, and form in its upper half, or basis, a central layer, which, however, is somewhat nearer to the anterior surface than to the posterior, and is sometimes invested by the fasciculi of the azygos uvulae, and at others is intercalated between the two muscles. The excretory ducts vary in their width, in the nature of their coats, and in their direction. At the posterior surface of the uvula in adults we find excretory ducts which become wider near their orifice ; but the opposite obtains in the ducts opening on the upper and lower surfaces of the soft palate. The direction pursued by the excretory ducts is very rarely rectninear; the greater number, after they have received aU their tributary branches, run from the deepest part of the mucosa perpendicularly towards the epithelium, then turn off at an angle, and course obliquely towards the free surface of the epithelium. They are for the most part lined with a simple cylindrical epithelium ; in other instances, but less fre- * Loc. cit. N N 2 510 THE INTESTINAL CANAL, BY E. KLEIN AND E. VERSON. quently, beneath the cylindrical cells a second layer of small round cells is found, and at the posterior surface of the soft Fig. 104. .A\ .J •*-<.- * •''vtsa; Fig. 104. Longitudinal section of the soft palate of a Child, a a, ciliated epithelium ; 5 h, mucous membrane of the upper surface ; c, glands ; d d, muscular fibres of the thyreo-palatiuus ; e e, muscular fibres of the levator palati ; /, mucous membrane of the lower surface ; g, epithelium of the lower surface. palate the excretory ducts of a few glands exhibit, even in the adult, for a short distance from the epithelial surface, a liriing of A. ORAL CAVITY, BY E. KLEIN. 511 ciliated cyliadrical cells* The laminated pavement epithelium of the surface may in some cases be followed for a short distance as a lining to the excretory ducts of the glands. The course and arrangement of the muscles in the soft palate are highly complicated. The only true longitudinal muscle contained in it is the azygos uvulse, or palato-staphyUnus, a double muscle, the two portions of which arise at the fibrous border of the hard palate, and are situated on either side of the median line. In the anterior part of the soft palate the two portions are distant from each other about their own diameter,-}- but near the base of the uvula they are in close proximity. They do not quite extend to the apex, but terminate at about the end of the second third, the fasciculi becoming fan-shaped anteriorly, and expanding to the greatest extent at the sides, consequently corresponding in their course, and terminating in the same mode as has been described in speaking of the muscles of the lips. In their passage through the soft palate, several smaU fasciculi are given oif from the principal mass, which, traversing the lobules of the glands, and surrounding them, re- join it, or dip into the mucous membrane, especially at its an- terior surface, and terminate in the mode described. The Musculus thyreo-pharyngo-palatinus]: constitutes the chief muscular mass of the soft palate. It is divisible, according to Luschka, into a thyreo-palatine and a pharyngo-palatine portion. The upper extremity of the former lies partly in front of and partly behind the Levatores, decussating with them to some extent. The greater number of the fibres of the pars thyreo-palatina lie ia front of the Levatores, and form a curved flattened muscle, with a maximum breadth of nine millimeters which is situated nearer to the hard palate than the arch formed by the junction of the two Levatores by about the breadth of this arch. The convex border of this portion is continuous with the fibrous border of the hard palate or aponeurosis of the tensor veli palati, whilst its concave border * E. Klein, he. cit. f Szontagh, loc. cit. X Luschka, Der Musculus pharyngo-palatinus des Menschen, Virckow's Archiv, Band xlii., p. 480. 512 THE INTESTINAL CANAL, BY E. KLEIN AND E. VERSON. is turned to-wards the similar concave border of the arch formed by the Levatores. The other fibres of the upper extremity of this pars thyreo- palatina, situated behind the Levatores, form in the adult several loosely connected fasciculi, much interrupted by fat ceUs, which, becoming more and more delicate towards the free border of the soft palate, course partly in front of the azygos uvulae between the glands of the anterior surface, and partly over or behind it between the glands of the posterior surface, either ending here or extending to the mucous membrane. The thyreo-palatine portion of the muscle just described receives reinforcing fibres from the Levatores ; * and a fasciculus is constantly given ofi" laterally from these where they unite to form an arch, which, subdividing, runs in front of the azygos to the opposite side, and there joins the innermost bundles of the pars thyreo-palatina. The whole of these fibres mn out- wards and downwards, descending with the arcus pharyngo- palatinus, and are partly inserted in the upper angle of the thyroid cartilage, and are partly united with the pars pharyngo- palatinus, forming the posterior waU of the pharynx. The pars pharyngo-palatina arises near the arcuate extremity of the pars thyreo-palatina, and the two unite together in the arcus pharyngo-palatiaus, and pass to the posterior wall of the pharynx. Besides what has been already stated respecting the Levatores veH palati, it still remains to be observed that the arcuate junction of these two muscles is situated in front of the azygos uvulae, and in the anterior half of the soft palate. , Finally, there is a small muscular fasciculus which arises from the transverse fibres of the tongue, and runs in the anterior arcus glosso-palatinus towards the base of the uvula, where it is partly lost in the mucous membrane of its anterior surface, and partly unites with the ultimate bundles of the thyreo-palatinus. The several fasciculi of the palatal muscles, like those of the tongue and hps, form a delicate plexus. A considerable quantity of adipose tissue generally enters into the structure of the palate in adults, being chiefiy found between the fasciculi * LuscKka, he. cit., p. 483. A. ORAL CAVITY, BY E. KLEIN. 513 of the th3n:eo-palatinus and the levator palati. It also con- stantly occurs between the first layer of glands of the upper surface, and is to be met with, in larger or smaller quantity, in various parts of the mucous membrane. The muscular folds of the mucous membrane which extend as the arcus glosso-palatinus and pharyngo-palatinus, from the soft palate to the root of the tongue and pharyngeal wall, ex- hibit no peculiarity of structure differing from that of the mucous membrane of the soft palate ; the epithelium, papillae, and muco-membranous tissue being in all essential respects similar. Elastic tissue, forming plexuses, is usually abundant in the mucous membrane of these folds. The lowermost glands diminish in number and size in adults, present the same dimensions as those of the uvula, and are united into a layer, the continuity of which is interrupted by a sparing, amount of loose connective tissue Containing fat cells surrounding the lobules and acini, and here and there by small muscular fasciculi. The tissue of the mucous membrane is frequently infiltrated at the free border of the folds with a greater or less number of lymph corpuscles. These infiltrated portions, in which may be recognised, besides numerous bloodvessels, a delicate cellular network with decussating fibres of connective tissue, are never sharply defined, but pass gradually into the adjoining tissue. Between the palatine arches the lateral walls of this part of the oral cavity, known as the Isthmus faucium, present a de- pression; from the bottom projects a swelling — the tonsil, which is sometimes so small in newly bom children as to be scarcely perceptible on inspection of the oral cavity from be- fore, and is sometimes so large that the two organs materially contract the dimensions of the isthmus. Their surface is lobulated by fissures of various depths and complexity. The whole organ is to be regarded as a thickened portion of the mucous membrane, presenting a lobulated surface, the proper membrana mucosa of which constitutes a kind of conglobate, gland substance (Henle), consisting partly of fibrous, and partly of adenoid tissue, in the meshes of which numerous Ijrmph corpuscles are contained. The epithelium is here tesselated and laminated ; papillae can scarcely be said to be present. Beneath the epithelium is a close plexus of vessels, and the 514 THE INTESTINAL CANAL, BY E. KLEIN AND E. VERSON. infiltrated mucosa is divided into portions resembling Peyer's patches by means of connective tissue cords proceeding from the submucous tissue. Acinous glands are distributed in the submucous tissue, and they are in contact externally with the muscular tissue of the pharynx. The Tongue. That surface of the tongue in Man which is directed towards the palate — dorsum of the tongue — presents different characters from the lower surface ; for in the former the papillary eleva- tions of the mucosa covered with tesselated epithelium project to a considerable extent, and confer upon it its peculiar furred appearance; whilst on the lower surface the papilUe of the mucous membrane do not in general project more than to half the thickness of the epithelium. The surface of the descending portion of the tongue in the newly bom child, again, presents different features from that of the ad'ult ; in the former, the surface of the jnucous membrane appears tumified, thesweUings being divided by elongated fissures ; ia adults, on -the other hand, it is beset in many places with numerous smaller and larger lenticular elevations, which some- times, possess a small opening. The mucous membrane on the lower surface of the tongue, when in the contracted condition, exhibits numerous fine parallel folds like those which, under aU circumstances, are to be found upon the sides, posterior to the level of the foramen caecum. The papillse freely projecting from the surface of the tongue . are termed, in accordance with their form, (a) filiform — papUlse filiformes; (b) club shaped — papiUae fungiformes; and (c) cir- GumvaUate — ^papillse circumvaUatse. The so-called filiform papillae are conical, and in the newly bom are simple and rounded at their extremity; whilst in adults they are compound, and frequently prolonged iuto hair-like processes. The clavate or fungiform papillae are thinner at the basis than at the apex, which appears expanded into a club-like body, and in adults is provided with secondary apices. The circumvaUate papiUae, lastly, are the largest, and are only distinguishable from the fungiform by the wall of mucous THE TONGUE, BY E. KLEIN. 515 membrane which surrounds them ; and this is so indistinct in most instances in newly born children, that no difference can be discerned between them and the clavate papillse. As regards the distribution of these various papillse on the tongue of Man, the papillse filiformes are spread in nearly equal numbers over the whole dorsal surface of the horizontal part, and on the edges. The fungiform papillse are found on the anterior portion of the dorsal surface, and chiefly near the tip and edges ; towards the median line of the posterior portion they become more sparing and small, and altogether cease at the root of the tongue. It only happens in some few cases that filiform papillse are found ra the latter region, and still more rarely the fungiform. The papillse circumvaUatse are most limited in number; they are placed on each half of the tongue at the junction of the dorsum and the root, and are so arranged that they form a V, the point of which is at the foramen csecum. The epithelium both of the upper and lower surfaces is tesselated and laminar ; in the filiform papillse of the tongue of adidts the pavement cells are arranged in an imbricated manner, and are provided with longer or shorter processes which project freely beyond the papiUse ; the most superficial flattened and homy cells sometimes form solid hairs or fibres, freely projecting beyond the secondary papillse. The epithelium of the tongue is elsewhere similarly formed to that of other parts of the oral cavity. The mucosa is thinner in the fore or horizontal part of the tongue in Man, and is, at the same time, much more intimately connected with the subjacent muscles than in the descending portion, where, on account of the abundant loose submucous tissue with numerous glands imbedded in it, it is easily mova- ble; its elements are the same as those of the mucosa in other parts of the oral cavity ; fibres of connective tissue being united into fasciculi, and forming a close network that is connected with the deeper tissues by strong trabeculse. The so-called septum cartUagineum of the human tongue, which, arising from the hyoid bone, appears as a dense vertical median plate situated between the Genio-glossi, and extending through the whole length of the organ, gradually diminishing 516 THE INTESTINAL CANAL, BY E. KLEIN AND E. VERSON. in height towards the apex, is, as Kolliker* has shown, incor- rectly named, since it is composed exclusively of connective tissue. The mucous glands of the human tongue occupy the sides and root of the organ ; amongst the former are those described by Blandinf and Nuhn.J Nuhn found at the apex of the tongue of Man, lying beneath the mucous membrane and a layer of longitudinal muscular fibres formed by the styloglossus and longitudinalis inferior, a symmetrically placed pair of glands, from seven to ten lines long, three to four and a half lines broad, and one and a half to two and a half lines thick, opening by five orifices on the lower surface of the apex. N. Ward§ once found at this poiut an azygous gland, placed transversely, one-third of an inch broad, and one-eighth of an inch long, with three fine excretory ducts. On the lateral border of the tongue, near the styloglossus, there may also be found a median and a more constant poste- rior group of glands, which either open close to the edge of the tongue, or more rarely in the floor of the mouth. The glands at the root of the tongue form, beneath the posterior non-papillated portion of the mucous membrane, a continuous layer of six millimeters in thickness, partly imbedded in the musculature. || The excretory ducts of these glands open, in the newly bom infant, iu the hollows between the ridges ; but in adults, in some instances, in the so-caUed crypts of the root of the tongue, which, according to Salter, IF constitute reservoirs for the acinous glands. Many of these reservoirs extend, according to this observer, as elongated, sometimes branched, passages for one-half to three-fourths of * Beitrdge zur Anatomie der MundhohU, Wiirzhurger Verhandlung, Band ii., p. 169. t Anat. topograph. Paris, 1834, p. \15. X A. Nulm, Ueher eine hisjetzt noch nicht naher heschriebene Driise im Innern der Zungenspitze, " On a hitherto nndescribed gland in the apex of the Tongue." Mannheim, 1845. § N. Ward, he. cit. II Henle, Splanchnologie, p. 141 . II Todd's Cyclopcedia, Vol. iv., p. 1140. THE TONGUE, BY E. KLEIN. 517 an inch beneath the surface, and receive at various points the excretory ducts of the mucous glands. In the wall of these so-called crypts of the root of the tongue, according to KolHker,* closed follicles filled with lymph corpuscles are imbedded. He describes each of these saccular glands which receive at their base the excretory duct of an acinous mucous gland, as consisting of a thick-walled capsule, surrounded externally by a fibrous sheath, and lined internally by a prolongation of the oral epithelium. Between these two, and contained in a delicate, fibrous, vascular, and at the free surface papiUated matrix, lie a number of closed lymph follicles of 01 to 025 of a millimeter in diameter, forming a continuous, but for the most part single layer. Huxleyt has corroborated generally the correctness of the description given by KdUiker of the glands at the root of the tongue, but finds the crypts of the mucous membrane sur- rounded, not by closed foUicles, but by an indifierent cell con- taining tissue, traversed by capillaries. Sappeyij: has only observed the acinous glands opening into the crypts; but not the closed follicles; and whilst Sachs§ is very doubtful of the presence of follicles in the wall of the sacculi, Franz Gauster and Eckhard|| give their support in. all respects to the state- ments of KoUiker. GerlachlT states that he has found follicles in the wall of some only of the lingual saccuh. The conclusions at which Arthur Bottcher ** arrived, have quite a different tenor. He found * Seitrdge zur Anatomie der Mundhohle, Wiirzhurger Verhandlung, Band ii., p. 177. t Huxley, " On the Ultimate Structure and Relations of the Malpighian of the Spleen and Tonsillar Follicles," MicroscopicalJournal, Vol. ii.,p. 74. X Recherches sur la structure des Amygdales et des glands situees sur la base de la Langue, Comptes rendus, 1855, No. 22. § Observationes de Lingua structura penitiori, Vratislav, 1856 ; and Zur Anatomie der Zungcnbalgdrusen und Mandeln, Reichert and Du Bois Raymond's Archivf. Anat. «. Physiologie, 1859, p. 196. II G. Eckhard, Zur Anatomie der Zungenbalgdriisen und Tonsillen, Vir- chow's Archiv, Band xvii., p. 171. ^ S^andbuch der Gewebelehre, 1854, p. 297. ** Arthur Bottcher, Einiges zur Verstandigung in Betreff der Balgdriisen 518 THE INTESTINAL CANAL, BY E. KLEIN AND E. VEESON. 1. That there are some tongues which do not possess any saccular glands. 2. That the occurrence of exceedingly well-developed sacculi is coincident with disease of the mucous membrane. 3. That between these two there are intermediate conditions in which it is often difficult to decide whether a slight elevation of the mucous membrane of the tongue, with a duct in the centre, is to be regarded as a saccular gland or not. He is therefore of opinion, (1) That in the healthy tongue there are no saccular glands; (2) That these are swellings caused by disease in the immediate vicinity of the ducts of the mucous glands; and that consequently the follicles in their interior are also neoplastic pathological formations. I am able to corroborate the statement made by Bottcher, that there are some tongues in which no follicular glands are present, and to add that in such cases the mucous membrane in different parts and to a variable extent of the root of the tongue, as well as the loose tissue of the soft palate of the uvula, and of the upper pharyngeal wall, is infiltrated with lymph corpuscles. These infiltrated parts are destitute of a distinct limiting membrane or capsule. The flat lenticular elevations of the root of the tongue usually present in adults are merely portions of the mucous membrane in which conglobate glandular substance is imbedded. The central orifice they exhibit is the entrance to a little pit which, like the projections themselves, is lined with tesselated epithe- lium. At the root of the tongue in the newly bom infant the mucous membrane presents no saccular glands. It only ex- hibits here and there in the above-described ridges, between :which the mucous glands open, isolated small or larger groups of cellular elements. These are also present at the bases of the papilla of this part, and in the tissue of the mucosa. The foramen csecum, situated in the descending portion of the tongue, though not always, and indeed, according to Boch- an der Zungenwurzel, " A few Observations explanatoiy of the nature of the follicular glands at the root of the Tongue ;" Virchow's Arckiv, Band xviii., pp. 190—220. THE TONGUE, BY E. KLEIN. 519 dalek, junior,* only thirteen times in fifty cases, is continued, by its fundus or posterior wall, which presents a larger or smaller opening directed backwards in the muscular substance of the tongue, into a simple or branched csecal ductus excre- torius linguEB, so called because it constitutes the excretory duct common to a large number of mucous glands. The epithelium of the foramen csecum is of the ordinary transitional variety ; that of its excretory duct, as well as of its cascal appendix, is cylindrical and ciliated. The foramen c^cum^ according to Bochdalek, is not formed by an increase in depth of the most posterior papilla circumvaUata. In regard to the lymphatics of the tongue, Sappeyf- has shown that delicate vessels proceeding from the close lymphatic plexuses of the mucous membrane penetrate into the papillse, and form a superficial network. According to Teichmann, % the lymphatics are confined to the mucosa and submucosa, and form a plexus with coarse deeply situated and more delicate superficial vessels. In the papillse fiUiformes, a few vessels with c^cal termina- tions, proceeding from a capillary ring, enter some of the papillse. At the base of the papillse fungiformes, again, a circular plexus of vessels is found, and lymph capillaries are present both in the circumvallate papillEe and in. the adjoining tissue. The muscular fibres of the tongue are vertical, transverse, § and longitudinal, the first set belonging to the musculus per- pendicularis at the apex, to the genio-glossus in the middle, and to the lingualis and hyoglossus at the sides. Between these vertically arranged fasciculi run those of the transversus linguse, and in part also of the styloglossus, directed in each half of the tongue from the septum towards the lateral surface. Finally, in immediate proximity with the mucous membrane, * Bochdalek, junior, Tleher das Foramen Ciscum der Zunge, Oester- reichische Zeitschrift fur Seilkunde, Nos. 36 — 46. t Sappey, Comptes rendus, 1847, p. 26. J Teichmaim, Das Saugadersystem vom anatomische Standpuncte. leip- z-'g, 1861, p. 113. § Salter, Todd's Cycloptsdia, p. 1125; and Kolliker, loo. cit., p. 169. 520 THE INTESTINAL CANAL, BY E. KLEIN AND E. VERSON. are the longitudinal fibres belonging to the longitudinalis superior and inferior, as well ^as the greater part of the styloglossus. As a general rule, the vertically ascending as weU as the transverse fasciculi penetrate into the mucous membrane through those of the longitudinal muscles, becoming, at the same time, considerably thinner. They also decussate with each other, both before they reach the longitudinal fibres, and after they have emerged from them, when they enter into the mucous membrane. The longitudinal muscles give off several small fasciculi and fibres to the mucous membrane. In the cat tte filiform papillae situated about the middle of the dorsal surface are best developed ; they are here also most numerous, and each is prolonged into one or several recurved horny points. Towards the lateral surfaces of the horizontal portion they rapidly diminish ia size, and at the edge cease to be distinguishable to the naked eye ; so that here the papillse fungiformes, which elsewhere on the dorsal surface are situated at tolerably regular distances between the filiform, are seen to project as whitish beads, at considerable dis- tances apart. It is only at the most anterior part of the tongue that the filiform papillse are distributed over its edges, and extend for a short distance on the inferior surface. At the border of 1;hat part of the tongue which corresponds to the junction of the horizontal with the descending portion is found a longitudinal series, from ten to fifteen m number, of cylindrical filiform papillse, capitate at their extremities, of which the centre ones are longer (three millimeters) than either the anterior or posterior (one millimeter). Towards the root of the tongue the filiform papillse decrease in number and size, and appear in the form of isolated very broad projections, ter- minating in a short, soft, recurved point. In rabbits, on the dorsal surface of the tongue, as far back as the descending portion, and on the upper part of this, only closely approxi- mated papillae filiformes are found, which are absent at the edges, except where the horizontal is continuous with the descending portion. Over the well-known whitish elongated oval elevation of the tongue of the rabbit the papillae are somewhat larger than on other parts of the dorsal surface. Behind this elevation the mucous membrane presents a smooth surface as far as two small projections constantly situated on either side of the median line, and apparently belonging to the papillae circumvallatEe. THE TONGUE, BY E. KLEIN. 521 At the junction of the horizontal with the descending portions on the border of each side of the tongue is found a sHghtly depressed semi-circular spot, the periphery of which touches the posterior part of the oval prominence. The surface is not smooth, but covered with delicate, "parallel, vertically arranged folds, on a few of which a filiform papilla may be here and there discerned. This portion, as well as the above-mentioned minute folds at the border of the tongue in man, and- the group of papillae found at the junction of the horizontal and descending portions of the tongue in the cat, correspond to the peculiar organ described by Weber,* and especially by J. C. Mayer, f in many mammals under the term of papUla hngualis foliata. The papiUsB of the tongue of the rabbit appear considerably shorter than those of man, and this is due to the absence of depressions in the epithelium between them. The thickness of the epithelium diminishes from before backwards, and also towards the sides ; yet, posterior to the oval prominence, is as thick as at the apex of the tongue. The structure of the mucosa does not differ from that of man. Its thickness also diminishes from the tip towards the oval prominence. At the root of the tongue the fasciculi of muscular fibres situated beneath the mucosa form a rectangular network, in the loculi of which are contained the lobules of the acinous glands. The excretory ducts of these glands penetrate the mucosa in a vertical direction to reach the surface. Numerous small masses of lymph corpuscles are to be met with around and between the lobules of the glands. In the depressed semi-circular portion of the border of the tongue the lami- nated pavement epithelium is much more attenuated on the margin of the folds than on their sides. The depths of the folds amount to 0'45 of a millimeter, and the mucous membrane projects into them in the form of an acute angle. The excretory ducts of large acinous glands open into the grooves intermediate to the folds, the relation of which to the muscular fasciculi is similar to that abeady described in the case of the glands at the root of the tongue. A considerable number of nerves, * Weber, in Hildebrandt's Lehriuch der Anatomie, Band., iv, 4. Aufl. p. 150. t J. C. Mayer, Untersuchungen aus dem Gebieie der Anatomie, etc. Bonn, 1842, p. 25. S22 THE INTESTINAL CANAL, BY E. KLEIN AND E. VEESON. the fibres of whicli are all medullated, are contained in the mucous membrane at the bottom of the folds. The transversus linguae exhibits a looser arrangement, as it extends from the middle line of the upper surface to the lower, in that its fasciculi describe arches, which diminish in length towards the border of the tongue. In the tongue of the/ro^ the papillae filiformes are distributed over the whole dorsal surface ; towards the posterior cornua they diminish in number and size, and cease at some distance from their apices. There is also a lateral zone of the dorsum extending along the whole length of the tongue, and from two to three millimeters in breadth, which is destitute of papillae. The fungiform papillae are similarly arranged. The two forms are most numerous and largest at the anterior part of the dorsal surface. The papilla filiformes are thin and long, but towards the cornua of the tongue they are somewhat broader. The epithelium, throughout the entire cavity of the mouth, consists of a laminated and cUiated columnar epithelium, with the exception of the apices of the papillte, where the most superficial cells are short cylinders, destitute of cUia.* Neither Hartmann nor Hoyerf were able to recognise the continuity of the processes of the columnar epithelium covering the papillae with the connective tissue corpuscles, as described by Billroth| and Axel Key. On the lower surface of the tongue the epithelium is formed by two or three layers of pavement cells, the most superficial in some parts bearing ciha. A nerve trunk, composed of dark-edged fibres, occupies the centre of the fungiform papillae, whilst at their periphery is a capillary plexus opening into a central vessel ; situated peripherically also are muscular fibres which frequently undergo division in their passage upwards. Moreover, transversely situated muscular fibres extend into the fungiform, § and into some of the filiform papillae, though they can seldom be followed to the apex. The glands of the tongue of the frog are pretty equably distributed over the whole of the dorsal surface ; anteriorly they are more closely assimilated to the type of the acinous glands than posteriorly. The * Leydig, Histologie, 1857, p. 307. Axel Key, Reichert and Du Bois' Archm, 1861, p. 228. Hartmann, idem, 1863, p. 634. t Hoyer, Mihroshopische Untersuchungen uber die Zunge des Frosches, Eeiehert and Du Bois' Archiv, 1859, p. 601. X Ueher das Epithel der Froschzunge, Miiller's Archiv, 1859, p. 159. § Waller, Philosophical Transactions, 1847. B. THE PHAEYNX, BY E. KLEIN. 523 excretory ducts, especially of the anterior part, support laterally and terminate at their extremities in hemispherical enlargements, or they pursue a closely coiled course, and are then more deeply imbedded between the muscles. As a general rule, they are only surrounded by muscular tissue at their fundus. The glands are lined by columnar epithelium, the cells of which become shorter in the deeper acini. A few of the cylindrical cells near the orifice sometimes support cilia. At the posterior part of the dorsal surface, and especially on the posterior processes of the tongue, the glands constitute longer o shorter tubes, which are for the most part inflated or irregularly prominent at their fundus. Here also their fundus is imbedded amongst the muscles which run up from the deeper parts and accom- pany the gland ducts for a variable distance towards the surface. The cylindrical epithelium with which they are lined behaves in the same manner as that of the glands of the anterior portion. Division of muscular fibres occurs, to a considerable extent, in the frog, as well as in the newt, calf, bat, sheep, goat, and cat, and also in man. In man, Rippmann* saw simple and individual muscular fibres run out into two, three, or even four moderately long branches. According to Remak,t microscopic ganglia are situated on the branches of the glosso-pharyngeus, and of the ramus lingualis. And he believes the same relations to subsist between the glands and ganglia of the tongue, as between the submaxillary gland and the ganglion submaxillare. B. Pharynx. With the pharynx the digestive tract begins to be indepen- dent, and at its lower part assumes a tubular character, whilst, at the same time, it is distinctly differentiated into mucous membrane, muscular layers, and an external investing fibrous membrane. * Th. Rippmann, Veher das Vorkommen von Theilungen der Muskelfasern in der Zunge der Wirielthiere und des Menschen, " On the occurrence of Division in the muscular fibres of Vertebrata and of Man; " Henle and Pfeuffer's Zeitschrift, 3. Reihe, Band xiv., p. 200. t Ueher die Ganglien der Zunge bei Saiigethieren und Menschen, " On the Ganglia of the Tongue in Mammals and in Man ; " Miiller's Archiv, 1852 Htft 1, p. 58. 524 THE INTESTINAL CANAL, BY E. KLEIN AND K. VERSON. The epithelium of the mucous membrane in the portions immediately adjoining the nasal cavity is laminar and tes- selated. This form of epithelium extends, accordiag to Schmidt,* to the posterior edge of the so-caUed pharyngeal tonsils, but their anterior portion, as far as the orifice of the Eustachian tube, possesses a columnar and ciliated epithelium. The distribution of the latter in the regions in question is most extensive in the new-bom child, extending here over the whole of the upper portion of the pharynx, known as the cavum pharyngo-nasale. In the adult, on the other hand, it never extends over more than the upper third. Both the epithelium and mucosa are similar in their characters to the same structures of the soft palate. The free surfacef of the nasal region of the pharynx, occupying the interspace between the Eustachian tubes, and extending from the posterior portion of the roof of the nasal cavity to the anterior border of the foramen magnum, exhibits in most instances a delicate longitudinal striation, with laminae or folds separated by deep fissures, which to some extent become united, giving rise to a plexiform pattern ; and fre- quently the surface is covered with low elevations, traversed by a variable number of short, often irregularly running fissures. These folds exhibit numerous whitish, poppy-seed- like enlargements, with a considerable number of roundish pores, which are partly recognisable as the entrance to little isolated pits of the mucous membrane, but are chiefly the orifices of acinous glands. A larger opening, though not constantly present, is found in the lower half of the median line of the roof of the pharyn- geal cavity. It constitutes the entrance to the process of the pharyngeal arch which ascends to the body of the occipital bone, and is usually surrounded by acinous glands, but some- times also by a muscle. It has been named by J. C. Meyer the Bursa pharyngea. * Schmidt, he. cit. t Luschka, Das adenoide Qewebe der Pars Nasalis des menschlichen Schlundkoppes, " The adenoid tissue of the nasal portion of the Pharynx of Man ; " Archiv filr wissenschaftUche Anatomie, v. Max Schultze, Band iv., Heft 1, Seite 5—9. B. THE PHARYNX, BY E. KLEIN. 525 The thickenings or folds of the mucous membrane of the pharyngeal arch, as weU as the walls of the bursa above de- scribed, consist of a loose vascular tissue infiltrated with lymph corpuscles, exhibiting in parts the same structure as that which we have seen in numerous portions of the soft palate. At those points where the poppy-seed-like bodies are observed, the mu- cous membrane presents, over a larger or smaller surface, an adenoid structure closely packed with lymph corpuscles. These infiltrated spots, although constructed on the same plan as the lymph follicles, have, like the similar spots at the root of the tongue, where they are more sparing iu number and smaller, no distinct investing membrane. Luschka* has denominated this part, first described by La- cauchie,f the TonsiUa Pharyngea, and he agrees with KoUiker in regarding it as an aggregate of lymphatic glands. Henle,J on the other hand,^ holds it to be conglobate gland substance. It forms a mass of about eight millimeters in thickness, which extends to between the orifices of the Eustachian tubes, from the posterior extremity of the roof of the nasal cavity, with an average length of three centimeters. The glandular tissue Hs in great part divided into laminae with deep intervening fissures, or is arranged in the form of round sacculi, the walls of which, having an average diameter of one millimeter, are lined by ciliated epithelium and a con- tinuation of mucous membrane, communicating with the ex- terior by a very narrow orifice. The tissue of the mucous membrane covering the arch of the pharynx is differentiated from that of the lower part by the circumstance that it exhibits over surfaces of considerable extent the characters of lympha- tic glandular tissue. The mucous membrane of the middle third of the pharynx, though more sparingly than in the upper portion, is also in- filtrated with numerous cellular elements, which are either irregularly distributed through its substance or lie collected into dense masses in a vascular stroma. * Lusclika, Anatomie des Menschen. Tubingea, 1862, Band i., Absclmitt 1. t Traits d^Hydrotomie, 1853, Tab. ii., fig. 10. X Henle, Splanchnologie, p. 146. O O 2 526 THE INTESTINAL CANAL, BY E. KLEIN AND E. VEKSON. In infants the mucous membrane exhibits a great number of oblong nucleated elements, the extremities of which are drawn out into fine pointed processes which penetrate between the fibres of the tissue. This peculiarity may be observed in several parts of the above-described portions of mucous membrane, and appears therefore to be characteristic of an embryonic con- dition of the tissue. Wherever the epithelium is laminar and tesselated, numerous papillse,; narrow at their base, and clavate at their free extremity, project from the surface of the mucosa, and penetrate the epithelial layers to about half their depth ; but where the epithelium of the roof of the pharynx is lami- nated, and composed of cylinders supporting cilia, the papillse are altogether absent. The large vessels form a plexue beneath the epithelium, giv- ing oif finer branches, which either pursue a longer or a shorter course parallel to the surface, or form loops immediately be- neath the epithelium. In the middle third of the membrane in adults, and especially in the lower parts, are numerous pa- pillse arranged with tolerable regularity. In the upper parts they are in some parts imperfectly developed, and here and there are altogether absent. In the lower third the papUlse are both constantly present and numerous. In the infant the papillw are only feebly developed, either in the form of slight sinuosities of the • mucous membrane projecting into the epithelial layers, or as sharply pointed papillary elevations composed of connective tissue and blood- vessels, especially over those parts of the membrane present- ing strise or folds, which penetrate. to a variable extent iato the epithelium. As it approximates the muscular tissue the structure of the mucous membrane becomes looser, forming the submucous tis- sue ; and the fasciculi, which constitute a plexus vnth meshes of various sizes, are arranged in the upper and middle third ia a horizontal direction, or run obliquely backwards and out- wards between the fasciculi of the muscular layer to the outer fibrous layer, as well as in the opposite direction from this in- wards and downwards, some few fasciculi penetrating between the muscles into the submucosa, in which they are gradually lost as they descend. In the lower third, the fasciculi of the B. THE PHARYNX, BY E. KLEIN. 527 mucosa pursue various directions, but those of the submucosa are chiefly directed downwards. The acinous glands of the pharjnax, especially ia the middle and lower parts of the upper third, form groups, the excretory ducts of which open with wide orifices. The individual glands are oval, with their long diameter parallel to the long axis of the tube. In the lower third they diminish considerably in number, so that at the upper part of this they only occur in an isolated condition, whilst below they are but rarely met with. The depth of the mucosa varies with the thickness of the glandular layer, but diminishes gradually in- the lower third towards the oesophagus. The larger nerve trunks He in the submucous tissue, and run for the most part in. a longitudinal direction, whilst their branches form a deep and a superficial plexus, in. the latter of which Remak* and BOlroth observed the presence of microscopical ganglia. The lymphatics of the pharynx are numerous, and, according to Teichmann,-f' are directly continuous with those of the nose, oral cavity, trachea, and oesophagus. The outer fibrous layer of the posterior waU of the pharynx^ attached above to the base of the skull, extending downwards, and containing a median tendinous fasciculus which arises from the tuberculum pharyngeum, consists chiefly of strong parallel bundles of fibrous tissue, with a variable amount of finer and broader elastic fibres. These for the most part de- scend obliquely with the fasciculi accompanying the nerves and bloodvessels, and with others derived from the submucous layer form sheaths' for the pharyngeal muscles, and give ofl" the secondary septa for the smaller muscular fasciculi. The 'muscular layers of the posterior, and partly also of the lateral, walls of the pharynx are so arranged as to form an es- sentially circular external and an internal longitudinal layer. The former is composed of the Constrictores pharyngis, the * Remak, Ueher peripheriseJie Ganglien an den Nerven des Nahrungsrohre&, Miiller's Archiv, 1856, p. 189 ; " On the Peripheric Ganglia of the Nerves of the Alimentary Canal." A contest respecting priority with Meissner, in which it was shown that Kemak had previously, in 1840, found ganglia in the tongue and on the pharyngeal branches of the Glosso-pharyngeus. t Loc. cit. 528 THE INTESTINAL CANAL, BY E. KLEIN AND E. VEESON. latter is formed by the Stylo-pharyngeus and Thyreo-pharyngo- palatinus,* from the pharyngo-palatine portion of which a few- fasciculi are given off which pursue a horizontal direction, uniting on the posterior wall of the pharynx with those of the opposite side to form a series of arches with their convexity directed downwards. A few small fasciculi are also given off from the most internal muscular bundles, especially at the lower part of the pharynx, which, running downwards, penetrate the mucous membrane obliquely, and terminate in it. The mucous membrane of the pharynx, which is connected by means of short connective tissue fibres with the posterior surface of the larynx, presents the same structure as that of the lower third of the posterior wall. The glands are here also elongated, and form a contiauous layer above, whilst they diminish in number below to such an extent that it is rare to meet with one on the anterior wall of the oesophagus. The excretory ducts of these glands are di- rected obliquely downwards, so that on examining transverse sections, numerous ducts may be found without any of the glands being present. They become somewhat wider beneath the epithelium, and here possess, lining their interior, a series of well-marked cylindrical cells, subjacent to which are two or three rows of smaller spheroidal cells with comparatively large nuclei. Adipose tissue is found in considerable quantity in adults, occupying the interspaces of the muscular fasciculi and of the glands of the mucous membrane situated on the posterior sur- face of the larjmx. C. CESOPHAGUS. Commencing at the level of the lower border of the cricoid cartilage, the alimentary canal extends, in the form of a com- pletely closed tube, to the foramen cesophageum of the dia- phragm. In the undistended condition the mucous membrane forms parallel longitudinal folds, and is attached to the sub- jacent muscular coat by loose connective tissue. * Luschka, Yirchow's Archiv, Band xKi., p. 485. C. THE (ESOPHAGUS, BY E. KLEIN. 529 In Man it is lined by laminated pavement epithelium, the cells of which, both in their form and arrangement, resemble those of the lower part of the pharynx. The membrana mucosa is situated between the muscular layer of the mucous membrane which commences with the oesophagus, and the epithelium, and it is separated by this muscular layer from the thicker layer of the submucous tissue which occupies the interval between the muscularis mucosse and the muscularis externa. In newly bom children* the mucosa exhibits in many parts the structure of adenoid tissue. In others, again, numerous bloodvessels are found, running for the most part in a longi- tudinal direction beneath the epithelium, and accompanied by a sparing amount of connective tissue derived from the external portion of the mucous membrane. In adults the longitudinal fasciculi of connective tissue de- rived from the submucosa run inwards between the fasciculi of muscularis mucosae, and then either pursue a sinuous course parallel to each other, or form plexuses. A great number of cellular structures are constantly found amongst them. The surface of the mucous membrane is beset in adults with a large number of conical papillse 03 — 0'5 of a millimeter in length, which project into the epithelium; but in children their presence is only indicated by sUght inflections of the line of attachment of the epithelium. The muscularis mucosse, or muscular layer of the mucous membrane, consists of fasciculi of smooth muscular tissue run- ning longitudinally, which are only feebly developed in the uppermost part of the oesophagus, where they are separated from one another by large quantities of the mucous tissue ■ lower down they become coarser and more closely approxi- mated, so that the muscularis mucosae here forms a continuous muscular layer. The septa of the several fasciculi are continuous with the mu- cosa on the one hand and the submucous tissue on the other. * E. Klein, Ueher die Vertheilung der Musheln des (Esophagus, etc. " On tlie arrangement of the Muscles of the CEsophagus ; " Sitzungsherichte der h. k. Akad. der Wissenschaften zu Wien. Mai heft, 1868. 530 THE INTESTINAL CANAL, BY E. KLEIN AND E. VEKSON. The thickness of this muscular layer is somewhat greater in general ia the anterior wall of the oesophagus than in the pos- terior. The submucous tissue is about four times as thick as Fig. 105. Fig. 105. Transverse section through, the lower part of the oesopha- gus of the newly horn Child, a a, epithelium ; h b, mucosa ; c, muscu- laris mucosae; d, submucous tissue; e, layer of circular muscular fibres; /, longitudinal muscular layer ; ff, external fibrous layer ; at h h, are seen two of the ganglia of Auerbach. the mucosa, and is composed of longitudinal fasciculi of con- nective tissue fibres that run parallel to one another, and are always intermingled with finer and coarser elastic fibres. Ves- sels and nerves derived from the muscularis externa are found in this loose tissue, the nerves running obliquely towards the muscularis mucosae. The fasciculi of the outer portion of the submucous tissue are directly continuous with the external fibrous membrane, and thus form the septa of the muscularis externa. Acinous glands are rare and isolated, and less abundant in the posterior wall of the oesophagus than upon the anterior. On the latter they generally decrease in number from above to near the middle, but increase to some extent from this point downwards. They are small and oval, with their longer diameter arranged vertically ; they lie in the submucous tissue, C. THE (ESOPHAGUS, BY E. KLEIN. 531 close to the muscularis mucosEe, which their excretory ducts penetrate obliquely in a downward direction, opening on the surface of the epithelium with a constricted orifice. The muscularis externa, or outer muscular coat, is composed in Man of an external longitudinal and an internal circular layer of fibres. The former is arranged in three divisions ;* the middle, and by far the strongest, arising from a triangular elastic membrane attached to the posterior surface of the cricoid cartilage ; the two lateral, which partly descend for a short distance internally to the circular layer of the oesophagus, arise from the elastic bundles ia which a portion of the Thyreo- pharyngo-palatinus muscle terminates. The longitudinal fibrous layer in its further course is strengthened by the musculus broncho-oesophageus.t The circular fibrous layer gives off on each side the musculus crico-pharyngeus, and receives accessory fibres in the thoracic cavity from the musculus pleuro-oeso- phageus.i The circular layer continually increases ia thickness as it descends, whilst the longitudiaal layer, which exceeds the circular layer in thickness m the first fourth, continually diminishes as it descends. The external muscular layer is not everywhere of equal thickness; in adults it is on the average 1'5 to 2 millimeters thick, and, according to Schmauserj§ is at the upper part more strongly developed on the anterior waU. than upon the posterior, — then diminishes as it descends upon both surfaces, but espe- cially upon the anterior, until in the lower third it is equally developed throughout the whole circumference of the tube. A few smaller fasciculi, both from the internal circular and from the external longitudinal fibrous membrane are given off, which descend vertically, internal to the former, and external to the latter ; the fasciculi are particularly large in the lower fourth, and are derived from the circular layer, becoming verti- cal as they descend. The tendons of the fasciculi of the smooth muscular tissue * Henle, Splanchnologie, p. 141. t Hyrtl, Zeitschrift der Gesellschaft der Aerzte zu Wien, 1844, p. 115; and Treitz, Prager Vierteljahresschrift, 1853, Band i. f Hyrtl, he. cit. § Schmauser, Dissert, inauguratis, 1866. 532 THE INTESTINAL CANAL, BT E. KLEIN AND E VERSON. of the oesophagus extend, according to Treitz,* into the external fibrous membrane. The fibres of the muscularis externa of the upper fourth of the oesophagus in Man are for the most part transversely striated. But besides these, fasciculi of smooth muscular fibres are met with sometimes running vertically ex- ternal to the longitudinal muscular layer, at others running circularly in the circular fibrous layer, and at others vertically between the fibres of this latter layer. In the second fourth the smooth muscular fibres are so abun- dant that they sometimes exceed those of the transversely striated, predominating especially in the anterior wall amongst the longitudinal, and in the posterior wall amongst the circular layers of muscular tissue. The muscularis externa, in its lower half, is composed of smooth fibres exclusively. Externally the muscular layers are invested by a fibrous sheath composed of connective tissue and elastic fibres, which for the most part run in a longitudinal direction. At certain parts between the circular and longitudinal mus- cular fibre layers the nerves form quite a continuous layer, the branches of which perforate the circular muscular coat, ia order to reach the submucous tissue. Amongst the nerves running between the circular and longitudinal layers ganglion cells, partly isolated, partly enclosed in a nucleated capsule, are found, as well as groups of ganglion cells united together by means of their processes ; moreover, a few ganglion cells occur in the smaller nerve trunks as they run through the mucous membrane. Remak-f- has described true ganglia as being situated on the oesophageal branches of the vagus. The lymphatics, according to Teichmann,j partly run in the mucosa, partly in the submucous tissue, but do not form a dou- ble capillary network as in the wider portions of the tube. In the (Esophagus of the Dog the muscularis mucosse does not • Treitz, he. cit. t Ueber peripherisehe Ganglien an den Nerven des mensehlichen Nah- rungsrohres, '■ On the peripheric Ganglia situated upon the Nerves of the Alimentary Tuhe in Man ; " Miiller's Archiv, 1858, p. 189. X Teichmann, Das Saugader System, " The Lymphatic System," loc. cit. C. THE OESOPHAGUS, BY E. KLEIN. 533 form a continuous 'layer, as in Man, but first makes its appearance in the middle of the upper fourth, in the form' of isolated longitudinal fasciculi, which, in the lower half, surround at various points the acinous glands, and sparingly accompany their excretory ducts nearly to the epithelium. The glands throughout the whole length of the oesophagus form a continuous layer, the thickness of which consider- ably increases in its lower part. In the loose submucous tissue, nodal points are scattered, consist- ing of stellate plexuses of elastic fibres which present a remarkable yellowish-green colour. The outer muscular layer of the oesophagus in the Dog is arranged in a much more complex manner than in Man. It is only in the upper half of the first fourth that it is composed of an external longitudinal and of a stronger internal circular layer. In the lower half of the first and the upper half of the second fourth, both layers are equally well developed, and are composed of fibres decussating obliquely, and at right angles. In the lowest part of the second, and throughout the whole of the third fourth, the inner layer is thinner, and becomes longitudinal, whilst the external is thicker, and is now circular. In the upper half of the inferior fourth, three layers are constantly present : an internal longitudinal ; a middle, . which is the strongest, circular ; and an internal, which is the thinnest, longitu- dinal. The latter is derived from the internal, but chiefly from the middle, which proceeded above from the external layer. In the lower half of the inferior fourth, three layers are constantly present : an internal oblique ; a middle, which is the strongest, transverse ; and an external, which is the weakest, longitudinal. The fasciculi of the outer muscular layer do not, therefore, pursue a rectilinear, but a well-marked spiral course. Smooth muscular fibres first make their appearance at about the commencement of the lowermost fourth of the external muscular layer, but even there they are confined exclusively to the innermost portion, which, immediately above the cardia is composed of smooth muscular fibres alone. The remaining layers are composed of striated muscular fibres up to the point of entrance of the oesophagus into the stomach. The nerves are arranged in the same manner as in Man, but they are more numerous. They He between the internal longitudinal and middle circular layers, and present ganglion cells which are either scattered or are arranged in series one behind the other. In the Rabbit the mucous membrane of the oesophagus resembles 534 THE INTESTINAL CANAL, BY E. KLEIN AND E. VERSON. ttat of Man, but its external muscular layer is like that of the Dog. The laminated pavement epithelium increases in thickness down- wards. The mucous membrane is generally of looser texture than in Man. When a muscularis mucosa exists, it is composed of an inner portion, which usually forms a delicate plexus, and a much thicker external portion containing longitudinal bundles of fibres, supporting, especially on its outer surface, large vascular trunks. The papillae of the mucous membrane are few in number in the upper part, of unequal size, conical, with a broad base ; but lower down they become more numerous, so that just below the middle they are in close proximity to each other. The muscular layer of the mucous membrane is deficient at the commencement of the oesophagus ; but at a somewhat lower plane it makes its appearance in the form of small scattered fasciculi, composed of a few unstriated fibres, running in a longitudinal direction, and separated by layers of mucous tissue of considerable thickness. In the lower fourth it forms a continuous layer about 0*04 of a millimeter in width, which is traversed by numerous vessels distributed to the papillae. I have not been able to demonstrate acinous glands in the oeso- phagus of the Kabbit. The external muscular layer, having an average thickness of 0'85 to 0'2 of a millimeter, is composed, like that of the Dog, of spiral fasciculi, which are thus arranged : In the upper- most portion there are two layers, nearly equal in thickness, of which the internal is circular, the external longitudinal in direction. In the second fourth the circular and longitudinal layers run more or less at right angles to their previous course, so that in the third fourth their relative position is entirely changed, and we now find an internal layer, consisting of longitudinal fasciculi, a middle of circular, and an external of longitudinal fasciculi. In the lowermost fourth, although the thickness of these layers differs, their disposition is unaltered. The most internal layer here becomes constantly thinner, whilst the middle and external progressively increase in thickness. The two first maintain the direction they possess above, but the greater number of the fasciculi of the external layer run obliquely. Unstriated muscular fibres first appear in the lower fourth, and in the external muscular layer of longitudinal fibres ; at first, only in the form of small fasciculi, but lower down increasing so remarkably in number and size that they soon outnumber the striated fibres, both in the external longitudinal layer and in the external portion of the middle circular layer. In the lower parts of the inferior fourth the C. THE (ESOPHAGUS, BT E. KLEIN. 535 smooth fibres do not merely replace the transversely striated, but occur in great numbers as a new formation, so that these external layers in the vicinity of the eardia exceed the two others in breadth. Ra^dtsch* has found the following arrangement of the smooth muscular fibres to obtain in the Horse, Calf, Pig, Cat, and Rabbit. In the Horse the muscular layers of the oesophagus are entirely composed of transversely striated fibres as far as the thickening that is found about 20 — 25 centimeters above the cardiac orifice ; below the thickening, smooth fibres make their appearance in the inner layer, whilst they do not present themselves in the external layer till near the eardia. In all the above-named animals the transversely striated elements extend in both layers of the oesophagus to a variable distance from the eardia, always ceasing sooner in the inner than in the outer layer. This last statement is, however, opposed to that which, as mentioned above, I have found to occur in the oesophagus of the Rabbit. Ganglion cells are here stiU more frequently met with than in the Dog ; not only scattered amongst the fibres of the nerves running in the external muscular layer, but also in the lower fourth, in the form of microscopic ganglia, situated between the middle and external muscular layers. The mucous membrane of the oesophagus of the Rat is precisely similar to that of the Rabbit, in regard to all its parts — epithelium, papillae, and mucosa — as well as in the distribution of the muscular layer of the mucosa. The external muscular layer generally divides into a stronger internal and circular, and a thinner external longi- tudinal layer. Here and there the external muscular layer exhibits in its lowest portions an internal, strongest, oblique ; a middle, circular ; and an external, thinnest, longitudinal layer. All the layers are free from smooth muscular fibres as far as the eardia. The oesophagus of Birds presents many points of difi'erence from that of Mammals. In the fowl the mucous membrane is from 0-5 to 0'8 of a millimeter thick, and is covered with laminated pavement epithe- lium, the uppermost cells of which are tabular, and separated from each other by a broad, remarkably sinuous, intervening substance ; those * J. Ravitsch, TJeber das Vorkommen quergestreiften Muskelfasern im CEsophagus der Haussaiigethiere, " On the presence of transversely striated muscular fibres in the CEsophagus of domestic Animals ;" Virohow's Archiv, Band xxvii., p. 413. 536 THE INTESTINAL CANAL, BY E. KLEIN AND E. VERSON. of the middle layers are polyhedral, but rather elongated; -whilst those of the deepest layers are spheroidal, but usually somewhat flattened by mutual pressure, and when they surround a papilla, are directed obliquely towards its longitudinal axis. The mucous layer succeeding to the epithelium is a thick felt-like structure, composed of decussating fibres of varying size. From the surface of the mucous layer numerous small, conical, vascular papillae project into the epithelium. The glands of the oesophagus are tubular, and are situated in the mucous layer ; they are limited ex- ternally by the muscular layer of the mucosa, and partially project through that layer with their extremities. The fundus of each ex- hibits from five to seven or more hemispherical projections, so that they resemble acinous glands. Their excretory ducts, as well as their puUulations, are bounded by a very thin membrana propria, lined by a delicate narrow columnar epithelium. In hardened prepara- tions the cylinders are usually found empty (cup or goblet cells, Becherzellen), the flattened nucleus alone remaining attached to one side. These glands are always isolated, increase in number towards the crop, and are more sparingly distributed and smaller as they recede from this towards the cervical and the thoracic portions of the oesophagus. The muscular layer of the mucosa forms a continuous longitudinal layer of smooth fibres, situated external to the mucosa and its glands, and presenting, where it is in contact with the fundus of a gland, a slight projection and attenuation. Here and there small fasciculi are given off', which run for some distance circularly, and then again become longitudinal. The submucous tissue, containing the larger vascular trunks in its meshes, is continuous with the mucosa and the external fibrous layer of the oesophagus. The external muscular layer is exclusively composed of unstriated muscular fibres, grouped into larger or smaller fasciculi to form an internal circular, and an ex- ternal, somewhat thinner, longitudinal layer. Between these two layers is an almost continuous nervous layer, in which are found numerous ganglion cells, either isolated or united into a plexus. Towards the crop the mucous layer becomes more attenuated, and the glands fewer in number ; but the circular muscular layer increases in thickness in relation to the longitudinal. In the crop itself the epithelium presents the same characters as in the oesophagus. The mucous layer is here thinner, and there are no glands. The external muscular layer is more attenuated than in the oeso- C. THE (ESOPHAGUS, BY E. KLEIN. 537 phagus itself. The muscular layer of the mucosa is equal in thick- ness to that of the oesophagus, and is partially separable into an internal circular, and an external longitudinal layer. Hasse* found no glands in the cervical portion of the oesophagus nor in the crop of pigeons, but in the thoracic portion flask-shaped glands appeared, with a long narrow neck, and an internal lining of tesse- lated epithelium. In incubating pigeons he observed a remarkable thickening at the sides of the crop, due to a growth of epithelial cells filled with oil-drops, and resembling those in the milk follicles of Mammals. In the Newt and Frog the mucous membrane of the oral cavity behind the tongue passes directly into the mucous membrane of the intestinal tract, which has now become converted into a complete closed tube. The oesophagus of the Triton consists of an epithelium, a mucous layer, an external muscular layer, and an investing fibrous membrane. The epithelium, like that of the oral cavity, is columnar. The several cells are conical, with the narrow end more or less prolonged ; whilst the base, directed towards the free surface, is beset with long cilia. Their shape may either be simply conical or strongly ventricose near the surface, and then, becoming suddenly attenuated, send a long process into the deeper-lying parts ; or they may exhibit, when examined in the fresh state, a nucleated swelling in this process. Between the penetrating processes of the superficial cells fusiform cells are interposed, and between these again are here and there spheroidal cells vsdth relatively large nuclei. In transverse sections of the longitudinal folds of the mucous membrane the penetrating pro- cesses of the conical ciliated cells are not directed perpendicularly from the surface, but are curved at their extremities. Hence in many parts these processes appear to be continuous with the elements of the mucous membrane. The mucous membrane consists of broad fas- ciculi of connective tissue, which present a looser texture toward the external muscular layer, and there form larger meshes, whilst nearer the epithelium the tissue is more compact. Fasciculi of connective tissue penetrate perpendicularly to the surface between the fasciculi of the external muscular layer, decussating once or twice at their en- trance into the mucous membrane, and thus forming numerous spaces * C. Hasse, Ueher den (Esophagus der Tauhen, etc., "On the (Esophagus of the Pigeon ; " Henle and Pfeuffer's Zeitschrift, 3. Reihe, Band xxiii., p. 101. 538 THE INTESTINAL CANAL, BY E. KLEIN AND E. VEESON. of considerable size, which are either occupied by thin-walled large vessels, or, being lined with epithelium, probably belong to the lym- phatic system. Amongst these fasciculi extending towards the surface are found a variable number of fusiform elements, with rod-like or elongated nuclei. These are directly continuous with the fusiform cells of the innermost fasciculi of the external muscular layer, and are consequently to he regarded as smooth muscular fibre cells. There is consequently here no independent muscularis mucosas. In the small and delicate meshes of the mucous layer, large, irregular, or spheroidal masses of protoplasm lie isolated from one another. The external muscular layer consists exclusively of smooth muscular fibres, the contour of which is either rectilinear or sinuous, and which contain an elongated and often pointed nucleus. It is not everywhere of equal thickness-, and does not throughout its whole circumference consist of two distinct layers ; on the contrary, the external fasciculi interlace to a considerable extent with the internal, so that in trans- verse sections a close network of muscular fibres is found, interrupted only by a small quantity of connective tissue. In many instances the direction of the internal fasciculi is horizontal, and that of the ex- ternal, oblique, or more rarely longitudinal. There are no glands. In the oesophagus of the Frog the mucous membrane is lined with ciliated epithelium, similar in thickness and form to that already de- scribed in the Triton. In preparations hardened in alcohol, nothing but cup- or goblet-shaped cells are to be found over tracts of con- siderable extent. The mucous membrane is strongly developed ; its fasciculi pursue a horizontal course parallel to one another from without inwards till they reach the epithelium, beneath which, becoming bent at right angles, they assume a plexiform arrangement. The portion in contact with the external muscular layer, that is to say, the submucous tissue, contains the larger vascular trunks in its meshes. The acinous glands in the Frog form an almost continuous layer from 0'4 to 0-5 of a millimeter in thickness. The acini vary in size, and are rounded or oval in form. They are lined by an epitheUum consisting of closely compressed, rounded, or flattened by mutual pres- sure, cubical, or cylindrical cells. No muscularis mucosse exists in the upper part, but in the lower there is to be found in patches situ- ated externally to the glands a not very strong layer of longitudinal smooth muscular fibres, from which, as well as from the circular layer of the external muscular coat of the upper part, a few fasciculi are given off, that penetrate between the glands. C. THE CKSOPHAGUS, BY E. KLEIN. 539 The external muscular coat consists generally of an internal circular and an external longitudinal layer. Fasciculi of fibrous tissue of various size, given off from the fibrous sheath investing the muscular coat externally, penetrate between the muscular fasciculi, forming thin septa, and constituting the support of the larger vessels and nerves as weU as of the capillaries and the smallest nervous twigs. Before we pass to the consideration of the histology of the stomach we must investigate the mode of transition of the several layers of the oesophagus into those of the cardia. In the^ oesophagus of man the laminated pavement epithelium ex- tends to the cardia, where it ceases with a dentated border, and is replaced by a columnar epithelium. The mucous layer in its more restricted sense becomes rapidly thicker, in consequence of the additional series of glands that here make their appear- ance ; so that the muscular layer of the mucous membrane becomes constantly separated by a greater distance from the epithelium, and at the same time diminishes in thickness. The submucous tissue in general diminishes in thickness at the cardia, and is divisible into an internal looser and an external more compact layer. In the former lie the great vessels, whilst the fasciculi of the latter penetrate between the fasciculi of the muscularis externa. There are no acinous glands immediately above the cardia. The external muscular layer shows the most important changes ; the circular muscular fibres which are directly con- tinuous with those of the cardia are most strongly developed just above it ; at the cardia itself, and just below it, they again diminish in thickness. The disposition of the longitudinal fibres is similar, except that their fasciculi frequently decussate so that they form a dense plexus. At the same time, after as- suming this plexiform arrangement, some of them extend into the circular muscular layer, surrounding its most external fasci- culi in order to become still more internal at a lower point. According to Henle,* the longitudinal fibres of the cesophagus partly terminate at the cardia, but the majority are distributed upon the stomach, diverging from one another in various * Henle, Splanchnologie, p. 161. P P 540 THE INTESTINAL CANAL, BY E. KLEIN AND E. VEESON. directions. The middle portion of the fibres of tiie right half of the oesophagus extends uninterruptedly in thick masses along the upper curvature of the stomach ; the remainder radiate upon the anterior and posterior walls of the stomach in slightly- diverging fasciculi, arranged in a plexiform manner towards the lower curvature, to which, however, they do not reach. 'From the left half of the oesophagus only delicate fasciculi extend to the upper border of the fundus. Two sets of fas- ciculi attach themselves to the right and left diverging longitu- dinal fibres of the oesophagus, which, slightly curved outwards, and altering their course from the horizontal to the vertical direction, extend over the anterior and posterior surfaces of the stomach. These two sickle-shaped bands of fibres which de- cussate in their course downwards from the cardia upon the anterior and posterior wall of the stomach, are the continua- tions of the circular fibrous layer of the oesophagus.. The laminated pavement epithelium at the cardia of the DoG is replaced, as in man, by simple columnar epithelium ; the mucous layer becomes thinner at the cardia, since the gland tubes there present gradually increase in size. Consequently the muscularis mucosae, which in the lowermost portions of the oesophagus was situated between the glands for an area of 0'5 millimeter in breadth, becomes more externally placed in order to form a continuous layer at the base of the new series of tubes commencing at the cardia. The acinous glands of the mucous layer of the oesophagus do not cease at the cardia itself, but, becoming at the same time smaller, reach to a distance of three millimeters below the line at which the columnar epithelium of the stomach begins. These are some- times, although rarely, only the lowermost lobules of a gland, the excretory duct of which opens directly at the boundary line between the oesophagus and stomach, so that above the upper wall at the inner end of the excretory duct the lami- nated pavement of the oesophagus ceases, whilst below the lower wall the columnar epithelium of the stomach commences. In other cases two rows of acinous glands are found at the commencement of the cardiac portion, the excretory ducts of which open between the tubes with narrow calibre, that here begin to be developed. C. THE CESOPHAGUS, BY E. KLEIN. 541 The submucous tissue of the cesophagus likewise diminishes in thickness as it passes through the cardia into the stomach. The external muscular layer undergoes the following changes at the same part : — The fasciculi of smooth muscular tissue of the inner layer of the oesophagus lying next to the cardia, after having re- markahly increased in size, and assumed a transverse direction, attach themselves, without any defined line of demarcation, to the circular muscular layer of the stomach, the fasciculi of which are likewise very strong. Those fasciculi of the inner layer that are more remote from the cardia, as they change their direction from the oblique into the longitudinal, enter the external longitudinal coat of the stomach, the innermost por- tion of which they form. They chiefly consist of smooth mus- cular fibres, and in order to reach the longitudinal muscular layer of the stomach, run outwards round the transverse fas- ciculi of the inner layer lying close to the cardia. The middle transverse layer of the lowest portion of the CESophagus ceases almost entirely after rapidly diminishing in thickness at the cardia, only a few transversely striated fibres, with the smaller part of the externallongitudinal muscular coat of the oesophagus, passing into the external longitudiaal muscular layer of the sto- mach, the most external portion of which they form. Amongst the transversely striated fibres which preponderate in this ex- ternal layer are a few fasciculi of smooth muscular fibres. The middle and strongest portion of the external longitudinal mus- cular coat commences at the cardia itself, and is. exclusively composed of unstriated muscle. This layer of smooth muscular fibres is consequently introduced between the fasciculi,, chiefly composed of smooth muscles, which are derived from the more remotely situated portions of the internal layer of the oeso- phagus and the transversely striated muscular fibres proceeding from the external longitudinal muscular tunic. Immediately after the passage of the oesophagus through the foramen oesophageum, isolated oblique and transversely striated muscular fasciculi are found in the external fibrous sheath. Whether these, are derived from the longitudinal muscular layer of the cesophagus, or from the surrounding tissues, I am not at present in a position to determine. p p ! 542 THE INTESTINAL CANAL, BY E. KLEIN AND E. VERSON. In Rabbits the mucous membrane at the passage of the oesophagus into the cardia presents the same features as in man ; hut the external muscular coat differs in some respects both from that of man and that of the dog. For the internal longi- tudinal fasciculi, after diminishing in number and size, com- pletely cease at the lower extremity of the oesophagus ; whilst both the middle circular, and the external longitudinal layers, after they have become entirely composed of smooth muscular fibres, and are increased in thickness, pass each in nearly equal strength respectively into the circular and longitudinal layers of the cardia. In the Teiton a few acinous glands occur just above the cardia, at the lower extremity of the oesophagus, in the form of a nearly circular zone, and exhibit the same structure as those in the CBSophagus of the frog. They pass directly into the tubular peptic glands of the cardia, the excretory ducts be- coming shorter, and their acini diminishing in number and size. The smooth muscular fibres first appearing in the form of small fasciculi around the above-mentioned acinous glands, are arranged where the tubular glands are developed, as an inde- pendent muscularis mucosse, situated externally to the tubes ; whilst the fasciculi of the external muscular coat, which in the lower part of the oesophagus are not distinctly separable into two layers, are here grouped into an internal circular and an external longitudinal layer. The same changes which occur in the oesophagus of the frog at the poiut of transition into the cardia are here in every respect repeated. The portion of the mucous membrane situ- ated internally to the acinous glands, between them and the epithelium, diminishes in thickness in proportion to the reduced length of the excretory ducts of the glands. At the same time the glands decrease in size, are arranged in closer proximity to one another, and pass by gradual transition into the peptic glands, which are at first vesicular, but subsequently more elongated and tubular at their fundus. The mucous layer consequently sufiers a transposition, in a topographical point of view ; for, whilst above it is situated between the epithelium and the glands, below it extends be- tween the glands themselves, whilst it diminishes in thickness D. THE STOMACH, BY E. KLEIN. 543 from the lower end of the oesophagus towards the cardiac orifice. Immediately above the cardia a muscularis mucosas is stiU found external to the glands in. the form of partly circular, partly longitudinal or decussating fasciculi of smooth muscular fibres, which, in proportion to the approximation of the glands to the surface, bend inwards in order that, since they always remain attached to the outer border of the glands, they may form a continuous muscularis mucosae investing the fundus of the gland tubes at the cardia itself. Where the acinous glands begin to undergo their modification, the submucous tissue of the oesophagus increases considerably in thickness, but again diminishes as soon as the tubular glands make their appearance in the mucous membrane. The ex- ternal musculature augments in thickness towards the cardia, and is so arranged that, as in the dog, the layer of circular fibres at the upper part of the stomach to a certain extent con- stitutes a sphincter. At the cardia numerous fasciculi from the external portion of the circular layer extend obliquely to the inner portion of the longitudinal layer, with which they become continuous after they have decussated with the fasciculi derived from the inner portion of the longitudinal layer, which are directed obliquely downwards into the external portion of the circular layer, D. Stomach. The mucous membrane of the stomach is in general easily moveable over the muscular layer, being connected with it by a very loose submucous tissue, and when the stomach is empty, or during the contraction of its muscles, it forms numerous transverse longitudinal folds of various size, meeting one another at oblique angles, and presenting a plexiform ap- pearance. This is particularly weU marked in the cardiac extremity and greater portion of the left side of the stomach ; whilst in the region adjoining the pylorus, as is very distinctly visible in the rabbit, where the mucous membrane is more intimately connected with the muscular layers, the folds of the former are either altogether absent, or only sparingly present. 544 THE INTESTINAL CANAL, BY E. KLEIN AND E. VEESON. The epithelium is of the simple columnar variety, and, com- mencing at the horder of the cardiac orifice in man, is equally dis- tributed over the whole surface of the stomach. The individual ceUs form columnar or truncated cones, and in preparations that have been hardened iu chromic acid are, over surfaces of con- siderable extent, cup or goblet-shaped. The mucous layer of the stomach in the new-born child increases in thickness, though not quite regularly, from the car- dia towards the pylorus ; the tubular glands of the stomach are imbedded in it, in close proximity to one another, separated only by a sparing quantity of tissue. At the cardia the glands com- mence as short indentations of the mucous membrane ; but, rapidly iucreasing in length, soon form cylindrical tubes opening separately, or by a single wider orifice common to two or even three. The fundus of the tubes is in most instances somewhat club-shaped, and more or less curved or contorted, and at the cardiac and pyloric portions it is divided into two or more smaller cylindrical branches. Commencing from the middle of the larger curvature, and proceeding towards the pylorus, the number of tubes in the fundus which do not present division at their extremities usually progressively predominates over those that are divided. At the pylorus itself, the nearer the point of its transition into the duodenum is approximated, the greater is the number of the tubes that assume the elongated simple form. According to Bisclioflf,* glands af peculiar form are present in the region of the pylorus ; according to Ecker.f the glands are generally only tubular, except those in the neighbourhood of the pylorus, which are acinous. K6lliker| found in a small zone of the cardia, and in the pale zone of the pylorus, compound tubular, but in the larger middle portion of the stomach, which becomes of a lively red colour during digestion, only simple tubular glands. The columnar epithelium is continued "into the gland tubes to a variable depth. The glands at the upper border of the cardia are lined throughout with this form of epithelium. At * Muller's Archiv, 1838, p. 513. t Zeitschrift fiir rationelle Medidn, N. F.. p. 243. X Gewehelehre, pp. 400 and 402. D. THE STOMACH, BY E. KLEIN. 545 a distance of from one half to two millimeters below the upper boimdary-line of the cardia, the columnar epithelium lining the tubes is replaced at the fundus of the glands by spheroidal or Fig. 106, Transverse section througli the fundus of the stomach in a Child, a a, cylindrical epithelium ; h b, peptic tubes ; c c, muscularis mucosse ; d d, submucous tissue ; e, circular muscular layer ; /, longitu- dinal muscular layer ; g, peritoneum ; h, gangHon of Auerbach. elongated dark or pale strongly granular cells, often resembling bi-convex lenses. This replacement quickly extends upwards,, so that the tubes soon appear to be lined with pepsine cells as far as their uppermost third. This relation obtains approxi- matively as far as to the middle of the large curvature. Com- mencing from the middle of the large curvature the columnar 546 THE INTESTINAL CANAL, BT E. KLEIN AND E. VEESON. epithelium reappears, extending farther down as the pylorus is approached, until at length it replaces the pepsine cells, even at the fundus of the tubes. In this respect there is, however, but little regularity, since tubes may be met with not far from the great curvature which are lined throughout with columnar epithelium ; whilst, on the other hand, others occur near the pylorus, which, for more than half their extent, are lined by pepsine cells. "We constantly meet at the pylorus with many (in some cases nearly aU) of the gland tubes, both simple and compound, but especially the latter, that are lined throughout by columnar epithelium, in close proximity to others in which the sides, and in part the fundus, of the tubes are liaed with pepsiae ceUs, or next to those ia which only the smaller part is covered with columnar epithelium. In the newly bom infant the columnar epithelium generally extends somewhat farther than half-way down the tube. After what has been stated above, it is impossible, therefore, to admit that there is any such distinction of two kinds of gland tubes, one lined by peptic cells, and the other ^ith cyliiidrical epithe- lium as has been represented by Henle,* Kblliker,-f- Donders,| and Leydig.§ Gerlach,|| some time ago, noticed that, although the columnar epithelium extended to a greater distance down the tubes near the pylorus than at the fundus, still glands may even there be met with, the bottom of which is not covered with this form of epithelial cell. MayerlT and even Henle** have seen gland tubes in the pyloric region of the stomach of an executed crimiaal lined throughout with peptic cells. The wall of the glands found in. the gastric mucous membrane is structureless. Henleff observed in it, as well as in the mem- brana propria of other glands, small stellate cells, which, in pre- parations long macerated in chromate of potash, become smooth * Splanchnologie, p. 157. ' t Wurzhurger Verhandlungen, Band iv., p. 52. X Physiologie, Band i., p. 204. § Histologie, p. 293. 11 Gewehelehre, p. 303. 1[ Berichte der Freihurgen naturwiss. Gesellsehaft, No. 9, p. 147. ** Loc. cit., p. 159. +t Loe. cit., p. 46. D. THE STOMACH, BY E. ELEIN. 547 and very finely granular. Henle also observed that the cells give off at the plane of the membrana propria from three to ten processes, which rup in all directions, and which, whether broad or narrow at their origin, gradually become attenuated and branched, the branches communicating with each other. He therefore considered it probable that these cells are of a nervous nature, although he has in vain endeavoured to trace their connection Avith nerve fibres. The tissue of the mucous layer is either a fibrous meshwork or adenoid tissue. The fasciculi of fine connective tissue oc- curring in and traversing the mucous layer in company with the vessels from the submucous tissue which penetrate the fasciculi of the muscularis mucosae, unite frequently in a plexi^ form manner between the gland tubes, and include between their fibres a variable number of lymph corpuscles. An adenoid network of cells, in the meshes of which lymph corpuscles are contained, is also found here and there between the extremities of adjoining gland tubes as weU as just below the surface of the mucous membrane. In newly bom infants the muscularis mucosae, or muscular layer of the mucous membrane, is from O'Ol — 0-05 of a millimeter thick, and in adults from 0'05 — 01 of a millimeter, and by its continuity separates the mucous from the submucous layer, forming consequently a level layer just external to the ex- tremities of the gland tubes. The fasciculi of this muscular layer of the mucous membrane commencing from the cardia run chiefly in a longitudinal direction, but the internal fas- ciculi are partly circular and partly oblique, and the exter- nal longitudinal or oblique. Where the fasciculi of the one or the other layer run obliquely, they decussate ; and if they were in the first instance internal and longitudinal, penetrate, after decussating, into the internal circular layer. They present an inverse relation, if before the decussation they constituted a portion of the internal circular layer ; for in that case, after the decussation, they enter into the external longitudinal layers. Both from the internal and external longitudinal layers of the muscularis mucosae small fasciculi are given off, which extend between the extremities of two tubes into the mucous membrane. Here they either run parallel, or, if they do not pass off at right 548 THE INTESTINAL CAIiAL, BY E. KLEIN AND E. VERSON. angles to the muscularis mucosEe, decussate with an adjoining fasciculus, in order then first to break up,fornung a kiad of pocket composed of smooth muscular fibres rurming perpendicularly to the surface and embracing the several tubes. The number of mus- cular fibres constantly diminishes towards the surface. When a few muscular fibres extend as far as the epithelium, they bend ia a direction parallel to the surface, and are no longer capable of being followed in the sub-epithelial tissue, or they run between the fibres of fresh fasciculi, which here and there course in a direction parallel to the surface beneath the epithelium. The submucous tissue which occupies the folds of the mucous membrane resembles that of the oesophagus, and just as the latter stands in relation with the septa of the muscularis externa, and of the external fibrous layer, so it is here in rela- tion with the peiitcaieal investment, with the septa of the muscularis mucosae, and with the mucous layer itself. The thickness of the submucous tissue in the stomach of the newly born child amounts, ia hardened preparations, upon the average, to 0'35 of a millimeter. Lymph follicles, either in the form of glandulse lenticulares, or aggregated into Peyer's patches, such as have been described as occurring in the stomach by Frerichs,* Bruch,-|- Bischoff,J and K6lliker,§ I have been unable to discover in any of the animals I have examined. It does indeed happen that certain portions of the mucous membrane of adults is more strongly infiltrated Avith corpuscles than others, but these spots have no definite limiting membrane. Th^ niay project to some extent from the surface, and may thus have given rise to the idea of their being proper lenticular glands. In regard to the lymphatics of the stomach, we know from the investigations of Teichmann,|| that in the dog they form a superficial plexus lying beneath the ceecal extremities of the tubular glands, and a deeper plexus situated between the muscularis mucosae and the muscularis externa, and conse- * Prerichs, he. cit. ■f Brucli, Zeitschriji filr raiionelle Medicin, Band viii., p. 276. \ Bischoff, loc. cit., Taf. xiv., fig. 4. § Gewebelehre, p. 403. II Teichmann, Das Saugader System, etc., a. a. 0. D. THE STOMACH, BY E. KLEIN. 549 quently in the submucous tissue. In the entire glandular bed no vessels of this kind are present. The vascular plexus above mentioned does not communicate with the capillary lymphatic system of the serous membrane directly, but through the inter- mediation of trunks provided with valves. As Eemak* has shown, and as has been corroborated by many histologists, the nerves of the stomach possess numerous ganglia, both in the muscularis externa and in the submucous tissue, I find in newly bom children, that the greater number of ganglia are situated between the fasciculi of the longitudinal fibrous layer reaching externally to the peritoneal investment, and internally to^the circular muscular layer, and forming, in parts, a con- tinuous chain. In the submucous tissue, as in other parts of the intestinal canal, the nerves form a plexus, in which, as has already been mentioned, numerous ganglia are also found. The external muscular layer presents, at the commencement of the large curvature of newly bom children, a thickness of 0"95 to I'l of a millimeter; the circular muscular layer has a thickness of 0'7 to 085 of a millimeter. The fasciculi of this last do not here run parallel, but frequently decussate. The fasciculi of the longitudinal muscular layer give off branching fasciculi, which, after frequent decussation, penetrate in an oblique direction into the circular layer. Smaller fasciculi also penetrate into the submucous tissue ; these are continuous with the inner portion of the circular layer, and originate the fibrae obUquse that wiU hereafter be described. According to Treitz,-]- they terminate in the mucous membrane with elastic tendons. In the greater portion of the cardiac extremity of the stomach, a distinct division of the muscularis externa is to be observed, into an internal circular, and an external longitudinal layer, having a thickness of 0'25 of a millimeter. In proportion as the pylorus is approximated along the greater curvature, the external muscular layer becomes stronger, which is effected chiefly by an increase in thickness of the circular layer, which amounts in the child to as much as * A. a. O. t Treitz, Prager Vierte^ahresschrifi, etc., he. cit. (550 THE INTESTINAL CANAL, BY E. KLEIN AND E. VERSON. 1-144 of a milKmeter. The fasciculi of the latter layer radiate obliquely, both towards the anterior and the posterior surfaces. The fibrse obliquse of the stomach, situated for the most part within the proper circular layer, have been accurately examined by GiUenskoeld * according to whom the layer of oblique fibres is not so sharply defined from the circular as this is from the longitudinal, but the several oblique fibres are continuous with the circular, and each set passes into the other. The oblique fibres form a girdle around the cardia, and run on the anterior and posterior surfaces of the stomach, as far as the antrum pylori. In accordance with his description, two portions of the oblique layer may be distiaguished ; one superior and horizon- tal running in a forked manner over the left side of the cardia, and extending to the antrum pyloricum itself, whilst the other consists of shorter fasciculi, that run downwards, and sooner enter the circular layer. At the plyorus itself, when the stomach is continuous with the duodenum, the circular muscular layer in the infent attains a thickness of 2' 64 millimeters, whilst the longitudinal layer is reduced to a minimum, the greater number of its fasciculi having entered the circular layer. The passage of the stomach into the duodenum is effected by this sphincter, which constitutes the valvula pylori. With the termination of the sphincter pylori, various changes occur ; the gland tubes of the mucous layer become more simple, equal in diameter throughout, and completely lined with cylindrical epithelium. They are now called the Crypts of Lieberkiihn^ Tn the submucous tissue, acinous glands occur in close con- tact with the muscularis mucosae (Brunner's Glands), which, at first small, soon increase in size, and penetrate with their excretory ducts the muscularis mucosae and the mucosa itself. "Where the first lobxili of these glands occur, small fasciculi are given off from the external portion of the muscularis mucosae, which run for a short distance external to the glands, and separate them from the adjoining submucous tissue. Acinous glands consequently first make their appearance at the commencement of the duodenum. * Gillenskoeld, Ueber die FihrcB Obliquis in Mac/en, "On the Oblique Fibres of the Stomach ; " Archiv fiir Anatomie und Physiologie, 1862, Heft 2. D. THE STOMACH, BY E. KLEIN. 551 [III the Dog the tubular glands of the mucosa, like those of man, commence as short involutions of the mucous membrane lined throughout by a continuation of the columnar epithelium of the surface. At the commencement of the cardia they are divided and irregularly dilated at their extremity. About three millimeters lower down they assume the form of simple tubes, slightly dilated at their extremity. At the same time the columnar cells are replaced at the bottom of the tube by secreting cells, which gradually extend towards the opening; the glands coincidently becoming considerably increased in size. The ducts either open separately or several together. From the middle of the larger curvature the pepsine cells are replaced agaia by columnar epithelium, in the same man- ner as in man. The thickness of the mucous membrane also increases to- wards the pylorus in the dog as in man. On the inner sur- face of the longitudinal fasciculi of smooth muscular fibres pro- ceeding from the oesophagus, and on the outer surface of the muscularis mucosae at the cardia, where the tubular glands begin to be lined with pepsine cells, a layer of circular muscu- lar fibres is superadded, at first feebly developed, but soon becoming thicker. The thickness of the muscularis mucosae varies ; in the fundus it amounts to 01 — 025 of a millimeter, and is here distinctly separated into an internal circular and an external longitudinal layer. In respect to their course and decussation, its fasciculi exhibit the same relations as in man. The quantity of muscular fibres penetrating into the mucous layer between the glands is larger in the dog than in man. The mucous membrane of the stomach of the Rabbit dimi- nishes in thickness from the cardia towards the fundus, and from this point increases again towards the pylorus. The gland tubes it contains are similar in form to those in the stomach of the dog. In the fundus the individual tubes are a little wider than in the dog, and open by twos or threes into cylindrical fossae, lined with columnar epithelium, which reach to one-fourth part of the thickness of the mucous membrane. The nearer the pylorus, the farther does the columnar epithelium extend down the tubes ; moreover, this, 552 THE INTESTINAL CANAL, BY E. KLEIN AND E. VEESON. both on the surface and in the tubes themselves, in prepara- tions hardened in chromic acid, is almost entirely composed of cup cells. The muscularis mucosse in the cardiac portion consists for the most part of longitudinal fasciculi, becoming somewhat stronger towards and in the fundus, and exhibiting here at most points a circular and longitudinal layer of equal thick- ness. In the pyloric portion of the stomach, the fasciculi of both layers completely decussate with one another, and it is only at certain points that a distinct circular and longitudinal layer can be distinguished. Numerous fasciculi here branch off into the mucosa. At the pylorus itself the muscularis mucosse, and especially its longitudinal layer, increases five-fold in thickness. The submucous tissue, which is here, as usual, continuous with the septa of the external and internal muscular coat that dip into the mucosa in company with numerous vessels, is thinner in the pyloric region tham at the fundus, and contains in its small meshes numerous spheroidal cells with a relatively large nucleus. The external musculature consists exclusively, as in man, of smooth muscular fibres, and exhibits the following arrange- ment : The circular layer is particularly strongly developed at the cardia, but gradually diminishes towards the fundus. The most external fasciculi of the longitudinal muscular layer of the cardia are intimately connected with the fibres of the investing membrane, pursue an obbque direction, and farther down enter the circular muscular layer. In the pyloric region the relations are altered, and the several layers have not only increased in thickness, but the innermost fasciculi of the circular layer become for a short distance oblique or longitudinal. At the pylorus itself the muscularis externa presents the same arrangement as in the stomach of the dog, The nerves and ganglia lying between the two layers of the muscularis externa form in parts a continuous layer, and in parts are sparingly distributed. Ganglia are not very fre- quently met with in the submucous tissue. The stomach of the Rat presents remarkable peculiarities of D. THE STOMACH, BY E. KLEIN. 553 structure. Its left half may be regarded as a continuation of the oesophagus, whilst the right half forms the stomach in the proper sense of the word. The mucous membrane lining the latter portion is of a reddish-brown colour on the surface, like that of the fundus of the above-described animals.. The two halves are divided by a fold which commences at the right extremity of the oesophagus that here enters the middle of the smaU curvature, and is so arranged as to open only into the left half; the communication of its orifice with the right half of the stomach being capable of entire occlusion by this arcuate fold. The wall of the stomach is considerably thinner in the left half than iu the right, at the cost both of the mucosa and of the muscularis externa. It is thinnest in the csecal dilatation directed upwards, which the left half of the stomach forms at the junction, of the large and small curvature. The left half of the stomach may also, from its structural characters, be re- garded as a continuation of the oesophagus. The laminated pavement epithelium increases in thickness from left to right to the summit of the fold, the height of which is about 1'5 millimeter, but again decreases on the right side, the uppermost cells first disappearing by becoming fused into a homogeneous layer; then the middle polyhedrie cells vanish, whilst the deepest cells, which are arranged on the fold in the form of palisades and are cylindrical, increase in height, and commencing from the middle of the right side of the fold, cover the mucous membrane as a simple columnar epithelium. The mucosa, which becomes stronger in passing towards the fold from the right, soon begins to form conical vascular pa- piUee, which are at first small, but with the increasing thick- ness of the pavement epithelium towards the summit of the fold increase in height. The muscularis mucosse exhibits the most important modifi- cations. It is to it that the existence of the fold is essentially due. The nearer the fold is approximated, the more distinctly does it become differentiated into internal circular and the external longitudinal layers. The former, rapidly increasing in thickness, ceases after at- taining its greatest thickness at the summit of the fold, only the uppermost fasciculi remaining, which are now continued o54 THE INTESTINAL CANAL^ BY E. KLEIN AND E. VERSON. into the circular layer of the muscularis mucosae of the right half of the stomach. The external fasciculi of the longitudinal layer extend directly as such into the right half of the stomach ; the internal fasciculi, however, decussate with the correspond- ing ones of the right half, and partly penetrate between the fasciculi of the circular layer. The muscularis externa also increases considerably in thick- ness towards the fold, attaining its maximum at its base, and then gradually diminishing. The tubular glands of the right half of the stomach are here also at first short, and lined by columnar epitheliimi, which, however, is soon replaced by rounded strongly granular pepsine cells, so that the columnar epithelium of the surface only penetrates as far as the upper fourth of the tubes. The muscularis mucosae of the right half of the stomach is thinner than that of the left, the fasciculi decussate to a con- siderable extent, but are here and there divisible into an internal circular and an external longitudinal layer. The proportion of smooth muscular fibres which are given off into the mucous layer is here also considerable. Numerous ganglia are situated on the nerves lying between the circular and longitudinal layers of the external muscular tissue. In Birds the laminated pavement epithelium of the oeso- phagus ceases at the commencement of the glandular stomach with a dentated border, and is replaced by a simple layer of cylindrical cells. The flask-shaped and, at their extremities, slightly lobu- lated glands of the mucous layer of the oesophagus, which have gradually augmented in number from above downwards, cease at the line where the columnar epithelium commences; and the muscularis mucosae lying external to the mucosa, which di- minishes in thickness where the oesophagus is continuous with the glandular stomach, becomes, in consequence of the disap- pearance of the loose submucous tissue, applied as a longitudi- nal muscular layer to the muscularis externa, so that it appears to form a single layer with this. In the lowermost portion of the oesophagus more or less sharply defined lymph follicles appear, which are either situated on the outer side of the glands, or externally between these nearly to the epithelium. D. THE STOMACH, BY E. KLEIN. 555 The surface of the mucous membrane exhibits a large num- ber of capitate elevations, at the rounded apices of which the orifices of the gland sacs are perceptible. It further presents, in passing from above downwards, a continually increasing number of microscopic villi, minute folds or processes, which nevertheless are only the optical expression of the free termi- nations of the septa between two adjoining inflections of the mucous membrane, or rather of two adjoiaing short tubes, opening in immediate proximity with one another. Bergmann* has described three types of glands : a. The well- known saccular glands, presenting a large central cavity, lined with cylindrical epithelium, which receives the orifices of all the smaller tubes lined with gland cells ; h. A second type, found in the starling, sparrow, yellow-hammer, and crow, in strix flammea and colymbus, in which the several tubes open^ by means of secondary ducts, into the principal excretory duct, which last may consequently be very short ; lastly, c. He constructs a third type of those in which all the several tubes do not open by a common canal iuto the gastric cavity, but where a number of excretory ducts open iu close proximity with one another, and the secretion of which is thus dis- charged into that cavity. (Cypselus apus.) Between the extremities of the gland-sacs and the muscular layer a sparing quantity of loose submucous tissue intervenes, which, on the one hand, is continuous externally with the septa of the muscular fasciculi, and on the other supports the vessels, accompanied by which its cords penetrate between the several groups of glands, partly separating their walls, and partly extending into the mucosa. Amongst these fasciculi of connective tissue run, not only vessels which coil around and penetrate between the individual tubes, but also smooth mus- cular fibres. In the inferior half of the glandular stomach the simple tubular glands increase in number and size towards the inter- mediate portion lying between this and the gizzard, in propor- t C. Bergmann, lEiniges iiher den Drilsenmagen der Vogel, " A few Remarks on the Glandular Stomacli of the Bird ;" Keichert and Du Bois Keymond's Archiv, 1862, p. 581, fig. c. Q Q 556 THE INTESTINAL CANAL, BY E. KLEIN AND E. VEESON. tion as the glan,d-sacs diminish in size. The muscularis externa consists of three layers, because at the entrance of the oeso- phagus into the digestive stomach, the submucous tissue disap- pears. These are thicker at the point, corresponding to the space between the extremities of two adjoining saccular glands, than in those places where they are directly attached to their convex external portion. At the point of transition of the glandular stomach into the intermediate segment the fasciculi of the outer layers decrease in number and size, but those of the middle and internal layers augment, so that in the intermediate seg- ment the external muscular tunic consists only of an external circular and an internal longitudinal layer. In the mucous membrane of the intermediate portion of the fowl, straight, closely arranged tubular glands are met with, the extremities of which are somewhat narrower than their ori- fices, and are lined with spheroidal cells which gradually change as they pass upwards into the columnar epithelium of the surT face. The tissue of the mucous membrane forms externally to the extremity of the tubes a thin, moderately dense layer, con- taining a variable quantity of lymph corpuscles, vessels, and nerves. The muscular tunic consists of an internal longitudinal and an external circular layer ; amongst the fasciculi of the latter are a few groups of fat cells. In the intermediate portion the secretion of the glands be- comes hardened into the form of a homogeneous thin layei; covering the surface of the epithelium, through which ho- mogeneous bands are prolonged in a vertical direction from the interior of the tubes. This layer investing the surface ac- quires a peculiar significance in the true muscular stomach or gizzard, where it forms a peculiar horny layer, at first thin, but gradually increasing in thickness as it descends, and when ex- amined in thin sections with transmitted light, presents a deep yellow colour. The surface of the mucous membrane invested with this homy and, by reflected light, dark brown layer^ forms at the commencement of the gizzard numerous tolerably regularly arranged corrugations, which however diminish in number and height, but increase in breadth downwards. The homy layer everywhere follows these elevations ; with the in- D. THE STOMACH, BY E. KLEIN. 557 crease of the muscular layer, the homy layer also augments in thickness. Leydig* originally stated that this layer is secreted by the gastric glands. It consists, in fact, of laminse superimposed upon one another (consecutively hardened) which are inter- rupted at the points corresponding to the orifices of the gland tubes, so that these are continued through the homy layer in the form of a canal destitute of waUs. It may be distinctly perceived in hardened preparations coloured with carmine that a homogeneous band proceeds as a direct continuation of the contents of the tube through the horny layer to the free surface. The columnar epithelium of the mucous membrane immediately subjacent to this layer is continued without interruption into the tubular glands. The several glands exhibit exactly the same structure as those of the intermediate portion. I am unable, at least in the case of the yeUow-hamm«r and fowl, to agree with the statements of IIasse,f according to whom two kinds of glands are present in the true stomach, — the simple and the compound tubular. The former, like the individual tubes proceeding from the gland-sacs of the crop, are partly lined with tessellated strongly granular cellsj and partly with columnar epithelium. As in the intermediate portion, there follows upon the gland- ular layei* a close web of decussating fasciculi, constituting a muco-membranous tissue. The muscular layer, which at the commencement of this region is still very thin,, becoming stronger as it descends by the development of numerous fasci- culi, is also limited upon its outer surface, where it is still somewhat thin, by a homy layer iu which ntimerous oblique strise are perceptible that are continuous with the pointed muscular fasciculi that here take origin. Still more externally succeeds the investing membrane composed of oblique fibres which in some places is composed only of the tendinous ex- pansion of the muscular fasciculi.. Both of the layers situated externally to the muscular laybr * Leydig, Histologie, p. 309. t C. Hasse, Beitrdge zur Histologie des Vogelmagens, " Essays on the Histology of the Stomach of the Bird ;," ZeiUchrift fiir rationelle Medicin, Band xxviii., p. 1, et seq. Q Q 2 558 THE INTESTINAL CANAL, BY E. KLEIN AND E. VERSON. diminish in proportion as that increases, so that where the muscular tissue attains its greatest thickness only a very few small strise of connective tissue lie on its outer surface. At the commencement of this region, as in the intermediate portion, the muscular tunic may be divided into two layers, an internal longitudinal, and an external circular layer. In their further course the former, which constantly receives fresh accessions of oblique fibres from the mucous membrane, becomes first oblique and then circular. The external circular layer is likewise strengthened by numerous fasciculi, originally extending obliquely from without inwards, and arising from the homy layer limiting the muscular tunic externally. A considerable number of vessels and nerves run in the investing sheath of connective tissue. After the remarks that have been already made respecting the passage of the oesophagus into the stomach of the Frog, little remains to be said in regard to the latter. The columnar epi- thelium of the surface, which, after treatment with chromic acid, is here likewise almost exclusively composed of well- defined cup cells, the individual cells of which exhibit at their attached extremity a longer or shorter cell process, contiaues without interruption into the closely approximated tubes of the mucosa. The cells lining the bottom of the tubes are spheroidal and finely granular. The ciliated epithelium of the oesophagus does not entirely cease at the cardia, but is here and there prolonged for some distance ; and even at a much lower level individual ciliated cells may occasionally be met with amongst the non-ciliated. The tubes, which are coiled or lobulated at their extremities, partly open by separate orifices, "partly unite by twos in cylindrical pits which, as above mentioned, are lined by cyliader epithelium. The muscularis mucosae consists of an internal thinner cir- cular and an external thicker longitudinal layer, the distinction between which is only clearly marked in the lower half of the stomach, whilst in the upper portion the fasciculi of the mus- cularis mucosae are almost entirely longitudinal, or decussate to some extent with one another. Everywhere small fasciculi are given ofl", which penetrate between the tubes into the mucosa. D. THE STOMACH, BY E. KLEIN. 559 In the lower portions of the submucous tissue I find isolated, distinctly defined, usually oval lymph follicles, flattened from within outwards, in the capsule of which are contained nume- rous fusiform cells, with oblong, flattened nuclei. Some of the follicles are bounded by the muscularis mucosae internally, and muscularis externa on their outer side, whilst others, as may occasionally be observed in the intestines of Mammals, pene- trate the muscularis mncosse, and extend to the cylindrical epithelium of the surface. The submucous tissue itself, like that of the oesophagus, is moderately compact, and about 02 of a millimeter thick. The ex- ternal muscular layer presents, though not uniformly an internal circular, and an external, much thinner, longitudinal layer. In some places, instead of the latter, a few oblique fasciculi are found, which lower down enter the circular layer. Towards the pylorus both the circular, as well as the longitudinal layers which have here become independent, increase in thickness. The nerves and ganglia present the same relations as in the intesti- nal canal of the Vertebrata.]' E. Small Intestine. By E. VERSON. The small intestine is a direct continuation of the stomach, and, like this, consists of an external peritoneal investment within which are two concentric tubes attached to one another by more or less dense connective tissue. The outer of these two is the muscular coat, the inner is the mucous mem- brane. The connective tissue forming the bond between them presents various degrees of thickness, but no peculiarities of structure ; it contains a few elastic fibres and numerous con- nective tissue corpuscles. The. relative thickness of the two tubes to one another is too variable to admit of any precise statement being given ; but in a general way it may be said that the muscular timic is about three times as thick as the mucous, and that in Man the thickness of the entire intestinal wall, including the peritoneum, can scarcely be estimated at more than one millimeter. Measure- ments, however, taken at various parts, wUl naturally exhibit considerable variations according to the conditions of contraction or relaxation present in the muscular fibres. The investing peritoneal coat is composed of ordinary con- nective tissue with elastic fibres, and is either directly applied -to the muscular tunic, or is attached to it by means of a small quantity of loose connective tissue. Its free surface is covered by a single layer of pavement epithelium, the cells of which seen in profile appear as thin scales with projecting nuclei. a. Muscular Coat. The muscular tunic of the small intestine is differentiated into two superimposed layers, which are distinguished in ac- E. THE SMALL INTESTINE, BY E. VEESON. 561 cordance with the direction of the fibres composiiig each, into an external longitudinal, and an internal circular. The former pursues the same direction as the intestine itself, the latter runs more or less at right angles to it, and embraces it with circular or spiral coils. A few fibres deviate from these two main directions, coursing round the muscular tube in a radial or oblique direction. Such fibres are occasionally found united into thick fasciculi in the upper portion of the duodenum, close to the pylorus, and they may be followed from thence, forming compressed spirals, into the longitudinal layer of the duodenum. The muscular tube of the small intestiue progressively diminishes in thickness towards the iliocsecal valve, the atte- nuation being particularly observable in the longitudinal layer, which in some of the lowermost parts may even be altogether deficient. The circular is generally thicker than the longitudi- nal layer, amounting in the adult to about 0"2 to 0'3 of a milli- meter, whilst the longitudinal layer scarcely exceeds 01 of a millimeter in thickness. This proportion may, however, be reversed, strata of the longitudinal fibres being here and there found with correspondiag diminution of the circular fibres. The anterior surface of the duodenum is covered, as is well known, by a single layer of peritoneum, whilst the posterior surface is uncovered. At the lower curvature it is attached to the abdominal wall by an organic muscle, to which Treitz * has applied the name of Suspensorius duodeni. This consists of a few fasciculi of the longitudinal layer, terminating in tendiaous fibres, that accompany the dense connective tissue surrounding the cseliac and mesenteric arteries, and are then lost. The fasciculi increase remarkably in breadth, and whilst they do not exceed two to three mOlimeters iu thickness, are almost ten times that breadth. Additional fasciculi not unfre- quently join them, derived from the diaphragm (right border of the foramen cesophageum and internal crua). The duodenum has yet another muscular attachment at the head of the pancreas. In the duodenum of the chUd I find * Ueber JEinen neuen Mushel am Duodenum des Menschen, " On a New Muscle of tlie Duodenum in Man." Prager Vierteljahresschrift, Band i. 662 THE INTESTINAL CANAL, BY E. KLEIN AND E. VEESON. the pancreas not in all instances sharply defined towards the longitudinal layer of muscles. This last frequently presents areas where acinous groups of the pancreatic follicles penetrate through foramina in it as far as the circular muscular layer, whilst at other points a few muscular fibres are given off from the longitudinal muscular tunic, which penetrate between the acini into the substance of the head of the pancreas. Even the circular layer may thus extend beyond its ordinary limits, and in longitudinal sections made close to the pylorus in the rat I have found a considerable fasciculus of smooth muscular fibres given off from it, which, like the fasciculi already de- scribed as entering the head of the pancreas, enter a group of Brunner's glands, and here similarly subdivide amongst the acini. In its further course the muscular tube presents nothing remarkable, apart from its gradual attenuation, until it reaches the valvula coli. Throughout this, as is particularly observable in the new -bom child, only the circular layer passes, whilst the longitudinal layer is interrupted ; and indeed the bands of the latter, proceeding on the one hand from the ileum, and on the other from the colon, become considerably attenuated towards the free border of the valve, whUst many muscular fascicuU interlace with each other, and, finally, as my preparations show, arch towards the adjoining circular fibrous layer. More or less considerable deviations from these arrrange- ments occur in. different animals. Thus I may mention, that in the cat the longitudirial fibrous layer does not enter iato the formation of the valve, but usually, like the peritoneum, extends uninterruptedly over it. On the other hand, the cir- cular fibrous layer of the small intestine bears the relation to that of the large intestine, of a thinner tube (ileum), which is so introduced through a lateral aperture in the wall of a thicker tube (colon), that it projects with a free border into the lumen of the latter. In the dog, the circular fibrous layer of the small intestine projects in this manner with its free bor- der, but this difference is observable, that the longitudinal fibres appear to be interrupted at the valve. If a portion of the muscular tube, which can easily be de- tached with the forceps, be placed in a mixture of one part of E. THE SMALL INTESTINE, BY E. VEKSON. 563 acetic acid and ninety -nine of distilled water, or in a solution containing 32-5 per cent, of liquor potassES (Moleschott), it may easily, after the lapse of a few minutes, be broken up into fibre cells which, especially after the action of the acetic acid, exhibit a distinct nucleus, with one or two nucleoli. The muscle cells appear smooth, or sometimes angularly folded, and are seldom longer than 0-225 of a millimeter, and broader than 0*005 of a millimeter. No difierences can be discerned in the size of the elements forming the longitudinal and circular fibrous layers respectively. In other Mammals, however, they may be both longer and broader, as is remarkably the case also in the Amphibia ; those of the Proteus and Salamander being surpass- ingly large. The several muscular fibres constituting the muscular tunic of the intestine are held together by a kind of cement. Their larger fasciculi are enclosed by bands of connective tissue, which divide the muscular substance when seen in cross section partly into numerous areas of equal size, and partly into larger seg- ments, which embrace the whole thickness of the muscular tunic. b. Mucous Membrane. The mucous membrane constitutes the innermost tube, and exhibits peculiar elevations which project in the form of folds and villous processes into the lumen of the intestine. The folds — termed also the valvules conniventes of Kerkrin- gius^run more or less at right angles to the long axis of the intestine, and are either parallel to each other, or unite at acute angles, and always become separated by wider intervals towards the lower part of the small intestine. The folds of Kerkringius are commonly regarded as persis- tent formations, because the muscular tunic does not enter into their interior. Nevertheless certain parts of the small intestine occur in children, where the muscular coat presents alternate contractions and relaxations. In the former these folds of the mucous membrane are sharply defined and pro- minent ; whilst opposite the latter the membrane is perfectly smooth, thus afibrdiug strong evidence that the folds in ques- 564 THE INTESTINAL CANAL, BY E. KLEIN AND E. VEESON. tion are in some measure dependent upon tHe contraction of the muscular coat. The villi of the small intestine, on the other hand, are eleva- tions of the mucous membrane of more limited extent, which make their first appearance in the descending portion of the duodenum, where they are most closely arranged, and, becom- ing more and more widely separated from one another, extend Fig. 107. Section of a villus. From the intestine of a Eabbit. a, epithelium ; b, stroma ; c, central cavity. to the free border of the iliocsecal valve. They vary consider- ably in form. Sometimes they are cylindrical ; at others coni- cal or clavate, or fl.attened and expanded like a leaf — variations that in part, at least, are occasioned by the degree of contrac- tion of the general muscular tunic and of their own muscular fibres, to which cause also their variation in length is attri- butable. In man the length of the villi is from 04 to 0'6 of a mniimeter, and the breadth from 006 to 0'12 of a millimeter. In every viUus one or two, or more rarely three, central spaces are found, constituting the origin of the lacteals. (See Chapter IX. on the Lymphatics.) E. THE SMALL INTESTINE, BY E. VEESON. 565 The finer structure of the parenchyma of the villi is pre- cisely similar to that of the rest of the mucous membrane, being composed of the tissue termed adenoid tissue by His ; that is, of a plexus of anastomosing corpuscles, in the meshes of which cells are contaiued. These characters are not, how- ever, equally well marked in aU classes of animals, and varia- tions may even be observed to occur in one and the same species, in accordance with age, the retiform tissue presenting a more uniform trabecular structure, or forming a delicate plexus of fibres, at the points of decussation of which a nucleus or two only may be discovered, the number of cells contained in the meshes having coiucidently undergone considerable diminution. A similar transformation of the adenoid tissue of the mucoiis membrane may also be observed at certain points immediately beneath the epithelium — a circumstance which has led to the admission of a separate basement membrane, situated between the epithelium and the mucous membrane. No such mem- brane, however, can either be isolated or shown to form a con- tinuous layer. Lymph Follicles. — At the free border of the jejunum and ileum roundish or elliptical areas occur, with, in the latter case, their long axes corresponding to that of the intestine, and hav- ing a length of 15 centimeters, and a breadth of 7'20 millimeters. Their surface is convex, projecting into the lumen of the tube, and has either a few villi scattered over it, or is altogether destitute of them. These are the Peyer's patches, which, when examined with low powers, or sometimes even with the naked eye, appear as a group of roundish, pyriform, or more flask- shaped corpuscles, the so-caUed follicles. These dip into the submucous tissue with their rounded extremities, whilst their thinner ends form projections on the free surface of the intes- tinal mucous membrane, and must consequently pierce the muscularis mucosae, the fasciculi of which, in point of fact, separate to permit the passage of the follicles. A single Peyer's patch may include twenty or more such fol- licles lying in close contiguity, and only separated from one another by thin prolongations of the submucous tissue. The inferior or deep surfaces of the follicles are somewhat flattened. 566 THE INTESTINAL CANAL, BY E. KLEIN AND E. VERSON. whilst towards their upper part, especially above the muscu- laris mucosae, the lateral boundaries disappear. When examined with the microscope, these bodies present a remarkable similarity in structure to the so-called medullary cords of the lymphatic glands, and have recently even been Fig. 108. Fig. 108. Longitudinal section of the small intestine of a Rabbit, z z, ■villi; J, crypts; p, a Peyer's patch; K, cap of a follicle; S, submucosa; m m, muscularis mucosae ; E, circular muscular layer ; L, longitudinal muscular layer ; P, peritoneum. regarded, in accordance with the views of Ziegler and Briicke, as really belonging to the system of lymphatic glands. However delicate a section may be that is made through a follicle, only an irregular accumulation of cells can be recognised ; but if these be removed by pencilling with a camel-hair brush, or, still better. E. THE SMALL INTESTINE, BY E. VEESON. 567 by agitation of the preparation in a test-tube half filled with water, a network or plexus of fibres conies into view, similar to, though somewhat closer than that presented generally by the mucous membrane of the smaU. intestine. The follicles consequently are composed of a plexus of fibres and of cells (lymph corpuscles) which fill the iuterspaces between them. But, just as the plexus of the mucous membrane presents his- tological difierences under various circumstances, so may the framework of intestinal follicles differ, sometimes appearing as a tissue of anastomosing cells, the nuclei of which coincide with the thickened nodal points (child, rabbit), sometimes as a plexus of rigid hyaline trabeculse (adult man, cat), and some- times as a fibrous network (young dog). The framework, whatever may be its form, is directly con- tiauous laterally and above the muscularis mucosae with the reti- cular tissue of the mucous membrane. In the deeper parts, on the other hand, the meshes gradually become more compact, and either, covered with epithelium, form the boundary of the so-called lymph sinuses, or, where these are deficient, are applied to the dense submucous tissue which constitutes the cord-like septa between the follicles, and extend to near the muscularis mucosae. But in the event of the septa not reaching so high, the follicles just below the muscularis mucosae may for a short distance be contiuuous with each other. Regarded from another point of view, however, the frame- work is ia direct connection with the vessels of the follicle, and, indeed, not only with the larger ones by means of their tunica adventitia, but also with the most delicate capillaries. This is efiected by means of a fibrous network, and in well-prepared specimens the capillaries may be frequently observed to give ofi" processes that suddenly become attenuated into fibres, which coalesce with those of the general mass. As in man, so in the greater number of animals, the follicles reach the surface of the mucous membrane, and elevate this in the form of a cap (rabbit, sheep, calf, pig). It occurs, occasionally, however, that the follicles do not reach the surface of the mucous membrane, be- coming continuous at some distance from it with the ordinary adenoid tissue of the membrane (cat). 568 THE INTESTINAL CANAL, BY E. KLEIN AND E. VERSON. Whilst the Peyer's patches constantly occupy the border of the intestine opposite the attachment of the mesentery, isolated or solitary follicles are distributed irregularly over its whole surface. These, like the Peyer's patches, are much more closely arranged in the lowest parts of the ileum. The number of Peyer's patches in the small intestine varies considerably. Authors calculate twenty to be about the average, though no definite limits can be given on either side. Where they are very numerous, they extend into the upper parts of the tube. Middeldorpf observed them even in the lower curvature of the duodenum. Glands. — The secreting glands of the small intestine are constructed upon two different types, the acinous and the tubu- lar, and are named after their discoverers, the former Brunner's glands, the latter, the Lieberkiihnian follicles. Brunner's glands agree exactly in their structure with that of other acinous glands of mucous membranes, and in man form groups of from five to ten acini, which open into a single excretory duct that traverses the mucous membrane, and opens on the surface. The diameter of the acini amounts to about 0"07 to 0'14 of a millimeter, and they consist of a structureless vesicle, the interior of which is lined with somewhat flattened cylindrical cells. The excretory duct is lined by similar epi- thelium. The glands of Brunner lie imbedded in the submucous con- nective tissue, and form small masses, which may however attain sufiicient size to cause the whole tunica nervea to dis- appear; and are bounded on the one side by the muscular tunic, and on the other by the muscularis mucosae. The latter, however, forms no absolute limit, some of the acini being occa- sionally found projecting through it against the mucous layer, « whilst, on the other hand, a few slender fasciculi of the muscle cells also accompany the connective tissue between the glandu- lar vesicles, and then divide. The greater portion of the glands of Brunner are found in the vicinity of the pylorus. In man, however, a few groups of these glands are distributed lower down the canal, whilst in other animals the whole series of glands form a single coherent E. THE SMALL INTESTINE, BY E. VEESON. 569 mass. The latter arrangement is remarkably well seen in the rat, in which animal the above-mentioned distribution of the muscular fibres between the gland vesicles can be easily demon- strated. The crypts of Lieherkuhn form tubular depressions of the mucous membrane, the bHnd extremities of which extend to Fi?. 109. Fig. 109. Crypts and interfollicular connective tissue. From the intes- tine of the Babbit. K, crypt ; a a, epithelium ; d, adenoid tissue, from ■which the cells have been removed by pencilling ; T, fibrous tissue ou the opposite side. the muscularis mucosae, and as they are arranged perpendicu- larly to the surface, they furnish a measure of the thickness of the mucous membrane itself Their length varies from 0"34 to 0'5 of a millimeter, their diameter amounts to 006 — 0'08 of a 570 THE INTESTINAL CANAL, BY E. KLEIN AND E. VERSON- millimeter. The crypts are usually held to consist of a structure- less membrana propria lined by a layer of cylindrical epithelial cells. The latter are identical with those forming the epithe- lium of the intestine generally, and the remarks that have been made respecting these apply to them also. The only slight difference that exists between them is, that the attached ex- tremities of the cells forming the epithelium of the crypts are for the most part broader than the free extremities, which is intelligible when it is remembered that their free surfaces bound a tube of narrower diameter than the cryptic membrane itself In very fine sections of the intestine, from which the epi- thelium has been completely detached by delicate brushing, or where the epithelium is accidentally absent, it may easily be demonstrated that the so-called membrana propria of the crypts is not entirely structureless ; for from the interfoUicuIar trabe- cular tissue a few delicate fibrils penetrate into the basement membrane, and, preserving the longitudinal direction of' the tube, run towards its orifice, near which they become continu- ous with a similar but transversely coursing fibrous tissue; this on the other hand, like the branches of a tree, is given off at almost right angles from the septal investing sheaths of the follicles. Such membranes moreover exhibit a beautiful rounded-polygonal pattern, corresponding to the bases of the detached epithelial cells. The Lieberkiihnian follicles occupy the whole free surface of the intestine, with the exception of the bases of the villi and the surface of the solitary glands. But whilst their orifices must necessarily be separated by the former, the tubes dilate beneath them in such a manner as almost again to come into contact, leaving only small interspaces for the passage of vessels and muscular fasciculi. They are usually altogether absent over the follicles, that is to say, of course, where these project into the lumen of the intestine, and here they are arranged like a coronet around the elevations, which has led to the employment of the term corona tubulorum by Johann Miiller. MuscuLAEis Mucosae. — Lying between the mucous mem- E. SMALL INTESTINE, BY E. VERSON. 671 brane and the submucous tissue, Middeldorpf * and Briicke f discovered a layer of organic muscidar fibres, wMch can be traced from one end of the intestinal canal to the other, and from which processes are given off in various directions. In the muscular layer of the mucous membrane two laminae of nearly equal thickness may be distinguished, named, in ac- corjiance with the prevailing direction of their constituent fibres, the circular and the longitudinal fibre layer, though in some places they run into one another. The muscular tunic frequently appears iuterrupted to permit the passage of the lymph follicles, and also to receive the csecal extremities of the Lieberkiihnian foUicles ; or, lastly, it may itself present a retiform arrangement, and it hence becomes in- telligible how sections of the intestine sometimes exhibit con- tinuous layers of circular and longitudinal fibres, sometimes only one of these, and sometimes neither. We find, also, that in animals the prevalent arrangement ap- proximates to one or other of these types, and I may mention that ia the child the circular layer is subordinate, so that the direction of the fibres is almost entirely longitudinal, separating in some places to form beautifiil plexuses, whilst in the rabbit the difference in the direction of the two layers is extremely well marked, though they are very thru. We have already alluded to the processes given off by the muscularis mucosae in speaking of the small fasciculi situated between the acini of Brunner's glands. Those, however, which pass towards the mucous membrane itself, and were discovered by Briicke J and KoIliker,§ are of greater importance, and are more constantly present. These form, on the one hand, long bands, sometimes not exceeding a single fibre cell in thickness, * De Olandulis Brunnerianis, Diss. Vratisl., 1846. ■f- Ueber ein in der Darmschleimhaut aufgefundenes Mushelsystem, " On a muscular system discovered in the Intestinal mucous membrane;" Akademie der Wissenschaften in Wien, Februar beft, 1851. X Lee. cit. J Ueber das Vorkommen von Glatten Mushelfasern in Schleimhduten, " On the presence of smooth muscular fibres in mucous membranes ;" Zeitschrift fUr wissenschaftliche Zoohgie, Heft 1, 1851. E E 572 THE INTESTINAL CANAL, BY E. KLEIN AND E. VEESON. which run up between the Lieberkiihnian glands, and, espe- cially near the free surface of the mucous membrane are not unfrequently connected by a few transverse fibres; and, on the other hand, strong fasciculi, as many as twelve fibre cells in thickness, which penetrate the villi, and extend throughout their whole length. The muscular fasciculi in some instances enter the villi in the form of separate cords, but in others (especially in the smaller villi) first intercommunicate and diverge from one another at the bases, so that a double layer of muscular fasciculi may almost always be distinguished. One, lying close to the central lacteal, and helping with the epithe- lium to form its wall, the other running upwards in the paren- .chyma of the viUi, traversing the meshes of the adenoid tissue, and frequently intercommunicating by anastomosing oblique fibre cells (His). The number of such fasciculi may amount to twenty or more in a single villus, as is well seen in the dog and cat, in which the longitudinal section of a villus often presents from seven to ten fasciculi in close proximity. In the almost mature embryoes of guinea-pigs, instead of completely formed villi, we find solid papiUiform masses of cells, with other similar structures presenting a central cavity extending for a variable distance towards the apex. In the latter a band of muscular fibres may be demonstrated, besides a few vascular loops, which, proceeding from the muscularis mucosa, arch over the apex of the csecal extremity of the cavity, and return again to the muscularis mucosae. I have obtained a preparation exhibiting similar features, from an adult cat, and I believe that this affords an explanation of the statement made by Bonders,* that transverse muscular fibres are present at the apices of the villi. I have myself not un- frequently seen them in the child, cat, and rat, and refer them to the above-mentioned loop running immediately beneath the free extremity. The fibre cells of the muscularis mucosse are shorter and more slender than those of the muscular coat of the intestine, being, according to Moleschott, scarcely 0"06 of a milli- meter long. The entire thickness of the muscular layer of the mucous membrane in man does not in general exceed 0021 * Fhysiologie, Band i. E. SMALL INTESTINE, BY E. VERSON. 673 of a millimeter, but may amount to oiily one half of this, or even less. Epithelixtm. — The free surface of the mucous membrane is covered with columnar cells, usually arranged in a single layer, but presenting at some points, — as for instance over Peyer's patches, — ^rounded cells between their attached extremities. The epithelial cells of the small intestine are sometimes columnar, sometimes conical, and in the latter case are attached by their apices, and present their bases to the cavity of the intestine. They undergo considerable modification from the action of reagents, becoming clavate, irregularly swoUen, drawn out into long processes, etc. The free border of the uninjured epithelial cells of the in- testine presents a broad seam or hem, which under favourable circumstances (with good microscopes) exhibits a fine striation running parallel to the long axis- of the cell. If the cells have already undergone change, the striae become irregular, some of the lines projecting beyond the others — others ceasiaig to pre- serve their parallel arrangement. It has been a - subject of discussion whether these strise are the expression of fine canaU- culi traversing the hem perpendicularly,* or whether they represent small rods of which it is composed.-(- This con- troversy has to a certain extent lost its importance, as neither the canahculi nor the rods furnish any satisfactory explanation of the mode in which the absorption of fat molecules is efi'ected. Besides the ordinary columnar cells of the intestine, and con- stituting a very remarkable and frequent appearance, are cup, bell, or goblet-shaped structures, the open mouths of which are directed towards the cavity of the intestine-, and which contain at their base a mass of protoplasm of variable size with or without a nucleus. Brettauer and Steinachf originally * Punie, Zeitschrift fiir wissenschaftliche Zoologie, Band vi. KoUiker, Wurzhurger Verhandlungen, ^and vi. + Brettauer and Steinacli, Sitzungsherichte der Kaiser. Ahademie der Wis- ienschaften, 1857. \ Loc. cit. B R 2 574 THE INTESTINAL CANAL, BY E. KLEIN AND E. VEESON. suggested that these structures were the results of the meta- morphosis of the cylinder cells. It still remains doubtful, how- ever, whether, as Henle* observes, these corpuscles are modified epithelial cells or represent morphological elements of a peculiar kind. The cylinder cells of the small intestine are structures of such delicacy that they can only be examined in the fresh state, without the addition of any reagents, and as they appear on folds of the mucous membrane excised from the living animal, the covering glass being very gently appKed. It is only in pre- parations thus treated that the intestiaal epithelium is dis- played ; it is only possible ia this way to obtain a bird's-eye view of the regular mosaic formed by the cells investing the villi from their bases, and it is only thus that we can convince ourselves that both terminal surfaces resemble one another, varying only ia their form and size. Even after the lapse of a few minutes, clear bright spots make their appearance at the bases of some of the villi, and in a short time goblet cells be- come visible. The adjustment of the focus renders it evident that these bright spots correspond to elevations which project at various points to an unequal height above or beyond the general level of the epithelium. Now, in regard to the occur- rence of these elevations and the production of spheroidal structures from columnar epithelial cells, already demonstrated by Briicke from examination of ceUs in profile, there can be no doubt that portions of the contents of these cells are thrown off very quickly after their removal from the living body, and give rise to such cup-like .structures. Strieker and Kocslakof have poiuted out that a process of this kind is extremely well marked in acute catarrhal inflammataon, the columnar epithe- lium of the catarrhally affected stomach and intestiae of the rabbit, even in a fresh condition, presenting throughout tracts of considerable extent cup-sha,ped cells alone. If we add to this that it not unfrequently happens for the greater part of the intestinal epithelium to become converted, after the action of reagents into cup cells, we cannot in reason deny that the latter may originate from the ordinary columnar cells. • Handbuch der Eingeweidelehre, 1862, p. 165. E. SMALL INTESTINE, BY E. VEESON. 675 There is in all this, then, but little that is opposed to the view expressed by Leydig and F. E. Schulze, that the epi- thelial cells are to be regarded as one-celled glands ; for we need only regard the material discharged by the cell as its secretion ; and the cell wall, with the remainder of the contained material, as the gland. Further, it may be remarked that up to the present time there is no evidence against the supposition that it is only at a certaiu period of their development that the cells undergo metamorphosis into goblet cells. Moreover, at present it cannot be denied that besides the epithelial cells from which the goblet cells already described originate, other peculiar gpblet or tubiform. structures are pre- sent. This has not indeed been absolutely demonstrated, but it constitutes no objection to the view that such structures cannot be seen ia the fresh state, and cannot be distinguished, from the artificial goblet cells under altered conditions.* The cup-cell metamorphosis affects not only the cellsjbut as Baschf states, the nuclei; for when the intestinal epithelium, of the frog is treated with boracic acid, similar appearances are frequently produced ia them.. The nuclei are then seen to be ruptured in one or two places, . and masses of their contents not unfrequently project from the opening. HeidenhainJ maintained that the attached extremity of tne cells of the epithelium of the villi, becoming gradually attenuated, is prolonged into a long process contiauous with the connective tissue corpuscles of the parenchyma of the villi. These state- ments have been accepted, however, by only a few histologists, and have been denied by many. Amongst the animaJs best adapted for the observation of the connection of the epithelium, of the villi with a subjacent plexus, the guinea-pig may be named. In these animals and in the rat the epithelium of the vUli frequently becomes de-- * The now extensive literature of this subject is fully given in Elmer's Treatise Zur Geschiehte der Becherzellen, " On the History of Goblet Gells." Berlin, 1868. t CentralblaU, 1869. X Die Ahsorptionswege des Fettes, "The Mode of Absorption of Fat;"~ Moleschott's Untersuchungen, Band iv. 576 THE INTESTINAL CANAL, BY E. KLEIN AND E. YEESON. taclied from the parenchyma, like the fingers of a glove, and a delicate network then comes into view between the paren- chyma and the epithelium, the threads of which are continuous now with the former, now with the latter. The appeai-ances presented, however, are essentially due to manipulation. The network is composed of .spheroidal cells, and the transition of such free but closely approximated cells into an apparent plexus may be distinctly followed. Whether these spheroids are modified red blood corpuscles, or descendants of the epitheUal or of some other cells, cannot be satisfactorily determined. Their appearance, and a comparison of them with red corpuscles altered by means of chromic acid, renders the former opinion the more probable one. In these animals then it is certain that no direct communication exists between the epithelium and the stroma. It is more difiicult to speak decisively on this point when the epithelium is not detached, siace it is frequentiy requisite to decide whether two fibres lying in close proximity are con- tinuous with each other, Nerves. — Two thick layers of ganglionic nervous masses are distinguishable in. the small intestine, one of which is si- tuated in the tunica submucosa, and the other between the circular and longitudinal muscular fibre layers. The former, first described by Meissner,* is arranged in the form of a flat layer, although a few gangha project towards the mucous membrane, and penetrate between the adjoining foUicles; the latter, discovered by Auerbach,-f- is more irregular, presenting nodulated ganglionic masses, which are particularly large and numerous where the septa of connective tissue dip into the circular muscular layer. The several gajigha may attain a diameter of 0"4 of a miUi- meter, and give off and are traversed by nerves varying from 0'002 to 0004 of a millimeter in diameter, that form a plexus the branches of which penetrate the circular muscular coat with the septa of connective tissue, and estabUsh a communica- tion between the two ganglionic layers. Other branches pass * Zeitschrift fur rationelle Medicin, Band viii., 1857. X Uebw einen Plexus Myentericus. Breslau, 1862. F. THE LAEGE INTESTINE, BY E. VEESON. 577 through the longitudinal muscular layers, to join the mesenteric nerves. A few small scattered ganglia are distributed in the course of these nerves. In regard to the further distribution of the nerves in the mucous membrane, no certain information has been at present obtained, and the same may be said of the mode of termination of the pale nerve fibres in the organic fibre cells of the muscular tunics. The nerve cells which, accumulated in numbers varjdng from three to thirty, form the ganglia, are in Man either unipolar or multipolar, and have a diameter of from O^OOG to 0019 of a mUlimeter. The nerves are composed of non-medullated fibres. Both the nerve trunks and the ganglia are invested by nucleated sheaths. F. The Large Intestine. The large intestine is the direct continuation of the small, and exhibits in its several divisions, the caecum, with the processus vermicularis and the colon, the same structure and arrangement of its constituent parts as are presented by the latter. It is lined by a single layer of columnar epithelium, the individual cells of which not unfrequently vary considerably in size and shape ; sometimes they are cylindrical or conical, vsdth truncated apices, and are therefore short and relatively broad, and sometimes they are thin, and externally run into long processes ; their nucleus is rounded or elliptical, and either occupies the centre or the lower, i.e. the external, third of the cell. In the newly bom child the cylindrical epithelium may frequently be seen to be detached from the subjacent membrane. The thick hem or border of the columnar cells, both in fresh and hardened preparations, presents the well-known fine striation. The mucous layer is similarly formed to that of the small intestine. It is composed of a very close, yet delicate plexus of cells, containing numerous lymph corpuscles in its meshes. In the newly bom child there are found, besides, numerous fusiform cells, similar to those met with elsewhere in embryonal connective tissue. The Lieberkiihnian crypts are imbedded in the mucosa. They form sometimes straight, sometimes slightly curved tubes, arranged either perpendicularly or some- 578 THE INTESTINAL CANAL, BY E. KLEIN AND E. VEESON. what obliquely to the surface, generally of equal size through- out, or more frequently swollen at the extremity,, and having a diameter of 0-06 — 008 of a millimeter, and a length of 0-35 of a millimeter. The epithelium lining each tube is a direct con- tinuation of the columnar epithelium of the siuface, and in no respect differs from it. Kg. 110. Fig. 110. Section of the large intestine of a Rabbit. J, crypts of Lieberkijhn ; a, epithelium ; 6, mucosa ; m, muscularis mucosae ; », gubmucosa ; K, circular muscular layer ; L, longitudinal muscular layer ; p, peritoneum. As regards the distribution of the crypts, they lie in close ap- position in the caecum and colon, whilst in the processus ver- micularis they are generally separated from one another by wider tracts of mucous membrane, and at the same time appear shorter and broader. The muscularis ttiucoscb is comparatively feebly developed ; its fascicuK are partially arranged into one internal circular and an external longitudinal layer, which generally decussate at the base of the crypts, but frequently give off numerous smaller fasciculi that penetrate the mucosa between the tubes, to which they hold the same relation as in the small intestine. G. THE RECTUM, BY E. VERSON. 579 The suhTnucous tissue is looser in texture, and hence forms numerous folds or rugae in the csecum and colon, which are capable of being obliterated by extension. The submucous tissue stands here also in connection with the mucosa by means of the septa of the fasciculi of the muscularis externa, and also by the vessels which traverse the muscularis mucosae. The muscularis externa, like that of the smaU intestine, is arranged in two layers, an internal circular and an external longitudinal ; the conjoint thickness of which in the caecum and colon of the child amounts to 0'6 — 07 of a millimeter. The thickness of the longitudinal layer is in inverse propor- tion to that of the circular ; at the longitudinal bands they are both of equal thickness, but in receding from these the circular layer increases as the longitudinal diminishes. The solitary folUcles, as is generally admitted, possess no lacteals ; but these, on the contrary, as Teichmann* has shown, are displaced by the follicles, so that their arrangement is much disturbed in their vicinity. The plexus surrounding the follicles consists, as shown by His, of wide lymph sinuses, which are lined by a flat epithelium.^. The nerves of the large intestine also present the same general relations as those of the small, both in regard to the plexuses they form between the two muscular layers, and to the ganglionic knots or swellings of Auerbach and of Meissner. The latter are usually spheroidal in form, of relatively large size, but containing singularly small cells. The cells may be traced in the form of small chains for a short distance in the course of the several nerve trunks. Each nodal point is invested by a layer of connective tissue, in which, besides spheroidal nuclei, fusiform cells with oblong nuclei can be clearly distinguished. G. Rectum. The thickness of the intestinal walls constantly augments as the anal orifice is approximated, so that near the middle of the ' Teichmann, he. cit. His, Zeitschrift fur wissenschaftliche Zoologie, Bande xi., xii., and xui. ; Frey, Virchow's Archiv, Band xxxvi. ■\ T. Recklinghausen, Die Lymphgefdsse, etc. Berlin, 1862. SSO THE INTESTINAL CANAL, BY E. KLEIN AND E. VEESON. rectum in the adult it attains a thickness of 3 — 4 millimeters The proportions are stiU more remarkable in the newly bom child, in which the parietes of the rectum are from 1'3 to 1-5 millimeters thick. This thickening is partly independent and proper to itself, being in fact due to the increase of its own muscular layers, but is in part also attributable to extrinsic causes ; the rectum, after leaving the peritoneum, receiving numerous muscular fasciculi from the adjoining parts, and in particular from the muscidus levator ani. The muscular tunics, of which the external here again forms a continuous layer, become in the lowermost parts constantly more and more closely connected with the adjacent tissues ; and as the mucous membrane gradually passes into the external skin, the organic muscular tissue of the intestine blends with the transversely striated muscle in the neighbourhood of the anus. The peritoneum also, where it invests the rectum, appears to be thickened, and the submucous tissue, which becomes steadUy thicker and denser below, is partly continued directly into the subcutaneous connective tissue of the regio anaUs, and partly penetrates in the form of bands between the divisions of the musculus sphincter extemus. MuscuLAH Tube. — The longitudinal fibrous layer of the intestine, which again forms a more continuous layer in the rectum, in consequence of the dilatation of the three ligamenta coli, still exhibits in the upper parts considerable differences in its thickness, suggestive of its previous fasciculated arrange- ment. In the newly bom child, at this level, variations occur to such an extent, that in some parts the thickness amounts to 0'23 of a millimeter, whilst in others it does not exceed 0'06 of a millimeter; and similar differences occur in the adult. The muscular bands gradually become extended by lateral expansion, decussate in some parts with the outermost fasciculi of the circiilar muscular layer (at the valves of Houston), and finally become associated with the innermost fasciculi of the musculus levator ani, which, at first separated from them by a thin layer of connective tissue from the posterior portion of the pelvic fascia, ultimately join directly with them at acute G. THE EECTUM, BY E. VEESON. 581 angles. A few millimeters higher a few fibres of the posterior portion of the longitudinal muscular layer mutually inter- penetrate with those of the muscuH recto-coccygei, which, pro- ceeding from the sacrum, here terminate. Three distinct portions of the musculus levator ani can be distinguished, each of which differs in the nature of its fibres from the other, the innermost being formed of organic, the middle of a mixture of organic and transversely striated, and the external (which constitutes the largest portion) of purely Fig. 111. Fig. 111. Longitudinal section of the musculature of the rectum. animal fibres. It is only the innermost of these three groups which enters into immediate relation with the rectum, its constituent fibres in part penetrating obliquely into the longi- tudinal muscular layers, and interweaving with them both in an upward and downward direction, and in part crossing them at right angles, and blending with the circular muscular layer. At the level of the sphincter internus the longitudinal fibrous layer becomes separated to some extent from the former, whUst fasciculi of connective tissue intervene between them ; and the 582 THE INTESTINAL CANAL, BT E. KLEIN AND E. VEESON. limits between the longitudinal muscular layer and the inner- most fasciculi of the levator ani, in consequence of their mutual approximation, can no longer be distinguished. The longitudinal muscular layer and the innermost fasciculi of the levator ani radiate out into numerous cords, which penetrate between the fasciculi of the musculus sphincter externus in such a way that the ring of the sphincter externus is split into a series of concentric zones ; these traverse its whole thickness, and finally terminate in thin tendons, which are lost in the skin of the buttock. The circular muscular layer at the beginning of the rectum still possesses a considerable thickness. In adults it measures somewhat less than one millimeter, and in the newly born child about 0'2 of a millimeter; but it increases in proportion as the anus is approximated ; it forms also temporary thickenings in the lowermost plicae sigmoidese, where it interweaves with the longitudinal muscular]ayer,receives numerous muscular fascicuh from the levator ani, and finally near the anal orifice augments to a thickness of five millimeters in adults, and of 0'5 of a milli- meter in the newly born child, causing an annular thickening termed the sphincter intemus. The upper margin of this ring is by no means sharply defined, whilst if a longitudinal section be carried through the lowermost part of the rectum, the thick- ening caused by the sphincter intemus is seen to be club-shaped. Immediately below the sphincter intemus, and situated somewhat more externally, the striated fibres of the sphincter externus begin to make their appearance, forming circles round the anal opening, and laterally blending with the most external fasciculi of the levator ani. Mucous Membrane. — The mucous membrane of the lower part of the rectum in man usually presents valve-like pro- cesses, running at right angles to the axis of the intestine, but usually extending over only a portion of the circumference. They are neither incapable of obliteration, nor invariably pre- sent, though the muscular tissue enters into their formation. In the great majority of cases I found them to be three or four in number, of which one, and indeed usually the lowest, ap- peared so far independent that a thickening of the circular G. THK EECTUM, BY E. VEESON. 583 mucular layer corresponded to it, amounting to nearly double that whicli this layer ordinarily presents. In a specimen ob- tained from a child I found that in this way the circular mus- cular layer, -which at first is 0-21 of a millimeter thick, becomes thickened opposite the fold to 0'4 of a millimeter, the longitudinal layer assisting in its formation by the incurvation of some of its fibres. The lowermost fold is situated about 5 — 6 centimeters above the anus (1 — 2 centimeters in the newly bom child), and occupies the whole of the right waU of the rectum, and from thence may extend to some distance, both anteriorly and pos- teriorly. The one immediately above is situated on the left wall, and the next again on the right, and so on at short inter- vals, alternating from side to side when several valves are present. The minute anatomy of the mucous membrane of the rectum presents the same features as those of other parts of the intesti- nal tract. Near the anus, however, the elastic fibres become more abimdant, the ceUular elements more sparingly distributed, the vessels less numerous, and ultimately it passes into the papil- lated external integument. The muscularis mucosae may be distinctly followed to the point of transition. This layer also, like all the other tunics of the intestine, increases in thickness in the reetum, so that it may equal, or even exceed, 02 of a millimeter, whilst the differentiation of its fibres into an external longitudinal and an internal circular layer is lost in the pre- vailing longitudinal direction they assume. Near the anal orifice its fasciculi are closely arranged in the form of cords, which cause the projection of the mucous membrane into seve- ral longitudinal folds (Colunmse Morgagni), and then become continuous with delicate tendons which terminate in the skin adjoining the anus. The tendinous mode of termination of the mtscularis mucosae is much more easily recognisable in animals than in man, from whom it is difficult to procure suffi- ciently fresh specimens ; in cases where, as in the rat and guinea- pig, the line of transition from the columnar epithelium of the intestine into the tesselated epithelium of the skin occurs abruptly, it exactly coincides with this line. The ascending processes which are here also given off by the muscularis mucosae to the interspaces between the Lieber- 584 THE INTESTINAL CANAL, BY E. KLEIN AND E. VEESON. kiihniarL follicles are connected witli eacli other by a few transverse fibres. These may be constantly seen around the orifices of the follicles immediately below the surface of the mucous membrane. The lymph follicles of the mucous membrane of the Rectum are of the solitary variety, and comparatively few in number. In their general characters they resemble those of the other portions of the large intestine. It is deserving of notice, however, that in the child I met with isolated masses of adenoid tissue below the sigmoid ciirvature imbedded amongst the interweaving fibres of the circular layer, or lying between these and the longitudinal layer of muscular fibres, which were continuous laterally with the interfibriUar con- nective tissue of the muscular tunics. It remains to be established, however, whether these perform the same functions as the true lymph follicles. At the thickened portion of the mucous membrane the Lieberkuhnian crypts appear to be elongated, their length being as much as 0'6 and 0'7 of a millimeter, whilst they may at- tain to 007 of a millimeter in breadth. In the newly bom child they have a height of about 0'3 of a millimeter and a breadth of about 0'05 of a mjiUimeter. The only part of the surface on which they are not found is that over the lymph follicles, on which ac- count the latter appear to be depressed, and can only be recog- nised with the naked eye as punctiform hollows. Elsewhere the crypts are situated in close apposition. They cease in the region of the Columnse Morgagni, in the lowermost part of which a few sebaceous follicles already begin to be visible. The epithelium of the large intestine, in conclusion, pre- sents no points of difference from that lining the small, and like it possesses a striated hem or border. I have, at least, ascertained this to be the case in man, the dog, cat, rabbit, guinea-pig, rat, and frog. Near the anal orifice, however, numerous roundish cells constantly make their appearance be- tween the columnar or conical ones, but this also occurs in many parts of the small intestine. The latter preponderate in number only as far as the Columnse Morgagni, where they are gradually replaced by several layers of rounded succulent cells the most superficial of which become more and more flattened G. THE RECTUM, BY E. VEESON. 585 till the transition into the ordinary tesselated epithelium is completed. In the child this transition is less sudden, because the projecting angles of the folds of Morgagni are already crowned with the pavement epithelium, though the more pro- tected deep fissures between the columnse always preserve an investment of cylindrical cells. PapDlse are first encountered where the pavement epithelium is completely developed — that is, immediately below the sphincter intemus. In the rat the ColumnaB Morgagni are absent, and the lowest crypts extend to the sphincter externus. These lowermost crypts are lined throughout by the usual form of columnar epithelium, but on the side of these orifices which is turned towards the anus a layer of pavement epithelium, four or five cells in thickness, immediately abuts upon the cyhnder ceUs, which last reach to the precise level of the orifice. This point coincides always with that at which the muscularis mucosa, be- coming obUque, runs out into points and is lost. Nbeves. — The plexuses both of Meissner and of Auerbach are con- tinued from the colon into the rectum, the development of the latter preponderating over the former. After the peritoneal investment ceases, the close nervous web from the plexus pudendalis joins it, containing ganghonic enlargements of considerable magnitude. The above plexuses contain both dark-edged and pale sympathetic nerve fibres, which branch and are distributed between the muscular fas- ciculi of the sphincter intemus and externus, and those of the external longitudinal muscular layer and levator ani. CHAPTER XVII. BLOODVESSELS OF THE ALIMENTARY CANAL. By C. TOLDT. Mucous Membrane of the Oral Cavitt. The mucous membrane of the mouth derives its supply of blood from various branches of the external carotid artery, the arterise labiales, buccinatoria, linguahs, transversa faciei pterygo-palatina, and alveolaris superior and inferior. The terminal branches of these arteries enter the submucous tissue of the' oral cavity after the trunks from which they proceed have become much dimiaished in size from giving off numerous branches to the muscles, glands, and other organs, and after having formed numerous anastomoses with each other and the adjoining arterial vessels. After reaching the submucous tissue they are distributed parallel to the surface, and by their numerous anastomoses form a wide-meshed plexus, from which branches extend into the connective tissue layer of the mucous membrane, where they compose a close terminal network, in- terlacing with the corresponding venous plexus. From this jBnally the minute branches for the papiUse are given off, the capillaries of which present considerable variety in the dif- ferent sections of the mucous membrane. The efferent vessels of the papillse discharge their blood into a close-meshed venous plexus, which decussates with the above- mentioned arterial plexus. The venous portion of the vascular expansion contained in the connective tissue of the mucous membrane is characterised by the large size of the vessels composing it, their comparatively straight course, and nume- rous anastomoses, whilst the arterial portion is greatly infe- rior to the venous ia the diameter of its constituent vessels, BLOODVESSELS OF THE ORAL CAVITY. 587 which are at the same time somewhat less numerous. As a general rule the arterial and venous trunks pursue a parallel course. The veins arising from- the plexus each run by the side of an artery into the submucous tissue, where, having collected together and freely anastomosing with each other, they form a wide-meshed plexus similar to and parallel with that formed by the arteries. These relations are met with throughout the whole extent of the oral cavity, except only that the closeness of the plexus presents considerable variation at different parts, in accordance with the greater or less development of the capillaries of the papillse. As a general rule, it may be stated that the larger the pa- pOlse, the more extensive is the capillary plexus ia their interior. At the Tnargins of the lips, where the largest papillse are found, from three to five branches of the terminal arterial plexus enter each papilla, and by their divisions and anasto- Fig. 112. Papillse of the lip. moses form an elongated but wide-meshed capiUary plexus (fig. 112). The transition into the venous channels takes place by one or more capillary loops usually situated at the apex of s s 588 BLOODVESSELS OF THE ALIMENTARY CANAL, BY C. TOLDT. the papillae. From this point the small veins, characterised by their large lumen and straight course, receiving lateral branches, and occupying the axes of the papillae, run towards the centre of their bases, and descend perpendicularly to the ve- nous plexus of the mucous membrane. This course enables them to be easily distinguished from the capillary arterioles which run obliquely towards the papillae. As we recede from the margin of the lips, the vascular arrangement of the papiUae assumes a more simple character, so that in those of the posterior surface of the lips the capillary loops are either simple, or have only one or two transverse branches. The papillae of the cheeks, in like manner, have only simple capillary loops. The papillae of the hard palate are of considerable height anteriorly, yet, for the most part, contain only a single vertical vascular loop; posteriorly, the height of the loops is much diminished, and on the soft palate they form only flat arches, which, originating in the relatively close-meshed plexus of the mucous membrane, present the convexity of their arches to the surface. The gums bear papillae on their free surface, the vascular plexus of which is nearly as much developed as in those of the lips, but in those of the lateral surfaces there is only a siagle capillary loop. The papillae on the floor of the mouth have single loops, with occasionally one or two cross branches. Langer * has very recently called attention to a remarkable arrangement that is found in the frog. In this animal the capillary vessels of the mucous membrane of the mouth and of the oesophagus as far as the cardiac orifice of the stomach pre- sent numerous diverticula, which project towards the free sur- face of the membrane, and, after becoming constricted, terminate in the capillary vessels. Langer is no doubt justified in re- garding these as a peculiar arrangement supplying the place of capillary loops, and adduces, in support of his opinion, the fact that in the toad these diverticula are replaced by the ordinary * Sitzungsierichte der k. k. Ahademie der Wissenschaften zu Wien, Band Iv., Abtheil 1 ; Ueher das Lymphgefdssystem des Fr.osches, " On the Lymphatic System of the Frog." BLOODVESSELS OF THE LINGUAL MUCOUS MEMBRANE. 589 capillary loops in the posterior parts of the mouth, and in the parts extending beyond to the entrance of the stomach. Mucous Membrane of the Tongue. The branches of the lingual artery, of which the dorsalis liaguse is distributed to the upper surface, and the arteria ranina to the middle and anterior portion of the tongue, run obliquely upwards and forwards into its substance, giving off numerous "-"ranches in their course, and ultimately, in order to reach the , . ^■>s membrane, penetrate the compact layer of connective ,. ,1^ linguse), which iuvests the muscular mass. On reacnm.g the ~i^ ° ^ ^ , , , , , , ^ r J. ""^us membrane, these branches break up into number oi termii., ^ . , • i ,, r. • i J j2 11 i? twigs, which then pursue a superficial urse, and finally form i^ . ,, .,, rrn, • 1 il^■e ^^ m the papiilse. The simple ffliform papili^-.^^^^^si£aTi-«~-:_^_„^g^l^ ^^^ course. Fig. 113. Fig. 113. Filiform papillae of the tongue. a siugle vascular loop ; but all the compound varieties, whether filiform, fungiform, or circumvallate, possess a system of vessels from which a loop is given off to each secondary papilla. Into every papilla two or more terminal arterial branches enter (fig. 113), divide in the interior, and then, after anas- tomosiag once or twice, give off a capillary braiich into each 8 8 2 590 BLOODVESSELS OF THE ALIMENTARY CANAL, BY C. TOLDT. secondary papilla. The capillary has a diameter of about 0-01 millimeter, and runs to the apex of the papilla, where it forms a loop, and, reversing its course, unites with others to form a venous trunk. The large papillae contaia two or more venous trunks. The larger and smaller papillse of the same variety, as well as the three subordinate forms of the papUlse, are not in any way distinguishable from one another by the arrangement of the bloodvessels, but essentially by the greater or less de- velopment of the vascular plexus, and the number of loops tha* are given off in each instance in correspondence with thp ber of the secondary papinse. ^^^^^^^ ^.^^ ^ The veins of the papiU^, which are of^co^- ^^^^^ ^^^ ^^^^ the circumvallate variety, run verticallv ^^^^ ^^^ ^ ^^^^ by their junctionma. those fr^^^ p^^^^^ ^.^^^^^^ ^^^^^^^ Jl'^iy^.^'^^paneioi) ^^^le arteries and the fascia linguse. ^Semeshes of this plexus are usually rounded in the anterior part of the tongue ; the larger trunks arising from it penetrate the fascia, and, runniug side by side with the arteries, receive numerous veins from the muscles, and dip into the substance of the organ, where they coalesce to form the large venous trunks. In the posterior part of the tongue, numerous large veins take origin from the above-mentioned venous plexus, and, after run- ning for some distance backwards on the fascia, combine at the root of the tongue to form the vense dorsalis linguse. The pos- terior parts of the mucous membrane of the tongue are conse- quently extraordinarily rich in veins. It only remains to be mentioned that both the arterial and venous system of the mucous membrane of the right and left halves of the tongue are everywhere in direct communication at the median line. Sacculae Glands of the Mouth and Phaetnx, and THE Tonsils. Arterial branches penetrate at various points through the fibrous sheath of the saccular glands into their interior, and give ofi" branches which supply the adenoid substance. Where this last is distinctly divided into follicles, the capillaries are BLOODVESSELS OF THE ACINOUS GLANDS. 591 distributed as in those of the intestine (to the description of which the reader is referred), except that their diameter is somewhat greater. But where the adenoid substance is dif- fused, the vascular plexus is quite irregular. The veins issuing from it are very numerous, and form short broad vessels, which for the most part run in the intermediate spaces of the adenoid substance, as well as immediately beneath the fibrous invest- ment, from which they finally emerge at various points. Arterial branches also pass towards the mucous membrane, covering the sacculi internally, running up the interspaces between the follicles, or traversing the layers of adenoid sub- stance, and finally terminating in flat capillary loops, which supply the papillse. From these large venous trunks arise, which unite with those originally in the adenoid substance. The bloodvessels in the several follicles of the tonsils exhibit the same relations ; the larger arterial and venous trunks run- ning and branching between them. Acinous Glands of the Alimentary Canal. All the various glands of the digestive tract present an es- sentially similar arrangement of their bloodvessels ; as may be seen in the mucous glands of the mouth, pharynx, and oeso- phagus, the salivary glands and pancreas, and the glands of Brunner in the duodenum. The larger bloodvessels distributed to these glands ramify m the connective tissue investing the lobules. A single arteriole and veinlet penetrate each of the smallest follicles, then break up in a tree-like manner, and are finally lost in the capillary plexus. The capillary plexus everywhere consists of arched, frequently branched tubules ; with a mean diameter of O'OOS of a millimeter, which are sa arranged around the glandular vesicles that each of the latter is surrounded by from two to four such arches. These vessels communicate uninterruptedly throughout the entire lobule ;. each lobule thus possesses its own circumscribed capillary system. A round-meshed capillary plexus invests the excre- tory ducts of the mucous foUicles as far as their orifice ; the ducts are also accompanied by two veins which here and there communicate, and near the surface of the mucous membrane 592 BLOODVESSELS OP THE ALIMENTARY CANAL, BY C. TOLDT. usually join by means of an anastomotic ring with the venous plexuses of the mucous membrane. Mucous Membeane of the Pharynx. The upper parts of the pharynx receive their supply of blood through the pharyngo-palatine and spheno-palatine branches of the internal maxillary artery, whilst the middle and lower parts are supplied directly from the external carotid by the ascending pharyngeal and palatine arteries. The terminal branches of these vessels run obliquely towards the surface of the sub- mucous layer, where they ramify, ultimately dividing into fine branches that run immediately beneath the epithelial layer of the mucous membrane. Capillaries, having a diameter of 0'006 of a millimeter, are given off from these vessels, which form simple loops in the serially arranged papillse. There is scarcely any region where papillae are found in. which the vascular loops present so much uniformity as here. The descending portions of the loops unite into veins that quickly acquire a consi- derable size, and these vessels communicate by numerous anas- tomoses, and run for the most part in the direction of the long axis of the pharynx, so as to form a plexus with elongated meshes. Sooner or later the larger venous trunks joiri the veins of the subjacent glandular or muscular layer. The ex- cretory ducts of the mucous glands are surrounded at their orifices with circularly arranged papillary loops. Mucous Membrane of the (Esophagus. The vascular plexus of the mucous membrane of the oeso- phagus, derived from the oesophageal arteries, and from small branches of the inferior thyroid and bronchial arteries, is extremely close. The larger vessels run longitudinally in the submucous layer, communicating from time to time by trans- verse anastomoses (fig. 114, a). The smaller branches reach the mucous membrane obliquely, and then usually become longitudinal and very sinuous in their course ; they also form a plexus with elongated meshes (fig. 114, b), from which the capillary loops, destined for the most superficial layer, arise BLOODVESSELS OF MUSCULAR COAT OF INTESTINE. 593 (fig. 114!, c). In the upper part of the oesophagus these last are very similar to those of the pharynx, but are less uniform near the middle. Here the capillaries form flatter arches, with their convexities towards the surface, from which two to five short loop-like processes arise. In the lower parts of the oesophagus the simple loops are again found; they become Fig. 114. I illi III I is ff rfflSnm Fig. 114. Submucous and mucous layers of the oesophagus, as seen with diflferent focussing. more vertical, their height gradually increasing towards the stomach, so that near the cardiac orifice they attain a con- siderable size. At the point where the mucous membrane of the stomach commences they suddenly cease with a dentated border. The venous trunks of the superficial regions of the mucous membrane accompany the corresponding arteries throughout their whole course. Muscular Coat op the Alimentary Canal. The layers of smooth muscular tissue investing the alimen- tary canal from the oesophagus to the rectum, possess a vascular system proper and peculiar to themselves. The larger vessels reach them by two routes : on the one hand, branches are given off from the vessels supplying the intestine. 594 BLOODVESSELS OF THE ALIMENTARY CANAL^ BY C. TOLDT. which penetrate the muscular tunic, and run for some distance between the longitudinal and transverse layers, to both of which their branches are distributed. On the other hand numerous vessels from the submucous plexus turn outward to the internal muscular layer, and penetrate the interspaces of its constituent elements. In the musculature of the sto- mach, which does not present quite such a regular arrange- ment, the larger bloodvessels nevertheless likewise run between the several layers and fasciculi. The ultimate arterial and venous branches run transversely to the direction of the longitudinal muscular fibres, and give off numerous long capillaries at right angles, having a diameter of 0007 of a millimeter ; these, frequently branching dichoto- mously, run parallel to the muscular fasciculi, and communicate from time to time by short transverse branches. A very regular capillary system with elongated rectangular meshes is thus formed. If the muscles contract, the capillaries are thrown into curves, so that their characteristic appearance is essentially altered. The vascular plexus of the muscularis mucosae exhibits a similar arrangement ; but, on account of the smaller thickness of the muscular layer, appears to have very large meshes. Mucous Membeane of the Stomach. The bloodvessels of the stomach enter it at the attachment of the peritoneal layers; each artery, accompanied by its corresponding veia, perforating the muscular tunic to reach the submucous tissue, in which they run for a variable distance, constantly giving off branches, or dividing dichotomously ; the terminal branches of adjoiaing arterial trunks form fre- quent anastomoses. The smallest arteries traverse the mus- cularis mucosae to reach the glandular layer, and divide into arcades of fine vessels, having an average diameter of 0'005 of a millimeter, which, winding spirally around the several gland-tubes (fig. 115), give origin to new arches, that do not, however, diminish in size. Every gland tube is thus sur- rounded by a system of capillary arches, which extends nearly to the surface of the membrane. At the same time it must BLOODVESSELS OF GASTEIC MUCOUS MEMBRANE. 595 not be supposed that each follicle possesses its own independent capillary system ; for, in point of fact, the capillary arches sur- rounding one freely communicate with those of the adjoining follicles. The rootlets of the veins commence near the orifices of the glands, in the form of thick arches, which run sinuously Fio-. 115. Vessels of the walls of the stomach, as seen on transverse section. towards the surface, and there unite to form smaller trunks. Several such trunks converge under the surface of the mem- brane to form a larger vein, which then descends vertically through the glandular layer. These vertical veins enter at Pig. 116. Fig. 116. Vascvilar plexus of the stomach, seen from the surface. right angles into a wide polygonal-meshed venous plexus, which lies above the terminal expansion of the arteries, situated between the muscularis mucosae and the glandular layer through the whole extent of the mucous membrane of the stomach. 596 BLOODVESSELS OF THE ALIMENTARY CANAL, BY C. TOLDT. Inasmucli as this plexus is exclusively composed of tubes of larger calibre, and is also exclusively fed by the above-described veins, it can be distinguished with remarkable facility when seen from the surface, as in fig. 116, from the arborescent terminal expansion of the arteries. From this venous plexus larger vessels take origin, which perforate the muscularis mucosES, join the arteries, and, accompanied by them, traverse the submucous tissue, where they unite with others to form strong vessels that perforate the muscular tunic of the stomach. Mucous Membrane of the Intestine. With the exception of the large intestine, the arrangement of the bloodvessels of the mucous membrane throughout the whole extent of the alimentary canal is essentially similar, being modified only by the number and size of the villi, the distribution of the glandular follicles, Peyer's patches, etc. The arteries reaching the intestine between the layers of the mesentery perforate its muscular coat with the accompanying veins, and run in the submucous tissue chiefly at right angles to the axis of the tube. They communicate with each other by longitudinal and oblique branches, and form a wide-meshed plexus. The venous trunks accompanying them likewise form a plexus, which may be distinguished from that of the arteries by the more frequent anastomoses and the larger size of the vessels. If the intestine of the mature fcBtus of the rabbit after injection be divided along the attachment of the mesentery, and the flat surface examined, this vascular network appears in the form of extremely delicate arcades, which, commencing at the attachment of the mesentery, extend on either side about one-third round the whole circumference of the intestine. Be- yond this point the arteries and veins pursue a separate course. The numerous branches proceeding from the submucous arterial expansion divide, after they have traversed the mus- cularis mucosse, and have reached the glandular layer of the Lieberkiihnian follicles, into capillary arches, which coil spirally around the glandular tubes, are about 0'007 of a milli- meter broad, and extend to the surface of the mucous mem- brane, whence branches pass ofi" to the villi. Other arterial BLOODVESSELS OF INTESTINAL MUCOUS MEMBRANE. 597 twigs ascend without branching between the gland tubes to supply the villi. There are no proper veins formed from the capillaries sur- rounding the tubular glands, but the vessels collectively trans- mit blood into the capillaries of the viUi. We must therefore regard the capillaries of the intestinal mucous membrane and of the villi as forming a common system, except that the latter receive special accessory arterial branches. The Fig. 117. Fig. 117. Vascular plexus of the intestinal mucous membrane, seen iu transverse section. capillary system of the villi lies close to the surface, being separated from the epithelium by only a delicate homogeneous layer, and is tolerably close (fig. 117). It consists essentially of tubes, averaging 0'009 of a millimeter in diameter, which pursue a slightly tortuous course in the long axis of the villi, and communicate by numerous transverse tubules. The arterial twigs above alluded to, arising directly from the vascular plexus of the mucous membrane, run singly or several in number to the villi, in which, after a short course, they break up into capillaries, and their terminal branches, after forming loops, may frequently be seen to enter the venous radicles. The relative numerical proportion of the longitudinal 698 BLOODVESSELS OF THE ALIMENTARY CANAL, BY C. TOLDT. and transverse capillary branches of the villi varies con- siderably in the intestines of different subjects, sometimes one and sometimes the other preponderating. The arrangement of the capillary plexus is also modified by the form of the vilU. In those that have a flat conical shape, as in the duodenum, the transverse branches are usually smaller in number, whilst in cylindrical villi the longitudinally running vessels are less developed, and the transverse branches are consequently more numerous. In strongly contracted villi the capillary plexus appears closer, and the vessels more tortuous. The plexus is usually also more dose near the apices of the villi. By the union of several arches of capillary vessels the venous radicles here originate, and, speedily coalescing, form a venous trunk of considerable size, which descends vertically through the villus, and joins with the veins of neighbouring villi. In their further course the veins thus formed descend through the glandular layer without receiving any other branches or forming anastomoses, and finally terminate by entering the venous plexus lying subjacent to that layer. Where the villi are absent, as in the large intestine, the transition of the ca- pillary plexus into the veins occurs in a precisely similar manner at the free margin of the folds which the mucous membrane forms around the opening of the tubular glands. The arrangement of the venous expansion beneath the Lieber- kiihnian glandular layer differs essentially from the arterial. WhUst the arteries break up in an arborescent manner into fine meandering branches, the veins are formed from the large venous trunks that descend from the villi. The venous plexus of the intestine is distinguished from the analogous one of the stomach by the more sharply defined limitation of the territory belonging to the several venous trunks, and by the more sparing occurrence of anastomoses. In the large intestine the arrangement of the bloodvessels is similar to that of the stomach, with the exception that the capillary system surroundiag the glandular layer is not so much ramified, so that in many parts only straight and but httle branched tubules are found between the glands from which the close superficial venous plexus proceeds. The trunks collecting the blood from these extend downwards BLOODVESSELS O^ PEYBE'S PATCHES. 599 through the glandiJa-r layer, and discharge themselves, like those of the st'^^°^' i^^o ^ wide-meshed plexus of large veins in the de.<^^^^ layers of the mucous membrane. Solitary Gland Follicles and Peyer's Patches. These obtain their vascular supply from the submucous plexus of the intestine. The arterioles destined for the follicles proceed iu part directly from the branches of the submucous plexus, and are partly branches of those trunks -which break up into capillaries for the layer of tubular glands. The former chiefly run towards the base, the latter to the lateral surfaces of the foUicles. The capillary system (fig. 118) consists of a Kff. 118. Fig. 118. Vascular plexus of an intestinal foEicle, seen in vertical section, plexus of vessels having a diameter of about 0-008 of a miUimeter, with rounded polygonal meshes, which invests the whole surface of the folUcle. From this plexus numerous fine capillary branches of OO04 — 0006 of a millimeter ia diameter pass radially into the iaterior of the follicle. Near the centre they form communicating arches, not, however, with much regularity, since it frequently happens that three or more join to form one. Moreover, some few anastomosing 600 BLOODVESSELS OF THE ALIMENTARY CANAL, BY C. TOLDT. branches run directly across to the opj^gjjjg gj^g j^ .■< occurs that in the centre of the follicles a no^^ vascular frequently remains, which, however; is not larger ri^^ i may be found between the capillaries in the periphery, q or more of these communicating capillary branches also iiy. quently extend straight through the middle of the follicle * The veins originate in the superficial plexus, especially from that situated at the base of the foUicle, form short trunks which pursue a tortuous course, and partly coalesce with the veins of the villi, and partly open directly into a branch of the venous plexus Ij^ng upon the muscularis mucosae. The bloodvessels ofPeyer's patches present a similar arrange- ment to those of the follicles. The plexus lying subjacent to them is characterised by its richness ; the larger trunks, both arterial and venous, completely surround the margin of the groups of folhcles, and send numerous branches beneath the follicles. The venous plexus is especially distinguished from that of the other parts of the intestinal mucous membrane by the circiimstance that, besides the vertically descending veins of the villi, numerous smaller and larger branches proceeding from the follicles unite at more or ^ess oblique angles to form larger trunks, and thus cause a considerable alteration in the otherwise characteristic appearance of this plexus. * For fui'tlier information the reader is referred to F. Ernst, Veber die Anordnung der Blutgefdsse in den Oarmhduten, " On the Arrangement of the Vessels in the Walls of the Intestine." Zurich, 1851. His, in the Zeitschrifi fur wissenschaftliche Zoologie, Band xi., p. 416. Frey, in idem, Band xiii., p. 28. END OF VOL. I. Printed by Watson and Hazell, London and Aylesbury.