THE NEW SYDENIAM SOCIETY. INSTITUTED MDCCCLVIII. VOLUME XL VII, MANUAL OP HUMAN AND COMPARATIVE HISTOLOGY. EDITED BY S. STEICKER. \x ASSISTED BY J. ARNOLD, BABUCHIN, O. BECKEE, BIESIADECKI, J. BOLL, E. BBUCKE, COHNHEIM, EBERTH, TH. W. ENGELMANN, GEBLACH, IWANOFP, E. KLEIN, W. KUHNE, LANGEB, V. LA VALETTE, LEBEE, LUDWJG, SIGMUND MAYEE, MEYNEET, W. MULLEE, OBEESTEINEE, PFLUGEB, PEEYEE, V. EECKLINGHAUSEN, A. EOLLETT, EUDINGEE, MAX SCHULTZB, F. E. SCHULZE, SCHWALBE, SCHWEIGGEE-SEIDEL, LUDWIG STIEDA, C. TOLDT, E. VERSON, WALDEYEE, AND OTHEES. VOLUME I. TRANSLATED BY HENRY POWER, M.B., LOND, F.R.C.S., OPHTHALMIC SUBGEON TO ST. GEORGE'S HOSPITAL, BXAMINEB IN PHYSIOLOGY AND COMPARATIVE ANATOMY IN THE UNIVERSITY OF LONDON. THE NEW SYDENHAM SOCIETY, LONDON. i +00^ a TEANSLATOE'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 " Kolliker'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 Hassall, 1849, or some of the still 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 first part appeared in this country ; for it was felt at once nothing could give a stronger guarantee VI TRANSLATOR S 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 find, 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. Becklinghausen'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 ........ 1 Ideal Type of a Cell 4 Physiological peculiarities of Cells 10 Phenomena of movement in Cells 11 Vlll CONTENTS. PAGE Changes of form occurring in Cells 14 a. From variation in temperature . . . .18 b. From mechanical influences . . . . .19 c. From electrical stimuli . . . .' . .20 d. From nervous excitation . . . . .22 e. From chemical stimuli . . . . . .22 Metamorphosis of Cell substance ...... 25 Structure of Cells 27 Characters of the Nucleus of Cells . . . . . .30 Cell Genesis . .33 Forms presented by Cells ....... 40 Modes of union of Cells ........ 41 Classification of Cells ........ 43 Formative activity of Cells . . . . . .45 Changes of Cells in Death . . . . . . .45 CHAPTER II. THE CONNECTIVE TISSUES. BY A. ROLLETT, PKOFESSOR OF PHYSIOLOGY IN GRAZ. Theories of the nature of Connective Tissue . . . .47 CONNECTIVE TISSUE . . . . . . . .52 The Cells of Connective Tissue 53 a. Amoeboid Cells ....... 54 b. Granular Cells ....... 55 c. Fusiform Cells 60 d. Stellate Cells 61 e. Pigment Cells ....... 61 Varieties of Connective Tissue . . . . . .63 Plexuses and Trabeculas ...... 63 Retiform Connective Tissue . ... . .65 Investing and supporting Connective Tissue . . 65 Trabecular Connective Tissue . . . .68 Intra-glandular Connective Tissue . . . .69 Fibrillar Connective Tissue 70 Elastic Fibres 81 Distribution of Fibrillar Connective Tissue . . . .84 Development of Connective Tissue ...... 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. GENEKAL CHARACTERS OF NERVOUS TISSUE. BY MAX SCHULTZE. The Nerve Fibres . . 147 Division of Nerve Fibres ....... 162 ^ripheric Terminal Organs ....... 165 In the Olfactory Nerves . . . . . .165 „ Gustatory Nerves 165 ,, 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 Ganglia . . 175 CHAPTER IV. THE TISSUE OF THE ORGANIC MUSCLES. BY J. ARNOLD. General characters of the Organic Muscles . . . .188 Structure of the Organic Muscles 190 x CONTENTS. PAGE Nuclei of the Organic Muscles 191 Connection and arrangement of the Fasciculi . . . .192 Vessels 194 Nerves ........... 195 Distribution 198 Mode of Investigation 200 CHAPTER Y. THE RELATION OF THE ULTIMATE FIBRES OF NERVES TO MUSCLE. BY W. KUHNE. 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 Reptiles, Birds, and Mammals ..... 216 History and Literature 227 CHAPTER VI. THE BEHAVIOUR OF MUSCULAR FIBRES WHEN EXAMINED WITH POLARIZED LIGHT. BY E. BRUCKE. . 235 CHAPTER VII. THE HEART. BY F. SCHWEIGGER-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. XI PAGB CHAPTER VIII. THE BLOODVESSELS. BY C. J. EBERTH, PROFESSOR OF PATHOLOGICAL ANATOMY IN ZURICH. General Structure of the Vessels ...... 264 Vasa Vasoruin and Nerves ....... 266 Arteries 267 Epithelial Layer . 267 Elastic Internal Coat 267 Internal Fibrous Coat „ 268 Muscular Coat .... ... 270 External Elastic Coat, or Tunica Adventitia . . 274 reins 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 PROF. F. v. RECKLINGHAUSEN. Structure of the larger Lymphatics ...... 297 ,, Lymphatic Capillaries 301 „ Stomata 807 „ Serous Canals 310 ,, Lymphatic Follicles ..... 326 ,, Lymphatic Glands ...... 329 ,, Medullary Cords . . . . . . 332 „ Lymph Paths • 334 ,, Trabecula3 of Connective Tissue . . . 334 The Chyle 340 Xll CONTENTS. PAGE CHAPTER X. THE SPLEEN. BY WILHELM MULLEK, OF JENA. General Structure .... ,, in Reptiles . ,, in other Vertebrata The Capsule of the Spleen Septa and Sheaths of the Veins Arterial Sheaths ... Bloodvessels ..... Lymphatics ..... Nerves ...... Development ..... 349 349 352 352 352 354 357 359 360 360 General Characters Capsule Follicles Vessels CHAPTER XI. THE THYMUS GLAND. BY E. KLEIN. 365 365 367 368 CHAPTER XIL THE THYEOID GLAND. BY E. VERSON. General Characters Vesicles . Framework Vessels . Lymphatics 370 371 372 372 372 CONTENTS. Xlll PAGB CHAPTER XIII. THE BLOOD. BY ALEXANDER ROLLETT. General Characters 374 Liquor Sanguinis ......... 374 Red Blood Corpuscles ... .375 Form and colour ....... 376 Size <; ... 380 Number 383 Alterations in . . . . • • • .384 1. From exposure to air . . . . 384 2. From mechanical agents 385 3. From drying 387 3. From venaesection ..... 388 5. From electrical discharges .... 388 6. From elevation of temperature . . . 392 7. From exposure to cold ..... 393 8. From exposure to water — Saline solutions . . . . . 394 Sugar ....... 396 Alkalies 398 Acids 399 Urea ..... .402 Neutral solutions of carmine . . . 402 9. Gases and vapours ..... 403 riews respecting the Nature of the Red Corpuscles . . . 406 Chemistry of the Red Corpuscles ...... 411 )lourless Corpuscles ........ 414 jvelopment of the Blood Corpuscles . . . . . 419 CHAPTER XIV. THE SALIVARY GLANDS. BY E. F. W. PFLUGER. reneral Plan of Structure ....... 423 Iveoli 423 Cells of the Alveoli . - 426 XIV CONTENTS. PAGB 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 Regeneration 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 CHAPTER XV. STRUCTURE AND DEVELOPMENT OF THE TEETH. BY W. WALDEYER. General distribution of Teeth in the Vertebrata .... 463 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 v . 479 Dentine and Cement . . . . ... 488 Kecent 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 . . 497 Gums • ... 504 CONTENTS. XV Structure of the Hard Palate „ Soft Palate Tonsils . PAGE . 505 . 506 . 513 TONGUE. Papillae . Septum Cartilagineum Mucous Glands Lymphatics Muscles . 514 515 516 519 519 Structure of its Walls PHAEYNX. 524 (ESOPHAGUS. Mucous Membrane . Muscular Layers Acinous Glands Lymphatics Structure of in Dog Rabbit . Horse Rat ... Birds Triton . Frog Transition of (Esophagus into Stomach 529 530 530 533 533 534 535 535 535 537 538 539 STOMACH. Mucous Membrane of Submucous Tissue . Lymphatics Nerves .... Muscular Coat . Structure of in Dog Rabbit . Rat. Birds 544 548 548 549 549 551 551 553 554 XVI CONTENTS. SMALL INTESTINE, BY E. VERSON. Muscular Coat of Small Intestine . 560 Mucous Membrane of Small Intestine . 563 . 565 Glands . 568 Muscularis Mucosae .... . 571 . 573 . 576 LARGE INTESTINE. Mucous Membrane of . 577 Glands of ..... . 577 Muscularis Mucosa3 .... . 578 Submucous Layer .... Muscularis Externa .... . 579 . . . 579 Nerves ...... . 579 RECTUM. Muscular Coats of . 580 Mucous Membrane .... .582 Lymph Follicles .... Epithelium .... ' ".'" Nerves . 584 . . 584 . . . 585 CHAPTER XVII. BLOODVESSELS OF THE ALIMENTARY CANAL. BY C. TOLDT. Mucous Membrane of the Oral Cavity . . . . . 587 Mucous Membrane of the Tongue . . . . . 589 Saccular Glands of the Mouth and Pharynx and of the Tonsils . 590 Acinous Glands of the Alimentary Canal . . ; . 591 Mucous Membrane of the Pharynx .... . 592 Mucous Membrane of the (Esophagus . . • . • 593 Muscular Coat of the Alimentary Canal . . . . .593 Mucous Membrane of the Stomach ...... 594 Mucous Membrane of the Intestine . . . ... 596 Solitary Glands and Peyer's Patches '.-,.. * . . 599 INTRODUCTION. GENERAL METHODS OF INVESTIGATION. BY S. STRICKEB. 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 modern 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 different 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 11 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 follow, 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 differ 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- ll GENERAL METHODS OF INVESTIGATION, BY S. STRICKER. ill nal images of various objects to be obtained. The examination of an object cannot be conducted by direct light with high powers, because the employment 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 uid — it is advantageous to use Briicke's doublet. This is laced in the arm of a Nachets' or Hartnack's stand, and the object is placed on the stage. The focussing can then be easily 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 dull 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, however, to attach them to an arm moving on a ball and socket joint, which again plays, horizontally and ver- B 2 IV INTRODUCTION. tically, 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 delicate 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 light proceeding from either a mirror or a prism. Simple micro- GENERAL METHODS OF INVESTIGATION, BY S. STRICKER. 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 in the first instance with a low power, and then to investigate the details of each part with a higher power. The very powerful 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 dned with colouring matters, and repeatedly washed, very tigh powers are in the first instance less instructive than Lower ones ; indeed, those who are not very expert in the of the instrument can actually see less with a No. 15 lan with a No. 8 Hartnack. However, the highest powers re even here very serviceable to the beginner, if he be engaged 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 still 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 Kuhne. It is indeed true, that in the perfectly fresh state the structure of the cornea cannot be satisfac- )rily ascertained, even with the Lest glasses. In this state VI INTRODUCTION. only those morphological elements are to be distinguished which refract light differently from the surrounding 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 full 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 ascertained, even with a simple microscope, by merely varying the inclination of the head. GENERAL METHODS OF INVESTIGATION, BY S. STRICKER. vii The simplest, but at the same time the most certain 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- ion of air bubbles is avoided. If the investigation is about be continued for some time, or if it be desired that the edium in which the object lies should not become concen- ted by evaporation from the edges, a brush dipped in oil y be drawn round the margin of the covering glass, which 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. Recklinghausen 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 Vlll INTRODUCTION. Any imperfections in 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 ; in other words, where practi- cable, only a covering glass should be used, the edges of which are oiled. 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 within 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 in 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 into a so-called gas chamber. In that part of the soft wall of putty which corresponds to the middle line 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 bull-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. STRICKER. 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 all into grooves cut in the slide. The spaces left can be filled up with putty. Fig. i. n « _J OIL 01 L_ Gas chamber, natural size. A, bird's-eye view ; B, longitudinal section through the middle line ; a a, wall ; b b, 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. n., that the flask containing hydrochloric acid gas can be raised by a string attached to the treadle, and passing over pulleys. 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 INTRODUCTION. duction of carbonic acid to an object under the microscope renders it requisite that we should be able to exchange it at will for atmospheric air. I introduce, therefore, between the wash bottle and the slide a T-shaped tube (a, fig. n.). The horizontal portion of this tube lies in the axis of communica- tion between the wash bottle and the slide ; 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. Fig. ii. 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 insufficient. 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 cell (fig. in. 6.) Fig. in. III. a. jr \ A II. A I. III Fig. in. a, Gas chamber, with mercurial valve, natural size. A I, bird's- eye-view ; A II, longitudinal section through the middle line; n n, groove ; //, clips ; gr, gas tubes ; r, object ; dd, covering glass in section. Fig. iii. 6, 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, Xll INTKODUCTION. dipping, therefore, into the mercury. If the cover glass is now kept down by clips, the gas chamber will be perfectly closed ; and no further explanation is required to show how the gas, whose effect is to be examined, 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 still 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 will. Various 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 GENERAL METHODS OF INVESTIGATION, BY S. STBICKER. xiii 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 into the arc of a constant current, increases with the diminution in diameter of the wire ; and indeed, according to Biess, 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 inconveniences ; and we possess in tin-foil 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 iir. TV. Slide adapted for being heated by means of electricity. Natural size. to glue it to a glass slide ; if now the extremities of the tin-foil are introduced into the arc of a constant current, the end in view is at once attained. • A very convenient method of introducing 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 clip the slide, they at the same time press on the broad end of the tin-foil 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 (6, 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 small, and should be in the field of the micro- scope. It will 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. STRICKER. 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 little water from time to time to supply the place of that rhich is lost by evaporation. Meidinger's arrangement gives off no injurious vapours, and lay therefore be enclosed in a little box, and placed beneath >r near the work-table. I transmit the conducting wires through loles 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 (54Q 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 Fig. vi. All. A I. 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 required must be ascertained by experiment. GENERAL METHODS OF INVESTIGATION, BY S. STRICKER. 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 p p. The springs which conduct the current through the instrument press upon these plates. Fig. vi. A n. is a longitudinal section of the stage in full work- ing order ; g g is 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 kkkJc 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 sufficient 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 XV111 INTRODUCTION. a plate of caoutchouc. The bulb, however, is not surrounded by a spiral, but by a metal shell, which resembles k k k in fig. vii., and to this the projecting rod k' is fastened. If the apparatus represented in fig. vn. 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. vi [. Slide capable of being heated, represented of natural size, kkkk, copper ring and rim imbedded in the plate o o ; qq, heating rod ; e e, c'ips. 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. n.) 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. STRICKER. XIX temperature of each part of the cover changes as the object glass sweeps over it, and must necessarily vary within certain limits, 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 investigations on the effects of heat in the gas cells. The reason that has induced me to describe the construction of the heatable gas cell at so great a length is, that it affords excellent results in quite another line of inquiry. 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 cell to contain more watery vapour, of which a part will 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 will 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. vili.) permits the passage of light ; and the preparation may again 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 two 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 6 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, Fig. VITI. ZD Metal slide for the conduction of water and steam, a a, conducting 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 cooling 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 effected. The temperature is ascertained by the thermometer, which occupies the position shown in the figure. Electricity is also an agent of considerable importance in microscopical investigations. Briicke, in his physiological inquiry into the tissues, employed a slide covered with tin- foil, as shown in fig. x. The slide s s was placed on two GENERAL METHODS OF INVESTIGATION, BY S. STRICKER. 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 will serve as conduct- ors. The distance of the laminae of tin-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 subjected to the action of weak acids or alkalies. At parts more remote from the electrodes changes also occur, XX11 INTRODUCTION. which, however, are not so remarkable as those which are induced by the chemical processes above alluded to. The effects 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, G the products of electrolysis first extend over the whole sur- face lying between the electrodes, and then the intensity of the current becomes extraordinarily reduced, frequently, indeed, to zero, on account of the pole becoming covered with bubbles of ;^as. On this account the employment of constant currents for microscopic investigation is scarcely to be recommended, for with the closure of even very weak currents, so violent a GENERAL METHODS OF INVESTIGATION, BY S. ST11ICKER. xxiii development of gas occurs, that but little confidence can be placed in the results that are observed to follow their passage. The amount of electrolysis that occurs with induction currents is much smaller, and they have therefore been most generally employed. The arrangement in which there is a single shock on opening and closure of the current is particularly advan- tageous. The shocks obtained from a Ley den jar are infinitely superior to the constant currents, because the instantaneity of the shock causes the disturbing influence of the evolu- tion of gas bubbles to be altogether abolished. It is not practicable to carry out the examination of tissues, under the influence of electrical currents, with the same elegance of detail as can be accomplished when a simple slide only is employed. The single circumstance that the tin-foil, in adhering to the glass, makes the surface irregular and uneven, renders it necessary that the sections of the preparation should be thicker, and proportionately interferes with the investiga- tion by means of high powers. I endeavour, therefore, to combine my researches with electrical currents, with those conducted in the gas cell. By this means I am able to avoid the inconvenience alluded to : for if the cavity of a slide, adapted as described above for a gas cell, be surrounded by a layer of soft cement, it is quite possible to place the electrodes in close proximity with the preparation which is on the inner side of the cover, and to examine it in consequence with high powers, I attach to each side of the slide a strip of tin-foil Fig. xi. which passes over the putty, and reaches its inner side (s s, fig. xi.) Cemented to the cover are also two small strips of tin-foil (fig. xi., s s'), which, running in the axis of the cover, leave between them a space of a few millimeters in diameter. The object is placed at this spot, and the cover is so disposed on the wall of putty that the metallic strips of the cover lie on the strips covering the putty, and the cover is then firmly pressed XXIV INTRODUCTION. down on the soft putty. The cell being now complete, the electric current is conducted by the strips of metal to the object, through which it passes at the same time; this lies immediately beneath the cover, and can therefore be examined with the highest powers. It is, moreover, no small advantage to combine the application of electricity with researches on the influence of gas, because we can neutralize or aid the effects of the current by the introduction of different gases. On breaking the current, heat is developed in the tissue. I have measured the amount thus set free in my arrangement of the induction current, and find that it amounts, when the core is fully thrust down, to about 3° C. (5§° Fahr.) If an uncovered drop of blood is under examination with strong ordinary lenses, these become dimmed at the instant of the passage of the cur- rent, but after a short period they again become clear. The preparation, however, very soon dries up. It is requisite in such cases to determine what are the effects of the sudden elevation of temperature, and what are those of the electric current alone. An additional means of research consists in effecting a change in the fluid components of a microscopic object. We have not as yet been able to succeed in combining this mode of investi- gation with the application of gases. A reliable experiment in which an alteration in the fluid is effected is only practicable when the object is placed between the slide and the cover, the borders of which at two opposite points at least have not been oiled. To one of these points a strip of filtering paper with sharply cut edges should be attached, and at the other the fluid which is to be applied may be introduced by a small tube, one end of which has been drawn out into a long point. When the strip of filtering paper is attached to the side of the cover, it sucks up the fluid of the preparation : a current is immediately es- tablished, which as a general rule carries everything off that is not firmly adherent. If a little time is now allowed to elapse, it is possible by the cautious application of a very small strip to cause a slow and feeble current to pass over the superficies of the preparation whilst the deeper part remains at rest. If at any time the fluid is altogether withdrawn, the cover sinks until the deepest layers of the solid elements which cling to the cover are pressed flat, unless, indeed, they are too resistant to GENERAL METHODS OF INVESTIGATION, BY S. STRICKER. XXV permit of such compression. As often, however, as a fresh drop is supplied from the other side, the cover again rises. In such experiments the focussing screw of the microscope must be deftly handled, if it be desired to keep the attention fixed on any given object. By the foregoing method a microscopic object can be washed in a chemical sense. Living morpholo- gical elements bear such an operation only so long as the fluid supplied is of an indifferent nature. The operation of washing can, however, be more freely performed in the case of dead tissues, to which, also, water and various reagents can be alternately applied. The formed elements may even be killed whilst under observation, and be then submitted to further reactions. Water may be transmitted so as to allow it to be seen how young cells become spherical, and how a dancing movement of the granules in their interior occurs, how the nucleus becomes more clearly visible, and how they ultimately burst. On the application of acids, again the definition of the nucleus may be seen to become sharper, followed by the shrivelling of the nucleus, whilst the material which surrounds it loses its well- defined contour, becomes paler, and gradually disappears. Formed elements with hard outline can be seen to swell up on the addition of alkaline solutions. Lastly, dissolved colouring matter may be introduced, and the gradual process of coloration of the formed elements or of certain constituents of the pre- paration may be witnessed. PREPARATION OF TISSUES. — If the constituents of the tissue- that is to say, the formed elements — do not form a solid mass, but only a loose texture with larger or smaller interspaces between them, no special preparation is required for their examination. A small quantity is placed upon the slide, and covered with a plate of thin glass. If the formed elements are in too close juxta-position, a drop of fluid may be added. It is to be borne in mind, however, that it is impossible to say of any fluid that it constitutes an indifferent medium for fresh tissues of all kinds. In all instances we must be prepared for changes taking place. Amongst those fluids which are most indifferent are, the fluid of the aqueous humour, the serum of XXVI INTRODUCTION. blood, and amniotic fluid in which a little metallic iodine* has been dissolved — the so-called iodized serum; finally, very diluted solution of neutral salts may be particularly recommended. If the formed elements have been already modified in their chemical characters by the addition of other reagents, if, for example, they have been soaked in a dilute solution of bichro- mate of potash, or of chromic acid, water alone may be added. Reagents which induce coagulation of the formed elements, and a consequent hardening of the tissues, cause them also to become cloudy. In order to examine such changed elements with any advantage by means of transmitted light, it is customary to apply highly refractive fluids, which, when they penetrate into their interior, render them transparent. The employment of these means have led to very remarkable advances in micro- scopic art. The highly refractive medium must be soluble in the fluid in which the tissues had previously been macerated. Glycerine is a highly refractive liquid of this nature, and it is soluble in water. Tissues can therefore be removed from watery solutions and immersed in glycerine, or what comes to the same thing, glycerine may be directly employed as a fluid for mounting microscopical preparations. Oil of turpentine is still more highly refractive, but it is insoluble in water. A tissue cannot therefore be removed from a watery solution into oil of turpentine. But alcohol is soluble both in oil of turpentine and in water. If, therefore, it be desired to impregnate a tissue with oil of tur- pentine, it is first removed from its watery solution into absolute alcohol, and from this into the turpentine. In cases where the tissue forms a membrane, it is only requisite to spread it out when fresh ; to add a drop of some indifferent fluid, and then to cover it with a plate of thin glass. This plan, however, is only feasible when the membrane is not too thick. As a general rule, fresh tissues are more or less transparent, but after death they become cloudy. When, therefore, dead membranes are spread upon the slide, and are required to be * The ainniotic fluid should be pure and almost destitute of smell. A trace of putrefaction renders it less available. The addition of iodine colours the fluid of a feeble yellow tint. GENERAL METHODS OF INVESTIGATION, BY S. STHICKER. XXvii examined with transmitted light, it is necessary, unless they are extremely thin, to add some highly refracting fluid. In the so-called parenchymatous organs — as the liver, spleen, and others — in the parts of the central nervous system, and in bones — nothing is usually to be seen, either in the fresh or in the hardened condition, so long as the connection of the morpho- logical elements is not disturbed. It is requisite, in such in- stances, either to tease out small portions with needles, or to cut very thin sections. a. THE PREPARATION OF SPECIMENS BY TEASING. — Speci- mens may be prepared in this way on the slide, a very small quantity of fluid being added : A minute fragment of the tissue should be placed on the drop, and then seized and torn by two sharp needles. Fibrous tissues can then be unravelled, as far as the vision of the observer and the optical means at his dis- posal will allow. The breaking up of tissues in this way is, however, accomplished, as a general rule, with less ease when fresh than after they have been macerated. The connecting substances which unite the formed elements are frequently of too firm a consistence to allow of their being thus torn, and the latter, therefore, are the first to yield, so that it is rare to see the formed elements whole and perfect. In such cases it is expedient to macerate the tissues for some time, in order to effect the solution of their connecting material. Solutions of potash have been applied, with this object in view, as well as of hydrochloric acid, bichromate of potash, Miiller's fluid, and very recently, with excellent results, iodized serum. Lime or baryta- water is to be recommended for the isolation of the fibrils of connective tissue, whilst for the separation of the fibres of transversely striated muscles the tissue should be macerated in very dilute sulphuric acid, at a temperature of 40° C. ; or it may be boiled in a mixture of chlorate of potash and hydro- chloric acid. The most delicate manipulation of all is required for the isolation of nerve cells and their processes. b. THE PREPARATION OF SPECIMENS BY SECTION. — It is only in some rare instances that sections can be made of animal tissues, either when fresh or after maceration, of sufficient deli- XXVlll INTRODUCTION. cacy to allow of examination with moderately high powers. Teeth, bone, and cartilage constitute, however, exceptions to this statement. Bone can, even when fresh, be cut into thin disks with saws, which may then be rubbed down with emery on a roughened glass plate, and polished on a hone. Cartilage requires no preparation, as thin sections may be readily cut from it with a sharp knife. The teeth are too brittle for the application of a saw. They should be attached to a cork by means of shellac, and rubbed down upon a whetstone. As a general rule, artificial methods of hardening the tissues must be employed. The simplest and most elegant mode is that of refrigeration. The tissue to be examined is placed in a little platinum capsule, and imbedded in the freezing mixture ; then, as soon as it has become hard, sections may be made with a cold knife. A second method of hardening that is in constant use is that by means of alcohol. The tissue, divided into small pieces, is placed in a flask containing absolute alcohol, which is renewed every few days, according to the amount of water present in the object. For membranous tissues, boiling in vinegar was at one time adopted, but so many better plans are now known, that it has with good reason fallen into disuse. If it be desired to harden the tissues by boiling, the best fluid is one which consists of eight parts of water, one part of creosote, and one part of vinegar ; in this the tissues should be allowed to boil for two or three minutes, and be then laid out to dry. After two, or at most three, days it acquires a consistence which is admirably adapted for permitting sections to be made. The thin sections should then be treated with a little dilute acetic acid, in which the tissues again increase in volume, and they can then be examined either in water or in glycerine. If boiled preparations remain for a long time uncut, they gradually acquire such consistence that they are no longer appropriate for obtaining sections. This inconvenience has led to the method of drying. It is, indeed, much more advan- tageous to dry fragments of tissue. It is to be remembered, however, that the morphological elements of the tissues, in all these modes of hardening, are not so perfectly preserved as when they are kept in fluids. A means of hardening, of very general value and application, is found in chromic acid. This GENERAL METHODS OF INVESTIGATION, BY S. STRICKER. xxix should be applied in solution, containing 0'25 to 2 per cent., and the perfectly fresh tissue ought to be placed in a large volume of the acid solution. The skin and all mucous mem- branes, the intestines, bladder, and conjunctiva, become in the course of a few days sufficiently hard to permit sections to be made ; and even this period can be shortened by removing the preparation from the chromic acid solution, and immersing it in alcohol, where it may remain for twenty-four hours. The proper hardening of the brain and spinal cord, however, re- quires a longer time. Large portions generally putrefy in the centre, though they harden at the surface. These parts of the nervous system should therefore be cut into small fragments. Here also the subsequent application of alcohol proves of great service. The bichromate of potash acts in the same way as chromic acid, but much more slowly, the effect produced in a few days by the latter requiring weeks with the former. At the same time, the bichromate of potash possesses the very great advantage that the tissues saturated with it do not be- come friable. Recently, perosmic acid and chloride of palla- dium have been recommended as means of hardening, the solution containing from one-fifth to one-tenth per cent. Various forms of apparatus have been constructed, by means of which fine sections can be made. It would be undoubtedly a great step in advance, if they could be made in any way which would render us independent of manual dexterity. But up to the present time these mechanical means have not attained sufficient excellence to lead to their general adoption. Sections are therefore still always made by the hand, and their beauty depends on the greater or less skill of the operator. The knives employed should always be of the best quality, and extremely sharp ; scalpels will be found to be best adapted for objects that have been hardened by boiling, whilst large flat blades are more appropriate for those that have been hardened in fluids. The sections, when made, may either be examined without further addition ; or they may be first prepared by means of needles, or be freed from adhering or imbedded morphological elements by the frequent use of a soft brush, or by blows with a delicate rod, or by shaking them in small test tubes. If the tissues are friable, or too small to be seized XXX INTRODUCTION. by the fingers, or possess a cavernous structure which it is desirable to preserve, or if they present irregularities and pro- jections of the surface, like villous processes, or papillse, and sections of these are required, the best method of dealing with the specimen is to imbed it. The process of imbedding consists in dipping the tissue into some liquid which will easily set, even at the ordinary tem- perature of the air. For this purpose we may employ, first, a mixture of wax and oil, and secondly, a concentrated solution of gum. The first is prepared by melting oil and wax, in equal proportions, in a porcelain capsule, by the heat of a lamp. The proportions of the two substances can, of course, be varied ; and, according to the peculiarities of the case, whether it is re- quired to be a little harder or softer, more wax or more oil must be added. The piece of tissue which is to be imbedded should first be kept in alcohol for a length of time sufficient to cause it to be thoroughly impregnated with that fluid, or, perhaps more correctly speaking, till the water it contains is as far as possible removed. This will occupy a longer or shorter period, in proportion to the strength of the alcohol; with absolute alcohol, and with small pieces of tissue, a few minutes are sufficient. The specimen is then to be placed in pure oil of cloves, which is far preferable to the oil of turpentine, that at one time was so generally used, partly on account of its more agreeable smell, partly because it is not so volatile, and partly also because it produces a consistence in the preparation more favourable to the obtainment of firm sections. The spe- cimen must remain in the oil of cloves till it is transparent, the infiltration of the oil being incomplete so long as any opaque spots remain visible. A little cone of paper may then be pre- pared, which is to be filled with the mixture, and into this the specimen is placed, whilst it is still fluid. Before the mass cools, the position of the object should be noticed ; and when it has become firm and opaque, its situation may be indicated by a mark on the surface of the wax, through which, when per- fectly cold and hard, the section can be carried. The section must be floated off from the knife. Imbedding is best adapted for very delicate objects, which have little consistency, and which cannot well be seized with forceps or needles. A portion GENERAL METHODS OF INVESTIGATION, BY S. STRICKER. XXXI of the wax will always be removed with the section, and must be detached from the knife by the aid of a little turpen- tine ; the preparation will then float off, and may be placed upon the slide, or in a little cell, without further trouble. If the preparation is to be subjected to no further manipula- tion, it is floated on to the centre of a slide, the superabundant fluid removed with care, and a drop of Canada balsam applied, after which a cover is placed upon it. The preparation is by this means completely preserved, and can be kept in this state and fit for examination for years. The process of imbedding in gum requires greater attention to minutiae ; but it is appro- priate for specimens which contain much connective tissue, and answers for them much better than imbedding in wax. The preparation need not be impregnated with oil. It may be macerated for twenty-four hours in alcohol, of ordinary strength, and from thence be removed into a paper cone filled with a very concentrated solution of gum; the whole cone must then be immersed again in alcohol. In the course of two or three days the gum acquires a consistence which renders it very fit for making sections. No definite statement can be made in regard to the degree of this consistence, since it must be proportionate to the hardness of the tissue. Better sections are made of very soft tissues when they are imbedded in a mass which is not too hard, and vice versa. The sections may be floated off by means of a little water, and be examined after the addition of a drop of glycerine ; or they may be subjected to further manipulation. In the former case, if it be desired to preserve the preparation permanently, the excess of glycerine is to be removed from the edges of the cover, and these may then be painted with a layer of varnish, which hardens on exposure to the air. For this purpose a solution of asphalt in turpentine, the so-called asphalt varnish, or some similar material, may be employed. The preservation of preparations in glycerine exerts no prejudicial influence upon them, and when it can be used it is preferable to Canada balsam. Sections which have been taken out of water may, however, be placed in alcohol, then in oil of cloves, and from thence they may be removed to Canada balsam, in which they may be preserved. The contours of morphological elements, not previously XXxii INTRODUCTION. visible, can often be made evident by treating the preparation with certain colouring matters. The principle of this means of research consists in the circumstance that various constituents of the tissues become quickly stained with colouring matters, or combine with them, whilst others do not. The tissues should be dipped in the solutions of the colouring agents, allowed to remain in them for some time, and then washed. Cceteris paribus, the concentration of the solution stands in inverse relation to the length of time required in order that certain effects should be produced. It is therefore advantageous to use very dilute solutions, and to prolong the time of their action. The more gradual this is, the more scope is afforded for exact researches. A division of the colouring reagents can be made — first, into those, the solutions of which, when examined by transmitted light, show the same absorption colours they impart to the tissues ; secondly, into those which impart to the tissue one of their own proper absorption colours ; and lastly, into those whose solutions absorb no definite colour, or are, as we are accustomed to say, colourless. In the two last-mentioned cases, after saturation with the fluid, some chemical process must take place. An example of the first kind is seen in carmine, the alkaline solutions of which impart their own colour to the tissues ; an example of the second kind is met with in chloride of gold, the solutions of which are pale yellow, whilst the tissues that are saturated with it assume a violet tint ; and an example of the third kind is found in nitrate of silver, the solutions of which are colourless, but yet stain the tissues of a dark brown hue. The secondary chemical change may either occur without further addition, or some means must be employed to induce it. When the tissues are macerated in dilute solutions of perosmic acid, they assume, sooner or later, according to their chemical nature, a black colour, without any addition ; but those which have been in solutions of nitrate of silver require exposure to light before the chemical change, which consists in the precipi- tation of silver, will occur. Gerlach introduced the method of examination by staining the preparation into practice. His first experiments were made with carmine. At the present GENERAL METHODS OF INVESTIGATION, BY S. STRICKER. xxxiii time, however, many colouring agents are employed ; specimens may be stained with tincture of saffron, with anilin, with indigo-carmine, hoematoxylin, and picric acid ; and also with nitrate of silver, chloride of gold, chloride of palladium, and perosmic acid. When fresh membranes are to be acted on by nitrate of silver or chloride of gold, the pieces should be cub from the living animal, and thrown into the solution without further preparation. The solution should be kept in a dark place as long as the action is allowed to proceed : the preparation should then be recovered by means of sharp-pointed glass rods, washed, and placed in the light. After fragments of tissue are taken out of solutions of silver, they may be placed in alcohol or glycerine, and then exposed to light ; or the specimen may be prepared for microscopic examination in glycerine, and allowed to remain in it for twenty-four hours. Preparations which have been in solution of chloride of gold, after having been thoroughly impregnated with it, should be placed in water slightly acidulated with acetic acid. If the action is required to be more intense, the membrane is to be well brushed, before it is removed from the staining fluid, with a wet brush. This is the best method of procedure, for example, with the centrum tendineum of the rabbit, which should be thus brushed both on the abdominal and on the thoracic surface, whilst the cornea need only be brushed on the anterior surface, and then removed from the liquid. In non-membranous tissues, just as in those which require to be broken or cut up for microscopical examination, the pre- pared specimen may be tinted whilst on the slide, after which it may be washed, and then covered in the usual manner. Solutions of colouring matters which only act on the fresh tissues, as, for example, nitrate of silver, can obviously only be applied to sections made from recent and therefore necessarily frozen tissues. On the other hand, colouring agents which, like carmine, do not affect the fresh tissues, can only be applied to sections which have been made from dried specimens, or from those which have been hardened by chemical reagents. The particular mode of treatment adapted to each tissue will be D XXXIV INTRODUCTION. described in the several chapters devoted to the consideration of each. The results obtained depend very much on the mea- sures adopted, though it was thought it would prove of advan- tage to give here a general account of them. Besides the mode of staining the tissues effected by dipping them in various solutions, another may be mentioned in which coloured fluids are injected into the vessels. Formerly injec- tions were only made with the object of rendering the lymph or blood-vessels visible by means of coloured material, and the structure of the vascular walls was wholly disregarded ; but in the present day injections are made with the object of ex- hibiting the structure of the parietes of the vessels. For this purpose, for example, a solution of nitrate of silver may be injected. Where, however, a solution of this kind is employed, the tube which is introduced into the vessel, and termed the canula, must be made of glass or platinum, and be connected with the syringe, which should be constructed of the same material, by means of an india-rubber tube. Instead of the syringe, an apparatus may be applied in which the injection fluid is propelled by the pressure of air. This mode of injecting, first introduced into practice by Ludwig, is far more certain and elegant than the old method of the syringe. The injection fluid is, once for all, placed in a Woulf 's flask, the size of which is appropriate to the quantity of fluid required to be used. Into one neck of the flask a tube is inserted air-tight, and reaching to the bottom, the upper extremity of which is bent at a right angle, and drawn out into a point : the other neck of the flask is surmounted with a short and also rectangularly bent tube. When this is connected with an apparatus from which air can be driven under a defi- nite pressure, the injecting fluid must be expelled from the opposite tube. If, now, a canula connected with a short india- rubber tube has been fastened into a blood-vessel, and has been subsequently filled with an indifferent fluid by means of a pointed glass tubule, the apparatus can be at once put into action ; and when it is seen that the injecting fluid begins to be discharged at the pointed extremity of the tube connected with the Woulf s flask, that point is quickly introduced into the india-rubber tube of the canula, and the apparatus is GENERAL METHODS OF INVESTIGATION, BY S. STRICKER. XXXV allowed to work as long as the injection will last. The mer- curial apparatus of Hering is well adapted for the expulsion of atmospheric air. If this is not to be obtained, I apply the jet of the waterpipe on the same principle. The atmospheric pressure of the apparatus is measured by means of a mano- meter, and the rapidity with which the injection is forced onward can be regulated by retarding or accelerating the entrance of the mercury or water. When the blood-vessels are to be injected, the canula must in all instances be introduced and fastened into the vessel ; but, in the case of lymph-vessels, according to Ludwig, the canula need only be stuck into the tissue, and firmly tied to it. The point of the canula should be cut like a pen, and there should be a groove behind the aperture to prevent the ligature from slipping. In the injection of blood-vessels, all means of escape should be stopped, with the exception of one; and when the fluid flows freely from that, no more fluid should be in- jected. The injecting fluid distributes itself gradually through all parts, if the pressure be steadily maintained. Even though it is discharged to some extent at one point, injections with solutions of silver should be kept up for at least half an hour, under very gentle pressure ; and, in this case, it is not requi- site to tie any vessels when the injection is completed. It is only requisite to throw the tissue into dilute alcohol, in order to preserve it perfectly. When it is only required to show the blood-vessels, and not the parietes of the vessels, coloured fluids should be employed ; and if the arteries and veins are to be distinguished, each system must be separately injected with a fluid, which must not traverse the capillaries. The material in which the colouring matter is suspended is usually wax, and the colouring substance some granular pigment, as ver- milion, red lead, etc. The injection can only be satisfactorily made with a warm syringe and warm tissues, as otherwise it cools too rapidly. After an injection of this kind has been made, the structure of the tissues can no longer be investi- gated. We can only discern one or more layers formed by the ramification of the vessels, and of course the object can only be examined by direct light. Injections thus made are also used for the so-called corrosion preparations. In the produc- D 2 XXXVI INTRODUCTION. tion of these, the organ, after being injected, is immersed in some reagent which destroys the tissue, whilst it leaves the injected mass intact. The form of the vascular network is thus obtained in coloured wax, and such preparations can be put up in various ways under glass and in frames. Injections made with transparent solutions are now very common. A canula is inserted into an artery, and the fluid allowed to discharge itself by a vein. The dissolved material penetrates the capillaries whilst the coarsely granular pigment is stopped in the larger vessels. In such preparations it is obvious that no difference can be seen between the arteries and the veins ; but, in this condition, they are not fit for microscopic exami- nation. It is still requisite to harden them by freezing mix- tures, or by means of alcohol, and then to make fine sections. In these injections it is always requisite that a certain fulness and tension should be given to the vessels ; their forms then assume greater definition, and are generally more similar to their natural condition. On this account it is advantageous to dissolve the colouring matter in something which will readily coagulate, and which consequently affords all the advantages of a hardened tissue. Fine gelatine is usually employed, and is dissolved in water over a water bath, the colouring matter already in solution being then added, and the warm mass intro- duced into a Woulf s bottle, which again must be immersed in a warm water bath. The injection with gelatine is sufficiently tedious if required to be done thoroughly, as the mass stiffens too easily. The organ to be injected should therefore be brought into a warm room, and, where practicable, placed over a water bath which is adjacent to the former one. The colouring matters usually employed are Prussian blue and carmine ; the latter not in a state of complete solution, but partly precipitated by the addition of a little weak acid from its alkaline solution. Thiersch, whose transparent injec- tions are perfect models of this kind of art, uses a transparent green and yellow. He obtains the former from chromate of potash and nitrate of lead, the latter from a mixture of this with blue. When the injection with gelatine is completed, the open vessels must be tied, and the organ introduced or sus- pended in alcohol contained in a wide-necked bottle, pressure GENERAL METHODS OF INVESTIGATION, BY S. STRICKER. XXXVll being carefully avoided. In order to obviate the inconveni- ences of the method of injecting with warm fluids, Beale recommends a fluid that can be used cold, consisting of colour- ing matter, water, glycerine, and traces of hydrochloric acid. When the organ has been injected, it is placed in absolute alcohol, and then treated as before. This mode of injection is very convenient, the vessels acquiring a very pretty colour ; but they can only be used on organs possessing a certain con- sistence. Lastly, the method of self-injection occupies an important position amongst the various modes of injection. It has long been practised in the case of the vascular system of the frog. A pointed glass tube, filled with the coloured injecting fluid, is inserted into the vena cava, and distributed through the system by the force of the heart itself. Kiihne and Chrzon- szczewsky have thus injected the biliary vessels of living animals by means of colouring matter introduced by the jugular vein. Toldt has very recently practised a similar method for injecting the lymphatics. In the case of the biliary ducts a colouring material (indigo-carmine) in solu- tion is employed, in order that it may be transmitted through the liver cells into the ducts ; but in the case of the lympha- tics a granular pigment (anilin) precipitated by water from its alcoholic solution, is introduced into the blood. Connected with the introduction of granular pigment is the method of colouring organs through the agency of the food, which has of late years assumed so much importance. This subject will be treated of at length in the first chapter of this work. [UKIVERSIT7] CHAPTER I. THE GENERAL CHARACTERS OF CELLS. BY S. STRICKER. INDEPENDENCE OF CELLS. — In the year 1835, Joh. Miiller commenced an essay on Organism and Life* with the following words of Kant : " The cause of the particular mode of existence of each part of a living body resides in the whole, while in dead masses each part contains this cause within itself." From this quotation it is sufficiently evident what role was at that time ascribed to the microscopic constituents of the body from the point of view taken by biologists. Fibres, cells, spheroids, and granules were distinguished under the micro- scope, and it was stated that these structures were not inde- pendent so far as their growth was concerned, but were subject to the influence of the vessels. They were on this account differentiated from vegetable tissues, which were supposed to possess an independent existence. A few experiments, how- ever, led to the establishment of certain analogies between vegetable and animal cells. Joh. Miiller himself, for example, pointed out the analogy that obtains between the cells of the chorda dorsalis and vegetable cells ; and subsequently, when Valentin discovered the nuclei of the cells of the epidermis, he commented upon their similarity to those of the cells of plants. Henlef made a decided step in advance when he proved that * Physiologie, Band i., 1835. f Symb. ad. Anat. vill. intest. Berlin, 1837. 2 THE GENEEAL CHAEACTERS OF CELLS, BY S. STEICKEE. the epidermis cells, as they become more superficial, increase in diameter. An instance was thus given of increase without the intermediation of vessels. Schwann* seized the various analogies and points of relation between the cells of animals and plants in a comprehensive and fundamental proposition. Animal cells, he said, are completely analogous to vegetable cells, and are quite as independent in their mode of growth. The vessels of the animal body only cause variations in the dis- tribution of the nutritious fluid. Joh. Miillerf at once and unreservedly adopted this proposi- tion. His observation, that the works of Schwann were the most remarkable that had hitherto appeared in the domain of histology, certainly greatly aided the rapid acceptance they everywhere obtained. Virchow had already compared the whole organism to a free state, containing individuals endowed with equal privileges if not with equal powers. The views entertained of the physio- logical significance of the constituents of the tissues, and espe- cially of the animal cells, became, in consequence, completely modified. An impulse leading to the further extension of these ideas resulted from the examination of the lower forms of animal life. DujardinJ had discovered in the year 1835 a con- tractile substance capable of movement in the lower animals, to which he applied the name of sarcode. The singularly interesting phenomena exhibited by the living sarcode has at- tracted the attention of many observers, as Meyen,§ Huxley, Max Schultze, and Joh. Miiller. It was regarded as limited to the lower animals; and though destitute of nerves, the possession of irritability was ascribed to it.[| Meyen's attempt to show that the Infusoria were unicellular organisms was indeed refuted, but it was admitted that a little mass of sarcode con- stituted a living and independent being. * Mikroskopische Untersuchunyen, 1839. t Jahresberichl, 1839. | Annal. des Sci. Nat., Tom. vii. § See the general literature of this subject in E. Hackel, Die Radiolarien, 1862. j| See Max Schultze's Organism d. Polythalamien, 1854. INDEPENDENCE OF CELLS. 3 The discovery of Siebold,* that the vitelline spheres of the egg of the Planarise exhibit alternate contractions and dila- tations, which, under favourable conditions, continue for hours, and the various subsequent discoveries of similar movements, or changes of form occurring in the colourless blood corpuscles, in pigment cells, and elsewhere, have led Kollikerf to express the opinion that the contents of all cells are contractile. Virchow^: gave a still more precise expression of opinion when he stated that ciliary movement is to be attributed to a contractile substance ; to which conclusion he was drawn by the discovery that under certain circumstances these move- ments, after having ceased, could again be excited by dilute solutions of the fixed alkalies. Leydig§ referred to the significance of the movements occur- ring in the spherules of the yolk, which he, in common with Ecker, regarded as evident phenomena of life. Kiihne|| undertook a series of comparative physiological and chemical researches on muscular substance and sarcode, and pointed out the similarity of the phenomena they presented in the act of dying. By all of these, however, the sarcodal substance was regarded as something different from animalcules, and as a material sui generis. Max SchultzelT was the first to show that sarcode is analogous to the body or contents of animal cells, and that on this account the infusorial animalcules possessed of inde- pendent life were simple or compound (fused inter se) cells. Schwann's views received support from these statements. According to the new doctrine, the cell was the typical form element of nearly the whole organic kingdom. The previous inquiries on the contractile sarcode could now be applied to the knowledge of the animal cell, and the renewed parallel * Froriep. Notizen, No. 380, p. 85. t Wiirzburg. Verhand., Band viii. | Virc how's Archiv, Band v. § Handbuch der Histologie, 1856. !| Miiller's Archiv, 1859, p. 817. 51 Muller's Archiv, 1861, p. 17. 4 THE GENERAL CHARACTERS OF CELLS, BY S. STRICKER. investigations between sarcode and the protoplasm of the plant on the one hand, and of animal cells on the other, under- taken by E. Briicke* E. Hackel,f Max Schultze,} and W. Kiihne,§ have, in a very short space of time, advanced our knowledge on these points to a greater extent than the inves- tigations of the preceding twenty years. Briicke, who regards the cells as elementary organisms, ad- mirably expresses the ideas, the development of which has been lightly sketched in the following passage : — " If we consider," he says, " how complicated the mechanical arrangements must be which lie at the root of the spontaneous movements of cells, and if we consider further that up to the present time we have only paid attention with the microscope to obvious and perceptible movements, and that no regard has been paid to the arrangements, by virtue of which the little organism nourishes itself, increases in size, and begets its like, nor any to those means by which it displays its specific attributes ; if we, I say, consider all this, we must necessarily recognise that we have to deal here with an organism, the complication of which, although, truly, not comparable with that of an animal, nor affording any good reason for believing that it is itself composed of innumerable small organisms, yet constitutes one to which we may fairly attribute the possession of a highly artificial structure, the essential architectural elements of which are, however, completely beyond our grasp." IDEAL TYPE OF A CELL. — Johann Miiller proved that the cells of the chorda dorsalis possessed proper walls. In similar cells from the frog, Schwann demonstrated the existence of a nucleus, and was by this discovery first led to perceive the analogy between the cells of animals and plants. Here, then, we have a cavity bounded by walls, in the interior of which is a nucleus. Scarcely any structure is to be met with in the whole range * Elementar-organismen, Wiener Sitzungsberichtc, 1861. t Loc. cit. J Protoplasm der Rhizopoden. Leipzig, 1863. § Protoplasma und die Contractilitdt. Leipzig, 1864. IDEAL TYPE OF A CELL. 5 of animal tissues which, is more suggestive of comparison with that which the botanists call a cell. (See p. 6.) All animal cells were at this time considered to be con- structed on the same principle, being held to possess a cell wall, enclosing a cavity, in which were fluid contents and a nucleus ; when the membrane was not visible, it was either supposed to have burst, or was admitted to be present. In the cells of the egg a membrane was recognised by Krause,* from the presence of a double contour line. This mode of proof was not, however, strongly supported. C. H. Schultz considered he was able to exhibit the membrane of the blood corpuscles by the action of water upon them, inasmuch as they swelled up in this fluid, and assumed a spherical form; he also believed the nucleus revolved in the interior of the sphere. The corpuscles of pus and of mucus had, however, even in the eyes of Schwann no distinctly demonstrable membrane; he regarded them as minute roundish masses, containing a nucleus, which might be termed cells, because this was the elementary form of all animal and vegetable cells. In accordance with the general views of Schwann, respecting the analogy of animal and vegetable cells, the ideal type of a cell was constructed. Individual and scattered opposition to this ideal type of a cell was ineffectual so long as the whole theory of Schwann was contested, as it was, for example, by Arnold.f With sure footing, and still resting on Schwann's conclusions, Leydig also abandoned the scheme of cell construction already mentioned.^ He maintained that the contents of the cell are of higher dignity than the membrane, and constitute the mate- rial basis for the sensible and irritable processes ; and that the conception of a cell requires the presence of only a little mass of substance, inclosing a nucleus. The cell membrane is, in his view, only the hardened external layer of the cell substance. Max Schultze was, however, the first who effectually directed * Miiller's Archiv, 1837, p. 139. t See his Anatomie, 1845, Band i., p. 144. J Loc. cit. 6 THE GENERAL CHARACTERS OF CELLS, BY S. STRICKER. the views of histologists away from the idea of the vesicular construction of cells. As has already been stated, Max Schultze had himself furnished a new definition of a cell, which con- stituted an extension of the theory of Schwann. Max Schultze also defined the cell to be a little clump of matter (proto- plasm), with a nucleus. The importance of this definition, however, did not lie in the fact that the existence of a mem- brane in many cells was denied — that had been already more or less positively stated before Max Schultze. The essential point was, that the identity of the so-called cell contents with the primary animal substance, or sarcode, was clearly recognised. Little advance had, indeed, been made in the way of estab- lishing a basis of life ; for nothing more was known of the processes which take place in the living substance, than of those that were carried on in vesicles — perhaps still less — for all the phenomena of diffusion were intelligible on the vesicular theory, whilst it was difficult now to account for them. Na- turalists, however, were familiar with irritable independently existing animals, but not with the idea of an irritable and independent vesicle obtaining its food by the laws of diffusion. The conception of a living cell body, or elementary organism (Briicke), has been an exceedingly satisfactory one /to biologists, on the same principle that it gives us a great degree of satisfaction to be able to attribute to some familiar I circumstance a noise in our sleeping apartment, on the origin of which we have long speculated in vain. Those membranes of the animal cell which did not exhibit a double contour, were compared by intelligent histologists, not with the cel- lulose investment, but with the primordial utricle of the cells of plants. Botanists* distinguish a cellulose investment in the cells of plants, with- in which is the protoplasm that includes the nucleus and the solid and fluid contents of the cell. The protoplasmic mass externally, where it comes into contact with the wall of cellulose, was supposed to be invested by a very thin membrane — the primordial utricle. But Pringsheimf has shown that such a primordial utricle does not exist, the * H. v. Mohl, Vermischte Schriften, Botan. Inhalts, 1845. f Ban und Bildung d. Pflanzenzellen, 18o4. IDEAL TYPE OF A CELL. 7 protoplasm lying in apposition with the inner surface of the cell wall. The term protoplasm had already been brought into use by Remakfor the contents of animal cells. Max Schultze proposed to apply the term to the living mass of the cell, and since then the word proto- plasm has been very generally employed. Max Schultze* takes the embryonal cell as the basis and starting-point of his definition. " The most important cells," he remarks, " those in which the fulness of cell life, the un- limited power of tissue formation, is most distinctly evident, are clearly the embryonal cells, which proceed from the division of the cells of the ovum. We may see in these the true arche- type of a cell, and yet they only consist of a little mass of protoplasm and a nucleus. Both the nucleus and the proto- plasm are products of the division of similar constituents of another cell. Such cells include a living force in their interior, essentially possessed by the protoplasm, although it is true that the nucleus likewise plays an important part, not hitherto known with sufficient accuracy. The protoplasm is no farther isolated from external objects than by the circumstance that it will not combine with the surrounding medium, and that it constitutes, with the nucleus, a single whole. A distinct membrane may, indeed, appear on the surface formed by the conversion of the outer layer of the protoplasm, but then it must be allowed to be an early indication of a retrograde process. A cell invested by such a membrane can no longer divide — that is a power possessed by the enclosed protoplasm alone. A cell with a membrane differentiated in its chemical characters from the enclosed protoplasm, is like an encysted infusorial animalcule." Bracket goes a step farther in his definition of a cell, maintaining that no proof has been given that the nucleus is indispensable to our conception of it. He rests his state- ment essentially on the fact that cells are known to occur in the cryptogamia in which no nucleus is visible. " We have," he says, " no positive information, either respecting the origin or the function of the nucleus ; even the constancy of * Loc. cit., p. 8. t Die Elementar-organismen, pp. 18 — 22'. 8 THE GENERAL CHARACTERS OF CELLS, BY S. STRICKER. its occurrence appears to be subject to certain limitations, especially if we consider the cells of cryptogams, and do not start with the presupposition that, even in those cases where no nucleus is visible, it must nevertheless be present." The opinion of Briicke undoubtedly gains in weight, the more care- fully the subject is considered. Max Schultze* has discovered a non-nucleated Amoeba (Amoeba porrecta) in the Adriatic ; E. Hackelf a larger non- nucleated Protista (Protogenes primordialis) in the Mediterra- nean ; and lastly, CienkowskiJ has described two non-nucleated monads, namely, Monas amyli and Protomonas amyli. Hackel states, in reference to his protista, that it propagates by division. It is, moreover, a fact, first made known by Y. Baer, that the germinal vesicle of the impregnated egg — that is, the nucleus of the ovum — vanishes, and that the further process of develop- ment commences with a new generation of nuclei. I must express, in regard to the egg of the frog, my entire concurrence with V. Baer in regard to the question at issue. I have under- taken a great number of comparative investigations between fertilised and unfertilised ova in the same mode as that em- ployed by him, and have found a germinal vesicle in the latter as a rule, whilst in the former there is only a cavity left, or even a total absence of any trace of its existence. But the ova of the more highly organised animals pass, as is well known, through various stages or grades of development till they reach a state in which their life terminates, and these ascending stages of deve- lopment may, without straining the point, be generally compared with the ascending grades of organisation which characterise the existing world. It is therefore but a step to admit that the commencing stages of the process of development correspond to the lowest forms of animal life. The existence of the non- nucleated cryptogams and of the non-nucleated protista which are now known, speak strongly in favour of such an analogy. But if we desire to be logical, if we do not desire to advance the statement that the non-nucleated bodies of the lower plants Organism der Polythalamien, 1854. Zeitschrift fur wiss. ZooL, 1865, Band xv. Max Schultze's Archiv, 1865. IDEAL TYPE OF A CELL. 9 and animals and the fertilised ovum occupy an unique and isolated position which is not assumed by any other being in the whole scale of creation, we must exclude the nucleus as an unnecessary factor in the ideal type of an elementary organism. We must also in future apply the histological term cell to the morphological elements of the higher animals or to independent living organisms, even if we are unable to discover anything more in their structure than that they are little masses of animal sarcode or protoplasm. Nor will any essential change be made in our views even if it be hereafter proved that there are cases where the nucleus is not only present but plays an extraordinarily important role. I* have shown that little masses of protoplasm, destitute of nuclei, and which might be presumed to be the remains of cells, may still present some of the phenomena of life. I also now know that in other places where many young cells are collected together, fragments or minute separated particles occur about the size of a nucleolus, which, if they become attached to the slide, sometimes exhibit very lively movements, and this espe- cially if the object plate be warmed to from 68° to 70° Fahr. May we now, in consequence of our new definition, consider these little masses as cells ? and shall we be justified in giving this name to all the minute particles which, when armed with instruments of still greater penetration, we may be able to per- ceive and find capable of spontaneous movements ? In the present state of our knowledge we shall certainly reply in the negative. We shall continue to regard such minute masses as living or organised matter without reference to their size, so long as the optical means of research at our disposal do not i permit us to make the observations necessary for a different statement. We cannot, however, term these masses cells, any more than we can apply the name of the whole animal to the excised heart of a tortoise. In order that we should apply the term " cell " to such an isolated fragment of living substance, it is necessary that we should recognise the whole group of phe- * Uber contractile Korper in der Milch, " On the cjntractile bodies in Milk," Wiener Sitzungsberichte, 1866. 10 THE GENERAL CHARACTERS OF CELLS, BY S. STRICKER. nomena which are characteristic of an independent animal — an independent organism. PHYSIOLOGICAL PECULIARITIES OF CELLS. — Contractile sub- stance, or protoplasm, appears, when examined with the best microscopes, to be homogeneous, or destitute of structure. It rarely occurs, however, in a pure state; for small particles are usually imbedded in it, which have either been taken up from without, or have formed in the interior as a consequence of chemical processes. If the protoplasm contain many coloured corpuscles, the cell is termed a pigment cell ; if it contain fat molecules, a fat or granule cell. The presence of small colour- less, dull, or shining granules is indicated by the term granular applied to the cell, and of such cells two kinds are distinguished — those that are coarsely and those that are finely granular. When other kinds of material are contained in the cell, their presence is indicated by appropriate terms. It is thus usual to speak of starch-holding cells, and the like. Since the researches of Hackel (see p. 16) have shown us that foreign matters can penetrate into the interior of the protoplasm, the origin of all such particles must be investigated. We must determine in every case whether a body which lies in the interior of the cell is the result of some chemical process in the interior of the protoplasm, or has been introduced from without. If particles of colouring matter are artificially caused to enter, as has been successfully accomplished by Eecklinghausen, Max Schultze, Billroth, Cohnheim, and others ; then the question as to whence the colouring matter proceeds is answered by the experiment itself. But it is more difficult to decide from whence those bodies that are found imbedded in cells proceed, which occur with- out the agency of the experimenter. The determination of this point may prove, however, of extraordinary importance. Since, for example, Preyer showed that portions of red corpuscles are eaten by the amoe- boid cells of the frog, we could not admit without much proof that the presence of red corpuscles in the interior of the white was due to the development of the former in the interior of the latter. * " The consistence of protoplasm varies within moderately wide limits. It may, like a fluid, form drops, assuming, when in small quantities, a spherical form, or may extend itself upon MOVEMENTS OF CELLS. 11 the slide like a gelatinous body ; or, lastly, it may contract up into a resistant ball. Protoplasm may therefore be said to be fluid, or solid, or gelatinous. Its states of aggregation are subject to constant change, and none of the ordinary terms employed for this pur- pose will be in all cases accurate. Protoplasm is termed a living substance, and the application of this term is based upon its exhibiting the sum of those phenomena which we have learned by experience to be cha- racteristic of living animals. These phenomena are active or spontaneous movement, nutrition and growth, and the capa- bility of reproducing its like. The movement of cells is easily to be seen. The changes of which it is the result take place in so short a space of time that they may be followed with the eye. The growth of the cells is a process of a slower nature, and cannot be directly observed ; nor has any one, as yet, been able to place the cells under the microscope, under such favourable conditions as to witness their increase in size. We must therefore be led by analogy to the conclusion that this really takes place. Various observations have been directly made on the nutri- tion of unicellular animals. It may be seen how they take up foreign bodies, and nutritious material, into their bodies, and some of the changes of the material introduced may be followed. It is difficult to observe the mode of nutrition that occurs in the cells of the compound animal body, because the nutritive materials are brought to them in the form of solution in the juices of the animal body. Moreover, the processes by which the dissolved substances penetrate the cells is concealed from our observation. The act of reproduction depends on two separate processes ; first, on the growth of the mother-cell, and secondly, on the detachment of the daughter-cell (birth). The latter alone is subject to direct observation, and usually this only is under- stood when reproduction is under consideration. PHENOMENA OF MOVEMENT IN CELLS. — We conclude that movement occurs in cells, either from certain movements of the 12 THE GENEEAL CHARACTERS OF CELLS, BY S. STRICKER. granules that are imbedded in the protoplasm, or from the occurrence of certain changes in the form of the protoplasm itself. The movement of the granules in this case is a passive movement. The granules which have been introduced from without, as well as those which have developed in the inte- rior, providing they are not too heavy, move as the result of the action of the forces we are about to consider. The movement of the granules is either continuous or vibratory. The continuous movement, again, presents two forms ; first, a relatively slow progression, corresponding to and following the changes of form of the cell. Engelmann* states particularly he has observed, in the corpuscles of the cornea, that they begin to move in order, from before, backwards, and refers to similar observations of Hofmeister on the Plasmodia of the Myxomycetse. Secondly, There is a swifter flowing movement that far exceeds the changes of form of the protoplasm in rapidity. Max Schultze describes the movement of the granules in the threads of sarcode that the Foraminifera project through the apertures of the shell, as a gliding or streaming motion of granules imbedded in a sarcodal substance .f "As the pas- sengers in a broad street swarm together, so do the granules in one of the broader threads make their way by one another, oftentimes stopping and hesitating, yet always pursuing a determinate direction, corresponding to the long axis of the thread. They frequently become stationary in the middle of their course, and then turn round ; but the greater number pass to the extreme end of the thread, and then reverse the direc- tion of their movement." It cannot be doubted that these continuous motions depend on vital processes in the cells. At all events, we are acquainted with no analogous phenomena in unorganised bodies. The vibratory movement of the granules calls to mind the so-called molecular movement of Brown. It may be witnessed in the salivary corpuscles, and under certain conditions in the * Ueber die Hornhaut. Leipzig1, 1867. t Das Protoplasm d. Rhizopoden, p. 11. MOVEMENTS OF CELLS. 13 colourless blood corpuscles, pus corpuscles, and others. On this account it has been doubted whether these movements really depend on the vital properties of the protoplasm. Such move- ments, it may be observed, occur also in dead cells, as in the case of granules that have escaped from cells undergoing disin- tegration, which continue to move, provided that the medium they enter does not present any obstacle. Similar movements, too, are found in cells that are clearly living. The dancing movement ceases in the interior of the corpuscles of saliva on the cautious addition of a solution of common salt, containing from J to 1 per cent. ; but this still per- mits the movements of fresh pus or lymph corpuscles to continue. Recklinghausen* has described similar phenomena in the latter kind of corpuscles. When the menstruum is diluted with water, they become spherical (an experiment that had already been performed by H. Miiller and Reinhardt),f and the granules in their interior begin to dance ; but as soon as the fluid becomes somewhat more concentrated in consequence of evaporation from the .margins of the cover, this vibratory movement ceases, and the corpuscles commence again to undergo their customary changes in form. We see here, then, clearly enough, that two phenomena alternate : if the corpuscles are spherical, the granules dance in their interior ; but if the corpuscles undergo changes of form, then the granules cease to vibrate. It is rare to see the so-called molecular movements in cells which change their shape. It may, however, be occasionally observed in the colourless blood corpuscles of the newt, after the addition of water. The question whether the vibratory movement of the granules stands in relation to the life of the protoplasm is only appli- cable to such living cells. Bruckel has referred to the possibility of this connection, in con- sideration of the circumstance that the movements are arrested by induction currents of sufficient intensity. * Virchjw's Archiv, Band xxviii. f Virchow's Archiv, Band. i. J Veber die sogenannte Molecularen, " On the so-called Molecules," Wiener Sitzungsberichte, 1862. 14 THE GENERAL CHARACTERS OF CELLS, BY S. STRICKER. Bottcher,* on the other hand, has expressed his doubt upon the existence of any such connection, on the ground that the granules which vibrate in the cells continue the same movement when they have escaped from the interior (by bursting of the cells), provided that the medium into which they pass is of an appropriate nature. Neumannf founded his objection on the fact that the vibratile move- ment still occurred in cells which were dead or on the point of death. The idea of a connection existing between the movement and the life of the protoplasm is essentially based upon these facts ; first, that the cells in which it occurs are living cells, and secondly, that changes in the phenomena of life induce, or are followed by, changes in the motion of the granules. In the meantime, observation of the movement of the granules alone cannot enable us to draw any conclusion in regard to its depend- ance on life, so long as it is only a vibratory and not a pro- gressive movement, and so long as some peculiarities are not discovered in these vibratory movements, which justify such a conclusion. a. CHANGES IN FORM of the entire mass of the protoplasmic mass are most strongly marked in the lower forms of animal life. Max Schultze,J in his description of the mode in which the Amoeba of Ehrenberg or Proteus (0. F. Muller) obtains its food, furnishes the following lively picture of its movements : — When an amoeba approximates another animal whose move- ments are not so swift as to enable it to escape from its enemy, it embraces it with its many-stalked body. The processes meet- ing on either side, coalesce, and after thus investing the whole mass with animal substance, the Amoeba maintains its grasp till it has abstracted all the portions that are soluble. On account of this remarkable peculiarity of the Amoeba, those cells which possess the power of spontaneously moving, are termed amoeboid cells. It is rare, however, for the cells of the more highly organised animals to move so rapidly as the Amoeba itself. * Virchow's Archiv, Band xxxv. t Reichert and Du Bois Reymond's Archiv, 1867. I Polythalamien, 1854, p. 8. CHANGES OF FORM IN CELLS. 15 Their movements are either limited to gradual change of form, or to the protrusion of processes which either drag the rest of the body after them, or are again withdrawn. The processes may assume the form of threads, swellings, tuberous elevations, or broad flattened projections or tufts, and may pre- sent the greatest diversities of form. If the alterations in shape are desired to be accurately noted, the cell must be placed upon a slide, or on a piece of tissue, or may even be attached to the cover ; for if the cells swim in fluid, it is possible they may turn, and thus present different surfaces to the observer. No conclusion can be drawn respect- ing the life of a cell, from the observation of a single change of form, since it is impossible to ascertain whether some unknown physical influence may not have wrought the change. Those alterations of form only which may be perceived in the object when the field of view is stationary, and when the object is adherent to the slide, and which are frequently repeated, enable us to determine the presence of life in it. Conversely also, we must not consider a quiescent proto- plasmic mass as necessarily dead, even if we are unable artifi- cially to excite movement by means of reagents. The proto- plasmic substance may possibly be encapsuled when it is not in a state to change its form, and even if it be naked, some unknown cause may hinder its movements. Hence, it cannot be said that the salivary corpuscles are dead, because as a rule they do not change their external form. Protoplasmic corpuscles are not only able to change their form, but their place also ; they can wander. This is accom- plished by the protrusion of one portion of their mass, which drags the rest after it. If such alterations of form are re- peated several times, and in the same direction, locomotion is effected. It must not be overlooked that entire cells may exhibit vibratory movements in fluids obviously subject to the laws of the Brunonian molecular movements. The stellate blood corpuscles of mammals, for example, do so as a rule. Such vibratory movements are to be clearly distinguished from the migrations of cells. Cells can only move from place to place when resting on a firm basis. They may swim in fluids, owing 16 THE GENERAL CHARACTERS OF CELLS, BY S. STRICKER. to the agency of currents, but not through their own active movements. The capability of moving from one place to another, possessed by the Amoeba, has long been known. The migratory power of the Foraminifera, by means of the processes of their struc- tureless substance protruded through the openings of their shell, has also been frequently observed. But Recklinghausen* was the first to notice that the cells in complex animal bodies can also perform movements of locomotion, and by his obser- vation introduced a fact to our knowledge having a very wide and important bearing. E. Hackel, whilst injecting Thetis fimbria with indigo, dis- covered that fine particles of colouring matter could penetrate into the interior of the blood corpuscles. The artificial intro- duction of colouring matters into cells is now termed giving them a supply of food. If, into the medium in which the cells are suspended (for example, blood plasma), a finely granular colouring matter be introduced, some of the particles of the latter are soon found to cleave to the surface of the cells, and to pass from thence into their interior. By the aid of this mode of supplying food, Recklinghausen has furnished the important proof that pus corpuscles are not always generated where they are found. He has shown that pus corpuscles can migrate into the meshes even of a dead cornea, and has by this observation opened up a new path for every department of pathological inquiry. These also are matters of fact that exert no little influence on physiology generally. If have myself shown that in the construction of the body of the embryo, the movement of masses of ce?ls to form the rudiments of organs, depends on the migration of the embryonal cells within the ovum. Cohnheim J has also very recently, by demonstrating that the colourless corpuscles can leave the vessels, and migrate, and that there may be a trans- plantation of living cells from one organ into another, and from one region of the body to another, furnished us with in- * Virchow's Archiv, Band xxviii. t Wiener Sitzungsberichte, 1864. | Virchow's Archiv, Band xi. CHANGES OF FORM IN CELLS. 17 formation, the importance of which cannot at present be estimated. Hering* has endeavoured to explain the passage both of v coloured and of colourless blood corpuscles through the walls of the vascular system, by comparing it with the filtration of colloidal substances. But in whatever way the process may be explained, the fact remains that the white corpuscles leave the interior of the vascular system, and are thus enabled to traverse various regions of the body. In stating that protoplasm is capable of active or vital movements, we have by no means admitted the existence of an immaterial force. Ed. Weber f has expressed himself very decidedly upon this point, and at the present day the position he took up is still tenable. " Ac- cording to my view," said Weber, " the movements of any living body are not dependent upon two kinds of force — namely, first upon forces which are exerted on this body by other bodies, and secondly upon forces which are exerted on this body by life ; but there is only one kind of force on which the movements of all bodies depend — namely, the force which is exerted on it by other bodies." We name the movements of certain bodies "vital," in the sense that the forces which we then call into play are subject to certain other varying influences, and we denominate the apparatus and the processes of which these influences are the result, "organization" and "life." It is customary also to call the vital movements of protoplasm Spontaneous. But this only shows that we are ignorant of the forces by which the movements are originated and sustained. We no longer term the movement of striated muscle spontaneous, because we know the external influences or stimuli through which it can be excited. And so also there can be no doubt that as soon as we have acquired a knowledge of all the external influences by which movements in protoplasm can be induced, we shall cease to term them spontaneous. Thus, in an analogous case, we say the production of heat by coal is immediately dependent on our placing it on the fire, i.e. on raising its temperature. Here the process of heating is the external influence or stimulus which induces a change in the molecular structure ; and as a consequence of this molecular change, active force is set free, which becomes perceptible to us in the form of heat. The production * Wiener Sitzungsberichte, 1868. t Miiller's Archiv, 1858. 18 THE GENERAL CHARACTERS OF CELLS, BY S. STRICKER. of heat by carbon is an independent power, dependent on the very nature of its substance, but it is by no means a spontaneous power. The analogy, however, has only a one-sided value, since, if the coal is once burnt, it can generate no new active force; but the contractile substance is capable of restitution. The movements of contractile substances may be altered, accelerated, retarded, or altogether stopped, by external in- fluences (stimuli), which may vary greatly in kind and degree. Amongst the known conditions that exert an influence on the movements of protoplasm, we may enumerate the variation of temperature. The oldest reference to this fact was made by Weber,* when he said the movement of cilia could be accelerated by warmth. Kuhnef also remarked that the motions of amoebse could be arrested by iced water, but that on raising the temperature they recommenced. Since Max SchultzeJ has made the warming of the slide an important assistance in micro-physiological investigations, we have learnt that the locomotive cells of warm-blooded animals can maintain their movements for a long time, external to the organism, if kept at the ordinary temperature of the animal from which they have been taken. We are unable, however, to give any precise statements possessing general application, respecting the influence of temperature. Still, as a general rule, an exaltation of a few degrees above the temperature at which the organisms customarily live, accelerates their movements, whilst a corresponding depression retards them. If the temperature exceed certain limits, how- ever, their life is imperilled. The eggs of trout, for instance, undergo segmentation capitally in iced water, but in a warm room soon die. The influence of temperature on the movement of cells is a point of particular interest in reference to their migration. Max Schultze§ has demonstrated that the colourless corpuscles * Canstatt's Jahreslericht, 1847, p. 59. t -Das Protoplasm. Leipzig, 1864. | Sch ultze's Archiv, Band i. § Loc. cit. CHANGES OF FOEM IN CELLS. 19 of human blood are capable of effecting a considerable amount of locomotion at a temperature of from 100° Fahr. to 104° Fahr. It is well known how great is the influence of particular tem- peratures on the development of the egg, and even if the movement of the cells is not the chief factor in this process, it certainly plays a very important part in it. We may readily conceive that an analogous influence must be exerted by any increase of temperature occurring in pathological processes. A peculiar effect of temperature is described by Kuhne,* as observable in the fresh-water amoeba, which at 95° Fahr. as- sumes a spherical form. Lastly, Peremeschkof states that the large cells at the bottom of the yolk cavity in the eggs of fowls, contract and dilate at a temperature of from 89*3° Fahr. to 93° Fahr. b. MECHANICAL INFLUENCES. — Kuhne was the first to com- ment on the effects of indirect mechanical irritation, stating that after he had stimulated the margin of the cornea in a frog, he saw stellate corpuscles become fusiform. Ij have made a few experiments on the effects of direct me- chanical irritation, and have observed that when blood diluted with a solution of common salt, containing one half per cent., is placed under a cover, and this last, by the withdrawal of the fluid, is allowed to sink to such an extent that the white cor- puscles are flattened out, they alter their shape with consider- able vivacity, especially if they are allowed to remain in this position for some time. If now a drop of fluid is brought to the margin of the cover, this will again be raised from the slide in proportion to the quantity added. The flat corpuscles may now be observed to contract into small angular lumps, and after a short time to change from this into a moderately expanded form. The compressed corpuscles here behave like the muscles of insects under the compressorium, which continue their movements for a time, * Protoplasma, 1864. t Wiener Sitzungsberichte, 1868. J Wiener Sitzungsherichte, 1867. 20 THE GENERAL CHARACTERS OF CELLS, BY S. STRICKER. even when the pressure upon them prevents any increase in thickness. It is evident from this experiment that protoplasm is an elastic body, since it contracts when the extending force is removed. The contrac- tion, however, appears to correspond here with the elasticity of the irritated substance, because a shortening occurs which is not maintained. An additional argument in favour of this view is, that the experiment is more successful when it is tried a second or third time. The corpuscles then contract much more energetically than at first. c. ELECTRICAL STIMULI. — The action of electric currents on protoplasm is very variable. The excitation of amoeboid movements by means of weak induction currents has, up to the present time, only been ob- served by Kiihne in amoebse, and by Golubew in certain white corpuscles of the blood of the frog. Kiihne* saw amoebae assume a spheroidal form, when made to form part of a constant current; whilst, after exposure to an intermittent current, the stellate corpuscles of the cor- nea became fusiform, and then reassumed their original shape. Golubewf states, from experiments made in Kollett's labo- ratory, that after being repeatedly irritated the cells become flattened, but even in that state exhibit changes of form. If stronger stimuli are applied to them in this condition, the disc- like mass again contracts and becomes spheroidal. He further observes that the fusiform colourless cells of the blood of the frog, which present no spontaneous movements, when mode- rately irritated, contract to spheroidal masses, but soon again revert to their original shape. IJ have observed contractions and dilatations to take place in embryonal capillary vessels after the action of induction currents. Kiihne§ has observed the following law of contraction in the protoplasm of Actinophrys eichhornii during the action of a constant current : — * Loc. cit. f Wiener Sitzungsberichte, 1868. | Wiener Sitzungslerichte, 1866. $ Loc. cit. CHANGES OF FORM IN CELLS. 21 Positive pole, or Negative pole, or electrode electrode entrance of current. exit of current. Closure - - Contraction 0 Current passing - Tetanus 0 Opening 0 Contraction. After being exposed to the action of moderately strong in- duction currents, protoplasm assumes a spheroidal form. This observation was first made by Kiihne in the amoeba, and has since been corroborated by Neumann, in regard to the colour- less corpuscles of human blood, and by Golubew in those of the frog. Kiihne states that amoebae which have become spherical from the action of induction currents, after a short time recommence their ordinary movements. Golubew makes the same remark, but observes that the movements of the colourless corpuscles of the frog are of a more undulatory cha- racter, though they send out, as usual, pointed processes. According to Neumann and Golubew, when strongly irri- tated, the granules in the spherical cells exhibit vibratory or so-called molecular movements. Briicke* saw salivary corpuscles burst under the influence of strong induction currents. Kiihne witnessed a similar pheno- menon in an amoeba. Kiihne describes the spheroidal condition of the amosba, produced by stimuli, as a kind of tetanus, and considers that, in the state of maximum contraction, these animals assume a spherical form. Hermann, however, suggests an essentially different explanation. It is possible, he remarks, that the excitation diminishes certain re- sisting forces which have previously prevented the cell from assuming a spherical form. The spherical form therefore, he thinks, may corre- spond either to the state of rest, or to the state of tetanus. Kistiakowsky f has observed an acceleration of ciliary move- ment to be produced by the constant current. EngelmannJ gives the following series of laws of this action : — * Ueber die sogenannte Molecular-beweguny, loc. cit. t Wiener Sitzungsberichte, 1865. t CentralUatL 1868. 22 THE GENERAL CHARACTERS OF CELLS, BY S. STRICKER. (a) Every variation in the intensity of the current, whether positive or negative, providing it be sudden, acts as an excitant. (£) A single variation in the intensity of the current induces a series of alternate contractions and relaxations. ( elliptical, or polygonal form, which, by their somewhat larger size (O'OOl to O'OOIS millimeters) and brighter appearance, serve to indicate the course of the fibres (fig. 33, a and &). 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 plexus. 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 chiefly in the vicinity of the spindle-like enlargements of the muscular fibres, dark peculiarly stiff filaments proceed, having a diameter of 0'00015 to 0'0002 millimeters. 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 NERVES 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) ; 6, nerve ramification in the muscular coat of a small artery (prepared in acetic acid, 1 per cent., and chromic acid, l-100th 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 mnde 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 off fila- ments, which, traversing the substance of the nucleus and of the muscular fibre in the opposite direction, enter the intra-mus- cular 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* had 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 applied the name of nuclear cor- puscles (Nucleoli, Kernkorperchen). 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 Nen-en der Gebdrmutter und ihre Endigungen in den Glatten Muskelfasern, " 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-called muscu- laris mucosa, 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 Eberth, 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 contain 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 ORGANIC MUSCLES, BY J. ARNOLD. sexual organs it occurs in the oviducts, in the broad and round and 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 pili ; and in the sebaceous and sweat follicles. Finally, the presence of smooth muscular fibres in the ciliary muscle, effecting 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 (0*01 per cent.), and solution of gold (01 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 0*05 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 chromic 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. Schulze), and picric acid (Schwarz) may be employed. CHAPTER V. THE MODE OF TERMINATION OF NERVE FIBRE IN MUSCLE. BY W. KUHNE. WE exercise control over our muscles through the agency of the nerves, and it is through the nerve paths alone that the will 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 still 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 domain 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 investigating the interesting small Tardigrada, recognised nearly all that we know at the present time regarding the ends of the motor nerves. In 1840, Doyere 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 Doyere long remained misunderstood, and passed into oblivion in consequence of the general acceptance of the view of Ernst Briicke and Joh. Miiller, to the effect that the primitive nerve fibres undergo division between the muscular fibres. It was, indeed, completely forgotten when K. 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 with 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 Yertebrata the muscles of the eye, as a general rule, contain but few mora muscular fibres than primitive nerve fibres. If we start with R 204 MODE OF TERMINATION OF MOTOR 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 all 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 all, the thin muscles which extend from the vertebral column to the skin in the Snake. These may be examined almost whilst yet still 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 Doyere 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 TERMINATION 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 respecting the termination of motor nerves since the time of Doyere. 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 still 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 by Mr. Bowman. The same parts were designated by Rollett "chief-substance disks." The muscle prisms have been also, after Mr. Bowman, termed " sarcous elements." B 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, filling the interior of a canal running 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 off radial processes which run towards the surface to join 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 terminate, appear to be the muscles of insects, and amongst these the best are the muscles of the great black water beetle (Hydrophilus piceus), which is to be preferred to the nearly allied Dytiscus marginalis. 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 TERMINATION OF MOTOR NERVES IN ARTICULATA. 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 all instances to consist only of a 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, with the extremities of two nerves, from tlie Hydrophilus 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 joins 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 will still be constantly 208 MODE OF 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 Doyerian eminence. 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 strise 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 Doyerian 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 VERTEBRATA. 209 statements respecting the form that the process of the axis cylinder 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 TERMINATION 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 all animals in which nerves induce the act of contraction, and conse- quently "in the 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 examine 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 with 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 sartorius — 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 continuity 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 will 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 all 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 TERMINATION OF MOTOR NERVES, BY W. KUHN-E. 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 sarcolemma 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 ; c c c, nuclei of the sheath of Schwann ; e, nuclei of the muscle. MODE OF TERMINATION OF MOTOE 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 off 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 fibrillated 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 well-known 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 still 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, running 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 measure 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 OF 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 in 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 silver, 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 cylinder and the sarco- lemma, which, after exposure to light, surrounded the muscular substance with a black layer beneath the sarcolemma. In this layer, stained with silver, the whole intra-muscular nervous apparatus appears as a white silhouette, indicating 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 silver 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 the 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 different 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 O5 per cent., or hydrochloric acid of O'l 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 difference 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 remains obstinately ad- herent to the fibre. An investigation by Rouget first led to exact conclusions in regard to the mode of termination of the nerves ; since it demonstrated the existence of the Doyerian 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 investigation of fresh muscle, such as can easily be obtained from Reptiles, that just beneath the point of entrance of the nerve, a mass of nuclei and granular substance, constituting a Doyerian 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 granular 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 ; whilst, 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 MOTOR 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 slightly 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 Keptilia presents all conceivable varieties, being sometimes higher, and sometimes lower ; sometimes having a long, elliptical, 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 alluded 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- TEKMINATION 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 agilis and L. viridis, the mode in 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,or the motor nerve plate. At whatever period after death the muscles may be examined A. Fig. 36. B. Fig. 36. Muscular fibres with nerve ends, from Lacerta viridis. A. Seen in profile ; pp, the terminal nerve plate ; s s, the base or sup- port of the 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. c. 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 tetanically 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 still 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 p« ex Le TERMINATION OF 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, but 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 stiffened 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 in which the muscle can no longer be excited to contract through the nerves, but is still capable of sponding 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 sufficiently 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 off 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 difference 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 s2 222 MODE OF TERMINATION OF MOTOR NERVES, BY W. KUHNE. changes of the terminal plate of the nerve depend on the post- 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 well 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 stiffened; 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 becoming 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 medullated 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 position of the TERMINATION 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 granules 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 mtra-muscular nerve termination loses the characteristic consti- tuents of the nerve medulla. The terminal nerve plate can be brought into view in an isolated condition, though certainly 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 all animals. 224 MODE OF TERMINATION OF MOTOR NERVES, BY W. KUHNE. According to Doyere, 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 Doyere'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- Fig. 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 Doyere ; N, nerve. able distance from the termination of the nerve. V. Greeif was unable to find, either on the nerve or on the muscle, anything 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 OF MOTOR NERVES IN VERTEBRATA. 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 Helix 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. Kouget, indeed, states that he succeeded in perceiving a prolongation of the axis cylinder 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 in need of confirmation. Engelmann, who also examined 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 Reptiles 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 intra-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 one mode of nerve termination, in which the nerve ends with a motor plate in 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. Greeff 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 should 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 fused 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 with the plates, and their subjacent protoplasm, from which they are rarely sharply differentiated. We need not despair of discovering their analogue in all nerve eminences, even in the minute ones of Milnesium, though perhaps better instruments and improved methods of investigation will 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 Rouget, 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 MOTOR NERVES IN VERTEBRATA. 227 contractile substance. This last idea is, however, opposed, from a morphological point of view, by a consideration of the mode of nerve termination 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 contrar}^ 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, in 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 cylinder 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. HISTORY AND LITERATURE. — 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, still be added, since the questions involved have given occasion to lively 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 inclines as much towards mor- phology as towards physiology, has to anticipate from hypotheses 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 in 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 K. 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 Reichert (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 supplied. 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 Xernatodes. At a somewhat later period, Schaafhausen ex- pressed himself in terms similar to those of Remak, 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 Schaafhausen 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 all 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. Resting 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 Rouget (29) agreed with him in all points, and now, whilst Beale (28) retained his first opinion as being applicable to all classes of animals, Rouget (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, BY 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 views 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 denned line belonging to the sarcolemma between the contractile substance and the substratum of the nerve plate which he obtained 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 with the sheath of Schwann. Neither a nerve eminence, nor any similar 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 MOTOR 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 Rouget obviously overlooked the entire expansion of the now no longer medullated nerve, after he had been accustomed to the in- finitely more sharply denned 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, and 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 all 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 Krause 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 Rouget (56) and Krause, who explain the whole appear- ance as a hitherto undescribed post-mortem phenomenon of coagula- tion, in contradiction to which, again, Rouget stated that the true termination of the axis cylinder in the nerve eminence consists in its metamorphosis into a granular mass with interspersed nuclei. Rouget 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 Rouget' 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 Rouget 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- colemrna, 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 delicacy and beauty of their form are lost in all but physiologically fresh specimens. LITERATURE. 1. DOYERE, Memoire sur les Tardigrades. Ann. des sciences nat., 2de Serie. 1840. PL xvii., Fig. 1—4. LITERATUKE OF THE TERMINATION OF MOTOR NERVES. 233 2. SAVI, Etudes anat. sur le syst. nerv. et sur 1'org. electr. de la Torpille. 1844. 8. BEMAK, Arch. f. Anat. u. Physiol., S. 189. 1843. 4. QUATREFAGES, Ann. d. Sc. nat., 2de Serie. 1843. T. xix., p. 299, PI. ii., Fig. 12. 5. E. BRUCKE u. JOH. MULLER, JOH. MULLER, Handbuch der Physiologic, 4. Aufl. 1844. Bd. i., S. 524. 6. E. WAGNER, Handworterbuch der Physiol., Bd. iii., S. 888. 7. KOLLIKER, Mikroskop. Anat., Bd. ii., 1. Halfte, S. 238. 8. REICHERT, Arch. f. Anat. u. Physiol., S. 29. 1851. 9. MEISSNER, Zeitschr. f. wiss. Zool., Bd. v., 1854, S. 234, u. Bd. vii., 1856, S. 26. 10. WEDL, Wiener Sitzungsberichte, Bd. viii., S. 298. 11. WALTHER, Zeitschr. f. wiss. Zool., Bd. viii., S. 163. 12. MUNK, Gottinger Nachrichten. 1858. Nr. 1, S. 11. 13. SCHAAFHAUSEN, Amtl. Ber. d. Naturforscher-Vers. zu Bonn, S. 193. 1859. 14. W. KUHNE, Monatsschr. d. Berl. Akad., S. 395, 493. 1859. 15. W. KUHNE, Arch. f. Anat. u. Physiol., S. 564. 1859, auch Myolog. Untersuch. 1860. 16. BEALE, Proc. of the Royal 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. MARGO, Sitzung. d. Ungar. Akad. d. Wiss. 14 Oct. 1861. 20. W. KUHNE, Ueber die periph. Endorgane der mot. Nerven. Leipzig, 1862. 21. KOLLIKER, Wiirzb. naturwiss. Zeitschr., Bd. iii., S. 1, 8. u. 22, Marz, 1862. 22. W. KUHNE, VIRCHOW'S Arch., Bd. xxiv., S. 462. 1862. 23. NAUNYN, Arch. f. Anat. u. Physiol., S. 481. 1862. 24. KRAUSE, Zeitschr. f. rat. Med., Bd. xv., S. 189. 1862. 25. KOLLIKER, Zeitschr. f. wiss. Zool., Bd. xii., S. 149. 26. KOLLIKER, Zeitschr. f. wiss. Zool., Bd. xii., S. 263. 27. MARGO, Ueber die Endigung der Nerven in der quergestr. Muskel- subst. Pest, 1862. 28. BEALE, Arch, of Med., Vol. iii., p. 257. 1862. 29. ROUGET, Note sur la terminaison des nerfs moteurs dans les muscles chez les Reptiles, les Oiseaux et les Mammiferes. Compt. rend. T. lv., pp. 548—551. Seance 29 Sept. 1862. 234 MODE OF TERMINATION OF MOTOR NERVES, BY W. KUHNE. 30. BEALE, Philos. Trans., June 19, 1862. 31. KRAUSE, Gottinger Nachr., Nr. 2. u. 3. 1863. 32. BEALE, Proc. of the Roy. Soc., June, 1863. 33. BEALE, Quart. Journ. of Microsc. Sc., p. 97. 1863. 34. ENGELMANN, Centralbl. f. d. med. Wiss., Nr. 19. 1863. 35. WALDEYER, Centralbl. f. d. med. Wiss., Nr. 24. 1863. 86. KRAUSE, Zeitschr. f. rat. Med., Bd. xviii., S. 136. 1863. 37. LETZERICH, Med. Centralzeit., Nr. 37. 1863. 38. ENGELMANN, Unters. iib. d. Zusammenh. v. Nerven. u. Muskel- fasern. Leipzig, 1863. 39. W. KUHNE, VIRCHOW'S Arch., Bd. xxvii., S. 508. 1863. 40. W. KUHNE, VIRCHOW'S Arch., Bd. xxviii., S. 528. 41. KRAUSE, Zeitschr. f. rat. Med., Bd. xx., S. 1. 1863. 42. KRAUSE, Gottinger Nachr., Nr. 18. 1863. 43. ROUGET, Journ. de la Physiol., Nr. 20, S. 574. 44. BEALE, Quart. Journ. of Microsc. Sc., p. 302. 1863. 45. WALDEYER, Zeitschr. f. rat. Med., Bd. xx., S. 242. 46. COHNHEIM, Centralbl. f. d. med. Wiss., Nr. 55. 1863. 47. W. KUHNE, VIRCHOW'S Arch., Bd. xxix., S. 207. 48. W. KUHNE, VIRCHOW'S Arch., Bd. xxix., S. 433. 49. KRAUSE, Zeitschr. f. rat. Med., Bd. xxi., S. 77. 50. W. KUHNE, Centralbl. f. d. med. Wiss., Nr. 24. 1864. 51. W. KUHNE, VIRCH. 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. ROUGET, Compt. rend, lix., p. 809. 57. ROUGET, Compt. rend, lix., p. 851. 58. KRAUSE, 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. KUHNE, Compt. rend. 1864. 62. W. KUHNE, VIRCH. Arch., Bd. xxxiv., S. 412. 63. GREEFF, Archiv f. mikrosk. Anat. von M. SCHULTZE, Bd. i., S. 101. 64. BEALE, Croonian lecture for 1865. 65. MOXON, Quart. Journ. of Microsc. Sc. Oct. 1866, p. 235. 66. TRINCHESE, Journ. de 1'Anat. et de la Physiol. 1867, p. 485. 67. ENGELMANN, Jenai'sche Zeitschr., Bd. iv., S. 307. 68. KRAUSE, 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 Nicol'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 which cut them at an angle of 45°. In those parts where the muscu- lar fibres running 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 Nicol'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 refractile, 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 T 236 MUSCULAR FIBRES IN POLARISED LIGHT, BY E. BRUCKE. Prof. C. Bceck,* of Christiania, 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 all the stronger shadows vanish ; but on this very account all 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 Gotheborg 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. Moiller's Archivfur Anatomie u. Physiologie^ 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 is, 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 refractile ? 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 6, 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. BRUCKE. in the direction of its length in a groove h 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 in each is parallel to the crystallographic 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 making 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 strise, where equal thicknesses of the latter lie over one another, whilst on both sides colours appear in 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 the ray, can be made to occupy the middle of the field. 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. If 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 = 0 ; 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 rerAains, 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 MUSCULAR FIBRES IN POLARISED LIGHT, BY E. BRUCKE. become thicker, and the transverse strise 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. Since 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. All 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 refractile bodies. These doubly refracting bodies I have called Disdia- clasts, after the phrase employed by Erasmus Bartholin, the BEHAVIOUR OF MUSCULAR FIBRES IN POLARISED LIGHT. 241 discoverer of double refraction in calc spar, in the title to his well-known treatise.* The composite nature of the sarcous elements furnishes an explanation of the various appearances presented by muscles in a state of rigor mortis. In my re- searches on the structure of muscular fibres with polarised light,f I have constructed nine different schemes, and we may not unfrequently see one and the same muscular fibre in dif- ferent parts representing 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 strise appear in these sections than in others, though they are neither shortened nor thickened by contraction. MargoJ 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 regular 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 sareolemma. If such terminal 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 silvery-grey clouds distributed in the dark * JExperimenta Crystalli Islandici Disdiaclastia quibus mira et insoliia Refractio detegitur. Havn, 1869. t Denkschriften der Wiener Akademie der Wissenschaften, Band xv.r Separataujlage Wien. bei Gerold. \ Uber der Muskelfasern der Mollusken, Sitzungsberichte der Wiener Akademie, 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 which neither sarcous elements nor isotropal intervening substance can be distinguished. 242 MUSCULAR FIBEES IN POLARISED LIGHT, BY E. BRUCKE. 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 in 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 " Annales de Chemie et de Physique," 4e se'rie, 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 Jeffrey'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. BEHAVIOUR OF MUSCULAR FIBRES IN POLARISED LIGHT. 243 one another or crossed, it presents a beautiful purple colour ; the muscular fibres then appear blue or yellow, 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 differences 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, attention 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 lamellae, 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. CHAPTEE VII. THE HEART. BY F. SCHWEIGGER-SEIDEK 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- Fig. 39. Small portion of a transverse section through the muscular 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-like structure, because the fine muscular fibres, dividing frequently and anastomosing with one another, form a close and continuous network * The contractile substance is transversely * The anastomosing muscular fibres of the heart, which had already heen depicted by Leeuwenhoek, were rediscovered by KoLliker. 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 Miiller's Archiv for 1850. MINUTE ANATOMY OF THE HEART. 245 striated, sometimes contains fat drops even when apparently healthy, and presents nuclei that are arranged at tolerably 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 yellow colour (fig. 40, A). Fig. 40. Fig. 40, A. Muscular fibres from the heart of Man, divided by trans- verse septa into separate nuc'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 different from that applicable to those of the vo- * Bonder's Physiologic des Menschen, 1859, p. 23. 246 THE HEART, BY F. SCHWEIGGER-SEIDEL. luntary muscles. Weismann* first established, from extended re- searches in comparative anatomy, that the relations in question are not the same for all 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 cells, the substance of which presented transverse striae (fig. 43). In Mammals, Birds, and Reptiles, 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 cells. Kolliker 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 Eberth| 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' in 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 cells.§ Here, therefore, in 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-cell trabeculae. 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 still 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 Physiologic, 1861, p. 42. t Zeitschriftfur rationelle Medicin, 3 R., Band xvii., p. 195. J Virchow's Archiv, Band xxxvii., p. 100. § As long as a division of the cells from, one another can be generally demonstrated we can obtain no correct estimate of the degree of coalescence that has taken place ; hence it is not easy to discover the difference that exists between the statements made by Kolliker in the fifth edition of his Handbuch der Gewebelehre, and those advanced by Eberth. 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 f 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 line a being easily distinguishable from a fissure (y) 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 flight of steps. Eberth found the borders of the cells 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, occupying 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. SCHWEIGGER-SEIDEL. have a length of about 0'014, and a breadth of about O'OOT mil- limeters ; whilst the muscle cells themselves measure, on the average, 0'050 to 0*070 millimeters in length, and 0'015 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. 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 well-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 in 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,^ 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 carnese, are particularly well marked in 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 lamellae are either connected with one another by extremely delicate connective tissue, or there exists between them certain smooth-edged * Remak, loc. cit., Rindfieisch Lehrbuch der Pathologischen Gewebelehre, 1866, p. 73. Eberth, in accordance with this view, represents longitudinal fissures as existing in the muscle cells ; but it maybe seen in his fig. 13, that thsse 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 fissuring 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 Archivfilr Anatomie und Physiologic for 1867, it is obvious from his ac- count of the appearances presented on transverse section, that he really treats of the sheaths of the perimysium. J See Henle, Handbuch der Systematische Anatomie, Band iii., Abth. 1 ; Gefasselehre, p. 54, figs. 40 and 44. 250 THE HEART, BY F. SCHWEIGGER-SEIDEL. fissures, which 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 in 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 fully treated of in 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 being 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 lamellae, but do not form a continuous layer, being arranged in separate bands, which vary in size, and sometimes attain a thick- ness of O10 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 when the section U 252 THE HEART, 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 distinctly 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,f 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, and is 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 elements 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 * Kolliker 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 Archiv, 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 O10 millimeters^ each of which consists of a cortical layer of transversely striated fibrillar muscle substance, and a hyaline 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 filled 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 Archiv, 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. Physiologic, 1867, pp. 245 u. 358 ; Lehnert, Max Schultze's Archiv fur Mikroskopische Anatomie, 1868, p. 26. U2 254 THE HEART, BY F. SCHWEIGGEK-SEIDEL. of these valves consists essentially of two lamellse, 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 in 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 thin membrane composed of cells which do not rest upon any special elastic substratum, except that perhaps the 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.*}* According to the statements of Oehl, J 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 chordas tendineae. Yillous 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 Donders, 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 Physiologische Heilkunde, 1856, p. 537 ; compare also Henle. f Amongst the most recent investigations on the musculature of the auriculo- ventricular valves are to be enumerated those of Gussenbauer, Sitzungsberichte der Wiener Akademie der Wissenschaften, Band Ivii., Abth. 1. J Mem. d. Acad. d. Scienze d. Torino, Vol. xx., 1861. MINUTE ANATOMY OF THE HEART. 255 The pericardium, 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 by means of a few finer tubes upon 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 lymphjvessels 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. * Virchow's Archiu, 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 lacunse 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 different 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 shown in the illustrations given by Lee * The isolated, somewhat flattened fibres, which intercommuni- cate by means of delicate fasciculi, consist chiefly 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, Plates ii. and iii. MINUTE ANATOMY OF THE HEART. 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 approximation 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 Archiv, Band xxx., p. 458. 258 THE HEART, BY F. SCHWEIGGER-SEIDEL. mitted that the difference between the vagus and the sympathetic, or, in other words, the difference between the inhibitory and the exciting fibres, is to be sought for in the circumstance that the one acts directly on the muscular substance, the other only indirectly through the in- tervention of the ganglion cells. The latter is supposed to be the mode in which the vagus acts, though no positive proof of the fact has hitherto been adduced. Kolliker, indeed, has convinced himself from anatomical investiga- tion that the vagus stands in no direct relation with the ganglion cells, but other observers do not agree with him ; and very recently Bidder,* who has also examined the subject anatomically, has stated that the spiral fibres are fibres of the vagus passing to the ganglion cells, whilst the straight fibres are given off by the cells, and are destined to be peripherically distributed. If, however, Bidder rests his view ex- clusively on the results of sections of the nerves made in frogs, his evidence is diminished in value to some extent, because in these ani- mals the Eami Cardiaci are the only nerves which pass to the heart ; and consequently, when they are divided, not only the inhibitory, but the exciting fibres would undergo degeneration. The further distribution of the nerves in the muscular sub- stance of the heart is difficult to follow, as they undergo rapid subdivision, or, at least, but few trunks can be seen. Hence it follows that the fibres are delicate and non-medullated. It is generally acknowledged that ganglia are distributed in the muscular substance. If, however, this be admitted on the au- thority of Kemak,f it is to be remarked that he observed their presence under the microscope only in the case of the calf. I have not been myself successful in discovering such ganglia lying between the fibres in the proper muscular substance, and can only admit that they may be found on a few traversing trunks or branches. Friedlander maintains that large numbers of ganglion cells are present in the muscular substance of the heart of the frog, as he believes he has demonstrated the constant existence of such * Archiv fur Anatomie u. Physiologie, 1868, p. 1. t Miiller's Archiv, 1844, p. 463. J Untersuchungen aus der Physiologische Ldboratorium in Wurzburg, Heft, ii., 1867. MIXUTE ANATOMY OF THE HEART. 259 cells in still pulsating portions of muscle, in which there were not, in some instances, more than two or three muscular fibres. His state- ments, however, are not sufficiently precise. He has given no de- scription of either the size, form, or appearance of the supposed ganglion cells, and has made no investigations to show their connec- tion with nerve fibres. We possess a few observations respecting the mode of ter- mination of the nerves in the muscular tissue of the heart, that have been made by Kolliker and Krause. Kolliker considers that in the frog the pale nucleated fibres running on and in the secondary muscular bundles, terminate in the same mode as the nerves of the voluntary muscles ; whilst Krause states that " the double-contoured nerve fibres of the cardiac muscle end in motor terminal plates ; and hence the peculiar operation of the cardiac nerves receives no explanation from the mode in which they terminate."* That the relations of the cardiac nerves must differ from those distributed to the muscles of the trunk is probable on a priori grounds, from the different arrangement of the mus- cular elements ; for, as the several muscle cells preserve their independence, it is easy to conceive that their mode of inner- vation would be peculiar, and would present an analogy to that of the smooth muscular tissue. Further inquiry is requisite to determine the precise mode in which the ultimate distribution of the nerves is effected, but the following re- marks may be provisionally made for the purposes of com- parison with the arrangements presented by other muscles. The nerves run in the connective tissue accompanying the capillaries and occupying the fissures between the muscle cells, and appear in the form of delicate nucleated fibres, resembling those which are elsewhere seen to constitute the peripheric terminations. It is difficult, even in very thin layers of muscle, to discover the extremely delicate fibres. The nuclei of the capillaries, of the nerves, and of the muscle, however different their characters may be, confuse the microscopic image to "so great an extent that no other course * Anatomic des Kaninchens. Leipzig, 1868, p. 178. 260 THE HEART, BY F. SCHWEIGGER-SEIDEL. is left but to isolate the nerves by dissolving out the network of muscle cells. If specimens be taken from the middle of the ventricular wall of Mammals, we may obtain, in successful cases, numerous nerve fibres, though usually only in fragments, and may see how frequently they divide, and, with great clearness, the mode in which they form networks (fig. 42). The divisions are, in some Fig. 42. Fig. 42. Isolated nerve fibres from the muscular substance of the wall of the ventricle. From the Dog. Magnified 500 diameters. parts, very numerous (a), though the lateral branches are for the most part torn off. We seldom meet with such a case as is repre- sented at b, and when seen, there must always remain a doubt whether a natural termination is under observation, because the fibrils issuing from the second nuclear swelling are so fine that no sure ground is afforded to determine whether or no they are broken off. In the Frog, the arrangement is so far different that no capillaries exist in the muscular mass, and MIXUTE ANATOMY OF THE HEART. 261 the individual bundles are composed of closely compressed fusiform cells. In fig. 43, two trabeculse are exhibited from the auricle, partially detached from each other. Fine nerve fibres, with the ordinary nuclei, intervene between them, and, after frequently undergoing subdivision, become closely applied to the muscular fasciculi. (The branch a runs beneath the Fier. 43. Fig. 43. Trabeculso of muscle from the auricle of the Frog, with the nerves. fasciculus.) Fine fibres are, as usual, given off from the cha- racteristic triangular nuclei, which penetrate into the interior of the fasciculus, and it may then easily be seen that the nucleated fibre c lies in a space between the muscle cells. By carefully isolating the tissues, very fine branched fibrils may 262 THE HEART, BY F. SCHWEIGGER-SEIDEL. be exhibited, which might be regarded as nervous in their nature, even without any direct connection with undoubted nerve fibres being discoverable. Such fine fibrils sometimes adhere firmly to the muscle cells. Notwithstanding the doubts that exist on some of these points, it may be regarded as well ascertained that the finer branches of the cardiac nerves lie between the proper elements of the muscle, and so come into immediate contact with the con- tractile substance which is here destitute of sarcolemma. As to what proportion the number of terminal nerve branches bear to the number of muscle elements, no positive statement can at pre- sent be made. I have not been able to observe any such direct connection between the nerves and the nuclei of the muscle cells as has been stated by Frankenhauser in regard to the smooth muscles.* It still remains to notice other parts in which ramifications of the cardiac nerves occur, and of these the first that may be men- tioned is the pericardium, in which, as in other serous membranes, networks of fine fibres are present. And, secondly, the endo- cardium, in which a very considerable development of nervous tissue exists. This distribution is not exclusively connected with the presence of muscular layers, since, besides motor, we must certainly admit the existence of other nerves with dif- ferent endowments. The latter terminate in the inner laminse of the membrane ; but their finer branches, in consequence of the elastic tissue present, are only to be discovered with difficulty, and require the application of chloride of gold.f They are nucleated, and form networks in the membrane which are analogous to those ordinarily found in serous membranes, except that the meshes are much narrower. Since, however, there is no regularity in their distribution, any attempt at comparative measurement would only be applicable to special * To enter more minutely on this subject, and to give the details required for making special investigations in it, would lead us too far, and the con- sideration of these points must therefore be reserved for discussion else- where. t The above statements are based on hitherto unpublished investigations that have recently been made under my direction by Dr. Schmulewitsch. MINUTE AX ATOMY OF THE HEART. 263 instances. The nerves terminate in a manner essentially simi- lar to those of serous membranes generally, though it is here extremely difficult to arrive at any positive conclusions. The plexus of coarser fasciculi lying in the subserous con- nective tissue, and therefore beneath the muscular layer of the endocardium, and which can easily be brought into view, must be distinguished from the fine networks of fibres above described. Isolated fibres are given off from them, which partly end in the muscles and partly enter into the formation of the above- mentioned fine networks. CHAPTER VIII. THE BLOODVESSELS, BY C. J. EBEBTH, PROFESSOR OP PATHOLOGICAL ANATOMY IN ZURICH. IN adult vertebrate animals the essential constituent of the bloodvessels is a tubular system formed of a single layer of flat cells, or of a delicate nucleated membrane, termed the endothelial tube by His,* the perithelial tube by Auerbach,f and the cell membrane by Remak.J This tube is the least variable part of the vascular walls, and is present alike in the finest bloodvessels, in the largest trunks, and in the dilated portions of the vascular system — the heart and the several sinuses — however much the other constituents of the vascular wall may vary. In a few organs, however, as in the spleen of Mammals, in the pulmonary organs of the Cephalophora,and in the gills of Crustacea, the pas- sages through which the blood courses appear to be destitute of a proper wall.§ The capillaries and smaller veins are formed of this tube alone, the elementary constituents of which are deli- cate, flattened, more or less fusiform, or polygonal cells, com- posed of a nucleus with surrounding protoplasm, and arranged for the most part parallel to the long axis of the vessels. In the heart and arteries, and in most of the veins, this cell tube is invested by connective tissue and by elastic and * Die Haute und Hohlen des Korpers. Basel, 1866. f Virchow's Archiv, Band xxxiii., 1865. J Miiller's Archiv, 1850. § Bidder, in his Beitrage zur Gynakologie und Geburtskunde, v. Hoist,- 1867, has incorrectly denied the presence of an endothelium in the margi- nal veins of the placenta. See Eberth, Virchow's Archiv, Band xliii., p. 136, 1868. MINUTE ANATOMY OF THE BLOODVESSELS. 265 muscular elements, which are frequently arranged in layers, but are often also irregularly combined into a tunic, that in opposi- tion to the internal cellular membrane may be called the external vascular coat or investing membrane. The thick- ness of this membrane does not increase proportionally to the diameter of the vessel, as there are wide vessels with very thin, and small vessels with comparatively thick coats. Amongst the Invertebrata, as in snails and mussels, even the large lacunar blood spaces which surround the viscera are bounded only by a very delicate cellular membrane, which invests the various organs as an external epithelial tissue, similar to the epithelium of the peritoneum. The smaller vessels have thicker walls in comparison with the larger, but the several components of the wall do not parti- cipate to an equal extent in producing this increase of thickness. It is chiefly effected by an augmentation of the muscular tissue, which becomes abundant in proportion to the diminution in the quantity of the elastic and connective tissue. The tissues which form the investing tunics are arranged in layers, the thickness of which, as well as the order of their succession, undergo many variations. The investing layer is limited internally by an elastic mem- brane termed the internal elastic coat. The external surface of this membrane is covered by a muscular layer composed of smooth muscular fibres, which are partly arranged in a circular and partly in a longitudinal direction. This layer is termed the middle coat in consequence of the position it occupies between the elastic coat on the one hand, and the external coat or tunica adventitia, composed chiefly of connective tissue and elastic fibres, on the other. To these tunics must still be added a fourth connective tissue layer — the internal tunic or internal longitudinal fibre layer, which lies between the endothelium and the elastic internal coat, and which I shall term the intermediate layer. In the arteries it is only present in the larger vessels, and is gradually lost towards the periphery. In the veins it attains its maxi- mum in some of the peripheral vessels, and diminishes towards the heart, so that it is almost entirely absent in such large vessels as the vena cava. 266 THE BLOODVESSELS, BY C. J. EBERTH. Besides the above-named elements the vascular walls contain elastic fibres and sheets, which sometimes appear as finer or coarser fibres arranged in a retiform manner, at others in the form of strong broad bands, and sometimes as fine striated lamellae and membranes. The elastic fibres form a network extending through the whole thickness of the investing layer, the proportional development of which varies not only in different portions of the vascular system, but also in the different coats. Such fibrous networks attain a great development in the arteries on the external surface of the muscular tunic, where they often form a strong and tolerably well-defined layer. (Henle's external elastic coat.) YASA VASORUM AND NERVES. — The tunica ad ventitia of the large arteries and veins possesses arteries, capillaries, and veins which may extend even into the external layers of the muscular coat. The inner fibrous membrane is destitute of vessels. Lymphatics have not hitherto been traced into the coats of the bloodvessels. The lymphatics of the endocardium only extend as far as the semi-lunar valves * In Amphibia and Reptiles, the large vessels, and especially the arteries, lie in the interior of immense lymphatic spaces, and are invested by the cell membrane of the lymphatics. The perivascular spaces in the brain and spinal cord of Mammals, which were formerly regarded by His as lymphatics,*)* are, according to his more recent investigations, as well as mine, only lacunae in the tissue, and possess no proper walls. With the exception of the capillaries, the presence of nerves has been demonstrated in all vessels, even in the tunica adven- titia of the non-muscular veins of the pia mater. These, partly consisting of dark-edged and partly of pale fibres, break up after they have traversed the tunica adventitia into a fine net- work. The fibres of this network, according to my observations on the small cutaneous vessels of the frog, are of the most deli- cate description, whilst the network is of the closest character. * Eberth and Belajeff, Virchow's Archiv, Band xxxvi., 1866, p. 124. t Zeitschrift fur wissenschaftliche Zoologie, Band xv., 1865, p. 127. MINUTE ANATOMY OF THE ARTERIES. 267 1 have not been able to convince myself of the precise mode in which they terminate, especially in regard to the muscles. Ganglion cells occur in the course of some of the afferent nerve fibres, and in the coarser plexuses. Beale* considers them to be very widely distributed. I have recognised them only in the inferior vena cava of the Frog, where they were first dis- covered by Lehmann.'f' Heaps of small, somewhat flattened, and closely compressed ganglion cells unite to form roundish nerve knots. ARTERIES. mu ere The arteries are distinguished from the veins by their thicker walls, resulting from the greater development of their uscular and elastic fibres. The thickness of the entire wall in- ases, though not proportionally to the increase of the calibre of the vessel. The thickness of the muscular tissue increases with the diminution of the calibre. The quantity of elastic fibres, on the other hand, increases with the calibre. The cellular layer of the arteries consists of fusiform or, occasion- ally, polygonal cells, which vary but little in diameter in the various vascular provinces. ELASTIC INNER COAT. — The innermost layer of the exter- nal vascular coat — the elastic membrane of Bonders, the elastic internal tunic of Kolliker, the elastic longitudinal fibre layer of Remak — consists in the finest vessels of a net- work of fine elastic fibrils, or of a delicate structureless elastic membrane, which, in collapsed or bent vessels, or when sepa- rated from its attachments, exhibits fine parallel, longitudinal, and transverse folds. It can be distinguished even in very fine tubes possessing only isolated muscle cells. Towards the larger vessels the membrane increases in thickness ; small rounded or elongated spaces occur in it, and it now appears as a fenestrated membrane thickened with longitudinal rugae (Arteria basilaris). In the larger vessels the fenestrae are more numerous; the * Philosophical Transactions, cliii., p. 562. t Zeitschrift fur wissenschaftliche Zoologie, Band xiv., p. 346. X 268 THE BLOODVESSELS, BY C. J. EBERTH. membrane, in consequence, assumes the appearance of a net- work composed of fibres of varying thickness, or of a fenes- trated membrane with plexiform thickenings. Large trunks, Fig. 44. Fig. 44. Endothelium of the carotid artery of Man, after treatment with nitrate of silver, a, cells; b, clearer; c, darker intermediate spaces ; d, intra-cellular circular and spotted markings. such as the axillary, carotid, pulmonary, crural, popliteal, and hepatic arteries, instead of a simple elastic membrane, possess two or three anastomosing lamellae, or plexuses of elastic tissue, a clear, but slightly fibrous connective tissue filling up their interspaces. INTERNAL FIBROUS COAT. — With the above membrane is associated a second, which, however, is not, as Henle* main- * Allgemeine Anatomic, p. 496. MINUTE ANATOMY OF THE ARTERIES. 269 tained, situated between it and the next coat, the so-called tunica media ; but, according to the observations of Kolliker,* Gimbert/f" and myself, occupies a position intermediate between the epithelium and the elastic inner tunic. Remak has desig- nated this layer as the innermost longitudinal fibrous coat ; Kolliker, as the striated layer of the internal coat. This coat consists of a finely granular substance, with delicate fibrils Fig. 45. Fig. 45. Elastic internal tunic of the basilar arteries. running transversely and longitudinally. The greater part of this tunic is destroyed by the action of potash. Externally, this membrane becomes more distinctly fibrous, and gradually passes into elastic networks and membranes. According to Langhans, J this layer is not distinctly fibrous in young persons, but indistinctly granular, the striation first becoming apparent after the membrane has attained a certain thickness. The tissue of this membrane contains numerous fusiform and stellate cells, lying in anastomosing canals, with relatively large nuclei, and with either finely granular or quite homo- geneous cell substance. Amongst these elements small granu- lation cells are sometimes found, respecting which it is a matter * Handbuch der Gewebelehre, 5. Auflage, p. 583. t Memoire sur la structure et sur la texture des Arteres, Journal de VAnatomie et de la Physiologic, par Charles Robin, p. 536, 1865. \ Virchow's Archiv, Band xxxvi., p. 197, 1866. 270 THE BLOODVESSELS, BY C. J. EBERTH. of doubt whether they are to be regarded as normal or patho- logical constituents. In some instances, the nuclei of the fusiform cells present so well marked a rod-like form as to lead to the supposition that smooth muscles are present. But, like Kblliker,* who first drew attention to them in the axillary and popliteal arteries, I have been unable to convince myself of the presence of smooth muscles in the internal coat of these vessels. On the other hand, I have met with isolated muscle cells in the internal longitudinal fibrous tunic in the hepatic and splenic arteries, and in the crural, at the points where they divide. COAT. — The transition of a capillary into an arterial tube commences with the appearance of scattered transversely disposed fusiform muscle cells, immediately exter- nal to the endothelial tube, and between it and the tunica adventitia. The muscle cells, which at first form only a single interrupted layer, gradually increase in number, and come to constitute an independent layer of cells, adjoining to and superimposed upon each other. Externally, this layer is, for the most part, sharply bounded by the external elastic tunic, or by the tunica adventitia, and internally by the inner elastic membrane. I find that a short portion of the pulmonary artery and the aorta, immediately above the attachment of the semi-lunar valves, are destitute of muscle. Many arteries possess no muscles whatever. Leydig f found none in tjie . aorta of Balaena musculus, nor in the aorta and other larger arteries of Raja batis, Spinax niger, and Polypterus, nor in the basilar artery of the brain of Scymnus lichia, the fine cerebral ar- teries of which, however, contain distinct circularly arranged muscles. With the exception of the largest arterial trunks, the mus- cular layers consist of finely granular connective tissue, con- taining scattered cells, and traversed by a few fine elastic fibrils, in which lie a number of muscle cells, more or less * Zeitschrift fur wissenschaftliche Zoo/o^e,Band i., p. 81, 1849. t Lehrbuch, 1857. MINUTE ANATOMY OF THE ARTERIES. 271 closely packed. In the more peripherically situated vessels the quantity of this intermediate substance diminishes, and the muscle cells are in closer proximity with one another. In the larger arterial trunks, as the aorta, pulmonary, subclavian, Fig. 46. Fig. 46. Small artery from the brain of Man. «, tunica adventitia ; a, a nucleus of the tunica adventitia ; b, muscle nucleus ; c, elastic in- ternal tunic ; d, cell membrane formed of fusiform cells. and carotid arteries, the intermediate substance is not only so abundant that the short and isolated muscle cells, and the smaller groups of such cells, are separated from one another by large intervening spaces, but the elastic tissue also attains its greatest development in the muscular layers. Associated with the fine and narrow-meshed elastic-fibre networks which traverse 272 THE BLOODVESSELS, BY C. J. EBERTH. the fibrous, granular intermediate substance, are a series of lamellae of tolerably even width, composed of elastic bands and fenestrated membrane. These, arranged at nearly regular in- tervals, constitute septa, dividing the muscular tunic into numerous layers. The lamellae are connected by numerous oblique anastomoses, and are also continuous with the fine elastic fibres. They chiefly pursue a transverse direction. In man, at least, there is always a layer of circularly arranged muscle cells, which, however, are strengthened by oblique or longitudinal muscular fasciculi, that are sometimes situated externally, sometimes internally, to the circular fibre layer, and sometimes occupy both positions. Scattered longitudinally and obliquely disposed muscle cells are found in the descending thoracic aorta between the trans- verse muscular fibres. The large vessels that, on account of their loose connections, are easily moved, like those of the viscera of man and mammals, the arteria lienalis, renalis, um- bilicalis, and dorsalis penis, are particularly characterised by longitudinal muscular bundles. The longitudinal muscles of the arteries are chiefly situated in the tunica adventitia, especially in its internal and middle Fig. 47. Fig. 47. Transverse section of the coats of the basilar artery, a, endothelium ; 6, elastic internal membrane ; c, muscle cells ; d, tunica adventitia. layers, where, however, they seldom form a continuous layer, but are united into fasciculi of greater or less strength (arteria renalis, lienalis, dorsalis penis). A well-developed longitudinal muscu- lar layer invests the circular fibrous layer, which is also strongly marked in the arteries of the mesovarium of Batrachia. The MINUTE ANATOMY OF THE ARTERIES. 273 adventitia of the crural artery contains a few short longi- tudinal fasciculi. According to Remak,* both in man and various mammals (ox, sheep, pig), small bundles of longitudinal muscles, apparent even to the naked eye as whitish masses, are recognisable on the external surface of the arch and thoracic portion of the aorta.f In oxen, sheep, and pigs, Remak was able to follow the longitudinal muscles as far as the iliac arteries, and in the sheep he found them in the pulmonary artery and its branches. In the arteries distributed to the Fig. 48. Longitudinal section through the coat of the thoracic aorta, a, elastic plates ; b, transverse muscles in section ; c, longitu- dinal muscles. viscera, Remak found external longitudinal muscles only in the trunk and in the primary divisions of the superior mesen- * Miiller's Archiv, p. 96, 1850. I can corroborate this statement in the case of the calf. 274 THE BLOODVESSELS, BY C. J. EBERTH. teric, the splenic, and renal arteries of oxen, but in the sheep they are scarcely perceptible in the arteria mesenterica. In both, the bundles are collected into a thick uninterrupted longitudinal layer. I was only able to find internal longitudinal muscles in the form of isolated cells in the internal longitudinal fibrous tunic of the hepatic, splenic, and crural arteries. I was not able to discover them in the remaining abdominal vessels, nor in the axillary and popliteal arteries, where Kblliker believed he had recognised them. A delicate layer, composed of contractile longitudinal fibres, exists, according to Kemak, in the internal longitudinal fibrous tunic of the renal, splenic, hepatic, and mesenteric arteries of man, the ox, sheep, and pig. These muscles, however, are only found near the origins of these vessels, and on the proxi- mal side of the point at which the branches are given off from the trunk. In oxen, these muscles form thick, strongly projecting longitudinal cords that are crossed by strong circu- lar fibres near the larger openings, and there constitute a kind of sphincter. Through these longitudinal muscles the openings of the less fixed vessels, given off at acute angles, are probably kept con- tracted when, in consequence of the strong contraction of the discharging vessels, the passage of the blood is checked. This longitudinal fibre layer is absent in those vessels where, on account of their fixity, and the equality of the strength of the blood column, this provision is not required, as in the inno- minate, carotid, and subclavian arteries. I have observed scattered longitudinal muscles in the tunica interna, at the points where branches are given off at acute angles, as at the division of the external iliac into the femoral and profunda arteries. Distinct external and internal longitudinal muscles are only found in the extremely muscular umbilical arteries. The cir- cular muscular layer is here lined internally by a continuous layer of longitudinal muscles, and externally by interrupted and slender muscular bundles, running in the same direction. EXTERNAL ELASTIC COAT, AND TUNICA ADVENTITIA.— The MINUTE ANATOMY OF THE VEINS. 275 external elastic tunic of Henle* exists as an independent membrane in the smaller and medium-sized arteries, with few exceptions (internal spermatic, splenic, renal, hepatic, brachial, crural, popliteal and plantar arteries). The basilar artery, the muscular tissue of which is poor in elastic fibres, loses this membrane completely, and presents instead a very loose network of fine elastic fibres in the tunica adventitia. The dorsal artery of the penis contains similar and numerous elastic networks. The aorta, axillary, carotid, subclavian, and pulmonary arteries, whilst they present largely developed elastic laminse in the muscular tunic, do not possess a proper external elastic membrane. Speaking generally, this membrane is formed by a network of fine elastic fibres, which is sharply defined internally towards the muscular layer, but which externally anastomoses with the elastic network of the tunica adventitia. The remaining por- tion of the adventitia consists of decussating fasciculi of con- nective tissue, with networks of elastic fibres. After what has been said, it is obvious that, whilst a descrip- tion can be given which shall be applicable to individual arteries, and to groups of arteries, no general statement can be given that is appropriate to the entire arterial system ; there is, in fact, a certain antagonism between the elastic element of the tunica adventitia and that of the circular muscular layer, as is well shown in the case of the basilar artery. Still more frequently, again, there exists a certain antagonism between the muscles and the elastic elements of the circular muscle layer. If, in any vessel, the muscles preponderate, the elastic fibres diminish and recede towards the adventitia. THE VEINS. Veins differ from arteries in possessing thinner walls, less elastic and muscular tissue, and for the most part a stronger tunica adventitia. * Allgemeine Anatomie, p. 502 ; Handbuch der Anatomic des Menschen, Band iii., p. 73 ; Gewebelehre, von Kolliker ; Luigi Fasce, Istologia delle arterie e delle vene degli animali vertebrati. Palermo, 1865. 276 THE BLOODVESSELS, BY C. J. EBERTH. THE EPITHELIAL LAYER consists of cells that, when compared with the corresponding structures in the arteries, present a more polygonal and less distinctly fusiform shape, and are consequently both shorter and broader. Their size varies in different regions. ELASTIC INTERNAL MEMBRANE. — The veins, like the arteries, possess an elastic membrane, situated immediately beneath the epithelium, and apparent even in small vessels. This tunic never acquires the size and strength it exhibits in the arteries, and usually appears as a delicate and rather loose network of fibres, which, for the most part, run in a longitudinal direction, and but rarely, as in the larger trunks, undergo development into a fenestrated elastic tunic. In the iliac and crural veins this coat appears in some places to be split into two laminae, which intercommunicate with one another by fine elastic fibrils. A delicate indistinctly fibrous connective tissue containing lon- gitudinally and transversely arranged short fusiform cells, occupies the interspaces of this network. The internal longitudinal fibrous tunic is situated between the epithelial layer and the internal elastic membrane, as in the arteries, but is developed to a much less extent. In some veins it is almost wholly absent, as in those of the neck, the axillary vein, the vena cava, the mesenteric and portal veins, the vena azygos, and the branches of the pulmonary vein. The thick- ness of this layer by no means corresponds with the size of the vessel. Thus it is absent in the vena cava inferior, both above and below the liver, reappearing in the iliac vein, and increasing gradually in strength until the popliteal is reached, where it attains its greatest thickness. At this part the membrane often forms thickenings, which appear even to the naked eye as small elevations and transverse rugae. On tracing it further towards the periphery its thickness will be found to undergo gradual diminution. .Its structure is essentially similar to that of the same layer in the arteries, with the exception that in many parts numerous muscles are present which fail to appear in the corresponding arteries. Thus the crural vein presents small bundles of longi- tudinal muscular fibres between the laminae of its elastic inner coat, and the popliteal possesses in the same layer an internal MINUTE ANATOMY OF THE VEINS. 277 longitudinal and an external transverse layer of muscular fibres. MUSCLES. — In accordance with the presence or absence of muscles in the walls of the veins, these vessels are divided into the muscular and the non-muscular. To the formor belong the veins of the pia and dura mater, the veins of Breschet in the bones, the veins of the retina, the lower portions of the veins of the trunk opening into the vena cava superior, the external and internal jugular veins, the sub- clavian veins, and the veins of the maternal portion of the placenta. In accordance with the arrangement of the muscular tissue, the veins may be divided into three groups ; namely, — Veins with longitudinal muscles, as those of the pregnant uterus. Veins with an internal layer of circularly, and an external layer of longitudinally arranged muscular fibres of which examples are found in the vena cava inferior, both in and below the liver, the vena azygos, and the portal, hepatic, internal spermatic, renal, and axillary veins. The third group includes veins possessing an internal and an external longitudinal and a middle transverse layer of muscular fibres. Amongst these are the iliac, crural, and popliteal veins, the branches of the mesenteric veins, and the umbilical vein. A fourth group includes the veins with circular muscular fibres, to which the veins of the upper and partly of the lower extremities, the smaller veins of the neck, the internal mam- mary vein, and the veins in the substance of the lungs belong. The arrangement of the muscles is thus seen to vary even in the same vascular region. The middle-sized branches of the mesenteric veins contain, for instance, two longitudinal muscular layers with an intermediate circular layer, whilst, on the other hand, the vena porta possesses a feebly developed internal layer of circular fibres, and an external longitudinal layer of con- siderable thickness. As regards the proportionate strength of the muscular coat, the veins of the lower extremity and vena umbilicalis occupy the first rank; and then follow in succession those of the abdo- 278 THE BLOODVESSELS, BY C. J. EBERTH. minal viscera, and of the upper extremity, which are about upon an equality ; and finally those of the thorax and neck. The longitudinal muscular coat is most developed in the inferior vena cava below the liver, in the iliac, portal, renal and mesenteric veins. The thoracic portion of the inferior vena cava has no con- tractile fibres in man, the ox, sheep, pig, and rabbit, whilst the hepatic portion of the same vessel in these animals possesses a strong circular muscular layer, In the superior vena cava of man, in opposition to that of the ox and sheep, there are no muscular fibres, and they first appear in the upper branches of the common jugular vein. Here, in consequence of the fixed position of the vessels, those obstacles are absent which render the passage of the current in the inferior cava difficult. On the other hand, according to Remak, in the superior cava of the ox and sheep there are internal transverse and external longitudinal muscles, an arrangement that may, perhaps, be rendered requisite by the different position in which the head is maintained, THE TUNICA ADVENTITIA of the veins, like that of the arte- ries, consists of bundles of decussating fibrils, the direction of which is for the most part longitudinal. As a general rule their diameter increases with that of the vessel, but there are many exceptions. The tunica adventitia of the veins is dis- tinguished from that of the arteries by its greater thickness and the small amount of elastic fibres it contains, as well as by the presence of longitudinal muscles in certain vessels. The external layer of longitudinal muscles belongs exclusively to the tunica adventitia. To whatever extent the longitudinal fibres may be developed, they never form a distinct coat as in the tunica adventitia of arteries, but only a coarse network con- structed of larger or smaller fibres, which are chiefly found in the middle and internal layers of the tunica adventitia, and diminish towards the outer. The limits between the layers of muscular and elastic fibres are never very well defined. THE VALVES OF THE VEINS cannot be regarded as true duplications of the internal tunics. The elastic finely fibrillated MINUTE ANATOMY OF THE CAPILLARIES. 279 internal membrane covers only the convex surface of the valves. The proper substance of the valve is composed of finely fibril- lated connective tissue with stellate and fusiform cells. The muscular fibres which have been described by Wahlgren in the larger valves, I have not been able to discover with certainty. The sacciform transparent appendages of the veins on the cardiac side of the valves of the veins (to be found in the axillary external and internal jugular and crural veins, as well as in the other branches), which, according to Remak,* consist exclusively of bundles of smooth muscular fibres, I find are not contractile. CAPILLARIES. Capillary vessels removed from living adult animals, and examined with due precaution, as, for example, those of the hya- loid membrane of Frogs, treated with the fluid of the aqueous, appear to be composed of a delicate, double-contoured, dull membrane, in which oval nuclei are imbedded at tolerably regular intervals. The parietes of these tubes are therefore not structureless. The capillaries of the hyaloid of the Frog appear to consist of a soft cloudy substance which in no respect differs from the substance of the delicate threads of protoplasm given off by the cells of the tunica adventitia. In young living animals, as in tadpoles, we may still more easily convince ourselves that the capillary wall is not completely structureless, but that granules are distributed through it in a stellate manner, and that in its general appearance it closely resembles protoplasm. The wall here frequently appears uneven and provided with small teeth, or prolonged into fine partly solid and partly hollow funnel-like and, for the most part, non- nucleated pointed processes. The substance of these is always more granular than that of the rest of the membrane. Such lateral processes are found also in adult animals, Strieker)- having seen them in the nictitating membrane of the * Uber contractile Klappensdcke an den Venen des Menschen, Deutsche Klinik, iii., p. 32, 1856. •\ Sitzunysberichte der Wiener Akademie, Band xii. 280 THE BLOODVESSELS, BY C. J. EBERTH. Frog, whilst I have also observed them in the hyaloid. Threads of a similar nature occasionally form connecting bridges between neighbouring vessels. The diameter of these processes is often far less than that of the capillary from which they spring, and is insufficient for the passage even of a single blood corpuscle. These outgrowths, which act as vasa serosa, and as the youngest sprouts of growing capillaries, render it highly probable that even in adult animals a new formation of vessels occurs, though, perhaps, only to a limited extent. In many and especially in large recently formed capillaries, whether produced under normal or under pathological condi- tions, as, for example, in the membrane capsulo-pupillaris, the wall may be almost immediately broken up into finely granular fusiform protoplasmic masses. A similar cellular structure may be rendered apparent in the Fig. 49. Fig. 49. Capillaries from the membranahyaloidea of the adult Frog, showing a thread-like solid anastomosis between them, a b, cells be- longing to the tunica adventitia. capillaries of adult animals by various modes of preparation. Thus Klebs* observed that in the urinary bladder of the Frog, after treatment with phosphate of soda, the nuclei of the capil- * Virchow's Archiv, Bandxxxii., p. 172, 1865. MINUTE ANATOMY OF THE CAPILLARIES. 281 laries were invested by a cloudy layer of protoplasm, which formed elongated fusiform bodies partly lying on the surface an d partly imbedded in the substance of the membrane Nearly coincidently in point of time, and apparently independ- ently of each other, Hoyer,* Auerbach,-f myself,J and Aeby,§ and more recently Chrzonszczewsky,|| have by means of nitrate of silver shown that the wall of the capillaries is divisible into nucleated areas. The action of the nitrate of silver is to colour the substance intervening between the cells of a brown or black tint, by which means the individual cells are brought into strong relief, and may be then isolated by treatment with a solution of potash containing 35 per cent, of the alkali (Aeby, Eberth). A cellular structure was subsequently shown to exist in the wall of the capillaries in almost all the organs of vertebrate as well as of many invertebrate animals, both by myself 1F and by Legros.** The plexus demonstrated by Fedenrff in and upon the capil- lary walls, after treatment with nitrate of silver, is entirely different from the foregoing, from which it is distinguished by the irregularity of its meshes. Its nature has not been satis- factorily ascertained. The form of the cells lining the capil- laries varies to a considerable extent. As a general rule, it is different in vessels of different calibre. Small capillaries pre- sent cells that are more fusiform in shape ; large capillaries, * Archivfiir Anatomic, dated Jan. 18, 1865. f Breslauer, Zeitung, Feb. 17, 1865. j; Sitzungsberichte der Physikal. Medicin. Gesellschaft zu Wiirzburg, Feb. 18, 1865; Medicinisches Centralblatt, No. 13, 1865; Tiber den JBauund die Entwickelung der Slutcapillaren, Erste Abhandlung, " On the Structure and Development of the Blood Capillaries, First treatise;" Wiirzburger Natunvissenschaftliche Zeitschrift, Bandvi., 1866. § Medicinisches Centralblatt, No. 14, 1865. j| Virchow's Archiv, Band xxxv., 1866. ^[ Loc. cit., Ueber die Capittaren der Wirbellosen, " On the Capillaries of Invertebrate Animals." ** Legi os, Note surT Epithelium des Vaisseaux Sanguins, "Note on the Epithelium of the Bloodvessels," Journal de VAnatomie et de la Physio- logic, Cinquieme Annee, 1868, p. 275. ft Sitzungsberichte der Wiener Akademie, Band liii., 1866. 2S2 TIIE BLOODVESSELS, BY C. J. EBERTH. cells that are more polygonal. After treatment with nitrate of silver, the cells appear bounded by sinuous outlines that are often cremilatcd. and lobed ; as, for example, in the pulmonary Fig. 50. Fig. 50. a, Small capillaries with fusiform cells, taken from th3 me- sentery of Leuciscus ; b, capillaries of the pecten of the eye of the Bird, exhibiting polygonal cells ; &', 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-like swellings. Many of these are composed of less deeply tinted substance, surrounded by the intensely brown cementing material, and perhaps consist of some modification of the latter, which is feebly acted on by nitrate of silver. The slighter staining 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 Fig. 51. Capillaries of the lungs of the Frog, with irregularly den- tated cells. «, 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. EBERTH. 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 off. 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 in different 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 wall (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 really 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, Sitzungsberichte der Wiener Akademie, Bandlvii., 1868. t Wiener Sitzungsberichte, Band Ivii., 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 . 52. Fig. 52. Capillaries from the hyaloid membrane of the Frog, a, capillary wall ; 6, nucleus of th j same ; c, cells of the tunica adven- tit:a ; d, processes of these cells clasping the capillary wall; e, stellate c?lls anastomosing with the cells of the tunica adventitia. become larger, a delicate tunica adventitia is superadded, which, in 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 Iwanoff * 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. CHRONSCZCZEWSKY! observed, in capillaries 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 off into many processes which often anastomose with the processes of the cells of the tunica adventitia. Towards the small arteries and veins the pericapillary 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 .} 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 Centralblatt, No. 9, 1868. t Virchow's Archiv, Bandxv., p. 172, 1866. J 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, when seen on the flat, the illusory appearance of a complete tunica adventitia. MINUTE ANATOMY OF THE 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. A rather large capillary from the hyaloid of the Frog, pre- senting a mtmbranous 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, with 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 lines. 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 fusion with one another, or the capillary wall has become only imperfectly differentiated 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 in 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 obtained from the occurrence of quickly consecutive anastomoses of vessels of various size. The * Wiener SitzungslericJite, Bande li. and Hi. 290 THE BLOODVESSELS, BY C. J. EBERTH. 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 wall, 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 aorta 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 branchiae 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-called chitinogen layer, whilst the pyriform or clavate bodies of the cells which conceal the nucleus are applied * Semper, ZeitscJirift fur wissenschaftliche Zoologie, 1856. Eberth, Blut- gefdsse 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 River Crab, a, cuticula ; b, 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 Wilhelm Miiller, in the spleen of mammals. * Hackel, Miiller's Archiv, 1857. Leydig, Lehrbuch, 1857, p. 385. Eberth, loc. cit. 292 THE BLOODVESSELS, BY C. J. EBERTH. In the process of reparation of a wound there also originate finer or coarser intercellular blood paths, destitute of definite walls, which occupy the interspaces of the granulation cells. 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 fusion 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 papillae of the comb of the cock, develop into actual cavernous spaces. Amongst these vascular plexuses there is one which lies in front of the coccyx 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, Artikel Wundheilung, " Reparation of Wounds," in Pitha's and Billroth's Handbuch der Chirurgie, pp. 553 and 555. t Steissbeindriise oder Nervendriise des JZeckens, " Coccygeal Gland or Nervous Gland of the Pelvis," Archivfiir Pathologische Anatomie und Physi- ologic, Band xviii., p. 106, 1860. Der Hirnanhang und die Steissdriise des Menschen, " The Pituitary Body and Coccygeal Gland of Man." Berlin, 1860. Anatomie des Menschlichens JSeckens, " Anatomy of the Human Pelvis." Tiihingen, 1864, p. 187. CAVERNOUS VESSELS. VASCULAR PLEXUSES. 293 round or slightly polygonal cells, replaced in recently born 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 justify 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 * Arnold,*!" 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- * Zeitschriftftir rationelle Medicin, Band x., 3 R., p. 293. Anatomtsche Untersuclnmyen. Hannover, 1860, p. 98. t ArcMvfur Pathologische Anatomic, xxxii., p. 293, 1865; xxxv.,p.454, 1866 ; xxxix., p. 220, 1867. t Zeitschrift fur rationelle Mcdicin, xxviii. 294 THE BLOODVESSELS, BY C. J. EBERTH. 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. ^?fei: «vc%iftj\vr ' ^~ ;- •-?%>"-? -_~'/'ll!y Fig. 55. Section of a naturally injected coccygeal gland, a, vessels ; b, collection of cells. * Archivfiir Pathologische Anatomic, 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 filled 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 Fig. 56. Fig. 56, A. Cellular vascular sheath, from the coccygeal plexus, a, connective tissue with scattered cells and nuclei ; b, round and polygo- nal cells lying" immediately upon ths capillary wall c. B. A capillary from tha 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 only a 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 cells, 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 cell 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 O8 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 PROFESSOR 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 into 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 the 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 lacunse, under which condition, however, they not unfrequently form investing sheaths for different organs. The lymph 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 distinct 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 those 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 approximative^ 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 fascise and such condensed layers of connective tissue as are found on the surface of the different 300 THE LYMPHATIC SYSTEM, BY F. v. RECELIXGHAUSEN. 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 these 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 walls, the muscular elements,5 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. Miiller, 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 only in 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. Teiehmann's Saugader system. 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 partially 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 still another circumstance that becomes intelligible from this comparison if we remember that certain sections of the lymphatic 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 will be understood how the latter stand in immediate relation with the lymphatic system, are in direct communication with it, and possess similar contents (see infra). This variability of form recurs in the narrowest section of the lymphatic system, that is to say; in the lymphatic capillaries. For even amongst Mammals we meet in certain organs with lacunae, representing the roots of the lymphatics ; whilst 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, like 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 lymphatics 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 capillaries 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 lymphatic 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 till 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 network 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 lie so deeply in organs destined for absorption, as, for example, in the villi ; 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 lacunse, 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 uber das Saugadersystem, Taf. 6, fig. 4. 304 THE LYMPHATIC SYSTEM, BY F. v. RECKLINGHAUSEN. 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 villi and in the epithelial cells. In all probability, there- fore, they press through the epithelial layer as undissolved Fig. 57. Fig. 57. Central tendon of the diaphragm of a Rabbit, treated with silver, and examined from the thoracic side. «, lymphatic capillaries with the contours of the epithelial cells ; b, 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 villi open directly into the central chyle vessel; and the sim- MINUTE ANATOMY OF THE CAPILLARY LYMPHATICS. 305 plest view is, that no special limiting membrane 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 (Kolliker). 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 lymphatic capillaries (fig. 57), which are usually strongly looped or sinuous, including polygonal, or riot unfrequently 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 tunica 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 unfrequently 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. RECKLINGHAUSEN. 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 fails. 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 brain. 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 appearances 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 * Handluch, 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 db 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 milk, 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 milk 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 round, 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. EECKLINGHAUSEN. 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 cisterna 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, «ven 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 junction of several epithelial cells. I recognised these spaces when I first began to employ silver as STOMATA OF THE CAPILLARY LYMPHATICS. 309 a means of staining the tissues; but have met with them under so many different 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, again, 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 in 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 in 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 still 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 in absorbing membranes, though this still remains to be satisfactorily demonstrated, notwithstanding that 310 THE LYMPHATIC SYSTEM, BY F. v. KECKLINGHAUSEN. Oedmansson, His, and others have described foramina present- ing features analogous to such stomata. We come now 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, in 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 villi, though in regard to the other rootlets of the lymphatic vessels, their existence appears less requisite, since their contents, apart from the lymph corpuscles which are probably formed in their interior, ordinarily 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 has been 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 maintained 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 Donders 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 Kb'lliker, 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 Kolliker 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. RECKLINGHAUSEN. 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 view held by Briicke and Ludwig; and Langer even pointed out that in 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 in 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 differ 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 lie. 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 still 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 lymphatic 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, Kolliker, and Leydig supposed, fused with the walls of the lymphatic vessels, but occupy the interior of the serous canali- culi, so that from this point 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 Kolliker, 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 distinguished 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 canaliculi are buried. Their form and arrangement, whilst 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 lacunae, 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 314 THE LYMPHATIC SYSTEM, BY F. v. RECKLINGHAUSEN". form of the cells ; in other words, that the solid 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 still 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 all 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 lamellse, 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 all 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 follows 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, as the cornea, tendons, fasciae, 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 filled with cells, 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 with afacility proportionate 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 lie, make their appearance. The serous canals have, however, very different forms in the various organs. They appear as distinct plexuses of subcylindrical 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, whilst 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, like 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 superficial 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. Ail 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 makes 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 riot unfrequently rather lies in close approxima- SEROUS 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 Fig. 58. Fig. 58. Central tendon of the diaphragm of a Rabbit treated with silver, «, lymphatic capillaries with epithelium ; b, commencement of the same; c, serous canals; d, 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 following facts may be adduced : 1. In A A 2 318 THE LYMPHATIC SYSTEM, BY F. v. KECKLINGHAUSEN. 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 manner 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. 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 ; b, their origin ; c, serous canals with communications ; d, serous 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 lymphatic 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 containing 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 fur wissenschaftliche Zoologie, Band xiii., Heft. 3, 1863. 320 THE LYMPHATIC SYSTEM, BY F. v. RECKLINGHAUSEN. 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 unfrequently 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 lacunae in the kidneys surrounding the tubuli uriniferi. Tomsa made inj ections of the nose of the dog, and saw plexuses 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 lacunae 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 hence are most probably analogous to these rather than to serous canals. The other theory, which refers the rootlets of the lymphatic system to 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 (K6 Hiker). 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-defined 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 wide 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 trabeculse, 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 324 THE LYMPHATIC SYSTEM, BY F. v. RECKLINGHAUSEN. 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 really interstitial spaces bet ween 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 the 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 careful 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 RELATION 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 first 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. Fuhrer, 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. KECKLINGHAUSEN. 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. Bb'hm 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 millet seed — the so-called 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 follicles 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 lymphatic 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 Kolliker) 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 differ 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 in 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 follicles 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. RECKLINGHAUSEN. 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 follicles 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 lacunae 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 continuous 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 follicles 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 follicular 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 arteiy 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, GLANDULE 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 furnished 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-called 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 medullary 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- i MINUTE ANATOMY OF THE LYMPHATIC GLANDS. 331 ceptible, as in the ox and horse, in both of which the medul- lary substance presents an intensely 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. Fig. 60. Vertical section of a lymphatic gland from the Ox. A, cor- tical substance ; B, medullary substance, a, capsule ; a', trabeculae ; b, follicles ; &', follicular cords (medullary cords) ; c, 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 indeed 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 BB 332 THE LYMPHATIC SYSTEM, BY F. V. RECKLINGHAUSEN. 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 stellate manner, and often con- tain nuclei or cells to which granular masses of pigment cleave. Fig. 61. Section of the medullary substance of a lymphatic gland from the Ox. a, follicular cords ; b, trabeculce ; c, lymph path. Mag- nified 120 diameters. These fibrils unite to form thicker fasciculi of connective tissue, the trabeculce, 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 off 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 ; lymph tubes of Frey). These medullary cords (fig. 61) have the same structure as the tissue of the lymphatic follicles (see above), consisting MINUTE ANATOMY OF THE LYMPHATIC GLANDS. 333 consequently of a reticulum of fibres enclosing lymph cor- puscle-like cells, and may correctly be termed follicular struc- tures, or follicular cords. The reticulum is distinguished from 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 indebted 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 in 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 smallness 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 trabeculse 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 corpuscles . B B 2 334 THE LYMPHATIC SYSTEM, BY F. v. RECKLINGHAUSEN. 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 still 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 true paths pursued by the lymph. They, for the most part, fill with great facility, and the injecting fluid, if composed of thick solutions of gelatine and some coarsely granular 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 follicular 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 lymph path. Thus it appears that although the reticulum is very compact near their surface, it will still permit solid corpuscles to pene- trate from the lymph path into the interior of the follicle, and therefore conversely it is probable that material particles — lymph cells, for example — may pass from them into the lymph path. We are thus able to differentiate three separate parts in the tissue of the lymphatic glands : (1) the follicular 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. £0), and, like this, consist of connective tissue, MINUTE ANATOMY OF THE LYMPHATIC GLANDS. 335 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 trabeculae, which ultimately become continuous with the con- Fig. 62. Fig. 62. Section of the medullary substance of a lymphatic gland from the Ox. a, follicular cord ; b, trabeculse ; c, path pursued by the lymph ; d, bloodvessels. Magnified 300 diameters. nective tissue of the hilus. 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, in such a way that the latter are only uninvested on the part looking towards the hilus. As they divide into rounded cords, the trabeculse come into much closer approximation ; the spaces which they invest are consequently smaller than the alveoli, and at the same time are in 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 cylindrical, 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 cortically situated follicles 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 trabeculae, and the spaces which intervene between the two are the lymph 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 approximation 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- ARRANGEMENT OF THE LYMPH PATHS. 337 trary, if the injection is sufficiently fluid, this may be accom- plished with extraordinary facility, especially when the mode of injection by puncture is adopted. In such cases it will be found that the vessels of origin 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 in 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, whilst 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, becoming consequently more attenuated. These finer 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 continuous and tubular efferent vessel. The follicular substance is chiefly developed in the dilatations near the point at which the vasa efferentia 338 THE LYMPHATIC SYSTEM, BY F. v. RECKLINGHAUSEN. are 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 Fig. 63. Fig. 63. Section from the medullary substance of a mesenteric gland of a Dog, after injection with silver, a, rootlets of the vas eflerens, 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 ; d, fibrils traversing the lymph path, upon which, again, as at d', an epithelium may be distinguished; e, fibrous intervening substance, which at e' forms trabeculae. 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. ARRANGEMENT 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 original lymph path, accumulations of cells occurred to form the follicular glandular substance. The 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 follicular 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 lymphatic 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 LYMPHATIC SYSTEM, BY F. V. RECKLINGHAUSEN. 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 follicular 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 trabeculaa upon the thicker fibrils (see fig. 63, 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-white 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 remaining 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 CORPUSCLES. 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 in all their characters with the colourless corpuscles of the blood. They show in 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 kill 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 nucleus which is usually strongly gra- nular. The corpuscles of the lymph, like the colourless cor- puscles of the blood, are not all 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 in 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. RECKLINGHAUSEN. ment of organization ; and even within a very recent period it has been sought to establish the view that the lymph follicles and the lymphatic glands are the only seats of origin of the lymph 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 lymph cell a young lymph corpuscle situated near the nucleus was suddenly ejected; I was 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 efferentia 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 (Kb'lliker). The follicular 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 Teichmann 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 CORPUSCLES. 343 quently by F. A. Hoffmann, under my direction, in 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 sufficiently 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 Yirchow, 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 afferentia, which would also pass out by the vasa efferentia. 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, in order to migrate in the well-known mode ; and thus the observation formerly made by Waller* in 1846, but again for- gotten, except in England, under the predominant influence 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 follow 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 small 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. Kosinski, Wiener Med. Wochenschrift, 1868, Nos. 56 and 57. ORIGIN OF THE LYMPH CORPUSCLES. 345 caution. I have especially observed that not only colourless cells escape from the blood path, but that migrating 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 wall (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 in 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 vermilion 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. Hering 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 insoluble 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 all 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 LITERATURE. BARTHOL, PANIZZA, Sopra il sistema linfatico dei Rettili Pavia, 1833 ; und JOSEPHUS MEYEB. Systema Amphibiorum lymph. Berolini, 1845. H. MULLER. Zur Morphologie des Chylus und Eiters. Wiirzburg, 1855. F. NOLL, HENLE'S Zeitschrift, Bd. ix. REMAK, MULLER'S Arch., 1850, pp. 79 and 183. A. KOLLIKER, Wiirzburg Verhandlung, iv. ; and Annales des Sciences naturelles, 1846 ; and Handbuch der Gewebelehre, 5. Auflage, 1867. 0. HEYFELDER, Ueber den Ban der Lymphdriisen. Breslau, 1851. E. BRUCKE, Sitzungsberichte und Denkschriften der Wiener Akademie, 1852—1855. BONDERS, Nederland. Lancet, 1852. CNOOP KOOPMANS, Nederland. Lancet, 1855. A. ZENKER, Zeitschrift f. wissensch. Zoologie, vi. ; FUNKE in idem ; RUD. HEIDENHAIN, Symbola ad Anat. Gland Peyeri, Breslau, 1859 ; and MOLESCHOTT'S Untersuchungen, iv. TH. BILLROTH, Beitrage zur pathol. Histologie. Berlin, 1858. Zeit- echrift f. wissenchaft. Zoologie, Bd. xi. VIRCHOW'S Arch., Bd. xxi. W. His, Zeitschr. f. wissensch. Zoologie, Bande xi., xii., xiii., u. xv. H. FREY, Vierteljahrschr. d. naturf. Gesellsch. in Zurich, 1860 u. 1862; Untersuchungen iiber denBauder Lymphdriisen. Leipzig, 1861. Also, Handbuch der Histologie u. Histochemie, 2. Auflage. Leipzig, 1867. L. TEICHMANN, Das Saugadersystem, vom anatomischen Standpuncte. Leipzig, 1861. W. KRAUSE, Anatom. Untersuchungen, 1860. BIBLIOGKAPHY OF THE LYMPHATIC SYSTEM. 347 PIERS WALTER, Unters. iiber die Textur d. Lymphdriisen. Dorpat, 1860. AD. KJELBERG, studier i Laran om lymphkarlens ursprung. Upsala, 1861. F. v. RECKLINGHAUSEN, Die Lymphgefasse und ihre Beziehung zum Bindegewebe. Berlin, 1862. Zur Fettresorption. VIRCHOW'S Arch., Band xxvi. Ueber Eiter- und Bindegewebskorperchen, idem, Band xxviii. W. MULLER, Zeitschr. f. rationelle Medicin, Band xx. C. JJUDWIG u. W. TOMSA, Sitzungsber. d. Wien. Akademie, Band xliii., 1861 ; und Band xlvi., 1862. C. LUDWIG, Ursprung der Lymphe, Wiener med. Jahrbiicher, 1862. W. TOMSA, idem, 1862. LUDWIG u. ZAWARYKIN, Zur Anatomie der Niere, idem, Band xlviii., 1863; u. Zeitschr. f. rat. Med., Band xx. E. OEDMANSSEN, VIRCHOW'S Arch., Band xxviii. C. LANGER, Ueber das Lymphgefasssyst. d. Frosches., Berichte d.Wien. Akadem., Bande liii. u. lv., 1866 u. 1867. FRANZ TH. SCHMIDT, Det folliculaere Kjertelvaev. Kopenhagen, 1862. N. KOWALEWSKY, Sitzungsber. d. Wien. Akademie, Band xlviii. C. HUETER, Medic. Centralblatt, 1865. L. AUERBACH, VIRCHOW'S Arch., Band xxxiii. C. LUDWIG, SCHWEIGGER-SEIDEL, DOGIEL, u. DYBKOWSKY, Berichte d. Kon. Sachs. Gesell. Leipzig, 1866, 1867. ENR. SERTOLI, Sitzungsber. d. Wien. Akadem., Band liv., 1866. GUST. HERBST, Das Lymphgefasssystem u. seine Verrichtung, Got- tingen, 1844. A. WALLER, The Philosoph. Magazine and Journal of Science, xxix., 1846. JUL. COHNHEIM, VIRCHOW'S Arch. Bande xl. u. xli. FRIEDR. ALB. HOFFMANN u. F. v. RECKLINGHAUSEN, Centralblatt, 1867 ; u. HOFFMANN, VIRCHOW'S Arch., Band xlii. Ew. HERING, Sitzungsber. d. Wien. Akad., Band Ivi., 1867. C. TOLDT, idem, Ivii., 1868. W. ENGELMANN, Ueber die Hornhaut des Auges. Leipzig, 1867. S. CHRZONSZCZEWSKY, VIRCHOW'S Arch., Band xxxv. N. AFONASIEW, VIRCHOW'S Arch., Band xliv. F. LOSCH, idem. C C CHAPTER X. THE SPLEEN, BY WILHELM MULLEB, OF JENA. THE structure of the spleen is intimately associated with that of the lymphatic glands. In both organs numerous trabeculae 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 contained in their respective vessels ; in the one case by lymph, 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 Ophidia and in 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 link 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. Fig. 64. From the spleen of the Tropidonotus natrix. a, follicle, with its capillary plexus ; b, 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 a1 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 cells. The deeper layers exhibit, in preparations that have not been injected, regularly c c 2 350 THE SPLEEN, BY WILHELM MULLER. 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 all 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 0'5 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 multiplication. 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 Yi 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 STRUCTURE OF 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 follicles, where the smallest arterioles break up into a very characteristic capillary plexus. This forms meshes of O015 — 0'03 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, whilst 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-walled veins which wind around the periphery of the follicles resemble the lymph spaces that surround 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, BY WILHELM MULLER. 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 flattened, 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 Carnivora, 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 off at regular distances, which are recognisable with the naked eye, and become continuous with cylindrical cords, the so-called 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 trabeculae 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 trabeculse 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 Ruminants ; 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 MU LLER. trabeculsB 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. Miiller). 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 partly as elliptical nuclei which only present small 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 O3 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-like 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 O3 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 the arterial branches to which they belong varies to some extent, according STRUCTUKE 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 in their characters with the lymph corpuscles of the several animals, and they are constantly found in various stages of development, some being 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 carmine, 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, furnishing 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 MULLER. exhibiting amoeboid movements (Cohnheim). 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 tissue composed of homogeneous intercommunicating 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 the Hedgehog. «, a M alpighian cor- puscle, with its vascular apparatus ; b, splenic pulp, with the interme- diary blood 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 distinctly fibrillar. It here becomes continuous on the STRUCTURE OF THE SPLEEN. BLOODVESSELS. 357 one hand by numerous processes with 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. BLOOD VESSELS 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 0'2 millimeter, 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 capillaries (Huxley, W. Miiller). At the surface of the Malpi- ghian corpuscles the capillaries 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 fully 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 MULLER. Schweigger-Seidel. After a longer or shorter course the capil- lary wall 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 strise, 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 intercellular 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 epithelial 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 pursues 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 different 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 Kolliker. 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. Kolliker 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 afferens of any group of lymphatic glands. The second is easily 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 which 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, BY WILHELM MULLER. 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. Miiller). 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 further 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 maintains, or from the detachment of the peripheric protoplasm of numerous cells,! 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 constantly filled with blood corpuscles. According to Peremeschko, there are now developed larger pro- toplasmic corpuscles in the tissue of the pulp containing from two to six nuclei, that are capable of performing amoeboid move- ments, and which, towards the end of embryonic 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 furnishes 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. LITERATURE. 1. MARCELLI MALPIGHII opera. Londini, 1686. 2. FREDERICI RUYSCHII, opera. Amstelodani, 1737. 3. JOH. THEOD. ELLER, De liene in HALLER'S Dissert, anat., Vol. iii. 4. CHRIST. LUDW. ROLOFF, De fabrica et functione lienis. Halae, 1750. 5. DE LA LONE, Sur la rate, Histoire de 1' Academic. 1754. 6. J. F. LOBSTEIN, De liene. Argentor. 1784. 7. GULIELMI HEWSONII, Opus posthumum. Lugd. Bat. 1785. 8. J. P. ASSOLANT, Recherches sur la rate. Paris, 1800. 9. A. MORESCHI, Del verso e primario uso della milza. Milano, 1803. De vasorum splenicorum constitutione. Mediol. 1817. 10. JOH. MULLER, 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. Reihe, Bd. viii. 12. SCHWAGER-BARDELEBEN, Disquisit. microscop. de glandul. ductn carentium structura. Berolini, 1841. 13. KRAUSE, Handbuch der menschlichen Anatomie. Hannover, 1842. 14. OESTERLEN, Beitrage zur Physiologic des gesunden und kranken Organismus. Jena, 1843. 15. ATTO TIGRI, Nuova disposizione dell' aparecchio vascolare san- guigno della milza umana Bologna, 1847. II Progresso, 1849. Gazetta medica italiana, Tom. iii. 1853. 16. A. KOLLIKER, Art. Spleen in TODD'S Cyclopaedia. London, 1849. Handbuch der Gewebelehre. Leipzig, 1867. 5. Auflage. 17. A. ECKER, Art. Blutgefassdriisen in RUD. WAGNER'S Handwor- terbuch der Physiologie. Braunschweig, 1849. 18. SCHAFFNER, Zur Kenntniss der Malpigh. Korperchen der Milz. Zeitschrift fiir rationelle Medizin, Bd. vii. 1849. 19. WILLIAM SANDERS, On the structure of the Spleen. London, 1850. 20. R. REMAK, Ueber runde Blutgerinsel und pigmenthaltige Zellen. Archiv fiir Anat. und Physiol. 1852. BIBLIOGRAPHY 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 Reptilien. Berlin, 1853. 23. RUDOLPH VIECHOW, Zur patholog. Physiologic des Blutes. 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 GRAY, On the Structure and Use of the Spleen. London, 1854. 26. GOETHIUS STINSTRA, Commentatio physiologica de funct. lienis. Groningen, 1854. 27. F. FUHRER, Ueber die Milz und einige Besonderheiten ihres Capillar systems. 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. 30. 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. MEISSNER, Zeitschrift fiir rat. Medicin. 3. Reihe, Bd. ii. 32. L. FICK, Zur Mechanik der Blutbewegung in der Milz. Archiv fiir Anat. und Physiol. 1859. 33. SAPPEY, Trait. d'Anatomie, 1859. 34. HEINRICH FREY, Histologie und Histochemie des Menschen. 2. Auflage. Das Mikroskop. Leipzig, 1867. 35. NICOLAUS KOWALEWSKY, Ueber die Epithelialzellen der Milzvenen und die MALPIGH. Korper der Milz. Archiv fiir pathol. Anat. . Bande xix., xx. 36. F. GROHE, Beitrage zur pathol. Anat. und Physiol. Archiv fiir pathol. Anal, Bd. xx. 37. LUDWIG TEICHMANN, das Saugadersystem. Leipzig, 1861. 38. AXEL KEY, Zur Anatomie der Milz. 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 MULLER. 40. FB. SCHWEIGGEK-SEIDEL, Untersuchungen iiber die Milz. Archiv fiir pathol. Anat., Bande xxiii. und xxvii. 41. LUDWIG STIEDA, Zur Histologie der Milz. Archiv fiir pathol. Anat., Bd. xxiv. Ueber das Capillargefasssystem der Milz. Dorpat, 1862. 42. A. TIMM, Zeitschr. fiir rat. Medicin. 3. Reihe, Bd. xix. 43. W. BASLER, Einiges iiber das Verhalten der Milzgefasse. Wiirz- burger med. Zeitschrift, Bd. iv. 44. W. TOMSA, Ueber die Lymphgefasse der Milz. Sitzungsberichte der k. k. Akademie zu Wien. 1863. 45. WILH. MULLER, Ueber den feineren Bau der Milz. Leipzig und Heidelberg, 1865. 46. PEREMESCHKO, Beitrage zur Anatomie der Milz und Ueber die Entwicklung der Milz. Sitzungsberichte der k. k. Akademie zu Wien. 1867. CHAPTER XI. THE THYMUS GLAND. BY E. KLEIN. IN Man and Mammals, at an early period of their existence, a placentiform lobulated body, called the thymus 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- lobes not pre- senting acute edges, and of nearly equal size, united together by a short cylindrical intermediate portion. The thymus of the new-born 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, follicles. 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- fracting 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 indifferent 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-walled 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 follicles 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, STKUCTURE OF THE THYMUS GLAND. 367 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 cells; but near the free surface of the folli 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 trabeculae, especially at their nodal points. These narrow-meshed networks are the pro- longations of the interalveolar or interfollicular lymphatic vessels. Lastly, there occurs a third kind of trabecular structure in the form of strong elongated fibres, which are stretched between adjoining vessels, or between these * Beitrdge zur Kenntniss der zum Lymphsysteme gehorigen Driisen, Siebold and Kolliker's Zeitschrift filr wissenschaftliche 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 bases 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 0'0075 to O009 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 O027 millimeter in diameter, and are composed of several simple vesicles that are collectively invested and united 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 follicular septa divide into numerous branches that everywhere surround the follicles, f The arteries give off 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 capillary network, by which they * Blutgefassdrusen in R. Wagner's Ilandworterbuch, Band i., p. 115. t Ecker, loc. cit., and His, loc. cit. STRUCTURE OF THE THYMUS GLAND. 369 are completely filled.* The very wide spaces charged with lymph cells, which immediately invest the follicles, 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 doubtful whether they are lymphatic vessels or sinuses investing the follicles. 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 all communi- cating with a common central canal. Jendrassik J 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 follicle, 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, small isolated groups of fat cells may be found in the investing sheaths of the follicles. * Kolliker, Gewebelehre, p. 485. f J. Simon, A Physiological Essay on the Thymus Gland. London, 1845. 4to. Gerlach, Gewebelehre Mainz, 8vo, Lieferung, 2 and 3. Ecker, loc. cit. J Anatomische Untersuchungen iiber den Bau der Thymusdruse, Sitzungs- berichte der k. Akad. zu Wien., 1856, Juli-heft. CHAPTER XII. THE THYROID GLAND. BY E. VERSON. 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 nucleoli. In this condition, however, the epithelium of the vesiculse is only encountered in quite young animals when examined with the microscope immediately 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 wall 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 colloid, though STRUCTURE OF THE THYROID 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 small. On the other hand, in a human embryo of the fifth or sixth month, I have found their diameter to be O0252 — 0'0336 millimeter, whilst their diameter in the newly born already amounts to O'l — O16 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 O'l 4 — 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 in 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, in an embryo of the fifth or the sixth month they were from 0-006—0-0095 millimeter long, and from 0*004— 0'005 milli- meter broad; in adults they attain the length of O'Ol — 0"16 millimeter; in the dog, from 0*008 — 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 372 THE THYROID GLAND, BY E. VERSON. 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 0'006 — O01 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 lying on either side of the trachea. A single median lobe occurs in Amphibia and Birds, which descends into the thoracic cavity. BIBLIOGRAPHY OF THE THYROID GLAND. 373 BIBLIOGRAPHY. PANAGIOTIDES and WAGENER in Froriep's Notizen, Band xl. PAXAGIOTIDES, De Glandulse Thyreoideae stractura penitiori. Berolin, 1847. Diss. ECKER, Versuch einer Anatomie der prim. Formen des Kropfes, etc., in HENLE and PFEUFFER'S Zeits. f. rationelle Medicin, Band vi. SCHAFFNER, Zur Histologie der Schilddriise und Thymusdriise, idem, Band vii. EOKITANSKY, in Zeitschrift der Wiener Aerzte, 1847, undDenkschriften der Kais. Akad. d. wiss. zu Wien., Band i., 1850. KOHLRAUSCH, Beitrage zur Kenntniss d. Schilddriise in MULLER'S Arch., 1853. EULENBERG, Untersuch. liber die Schilddriise in Arch. d. vers. f. gem. Arbeit, Band iv. FREY, im. viii. Bde., d. Vierteljahr, d. naturforsch, Gesellschaft 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 all 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 uniform 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 living 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 various angles, though when in large only * Compare Kiihne, Lehrbuch der Physiologischen Chemie. Leipzig, 1866, pp. 162 to 174. RED CORPUSCLES OF THE BLOOD. 575 very gradually, as often occurs in the blood of cold-blooded animals ; or if larger quantities of fibrin quickly separate, the whole drop of blood solidifies, 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 shall hereafter revert to the behaviour of the blood cor- puscles in the fibrinous 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 Milne Edwards, Lemons sur la Physiologie et VAnatomie comparee. Paris, 1857, T. i., p. 41. 376 THE BLOOD, BY 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 will 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, Ammocostes) are known to possess circular disks. A small 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 haemoglobin, 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 oxy haemoglobin 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 Kiihne, Lehrbuch der Physolog. Chemie. Leipzig, 1866, p. 196. t Virchow's Archiv, Band xxiii., p. 446. t Max Schultze's Archiv, Band ii., p. 92. § Pfliiger's Archiv, 1868, p. 651. RED CORPUSCLES OF THE BLOOD. 377 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 haemoglobin on alternate exposure to 0 and CO2. 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 hsemoglobin 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 hollowed surfaces, and resemble a finger biscuit, or a section carried through the axis of a bi-concave lens (fig. 66, fr). Such a corpuscle, as it again revolves, places itself upon its edge again, and, in short, 378 THE BLOOD, BY ALEXANDEK 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 b. 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 will understand Fig. 67. 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. Schultze-f constantly found in the blood of .*• See Rollett, Wiener Akadem. Berichte, Band L, Abth. ii.; p. 183. t Archivfur Mikroskop. Anatomic, Band i., p. 35. RED 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, in accordance with the frequently cited observation, though standing much in need of confirmation, of Lehmann,* the blood of the hepatic vein con- tains corpuscles of smaller size and more spheroidal form than usual, whilst those of the portal vein 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 in 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 light experiences in the focal plane of the microscope when it traverses objects bounded by circular contours.-)- The appearance presented by human blood corpuscles is dif- Fig. 68. ferent from that of the corpuscles of animals with elliptical corpuscles. External to the elliptical 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 Mikroskop, Theil i., p. 184, et seq. Harting, Das Mikroskop. Braunschweig, 1866, Band ii., p. 26, et seq. E E 380 THE BLOOD, BY ALEXANDER ROLLETT. 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, fr). 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 striae. This spot corresponds to a structure which possesses no ana- logue in the fully developed blood corpuscles of Man and Mammals, but behaves itself quite differently from the remain- ing substance of the corpuscle, and shows at least as great 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 fully 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 CORPUSCLES. — 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 Microscopic, etc., Paris, 1843, p. 70 ; Comptes Rendus, T. xiv., p. 367. SIZE OF THE RED CORPUSCLES. 381 scopic 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 all 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 employment 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 : — Min Mar. Diameter of disk . . . 0-00774 (0-00640 0-00860) Greatest thickness of the disk 0-00190 In six males and three females a minimum was observed of 0'0045 millimeter, and a maximum of O0097, 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 — O006 millimeter ; and from these, gradual transitional forms may, according to Max Schultze, be traced up to those of ordinary diameter, from 0-008 to 0-010 millimeter. We are indebted to Welcker for exact measurements of the * Das Mikroskop, etc., Band ii., p. 288, et seq. t Zeitschrift fur rationelle Medicin, 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. cit., p. 263. B E 2 382 THE BLOOD, BY ALEXANDER ROLLETT. corpuscles in various animals, and a few of his mean values will be found in the subjoined 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 ^ mm. and the short to ^ mm.).-f> The largest known, according to Riddel, f 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. rit.t p. 279. I. CIRCULAR CORPUSCLES. Dog . . . 0-0073 Cat . . . 0-0065 Rabbit . . 0-0069 Sheep . . . 0-0050 Goat (old) . . . 0-0041 Goat (8th day) . . 0-0054 Moschus Javanicus . . 0-0025 Petromyzon mari. . . 0-0150 Ammoccet branch. • . 0-0117 II. ELLIPTICAL CORPUSCLES. a, Long diameter ; b, short diameter. a. b. Lama 0-0080 0-0040 Pigeon (old) 0-0147 0-0065 Pigeon (fledged) . 0-0137 0-0078 Pigeon (fledged) . 0-0126 0-0078 Duck 0-0129 0-0080 Fowl 0-0121 0-0072 Ran a temp or aria 0-0223 0-0157 Rana temp, (dry) 0-0214 0-0156 Triton Cristatus . 00293 0-0195 Proteus (1 and 2) . | 0-0582 0-0579 0-0337 0-0356 Sturgeon ^', 0-0134 0-0104 Cyprinus Alburn . 0-0131 0-0080 Lepidosiren Annectens . 0-0110 0-0290 t Milne Edwards, loc. cit., p. 89. I Journal de la Physiologic, Band ii. Paris, 1859, p. 159. § Loc. cit., pp, 265—275. NUMBER OF THE RED 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, carefully lined the interior 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 0*0,001,280 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 modified 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 indifferent fluid (six grammes of Na. Cl. in one litre of water, according to Welcker), a small quantity of the mixture is taken up in 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 into squares, and the corpuscles in the several squares can then be successively counted. In one experiment Vierordt used 0'0005 — 0*0008 cubic * VieTor&t,ArchivfurPhysioL Heilkunde, Band xi., pp. 26, 327, 854; xiii., p. 259 ; Grundriss der Physiol, 3. Auflage, 1824, pp. 8, 9. Welcker, PragerViertel/ahreschnft.Tta,nd.xliv.,-p.6()', und Zeitschrift fur rationelh Medicin, 3 R., Band xx., p. 280. 384 THE BLOOD, BY ALEXANDER ROLLETT. 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 millimeters. 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 under 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 flask, 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 RED CORPUSCLES. 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 still 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 will 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. f Opus posthumum, pp. 19, 20. 386 THE BLOOD, BY ALEXANDEE ROLLETT. versing the angles of division of the vessels, were facts well known to the older observers. Lindwurm,* in thick solutions of mucilage; Hassall/fin micro- scopic coagula ; and Henle,J 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° C. (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 circulating. 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. According to Rollett, in the circulating blood of Mammals, as, for instance, of guinea-pigs, that have been narcotised with * Zeitschrift f'dr rationelle Medicin, Band ~vi., p. 266. f Microscopic Anatomy, p. 31, et seq., plate ii., fig. 6. J Canstatt's Jahresberichte, 1850, Band i., p. 32. § Rollett, Sitzungsberichte der Wiener Akademie, 1862, Band xl., vol. i., pp. 65—71. II Handbuch der Anatomic, 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 in the red corpuscles during their transit through the vascular wall. Lastly, it is to be observed that the blood corpuscles, not- withstanding 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 || has observed that when a thin layer of blood corpuscles is dried upon glass, * Sitzungsberichte der -Wiener Akademie, Band 1., p. 196. f Loc. cit., Band lii., p. 386. I Loc. cit., Band Ivi., p. 13. § Hensen, Zeitschrift fiir wissenschaftliche Zoologie, Band xi., p. 260. Vintschgau, AttideW Institute Veneto. Extr. dal\o\. vii., ser. iii., pp. 3 — 6. || Die Diagnostik verddchtiger Flecke. Mitau and Leipzig, 1848, p. 3, et seq. 388 THE BLOOD, BY ALEXANDER ROLLETT. 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 small 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 •(• and Preyer, { 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. cit., p. 261. t Experimental Studien itber die Histologie des B lutes. Leipzig, 1863, p. 8. J Virchow's Archiv, Band xxx., p. 417. § Quarterly Journal of Microscopical Science, No. 13, 1864. || Rollett, Sitzungsberichte der Wiener Aka lemie, Band xlvi., pp. 92 — 97 ; Band xlvii. pp. 356—390 ; Band 1., pp. 178—202. CHANGES IN THE RED CORPUSCLES BY ELECTRICITY. 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 tin-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. If 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 assuming 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-foil 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 used, as the THE ^ 390 THE BLOOD, BY ALEXANDER ROLLETT. 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, 6) ; 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, all the spikes are withdrawn, and a coloured cor- puscle results (fig. 70, 6),which then loses its colour, and a smooth colourless body is left (fig. 70, /), that long remains in the fluid 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 6). 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, 6) and to the second (fig. 70, c) stage in the blood corpuscles of CHANGES IN THE RED CORPUSCLES BY ELECTRICITY. 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 dull 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. Neumann 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 ROLLETT. 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 Kollett,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 Bind- 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 in 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, Rollett ascertained the temperature at which the blood corpuscles became spheroidal to be between 40° and 50° C. (104°— 122° F.) The changes in 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 xlvii., p. 359 ; Band Hi., p. 257. A. Schmidt, Virchow's Archie, Band xxix., p. 29; Hamatologische Studien. Dorpat, 1865, p. 116. Neumann, Refchert and Du Rois' Archiv, 1865, pp.682— 690. t Centralblatt fiir die medicin. Wissenschaften, 1863, p. 851. J Loc. cit., Band 1., p, 192. § Loc. cit. i! Loc. cit., p. 1. CHANGES IN THE RED CORPUSCLES BY 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 in 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 distin- guished. The reagent may be intimately commingled with the * Rollett, loc. cit., Band xlvi., pp. 74, 75. 394 THE BLOOD, BY ALEXANDER ROLLETT. blood by mechanical means, in which case it is only possible to observe the final changes effected 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 thin 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 WATER 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 all the several and corresponding diameters, so that variable and Fig. 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, 666). 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, loc. cit., p. 437. F F S96 THE BLOOD, BY ALEXANDER ROLLETT. 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 stiU 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, 1865, 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 * Kolliker, Zeitschrift fur wissenschaftliche Zoologie, Band vii., p. 184. Botkin, Virchow's Archiv, Band xv., p. 176. Bursy, Ifeber den Einfluss einiger Sake aufdie Krystallisation des Blutes. " On the Influence of some Salts on the Crystallization of the Blood." Inaug. Diss. Dorpat, 1863. t Zeitschrift fiir wissenschaftliclw Zoologie, Band ix.,, p. 261. 398 THE BLOOD, BY ALEXANDER KOLLETT. 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 beonore 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 all 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 ihave 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 T?E RED CORPUSCLES. 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 still 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 form, 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 lime 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);*f- 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 hseniatin; 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 ROLLETT. 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 effects 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 exhibited 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 effected on corpuscles of the fresh blood of the Triton by the action of a two per cent, solution of boracic acid, and we shall 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 greater number of * Allgemeine Anatomie, p. 431. t Loc. cit., pp. 28, 29. % Sitzungslerichte der Wiener Akademie, Band Ivi., p. 79. ACTION OF ACIDS ON THE RED CORPUSCLES. 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 slide. If the corpuscles are so modi- fied by freezing, by shocks of electricity, or by ether or chloroform (the changes effected 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 still acquire their deep tint from the colouring matter contained in the sur- rounding fluid. Brlicke also observed the corpuscles discharge their nuclei from the action of boracic acid. /. If it be desired to ascertain what alterations are effected 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 small proportion of sugar or of salt. In such investigations it will 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 all 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 potassse, 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,f 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 Loc. cit., pp. 679—681. 402 THE BLOOD, BY ALEXANDER ROLLETT. alkalies can, according to Addison, be changed by acid solu- tions into the form they induce, and vice versa. 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 affects 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 * Hiihnefeldt, Chemismus in der thier. Natur., 1840, p. 60. Kolliker, Zeitschrift fur wissenschaftliche Zoologie, Band vii., pp. 184, 253. Botkin Virchow's Archiv, Bandxx., p. 37. Heusen, loc. cit., p. 264. Vintschgau' loc. cit., p. 13. Preyer, loc. cit., p. 432. Kneuttinger, loc. cit., p. 56. t Kneuttinger, loc. 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. Rindfleisch* has described a remarkable alteration effected in the blood corpuscles of the frog by the addition of soluble anilin blue. They are then found to become nucleated spheroids, which quickly assume a blue colour, but it is only in solutions containing about a half-gramme 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 swells 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 Pfluger's Archiv, 1868, p. 590. 404 THE BLOOD, BY ALEXANDER ROLLETT. 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- \ Harless, Monographie uber den Einfluss derGase auf die Form. 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 remains persistent. A. Schmidt" showed that ozone gave a carmine tint to the blood by destruction of the blood corpuscles. b. Ether,-f- 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 circular disks the border becomes thickened,1F and in place of the central depression a navel-like 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. Whe'n 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 denned. 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. f V. Wittich, Journal fur praktische Chemie, Band Ixi., p. 11; and Konigsberger Medic. Jahrbilcher, Band iii., p. 332. L. Hermann, Reichert and Du Bois' Archiv, 1866, p. 27. \ Chaumont, Monthly Journal of Medicine. Edinburgh, 1851, p. 470. B 6 ttcher, Virchow's Archiv, Band xxxii., p. 126; Band xxxvi., p. 342. Kneuttinger, loc. cit., p. 48. A. Schmidt and Schweigger-Seidel, Berichtc der Konig. Sachs. Gesellschaft der Wissenschaften, 1867, p. 190. § Hermann, loc. cit. || Hermann, loc. cit. Kneuttinger, loc, cit., p. 44. 5[ Hermann, loc. cit., p. 31. A. Schmidt and Schweigger- Seidel, loc. 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 effect 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 cell 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 fully into that subject, but shall refer to the communications of Bottcher, Klebs,f A. Schmidt, and Schweigger-Seidel.J We must deal differently with the ques- tion, whether the red blood corpuscles do, or do not, possess a membrane. * Virchow's Archiv, Bande xxxvi. and xxxix. t Virchow's Archiv, Band xxxviii. J Konig. SZchs. Geselkchaft, 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 diffusion current setting from the interior. Briicke,f 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 all 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 well 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 Pflanzlichen Organismen. Berlin, 1839, p. 74. f Berichte der Wiener Akademie, Band xliv., p. 389. 408 THE BLOOD, BY ALEXANDER ROLLETT. 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 Schultze 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 destroyed^rendering 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 xlvi., pp. 73, 94, 95, and 98. STRUCTURE OF THE RED BLOOD CORPUSCLES. 409 a 6). A retraction of the cell contents from the membrane has here been considered to occur, and we may associate with this the forms which Kemak* 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 application 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, Bandxxx., p. 417, Taf. xv., figs. 26 and 27. J Zeitschrift fur wissenschaftliche Zoologie, Band xi., p. 260, etc. § Das Protoplasma der Rhizopoden uud der Pflanzenzellen. Leipzig, 1863. || Untersuchungen uber das Protoplasma und die Contractilitdt. Leipzig, 1864. 410 THE BLOOD, BY ALEXANDER ROLLETT. 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. Strieker^ agrees with Briicke in considering the oekoid to be the part enclosing the colouring matter, and as that which under certain 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 ? KlebsJ regarded the blood corpuscles of Mammals as contrac- tile bodies, in 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 * Wiener BericUe, Band Ivi., p. 79. t Pfliiger's Archivfilr Physiologic, 1868, p. 591. I Centralblatt fur die medicin. Wissenschaften, 1863, p. 851. CHEMICAL CONSTITUTION OF THE RED CORPUSCLES. 411 condition, and the spherical form to the state of death. Rollett,* 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 Kuhne+ expresses him- self in similar terms. We arrive here, 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 resembling 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, will probably long remain a subject of uncertainty; to the illumination of this darkness we may, however, soon attain. OUTLINE OF THE CHEMISTRY OF THE RED CORPUSCLES. — The best-known constituent of the red blood corpuscles is hse- t Wiener Akad. Eerichte, Band 1., pp. 190—200. * ArchivfUr Mikroskop. Anatomic, Band i., pp. 33, 31. t Physiolog. Chemie. Leipzig, 1866, p. 191. G G 412 THE BLOOD, BY ALEXANDER ROLLETT. moglobin ; this can easily be obtained in the crystalline condi- tion. Haemoglobin 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,f Kunde,J 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, Rollett has shown that freezing and subsequent thawing of the blood, as well as the discharges of voltaic electricity ; Rollett 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 ; Y. Wittich, that the addition of ether, or transmission of ether vapour ; Bottcher, that the ac- tion of chloroform ; and Kiihne, that the alkaline 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 * Miiller's Archiv, Jahrgang, 1849, p. 197. t Zeitschrift fur rationelle Medicin, N. F., Band i., p. 172 ; Band ii., p. 199. % Idem, Band ii., p. 271. § Handbuch der PhysioL Chemie, Band i., p. 365 ; Band ii., p. 151. 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 in 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 Prey erf 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. Yon Lang also first demonstrated that crystals of haemoglobin, 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 haemoglobin, 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 different 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- * Sitzungsberichte der Wiener Akademie, Band xlvi., p. 85, et seq. t Pfliiger's Archiv, Jahrgang, 1868, p. 365. 1 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 haemoglobin 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 COLOURLESS MORPHOLOGICAL 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 cell 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, like 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 35° 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, Memoir e de la Societe de Biologie, 1850, Tom. ii., p. 103. Lieberkiihn, Miiller's Archiv, 1854, p. 11, et seq. t Archiv fur Mikroskop. Anatomie, 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 anilin blue, and also milk globules, into 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 cell substance. There is a statement frequently met with in* books, that, under certain circumstances, fat drops are met with in the blood, often in such quantity that the serum acquires a milky appearance, as in sucking animals,* and after the use of olea- ginous 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 ingested 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 in 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 (Kneuttinger). 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 * Schlemm and Joh. Miiller, Froriep's Notizen, Band xxv., 1829, p. 121. f Kiihne, Physiolog. Chemie, p. 181. Kolliker, Gewebelehre, 18(37, p. 620. J Loc. cit. § Rust's Magazine, Band Ixvi., p. 171 ; Virchow's Archiv, Band xviii., p. 221 ; Zeitschrift fur wissenschaftliche Zoologie, Band xi., p. 344. Hensen, loc. cit., p. 259. Max Schultze, loc. cit., p. 39. Kneuttinger, loc. cit., p. 5. 416 THE BLOOD, BY ALEXANDER ROLLETT. The variations depend upon the 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 minutes 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 Corpusculorum Sanguinis Alborum. Diss. inaug. Lips., 1855. E. de Purg,Virchow's Archiv, Band viii., p. 301. Marfels, Moleschott's Untersuchungen zur Naturlehre, etc., Band i., 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 likewise 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 milk globules and particles of colouring matter .-)• 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-corpuscle-holding cells. When acted upon by induced currents, and the discharges of voltaic electricty, these cells become round, § just as occurs, according to Kiihne, in amoebse 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 in 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 original 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). * Rindfleisch, loc. cit., p. 21. Kneuttinger, loc. cit., p. 10, et seq. Golu- bew, Sitzungsberichte der Wiener Akademie, Band Ivii., p. 555. t Recklinghausen, Virchow's Archiv, Band xxviii., p. 185 ; Die Lymphr gefdsse und ihre beziehung zum Bindegewebe. Berlin, 1862, p. 22. \ Loc. cit., p. 423. § Neumann, Reichert and Du Bois' Archiv, 1867, p. 31. Golubew, loc. cit., p. 555. 418 THE BLOOD, BY ALEXANDER ROLLETT. After the continuous application of strong shocks the white corpuscles become destroyed, molecular movements occur in the swollen cells, 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 obtained from a Newt or Frog, be brought upon a glass cover placed over a moist cell, 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 still 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 Ton Recklinghausen,-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. Yon Recklinghausen, 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 furnished some * Pfluger's Archiv, 1868, p. 660. t Max Schultze's Archiv, Band ii., p. 137. DEVELOPMENT OF THE BLOOD CORPUSCLES. 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 CORPUSCLES. 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 (Afanasieff), hanging together in isolated groups (blood islands, Wolf and Pander), or they may originate, according to the view of His, in the form of groups, from large masses of protoplasm in the walls of the vessels, and at a later period burst into their lumen. 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.H * CentralUatt fur die medicin. Wissenschaften, 1867, p. 865. t Loc. cit., p. 566. f Wharton Jones, Philosophical Transactions, 1846. Hensen, loc. cit.t p. 263. § Afanasieff, Sitzungsberichte der Wiener Akademie, Band liii., p. 560. || His, Untersuchungen uber die erste Anlage des Wirbelthierleibes. Leipzig, 1868, p. 95. 1[ Untersuchungen uber die Entwickelung der Wirbelthiere, Berlin, 1855. p. 164 ; Miiller's Archiv, 1858, p. 178. 420 THE BLOOD, BY ALEXANDEK KOLLETT. In the tail of young tadpoles the newly formed vessels are found to be filled 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 the 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 (Kolliker), 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 (Kolliker). The non-nucleated first appear at a later period, their relative number then undergoing a constant increase. According to Kolliker, 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 foetuses that are thirteen inches in length. According to Robin,-)- 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 still discoverable in embryoes of the fourth month, and even at still later periods. As has already been mentioned, the red blood corpuscles can * Kolliker, Zeitschrift fur rationelle Medicin, Band iv., p. 112; Gewe- belehre. Leipzig, 1867, p. 637. E. H. Weber and Kolliker, Zeitschrift fur rationelle Medicin, Band iv., p. 160. t Journal de la Physiologic. Paris, 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 in 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 still 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 cells 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 medulla of the bones ; but in regard to the period* of the occurrence of which during life nothing is at present known. * Kiihne, 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 in 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. Kollikerf adverts to the fact that he long ago found similar forms in the blood of the young sucking mouse. The mode in which they originate from the nucleated white corpuscles, and the stages of their conversion into the ordinary form of the red blood corpuscles, still 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 Neumann^ to the nucleated red corpuscles constantly pre- sent in the medulla, and especially in the red medulla of bones (Man, Rabbit) ; and Bizzozero§ has corroborated the obser- vations of Neumann in the case of Man, the Rabbit, 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 further communications on this function of the bony marrow have just been made by Hoyer.|| * Virchow's Archiv, Band xxxiv.,p. 138, Taf. iv. f Gewebelehre. J Centralblatt fur die medicin. Wissenschaft. Jahr., 1868, p. 689 ; and Archiv fur Heilkunde, 1869, p. 640. § Centralblatt, 1868, p. 881 ; and 1869, p. 149. j| Centralblatt, 1869, pp. 244 and 257. CHAPTER XIV. THE SALIVARY GLANDS. BY E. F. W. PFLUGEK. § 1. GENERAL PLAN OF STRUCTURE. — The salivary glands represented by the parotid, submaxillary and sublingual glands, when examined with the naked eye, appear to be rounded or polygonal yellowish-white masses, flattened by mutual pressure, and opening by hollow 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 epithelial 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 O030 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. PFLUGER. 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 fj) 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 injected 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. Recently 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 in 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 in a wide hyaline sac which they by no means fill. 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 Bollf 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 Franz Boll, Ueber den Bau der Thrdnendriise im Archw f. Mikroskop. Anatomie, Band iv., 1868, p. 146. ALVEOLI OF THE SALIVARY GLANDS. 425 be brought into unison with 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 into prominent relief, and although the quadri- polar flattened cells regarded by Boll and Kolliker as consti- tuents of the membrana propria frequently contain a very brilliant 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 investment to all the alveoli. (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 Kolliker has not, consequently, at present received adequate confir- mation. In the next place, as regards the contents of the alveoli. These consist of cells filled 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. PFLUGER. 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 all 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 in 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 still more intimate union between them. The proto- plasm of the salivary cells is tenacious, finely granular, and frequently striated. A cell 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 O014 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 refractile, 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 millimeter. 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 C. Otto Weber, as well as by Boll, whilst by Kolliker 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 cell, receiving as it leaves this a sheath of the cell membrane, that, upon the Fig. 75. 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 hollow, 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, Gianuzzi, Boll, and Kolliker. According to the descriptions given by Schliiter and myself, the cell processes are often of great length, branch, coalesce (Schluter), and support the alveolar cells like berries. There is never more than one nucleus in each salivary cell. * R. Heidenhain, Studien des physiologischen Instituts zu Hreslau, 1858, Taf. iv., fig. 13 x. H H 428 THE SALIVARY GLANDS, BY E. F. W. PFLUGER. 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 inclined, 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 submaxillary 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.^ The elimination of the mucus is effected by exciting the gland to * See Heidenhain, loc. cit., p. 6. t S. Gianuzzi, " On the effects of acceleration of the blood currents on the secretion of Saliva ; " Ber. d. K. Sachs Ges. d. wiss. Math. Phys. Classe, Sttzung vom Nov. 27, 1865, :£ Heidenhain, loc. ctt., Taf. ii., fig. *. STRUCTURE OF THE EXCRETORY DUCTS. 429 react through the nerves for many hours, whereby the mucus and the mucus-forming materials are 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 believe 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 sufficient explanation of the occurrence of a complete mar- ginal zone in the alveolus. But since the term " demi-lune " can possess such different 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 killed 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 still 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 advance 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. Fig. 76. Transverse section of a fresh 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 0'004< 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 STRUCTURE 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 cell 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 epithelial cells 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 SALIVAKY GLANDS, BY E. F. W. PFLUGER. 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 effected 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 with 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'OOT 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 with these excretory ducts lined by pavement epithelium, communicate with the alveoli, and in what way this communication, if pre- sent, is effected, 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 effected by means of very fine passages (salivary capillaries). DISTRIBUTION OF THE NERVES IN THE SALIVARY GLANDS. 433 The proper excretory ducts (Ductus Whartonianus, Stenonianus, etc.) are generally admitted to be lined by an epithelium, con- sisting of a single layer of short cylindrical 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 well as by smooth muscular fibre cells. § 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 different 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. 6. 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 fibrilfce, which, lying in close apposition, give the impression of a finely granular, 434 THE SALIVAKY GLANDS, BY E. F. W. PFLUGER. 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 all the objections that have been raised on various sides against the nervous nature of the fibres of Remak. - Fig. 77. Fig. 77. The preparation was taken from the submaxillary gland of the Ox, and was blackened with perosmic acid. Magnified 590 diameters. The medullated fibres, which are present in extraordinary numbers in all parts of the salivary glands, and of all sizes down to those of only 0-0015 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 in the fibres 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 osinic acid, 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 lie 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 perosmic 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 medullated 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. Fisr. 81. Fig. 80. Fig. 80. Showing an axis cylinder breaking up into fibrils which are continuous with the fibrils of the columnar epithelium. Magnified 590 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 (n), 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 epithelial 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 finer and the finest medullated 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, exhibiting a medullated nerve, becoming continuous with an axis cylinder which passes directly into the pro- cess of a cylinder cell, and directly open* 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 cell, 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 careful consideration. Two kinds of nerve termination are to be distinguished in the alveoli : — I. The most important is that of the medullated 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 off at the point where they penetrate it several branches, which run for DISTRIBUTION OF THE NERVES IN THE SALIVARY GLANDS. 439 some distance on its outer surface to the nearest epithelial cells, 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 Fig. 84. Fig. 84. From 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 medullated and Fig. 85. Fig. 85. From the Rabbit, after maceration in iodized serum, show- 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 SALIVARY GLANDS, BY E. F. W. PFLUGER. salivary glands of the ox and rabbit (submaxillary and parotid glands) (figs. 87 and 88). Fig. 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 . Fig. 87. Fig. 87. Termination of a medullated £bre of average thickness in the large salivary cells of an alveolus. From 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. 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 medullated fibre be deprived of its medulla by pressure. There then remains a pale fibre composed of extraordinarily fine Fiar. 88. 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. From 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 especially important, because it constitutes a clear evidence of the abso- lute continuity and fusion of the axis cylinder a,nd 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. PFLUGER. 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 cell. 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 medullated 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 doubtful. 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 aveoli, and containing one or more fine fibrils, that are lost in the gland vesicles. They rarely occur in comparison with the medullated fibres, but are more stable on account of their sheath, so that they alone can be seen in some of the modes DISTRIBUTION OF THE NERVES IN THE SALIVARY GLANDS. 443 of preparation, on account of the fluidity of the medullated fibres. 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 (Kolliker, Boll, Heidenhain) 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 Kolliker and Boll, 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- I I 444 THE SALIVARY GLANDS, BY E. F. W. PFLUGER. tions, 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, ABC). 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, A, B. Multipolar cells in connection with, salivary cells. Magnified, A, 480, B, 590 diameters. C. Peculiar cells with round thick processes, and containing retrac- 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 still 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 Kolliker, Heidenhain, and Boll ; 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 fibre, 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 cells also present' this character under the most various modifications in 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 in 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 nucleus in some of these remarkable cells is round, as was also observed by Boll ; and is at the same time transparent, and almost entirely fills the cell. This peculiarity is presented also by other peripheric ganglia, as the granules of the rods and cones of the retina, which unquestionably represent bipolar nerve cells. Moreover these cells exhibit a pale striated protoplasm, the fibres of which may be followed into the similarly striated, and in parts highly refractile, cylindrical processes. Such cells consequently, taken as a whole, exactly resemble, and would be held by all to constitute, ganglion cells. Besides these, we find other cells with ellipsoidal or flat nuclei, which are partly round and partly present flat processes and membranous cell substance, and are quite transparent. Finally, there are still others, lying within the young alveoli i i 2 446 THE SALIVARY GLANDS, BY E. F. W. PFLUGER. which possess granular soft protoplasm in sparing quantity, contain round highly refractile nuclei, and possess numerous cylindrical highly refractile processes. These are undoubtedly in an early stage of development (fig. 90, c). Even if these cells form a reticulum, this furnishes no evidence of their indifferent nature, since all ganglion cells are beyond doubt parts of the great network of animal tissue. Lastly, even if, looking at the great variety of multipolar cells, it be admitted that we are here dealing with cells of different nature and attributes, it still appears to me that we have ob- tained a sufficient answer to one of the above alternatives, and that the multipolar cells must be regarded as small ganglion cells. The mode of termination of the nerves here described I have termed that " effected by the means of multipolar cells," an expression which is only in accordance with fact, and to which, consequently, no objection can be raised. The remarks hitherto made upon the relation of the nervous system to the salivary glands refer exclusively to the sub- maxillary gland. At the same time I have convinced myself that the alveoli of the parotid gland enter into relation with strong medullated nerves in the same manner as has been just described in the case of the submaxillary gland. The parotid, moreover, as well as the sublingual gland possesses salivary tubes presenting similar structural features. Krause has demonstrated the presence of similar multipolar cells in the parotid, and I have also more recently found them in the sublingual gland. If we take into consideration the very similar structure that is thus exhibited by these glands, and the dependence of their activity upon the nervous system, we can scarcely hesitate to believe that a com- plete agreement prevails also in regard to the mode of termi- nation of their secretory nerves. As regards the sensory elements of the nervous system, W. Krause* has discovered a simple kind of Pacinian corpuscle, to which he has given the name of " Terminal Gland Capsules." In the majority of animals, however, they are rarely present. * Zeitschrift fur rationelle Medicin, Band xx., p. 60, 1849. DISTRIBUTION OF THE NERVES IN THE SALIVARY GLANDS. 447 The structure of the larger ganglia which are found in the course of the nerve fibres and trunks still remains to be con- sidered. The ganglion cells occur partly isolated and partly in groups which accompany the nerve cords for a considerable distance, or form roundish knots enclosed by a dense sheath of connective tissue. These knots attain the size of O'OGO milli- meter and more. The nerve cells lying in their interior (fig. 91) have a diameter of O028 millimeter, with a nucleus of the diameter of O012, and a nucleolus of 0'002 millimeter in diameter. We meet also with much smaller ganglion cells, which are not larger than salivary cells, with a diameter of or about 0'014 millimeter. The cells accumulated in one group do not mate- Fig. 91. Fig. 91. Ganglionic knot from the submaxillary gland of a Kabbit. Magnified 480 diameters. rially differ from one another in their general magnitude. The ganglion cells include a spheroidal or oval, transparent, delicate, but sharply defined nuclear vesicle, and when in their fresh state their protoplasm is very delicate and confusedly granular. In the smaller forms the cell contents are sometimes rather more granular, but the nucleus is always as clear as water. The groups are constantly in connection with afferent and efferent nerve fibres. In some instances a single ganglion cell is found in the course of a fibre of Remak. It is remarkable that a large ganglion cell of this kind, having a diameter of O042 millimeter (see fig. 92), may contain several nucleoli; and, moreover, at the point of transition into the nerve fibre, may present a slight deposit of protoplasm, with several ganglionic 44S THE SALIVARY GLANDS, BY E. F. W. PFLUGER. nuclei ; and I desire especially to direct the attention of ob- servers to this singular form of ganglionic substance. The relations of the ganglion cells of the gland are also deserving of special investigation, which will certainly bear on the phy- siological point of whether the sympathetic is distributed ex- clusively to the bloodvessels, or whether it does not stand in intimate relation to the secreting cells. 92. Fig. 92. Solitary ganglion cell with a deposit of nucleated ganglionic protoplasm. From the submaxillary gland of the Rabbit. Magni- fied 480 diameters. § 5. THE REGENERATION OF THE GLANDULAR EPITHELIUM. — I have already called attention, in my work on " The Termi- nation of the Secretory Nerves in the Salivary Glands," to the alveolar-like small projections or bud-like processes of the so- called excretory ducts, and have there expressed the opinion that, both in the primary embryonal development of the gland, as well as in the adult, new salivary cells and alveoli develop from the salivary tubes. I am now in a position to describe the process with accuracy. If the salivary tubes isolated by any of the ordinary modes, or sections of them, after the action of hardening agents, be carefully examined for the brush-like processes of the cylindrical epithe- lial cells, it is easy to observe that the fibrils in various salivary tubules, or even in separate sections of the same tube, may present a very different appearance. As a general rule, even with the highest powers, they appear as immeasurably fine varicose fibrils (fig. 76). But all conceivable intermediate or transitional forms may be met with, up to moderately thick fibres (0-001 millimeter) (figs. 93 and 94). In proportion as they increase in size they lose their soft pale appearance, acquire high refractive MODE OF REGENERATION OF THE GLANDULAR EPITHELIUM. 449 power, which begins to be apparent at the free extremity of the cylindrical cells, and gradually extends towards that extremity to which the fibres are attached. The end of the fibre frequently Fig Fig. 93. Cells. From the submaxillary gland of the Rabbit, after maceration in iodized serum. Magnified 590 diameters. Fig. 94. A, B, C, D, E, isolated cylindrical cells with processes containing nuclei. A, B, D, E, magnified 590 diameters ; C, magnified 1,200 diameters, r, G, H, cylindrical cells with processes, which are evidently young cells, and form at G a beautiful mosaic. Magnified 1,100 diameters. 450 THE SALIVARY GLANDS, BY E. F. W. PFLUGEE. breaks up into several filaments, so that groups of branched processes appear to have budded forth from the columnar cells, which often form thick brushes, the base of which is formed by the small columnar cell. In the next place, the free extremity of these fibres is enlarged into a kind of head, resembling a small club, that forms a minute corpuscle (fig. 94). These clavate extremities may be seen to increase in size till they are clearly distinguishable as cell nuclei, surrounded by a sparing quantity of protoplasm. This process of formation of nuclei commences from infinitesimally small points in the fibre, and extends towards the columnar cells, so that two, three, or even very many may originate in one fibre. The small clavate ex- tremities gradually enlarge to form salivary cells, and after a time it is not difficult to find such epithelial cells constituting the mosaic-work of the alveoli, and directly continuous with the columnar cells by means of processes (fig. 94, E). Usually the processes are of such a form that the fibres of the brush attached to the columnar cell increase in size as they recede from it, and develop a very delicate protoplasm, in which larger or smaller nuclei are contained. Since it always occurs that a large section of a salivary tube is implicated in this remarkable process of cell formation, and since the most active growth takes place upon the mem- brana propria, the wall will be found to be enormously thick- ened and laminated, with primary and secondary projections, whilst the young cells enlarge and arrange themselves in the form of a mosaic. But coincidently the connective tissue pro- jects inwardly into the thick wall, separating off the cells into alveolar-like groups. I have observed this process of the projection of alveoli en masse, as it were, from the salivary tubes of a columnar cell, particularly well in the sub- lingual gland of the rabbit. The degree of ripeness which the various cells contained in one alveolus exhibit is not always the same ; thus it is customary to meet with a few young cells at the periphery of the alveoli in mucous glands (such as the submaxillary of the dog, ox, and rabbit). How is this process of new formation of salivary cells to be explained ? They are formed in the processes of the columnar cells, without the nucleus being in any way implicated ; for, even when these MODE OF REGENERATION OF THE GLANDULAR EPITHELIUM. 451 processes contain numerous nuclei, the nucleus of the columnar cell still appears to be always perfect, spherical, sharply de- fined, and without a trace of gemmation. Even with the highest magnifying powers I have never observed any indica- tion that a filament was given off from the nucleus which could serve as a point of origin for the young nuclei. A few processes even pass over the nucleus through the columnar cell, Fig. 95. Fig. 95. Multiplication of nuclei in the dilated and swollen processes of the columnar cells. A, formation of small multipolar cells ; B appears to be a dilated process of a columnar cell. Magnified 590 diameters. and their striae run parallel to its axis as far as to the free sur- face directed towards the cavity of the salivary tube, so that it scarcely appears to be possible that the nucleus originating in the extremity of such a process could be derived from the nucleus of the cylinder cell. The latter is almost always single, rarely double. Very small and non-nucleated columnar cells, pos- sessing processes that are filled with small nuclei, are also some- times present (fig. 93). As on this ground I do not feel myself justified in attributing the origin of the new nuclei developing in the processes to that of the columnar cells, we must admit that we have before us a case of free cell formation, if under this term we understand that mode of cell increase in which the newly developed nucleus originates independently in a cell, and is not a morphological element proceeding from a division of a previously existing nucleus. When we see the axis cylinder and its fibrils to be directly continuous with the fibrils of the 452 THE SALIVARY GLANDS, BY E. F. W. PFLUGER. columnar cells, without any difference being perceptible be- tween the axis cylinder and the fibrils of these cells, we may legitimately describe the nerve as extending to the point where it joins the substance of the body of the cell. That is the most natural explanation that can be given. This explanation, how- ever, possesses the greatest significance in regard to the mode of development of the glandular epithelium, because it directly follows that the young nuclei originate in the axis cylinders, and that the gland cells which at a later period seem to con- stitute a thickening of the axis cylinder bud forth, as it were, from the nerves. This explanation renders it intelligible why the nucleus of the columnar cells are so indifferent during the multiplication of the epithelium. In opposition to this view, which I regard as the most probable, it may be urged that, in consequence of the intimate fusion of nerve substance and epithelium at the periphery, no sharp limit can be drawn, showing where the one ceases and the other begins ; and that, moreover, it is probable that imperceptibly fine processes are given off by the nucleus of the columnar epithelial cells, which become detached at an early period by fission. That the nuclei of the salivary cells have processes, cannot, however, be re- garded as forming a valid objection to my view, since the young nuclei may really be thickenings of the axis-cylinder fibrils. I may further adduce, as a weighty argument in favour of my view, that the fibrils of the axis cylinder do not terminate at the surface of the fully developed salivary cells, but, as in the case of the ganglion cells, may be traced into their very substance. Now, since the finest axis cylinders and fibrils extend to the columnar epithelial cells, and are connected with the processes that are in course of development, and since portions of these processes subsequently become large salivary cells, connected with thick medullated nerve fibres, it follows that the nerves must increase coincidently with the young epithelium to which they belong. Amongst these metamorphoses there also occurs a mode of termination of the medullated nerves, to which I some time ago called attention, and which consists in the nerve suddenly undergoing frequent division, then enlarging, and containing finely granular protoplasm, with many nuclei of MORPHOLOGICAL CONSTITUENTS OF THE SALIVA. 453 various sizes. I have named this mode of nerve termination, that by a " protoplasmic foot." If, as I have sometimes ob- served, many of the nuclei appear to be provided with fibres, which can be followed into the interior of the nerve fibres, it is highly suggestive of the development of the gland cells from the nerves. In regard to every explanation it must be observed that transitional forms may occur, respecting which it is impossible to say whether they are epithelial or nervous. The continuous and luxuriant neoplastic formation taking place in the sub- stance of the salivary ducts presupposes their regeneration, respecting which I have formed my own opinion, but have arrived at no definite conclusion. In like manner the per- sistent neoplastic formation of the alveoli in adult animals determines an atrophic detachment of those already present. In Moles I have sometimes found the alveoli with pale offshoots of various forms, and pale finely granular contents, which may be such atrophied and separated alveolar segments. I first comprehended the complexity of all forms of salivary glands when I recognised the constant production and disinte- gration taking place in them, which is referrible to the nerve substance. § 6. THE MORPHOLOGICAL CONSTITUENTS OF THE SALIVA.— Healthy saliva contains no morphological elements, but forms a transparent perfectly homogeneous fluid. But when the mucous membrane is irritated, either by ligature of the excre- tory duct, or by the introduction of a canula into its interior, we obtain isolated morphological elements, which are conti- nuously developed by a kind of catarrhal condition and exuda- tion. The appearance of these has led some observers to the belief that normal saliva contains formed elements, and con- tinually carries off glandular epithelium. As recent investi- gations have been in direct contradiction to these statements, I may perhaps be allowed briefly to state the grounds on which my opinions are based. When, in a dog, the duct of Wharton and the nerves supplying the submaxillary gland have been exposed, isolated, and divided, a watery saliva flows from the duct, as transparent as a dewdrop. The secretion found in the 454 THE SALIVARY GLANDS, BY E. F. W. PFLUGER. duct is also clear. If a canula be now introduced, and firmly tied in, and the nerves be irritated, the fluid immediately be- comes cloudy ; but when a few drops have been discharged, it again resumes its transparency. The first drops discharged on irritating the nerves, after the introduction of the canula, are those which were already in the duct, and were originally transparent, but have become cloudy whilst still in its interior, for the clear secretion extracted from the freshly excised duct remains clear when exposed to the air. Contact with the wall of the duct has consequently rendered the secretion cloudy. If we examine the first drops microscopically, we shall find they contain isolated cells and groups of epithelial cells with nuclei, unquestionable medullated nerve fibres, connective tissue, etc.; in a word, constituents which have been detached from the mucous membrane of the duct by the canula, and which there is no object in describing further. As soon as a stronger salivary current is induced by excitation of the chorda tympani, these detached elements are completely washed away, the fluid again becomes quite clear, and no longer contains any morphological elements. After a short time, however, they re- appear in sparing number as the so-called salivary corpuscles, that is to say, as small, finely granular, nucleated cells, present- ing in some instances amoeboid movements, whilst the fluid is rendered cloudy by the presence of fine granules. These bodies, however, it may be easily shown, always proceed from the wall of the excretory duct after it has become affected with catarrhal inflammation, and not from the gland ; for if the nerves are irritated sufficiently long to cause a flow of perfectly clear saliva from the india-rubber tube of the canula, and the ex- citation be then interrupted for ten minutes, and, before it is recommenced, the saliva stagnating in the caoutchouc tube from the previous irritation be pressed out, it will be found, when collected, to be as clear as before. If the excitation be now reapplied, we obtain, since the canula is of very small diameter, for the first three or four drops, that which has collected in the excretory ducts from the previous irritation. These three drops are quite cloudy from exudation and detached cells, but are followed immediately by saliva as clear as water ; that is to say, as soon as the exudation has been washed out of the duct. I CHANGES CONSEQUENT ON FUNCTIONAL ACTIVITY. 455 have estimated the capacity of the duct from the canula to the gland, and am of opinion that it will contain about three drops. The quantity is certainly very much smaller than the total secretion which, in the period before the renewed excitation, stagnated in the very numerous and, in some instances, very wide ducts. Thus it appears that the originally clear saliva contained in the duct has become cloudy, and obviously in consequence of a pathological process ; for, if a freshly exposed duct be emptied of its contents, even if the dog have previously discharged no saliva, the secretion obtained on section is clear. The saliva caused to flow by irritation of the sympathetic nerve contains a large number of spheroidal particles of mu- cus, together with morphological elements of a less clearly definable nature, but representing products of disintegration. Heidenhain, however, was frequently unable to discover any morphological elements. As this kind of saliva can only be obtained in small quantity, the exudate that is poured forth may perhaps never be completely washed out and evacuated, and as only a small quantity of saliva appears at long inter- vals, the fluid essentially consists of this. Heidenhain has shown that when the excitation is long maintained it becomes clearer. The relations of the sympathetic nerve to the salivary glands are, however, involved in much obscurity. From what has now been adduced, it will be seen that fur- ther observations are required before it can be admitted that the saliva naturally contains formed elements. § 7. OF THE ALTERATION OF STRUCTURE IN THE GLANDS CAUSED BY THE PERFORMANCE OF THEIR FUNCTIONS. — When the salivary glands have been long in action, they become lighter, softer, paler in appearance, and both absolutely and relatively poorer in solid constituents. After being long at rest the inverse changes occur, and they assume a yellower colour. This last I believe to be occasioned by the accumulation of numerous molecules in the salivary cells. The gland becomes "charged." Heidenhain has recently expressed the opinion, that in some animals (Carnivora and Herbivora) the secretion is accompanied by the disintegration of a certain proportion of salivary cells, the place of which is supplied by a new genera- 456 THE SALIVARY GLANDS, BY E. F. W. PFLUGER. tion developed at the periphery of the alveoli In rabbits, the secretion of saliva in the submaxillary gland is effected, ac- cording to Heidenhain, exceptionally without demonstrable disintegration and neoplastic cell formation. The important and novel principle in respect to the action of the nerves, established by the observer just mentioned, can- not be here passed over in silence. I have placed an investi- gation into the accuracy of his statements into the hands of my pupil, Herr Anton Ewald, of Berlin, who has been for some time engaged under my superintendence with the structural changes induced by excitation of these glands, and has pur- sued precisely the same method as that adopted by Heidenhain. After one submaxillary gland had been excited for a consider- able period (as long as for seven hours) whilst the other had been kept at perfect rest, both were removed from the living animal, and from these thin sections were made with a razor, which were immediately thrown into a large quantity of abso- lute alcohol. By this means we avoided, as far as possible, in the unexcited gland, which is charged with mucus-forming sub- stance (" mucigen "), the production of any material structural alteration through the post-mortem formation of mucous vesi- cles in the alveoli, consequent upon displacement of cells and pro- toplasm. This precautionary measure was not unnecessary; for in the gland, which has been for a long time actively dis- charging its function, no more " mucigen " is contained, and, therefore, in this case, no alteration of structure can occur from the formation after death of mucous vesicles. When both glands had been hardened for an equal time in alcohol, very fine sections were prepared, macerated for the same period in the solution of carmine in glycerine, employed by Heidenhain, and finally, after the most careful {washing, examined in glycerine. It is obviously a matter of great im- portance that the sections should be made as fine as possible, and all those that are thicker than the diameter of a salivary cell should be rejected. If the cell mosaic lining the interior of the alveoli of the quiescent gland be examined, we find for the most part a single layer of sharply defined transparent poly- gonal cells flattened by mutual pressure, which, however, are not perfectly hyaline, but exhibit a delicate striation, as though CHANGES CONSEQUENT ON FUNCTIONAL ACTIVITY. 457 a perfectly transparent substance were traversed by numerous extremely fine pale fibrils. These salivary cells, which, on account of their contents consisting in the Dog chiefly of mucus, with but little albumen, Heidenhain has termed " mucous cells," are more or less, though in general but slightly, tinted with carmine. When the staining is more strongly marked, the cells contain albumen. A structure, which is probably the nucleus of the mucous cell, lies together with a little protoplasm at the peri- phery of the alveolus, and resembles the process of the cell in being stained of a deep red colour. Inasmuch as all the pro- cesses, together with the nuclei and protoplasm, are situated at the periphery of the alveolus, a broad red zone is here fre- quently formed. Here and there one or more salivary cells appear more or less deeply tinged with carmine. These cells are named by Heidenhain the " crescent." He regards them as the earlier stages of development of the cells which gradually become " mucous cells," which, I think, is not improbable. He silently acquiesces in the view I have stated above, that all salivary cells do not behave in the same manner with reagents, a difference that I am disposed to attribute to their various grades of development. If we now consider the excited gland, the differences which present themselves are, that all the cells are stained with car- mine, though perhaps only slightly, some being more strongly tinted than others — the staining, however, independently of the protoplasm, being, on the whole, less marked than in the quies- cent gland ; that no evidences of multiplication by fission of the young cells at the periphery of the alveoli are visible, in corroboration of which I may refer to Plate i., figs. 84 and 85 of Heidenhain's Essay ; that all the contour lines are remark- ably pale and softened off, especially those separating the alveoli and the salivary cells, which are no longer defined by thick lines; that the nucleus is less reddened, more delicately contoured, larger, and, generally speaking, spheroidal. The effects of the excitation consequently are, that instead of cells not becoming stained with carmine, with round nuclei shrinking in alcohol, and becoming intensely stained with carmine, we obtain cells reddening with carmine, containing nuclei which undergo no shrivelling in alcohol, and are less deeply stained with carmine. 458 THE SALIVARY GLANDS, .BY E. F. W. PFLUGER. Heidenhain draws the conclusion from these facts, that the first form are disintegrated in the act of secretion, whilst the second are newly developed. There still remains the possibility that the " mucous cells," in consequence of their persistent activity, have undergone an essential alteration in their chemical constitution, to which the differences in their appearance are attributable, accord- ing to whether they have been at rest or long in action. I cannot, however, deny that the completely different appearances (see fig. 95) presented, strongly support Heidenhain's opinion. Heidenhain lastly adduces, in support of his opinion, the circumstance that he was able to isolate a larger number of cells undergoing fission from the excited gland, after macera- tion in iodized serum, than in that which has been kept at rest. The epithelial cells of the salivary glands of the dog are generally isolated with difficulty. The isolation of the younger cells in the excited gland may perhaps be facilitated by this very excitation rendering them looser, softer, and more watery, as Heidenhain himself remarks. May not also the continuous streaming of saliva, rich in the corroding carbonate of soda, favour their isolation ? It is further noticeable that, according to Heidenhain, these young cells, after long macera- tion, become isolated sooner than other kinds of epithelia, showing that, under favourable circumstances, they are formed earlier or in larger numbers. I must further observe, that, in accordance with my experience, I can demonstrate in every quiescent salivary gland thousands of epithelial cells in the act of multiplication. The sublingual gland of the rabbit is particu- larly well adapted for this purpose, offering the additional advan- tage that, like the submaxillary gland of the dog, it exhibits large and beautiful mucous cells and semi-lunar bodies. In any such gland, thousands of young epithelial cells, developing by the process of gemmation, may be discovered. I hold a gradual process of disintegration of the alveoli to be highly probable, on the ground of that regeneration of salivary cells which I discovered to proceed from the cylinder cells of the excretory- ducts. The question as to how far the nervous system exerts a primary or a secondary influence on this vegetative process still demands further investigation. CHANGES CONSEQUENT ON FUNCTIONAL ACTIVITY. 450 Fig. 96 A. Fig. 96 A. Quiescent gland. Fig 96 B. Fig. 96 B. Exhausted gland from the Dog, after Htidenhain. K K 460 THE SALIVARY GLANDS, BY E. F. W. PFLUGER. § 8. THE STROMA OF THE SALIVARY GLAND. — The connective tissue consists partly of membranes, partly of fasciculi of fibres, which form a porous network traversing the whole organ, and are commingled with a larger or smaller number of elastic fibres, that are often developed to a very large extent. The nuclear structures are not in general readily demonstrable, but when present, appear as small oval, sharply defined, highly refractile corpuscles. In some places, finely granular nucleated cells are found, with thick processes, which must, in all proba- bility, be also regarded as amongst the cellular elements of the connective tissues. As we have already mentioned, pale, flattened connective tissue cells form, according to Boll and Kolliker, a reticulum around the alveoli. In regard to the presence of the muscular fibres that Schluter states he has seen in the stroma, I beg to observe that I have recently directed my especial attention to the determination of this point, which on physiological grounds is of great impor- tance ; and that in sections of the gland which had been stained with carmine, hardened in alcohol, and examined in glycerine, I have been able to satisfy myself of the presence of, in some instances solitary, in others of fasciculi of smooth, fusi- form muscular fibre cells, with elongated rod-like nuclei, that certainly could not be regarded as constituents of the vessels, and must confer some, though perhaps only slight, contractility on the stroma. The connective tissue stroma intervening between the alveoli attached to a single excretory duct is exceedingly small in quantity, so that the alveoli lie closely compressed and flattened against one another. The several grape-like masses of glandular substance belonging to different small excretory ducts are sepa- rated from one another by broader bands of connective tissue, in which, when the animals are fat, fat cells are seen, resulting from the conversion of connective tissue cells, so that treatment with perosmic acid brings into view a delicate marbling, formed of black lines, in eveiy fresh section of a gland. Where the secondary and tertiary groups of grape-like glands belonging to a larger excretory duct are united into a compact mass, numerous lobules are formed, visible with the naked eye, and divided from one another by fissures. The walls of these MODE OF INVESTIGATING THE SALIVARY GLANDS. 4G1 fissures are composed of connective tissue fibres, and I have observed them to be lined by an indistinct endothelium. Nevertheless, I have, up to the present time, found no func- tional peculiarity connected with these structural features. I do not in the least doubt that the fissures belong to the lymphatic system, as Gianuzzi maintains. Nothing definite is known in regard to the anatomy of the bloodvessels, which stand in such a remarkable relation of dependency to the ner- vous system, nor yet in regard to the lymphatic vessels. The capillaries wind around them in close contact to the membrana propria forming a very close plexus, derived from different quarters, and show no points of difference from the ordinary arrangement. § 9. MODE OF INVESTIGATION. — If it be desired to obtain a general view of the arrangement of the alveoli, excretory ducts, cells, and stroma, fine sections should be made of hardened glands. The hardening is best effected by placing thin portions, whilst still warm from the body, in absolute alcohol. Fine sections can then be made, tinted as usual with carmine, and examined in glycerine. In order to study the finer structural relations, every method of hardening must be avoided. Sections made with very sharp knives of the perfectly fresh gland, can be examined in iodized serum, or in chromic acid containing from 25 to 50 per cent., to which a little iodized serum has been added. When thin sections, thus made, are carefully broken up with needles, isolated alveoli may be obtained, with salivary tubes, epithelial cells with nerve terminations, and the like. The isolation of the epithelial cells is best effectedby the appli- cation of iodized serum, in which the gland has been allowed to macerate for from four to six days, or still better, by treatment with iodized serum, subsequent to maceration in chromic acid of one half per cent. The chromic acid macerates the glands most advantageously, if one or two glands have previously been lying in it for one or two days. When quite freshly applied, the volume of this reagent should not exceed from two to four times the volume of that of the gland. Another method of isolating the elementary constituents, especially of the glands in the rabbit, consists in placing the latter in a small test tube, and adding from four to eight drops of solution of chromic acid, XX 2 462 THE SALIVARY GLANDS, BY E. F. W. PFLUGER. containing one-fiftieth per cent. After the course of an hour, when the organ appears hardened and translucent by imbibi- tion, fine sections may be prepared and broken up by fine needles in the same solution. Solution of caustic alkali, containing 33 per cent., is also well adapted for the isolation of the elementary parts. As soon as the gland has become brown, which occurs in a quarter or half an hour, the tissue can be easily broken up. The liquid in which the preparation is examined, it is obvious, must not be water, but always the same solution of alkali. A method especially adapted for the demonstration of the mode of nerve termination is that introduced by Max Schultze, which consists in laying the fresh gland in perosmic acid, and thus staining the medullated nerves of a dense black colour, causing them to resemble tubes injected with ink, whilst the epithelial cells, examined in thin layers, are scarcely, if at all, coloured. The salivary tubes only assume a brownish tint. CHAPTER XV, STRUCTURE AND DEVELOPMENT OF THE TEETH. BY W. WALDEYER, HARDENED structures of the animal organism, similar to those which are called teeth, though certainly presenting very vari- ous histological structure, are found widely distributed both amongst the vertebrate and the invertebrate series. o With the exception of the larval form of Petromyzon (Ammoccetes); of Amphioxus, Accipenser, and the Lophobranchii (Cuvier), amongst Fishes; of some Toads (Pipa), amongst Amphibia; of the Chelonia, amongst Reptiles ; of the entire class of Birds ; and of the Myrmecophaga, Manis, and Echidna, amongst the Mammals, all vertebrate animals possess teeth. In the whale-bone Whale they are present in the foetal state. The anatomical model of a tooth of a vertebrate animal is a large papilla of the mouth or of the pharyngeal mucous membrane, which, in consequence of chemical and histological conversion of its constituents, has acquired a remarkable degree of hardness. And, according to whether the connective tissue substance of the papilla participates in the hardening or not, two large groups of teeth are distinguished — dentinal teeth and horny teeth. The horny teeth are by far the most simple in their struc- ture. They appear as more or less developed papillae covered with a thick horny investment. They are never continuous with portions of the skeleton, but constitute the transition to other horny formations, as hairs, stings, etc. True horny teeth are met with in the Petromyzidse, the Myxinoids, and in Ornithorhyncus. The whalebone of many whales, and the horny masticating plates of Rhytina Stelleri, though remark- 464 STEUCTUKE AND DEVELOPMENT OF TEETH, W. WALDEYER. ably complex structures, yet clearly belong to the same series of formations. Fig. 97. Fig. 97. Premolar tooth, of the Cat, in situ. Vertical section, magni- fied 15 diameters. 1. Enamel with decussating and parallel striae. 2. Dentine with Schreger's lines. 3. Cement. 4. Periosteum of the alveolus. 5. Inferior maxillary bone. In the dentinal teeth the connective tissue matrix of the papilla plays a most important part in the hardening process, which here proceeds in a manner precisely similar to the ossify- GENEKAL STRUCTURE OF THE TEETH. 465 ing process, except that no true bone is formed, but only an allied substance of much harder consistence, and differing more or less in histological structure, termed dentine. The epithelium of the tooth papilla either atrophies to a rudimentary horny investment, the cuticula (membrane of the enamel), or it becomes elongated in a remarkable manner into long petrified prisms, which collectively invest the dentine, and are known as the enamel. In addition to these there is found an accessory structure, the cement, a true bony substance, which especially invests the fangs of the teeth. Dentinal teeth are con- stantly attached to the parts of the skeleton surrounding the mouth and pharynx, and for the most part to the lower jaw. From the simple arrangement of the three chief constituents of the teeth, as they occur in man, for example, there are manifold and complex variations. Amongst these may be enumerated in particular the so-called folded enamel teeth of Bodentia, Solipedes, and others, and the compound teeth of many fishes and fossil reptiles (Labyrinthodon), of the elephant, etc. The "folded enamel" teeth, dentes complicati, are formed on the type of a simple tooth. The dentine of the crown is, however, folded like a ruff, and the enamel and cement dip in to form a covering to the surface of all the sinuosities. Of the dentes compositi two principal forms can be distinguished. In one, a common stem or trunk is present, which gives off a number of separate tooth- lets (G-aleopithecus, Labyrinthodon), whilst in the second a common tooth pulp is absent, and instead we find, as in many fishes and Orycteropus, numerous independent toothlets proceeding from the jaw, and united to form a common tooth. The pulp of the teeth of the Labyrinthodonts is therefore comparable to the compound filiform papillae of the tongue ; whilst the true compound teeth of the second class bear the same relation to simple teeth that the hoof does to hair. The several back teeth of the Elephant have the characters of the first kind; each separate tooth, however, presents folding of the enamel, so that a highly complex structure results. On the other hand, the structure of a tooth may be simplified by the absence of one or two of the above-mentioned dentinal tissues, especially the enamel, or the enamel and cement. Thus the tusks of the Elephant and the teeth of the Edentata have no enamel ; and again, in the case of the Rodents, the masticating surface of their incisor teeth has no enamel. According to Owen (34), the pharyngeal teeth of Labrus are composed of ordinary dentine alone. Amongst 466 STRUCTURE AND DEVELOPMENT OF TEETH, W. WALDEYER. Fishes, as, for example, in the Pike, a common arrangement is the combination of a central mass of vascular dentine (vaso- dentine, Owen), with a thin cap of ordinary dentine, which in the most external layers is homogeneous, and very hard (vitro -dentine, Owen, 84). Compare fig. 99. DENTINE (Substantia Eburnea, Ebur). — Dentine forms a yellowish- white, highly elastic, but friable mass, presenting a finely fibrous, peculiarly lustrous fracture, and is one of the hardest constituents of the animal body. Its chief components are a very firm matrix, analogous to compact bony tissue, and extremely fine, frequently branched fibres — the dentinal fibres of Tomes (40) and Kolliker (58), which occupy fine canals, the dentinal canals traversing the matrix. The dentinal fibres are enormously elongated processes of the the so-called dentinal cells, or cells of the dentinal pulp (odontoblasts). Dentine conse- quently corresponds to bone, with this difference, that instead of cells it contains the long processes of cells in its calcified matrix. In regard to the other characters of the matrix, it presents a similar uniformity of appearance, and a similar chemical com- position, to that of compact bone. After treatment with acids (especially with dilute hydrochloric acid) a material, dentinal cartilage, is obtained which is precisely similar to ossein, except that it is of somewhat firmer consistence. The dentinal fibres constitute the soft parts of dentine. They do not lie in direct contact with the hard matrix, but are invested by sheaths, the dentinal sheaths of E. Neumann (48), which are intimately connected with the matrix. After the fibres have been removed by maceration, or by incineration of the tooth, the dentinal sheaths remain, and even after destruc- tion of the matrix by boiling in strong muriatic acid or in caustic alkalies, they constitute the only perfectly indestructible residue of the tooth. They form the white finely fibrous felt which still remains after treatment with the above-mentioned reagents. The dentinal sheaths, it is highly probable, belong to the category of elastic limiting layers which not unfrequently form around the cavities of the connective tissues. E. Neumann considers them to be calcified (see also p. 125). The dentinal matrix, then, is traversed by a number of fine STRUCTUKE OF DENTINE. 467 canals, having walls of a peculiar nature — the dentinal sheaths — in which lie the dentinal fibres. The dentinal canals com- mence with small circular openings on the inner surface of the pulp cavity, and pass radially outwards through the dentine, making numerous spiral turns in their course (Welcker, 41). Fig. 98. Fig. 98. Canine tooth of Man, presenting a portion of the transverse section of the root. 1. Cement with large lacunae and parallel striae. 2. Interglobular substance. 3. Dentinal tubules. Magnified 300 diameters. As a general rule each tubule extends from the pulp cavity to the enamel, or cement, giving off in its course numerous delicate transverse branches. By means of these transverse branches both the tubules and their contents — the dentinal fibres — anastomose with each other. In sections made from 468 STRUCTURE AND DEVELOPMENT OF TEETH, W. WALDEYER. fresh teeth, examined with high powers (500 — 1,000), it is not difficult to recognise, especially in the central section of the course of the tubules, which is of considerably larger diameter, the pale homogeneous dentinal fibre. The lining of the tubules (dentinal sheaths) can only be satisfactorily seen in cross section, when they appear as delicate yellowish rings, in the interior of which the transverse section of the dentinal fibre is perceptible in the form of a minute dark point. I, at least, agree with Kolliker (58) in this interpretation of the appear- ances seen on cross section. Carious teeth prove very service- able in exhibiting these relations * The dentinal tubules are best examined in fine sections dried in air. They then make their appearance, filled with air, in the form of strongly defined very dark tubules or lines, enabling them to be traced to their finest ramifications. In regard to the mode of peripheric termination of the dentinal tubuli no positive conclusion can be drawn. Yet exact infor- mation on this point is of considerable importance, because Tomes (29) has directed attention to the sensibility of the peripheric portion of the dentine. Wherever the terminal loops occur the dentinal tubuli must also end in the same manner; nevertheless, it is difficult to demonstrate actual terminal loop-like structures. Extremely fine processes of the dentinal tubuli run towards the enamel, and are lost at the surface of the dentine. At this part also larger or smaller irregularly defined cavities are found, the interglobular spaces of Czermak (33), which will be more fully considered hereafter. The dentinal tubuli open into these interglobular spaces, and from them again fine processes extend towards the enamel, A direct passage of the dentinal tubuli into the enamel does not occur. Tomes (29) and Kolliker (58) are strongly of opinion that some of the dentinal tubuli, with their soft contents, penetrate into the enamel. This they think especially occurs amongst the Rodents and Marsupials. I have not, however, been more successful than Hertz (52) in con- * In the vicinity of carious portions of tooth, both the soft dentinal fibres and the dentinal sheaths are thickened, so that in transverse sections both come very clearly into view. STRUCTURE OF DENTINE. 469 vincing myself of this fact. No conclusion can be drawn with positive certainty from sections, since the slightest deviation from parallelism in the surfaces may easily produce deceptive appearances. So, again, fissures in the enamel, and inequalities of the adjacent surfaces of the dentine and enamel, might easily lead to the view supported by Tomes. The question can only be determined by the examination of young teeth in process of development ; but I have never been able to discover anything of the kind. Intervening between the dentine and the cement is a considerable quantity of the already mentioned interglobular substance, and the greater number of the dentinal tubuli open into its irregular spaces. These again are continuous with the lacunae of the cement by means of fine canaliculi. The tubuli may be followed quite to the free surface of the masticatory surface of the incisor teeth of the Rodents, where the dentine is freely exposed ; but it appears to me that in the peripheral portions of these tubules the dentinal fibres are atrophied. If we now proceed to consider the dentinal fibres with more minuteness, no further reference to their course and direction is needed, since these are determined by that of the tubules, which have already been sufficiently described. At the same time it is not easy to decide whether the fibres are present in the finest peripheric ramifications of the tubules. In young teeth this is certainly the case, but in those that are older atrophy of the fibres appears to be concurrent with oblitera- tion of the canaliculi. We may seek in vain, even in young dentinal fibres, for rudiments of nuclei, although both the history of their development and several pathological appear- ances (as for instance those accompanying caries) might lead us to expect their presence. The fibres easily stain with carmine. They possess a remarkable degree of extensibility, so that, especially in young teeth, the dentinal cells may be separated to a considerable distance from the dentine without rupture of the processes, which then appear like harp strings stretched across the interval. Salter (51), in recently describing the fibres as tubules, because, when dry, they appear to contain air vesicles, and exhibit a dark central point on section, has probably had the dentinal sheaths under observation. The fibres are really completely solid and homogeneous. There are some remarkable deviations from the above-described 470 STRUCTURE AND DEVELOPMENT OF TEETH, W. WALDEYER. structure of the dentine. The interglolndar substance is in the first place a structure tolerably widely distributed. Ozermak has described under this name those parts of the dentine which, when thin sections are dried in air, appear beset with irregular spaces and cavities. The walls of these spaces, especially if they form a deep notch, often pro- ject in the form of spheroidal masses or dentinal globules. Indica- tions of a spherical form which sometimes occur in the compact dentine are explicable on the supposition that the interglobular spaces have been obliterated by calcification of their soft contents, the contours of their original walls being to some extent retained. The contents of the interglobular spaces consist of a soft mass. In the young fresh teeth of the calf, rounded and stellate cells may frequently be seen in the larger interglobular spaces, with processes which extend into the dentinal canals opening into them. At a later period the cells atrophy, or their protoplasm becomes converted into a substance analogous to the dentinal cartilage. In immediate proximity to the cement, a layer of very small, closely compressed interglobular spaces is very constantly present, forming the granular layer of Tomes. The interglobular spaces, with their soft contents, are therefore only the result of a somewhat irregular process of dentinification, and are analogous to the small irregular medullary cavities found in the interior of compact bone. In the dentine of many animals, especially of Fishes, of some Ro- dents, in the central portion of the tusks of the Elephant, the molar teeth of the Iguanodon and others, vascular canals exist analogous to the Haversian canals of bone, constituting the vaso-dentine of Owen. In Man this form of dentine is only met with as a consequence of the secondary ossification of the pulp. In many Fishes (Kolliker, 45) the bones of the skeleton consist in great part of true dentine ; whilst conversely we find in the dentine of the teeth, especially in pathological conditions, masses with bone lacunae, termed Odontomes by Virchow, and Osteo-odontomes by Hohl, which occur in the dentine near the cement, or in ossifications of the pulp, and form the osteo-dentine of Owen. Transitional forms, between vaso-dentine, osteo-dentine, and ordinary dentine, are frequently met with in Fishes, as, for instance, in the Pike. In the Cetacea, Dugong, and Physeter, again, the peripheric layer of the dentine, which contains a large number of small interglobular spaces and true bone corpuscles, passes without interruption into the invest- ing cement, so that it is impossible to draw here any definite line between osseous substance and dentine. Schreger (7) first recognised a system of concentric lines running STRUCTURE OF THE ENAMEL. 471 parallel to the contour of the teeth in dentine, which in large teeth can be easily seen with the naked eye, or with a low magnifying power. In true dentine they present on section a characteristically decussating course with small rhomboidal meshes between them. As Retzius (19) and Owen (25) first correctly stated, the lines of Schreger are occa- Fig. 99. Fig. 99. Apex of a tooth from the lower jaw of the Pike (Esox lucius). Magnified 80 diameters. The central portion consists of vaso- dentine, which is covered with true dentine ; external to which again is a thin layer of vitro-dentine. sioned by the corresponding primary curvatures of the dentinal tubes. Owen (25) describes in addition a second system of parallel curved lines in dentine, the contour lines occurring especially in the tusks of the elephant, produced by regularly intercalated strata of small cells (probably finely granular interglobular substance). Czermak and Kolliker give similar illustrations, drawn from the teeth of man ; we are not however justified from these appearances in concluding that dentine possesses a lamellated structure. ENAMEL (Substantia Vitrea; Subst. Adamantina; Encaustum; Adamas; Email). — Enamel is the hardest substance met with in the Vertebrata, being in this respect about equal to Apatite (F. Hoppe-Seyler, 69). With its translucent mass and bluish tint it forms a kind of cap of various thickness, investing the 472 STRUCTURE AND DEVELOPMENT OF TEETH, W. WALDEYER. crown of the tooth, usually following its contours with accuracy. Its surface, especially at the sides, exhibits very fine, nearly parallel, transverse striae (Czermak), which are probably re- ferrible to the papillary structure of the enamel organ (see this). Coarser projections with deep grooves, which have like- wise been described by Czermak, must be regarded as patho- logical formations. In young teeth, examined at that stage in which the enamel is still soft and capable of being cut with a knife, it is easy to demonstrate that it consists of rather elongated prisms of about 3 — 5 /i long, which are called enamel fibres, or enamel prisms (see fig. 103, 4 and 5). It is impossible to avoid perceiving a certain similarity in form between these and very long columnar epithelial cells, like those which form the fibres of the lens. This is especially obvious in fine transverse sec- tions, which exhibit a delicate mosaic with six-sided areas. After cautious treatment with dilute hydrochloric acid and subsequent boiling in S 03 (Beigel (50), whose method other- wise affords no special advantage), the enamel prisms can be easily isolated in adults. Their extremities are often pointed like a needle, which, however, appears to depend only on ir- regular fracture. By the same means, also, it can be shown that the prisms partly run in a straight direction, and partly in curves ; but I have not been able to satisfy myself that angular or zigzag curvatures occur, as stated by Czermak. The dark transverse striae and slight varicosities which, especially after the addition of very ' dilute hydrochloric acid, occur at regular distances from one another in the isolated prisms of enamel, are very remarkable. If the treatment with hydro- chloric acid be continued for some time longer, the fibres split in the direction of the clear transverse lines into small cubic fragments of nearly equal size (3 — 4 ju). It still remains a question how the transverse bands are to be ex- plained. The circumstance that they are generally absent, or at least are not so well marked in young soft fibres, and that their relative thickness nearly corresponds to the thickness of the fibres, has led me (49) to express the opinion that they might proceed from the de- cussation of the fibres. I am well aware of the grounds adduced by Hertz (52) against this supposition, and which are assented to by STRUCTURE OF THE ENAMEL. 473 Kolliker; but I must still consider it doubtful whether all enamel prisms exhibit transverse striae and varicosities. Hertz returns to the intermittent (schubweise) calcification of the enamel cells formerly admitted by Hannover (39). But the mode in which so regular a transverse striation is thus produced, is, to me at least, unintelligible ; besides, no evidence can be brought forward showing that a laminated mode of formation occurs in enamel. The enamel fibres lie in close contact with each other, with- out any demonstrable intervening substance. They appear to be completely solid, and extend for the most part through the whole thickness of the enamel. At the same time they pursue a very various course, which finds its expression in the well- known decussation of the prisms. We accordingly find that alternate layers of enamel fibres appear on section to run verti- cally and transversely, in consequence of which a peculiar and sometimes very regular pattern is produced. The enamel prisms must therefore also pursue, in the form of fasciculi, a various and often decussating course towards the surface of the tooth. A second pattern presenting itself in the enamel is formed by the so-called brown parallel strice of Retzius, which are superim- posed lines coursing in the same direction, and regarded by Kolliker as the expression of a laminated mode of formation of the enamel. These are frequently (see fig. 97) very fine, and closely applied to one another; some appearing to be more conspicuous than others. No satisfactory explanation of this phenomenon can at present be given. Hertz attributes it to deposits of pigment in the enamel prisms, as occurs, for example, in the beaver and squirrel, where it is due, according to V. Bibra (68), to the presence of oxide of iron; and in these Rodents, according to Wenzel (66), such deposits are already present in the protoplasm of the enamel cells ; still, no positive state- ments can at present be made on this point. Other kinds of strias, again, may be perceived on examining transverse sections, and most distinctly after brushing with dilute hydrochloric acid (1 : 12, Hertz), which are caused, according to Czermak, by the regular zigzag course, or, according to Hannover, by twisting or spiral turns of the prisms. An explanation will be hereafter given of the decussation of the prisms, as well as of their various course (see the Development of the Enamel). The observations of Hoppe-Seyler (69) on the behaviour of the enamel 474 STEUCTUEE AND DEVELOPMENT OF TEETH, W. WALDEYER. in polarised light are replete with interest. According to these, fully developed enamel exhibits strongly negative double refraction, and is probably uniaxial ; whilst young enamel presents positive double re- fraction. Adult enamel becomes positive on being exposed to a tempe- rature of 800° C. Hoppe-Seyler (69), in one of his analyses, found the composition of the enamel of the newly born infant to be P05 3 Ca 0 0 = 75-23, C Oa, Ca 0 = 7-18, Cl Ca = 0-23, P05 3 Mg 0 = 1-72. Organic compounds = 15'59. The enamel of adults contains only from one to three per cent, of organic constituents ; but, on the other hand a large quantity of phosphate of lime. A remarkable feature is the presence of a small proportion of fluorine, THE CTJTICULA (persistent capsule of Nasmyth, 22 ; schmel- zoberhautchen of Kolliker) forms an extremely resistant invest- ment not more than 1 — 2^ in thickness, covering the exposed portion of the teeth, and disappearing wholly when they are mature. When the enamel is present, the under surface fre- quently presents the impression of prisms in the form of small square areas. Kolliker and others more recently have improperly applied the term enamel membrane to the cuticula, since it is developed with equal distinctness in teeth in which the enamel is absent, as for instance in the Pike. In young teeth, examined when in the act of perforating the gum, the cuticula may be easily detached as a whole after slight action of hydrochloric acid. It may then be tinted with solution of nitrate of silver, which causes the appearance of figures similar to large epithelial cells. These, as the history of the development of the teeth shows (see this), are the corni- fied cells of the so-called external epithelium of the enamel organ, from which the cuticula is formed. The chemical relations of the cuticula dentis indicate that it belongs to the category of horny substances. According to the statements of Kolliker (58), which I am able to corroborate, boiling water and mineral acids exert no action upon it, except that it is stained of a yellow colour by nitric acid. When boiled with caustic potash or soda, it softens, and when burnt yields a smell resembling that of horn. I have not been able to prove the presence of lime in the cuticle of man ; small traces of STRUCTURE OF THE CEMENT. 475 this substance could always be referred to imperfect purification of the membrane from enamel or dentine in contact with it ; so that it is questionable whether it undergoes any calcification. Kollmann (67a) has recently admitted this, but offers no proof. CEMENT (Zahn-kitt, osteoid substance, cementum, tortex os- seus, crusta fibrosa). — The cement is a true bony structure essentially belonging to the periosteum of the alveolus, and in man and many of the vertebrates forms a thin investment to the fangs of the teeth. Intimately connected with the dentine, it commences as a delicate covering at the neck of the tooth, where the enamel ceases, and is thickest at the apices of the roots and in the depressions between the roots of the molar and bicuspid teeth. In the folded enamel and compound teeth the cement penetrates deeply in the form of a moderately thick layer between the projections of the crown, or serves as a connecting substance to the several toothlets ; it is therefore situated for the most part external to all the other constituents of the tooth. The Pachydermata and others have also a special covering of cement, investing the whole crown of the tooth as a secondary formation (crown cement). Both in its chemical and microscopical characters, cement is closely allied to bone. The lacunae are for the most part large, and possess an enormous number of very long canaliculi, es- pecially in the Cetacea. When the cement is extremely thin, however, they may be entirely absent, and it then presents on section a perfectly homogeneous and vitreous appear- ance. A similarly very hard lamella, destitute of lacunae, occurs also in the outermost portion of the thicker layers of cement. Haversian canals, which sometimes open into the pulp cavity (Salter, 58) are found when the cement is thick, though it is rare to find any lamellated arrangement of the matrix. Kolliker (58) has described peculiar cavities in the cement, which he considers to result from pathological processes. Skarpey's fibres also occur, and I have found the cement of the dog to be that best adapted to show them. The thick capsule-like investments surrounding one or several lacuna, first noticed by Gerber (24) in the cement of the horse, are deserving of especial mention. These lacunas, with their thick capsules, can be easily isolated in diluted acids, and may be L L 476 STRUCTURE AND DEVELOPMENT OF TEETH, W. WALDEYER. regarded as nests of osteoblasts formed in the process of ossification, and surrounded by thick sheaths of connective tissue. SOFT STRUCTURES OF THE TEETH. — The soft tissues be- longing to the teeth include the tooth pulp and the gums. The former is the vascular and nervous matrix of the dentine, and the remains of the original tooth papilla. It constitutes also the model of the tooth on which the hard structures are formed like a cast, and therefore presents, in accordance with their difference in shape, an extremely various form. In old teeth, where the hard parts predominate to a remarkable extent, there remains only an inconsiderable residue of the pulp en- closing the cavum dentis, and in the human tooth it is reduced to a very slender thread containing a few vessels and nerves. The pulp is immediately connected with the periosteum and base of the alveolus by means of the foramina dentium. In the incisors of the Rodents, which produce new dentine con- tinuously, the pulp, even in adults, retains its original character, and its structure can there be best studied. The principal portion of a good specimen of young pulp con- sists of indistinct finely fibrous connective tissue containing numerous cells, that recalls in many respects the mucous tissue of old atrophied umbilical cords, the elastic tissue only being absent. On account of the numerous large vessels which break up immediately beneath the surface into a plexus of capillaries of moderate width, the tissue appears quite cavern- ous. The external layer of the pulp is formed by a layer of large cells, of elongated form, and provided with numerous processes, called Odontoblasts (49, 59), which are arranged so as to form a kind of columnar epithelium * These cells (see figs. 102, 103) are from 20 to 30 fi on the average in length, and about 5 // in breadth. They are finely granular, and destitute of a membrane. The moderately large rounded or ovoid nu- * The names formerly applied to them were dentinal cells (Elfenbein- zellen). Kolliker terms this entire layer of cells membrana eboris, because after the pulp has been withdrawn it usually cleaves to the inner surface of the tooth in the form of a continuous membrane-like layer. STRUCTURE OF THE DENTAL PULP. 477 cleus is usually contained in that end which is turned towards the pulp. In adults, as Boll (59) remarks, the form of the cells is very slender, whilst in young teeth they are more or less compressed. Three kinds of processes may be distinguished in these cells. The dentinal process, the pulp process, and the lateral processes. The dentinal processes constitute the above- described dentine fibres ; it need here only be repeated that from one cell several dentine fibres are frequently given off (Boll counted as many as six). Such odontoblasts, with several dentinal processes, 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 the 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 & per cent., a very large number of non-medullated extremely fine nerve fibres, which exhibited a silky lustre, and were gradually but directly con- tinuous with the medullated 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 gum is distinguished from the other portions of the oral cavity by its vascularity and its large papillae, which L L 2 478 STRUCTURE AND DEVELOPMENT OF TEETH, W. WALDEYER. again, like the papillae 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 lamellae of horn, are met with, either imbedded in 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 Periodontium, 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 Echinus 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 EchinidaB 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 tbose of the keel. Between these prisms, which in part run parallel to one another, and partly decussate in each plate, lie thin lustrous calcareous plates which often exhibit .an extremely delicate 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, tbey 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 Mollusks, Worms, and Arthropods the oral or gastric teeth are composed of chitine, which is sometimes impregnated with lime .or silica. It may be said generally that the teeth amongst the Invertebrata are to be regarded as pure mineral * Miiller'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 Vertebrata 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 mucous tissue the dentine and cement. The " enamel 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 connective 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 * Kolliker (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 STRUCTURE AND DEVELOPMENT OF TEETH, W. WALDEYER. longitudinal furrow, 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 projecting 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. Fig. 100. Upper jaw of a foetal sheep three centimeters in 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. enamel 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 (Kolliker, 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. Ko Hiker (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 Fig. 101. Fig. 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 papillse of the dental sacculus. 4. Secon- dary enamel germ ; rudiment of the permanent tooth. 5. Dental germ. 6. Lower jaw. 7. MeckeFs 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. tit., 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