;' ■: .■ ^-Doctor* of *Veterinary *Sui^ery^- PHILADELPHIA, PA. OFFICE: No. 1513 Race Street. Graduate of American Veterinary College, University of the State of New York. p^atosroell 1(976 THE ^lotwcr ICibrarg THIS BOOK IS THE GIFT OF J^M^, ife>; . . ^1 *&'**« ■ H !:$>; 1 % J = = . H -'ft 1 ■iiBJIIr 1 ' ■ : H 1 1 .- H 1 H n>v.ii.i* 1 " --mm *V„. 1 1 <:.m *** ■ 1 ■■ 1 \ ' 1 ■1 fflL^f II mM^AW- ■ hm I I I - A ,::I : --'- :i: i f ^^H **f- Cornell University Library QM 551.F89C 1878 Compendium of histology. 3 1924 001 039 506 The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://archive.org/details/cu31924001039506 ®ranslatt& from tf)t (fitiutan, is jtrmissioix of tfje &uti)or B V=> GEORGE R^CUTTER, M.D. SURGEON NEW YORK EYE AND EAR INFIRM.\r\ ; OPHTHALMIC AND AURAL SURGEON TC ST. CATHERINE AND WILLIAMSBUKGH HOSPITALS; SECRETARY OF THE NEW YORK OPHTHALMOLOGICAL SOCIETY, ETC.. ETC. ^ ' G. P. PUTNAM'S SONS, P 89 c i8?6 - ."Mo I . J6 7& TRANSLATOR'S PREFACE. The science of Histology has made rapid advances of late years, and many new facts have been acquired in this depart- ment. This will be readily appreciated by those who are familiar with the excellent and exhaustive text-books of Frey and Strieker. But many are intimidated by the very copiousness of such works. Even in Germany, where thoroughness is the great excel- lence, there is a demand for a compendium. That Professor Frey's little book meets this want, is proved by its enormous sale and the favorable notices of the press. I hope that this translation may meet with the same kind reception as did that of our Author's work on Microscopic Technology. GEORGE R. CUTTER, M.D., No. 228 East Twelfth Street, New York. August, 1876. TRANSLATOR'S PREFACE TO THE THIRD EDITION. It has afforded me no small gratification that my translation of Professor Frey's work should have met with so very favorable a reception, both by the profes- sion at large and by the medical press. Though brought into direct competition with several very able and well established works on the same subject, it has been adopted as a text-book by the more prominent colleges of Great Britain, the United States and Japan. It was found necessary to make but very slight changes in the present edition. George R. Cutter, M.D., No. 312 Second Ave., New York. January, 1878. AUTHOR'S PREFACE. HISTOLOGY has, in the course of a few decades, triumphantly won its field ; it has become an integral part of medical studies. The hand-books have necessarily become constantly more voluminous, in consequence of the immense wealth of materials. A short compend of the most essential facts is desirable for students and practicing physicians. I have often heard this wish expressed. May the attempt, which I herewith venture, be, therefore, indulgently received. The defects of this little book are very well known to the author. H. FREY. Zurich, July 10th, 1875. CONTENTS. FAGH Translator's Preface hi Author's Preface „ FIRST LECTURE. General : the protoplasma, the cell, and its derivatives i SECOND LECTURE. Classification of the tissues. — Blood, lymph, chyle 2C THIRD LECTURE. The epidermis, or the epithelium 28 FOURTH LECTURE. The connective-substance group. — Cartilage, gelatinous tissue, reti- cular connective tissue, fat. 41 FIFTH LECTURE. Connective tissue 51 SIXTH LECTURE. Bone tissue 6a SEVENTH LECTURE. Dentine, enamel, lens tissue 73 EIGHTH LECTURE. Muscular tissue 79 NINTH LECTURE. The blood-vessels 89 TENTH LECTURE. The lymphatics and the lymphatic glands 102 ELEVENTH LECTURE. The remaining lymphoid organs, with the spleen. — The so-called blood-vascular glands 117 TWELFTH LECTURE. Gland tissue 128 THIRTEENTH LECTURE. The digestive apparatus, with its glands 139 FOURTEENTH LECTURE. Pancreas and liver 1 50 FIFTEENTH LECTURE. The lungs 157 SIXTEENTH LECTURE. The kidney, with the urinary passages 163 SEVENTEENTH LECTURE. The female generative glands, the ovary with the efferent apparatus. . . 1 73 EIGHTEENTH LECTURE. The male generative glands, the testicles with the efferent apparatus. 183 NINETEENTH LECTURE. Nerve tissue 102 TWENTIETH LECTURE. The arrangement and termination of the nerve fibres 202 TWENTY-FIRST LECTURE. The central organs of the nervous system, the ganglia, and the spinal cord 215 TWENTY-SECOND LECTURE. The central organs of the nervous system, continued — the medulla oblongata, and the brain 224 TWENTY-THIRD LECTURE. The organs of sense — skin, gustatory, olfactory, and auditory ap- paratus 234 TWENTY-FOURTH LECTURE. The organs of sense, continued — the eye 246 Index 2 6 5 Compendium of Histology. FIRST LECTURE. GENERAL : THE PROTOPLASMA, THE CELL, AND IT£ DERIVATIVES. A DEEP aby9S separates the inorganic from the organic, the inanimate from the animate. The rock-crystal on the one side — vegetable and animal on the other ; how infinitely- different the image ! Is it, then, many will inquire, possible to bridge over this gulf? We answer, not at the present time. It is, perhaps, reserved for future generations of men to fill up this yawning chasm, by the aid of a more thorough knowledge of nature, and to comprehend the sphere of the material world as a unit. What, we ask further, is the primary beginning of the organic ? An admirable English naturalist, Huxley, suc- ceeded, in the year 1868, in making a marvelous dis- covery. The bottom of our seas, at the most considerable depths, is covered over large tracts with a strange shiny substance. When this thing, called the ba- thybius, is drawn up by the F ig. i.-Bathybius. FIRST LECTURE. dredge, and placed under the microscope —under that instru- ment which has conquered the mighty world of minuteness for natural science— a very peculiar image is presented to the astonished eye. We perceive a transparent jelly, with diminutive granules in its interior. We also frequently meet with small cor- puscles, surrounded by this, consisting of carbonate of lime. They look like our modern sleeve buttons. And this mass lives ! It changes from one shape to another in slow metamorphosis, exhibiting a constant, though sluggish restlessness. Separated portions present the same slow mu- tability, the same life. The mass formed by this bathybius is a nitrogenous carbon compound, distended in water, and of an extremely compli- cated chemical structure. It belongs to the group of albumin- ous bodies, and is called protoplasma. It coagulates in death, and also at a relatively slight elevation of temperature. The granules it encloses consist partly of coagulated albuminous substances, partly of fat; mineral substances are also not wanting. Leaving the dark deep, and turning to the sunny surface of the seas, we here meet with numerous small lumps of protoplasma, which show the same vital transformation s , shooting out process- es, sometimes short, f^WS. k *]v"'' ' ®€> ^^llfSfik 6 * sometimes longer, and 'fl drawing them in again ; such is the protamceba of our Fig. 2. These are the simplest organisms or forms of life. They increase by division. One of our most distinguished investigators, Haeckel, has called such a lowest being a cytode. We meet with similar organisms intermingled with these cytodes in the water ; as, for example, the amoeba (Fig. 8), Fig- 2. — Protamceba. A, undivided : B, commencing, and C, completed division. THE PPOTOPLASMA AND THE CELL. Fig. 3. — Amoeba ; tf, nucleus ; /■, vacuoli ; c, alimentary budies taken in. though in the interior of this constantly change- able protoplasma, to- gether with excavations (b), and small foreign bodies (c), accidentally taken up from the neigh- borhood, a roundish structure with small punctiform contents (a), is found. The contained body bears the name of the kernel or nucleus ; the small bodies enclosed within the latter are called nucleoli. The entire creature has the significance of a simple naked cell. What service the nucleus renders the amoeba we are, at present, unable to say. We now leave these lowest creatures, and pass, at a bound, to the highest animal form — to examine the human body. Its parts have been called organs since the primitive days of medicine. They correspond to the separate pieces of one of our machines. It was also long since known that certain substances of our bodies, such as bone, cartilage, muscle, and nerves, were re- peated in all portions of the organism and, slightly or not at all changed, enter into the structure of the most different parts of the body. These substances, which may be compared to _the different materials of which the machine is formed, were early known to be composed of still smaller parts. They were compared to the products of the loom, and designated as tissues. This name has been retained, and that branch of anatomical science which treats of these homogeneous parts, is called the science of tissues, or Histology. On attempting, with the aid of the knife and scissors, to separate such tissues, we, at first, succeed very readily ; the fragments permit of a new division, and this may, perhaps, be repeated on those thus obtained. But at last — sometimes sooner, sometimes later— a period arrives when even the finest and sharpest tools become unserviceable ; they are too blunt, too coarse. 4 FIRST LECTURE. Here, where the mechanical analysis terminates, the optical begins, by means of the microscope. The latter is an extra- ordinarily delicate one ; the fragment, which the anatomist's scissors are unable further to divide, now proves to be infi- nitely compounded ; it may still consist of thousands of the smallest elements. These elements are again, in their turn, cells or their derivatives. Thus, this structure, which forms in an independent manner the body of an amoeba, now constitutes our tissues, although in a very conditional independence. The cell has, therefore, entered into the service of a mighty unity ; it has to sub- ordinate and conform itself; nevertheless, the thing remains a living individual, comparable to the officer of a modern state department. As he fulfils his individual duty in the service and as a member of a great whole, so, also, does the" small cell labor unremittingly until its death. It appears of interest that these very small living foundation- stones in the body of the higher animals always form cells, and that the cytodes of Haeckel have disappeared. We have just said that the cells of the human organism were very small. Their diameter varies, in fact, a A from 0.076, 0.0375, 0.0228 down to 0.0057 mm - &|i Thus it becomes possible that a small particle "N^ of the substance of the body, about a cubic milli- / metre, may contain an extraordinary multitude Pof them. It has been computed that such a particle of space of the human blood is capable rf*| of containing five million red cells, though it is ^* A true they only measure 0.0077 mm - e^-'&M V The ce ^ s P resent very considerable variations. \- Sri The latter are gained subsequently with the devel- ^ ^ opment of the body. In the earliest period of *-*& embryonic life they were all still very similar. ccn^wMTludeus The primitive form of a cell is that of a globe andprotopiasma. or of a body approximating a sphere. Thus ap- pear the cells d, e, g, b of our Fig. 4. The cell, also, from THE PROTOPLASMA AND THE CELL. 5 which in a momentous manner the bodies of all the higher animals have proceeded, the ovum (Fig. 5), presents itself as an elegant spheroidal structure. From this primitive form two other forms, resulting from compression and adaptation, may be readily traced ; the tall, slender, or, as we say, cylindrical cell (Fig. 6, b), and the flattened. The latter finally assumes the form of a lamella or scale (Fig. 7). The bodies of other cells grow in two opposite directions, like processes. We thus obtain the spindle-shaped cell (Fig. 4, c, f). When such processes are numer- ous and are also branched, a singular thing appears, the stellate cell (Fig. 8). Fig. 5. — Young ova, from the ovarium of a rabbit. Fig. 6. — Cylindrical cells from the human small intestine; £, ordinary elements; a, so-called Becher-cells. Fig. 7. — Epithelial scales from the human month. The quantity of the cell protoplasma, and hence the magnitude of the body of the cell, is subject to great variation (Fig. 4). While protoplasma occurs originally in every cell, it may subsequently be replaced by other materials. Thus, in the cells of our Fig. 7, a harder, more water- less substance — keratine — has been substituted. Other cells obtain a lodgment of dark, black pig- ment granules of great chemical resistance (Fig. 9). These dark molecules are called melanin. One of the most widely diffused structures of the human body is the 6 FIRST LECTURE. colorless globular lymphoid cell. It also occurs in the blood (Fig. 10, d), and is at last transformed into a disc-shaped Fig. 9. — Pigmented connective- tissue curpuscle (stellate pigment cell from the mammalial eye). 'Qt Fig. 10. — Disc-shaped cells of human blood, a, a, a. At£, half from the side ; at r, seen entirely from the side; d, lym- phoid cell. structure {a, b, c), whose cell body contains a homogeneous red substance, of an extremely complicated chemical constitution, haemoglobin. Other cells subsequently become reservoirs of fatty matters, often in a high degree. We now pass to the kernel or nucleus. Its medium diameter may be assumed to be from 0.007 to 0.005 mm. It is originally a vesicle (Figs. 4 and 5), that is, a structure en- veloped by a delicate covering. Nucleoli occur singly, double, or in greater number (Auerbach). Attention has very recently been directed to a circle of small molecules deposited between the nucleolus and the wall of the nucleus, and called the granule-sphere. The nucleus may subsequently lose this vesicular character and assume a different arrangement. Thus it not unfrequently changes, later, into a firmer, more homogeneous structure (Fig. 7), or becomes granular. Should the growing cell be- come considerably lengthened, the nucleus also frequently assumes a more elongated form. As a rule, the nucleus remains a definite, tolerably con- servative constituent of the cell. Nevertheless, we meet with others of the latter which have lost by age the nucleus of an earlier period of life. Such non-nucleated cells form the most THE PROTOPLASMA AND THE CELL. 7 external layers of the epidermis covering our skin (Fig. 1 1). Other cells (Fig. 12) contain, in complete contrast, double nuclei. Their signification will occupy us later. Very singu- lar structures, of irregular form, and, in part, of extraordinary Fig. 11. — Non-nucleated cells of the epidermis. Fig. 12. — Cells with double nuclei ; a, from the liver, b from the choroid of the eye, and c, from a ganglion. V[Z. 13. — Multi-nuclear giant cell from the bone marrow of the new-born. dimensions, occur in the bone marrow, and also in many ab- normal tumors. They have been called myeloplaxes and giant cells (Fig. 13). Their larger specimens may contain a multitude of nuclei. In these two things, the protoplasm and the nucleus, we have become acquainted with the essential constituents of the cell. The youthful cell shows nothing further. Later, it may become different. The surface of the cell body hardens, or from this vicinity is formed a firmer envel- oping layer. Thus we have, when this remains very thin, what is called a cell membrane, while to a thicker covering is given the name of the cell capsule. We just said, " this may occur ; " but it need not. At the present time we occupy a standpoint different from that of 8 FIRST LECTURE. our predecessors. Towards 1840, Schwann, the founder of modern histology, erroneously ascribed the cell membrane as a third essential constituent to every cell, so that the cell would have two concentric envelopes, that of the vesicular nucleus and the external one of the cell body. The still fre- quently used name of "cell contents" is derived from that period. It is impossible for any one to demonstrate where such a membrane really begins ; that the surface of a cell prptoplasm in contact with the surrounding objects may, and, in fact, often does become more solid, would not be denied by any one ac- quainted with the great changeability of protoplasm. We may only speak of a cell membrane when we are able to iso- late the thing, and thus place it with certainty before the mi- croscopist's eye. A smooth, sharp, dark line of demarcation on a possibly strongly changed cell corpse gives us neverthe- less no proof of a membrane. We shall find later, it is true, that the isolation of an envelope on a fat cell, for instance, is very easy. Tak- ing, by way of example, our Fig. 14, the lateral surfaces of the cylindrical structure a are provided with a cover- ing which is certainly recognizable. Above, at the broad part, it is other- wise. Here the cell membrane is wanting ; and a thicker covering piece, permeated by very delicate longitudi- nal canals, overlays the protoplasm. We perceive a cell cap- sule on the mammalial ovum (Fig. 5, 2), while a more youthful ovulum (1) still appears membraneless. In cartilage tissue- cell capsules are quite ordinary occurrences ; we shall there be more intimately occupied with them. We proceed further; we inquire after the life of the cell. A life we have already ascribed to it, although a limited one in the service of the whole. Can this, however, be demonstrated ? This question is asked by many. We answer, yes. We recall to mind that Fig. 14. — Cylindrical epithelium from the small intestine of the rabbit ; a. Side view of the cells with the thickened and somewhat elevated seam, which is permeated by porous canals ; b, View of the cells from above, whereby the ap- ertures of the porous canals appear as small points. THE PROTOPLASMA stND THE CELL. '■which we remarked above concerning the bathybius and proUmceba, that constant mutability, that vital power of contraction of the protoplasm. Numerous cells of our body, a?, for instance, the lymphoid cells (Fig. 10, d), show the sane, and possess an " amoeboid" change of shape. When, by an artificial experiment, we produce an inflam- mation of the eyeball of a frog, instead of the clear aqueous of the normal condition, the contents of the anterior chamber soon appear more cloudy. In this less transparent fluid, we now meet with innumerable lymphoid cells which, in this case, are called pus corpuscles. If we subject these cells in a conservative manner to micro- scopical examination,' we rec- ognize, the vital metamor- phosis, already familiar to us, of the protoplasm. Every shape which our Fig. 15 pre- sents — and innumerable oth- ers also — may, one after the other, be assumed by one and the same cell, till finally, in death, it comes to rest as a spherical body (/). Formerly only these corpses were known. Still other remarkable things are connected with these pe- culiarities of the protoplasm. If to this cloudy aqueous of the eye we add inoffensive col- oring matters in a condition of the finest division, indigo or carmine, for instance, we see that the always restless proto- plasm gradually takes up into the cell body one colored gran- ule after the other (b). Even larger structures may be thus introduced. Fragments and even whole red blood corpuscles may thus enter into the lymphoid cells of the spleen. The amoeba (Fig. 3), received its small alimentary corpuscles in exactly the same way. 1* Fig. 15. the frog ; t living cell ; -Pus cells from the inflamed eye of , to /.-, the changes in the form of the /, dead cell. This introduction may take place, in 10 FIRST LECTURE. both cases, at any portion of the outer surface ; the latter is, indeed, similar throughout. By means of this vital transformation, our lymphoid cell is able, like an amoeba, to shove itself over whatever it rests 1 on ; and thus, very slowly and sluggishly, it is true, wander about. This may be observed in the pus cell in the cloudy aqueous mentioned. In the magnificently transparent cornea of the normal eye of a frog, the lymphoid cells may be seen to wander through the corneal canals in the most distinct manner, so that they gradually pass over the entire micro- scopic field. This has been rather drastically expressed by the words, " the cells devour and march." Such amoeboid cells may wander into other cell forms which have come to rest. The surfaces of the body have cell layers which are called epidermis or epithelium. This tis- sue participates actively in the catarrhal irritations of the mucous membranes. Lymphoid cells then wander from the deeper layers of the latter into the bodies of these epithelial cells (Fig. 16). These strange cells had already been ob- served before the vitality of the protoplasma was conjectured. The process was then naturally not understood. It was then imagined that the lymphoid cells were produced within those of the epithelium. A form of cell has long been known, a species of epithelium, which presents the most strik- ing vital phenomena. This is the ciliary cell (/). Very small and thin cilia, which cover the free surface of the cell body, are constantly occupied in a to and fro motion. These vibrations are repeated with such extraordinary rapidity that the human eye is unable to dis- Fig. t6. — Pus corpuscles in the interior of epithelial cells from the human and mam- nialial body ; «, Simple cylinder cell of the human biliary canal ; b, one with two pus cells ; c, with four, and */, with many of these contained cells ; e y the latter isolated ; f, a ciliated cell from the human respiratory apparatus with one, and g; a flattened epi- thelial cell from the human urinary bladder, with numerous pus corpuscles. THE PROTOPLASM A AND THE CELL. \\ tinguish the individual ones. It is only on the death of the ciliated cell, when these oscillations are retarded, that they can be counted. We now know that these fine cilise are pro- toplasma threads, and that their movements fall within the vital sphere of that remarkable substance. The rapid work of these small hairs and the sluggishness of ordinary proto- plasm, it is true, present a difference which is still inexplicable. Where there is motion in the domain of animal life, there is also sensation. Have the cells, the vitalized, minimal cor- ner-stones of our bodies, the latter capacity ? We may affirm this unreservedly. When these changeable figures, as they were represented in our Fig. 15, are subjected to a weak electrical irritation, they rapidly return to the spherical form, to subsequently recommence the old play of forming processes. Every organism, even the smallest and most simple, has a transmutability ; that is, it gives off altered unserviceable par- ticles of matter, it receives into itself new matter, and trans- forms it into the constituents of its own body. The mass of the organism then increases, it grows. All this happens, likewise, to the cell. The perception of these vital actions is rendered difficult by the smallness and the obscure existence of our structures. That the cells grow may be abundantly shown and with the greatest certainty, as, for example, in the fat and cartilage tissues. That they take up and transmute matter ; that is, make it something chemi- cally different, may also be perceived without trouble. Melanin, the black pigment we mentioned above, is wanting in the blood. It is formed by the cell (Fig. 9). Choleic acid salts and biliary pigment, the former, at least, certainly not present in the blood, are productions of the living hepatic cell. The latter presents us, furthermore, with a striking example of the exchange of matter. Both the substances just mentioned appear later as ingredients of the bile. We could readily cite many such occurrences, but these few remarks may suffice ; they show, at least, the coming and going of the materials. The law of destruction adheres like a curse to the heels of 12 FIRST LECTURE. the Organic, from the infusoria, whose life is counted by hours, to the oak, whose existence lasts centuries, throughout this limited duration of life. Concerning the human organ- ism, this highest cell-complex, there is a very ancient, well- knpwn saying that it lives seventy years, and at the furthest eighty. We now encounter the question : Are the cells, those vital corner-stones of our body, once for all present, to remain with us permanently as faithful companions to the day of death ? Or does our body-cell, that delicate little thing, pos- sess a more limited and, perhaps, compared with human life, only a very short existence ? We answer unreservedly in the latter acceptation. The life of the body is long, under fortunate circumstances ; that of our cells is short. We can present but a very defec- tive proof of this, however, at the present time. We again present a few examples. We have said above that the outer surface of our body is covered by layers of cells. The superficial layers are in loose connection ; they are cells in old age. The friction of our clothing daily removes im- mense numbers of them. A cleanly person, who uses sponge and towel energetically every day, rubs off still greater quan- tities. This takes place very actively in our mouth every day. We swallow ; our tongue acts in speaking ; drink and food pass this entrance of the digestive apparatus. Every one knows this. The mucous membrane of the mouth is, again, covered with a thick layer of epithelial cells. Here, also, many thousand senile cells are rubbed off daily. That which began at the entrance is continued throughout the entire di- gestive apparatus. An excess of cells is thus lost daily. To show the duration of life of a cell variety, let us turn to the human nail. The latter, growing from a fold of skin, is a cell-complex. In the depth of the furrow, youth prevails ; at the upper border— which we trim — old age. The deceased physiologist of Gottingen, Berthold, proved that a nail cell lives four months in summer and five in winter. A person, THE PROTOPLASMA AND THE CELL. 13 dying in his eightieth year, has changed his nail two hundred times, at least — and the nail appeared such an inanimate, ap- parently unalterable thing ! We consider the nail cell a relatively long-lived constituent of the body. We believe that most of the cells of our body have a very much shorter existence. We repeat, however, that it is a matter of belief, for no one can prove it, at pres- ent ; but everything compels the view that, for example, the red blood corpuscles, of whose multitude we spoke above, have a much shorter existence than the elements of the nails, and they are certainly resembled by many other cell- varieties. Most cells being destined to an early death, how do they die? Science can give to this, at present, but an insufficient answer. Certain cells, those of the outer surface of the body and of many mucous membranes, dry up in their old age ; the connection with the vicinity dissolves, the thing falls from its bed. The red blood cells die by being dissolved in the blood plasma. Others stick fast in the complicated tissue of the spleen, and are likewise children of death ; for the blood corpuscle lives only in the perpetual motion of the current ; rest stamps it with the impress of death. Other cells show in their old age granules of lime salts. They mummify. In this condition they may, as cell corpses, possibly remain for a still longer time constituents of the body. Generally, however, they soon afterwards become dissolved. A very disseminated form of death of ani- mal cells, in healthy as in unhealthy life, is the so-called fat degeneration. In the place ... Fig 17.— Fatty degen- 01 the protoplasma, we perceive, in increas- eratedceiisfromtheGraa- _ fian follicles of the ovary. ing quantity, molecules of fatty matter (Fig. 17). They finally destroy the cell life and cell body. The human body daily loses, therefore, immense numbers of its living corner-stones. How does it replace this loss ? We here enter a very interesting department of our science. 14 FIRST LECTURE. Schwann, the founder of modern histology, taught : " What the crystal is in regard to the inorganic, so is the cell in the sphere of life." As the former shoots forth from the mother- lye, so also, in a suitable animal fluid, are developed the constituents of the cell, nucleolus, nucleus, covering, and cell contents. This view was embraced during many years. It explained everything so conveniently ! This was, however, over-hasty. Two highly endowed in- vestigators, Remak and Virchow, exposed the error ; the former for the embryonic, the latter for the diseased human body. The organic kingdom forms a continuity from the Bathybius to man. We do not hesitate an instant to acknowledge that this is also our conviction. There is an old well-known saying : " Omne vivum ex ovo," and in imitation of this sentence : " Omnis cellula e cellula." The cell arises from the cell ; a spontaneous origin, in the sense of Schwann, does not occur. We know but one certain method of increase of the cells of our body. The protamceba, Haeckel's non-nuclear cytode (Fig. 2), divides itself into two beings by constriction. Each portion grows, by a predominant reception of material, to a new protamceba. This is also the method of propagation of the nucleated cell of the human body. Nucleus and protoplasm divide ; from one structure are formed two, and so forth. Our figure (Fig. 18) shows this multiplying process of embryonic blood corpuscles. When, however, the cell has once become surrounded by an V™i a ZZ™Zri\o7:^ envel °Pe or a capsule, when the proto- processofdn-smn. plasma is imprisoned, then (Fig. 19) the contrast of the active and the passive is strikingly presented. The capsule remains stiff and quiet, the cell in prison THE PROTOPLASMA AND THE CELL. IS Fig. i a, cell cells ; e I. — Diagram of dividing incapsulated bone cells ; jody : 6, capsule ; c, nucleus ; d t endogenous supplementary capsule formation. maintains the old life. This multiplying process was, in old times, badly enough designated " endogenous cell for- mation." Mother and daughter cells were spoken of. The so- called mother cell is nothing but the cell capsule. Does the process of division of the human cell take place slowly or rapidly ? We be- lieve the latter ; al- though a proof can scarcely be presented here. In the lower animal groups, at all events, processes of division occur which are completed with great rapidity. We cannot yet leave the process of division, for we now encounter the question : Which constituent of the cell, nucleus, or protoplasm, here assumes the chief role? That a non-nucleated lump of proioplasma is capable of dividing, is shown by the protamceba. It is possible that the nucleus is only passively simultaneously con- stricted, an opinion to which we are inclined. Meanwhile cells which, in the undivided body, present two sep- arated nuclei (Figs. 12, 18, 19), and the multi-nuclear myeloplaxes (Fig. 13), constitute a certain objection. Once more, therefore, uncertainty. The blood, lymph, and chyle consist of cells suspended in a large quantity of fluid ; in the as we already know, these bodies are present in mous numbers. Something similar is presented pathological product — pus. Should one speak here Fig. 20. — Simple flattened epi- thelium ; a, of a serous mem- brane ; b. of the vessel*. blood, enor- by a of tis- r6 FIRST LECTURE. sues ? According to our opinion it is permissible ; still, we readily admit, the opposite view may be defended. Other tissues, such as the epithelium or the epidermis (Fig. 20), present the cellular elements in close conjunction. At the same time, even the first examination teaches us that our cells are not loosely crowded together ; they are intimately united ; they are plastered or cemented together. This Fig. 21. — Capillary vessel from the mesenlerium of the Guinea- pig, after the action of the ni- trate of silver solution ; a, vascu- lar cells ; b t their nuclei. Fig. 22. — Cells of the enam- el organ of a four months' hu- man embryo. substance, which is of very frequent occurrence in a minimal thin layer, is called either the tissue cement or the intercellu- lar substance. If a portion of such tissue is placed for a short time in a very dilute solution of nitrate of silver and then exposed to the light, the tissue cement becomes black. This excellent accessory is nowadays very frequently used. In this manner we years ago recognized that the finest blood- THE PROTOPLASMA AND THE CELL. 17 vessels, the capillaries, were formed of cemented, elongated cell lamellae which become curved and joined together as a tube (Fig. 21). Stellate cells (Fig. 22), may blend together through theii processes, and form a very delicate net-work. The meshes may be filled up with homogeneous gelatinous matter, and also with a multitude of lymphoid cells. In the former case we again have a variety of intercellular substance. The latter acquires a considerable thickness in many tissues, as in cartilage. At first (Fig. 23), this intermediate substance is homogeneous throughout. This condition is either main- Fig. 23. — Cartilage of a young sheep ftEtus. Fig. 74. — Cartilage from-the auricle of a calf's ear; a, cells, b, intercellular substances; c, elastic fibres of the latter. tained, or else fibres subsequently shoot out from the inter cellular substance. Frequently (Fig. 24), we meet with them crossed in a felt-like or reticu- lated manner. They present an obstinate power of resistance to reagents. Such fibres are called elastic. Therefore — we repeat it — the elastic fibre is the result of a subsequent metamorphosis of an originally homogeneous substance. Connective tissue is infinitely diffused through the human body. A small piece of this, taken from the embryonic body, shows us, together with cells, bundles of very fine fibrillse, the connective-tissue fibres (Fig. 25). They have a quite similar origin. Subsequently, the con Fig. 25. — From the tendon of a hog's em- bryo ; rt, the cell ; /', connective tissue fi- brillse. i8 FIRST LECTURE. nective tissue has also formed those elastic fibres, which we have just met with in cartilage. From whence, however, does the tissue cement and the intercellular substance come ? Have they been inserted from the neighborhood between the cells, or have the cells them- selves produced these substances ? The latter is the case. These substances were once con- stituents of the cell body, at one time represented protoplasm. The formation of these substances was sometimes compared more to a secretive act of the cell, at others, more to a meta- morphosis of the outer portion of the cell body. We think both occur, and the difference between these views is, in fact, of little importance. A deposition may also take place from without upon a single cell or a cell-complex and enter into a closer union with it. The mammalial ovum (Fig. 5), shows a capsule. It is the elaboration of the small cells (a) covering the ovu- lum. The capsule of the cartilage cells appears very similar to the ovum capsule. Its origin, however, is entirely different. The cartilage cells have themselves formed the car- tilage capsule. We shall return to this subject later. The glands (Fig. 26), con- sist of secretory cell-com- plexes surrounded by a hyaloid covering, the so- called membrana propria. This is not a secretory pro- duct of the cell-aggrega- tion, as was formerly assum- ed. The membrane is trans- formed from the connective tissue adjacent to the glandular cell-aggregation. It may remain structureless, but extremely flat stellate cells may also enter into its structure. They then appear as delicate, rib-like thickenings of this membrane. Fig. 26. — Tubular glands from the Urge intes- tine of the Guinea-pig. _ At «, a gland with the membrana propria showing in places ; at 6, escape of the contents through a rent in the latter. THE PROTOPLASMA AND THE CELL. '9 We will add one more example of a widely diffused cell transformation ; we allude to the transversely striated volun- tary muscle. This, a thick, cylindrical fibre, not unfrequently of considerable length, consists of a contractile, longitudinal and transversely striated substance. In the outer portions of the latter lie numerous nuclei with adherent proto- plasma remains. It is surrounded by a hyaloid sheath. The whole, how- ever, arises from a single cell (Fig. 27). This (a), with a continual increase of the nuclei, grows into a thread ; the proto- plasma is transformed into the longitudi- nally and transversely marked substance (c); only a scanty remnant surrounds the nucleus, forming it into a rudimentary cell, and the homogeneous covering of the thing is derived from a transforma- tion of the adjacent connective tissue. The examples presented may suffice. They show, at least, how the most het- erogeneous may result from what was originally similar, through subsequent cell metamorphosis, and they attest the high signification of the cell in the structure of the organism. Fig. 27. — : Development ol the transversely striated mus cular fibre (sheep embryo). ''-V'wAVA/A. vC"^u v. v ^i. y"---, wkvW. SECOND LECTURE. CLASSIFICATION OF THE TISSUES. — BLOOD, LYMPH, CHYLE. A CLASSIFICATION of the tissues was, in the course of time, often attempted ; but it is, and remains, a very difficult thing. A scientifically adequate arrangement can be founded only on the course of development of the elements. The latter is unfortunately not yet accurately established throughout. One might nevertheless proceed with strictness, by the aid of the history of development ; the three well-known germinal plates from which the embryo arises might be employed as a basis of the arrangement. Still the representation of the tis- sues thus arranged would be attended with not inconsiderable difficulties. We will, therefore, employ a preponderating artificial classification, which, with all its defectiveness, possesses, at least, the advantage of presenting the material in a more convenient form to the learner. We distinguish : A. Tissues of simple cells with fluid intermediate sub- stance : I. Blood; 2. Lymph; 3. Chyle. B. Tissues of simple cells with scanty, firm, structureless intermediate substance : 4. Epithelium; 5. Nails; 6. Hair. C. Tissues of simple or metamorphosed cells, with partly still homogeneous, partly fibrous, and, not rarely, more firm intermediate substances (connective-tissue group) : 7. Carti- lage ; 8. Gelatinous tissue and reticular connective substance ; 9. Fat tissue; 10. Connective tissue; 11. Bone tissue; 12. Dentinal tissue. D. Tissues of metamorphosed, as a rule, unfused, cells, with scanty structureless intermediate substance: 13. Enamel tis- sue ; 14. Lens tissue ; 15. Muscular tissue. CLASSIFICATION OF THE TISSUES. 21 E. Compound tissues : 16. Vessels ; 17. Glandular tissue ; and 18. Nerve tissue. We shall, therefore, proceed in this manner, and turn first to the blood. " Blood is quite a peculiar sort of juice," Goethe lets his Mephistopheles say. Modern science, after nearly a hundred years, endorses the apothegm completely. If a little drop of this fluid, which appears homogeneous to the naked eye, is spread out in a thin layer under the micro- scope, we are surprised by a peculiar image. The homoge- neous red has disappeared ; we perceive innumerable yellow- colored cells in a colorless fluid. The fluid is called plasma, the cells bear the name of the colored or red blood corpuscles (Fig. 10, a, b, c). Among the colored companions, still another, though not abundant, colorless structure may be noticed by closer examination. This is the lymphoid cell of the blood, the so-called white blood corpuscle (d). The human red blood cells are diminutive structures ; they measure only 0.0088 too.0054 mm. Their smallness and their innumerable quantity renders it possible thata small space — a cubic millimetre of blood — may contain five millions of them. Their form, as Fig. 10 showed, is spherical, the periphery appears yellow, the centre bright and nearly colorless. When the blood corpuscle rolls over the microscopical glass slide, the side view presents the appearance of c. Our cell, conse- quently, represents a cir- cular disc, with excavated central portions of both broad surfaces. Fig. 28. — Red blood corpuscles of man ; a, treated with water ; b, in evaporating plasma ; c, dried ; a, after coagulation ; e, rouleaux-like arrangement. The red blood corpuscle is, besides, a very changeable 22 SECOND LECTURE. thing. In evaporating blood it becomes indented (Fig 28, b). Rapidly dried, it presents the appearance of c. On the addition of water, the cell becomes globular and loses its color. The coloring material, an extremely complicated sub- stance, called haemoglobin, has now become dissolved. Something similar is also seen in previously frozen blood. The colorless residue is called stroma. A series of reagents, which have been applied to our structures during many years, act similarly, some distending, others shrinking ; but by no treatment does a nucleus make its appearance. The human red blood corpusqle is, therefore, a non-nucleated cell. Has the thing a membrane — does it possess a covering ? we ask further. We answer negatively. An interesting ex- periment is here, according to our opinion, decisive. When living blood cells are warmed to 52° C, they commence a marvelous transformation. Indentations of the border rapidly Fig. 30.— Colored blood cells ; i, from man ; 2, camel ,• 3, pigeon ; 4, proteus ; 5, water salaman- der ; 6, frog ; 7, cobitis ; 8, ammocoetes. At a, surface view ; b, profile (mostly after Wagner). occur, and partial constrictions of the cell body rapidly follow, which either immediately break off or remain in connection CLASSIFICATION OF THE TISSUES. 23 with the main portion by means of a thin, pedicle-like bridge. The strangest appearances are hereby presented to the eye. It is plain that only a membraneless cell body can present such constrictions. The cells, these living corner-stones of our body, are other- wise quite similar in the various vertebrate animals ; it is not so, however, with the blood. The differences in most of the mammalia are certainly slight. The form remains ; only the diameters vary somewhat. A few ruminants, the camel, al- paca, and llama, have oval cells (Fig. 29, 2). The blood corpuscles of birds (3), amphibia, and most fishes (3), appear elliptic ; but in the middle of both broad surfaces we meet with an elevation. The diameter changes in an interesting manner. In birds, it is 0.0184 to 0.01 50 mm. ; in the squamigerous amphibia, 0.0182 to 0.0150; in osseous fishes (7), 0.0182 to 0.0114. Our cells reach prodigious dimen- sions in the ray and shark, 0.0285 to 0.0226 mm. ; then among the batrachia, the frog (6) and the toad have blood corpuscles of 0.0226 ; the triton (5), up to 0.0325 mm.; and the salamander has still larger. The group of the pisciform amphibia have the largest of all. In the proteus they measu're 0.057 mm - The cyclostomen, a low group of fishes, have, strangely, again, spherical bi-concave discs measuring 0.0113 mm. (8). All these blood corpuscles behave, with reagents, similar to those of man and the mammalia. But in them all, on the contrary, there is a nucleus. Even in the dying cell it is visible. Many reagents — for example, water, very dilute acetic acid — let it show out from the now discolored cell as a granular structure (Fig. 30, a, b). The second element of the blood, the lymphoid cell, is much more homogeneous. The form is, throughout, spherical ; the size is, in man (Fig. 10, d; Fig. '31, 1 to 4), rarely FlG . 3C) ._Bi „d 0.005, generally 0.0077 to 0.012 mm. The gfiLL-'nuciSf * most of our structures, according to this, exceed the dimensions of the colored corpuscles. It is the same in the mammalia. In the remaining classes of the 24 SECOND LECTURE. vertebrates, however, the lymphoid cell is smaller than the colored element. j They show a molecular proto- © © ® plasma, with a granular contour. , <• A few lymphoid cells harbor, in "/8\ C) fP fii) addition, fat molecules (4). If water ©V-V ^_. _ ^-^. be allowed to act on them, the e \_) \£y V ) nucleus immediately begins to de- a * , •* tach itself (5). After this we have fig. ^.-Lymph cells ; at i to 4 ,un- nuc i e ar forms, such as the cells 6, 7, changed ; at 5, the nucleus and hull ' J ' ' sKcut™^.^^ and 8 possess. Other cells show a "to'^ecesS^^freetcieTr reniform (9), or triplicate nucleus substance - (10, 11). This artificial production may finally break up into a number of small fragments (12). The lymphoid cells adhere readily, they are of a somewhat sticky nature. Their specific weight is less than that of the red blood corpuscles. During life we meet with the already described amoeboid change of form, as well as a locomotion thereby induced ; this takes place most actively in diluted plasma (Thoma). The cells can also be made to take up small foreign particles. There are one, two to three colorless blood cells to 1,000 red ones in man. The number increases after a plentiful meal, after the loss of blood, and also under conditions which indicate a more active blood formation. An interesting phenomenon is presented by the spleen. The blood flowing into it shows the usual small number of lymphoid cells, while in the blood of the splenic vein 5, 7, 12, 15, and more of them occur. In the lower groups of vertebrate animals, the number of the color- less cells is more considerable ; in the frog, the proportion of lymphoid cells to red blood corpuscles is 1 : 4-10. The web of the frog and the tail of its larvae are adapted to examinations of the circulation. The wonderful spectacle (Fig. 32), shows how the colored blood corpuscles readily and rapidly pass along and among each other, while the viscous lymphoid cells move much less rapidly, and not unfrequently adhere for a time to the inner surface of the vessel. CLASSIFICATION OF THE TISSUES. 25 Fig. 32. — The 'blood current in the web of the frog ; a, the vessel ; b, the epithelial cells of the tissue. But whence do our lymphoid cells originate ? First, from the lymph- and chyle, that is, from the lymphatic glands, then from the spleen and bone marrow. They are carried away from both the latter parts by the blood cur- rent. What becomes of our cells in the veins ? They become, in part, grad- ually transformed into red blood corpuscles, and cover the loss of the latter. Whether, however, a greater or only a lesser portion undergoes this metamorphosis, we are not yet able to say ; for this, we must first learn more accurately the duration of the life of the red blood corpuscles. The manner of this metamorphosis we can state in some degree. The globular form changes to the specific one of the red blood cell, and the protoplasma is replaced by a homo- geneous colored substance. In mammalia and man, finally, there is also a loss of the nucleus. Isolated examples of such intermediate forms have been recognized in the blood for years, especially in that of the spleen, the mammary ducts and the bone medulla. The bright red color of the arterial, and the dark of the venous blood is caused by a combination of oxygen with the haemoglobin, or a reduction of the latter. Prolonged changes in the form of the blood corpuscles likewise exert a modifying effect on the color. Distended, they lend a darker color to our fluid ; shriveled, a brighter one. When a drop of blood is left to itself, it coagulates. The filiform separation of the fibrine is shown in our Fig. 28, d. When blood is beaten, that is, the fibrine caused to coagu- late, the cells sink, the red ones more rapidly, the colorless 26 SECOND LECTURE. lighter ones more slowly, the former arranging themselves in rolls (e). We come, finally, to the blood formation of the embryo. The flat germinal layer, from which the human body arises, consists of three membranous cell layers lying one over the other, the horn layer (Hornblatt), the middle germinal layer, and the intestinal gland layer (Darmdriisenblatt) (Remak). The heart, vessels, and blood proceed from this middle layer, from which, besides, many parts of the body originate. The first blood appears very early, and consists only of colorless cells, formed of protoplasma and a vesicular nucleus. The homogeneous yellow substance gradually replaces the molecular protoplasma. We have now before us, nucleated colored blood corpuscles (Fig. 18, a), of 0.0056 to 0.016 mm. At this period an increase also takes place by the way of division (a to/). Later, this procedure becomes extinct, and the cells assume more and more the specific form, the nucleus at the same time disappearing. Let us now proceed to the lymph and chyle. The fluid of the living blood, the plasma, constantly passes through the thin capillary walls into the adjacent tissues. It brings to the latter the nutrient materials, to the one these ; to the second, again, others. The fluid becomes impregnated, however, with the products of decomposition of the tissues. The latter are again different. The tissue fluids, which are in consequence so variable in their chemical constitution, finally collect in the fissures and spaces of the body. Thin-walled vessels are gradually de- veloped from these; and then, uniting in larger trunks, they finally enter the blood passages. These are the lymphatic vessels; and the fluid contents, whose nature we have just de- scribed, are called lymph. The walls of the intestines also have their lymph districts. Towards the close of active digestion they contain tempora- rily another cloudy or white fluid, which is very rich in albu- men and fat. This is the lacteal juice or chyle. The canals bear the name of the chyliferous system of vessels. CLASSIFICATION OF THE TISSUES. 2^ The lymph appears colorless and clear as water. Taken from the smallest vessels, it may be without cells. It con- tains large quantities of them when drawn from the larget vessels, especially just after the passage of the latter through lymphatic glands or allied structures. Nevertheless, it is infi- nitely less rich in cells than the blood. They are the same lymphoid cells we became acquainted with in the blood (Fig, 31) ; further description is therefore unnecessary. The lymph presents nothing further. In the chyle, on the contrary — and they cause the cloudy or whitish appearance of the fluid— we meet with innumerable infinitely fine dust- like molecules. With a strong magnifying power they show a peculiar, dancing, driving about, the so-called Brunonian molecular movement. But there is nothing strange in this. It is natural to all very small bodies suspended in water, small particles of fat, the smallest crystals, carmine granules, and the like. These dust-like particles consist of fat, sur- rounded by a very thin albuminous covering. Red blood corpuscles may be met with in the lymph and chyle as incidental constituents, and occasionally as transition forms. I have seen the latter in the thoracic duct of the rabbit. Red blood cells, pressed out from the blood-vessels, may also finally reach the lymphatics. There is no doubt that the actively emigrated colorless blood cells often penetrate these passages, and thus again commence the journey back into the blood. THIRD LECTURE ZLz, THE EPIDERMIS, OR THE EPITHELIUM. UNDER epithelium we understand closely-arranged cell lay- ers, held together by a minimal quantity of cement (p. 16); it covers the surface of the body, the external as well as the internal. All three plates of the germinal layer (p. 26), participate in the production of the tissue under examination. The horn layer supplies the covering of the corium, the so-called epidermis. The lower germinal plate forms the epithelium of the diges- tive apparatus and the organs arising from the latter. Not less important is the r61e of the middle cell layer. Manifold cavities originate in it ; the passages of the vascular system, the so-called serous sacs, the articular cavities, down to innu- merable small and diminutive tissue spaces. All these again have their epithelial cell covering. The latter is now called endothelium. The principle is correct ; but the boundaries cannot yet be sharply drawn throughout. Epithelium consists either of a simple cell layer, or the cells are stratified more or less manifoldly over each other. We distinguish, therefore, unstratified and stratified epithe- lium. The latter originates in the horn layer. The former is due to the intestinal gland, as well as the middle germinal plate. The form of the cell varies. Many kinds of epithelium present only thin, flat, scale-like cells (Figs. 7 and 20). We speak now of flattened or pavement epithelium. In other varieties the cell is tall and slender. This is called cylindrical epithelium (Figs. 6 and 14). When the surface of the cylin- drical cells has vibratory cilia? (Fig. 33) we have the vibratile or ciliated epithelium. THE EPIDERMIS. 29 Fig. 33. — Various forms ul ciliated epithelium. The simplest unstratified pavement epithelium belongs in most, but perhaps not all its occurrences, to the endothelium. We find it in this Svay on the surface of the serous sacs, on the posterior wall of the cornea of the eye, over the lateral surfaces of the synovial capsules of the joints. The same endothelia are met with on the inner surface of the cardiac cavities and the vessels. These cells, very thin lamellae, appear sometimes broad and short (Fig. 20, a), on the serous membranes, again very narrow and long (b) on the inner surface of the arteries. The endothelium of the veins has a median character. A larger blood-vessel is a complicated thing. In proportion as we descend to the smaller and still smaller branches, one outer layer after the other disappears from this complicated structure, and at last only the inner- most endothelial layer remains. Large cells with lapped edges, and — induced by the position of the vascular tube — now much more strongly incurvated and in close connection, constitute the walls of the capillary (Fig. 21). The lymphatic vessels are also formed in the same manner, though their finest canals — and they occur in immense numbers throughout the body — show the outer surfaces of these endothelial cells grown into an intimate connection with the neighboring tissue, so that one might here speak of lacunar. The terminal respiratory portions of the lungs, the air vesi- cles or alveoli, have a layer of simple flattened epithelium which does not belong to the endothelium. We pass over the others at present. An interesting variety is found at the outer surface of the Fig. 34. — Endothelial cells after treatment with nitrate of silver. $0 THIRD LECTURE. retina. They were formerly called polyhedral pigment cells (Fig. 35). Their surface presents a delicate mosaic, as a rule, of a hexagonal form, of 0.0135 to 0.0204 mm. The quantity of the pigment granules embedded in the soft, homogeneous substance of the cell body varies, so that the nucleus is some- times visible, at others concealed. The outer portion of the cell remains free f.g. 3s -Pigment epithe- from these melanine molecules, which SSpf * e crdinar y °Lx h a! appear to form small crystals (Frisch). fCnaloni! 1 i ' alarKer ° cta " The profile view shows, however, that our cell, far from constituting a flat struc- ture, possesses, rather, a certain, sometimes a considerable, height, which, at least, equals the diameter. It is thus in the lower vertebrate animals ; here their body sends downwards a number of filamentous and spiny processes. The latter, at first, still contain pigment molecules, and surround in a sheath-like manner the rods and cones, the marvellous termi- nal apparatus of the retina. This is less frequent in mam- malial animals. These pigmented cells extend beyond the limits of the specially nervous portion of the retina, over the so-called ora serrata, where they become smaller, more rich in pigment, and are in thin layers. In this manner they then cover the ciliary processes and the posterior surface of the iris. Certain of the mammalia (the carnivora and ruminantia) have a bright, glistening place in the interior of the eye, called the tapetum. Our retinal epithelium is here unpig- mented. In albinos this is the case throughout, and the cells present the appearance of a delicate pavement epithe- lium, as, for instance, in the white rabbit. Many mucous membranes present material, and sometimes very considerable, layers of pavement epithelium. Among these are the conjunctiva of the eye, the mucous membrane ,of the nostrils and of the anus, the mouth and pharynx, the oesophagus, the urinary passages, and the vagina. In the most superficial layers of the conjunctiva (Fig. 36, a) THE EPIDERMIS. 31 we meet with flattened, not inconsiderable cells. In the middle layers these elements become smaller, but taller, more round, and, in the deepest layer (b), at last, cjdindrical. Fig. 36. — The cornea of the rabbitin vertical transverse section, after treatment with chloride of gold ; a s the 'older, ^, the young epithelial cells of the anterior surface ; c, corneal tissue ; d, a nerve branch ; e, finest nerve fibres or primitive fibrillai : f, their distribution, and termination in the epithelium. With a greater increase of the epithelial stratification, the number of the upper and middle cell layers is much more considerable. All the cells have a nucleus. The lowermost have a soft protoplasma body ; the superficial (Fig. 7) have become more solid and harder; they consist of corneous matter, or kera- tine, a derivative of the albuminous group. These cornified cells absorb weak alkaline solutions with avidity, becoming, at the same time, distended to a globular form. A vertical transverse section, after the manner of our draw- ing, favors the supposition that our cells have a pretty regu- lar form. When, however, the cell cement has been dissolved by a suitable macerating medium, an entirely different appearance is presented. The stratified pavement epithelium now ap- pears very much more like extremely polymorphous cells. They lock into each other with their pointed and leaf-like processes ; the convex surface of one cell is in contact with the concave surface of its neighbor ; the surface is rough and 32 THIRD LECTURE. sometimes indented (Lott, Langerhans). This was first seen in the epithelium of the urinary bladder. When the epithe- lial stratification is more developed, the cells of the lower and middle layers lock into each other with their enormous spines and ridges, like two brushes pressed together (Fig. 37). These "spinous and dentate cells" 0!*>n. .t0:-:> ; (Schultze) lead to an intimate clinching. a i''-W/'X:-%'% This connection is, however, again dis- ^■''H/S^,;:';; 1 :;/ solved upwards, and their deciduousness :> o ■3 is thus promoted. rells ^u~: : :S*%i'^'-'J? The most dense formation of flattened epithelium covers the human corium. It ^\'lS?!?£v has long- been known under the name of ^''ffi 1 )^ tne epidermis. This corium projects in small papillae of various shapes. They are called the sensi- I?J, 7 f™™ e r =pf r tive or tactile papillae. The epidermis mfsT*,°ceii h f™m l a e ?apT forms a smoother covering over the whole ; '.on y gur° r ° f "* human its deeper cell layers must, therefore, fill up the valleys between these papillae. These younger cell layers, which have a not inconsiderable - thickness between the papillae, while they are but slightly developed over their apices, present all the characteristics of a stratified epithelial mucous membrane. Collectively, it is called the Malpighian rete mucosum, or rete Malpighii* The layers of old cornified cells make their appearance by an abrupt transition. They bear the name of .the epidermis in the strict sense of the word. Its thickness varies considera- bly ; it may exceed a Paris line. The number of layers varies, in consequence, extraordinarily. The latter are the same scales as those on the surface of the mucous membranes, though the cells in contact with the atmospheric air have be- come dryer and harder. The nucleus, which these cells for- merly possessed, has likewise been lost by the old, effete epidermis scale. They measure 0.0285 to 0.0450 mm.; in the mucous epithelium of the mouth, 0.0425 to 0.075 mm. We will speak of the color of the human skin. If we THE EPIDERMIS. 33 cover a red cloth with a piece of milk-glass, we have the flesh color presented to our eyes, and the thicker the piece of glass selected, the lighter the tone will be. It is thus with the complexions of Europeans. The corium during life appears red, in consequence of its extreme richness in blood ; the epidermis is semi-transparent, whitish or whitish- yellow. The thinner the latter, the redder the color (lips, cheeks) ; the thicker the cell covering (the foot-sole, frequently the palm of the hand also), the paler the surface of the body. In the skin of the dark human races, that of the negro, the nuclei in the deeper layers of the epidermis are diffuse brown ; the cell bodies are also somewhat darker, and may also contain pigment molecules. In the darker portions of the bodies of the light races (the nipple and its areola) the same condition prevails. The coloring matter here conceals the red of the cutis. All stratified epithelia, as we already know from what has preceded, are of a perishable nature. Millions of the super- ficial cells fall off daily, from rubbing, pressure, etc. The new formation takes place at the deepest layer, by a process of division. Between the latter cell layers, finally, immi- grated lymphoid cells may also be met with. The second form of epithelial tissue, the cylindrical, be- longs to the digestive apparatus, from the entrance to the stomach to near the anus, likewise to the ducts of the liver and pancreas, the ducts of the lacteal and lachrymal glands, and also some portions of the sexual apparatus. We there (Fig. 6, b, 14, a) meet, as a rule, with a single row of narrow, vertically elongated cells, with a sometimes super- ficially, sometimes more deeply lying nucleus, which contains a nucleolus. A thin layer of cement substance unites our cells, which, seen from above (Fig. 14, b) present a fine mosaic. Their height and breadth vary. In the human small intes- tine, the former is 0.0182 to 0.027, the latter 0.0057 to 0.009 mm. The lateral walls show an envelope ; the free base may present naked protoplasma, as in the stomach ; it may, also, how- ever, show a different character. This is the case in the 2* 34 THIRD LECTURE. small intestine (Fig. 14, a). There occurs here an already mentioned covering piece, 0.0017 to 0.0025 mm. high, formed of a firmer, very changeable substance, and permeated by very fine canals, the so-called porous canals. We shall have to mention the latter later in alluding to the absorption of the chyme. That the cylindrical epithelial cells, many of them at least, are destroyed by a mucous metamorphosis of their interior (" Becher cells ") we have shown in Fig. 6, a. The reparation remains unclear. It is not accurately determined that there is a deeper, younger layer of cells destined to this purpose. Vibratory or ciliary epithelium (Fig. 29) is formed of modi- fied cylinder cells. The same cell bodies, with similar varia- tions in height and diameter, present themselves. Only the free surface, which has the ciliae, those most restless proto- plasma filaments (p. 10), causes the peculiarity. Ciliary epithelium lines the human respiratory apparatus. Commencing at the base of the epiglottis, it covers the larynx, with the exception of the lower vocal cords, which have stratified pavement epithelium ; also the trachea and the bronchi, as far as their finest ramifications, but not the respi- ratory vesicles of the lungs (p. 29). We meet with it, fur- ther, in the olfactory organ, with the exception of limited places. The oviducts and uterus of the female, the vascula efferentia, the coni vasculosi, and the canal of the epididymis, as well as the upper half of the vas deferens, have this variety of epithelium. Finally, to pass over its more limited occurrence, the cavernous system of the spinal cord and brain " vibrates " in the embryo and neonatus. The ciliae are often of considerable size in the lower ani- mals ; in the higher, they become smaller and smaller. They appear exceptionally long, measuring 0.0226 to 0.034mm., on the large epithelial cells of the canal of the epididymis, and very short, 0.0056 to 0.0038 mm. , in the respiratory apparatus. A high degree of perishableness is impressed, as a character- istic sign, upon them all. Whether compensatory cells occur in ciliated epithelium is, perhaps, not yet accurately deter- THE EPIDERMIS. 35 mined. They have, at all events, been frequently admitted. Mucous metamorphosis, as in the cylinder cells, is also fre- quently met with here. Lymphoid cells may also occur between the cylinder and the ciliated cells ; indeed, they may even penetrate to the in- terior of the cell body (comp. Fig. 16). Let us here devote a few words to the remarkable ciliary motion. Discovered in olden times, subsequently, especially of late days, frequently investigated, it has not yet been satisfactorily explained. Its occurrence in the animal kingdom is quite variable. Sometimes this part vibrates, at others that, sometimes nearly all the surfaces ; at others, as in the arthro- poda, not at all. What purpose does this wprk of the ciliae serve ? , If we fold a suitable detached piece of mucous membrane and examine the edge of the fold, we have the appearance of an undulating border, of a flickering candle-flame. If we look from above downwards on to it, it suggests the comparison to a field of grain agitated by the wind. Small bodies suspended in the fluid medium, color granules, blood cells, sweep past the folded border, when we examine with a high magnifying power. When we use very weak lenses, the excursion proceeds more slowly; a cell will require several minutes to make its course. When the ciliary motion is still in full vital energy, and several vibrations then take place in a second, the human eye is powerless. It is only when the action becomes retarded that we perceive the separate motions — the regular, syn- chronous, and homogeneous vibrations of the ciliae. At- tempts have been made to distinguish several varieties of these vibrations ; as for example, a hook-like and an oscilla- tory. We pass over this ; but we must here mention an apparently strange condition. In the ciliary movement, we see the cilia; vibrate towards one side, and the small passing bodies take the opposite direction ! 36 THIRD LECTURE. The matter is readily explained. We first recognize the slower, less energetic direction of the vibration ; the other, more rapid and powerful, we do not yet perceive. In which direction, however, will the current be driven ? Manifestly, in the latter. Engelmann explains the more sluggish move- ment as a vital act of the protoplasma ; the more rapid, as the effect of elasticity. We agree with him. Later, as death approaches, both movements become dis- tinct. The current finally ceases, only a to and fro fluctuation still remains. The ciliary movement has nothing to do with the blood current, or with nerve life. It perishes rapidly in warm- blooded animals, often very slowly in the lower cold-blooded creatures. An elevation of the temperature to 44 and 45 C. kills them, likewise increasing cold. Everything which exerts a chemical influence likewise produces a destructive effect, occa- sionally with a temporary increase of the vibration — water, for example. It is an interesting observation, that dilute solutions of potash and soda may temporarily excite the paralyzed vibratory phenomenon to renewed energy (Virchow). The true epithelium — that is, so far as it originates in the corneous and intestinal gland layers — is developed very early. Even in the human embryo of five weeks, according to Koelliker, the surface of the body is covered by a double layer of cells, a deeper one consisting of smaller rounded structures, and an upper one of larger, flatter, indented bodies. The former represents the primary rudiments of the rete Malpighii, the latter, the horny layer. Closely related to the epidermis, and arising from it in the third month of fcetal life, are the human nails. These obtuse quadrangular plates are arched outwards, and lie posteriorly, with the so-called nail roots, embraced within a deep furrow of the skin. At the sides, the furrow becomes from behind forwards more and more shallow. The anterior border of the nail remains free. The portion of the cutis covered by the nail bears the name of the nail-bed. The latter shows lon- gitudinal rows of cutaneous papillae. THE EPIDERMIS. 37 Fig. 38.— Cells of the horny layer of the nail ; a, rt, view from above . b, b t seen from the side The nail consists of two strongly demarcated layers, a .deep and a superficial. The former is the ordinary Malpighian mucous reticulum, such as is shown by any other part of the skin. The superficial layer, corresponding to the horny layer of the epidermis, has gone through the process of hornification in a much higher degree than occurs elsewhere. At the first consideration, we perceive only a brittle, homogeneous substance. The power of refrac- tion of all its constituents has become equal. Reagents, and above all, solutions of the alka- lies, are here of inestimable value. With them we dissolve the cement substance and re- store a recognizable appear- ance to the cell. The latter, an originally flat thing, measures °-°j7S t0 0.0425 mm., but, dif- fering from the ordinary epider- mis cell, contains a lens-shaped granular nucleus, as may be readily recognized from Fig. 38, a and b. Concerning the duration of the life of the nail cell, see p. 12. The highest variety of epider- moidal tissue is represented in man, by the hair. An extreme complication of structure welcomes us here, all at once. The hair (Fjg. 39). lies in an obliquely directed sac, an invo- lution of the coriuifi, and fre- quently likewise of the subcutaneous cellular tissue Fig. 30. — Human hair ; k)> the cells of the hair bulb are perceived to be *""'^3§lpSSP*i»^33SB[ transformed into larger polyhe- faSHr^ dral elements of 0.015 1 to 0.0226 jsK&Sm mm. Further above follows ^-'ilsllllw the drying and shrinking of the ^fflf"' elements, which have in the mean time become non-nucleat- _ „ ,. ,,,.,, Fin. 41. — Rudiments nf the hair of a rul- ed. Very Small air Vesicles man embryo of 16 weeks : a, 6, epidermal J layer; m, in, celts of the rudiments of the enter the innumerable small *! air; «"> structureless membrane covering them. spaces. A white hair thus re- ceives its appearance, while in colored hairs the serrated sub- stance glistens through the coloring of the cortex, as if tinged. We have still one structure remaining, the epidermis or cuticle of the hair (Fig 39,/, 40, b). A double layer of hy- aline obliquely standing cells covers the hair, as long as it is surrounded by the sac. With the latter terminates the outer cell layer, but not so the inner one. This covers the free hair, as a system of quite obliquely arranged, flat, non-nu- cleated lamellae, covering each other in a tile-like manner, like a scaly coat of mail. Not unfrequently, after -pressure and maltreatment, the lamellae present the appearance of regular transverse fibres (Fig 39, /*). Hairs are found over nearly the whole body, as so-called lanugo hairs, and in limited places as thicker, coarse hairs. 40 THIRD LECTURE. Its smooth or frizzled condition depends on the cross section In the former hair it is round, in the latter oval or reniform. The growth of the hair takes place by a cell increase from the lower portion of the hair bulb. So long as the sac with its papilla remains uninjured, it regenerates the lost hairs ; that is, such as are stunted in their hair bulbs and are separated from the papillae. This power of reproduction is tolerably ener- getic, for the physiological loss of hair is not inconsiderable. The origin of the embryonic hair commences at the end of the third or the beginning of the fourth month (Fig. 41). The epidermis forms with its deeper cells (b) a knobby down- ward growth. A structureless boundary layer, furnished by the impressed corium (z), leads to the formation of the hair sac. From the cell aggregations (in, m), are developed both the root-sheaths and the entire true hair with its cuticula. The hairs, like the nails, are, therefore, secondary epidermoi- dal structures. FOURTH LECTURE. THE CONNECTIVE-SUBSTANCE GROUP. — CARTILAGE, GEL.A TINOUS TISSUE, RETICULAR CONNECTIVE TISSUE, FAT. Connective tissue, fat tissue, cartilage, bone, dentine, are well known constituents of the body. Their finer structure proved extremely heterogeneous at the commencement period of modern microscopy. It was in the year 1845 that Reichert recognized all these things as members of a natural unity. Science is indebted to him for the exposition of a " connective-substance group." Here Virchow accomplished further progress in the domain of pathology ; and, indeed, also committed errors. Much labor has subsequently been bestowed upon this group ; we have made further progress, but are still far enough removed from a conclusion. All these tissues mentioned — and to these are to be added, as new acquisitions, gelatinous tissue and the reticular con- nective substance — arise from the middle germinal layer (p. 26). They are originally similar, but then, pressing on to- wards maturity, they assume quite variable forms. Connect- ing intermediate forms, however, remain. No one can, for example, draw a sharp boundary between gelatinous and ordinary connective tissue, or between the latter and carti- lage. We meet in places, therefore, with a continuous tran- sition of one connective substance form into another. Truly different tissues never do this. We meet, furthermore, in the animal kingdom, very frequently a substitution of one tissue of our group by another. That, for example, which in one creature is connective tissue is in another gelatinous tissue, or even bone. A temporary substitution also occurs. The parts of our skeleton were, for the most part, formerly cartilage. In morbid growths we meet with extraordinary frequency with such substitutions of the one for the other. 42 FOURTH LECTURE. The connective-substance group, occurring throughout, forms a large part of our body, the general frame-work, in which the other tissues are embedded. They have rightly been called the scaffold and supporting substance of the body. Let us now examine their individual varieties. Cartilage tissue makes its appearance very early in the con- struction of the body, though frequently to disappear after a short duration of life. Most cartilage, accordingly, does not become old. Even at the hour of birth a considerable por- tion of the cartilage has fallen a sacrifice to a new secondary tissue, the osteoid or bone tissue. A portion of the cartilage lasts, however, till the death of the person, and may thus reach a great age. The texture is distinguished, according to several varieties of the mature tissue, into : a, the hyaline ; b, the elastic ; c, a rather uncertain variety, the connective-tissue cartilage, an intermediate thing between cartilage and connective tissue. In its first embryonic appearance, the progressing cartilage presents small spherical protoplasmic formative cells with vesicular nuclei and rather scanty homogeneous intermediate substance. The latter is still soft, and consists of albuminous matter. Soon, however, the cells increase in size ; the inter- mediate substance is augmented, and becomes more firm (Fig. 23). A chemical change also takes place gradually ; it becomes a gelat- inous tissue ; on boiling, it yields chondrine. When the intercellular substance retains its original homogeneous character, it forms hyaline cartilage. Thin sections appear transparent like glass. The cells (Fig. 42) have also, fig. ^.-Diagram of a perfectly in the mean time, assumed quite a mature hyaline cartilage, with quite • ,• ,1 ■ a variety of cells. variation in their appearance. They appear larger, round, oval, wedge-shaped. A portion of them show capsules, and not THE CONNECTIVE-SUBSTANCE GROUP. 43 Fig. 43.— Thyroid cartilage of the hog The basis sub- stance is divided into cell- districts. unfrequently the latter envelop so-called daughter cells (comp. Fig- 19). How have these capsules and the intermediate substance been formed ? Concerning this there has been much discussion. Nowadays we must say that both are cell products, are substances yielded by the cell, and were formerly a part ol the cell body itself. In the ensiform process of the sternum of the rabbit, it is easy to recognize, without re- agents, that the intercellular substance is formed only of the cemented capsules of the cartilage cells (Remak). By the aid of macerating media this can also, with greater difficulty, it is true, be demonstrated in other mammalial and human cartilage (Fig. 43). Here, also, the appar- ently homogeneous intermediate substance becomes divided into a system of concentric capsule lay- ers, which embrace within them the cell or the cell group. The individual capsular systems are cemented to each other and like- wise the external capsules of ad- joining cells. From the similarity of the power of refraction is caused the phantasm of homogeneous- ness ; the cartilage cell lies in a chasm. When the innermost, last-formed capsule has preserved an additional, peculiar exponent of refraction, we perceive this (Figs. 42, 44) as something dif- ferent from the remaining intermediate substance. This division of the cells within their cavities, or, which amounts to the same, within their capsules, gains consider Fig. 44. — From the costal cartilage of an old man. 44 FOURTH LECTURE. able dimensions in many mature cartilages (Fig. 44, a), so that we may meet with enormous capsules of 0. 1 to 0.2 mm. with whole troops of contained cells. Not unfrequently, how- ever, this exuberant increase foretells the approaching disap- pearance of the tissue. Depositions of fat in the cell body, especially in the vicinity of the nucleus, then form very common transformations. They may begin very early. Later, the nucleus frequently becomes invested by a coherent spherical shell of fat (Fig. 44). A subsequent metamorphosis of the apparently homoge- neous intercellular substance into firm, delicate fibrillae, which resist acetic acid, is frequently observed ; this is especially constant in the interior of old costal cartilage (Fig. 44). Calcification is, finally, a quite frequent occurrence in car- tilage undergoing retrogression. Dark granules or crumbs ^^^^^^^_ a „_ of lime salts surround the cells or cell ^gjjpjlj groups, at first in an areolated man- |H ner. They increase in quantity ; the whole intermediate substance acquires a dark, granular appearance ; the cap- sules also become implicated in the deposition, and finally all is black and opaque ; only the cells glisten through ca^no?h7a?nT™aS g g =. caIc:fi - as bright gaps. The older investi- gators could not master this. Now- adays we readily succeed by the aid of decalcification with chromic or lactic acids. This calcified cartilage is, however, far from being or from becoming bone. We shall hereafter return to this subject. Hyaline cartilage substance constituted originally almost our entire skeleton, with the exception of the portions form- ing the vault of the cranium and the bones of the face. This is the transitory cartilage. Remains of the same form the articular and costal cartilages and others. Other masses of cartilage have nothing to do with the skeleton. To these belong the larger cartilages of the larynx, and the cartilage THE CONNECTIVE-SUBSTANCE GROUP. 45 of the trachea and bronchia. The cartilage of the nose also appears to be hyaline. The young, healthy, hyaline cartilage, but not that which is growing old, is without vessels. An interstitial growth is evident ; the increasing size of the cartilage cells, the expansion of the capsules, and the increase of the intermediate substance remove every doubt. Is there, besides, an increase of substance by apposition ? This is not known. The nutrition takes place either from the blood- vessels of a connective-tissue covering, the perichondrium, or, when the cartilage envelopes the bone, from the adjacent vessels of the latter. Elastic or reticular cartilages arise from a supplementary metamorphosis, which commences during the embryonic pe- riod. Their number is not large. Among these are the epi- glottis, the Santorinian and Wrisbergian cartilages of the larynx, the Eustachian tube, and the cartilage of the ear. The arytenoid cartilages of the larynx and the symphyses of the vertebrae present the same peculiarity only partially. In reticular cartilage (Fig. 24) we generally meet with more abundant cartilage cells, surrounded by a homogeneous area, and the remaining intermediate substance permeated by a close net-work of fine elastic fibres. Considerable variations occur, however, in the different varieties of animals (Hertwig). By connective-tissue cartilage is denoted a substance which presents small cartilage cells, surrounded by bundles of a con- nective tissue which becomes homogeneous in acetic acid. This variety is met with, for example, in the cartilaginous lips of the joints, and locally in the vertebral symphyses ; other parts of the latter present hyaline cartilage ; still others, only ordinary connective tissue. In the so-called cartilages of the eyelids only connective tissue can be recognized. We pass to the gelatinous tissue and reticular connective tissue. Cartilage presented the quality of solidity ; gelatinous tis- sue shows the character of softness in the highest degree. Its most simple variety, the vitreus of the eye, is the richest 46 FOURTH LECTURE. in water of all the tissues of the body ; it contains only I. 5 per cent, of solid constituents, of which a part must still be referred to a delicate pellicle surrounding and permeating the whole. And yet the origin of the cartilage and corpus vit- reum are similar. We again meet with rounded, indifferent cells with a homogeneous, intercellular substance. In car- tilage (Fig. 23) the latter early solidifies ; in the vitreus it becomes watery and swells up, so that in a human embryo of four months (Fig. 46) the protoplasmatic cells, meas- uring 0.0104 to 0.0182 mm., are separated by considera- ble intermediate gelatinous tissue. The latter gives the reaction of mucous sub- ul ,G emb 6 ryI Tissueofthevi,re ° usbod> ' of! ' hu ' stance or mucin, that sub- stance with which we have already become acquainted (p. 36), as a product of the meta- morphosis of the epithelial cells. For this reason our tissue has already been given the name of mucous tissue. In the vitreus of the mammalia after birth, the formative cells become arrested, and, widely separated by the interven- ing gelatinous tissue, are only with difficulty recognized. A higher development of the gelatinous tissue is consti- tuted by the so-called enamel organ of the progressing tooth. The teeth, as is known, are formed and concealed in the jaws ; the crown is first formed and the root last. The former is covered, at its commencement period, by a cap or bell-shaped structure, from the concave under surface of which the for- mation of the enamel takes place. Hence the name. Here (Fig. 22) we meet with a net-work of delicate, nucle- ated stellate cells with a varying number of processes. Some- thing like a cell division (6) is occasionally seen. The meshes are filled with a homogeneous gelatinous tissue containing mucus. The same condition prevails, at an early period, in the Whartonian jelly of the umbilical cord. Later, we meet, in THE CONNECTIVE-SUBSTANCE GROUP. 47 addition, with connective-tissue bundles which lie externally to the now flattened cells. The system of spaces is again filled with gelatinous substance. This is a tissue, therefore, which early disappears. Under reticular connective tissue (Fig. 47) we understand a cellular tissue, in the meshes of which lie innumerable lymphoid cells. His has called this adenoid tissue. It appears to be frequently a second- ary formation, proceeding from metamorphosed common connect- ive tissue of the foetal body. Reticular connective tissue pre- sents, in addition, many changes, according to age and locality. As its element (Fig. 8), we meet with a delicate, stellate cell with a nucleus of 0.0059 to 0.0075 mm - an d a moderate-sized protoplasma body, numerous processes, which repeatedly divide and thereby become constantly finer. By the conjunction of such adja- cent branches, which have often arisen under a right angle, smaller nodal points are frequently formed, in which a nucleus is naturally wanting. The delicate, mostly polyhedral meshes are usually rounded, but may also assume an elongated form. They are smaller in the new-born than in the adult. In the latter, during the period of health, the nucleus and cell body are usually shrunken, so that they may be overlooked. In irritated con- ditions, however, the former tense condition is rapidly re established in the swelling tissue. Such reticular connective tissue is met with in the lymph glands, as well as in a series of allied parts of the body, which we will combine as lymphoid organs, such as the tonsils, thymus gland, and Peyer's follicles. The Malpighian cor- Fig. 47. — From a lymphoid follicle of the vermiform appendix of the rab- bit. Fig. i. reticular t'ssue with the meshes, 0, and the remainder of the lymph cells, a ; most of the latter hive been artificially removed. Fig. fc. more superficial. The latter sends out 4 s FOURTH LECTURE. puscles of the spleen also belong here. The tissue of the spleen pulp is still more strongly modified. The mucous membrane of the small intestine also contains our tissue ; although the number of lymphoid cells is here much less, and the cell processes not unfrequently appear broader, lamelliform. In the large intestine, finally, something inter- mediate between our tissue formation and ordinary con- nective tissue is met with. We now turn to the adipose tissue. True connective tissue, to the consideration of which we shall soon arrive, appears partly as a firm, partly as a loose texture. In the latter case, as under the corium, under mucous and serous membranes, etc., it encloses irregular communicating spaces. These are frequently occupied by groups of peculiar cells, overladen with fat. This is fat tissue (Fig. 48, a). I w * \^ U ^ e ce ^ s appear large, measuring 0.076 to 0.13 mm., with nuclei of 0.076 to 0.009 mm. A thin covering closely en- velops a single large drop of fat. The latter, from its strong refractive power, conceals the nucleus and the outlines of the envelope. An appearance is thus caused as if there were free drops of fat, with a dark periphery by transmitted light, yellow- ish, silvery and bright by incident illumination. Still, the always considerable diameter, a slight polyhedral flattening of the elements which are closely pressed together, avert the mistake. Free fat forms spherical drops of every possible size (b). The envelope, after its rupture and the escape of the con- tents, may be demonstrated as a thin, collapsed sac (c), like- wise in an intact condition, after drawing out the fatty con- tents with alcohol or ether. The nucleus, lying quite excen- trically, is readily recognized after tingeing with carmine. Fig. 48, — a, human fat cells, lying together m groups ; b, free globules of fat ; c, empty envelopes. THE CONNECTIVE-SUBSTANCE GROUP. 49 The fat of the human body is a mixture of an oleaginous substance, triolein, which contains in solution certain quanti- ties of more solid matter, tripalmitin and tristearin. When the latter increase, there are, on the cooling of the body at first, depositions of tuberculated forms, and finally of crys- talline. We now perceive irregular needles, at one time tuft- shaped and stellate, radiating from a central point, again in crowded aggregations filling the whole cell. On warming they again disappear. Adipose tissue takes a very active part in the material changes of the body; it is likewise a very vascular substance. As a result of prolonged starvation, in exhausting diseases, a portion of the fatty contents disappear from the cell (Fig. 49). The fat drop (d) is at first but slightly re- moved from the membrane. A spherical cortex of gela- tinous, finely granular sub- stance (protoplasma?), sur- rounds the former ; the nu- cleus now becomes visible. The progressing deprivation of'fat is shown by the cells a to f and h. Finally {g), only a few fat globules remain ; the entire cavity is now occupied by the gelatinous matter. Such examples have been designated, not especially happily, as fat cells " containing serum." If the body outlasts this condition of emaciation, and sub- sequently, by a more abundant nourishment, resumes the old full appearance, the cells have again become filled with the fatty contents. The massiveness of the adipose tissue varies considerably. It is greater in children and women than in men ; more con- siderable in the blooming period of life than in senility. Here, above all, individuality asserts itself very powerfully. In high degrees of obesity, fat cells frequently occur in places where they do not belong, as, for example, between the mus- cular fibres. In far advanced emaciation, the panniculus adi- Fig. 49. — Impoverished fat cells from the sub- cutaneous cellular tissue of a human cadaver. SO FOURTH LECTURE. posus disappears ; though certain parts, like the orbital cavity and the medulla of the central portion of the hollow bones, still obstinately retain the fatty contents within their cells. Adipose tissue is of a secondary nature. It is entirely wanting in the earlier embryo- nic life. The fat cell arises from a metamor- phosis of the cells of the connective tissue. The ordinary flat, lapped and pointed ele- ments of the latter (Fig. SO, a) take up fat drops in increasing quantity (b) ; these flow together, the cell becomes rounder, losing its processes (c), and finally assumes the well-known appearance (d). There is also another coarsely granular connective-tissue cell, to which more attention has only re- cently been called, and which may possibly be transformed into a fat cell. We regard the so-called cell membrane as a boundary layer formed from the adjacent connective tissue. Fig. 50. ^Transfor- mation of the connect- ive tissue corpuscles into fat cells, from a human muscle, serving at the same time as a diagram of the embryo- nic origin. FIFTH LECTURE. CONNECTIVE TISSUE. TRUE connective tissue, the " cellular tissue " of the oldet anatomists, is very extensively diffused throughout the body. As a member of the whole tissue group, it also consists of cells and intercellular substance. The latter, on boiling, does not yield the chondrin of cartilage (p. 42), however, but ordinary glue or glutin. The intercellular substance here shows a further metamorphosis in a double direction ; firstly, into the so-called connective tissue bundles and fibrillae ; and secondly, into the multiform elastic elements. The latter form fibres, reticular fibres, perforated membranes, limiting layers around connective- tissue bundles, and also around spaces which con- tain cells. The longest known is the gelatine yielding fibrilla, the constituent which im- mediately attracts the eye. It appears in the form of a very fine, hyaline, un- branched filament, 0.0007 mm. in diameter, often very extensible, and at the same time possessing elas- ticity (Fig. 5 1 , to the left). These very readily isolat- able fibrillae very commonly unite into sometimes thinner, sometimes thicker bundles (in the fig*ure to the right). Their elasticity very frequently produces an undulated or curly Fig. 51. — Connective-tissue bundles. 52 FIFTH LECTURE appearance in separated portions of the tissue. The inter- weaving of the fibres varies considerably. When loosely in- terwoven, the bundles running in one plane are united by homogeneous, membranous intermediate substance. Acetic acid, an important reagent, causes the bundles to swell up rapidly and the fibrous appearance to disappear. By washing out, or neutralizing that reagent, the former ap- pearance is restored. Previously, the excess of connective-tissue fibrilla very fre- quently concealed the intermingled elastic elements. Now, in the acid preparation, the latter make their appearance Fig. 52. — Human elastic fibres. (Fig. 52). We perceive, firstly, the finest, frequently corru- gated fibrillas without ramifications id). They remind one of the connective-tissue fibrillae ; but the darker appearance, and the power of resisting acetic acid, permit of no mis- take. Other elastic fibres are larger. Very frequently there are ramifications, and by the com- munication of the branches an elastic net-work is formed. We perceive such an one at b, with large meshes, and fibres which measure only 0.0014 to 0.0025 mm. in thickness. CONNECTIVE TISSUE. 53 If we search further, we meet with transitions to broader and thicker ramified fibres (c), which, in contradistinction to the extensible finer ones, gradually assume a considerable inflexibility and brittleness. Their diameter may increase to 0.0056 to 0.0065 mm. In other places, the walls of the larger arteries, we find co- herent elastic membranes, in which fine fibrillse and reticular fibres are embedded as ledge-like thickenings. There also occur homogeneous layers of elastic sub- stances which are perforated with little holes (Fig- 53i l )- Between these and a small- meshed reticulum of very broad, flat elastic fibres (2) it is, indeed, often impossible to make a demar- cation. These changing elastic ele- ments are met with in still another condition. They form a structureless sheath around many connective-tis- sue bundles. As surely as an innumerable quantity of these bundles are without envelopes, and exhibit only a fibrillated cord, even so little can the presence of a sheath around others be doubted ; as on those which pass from the arachnoid, at wo *rkfrSTthe aorta : the base of the brain, to the &£ °* : 2 - of the larger blood-vessels, on the fasciculi of the tendons, on much of the subcutaneous cellular tissue. If we apply re- agents which produce considerable swelling, as acetic acid, a strange appearance is caused (Fig. 54). The sheath is torn into transverse portions, and these rapidly contract between the protruding portions of the connective-tissue bundle to Fig. 54. — A con- nective-tissue bun- dle, from the base of the humanbrain, treated with acetic acid. 54 FIFTH LECTURE. very delicate rings, which have a striking resemblance to an elastic fibre. Cotton fibres undergo a very similar change on the addition of ammoniac copper ; only, everything is here more massive and easier to observe. The most difficult part in the investigation of the connective tissue is formed by the cellular elements, the connective-tis- sue corpuscles of an earlier period. After manifold strayings, a greater light has only of late years been disseminated. Since the cells were, as a rule, usually concealed by the substance of the fasciculi, acetic acid was formerly generally used for the recognition of the former. This, and even water, immediately distorts the cells into caricatures. The latter have been almost universally known and described for tens of years ; and capital has been made of them ! The cellular elements are distinguished into non-essential migratory, and essential fixed. The former are lymphoid cells, which, having escaped from the blood and lymphatic vessels, slowly wander through the channels of our tissue. The ordinary fixed connective-tissue cell appears as a simple or complicated lamellar structure. An oval nucleus is surrounded by some protoplasma. The thin structure becomes extremely pale and veil-like at the periphery, and runs out into points or fibrillar. Very frequently, how- ever, there is also a vary- ing number of lateral plates resting at different angles over the middle of these chief plates (Fig. 55, a), so that a certain resemblance to an irregular, crumpled shovel edge is produced (Ranvier, Waldeyer). Such cells lie in the firm connec- tive tissue, in the spaces between the fasciculi, and have, according to our views, as- sumed the described forms subsequent to the growth in thick- ness of those fasciculi. The procedure may be illustrated by Fig. 55. — Cells of human connective tissue ; a, flat and shovel-shaped elements ; b, coarse granu- lar cells. CONNECTIVE TISSUE. 55 placing a lump of warm, soft wax between the points of three fingers and pressing them together. There is still another cell formation met with in connective- tissue structures ; they are often very rare ; in places, how- ever, quite numerous. They are larger, coarse granular structures, with a nucleus and an either rounded or spindle- shaped body, without that system of lamellae and processes of the previous form (J>). They have been met with in the vicinity of vessels, especially arteries, and have received the name of plasma cells (Waldeyer). Fat cells may proceed from both varieties of cells, the flat and the coarse granular (p. 49). Connective-tissue cells also assume an extremely peculiar appearance from receiving melanine granules into their body (Fig.. 9). This is the "stellate pigment cell" of the earlier histologists. The coal or brown-black molecules are smaller than in the pigmented epithelium (p. 30). In man such cells are limited almost exclusively to the eye. In the lower ver- tebrates, such as many of the amphibia, this process of pig- ment embedding is enormously diffused, so that in every little piece of connective tissue the strangest cells are met with, occurring in every possible stellate form. The flat connective-tissue cells and their colored associates (Fig. 56), show a slow, but unmistakable vital contractile power. This is not yet recognized in the plasma cell. Connective tissue, whose immense diffusion in the humati body we have al- ready mentioned, by the „ , „ , , , . . . J J Fig. 56.— Gradual change of form of a pigmented arrangement and interlaC- connective-tissue corpuscle from a water newt, during & 45 minutes. ing of its bundles, by its very dissimilar proportion of elastic elements, the extremely variable vascularity, and, finally, by the commingling of insol- uble elements, forms substances which appear to the naked 5 6 FIFTH LECTURE. eye as quite dissimilar things, and which in reality are very nearly related. The usual system of anatomy recognizes primary bundles, that is, simple fibrous cords. A portion of these, held together by loose connective tissue, constitute secondary bundles, and from these latter tertiary are formed. We have, firstly, as a badly selected name runs, " form- less " connective tissue. Soft and extensible, it forms the general filling up substance of the organism. Membraniform connective-tissue bundles with homogeneous interstitial sub- stance (Fig. 51), form thin lamellae, which superimposed on each other at various angles, incompletely limit cavities. These v are the so-called " cells'' of the older anatomists, who gave our tissue the name of cellular tissue. The lamellae are often nearly in contact with each other, but the space enclosed by them may also be completely filled by collections of fat cells. Where structureless connective tissue occurs in greater quan- tity it has received special names. Thus, one speaks of sub- cutaneous, submucous and subserous connective tissue. Elastic elements are here met with, sometimes scanty, some- , ; mes more profuse, but never in excess. We now come to the formed connective tissue, with its nu- merous varieties. This constantly arises from the formless variety without any sharp demarcation, so that this division of the anatomists is entirely artificial. We enumerate here: i. The corneal tissue. The cornea has on its anterior surface stratified pavement epithelium, on its posterior a simple cell covering. Under both epithelial coverings there is a hyaline layer. The anterior is called the lamina elastica anterior, the posterior the Descemet's or De- mours' membrane. The hyaline corneal tissue consists of a net-work of decussating bundles, which may be divided into fibrillae of extreme delicacy. The whole is permeated by a system of passages which have a sort of parietal layer. In these lie the " corneal capsules," which are flattened cells, comparable to a paddle-wheel. Wandering lymphoid cells are also not wanting. CONNECTIVE TISSUE. 57 2. Tendinous tissue. Longitudinal bundles of a fibrillary connective tissue with an elastic boundary layer arranged in a compact manner are met with. Between them one recog- nizes in transverse sections a system of indented and stellate spaces. In these lie, arching over the connective-tissue bundles, ordinary lamelliform and shovel-shaped connective- tissue cells, and also, isolated lymphoid corpuscles. Only scanty, fine, elastic fibres occur in this extremely bloodless tissue. 3. The ligaments are, with the exception of the elastic, formed like the tendons. 4. The connective-tissue cartilage (see p. 45). 5. The so-called fibrous membranes. Firmly woven, non- vascular structures with a varying intermixture of elastic ele- ments. Among these are the dura mater of the brain and spinal cord, the sclerotic of the eye ; the firm envelopes of many organs, for example, of the kidneys, testicles, and spleen ; furthermore, the fascias of the muscles, the coverings of the nerve trunks (the perineurium or neurilemma), the covering of the cartilage and bone (the perichondrium and periosteum). The latter is permeated by numerous blood- vessels, but which serve principally for the nutrition of the invested bone. 6. The serous membranes , which formerly were erroneously considered as entirely closed sacs, consist of a but slightly vascular net-work of connective-tissue bundles, occasionally with a considerable contingent of elastic-reticular fibres. The free surface is covered by endothelium. To this variety be- long the pleura, pericardium, peritoneum and tunica vaginalis propria of the testicle. As more incomplete structures, we mention the arachnoid membrane of the brain and spinal cord, the synovial capsules (having a serous membrane only at the sides, and here covered by a simple layer of epithelial cells), and also the mucous pouches and the sheaths of the tendons. The serous cavities, like the passages between the connective-tissue bundles, must be regarded as belonging to the lymphatic apparatus, as we shall perceive hereafter. 3* 58 FIFTH LECTURE. 7. The corium. More firmly interwoven, decussating con- nective-tissue bundles with numerous elastic fibres. The closely interwoven, very vascular tissue projects towards the surface in small papillae of varying shape, in the form of the tactile bodies. It is continuous below, without any sharp demarcation, with the subcutaneous cellular tissue. Other foreign constituents consist of hairs, involuntary muscles, glands, nerves. As a covering, we are already familiar with the epidermis, the thickest pavement epithelium of the body (P- 32). 8. The mucous membranes. Also extremely vascular, but less compactly arranged, and with fewer elastic elements. In places it is enormously rich in glands. Smooth muscles form a widely diffused constituent. The surface frequently projects in papillae. The ordinary connective tissue of the mucous membranes may, however, be replaced by reticular connective tissue (p. 47). We already know that the epithe- lial covering differs exceedingly (pp. 30, 33, and 34). 9. The vascular membranes of the central nervous organs and of the eye ; that is, the pia mater, choroidal plexus and choroid. A thin, soft connective tissue, in the' choroid a reticulum of pigmented cells, here shows throughout an enor- mous wealth of blood-vessels. 10. In the structure of the vascular walls connective tissue plays an important r61e. Nevertheless, the elastic element often increases to such an extent, that the connective-tissue bundles and cells recede. One speaks then of " elastic " tissue. 11. This predominance of the elastic elements is also pre- sented by the ligaments and membranes of the respiratory organs, and likewise by the tissue of the lungs. The same is also seen in the outer layer of the oesophagus, the yellow ligaments of the vertebral column, and the ligamentum nuchae of mammalial animals. Many of the latter structures have lost all connective-tissue bundles. Connective tissue possesses but slight vital dignity ; it comes into consideration in the structure of the organism, in CONNECTIVE TISSUE. 59 consequence of its physical properties. Only the more vas- cular connective-tissue structures take a more active part in the normal material changes. During abnormal conditions, however, our tissue assumes a new and more vigorous life. From the cells other tissue elements may be formed. To determine the magnitude of this participation more accurate studies are indeed necessary, for the wandering lymphoid cells also play their part, and, in our opinion, in a very important manner. We also mention the origin of the con- nective tissue. The terminations are again similar to those of cartilage. Mem- braneless protoplasmatic stellate and spindle cells are noticed at an early peri- od, held together by a scanty intercellular substance, which is at first homogeneous. A transformation soon takes place in the latter and in the cells, the processes of the latter dividing into groups of fine connective-tissue fibrillae (Fig. 25, b). These bundles of fibrillae gradually ap- proach the cell nucleus. The original cell protoplasma also becomes changed into bundles of fibrillae ; new protoplas- ma, taking the place of the old, surrounds the nucleus, to subsequently pass through the same process of metamorphosis (Fig. 57, A), till at last the cells lie outside of their children, that is, the bundles formed from them, in the shape of lamellae, with notched margins, or irregular, paddle- wheel-like structures (see above). In this intercellular substance, the genesis of which we now understand, the formation of elastic fibres and reticular fibres also takes place subsequently (B). How far the cellu- lar elements participate in this requires still more accurate investigation. Fig. 57- — From the Iiga- mentum nuchas of a hog's embryo. A, side view ; a. spindle cells in a fibrous ba- sis substance, b ; B s the elastic fibres c, brought out by boiling in' a solution of potash (alcohol preparation). SIXTH LECTURE. BONE TISSUE. We now turn to the most complicated variety of connective substance : we refer to the osteoid or bone tissue. It is distinguished for its considerable hardness and firm- ness. In man, this member of our tissue group is, with the exception of a covering to the tooth root, limited exclusively to the bones. The anatomists divide the latter into long or cylindrical, broad or flat, and, finally, short or irregular bones. Let us begin with the middle portion or diaphysis of the former, taking a radial longi- tudinal section sawn out from the dry femur (Fig. 58). A very peculiar appear- ance is presented. The thin lamella is permeated by a system of longitudinal canals, connected, in a reticular man- ner, with a medium width of 0.1 128 to 0.0149 mm. (a). The transverse branches open out onto the surface of the bone, as well as inwards into the medullary canals, and re- ceive the nutrient vessels from both sides. They bear the name of the medullary or Haversian canaliculi. Tr; nsverse sections (Fig. 59) naturally present an entirely different appearance. The rounded and oblique spaces (c) Fig. 58. — Vertical section through the human femur ; a, medullary canals ; b, bone corpuscles. BONE TISSUE. 6\ y '.,W:- Fig. 59. — Transverse- section of a humnn metacarpal bone : a, outer surface ; c. medul- lary canals with the special lamellae ; d, inter- nal general lamellae ; e, bone corpuscles. are transversely or obliquely opened longitudinal canals. Communicating horizontal canals are now also seen opened in a longitudinal direction or obliquely. The bone substance pre- sents, as is shown by the transverse section, a lamel- lated structure. There is a double system of layers, however. Firstly, we meet with plates which pass through the entire thickness of the bone, in contact ex- ternally with the periosteum and internally limiting the great medullary canals. They are called general or funda- mental lamellae (a, d). An- other uncommonly abundant system of lamellae surround the individual medullary canals with a varying number of layers. These are the special or Haversian lamellae (around c). The thickness of both varieties of lamellae varies from 0.0065 to 0.0156 mm., and the ar- rangement is often far removed from making any claim to regularity. This stratification may also be recognized in longitudinal sections as a system of lines, though with less distinctness. A plate of dry bone, let it be taken from where we will, always presents a further extremely peculiar structural con- dition ; it appears black by transmitted and white by incident light, and consists of a marvellously complicated very fine canal-work with indented and radiated nodal points. The former passages are badly enough named calcareous canali- culi : the dilatations bear the name of the bone corpuscljs r lacunae (Figs. 58, 59). The form of the lacunae (Fig. 60, a) may be illustrated by calling them lens-shaped, or by comparing them to the figure 62 SIXTH LECTURE. Fig. 60. — Lacunae (tr, a) with their numerous offshoots, opening into the transversely divided Haversian canal produced by two human hands when their volar surfaces rest over each other. The length is 0. 1805 to 0.0541, the breadth 0.0068 to 0.0135, the thickness 0.0045 to O.009 mm. The offshoots of this system of cavities, very nar- row canals of 0.0014 to 0.0018 mm. diameter, permeate the entire tissue in innumerable multitudes, ramifying irregularly in a radial direction. They open (1) in the Haversian canals (b), (2) on the surface of the bone, and (3) in the large medullary cavity in the interior. Transverse and longitudinal sections (the tan- gential must also be added) teach this most distinctly. In the dried bone, the marvellously complicated system of canaliculi has become filled with air in a condition of the finest division. An earlier epoch erroneously assumed the contents to be inorganic hardening material, to be the finest molecules of the so-called bone earths. Hence the name of the " calcareous canaliculi." If we place the small thin plate in turpentine oil, the thousands upon thousands of finest canali- culi rapidly fill with the fluid through capillary attraction. The bone corpuscle now presents the appearance of a cavity; the fine canaliculi disappear more or less in the basis sub- ^s^. stance. But what does this remarkable canal work contain during life? We answer to this, there is in the lacunae a protoplasmatic membraneless cell (Fig. 61, b). Whether this bone cell, the equivalent of the connective-tissue corpuscle, sends off capillary offshoots into the lacunae, which is very prob- able, we do not yet know. The latter canalic- ular system is certainly filled with transuded blood plasma. This fluid must, besides, be rather stagnant, for the frictional Fig. 61. — From the fresh ethmoid bone of the mouse; a basis substance; £, the bone cell. BONE TISSUE. 63 resistance here imposes a veto to the circulation which is with difficulty removed. Are the lacunae and calcareous canals only cavernous sys- tems excavated in the hard, solid basis substance, or have they a special parietes ? After energetic macerating media, the previously decalcified bone presents a thin resistant boundary layer around the lacunae and canaliculi. It appears to be a decalcified elastic substance. It was formerly errone- ously considered to be a cell membrane. Having become familiar with the most essential portion of the structure in the diaphysis, let us now turn to a very short discussion of the other parts of the skeleton. The beauti- ful regularity here disappears, sometimes to a less, sometimes to a greater degree. Even in the epiphyses of the cylindrical bones, in consequence of the thinness of the osteoid plates, the systems of lamellae are present in a far less developed condition around the Haversian canals, and the inner funda- mental lamsllae are absent. In spongy bone tissue the laminar arrangement may still be distinctly recognized in the thick trabecular and plates, while it disappears more and more with the decrease in size. In the cortical layers of flat bones, the medullary canals run parallel to the surface, gene- rally starting from a point and assuming a radiate direction. In the short bones the course generally preponderates in one direction. Funnel-shaped apertures of the Haversian canali- culi may join together and form small medullary cavities, the prefigurations of the larger, etc. The bones contain but little water, the compact having 3 to 7, the spongy 12 to 30 per cent. The organic, form-deter- mining basis, amounting from 30 to 45 per cent, in the dry bone, is transformed by boiling into glutin, that is, the ordi- nary glue of the connective tissue. This is diffusely hardened by the embedded bone earths. By this is understood a mix- ture, amounting from 51 to 60 per cent, of lime salts with a slight admixture of magnesia salts. The bone earths yield about 86 per cent, of phosphoric acid, 9 of carbonate of lime, 3.5 of fluoride of calcium, and 2 of phosphate of magnesia. 64 SIXTH LECTURE. When the bone is carefully decalcified its texture remains as of old. It is easy to cut the mass, which has now become semi-transparent. It is badly enough named the bone car- tilage. In the mechanical construction of the body, the bones come into consideration by reason of their solidity. They serve as a protection to softer organs, and form systems of levers moved by muscles. The less the proportion of bone earths contained, the greater the flexibility and cohesion. A preponderance of these mineral substances, on the contrary, renders the bone inflexible and brittle. The mutability of its materials is very considerable. In harmony with this is the double system of canals for the blood-vessels and lacunae. The larger cavities of the bone become filled with so-called bone marrow. This occurs in a double form, though with transitions. In the central portion of the long bones it appears as a yellow marrow, that is, as fat cells contained in loose connective tissue (p. 50). In the epiphyses, on the contrary, as well as in flat and short bones, we find a softer reddish or red substance containing, together with scanty connective tissue and isolated fat cells, very numerous lymphoid cells of 0.009 to O.oi 13 mm. The latter elements, according to Neu- mann and Bizzozero (p. 25), present transitions into red blood corpuscles. Finally, we meet in the bone marrow, especially towards the surface, the myeloplaxes, which have become familiar to us in Fig. 13. The veins are without endothelium ; they consist only of an adventitia (Hoyer). Altogether, the vessels of the medulla promise still further interesting conclusions. We now turn to the theory of the origin of the bone tissue, osteogenesis. It forms a very difficult and complicated sec- tion of histology. With the exception of a number of the bones of the cranium and face, as we have already said, all portions of the skeleton are preformed in cartilage. They afterwards present bone substance. During a long period the direct metamorphosis of the BONE TISSUE. 65 former tissue into the latter was unhesitatingly accepted. Sharpey, Bruch, H. Mueller, first demonstrated the erro- neousness of this hypothesis. Disregarding rare exceptions, the facts run, nowadays, in this way : The calcified cartilage does not become osteoid tissue, but rather melts down, and in the system of cavities thus obtained, the bone substance produced by the peri- osteum is established as a new tissue. If we take a cartilage which is destined to end in this man- ner, two different processes are presented : 1. A local softening of the cartilage tissue (of the celis as well as of the intercellular substance) has taken place from the surface in an inward direction. Very irregular, manifoldly ramified passages have thus been formed. Vessels have grown into the latter from the perichondrium, accompanied by lymphoid and unripe connective-tissue cells. This sub- stance has been not badly named the cartilage marrow. Until recently, it was erroneously assumed that the so-called cartilage marrow cells represented derivatives from cartilage cells which had penetrated the softened portion. 2. In the centre of such a cartilage, a calcification of the intercellular substance (p. 44) and very generally, also, an energetic forma- tion of so-called ri > «,,*> ei^.o®^-, ^ ,s . daughter cells f l/ft' fe^^^SfeM" occurs (Fig. 62,. fWfe3«|^^SS been called the ^Ms§2^^%«L point of ossifi- .- 111 Fig. 62.— Dorsal vertebra of a human fetus of ten weeks in vertical CailOn D a a i y sect ; on . Ui calcified ; *, soft cartilage. enough, we add. For, although a further melting down of the calcified tissue occurs here forthwith, and, in the spaces thus formed, the first deposition of osteoid tissue commences immediately after- wards, this calcified cartilage has nothing whatever to do with the latter. The two metamorphoses just mentioned proceed rapidly 66 SIXTH LECTURE. side by side and against each other. The calcification of the cartilage spreads peripherically ; the liquefaction and re-forma- tion of the cartilage canals is constantly increasing in extent, and likewise in the domain of the calcified cartilage. Fig. 63. ^Ossifying border of a phalangeal epiphysis of the calf, in vertical section. At the upper part, the cartilage, with its irregularly disposed capsules, containing daughter cells;' a, smaller medullary spaces, appearing in part as though closed, drawn empty ; 6, the same with narrow cells ; c, remains of the calcified cartilage ; rf, larger medullary spaces, on the walls of which are depo- sitions of thinner or thicker bone tissue, and in the latter case stratified ; e, developing bone cell ; /, an opened cartilage capsule, with an embedded bone cell ; g. a partially filled cavity, covered externally with bone substance and containing a narrow cell ; /*, apparently closed cartilage capsules containing bone cells. The latter must naturally first become physiologically decalcified before undergoing solution. This removal of a but just deposited lime salt is, up to the present time indeed, somewhat enigmatical. Let us look at Fig. 63. At the upper part, the cartilage BONE TISSUE. 6 7 still presents the old soft appearance. The cartilage cells lie here, in an epiphysis, irregularly. In a diaphysis they would be seen pressed together in longitudinal rows, or " ranked," as it has been expressed. Below, however, we meet with a cavernous tissue, the spaces of which, as a result of the prepa- ration, in places no longer lodge the cartilage marrow con- tents (a), while it still remains preserved in others {b, d). Cloudy, dark trabecular of the most irregular form constitute the last remains of the liquefying decalcified cartilage (c). Even these trabecular remains are deprived of further re- pose. Fig. 64.— Transverse section from the femur of a human embryo of about eleven weeks ; a, a transverse, and b, a longitudinally divided medullary canal ; c % osteoblasts ; d, the more trans- parent, younger, e, the old?r bone substance ; /, lacunae with the cells ; g, cells still limited to the osteoblast If the contents of these cavernous passages are attentively examined at this period, their peripheral cells are found to have assumed an anomalous shape. They resemble, with their cubical bodies (Fig. 64, c), an irregular, badly developed cylinder epithelium. Gegenbaur, their discoverer, has 68 SIXTH LECTURE. called them osteoblasts — and rightly, for they form the osteoid tissue. As in a line of inordinately crowded soldiers, one or another will be pressed out in front, so does it happen to cer- tain of these osteoblasts (g). They now assume indented or stellate shapes ; homogeneous, but very soon diffusely calci- fied intercellular substance then appears around them. The latter as a thin layer — we might say, covering the irregular surfaces of the still remaining calcified cartilage trabeculae like a wax impression — is the first lamella of the osteoid sub- stance ; the indented osteoblasts form the first bone cells, however. Our Fig. 63 shows this at its upper portion (a, a, a), also at the left, halfway up (c, d). Concerning the conception of the intercellular substance, whether it arises from a secretion ot the cells or from the metamorphosed cell bodies, the same uncertainty of opinion prevails as with other members of the connective substance group. We have here still more peculiar illusive appearances to consider. It is comprehended that by the continual lique- faction of the cartilaginous trabeculae the cavities of the tissue become opened, and must then serve for the deposition ot bone cells and homogeneous basis substance. When the conditions are as at/ of our Fig. 63, the matter is at once clear, the place g is also, in a measure, appreciable. When, however, the cavities are ruptured from below or above, this does not fall within the plane of the section, and we have the deceptive appearance of closed cartilage cavities with endo- genous bone cells. This, which thus occurred for the first time, is repeated in rapid sequence manifoldly after each other. Lamella upon lamella with enclosed bone cells result (Fig. 63 in the lower half). We obtain in this way a stratified osteoid tissue. The remains of the cartilaginous tabecuke disappear more and more with the continuing process of liquefaction. But this thing, in its wild, confused irregularity is very dif- BONE TISSUE. Qg ferent from the bone tissue which appears in such elegant regularity at a later day.* Now, how does the latter arise from the former? Two different opinions exist on this subject. According to the first, and we adhere to this for the most part, the osteoid tissue, which is formed at the expense of, and within the fcetal cartilage, the so-called endochondral bone, has not a happy life. It yields to an early death, a speedy process of lique- faction, in order to permit the formation of the large medul- lary canals. On its surface is deposited, by the periosteum, into which the perichondrium has now become changed, and with the aid of a deeper osteoblastic layer, new bone tissue which, with a supplementary loss of its inner layers, persists in the outer portions and causes the regular, beautiful struc- ture of the bone. This may be denoted as the apposition theory of osteogenesis. Koelliker has recently re-entered the lists for this with great energy. Another view rejects the resorption of the endochondral osteoid tissue absolutely, and explains the transformation of the irregular cavernous bone of the commencement period into the regular of the later period of life, by interstitial growth alone. An industrious Russian investigator, Strelzoff, supported by German predecessors, has recently endeavored to substantiate this with greater accuracy. We cannot enter further into this actually burning contro- versy. The truth, according to our views, lies more towards the former side. Nevertheless, the young bone certainly has an interstitial growth, which ' Koelliker also, naturally, acknowledges ; but to what degree this occurs no one can, at the present time, state with accuracy. A resorption is surely, also, not wanting in the normal bone. This is proved by the 'Haversian spaces of healthy bone, if we disregard the long known abnormal resorption processes. Those who deny the demonstrative force of such facts are, in our opinion, not to be reasoned with further. * The central portion of the cylindrical bone has also once had the same cav- ernous structure that is presented by the epiphysis. 70 SIXTH LECTURE. Let us then investigate these Haversian spaces. Our figure (Fig. 65), shows us three Haversian lamellar systems. The two hatched ones {a, a), present inter- nally an indented resorption line (b, b). New bone lamella:, maintaining the outline, have been deposited on this. To the right (c), a second liquefaction has overtaken the latter, for which a new lamellar formation endeavors to compen- sate 4 Fig. 65. — A human metacarpal bone in transverse section : «*, a Haversian lamella system of the ordinary variety ; >, bright zones ; c, nuclei ; d. interstitial granules (alcohol preparation). absorption of water. When the sarcous por- tion has been torn by traction, the sarcolemma, or primitive sheath (Fig. 76, a), appears most distinctly. It is a hyaline, aggregated, elastii membrane. Directly superimposed on this envelope, one meets with numerous oval nuclei (Fig. TJ , c), measuring 0.0074 to 0. 01 13 mm. The lateral surfaces, and the pole of the latter, are sur- rounded by a small quantity of a protoplas- matic substance (d). This, a cell rudiment,, has been called a muscle corpuscle (M. Schultze). This is the condition of the human muscle. In the lower animals, however, the nucleus also lies in the interior, and the same is the case in our heart muscle. All this is readily understood. Extraordinary difficulties are, on the contrary, presented by the sub- stance surrounded by the sarcolem- ma, the sarcous elements. It is, in the first place, very changeable, and, with its infinitely delicate structure, we soon arrive at the limits of the microscopic solution possible at present. In many cases, and regularly after the use of certain reagents, the sarcous elements appear as a bundle of fine, transversely striated, elongated fibrillar, measuring O.OOi I to 0.0022 mm. It would appear, therefore (after the manner of the connective tissue), to be a primi- tive bundle. With other methods of treatment, and also in the living muscle, we MUSCULAR TISSUE. 83 see little or nothing of these fibrillae. The filament permits the recognition of transverse lines only. It now appears, comparable to a Volta's pile, to consist of discs piled upon each other. The fibrillae, as well as the transverse discs, were both re- garded as normal, pre-existing structures, and in this, accord- ing to our view, a double error was committed. In the living muscle there are neither fibrillae or discs. The first who here trod the correct path, a generation since, was the Englishman. Bowman. It is true that, with the opti- cal aids of that period, he was unable to exhaust the subject ; but we are also unable to do so at the present time, although we have at our disposal much more perfect microscopes. According to the view of this distinguished investigator, the muscular filament consists essentially of an aggregation of small bodies, the sarcous prisms or sarcous elements which, united and holding to- gether in the transverse direc- tion, afford the appearance of a disc or a thin plate {disc according to Bowman) (Fig. 77, a) while, disposed in the longitudinal direction, they pre- sent that of the fibrillae (Fig. 78, I, a, b). Accordingly, neither fibrillae or discs pre-exist. There is merely a disposition present in the muscular filament to become divided, sometimes in the transverse, sometimes in the longitudinal direction. The cohesion in the latter direction is certainly the strongest ; for the fibrillae in the dead element are met with more fre- quently than transverse plates. Let us next examine the muscular filament somewhat more closely, with the aid of the highest magnifying powers. The transverse lines are readily resolved into dark trans- verse zones, separated by more transparent ones (2, a, b). Fig. 78. — Two muscular fibrillae. from the proteus. I, and the hog, 2, magnified i,o:>o times ; a, sarcous prisms ; b, bright longitudinal connecting medium. At a* the sarcous elements are further apart, and the transverse connecting medium is visi- ble ; c, nucleus. 84 EIGHTH LECTURE. The former consist of sarcous elements (a*) placed nearer each other. This may also be recognized without trouble by the aid of good and strong magnifying powers. They are elon- gated prismatic bodies, measuring 0.0017 mm. in the proteus, 0.0013 m trie fr°g> 0.00 1 1 to 0.0012 mm. in the mammalia and man. The sarcous elements must, naturally, be joined one to the other. If we split off one of the finest longitudinal filaments, that is a so-called muscular fibrilla (1), the longitudinal series of sarcous elements (a) are held together by the transparent longitudinal connecting medium (t>). If we examine a mus- cular filament split up into transverse plates, the dark and light transverse zones are found to be connected by a trans- verse connecting substance, which extends over the outer surface from a and b of our Fig. 78, 2. Here the longitudinal connection is naturally, completely dissolved. Up to about ten years ago, we thought the matter might thus be passably explained ; but newer observa- tions have been added and further doubts have arisen. In the year 1863, the Englishman, Martyn, had already seen a dark trans- verse line in the transparent longitu- dinal connecting medium. These ob- servations were afterwards corroborat- ed and extended by Krause (Fig. 79). Let us name this thing (a), therefore, Krause's transverse line or disc. But with this we have still not reached the end. At the same time another competent investigator, Hen- sen, found the dark transverse zone, the transverse series of sarcous elements, divided by a transparent transverse line, This is the Hensen's middle disc. Granules which were contiguous above and below to Krause's transverse line Fig. 79. — Krause's transverse discs ; a, a, I, a muscular fibnlla without ; 2, one with strong longi- tudinal traction, both very strong- ly enlarged (MartynJ ; 3, muscu- lar filament of the dog imme- diately after death. MUSCULAR TISSUE. 85 Fig 80.— Piece uf a dead muscular fila- ment from the fly, after Epgelmann ; a, trans- verse discs ; b, acces- sory discs. were subsequently designated by Engelmann as accessory discs (Fig. 80 b). From these singular observations, which touch and, perhaps, in part, exceed the limits of microscopic analysis, we are at present un- able to derive an anyways reliable conclusion. An old observation of Bruecke's is also in- teresting. The Bowman's sarcous elements refract the light double, the longitudinal con- necting medium refracts simply. We pass, finally, to some more simple structural conditions of the transversely striated muscle. Among these are the so-called interstitial granules, small fat molecules (Fig. "]"] , d), which, commencing at the nuclear poles of the muscular corpuscles, permeate the filament in a linear longitudinal direction over shorter or longer distances. The preparation of transverse sections through the frozen muscle (Fig. 81) was taught by Cohnheim. Groups of sarcous elements (a) are here recognized as a mosaic of small areas of transverse to hexagonal shape. Enclosing these are noticed a system of transparent, glistening lines (c) which must belong to the transverse connecting medium. A modification of the transversely striated muscles is met with in the tongue and heart of the mammalia and man. These are rami- fied and reticularly connected filaments. In the former organ are noticed frequently repeated divisions at acute angles. In the heart (Fig. 82), a narrow-meshed net-work is constituted by the abundant formation of anasto- moses. A sarcolemma is probably wanting in these dimin- ished filaments. The latter, furthermore, show strongly pro- nounced transverse and longitudinal markings. It is an interesting circumstance, finally, that this muscular reticulum consists of cemented cells (Fig. 82, to the right). Fig. 81. -Trans- verse section through a frozen muscle of the frog ; a, groups of sarcous elements ; c, transparent trans- verse connecting me- dium ; b, nucleus. 86 EIGHTH LECTURE. Fig. 82. — Muscular filaments of the heart. To the right appear transparent boundaries and nuclei. The remaining transversely striated muscles show the fila- ments arranged parallel, slightly prismatically flattened against each other (Fig. 83, a), and in man containing the muscular cor- puscles (e) in their periphery. Between them occurs a scanty amount of connective tissue, the highway for vessels (d) and nerves. With rich living this may develop fat cells (Fig. 50). A varying number of muscu- lar fibres unite into bundles, measuring 0.5 to 1 mm., which are separated from the neighborhood by abundant connective tissue. Such primary bundles then unite into secondary ones. The con- nective tissue covering of the muscle bears the name of peri- mysium externum, in contradistinction to the perimysium internum of the inner connecting substance between the fila- ments and bundles. Smooth muscles also show a bundle-like grouping. We come, finally, to the con- nection with the tendons. The latter tissue has already been de- scribed above, page 57- With a rectilinear insertion (Fig. 75) the sarcous substance (a) appeared to pass immediately over into the tendinous bundle (b) ; not so, however, with an oblique insertion, where an inter- rupted muscular end becomes ap- parent. Weismann first obtained convincing appearances here by Fig. 83. — Transverse section through the human biceps brachii ; a, the muscu- lar fibres ; b, section of a larger vessel ; c, a fat cell lying in a large connective- tissue interstice ; d, capillaries cut across in the thin connective-tissue layer be- tween the several fibres; e, the nuclei (niuskelkorperchen) of the latter lying On the sarcolemma. MUSCULAR TISSUE. 87 means of potash solutions (Fig. 84). The end of the filament, sometimes rounded, at others pointed, and again irregularly- shaped, is always covered by sarcolemma (b). The tendinous bundle is attached by a corresponding excavation (c, d). During life the whole is united in the firmest manner by means of a cement substance. The muscular filaments are of various lengths, but according to Krause do not exceed four centimetres. They termin- ate, therefore, repeatedly far from the end of the entire muscle, in its interior and in the form of points. The muscular filament consists of vari- ous albuminous bodies. The sarcous elements, transverse and longitudinal connecting medium, are formed of modi- fied members of this so little understood group of substances. The proportion of water present is considerable, corresponding to the -softness of the tissue. We turn to the embryonic development of our tissue. * The elements of the smooth muscles present nothing but cells grown into a spindle shape (Fig. 74). The rounded or oval developing cells {a, b) simply exchange their protoplasma with the homogeneous sarcous substance, the nuclei assume the rod form, and an envelope is altogether .wariting. We have already (Fig. 27) briefly mentioned the origin of the transversely striated fibre. After the example of Schwann, they were formerly considered to arise from the fusion and metamorphosis of formative cells arranged in rows. In the heart muscles, as we have already seen, something of the kind does, in fact, take place; but not so in the remaining voluntary muscles. Here the element is a single cell, which, it is true, undergoes a much more extended development than the contractile fibre cell of the smooth tissue. -Two muscular fibril las (<*,_ b) after treatment with solution of potash, the one still in connection with the tendon (r), the other separated from the same (,/). EIGHTH LECTURE. In small embryos one obtains thin (0.CO45 to 0.0068 mm.), but long (0.28 to 0.38 mm.) spindle cells, with one or two vesicular nuclei, and in the centre commencing for- mations of transverse lines, that is with a transformation into sarcous elements. With an increase in nuclei, the structure increases not only in length but also in breadth. The transverse striation advances towards the ends, but leaves the axial portion still free. We still meet here with the old protoplasm. Later, however, after the longitudinal markings have also appeared, this protoplasma has disappeared, with the exception of a slight residue, which surrounds the nucleus and thus forms the muscle corpuscle. We find the latter, at last, in mammalia and man, displaced towards the periphery. We have already above (p. 82), declared the sarcolemma of the transversely striated filament to be a homogeneous boundary layer furnished by the adjacent connective tissue. All investigators do not, however, coincide with Our view. The muscular filaments of the new born are still much finer than those of the adult. The subsequent increase in thick- ness explains in great part the growth of the muscle in transverse diameter. New fibres are also subsequently developed (Budge). This has, it is true, been recently disputed. Weismann observed that the muscles of the frog divide in a longitudinal direction, with a prodigious increase in their nuclei. One then sees regular columns of nuclei de- scending near each other. The filament di- vides, one becomes two, which subsequently acquire the normal diameter by a growth in thickness. The two products of division may afterwards repeat the same cleaving pro- cess. A single muscular filament may in this way finally become a whole group of filaments. Among the forms of retrogression of our tissue, fatty degeneration is the most frequent (Fig. 85). 85. eratpd human muscular fibre ; a, slighter ; b, increased ; c, highest degree. NINTH LECTURE. THE BLOOD-VESSELS. One cannot really speak of a vascular tissue. Only the innermost layer consists of a simple layer of closely cemented endothelial cells. This is the original stratum ; it forms the simplest, finest vascular tube. All the remaining layers, on the contrary, which by their further aggregation reinforce the walls of the vessel — and they commence very soon — belong to tissues which we have already discussed ; they consist of connective tissue and elastic substances, as well as layers of smooth muscles. The blood is conducted from the heart, as is known, by immensely ramified systems of arteries. Its return is consigned to the not less ramified veins. Between them is intercalated, but without any sharp demarcation, the district of the capillaries. They maintain the nutrition of the organs and tissues, as well as the secretion of the glands. The finest capillaries — they do not by any means occur in all parts of the body, however — have a calibre which just suffices to permit the passage of the blood cells, one after the other, though often with a certain lateral compression. Their lumen may, therefore, be assumed to be for man 0,0045 to 0.0068 mm. In other parts of the body, however, the finest capillaries present double this diameter. Without being treated with a suitable reagent, their struc- ture appears extraordinarily simple. A hyaline, structure- less, extensible and elastic membrane contains embedded, from place to place, rounded or elongated oval nuclei of 0.0056 to 0.0074 mm., with nucleoli. In the finest capil- laries the nuclei lie in the simplest manner behind each go NINTH LECTURE. other ; in somewhat larger ones an alternating position begin? to take place. If, however, we force a stream of dilute nitrate of silvei solution through our capillary, it then appears to be com- posed of the plates and curved, nucleated, endothelial or vas- cular cells represented in Fig. 21. With stronger magni- fying powers (Fig. 87), one recognizes in places, between the Fig. 86. — i, capillary with a thin wall, and the mclei a and b ; 2. capillary with double contoured walls : 3, small artery, and the middlelayer b. ith the endothelial layer a, Fig. 87. — Capillary from the mes- entery of the frog. At a and d, small apertures, '■ Stomata." endo': elia, larger and smaller, mostly rounded, dark cor- puscles {a, a) or light circular markings {b). There are small openings here, through which the lymphoid cells, by their vital migration (p. 10), probably make an active exit, and the colored elements of the blood are passively forced out (p. 27). The former marvellous emigration has been known for years (A. Waller, Cohnheim). In other capillaries (Fig. 86, 2) the walls are circumscribed by a double line. Here, there already appears to be the pri- mary rudiments of a so-called tunica interna or serosa. THE BLOOD-VESSELS. 91 More frequently, there are capillaries where the endothelial tube is surrounded by a connective-tissue layer, a so-called adventitia capillaris. The latter is, for a certainty, the primary rudi- ment of the layer, which with in- creasing complexity occurs in all the larger vessels as the most external layer or adventitia. We here meet at first with either ordinary connec- tive tissue, which has indeed re- mained at an earlier stage, with lon- gitudinally arranged nuclei or cell remains (Fig. 89, d), or, when capil- laries of lymphoid organs are con- cerned (Fig. 88, b), the reticular con- nective substance has become spread over the endothelial tube in an ele- gant manner, and the capillary is kept distended by this cellular reticu- lum, like the embroidery in a frame. Passing, now, to somewhat larger trunks, numerous variations of the structure occur. They coincide in part with the nature of the vessel, whether arterial or venous branches ; they are also, in part, of a more individual or local nature. Frequently, when we follow the capillaries towards the arterial tubes, we perceive branches where a layer, striking the eye by its transversely arranged nuclei (Fig. 86, 3, b), is met with around the endothelial tube (a). The former con- stitutes the very commencement of the muscular middle layer or tunica media of the vessels. An equally large venous branch usually has in the place of the latter layer a con- nective-tissue adventitia. Still, it often enough occurs in the finer arterial branches also, spread out over the muscular layer. Let us take a small arterial trunk, after the manner of our Fig. 89. The endothelial tube is not drawn here. Lying on Fig. 88. — Capillary vessels and fine branches of the mammalia ; a. capil- lary vessel from the brain : £, from a lymphatic gland ; c, a somewh.it larger branch with a lymph-sheath from the small intestine ; and d, a transverse section of a small artery of a lymphatic gland. 92 NINTH LECTURE. this, and consequently as the innermost layer of the figure, we recognize at b a homogeneous, longitudinally striated, elastic membrane, the tu- nica serosa of the older anatomy. The same is surrounded by a layer of transversely running con- tractile fibre cells at c. The connective-tissue layer d, with longitudinally ar- ranged cells, forms the last. Under certain circumstan- ces, it may be very much thicker than in our figure. Other small arterial trunks show the muscular layer to be constituted by several layers of fibre cells, lying over one another, as in Fig. 88, d, where the adventitia is again formed of reticular connective tissue. Larger trunks, finally, can no longer be surveyed in their totality, under the microscope. One must, therefore, exam- ine singly the separately prepared layers, or make longi- tudinal and transverse sections through the hardened walls. The further transformations, from those immediately fol- lowing up to the most remote of the largest blood-vessels, consist in the following : The endothelial tube always remains a single layer; the connective-tissue adventitia does the same, but it increases in thickness ; the connective-tissue bundles become more distinct, and elastic fibre reticula are more and more frequent, especially in the arteries. Both the middle layers, the serosa and media, begin on the contrary to become stratified ; each of them consists of an increasing number of layers lying over each other. On this depends the growing thickness of the vascular walls. The inner Fig. 89. — A small arterial trunk. At 6, the homo- geneous, non-nucleated inner layer ; c, the middle lajer, consisting of contractile fibre cells; d, the con- nective tissue external layer. THE BLOOD-VESSELS. 93 group of layers essentially preserve in their membranous- layers the nature of the elastic tissue, and present the most heterogeneous varieties of the same with a longitudinal arrangement. The middlemost group changes into a system of alternating layers of elastic tissue and smooth muscles, both with a transverse direction, or also of connective tissue. The tunica media remains much thinner in veins than in arteries of similar size, and the result is that the walls of the former vessels are thinner. The endothelial cells of the arteries appear as narrow, lancet-shaped lamellae ; those of the veins are shorter and broader (p. 29;. Taking a small vein of about 0.25 mm. in calibre, we find succeeding the epithelium a serosa with fine, elastic, longi- tudinal reticula. The middle layer consists of several mus- cular layers, which have between them elastic reticula and connective-tissue layers. The adventitia shows longitudinally running connective tissue and a contingent of elastic fibres. The appearance is different in middle-sized veins. The serosa has here becorne a group of layers. We now meet with homogeneous or striped layers with longitudinally arranged spindle cells, elastic membranes or elongated reti- cula. Indeed, even the elements of the smooth muscles may be continued in these inner groups of layers. The middle layers consist of connective tissue running transversely, with elastic reticula arranged in the same manner, and smooth muscles. Nevertheless, isolated elastic layers with longitu- dinal fibres also occur here. The adventitia is as usual; still it may also harbor contractile fibre cells. The largest veins possess a similar serosa, though without the smooth muscles, while the media remains undeveloped and may be entirely absent. It shows scanty muscular elements, permeated by transverse connective tissue. Elastic longitudinal fibro-reticula have likewise maintained their posi- tion here. In the thick adventitia of many veins, one meets, toward the interior with thick longitudinal muscles, as, for instance, that of the pregnant uterus, while the sinuses of the dura mater ar. entirely without muscles. 94 NINTH LECTURE. In the smaller arteries, the serosa and adventitia remain toler- ably unchanged. Still, there frequently occur in the former reticular perforated elastic layers, so-called " fenestrated mem- branes," or free elastic longitudinal reticula; the media pre- sents several layers of transversely directed muscles, lying over each other, and an elastic net-work is also developed in the fibrillated outer layer. In the larger branches, the stratification of the inner and middle layers increases. In the latter, elastic plates with transverse fibres, are now interpolated between the muscular layers, and the elastic reticulum of the adventitia becomes thicker. The largest arteries (Fig. 90) show under the endothelium (a), strongly stratified, the group of the inner vascular mem- brane (b). The several lamel- lae, in varying texture, present the entire multifariousness of the elastic tissue. Inwards, towards the endothelial cover- ing, one may, indeed, meet with more homogeneous, or more striated layers with cellu- larreticula imbedded overeach other (Langhans, von Ebner). In the more middle group of layers the membranous character of the elastic fibrous net-work {d) becomes more and more prominent. Their fibres may be thinner or thick- er ; the membranous connect- ing substance may appear whole or perforated. The num- ber of these elastic layers may increase to 30, 40, 50, and more. The muscles of the middle layer (1?) appear unequally developed ; frequently not Fig. 90. — Transverse section through the walls of a large artery : a, endothelium ; £, sero- sa ; c. outer layer of the same ; d, elastic, e, mus- cular layers of the media ; g, adventitia ;/, their elastic nbro-reticula. THE BLOOD-VESSELS. 95 to a high degree. The direction of the fibres is by no means exclusively transverse. In the outer portions of the media, fibrillated connective tissue occurs (Schultze, von Ebner). In the adventitia (g), finally, the elastic fibro-reticulum (/) acquires in an inward direction, in large mammalia, a very prodigious development. The valves of the vessels consist of connective tissue with elastic intermixtures, and the endothelial covering. Vasa vasorum is the name given to the capillary vessels which occur in the middle and outer layers of the larger trunks, and supply the nutritive materials to the walls of the vessel. The vascular nerves terminate at the muscles of the media. We pass to the arrangement of the capillary vessels in the human body. It is known that they do not occur everywhere. Thus, the epithelial struc- tures, with the crystalline lens, the cornea of the eye, and the permanent cartilages are non-vascular. A peculiarity of the capillary division fc> hi utfi Fig. qi.— Vascular net- work of a transversely stri- ated muscle ; a, arterial, b, venous vessel; c, d t the capillary net-work. Fig. 92, — A pulmonary alvenlur of the calf ; ff, larger blood-vessels, wn ch run in the pari- etes of the alveoli ; 6, capil ary net-work ; c, epithelial cells. consists in this, that the tubes by giving off branches do not become narrowed to a noticeable degree, and that by NINTH LECTURE. the conjunction of the branches there are formed reticula of more regular, and frequently of extremely characteristic form. The diameter of the capillaries (see above) is by no means the same in the different portions of the human body. The brain and retina present the finest of 0. 0068 to 0.0065 mm , and less. The muscles have somewhat larger ones of 0.0074 mm. The calibre is again increased, somewhat, in those of the connective tissue, the external integument, and the mu- cous membranes. The lumen is greater in the capillaries of most of the glands, such as the liver, the kidneys, and the lungs. Here we have a diameter of 0.0099 to 0.0135 mm - The most considerable ones, finally, of 0.0226 mm., are seen in the bone medulla. That, with the larger blood corpuscles, even the finest capillaries of animals have a more considerable calibre, it is hardly necessary to remark. The capillaries are sometimes more profuse, sometimes more scanty, in a part of the body. The size of the portion of the tissue comprised within their net-work is, accordingly, quite variable ; it is small in the vascular, large in the non-vascular parts. The former have an energetic, the latter a sluggish assimilation. The lungs (Fig. 92) appear uncommonly vas- cular. Their capillary net- work, serving for respiration, is the most compact of the organism. The other glands approxi- mate. The fibrous membranes, the tendons, the neurilemma are quite non-vascular. The form of the capillary net-work is determined by the shape of the parts to be circumvoluted, the nature of the several elements, or of their arrangement. We have, firstly, the straight, capillary net-work. A trans- versely striated muscle (Fig. 91) may represent this. The several filaments are surrounded by the uncommonly elongated meshes (c). The involuntary, smooth muscles also possess the same capillary net-work. Here, however, from the thin- ness of the elements, a bundle of fibres takes the place of the transversely striated filament. Other parts with elongated elements — for example, the gas- THE BLOOD-VESSELS. 97 Fig. 93.— Vessels of the fat cells. The arterial (a), venous branches {c) t with the rounded capillary net' work of a fat lobule. trie mucus membrane, with its long, thin, tubular glands — show a similar straight net-work. We are familiar, from Fig. 48, with the fat cells, large, rounded structures. Their capillary reticulum, in correspondence with this, forms rounded meshes (Fig. 93). The small, ar- terial branch (a), and the small, venous branch (b) of an aggregation of these fat cells appear very dis- tinct. We shall later, at the glands, become acquaint- ed with very extended organs of a racemose structure. A rounded or elongated saccule (acinus) surrounds an aggregation of smaller parenchyma cells. The acini are likewise circumvoluted by a complete, quite similar, round net- work, like the indi- vidual fat cells. A handsome, very characteristic ar- rangement is pre- sented by the capil- laries of the liver (Fig. 94). The liver — we shall return to it in greater detail subsequently — is di- vided into so-called lobules, into collections of radially arranged cells. The ex- tensively developed • capillary system maintains the same arrangement — a rounded, stellate one. Fig. 94. — The capillary net-work of the rabbit's liver, crossed by a branch of the portal vein. 9 3 NINTH LECTURE. The human corium projects in microscopically small papil- lae, which the thick epithelium (p. 32) surrounds with a smooth surface. The greater part of these papillae contains a capillary vessel, which ascends on one side, bends over the top of the papilla, and descends on the other side. This is the capillary loop. Larger papillae occur on many of the mucous membranes ; thus, on the dorsum of the tongue, as the so-called gustatory papillae, the whole small intestine, as intes- tinal villi, to omit others. The simple capillary loops are here no longer suffi- cient (Fig. 95). Between them are inter- posed communicating capillaries and capil- lary net-works. Thus arises the looped net-work. A quite peculiar formation is presented by the cortical layer of the kidney, in the so-called glomerulus or vascular coil (Fig. 96). A microscopic arterial branch (to the right) divides, and each branch forms a convolution of closely crowded capillaries. These portions, with educting canals, reunite, at last, into a single abducting vascular tube. We here speak, therefore, of a centripetal (vas afferens) and a centrifugal vessel (vas efferens). From the latter arises, further below, a new capillary reticulum. To study the capillaries, they must be injected from the larger trunks with transparent, colored (with carmine, Prussian blue) gel- atine, at an elevated temperature. Opaque, granular masses (cinnabar, white lead, chrome yellow) were the more imper- i • a • / Fig. 95. — An intestinal vil- lus ; «, the cylindrical epi- thelium with its thickened seam ; £, the capillary net- work ; c, longitudinal layers of smooth, muscular fibres ; d^ central chyle vessel. Fig, 96. — Glomerulus of the hog's kid- ney. THE BL O OD- VESSELS. gg feet accessories of an earlier epoch. They are rarely used at present. Other vehicles for the coloring material, resin- ous, waxy masses, or etherial oils, are, at the most, only here and there employed for very special purposes. The embryonic origin of the vessels is still attended with many obscurities. The heart, a production of the middle germinal layer, is formed very early, and enters soon afterwards into activity. It is hollow from the commencement, and the large, adjacent blood-vessels likewise appear to possess the same charac- teristic. With regard to the more particular details of this process, we must state that our present knowledge is little satisfactory. According to Klein, the first large vessels of the hen's em- bryo are formed from cells of the middle germinal layer. The contents of the latter soon liquefy. A protoplasma shell now invests the enlarged and macerated cell-body with the original nucleus. From such cells are derived the first vascu- lar wall, or endothelial tube, as well as the first blood corpus- cles. The cell is said to swell, and the nuclei increase, and, as during this increase the nuclei assume a regular position, the protoplasma mantle finally divides into flat, endothelial cells. From these endothelial walls the first blood corpuscles are also said to take their origin by a process of constriction. They are said, however, to have another origin, also. The first vascular walls and the first blood corpuscles, therefore, derive their origin from the same cells. We add to this the important fact that it is only subse- quently to the use of nitrate of silver solution that the pri- mary vascular wall is resolved into the familiar endothelial cells. A process of aggregation then leads, in a secondary man- ner, to the formation of the additional external vascular layers, a serosa, media, and adventitia. There is here, also, a great want of accurate observations. Capillaries — we assume, at first, a homogeneous, nucleated protoplasma tube— are present at an early period. IOO KINTH LECTURE. They soon present further metamorphoses. These may- be beautifully recognized in the transparent tail of the tad- pole (Fig. 97). It is a sort of budding process. Fig. 97. — Development of finer capillaries in the tail of the tadpole ; /, A protoplasma bud» and cords. From the parieties of already mature neighboring capilla- ries is supplied a protoplasma, capable of further independent development, in the form of pointed cones (Fig. 97, 1, 2, /, /). By their confluence (2) the latter are, at first, trans- formed into solid cords. If, then, the axial portion of the meanwhile enlarged cord melts down, we have the proto- plasma tube (3, p). By a further metamorphosis of the lat- THE BLOOD-VESSELS. 101 ter, the formation of new nuclei appears to take place The endothelial tube is finally established by the protoplasma walls and the young nuclear formation. The abnormal new formation of vessels in later life likewise follows the old embryonic law. TENTH LECTURE. THE LYMPHATICS AND THE LYMPHATIC GLANDS. WHAT is understood by lymph we have already mentioned in our second lecture (p. 27). It was the blood plasma which had passed out through the capillary walls, and which gave off the dissolved nutritive constituents to the tissues, and took up in exchange the products of the decomposition of the lat- ter. We even then mentioned that this fluid, which is unin terruptedly supplied from the blood current, must necessarily be removed. The arrangement serving this purpose must now be discussed. Our present course will, however, be the reverse of that followed in the previous lecture ; for the large and medium lymphatic discharge tubes are more accurately known, while numerous uncertainties still prevail concerning the knowledge of the finer and finest elements. Let us commence with the ductus thoracicus, the terminal large discharge tube of the lymphatics. We here meet with a condition corresponding to the walls of the veins. The endothelium is surrounded as a serosa by several layers of a striated substance, and then by a net-work of longitudi- nal elastic fibres. As a middle layer, we have next, longitu- dinally running connective tissue, and then transverse mus- cles. The adventitia also shows remains of the latter tissue. Valves are not wanting here, nor afterwards in the finer lymphatics. Descending to the latter, the stratification, as in the veins, becomes more simple ; but more accurate studies are here still necessary. In small trunks of 0.2 to 0.3 mm., the four characteristic vascular layers have been found still present. The adventitia, media and serosa gradually disappear, and THE LYMPHATICS AND LYMPHATIC GLANDS. 103 we have remaining only the endothelial tube with cells simi- lar to those of the blood-vessels. Here also we still meet with valves and isolated nodal or ampulla-like enlargements. Such vessels remain distinctly demarcated from the immedi- ate neighborhood. The relation of these passages to the blood-vessels varies greatly. For the most part, both vessels simply run alongside of each other. Not unfrequently an arterial branch is accompanied by a pair of lymphatic canals. One may then readily commit an error, namely, the assump- tion that the blood current is invested by a lymphatic. The latter condition does, indeed, actually take place (Fig. 88, c), although rarely, as many assert. At last, however, the appearance of the lymphatics changes ; the outer surface of our vascular cells has now grown firmly together with the surrounding tissues ; thus there arises at the first examination the impression of a cavity and cleft. For- merly this was generally considered to be the true interpretation, until the employ- ment of the dilute solution of nitrate of silver opened- our eyes (Fig. 98, a). For the examination of the finest termi- nal lymphatics, artificial injections are nat- urally again requisite ; and, indeed, to a higher degree than in the capillaries of the blood passages, where under favorable conditions the colored cells permit the fine tubes to stand out. The lymph, a colorless fluid, poor in cells, does not do this, as is known, and only the chyle ves- sels, overladen with fat, become at times distinctly prominent without any further assistance. But, as is known, the lymphatics have no affluent tube comparable to an artery ; they show merely a capillary divi- sion and effluent canals, comparable to the veins. Filling the latter downwards is, almost without exception, prevented by the resistance of the valves. A highly celebrated modern anatomist, Hyrtl, rendered the service of discovering a very Fig. 98. — Lymphatic ca- nal from the large intestine ot the Guinea-pig; a, vas- cular cells : b, spaces be- tween the same. io4 TENTH LECTURE. simple and at the same time extremely effective method of injection. We allude to his " puncturing method." The point of a fine canule is carefully forced into a tissue which is thought to contain lymphatics, and an attempt is made to carefully and slowly inject a wounded lymphatic. Many of the attempts are, it is true, thoroughly unsuccessful, still practice makes the master, and with patience and perse- verance the object is finally accomplished. Teichmann's ele- gant work on the lymphatics, not to mention others, has shown this. Let us commence first with the chyliferous vessels which, at the termination of an abundant digestion, by their fatty contents stand out as dark canals. In the intestinal villus (Fig. 95), there lies, occupying the axis, a cascal canal (d), surrounded by a looped reticulum of capillaries (b, 6). Its transverse diameter is 0.0187 to 0.0282 mm. At the first cursory examination it is a lacuna; with more accurate investigation one recognizes here, as elsewhere, the thin walls formed of plates of cemented endothelial cells. The condition just mentioned also characterizes the re- maining portion of the lymphatics. The canals of the latter are more irregular, angular and wider, and situated nearer the interior. They are again surrounded by the external, much finer and more regular capillary net-work of the blood current. Let us now pass from the intestinal villi, further down- wards, and examine the infe- rior flatter portion of the mucous membrane of the small intestine in which these caecal lacteals from the intes- tinal villi bury themselves. 99. Here, in connective tissue con- m Fig. 99. — Transverse section through the mu- cous membrane of the small intestine of the rabbit (near the surface); <», the reticular con- nective tissue containing lymph cells ; b, lymph canal ; c, transverse section of a Lieberkiihn's gland ; the same with the cells ; e,/ t g- t blood- vessels. Let us look at Flo-. THE L YMPHA TICS AND L YMPHA TIC GLANDS. 105 taining lymphoid cells (a), we discover the sections of blood- vessels (e, f, g) and of glands (d and c). Our attention is then attracted by an oblong cleft (6). It is a lymphatic canal consisting of endothelium. Our three drawings, Figs. 100, 101 and 102, contain further representations of such lymphatic passages. The caecal commencements are quite perceptible in the first two Fig. 100. — A colon papilla of the rabbit, in perpendicular section ,' a, arterial ; 6, venous trunk of the submucous tissue ; c, capillary net-work ; d, descending venous branch ; /) with a muscular admixture. This capsule continues inwards in a similarly constituted but perforated septum (Fig. 104, b, c, 105, g, k), which finally unites towards the hilus in a thicker connective tissue mass (" hilus-stroma " of His). In the lymphatic glands of large animals this " septum system " is immensely developed ; in small creatures it is often uncom- monly slight. We distinguish in the lymphatic glands a cortical and a medullary layer. The former consists of rounded or irregular bodies of 0.5 to 2 mm. and more, the follicles (d), which in the smaller organs are placed in single, and in larger glands in double or manifold rows. The medullary substance is composed of reticularly united strands, which spring from the inner side of the follicle, pass through the septum, and thus constitute a connection be- tween these structures of the cortical layer (Fig. 104,^,105, d, e). The transverse diameter of the strands varies extraor- dinarily, from 0.04 too. 13 mm. and more. THE LYMPHATICS AND LYMPHATIC GLANDS. 109 The follicles and medullary strands are never closely applied to the sheath and septa (Figs. 104, 105 ) ; a system, of clefts is always left. We shall soon learn their signification. The follicle (Fig. 105) consists of reticular connective tissue Fig. 105. — Follicle from a lymphatic gland of the dog, in vertical section ; a. reticular frame- work of the more external, d, apex of the follicle ; /, basis portion ; f, lymph-passages around the follicle : i, at the base of the same : k, lymphatics of the sub-mucous tissue ; /, lymphoid tissue of the latter. an elongated thing, reminding one of the sole of a shoe, is met with. A similar appearance is presented by the Peyerian follicles in the ileum of the ox. Let us now pass to a closer analysis of our structure. LYMPHOID ORGANS. IIS In the follicle (Fig. 109), we distinguish three parts, the apex (d), covered only by epithelium, and projecting between adjacent villi (a) into the lumen of the intestine, then a middle zone (at the elevation of c), and, finally, a basis portion (/). The middle zone and basis portion are buried in the sub-mu- cous cellular tissue. Here — and we are reminded of the tonsils and trachoma follicles — the middle and lower portions are united by a more narrow-meshed lymphoid tissue. The sur- faces of both these parts are again surrounded by a lymphatic canal-work in a reticular form. Not so in the follicles in the small intestine of the ox, and in the processus vermiformis of the rabbit. In these the basis portion is surrounded, similar to the follicles of a lymphatic gland, by a connected cup-like UUr Fig. iio. — Transverse section, through the equatorial plane of three Peyerian follicles of the rabbit ; a, the capillary net-work ; l>, the larger annular-shaped vessels. lymphatic investment space, while in the middle zone, it is true, the reticular passages are still retained. The lymphatic injection shows interesting conditions, re- minding us of those of the lymphatic glands, and the discover- Il6 ELEVENTH LECTURE. ies made in the tonsils and trachoma follicles confirm what follows. The chyle vessels of the intestinal villi {a), are the vasa aflferentia (p. 108). Passing further down, they form the lymphatic net-work (g, i), which surrounds the follicle, as the thread does the toy ball of the child. From these arise, at the base of the follicle, the efferent lymphatics (k), compar- able to the vas efferens of the lymphatic gland. The capillary net-work of the Peyer's plates appears extra- ordinarily developed. Fine capillaries permeate the follicle in a radial direction (Fig. 1 10, a) ; additional tubes (b) form a no less elegant interfollicular net-work. The thymus consists of lobular groups of a reticular con- nective tissue containing lymphoid cells. The interior of the lobule is hollow, connected on all sides with a convoluted main canal. Here we also meet with an elegant capillary retic- ulum, which differs in man and the calf in the arterial and venous arrangement. The lymphatic passages require more accurate investigation. The retrogression of the enigmatical organ begins before and with puberty. Fat cells in great quantity are developed at the expense of the lymphoid tissue. The spleen constitutes the most difficult organ of the lym- phoid group. It has been the object of many researches in old and modern times. We have, indeed, progressed further than our predecessors, but much still remains a matter of contro- versy. I here give only what I, after numerous personal studies, regard as correct. Similar to a lymphatic gland, our organ is surrounded by a fibrous envelope containing sometimes more, sometimes less smooth muscular tissue. This sends off again, in an inward direction, an interrupted system of septa. The latter, also called the trabecular system of the spleen, is extensively de- veloped in large mammals, while in small creatures (marmot, rabbit, Guinea-pig, rat and mouse) only scanty rudiments of it are met with. We are, therefore, once more reminded of the lymphatic glands (p. 108). It is best to commence the investigation with one of the latter LYMPHOID ORGANS. 117 creatures, a rabbit (Fig. m), for instance. In the larger mammals, this system of septa considerably impedes our com- prehension of the relations, which is already difficult. The soft spleen tissue proper consists of two substances. In the first place, we find, scattered throughout the entire thickness of the organ, rounded, oblong or irregular structures Fig. hi. — Rabbit's spleen ; a, Malpighian corpuscles ; b, reticular frame-work of the pulp. of a whitish color. Sometimes they stand out sharply, at others they can only be recognized with difficulty. In many species of animals they are observed crowded, in others more scanty. Their size slowly decreases in the smaller mammalia. These are the Malpighian corpuscles of the spleen or — let us say at once — the lymphoid follicles of our organ (a). Between them appears a very soft, and in consequence of its immense wealth of blood, dark red mass, the so-called spleen-pulp. The microscopic analysis of the same shows a system of reticularly connected canals {b), which connect adjacent Malpighian corpuscles with each other, and leave a likewise retiform space — 01 cavernous system between them. The pulp is, therefore, suggestive of the medullary substance of the lymphatic glands, as are the Malpighian corpuscles of the follicles of the latter. n8 ELEVENTH LECTURE. Both portions of the spleen tissue are, however, shoved through each other ; it is, therefore, impossible to speak here of a special, cortical, or medullary layer. We next examine the lymphoid follicle ; and here we again meet with the old familiar reticular connective tissue, filled with an excess of lymphoid cells, forming in the interior a larger meshed, on the surface a more narrow meshed reticu- lum. The capillaries of the interior are also readily recog- nized. The tissue— we repeat— of the pulp strands (Fig. 112, a) ■^$M> Fig. 112. —From the pulp of the human spleen brushed preparation (combination); a, pulp strand with the delicate reticular frame-work ; ^, transverse section of the caverni ; c, longitudinal section of such a one ; d, capillary vessel in a pulp tube dividing up at e ; /^ epithelium of the venous canal; g; side view of the latter ; k, its transverse section. arising from the surfaces of the Malpighian corpuscles pre- , sents, on the contrary, a considerable modification of the reticular connective substance, of extremely fine delicate tex- ture and with very small meshes, so that only one or a few lymphoid cells find room in the latter. The surface of this pulp tube preserves the same reticular character. If we adjust the focus to the fundus of the caverni invested by them, we find numerous transversely arranged fibres (c). These pas- sages are lined with flat, spindle-shaped cells (/), which, indeed, as the transverse section {b) teaches, have globular nuclei. We have once more before us a vascular endothelium ; LYMPHOID ORGANS. 119 only its cell borders are, by way of exception, not cemented to each other. If we also add to this that capillaries run in the axis of the pulp strands, and that in the narrow reticulum of its tissue regular red blood corpuscles are met with, some- times fresh and unchanged, sometimes shrivelled and in va- rious stages of disintegration, we have then described the most essential portion of the structure of the tissue of the spleen. In order, however, to gain a further insight, we must now turn to the vascular arrangement of this strange organ. This is very complicated and quite peculiar, and it is just here that the views of investigators are diametrically opposed to each other. The arteria lienalis buries itself, in the ruminantia unrami- fied, otherwise, as a rule, with several branches, directly into the so-called hilus. The latter become further divided in the interior, and finally break up, at an acute angle, into anumber of fine terminal branches. These, called penicilli, and pecu- liarly formed, resemble the branches of a willow stripped of its foliage. On these branches (but no longer on the penicil- lus) sit the familiar Malpighian corpuscles, like the berries on the stem of the grape. The arteries and the veins are still invested by a connec- tive-tissue sheath, which is continuous with the septum sys- tem of the organ. This sheath, like the entire vascular expansion, is very different in the several varieties of animals; it is slight and rudimentary in the small, complicated and thick in the large mammalia. Pausing now, however, at that of man, we find the arteries and veins, already divided into 4 to 6 branches, passing in and out of the organ. Up to trunks of 0.2 mm. they are invest- ed in com-non by a connective-tissue sheath. The latter has at first a parietal thickness of about 0.25 mm., diminishing to 0.1 mm., whereby arteries of 0.2 and veins of 0.4 mm. are still invested in common. There is now a gradual sepa- ration of the venous from the arterial branches. The sheath in its original condition is continuous for a less distance over 120 ELEVENTH LECTURE. the arteries ; it is gradually changed into a reticular connec- tive tissue containing lymphoid cells, a metamorphosis in which the adventitia soon participates. The sheath struc- ture is extended somewhat further over the venous branch ; at last its fibres begin to separate, and it is also lost in the sep- tum or trabecular system of our organ. From this lymphoid metamorphosis of the artery arise the already familiar Malpighian corpuscles of the spleen. They lie in part on the point of ramification of arterial branches, in part laterally on the unramified vascular tube. Finally — and it is a frequent occurrence — the arterial branch passes through the centre of the follicle. If we examine more closely, we find that no line of demarcation can be drawn between the separate follicles and this elongated lymphoid covering of the arterial branch. Every Guinea-pig's spleen teaches us this. In the follicle, we never meet with a venous branch, but, rather, a capillary reticulum with rounded meshes, sometimes scantily and poorly developed, sometimes more abundantly. The source of supply varies ; sometimes it is branches of the follicular artery, sometimes it is through the adjacent pulp- lubes. We have now to follow the further course of the arterial offshoots, the so : called penicilli of the spleen. They enter the pulp-tubes of our organ, to pass through their axis and to become capillaries. The capillary reticulum of the Mal- pighian corpuscle also, at last, sends its offshoots down into the adjacent pulp-tubes (Fig. 113, e). Now, these capillaries of the pulp-tubes are quite peculiar. We follow them by the greatest attention for a certain dis- tance (on an uninjected spleen or in a good injected prepara- tion), then the capillaries (Fig. 112, d) commence to be uncertain and indistinct (e). Separated cell-demarcations may still be recognized ; but soon even these disappear. We are in the presence of a lacuna — a finest blood current with- out walls (Fig. 113, e). Let us recall to mind that the tissue of the pulp-tube pre- LYMPHOID ORGANS. 121 sents a reticulum with very narrow meshes, in the interspaces of which one, or, at the most, a few lymphoid cells find place ; and let us not forget that the pulp-tubes possess, su- perficially, the same reticular character, covered by an en- dothelium consisting of separate, uncemented cells. Fig. 113. — From the spleen of tlie hedgehog : «, pulp, with the intermediate currents ; £, fol- licle ; c, boundary layer of the same ; g, its capillaries ; e, transition of the same into the interme- diate pulp-current ; yj transverse section of an arterial branch, at the border of the Malpighian corpuscles. If we adhere to this previously described textural condi- tion, the lacunar capillary blood current, which arises after the loss of the capillary walls, will present no further con- siderable difficulty. As the failing branch of a drying brook wanders at last between the pebbles of its bed, slender and scanty, so is it with these finest blood currents. The lym- phoid cells resemble the pebbles. Still, the blood current contains cellular elements and the red blood corpuscles in excess. A portion of the latter slip through with their pliable, smooth surface ; others stick fast. For our colored elements, however, as we have already learned, movement is life, rest is death. Thus are explained those numerous corpses and fragments of the colored blood cells in the spleen, which we mentioned above (p. 119). Something additional is also satisfactorily explained by this. The closely crowded amceboid lymph cells are capable of taking up into themselves the imprisoned blood. corpuscle 6 122 ELEVENTH LECTURE. or the fragments of its corpse (p. 9). These are the blood- corpuscle-containing cells of the spleen, occurrences which, many years ago, caused so much racking of the brains, and yet are, at present, so easy to interpret. Let us remember the amoeba of our Fig. 3. We have remembered the dead : let us now return to the living. What becomes of these finest blood currents after they have successfully passed through the narrow mesh- work of the pulp-tubes ? If our description has thus far been altogether comprehen- sible, the answer follows of itself. These currents enter the system of caverni, which Fig. 112 shows between the pulp- tubes b and c. Let us pause for a moment. If we inject a rabbit's and a- Guinea-pig's spleen, or the organ of a new-born child, from the vena lienalis, it is a mere child's play to instantly fill these reticular spaces between the pulp-tubes (Fig. 114, c). Thus — we return to the inverted course once more — the lacunar pulp current passes over into these spaces of the pulp, into the " cav- ernous veins " of Billroth. From the latter, presenting many di- Fig. T14, — From the sheep's spleen (double injection) ; w'th many peculiarities, united in im- the calf - mense numbers, constitute the testicle and kidney. We speak now of the tubular glands. Another modification is formed by the so-called convo- luted glands (Fig. 119). The terminal portion of this small organ presents a peculiar convolution like the coil of a pack thread. 2. Another uncommonly diffused form is the racemose gland (Fig. 120). The membrana propria here appears as a microscopically small, rounded, elongated or irregularly formed saccule.* These " gland vesicles" are united at their openings in groups, and in this manner a lobule or acinus is * It has been proposed to include the small racemose structures of the mucous membrane among the "tubular" glands, on account of their elongated saccules. GLAND TISSUE. 131 Fig. 120. — Human racemose p.ila- tine glands. formed. It may acquire an excretory duct, and then the race mose gland, in its smallest and most simple form, is complete But these most elementary structures are rare. Asa rule (Fig. 120), several acini form the still small gland body. In larger and large organs the num- ber of the gland lobules becomes very great. It is scarcely necessary to remark that transitions occur between the tubular and racemose glands. 3. Finally, we have another gland with closed rounded gland capsules, which latter are contained in abun- dant connective tissue. This is the ovary. These rounded structures, which are constituted by a connective-tissue wall, are called the Graafian follicles. Among the cells it con- tains, one is noted for its size. This is the ovum (Fig. 5). That the latter becomes free by the rupture of the follicular wall, we have mentioned above. Let us also add that the ruptured follicle is incapable of further repair, but rather goes to ruin by a process of cicatrization. The conditions are, therefore, in contradistinction to those presented by other glands, peculiar and anomalous enough. The second' and much more important constituent of our organ is presented by the gland cells. We shall subsequently see that they are nearly all derivatives of Remak's corneous and intestinal-gland layer. Even in subsequent life, this epi- thelial character is not renounced. The inner surfaces of the membrana propria are thus lined, sometimes simply, sometimes in strata. In the excretory portion of the gland, an ordinary epithelium subsequently makes its appearance. The gland cell may be called a micro- scopically small chemical laboratory. With its body it forms the secretion, or changes the formative material received from the blood into the latter. For this purpose our cells require a certain magnitude. 132 TWELFTH LECTURE We shall, therefore, comprehend that those cells, flattened into the thinnest plates, such as we previously met with in the pavement epithelium, are absent. The gland cell is a membraneless, cubical thing, occasion- ally somewhat flattened from above downwards, irii other cases rendered cylindrical by lateral compression. The for- mer shape is represented by the cells of the liver, with a size of 0.018 to 0.226 mm. (Fig. 121). The cells (Fig. 122, b) of the "gastric mucous glands" of the dog are taller and more slen- der. The elements of the Lieberkiihnian glandular tubes of the small intestine have likewise assumed the cylindrical form, as our Fig. 117, b (representing a longitudinal sec- tion of this tube) teaches. Gland cells covered with cilise are very rarely met with in man. They are only known in the uterine tubes. Many gland cells — we here allude chiefly to those of the liver and kidney— appear to constitute tolerably permanent structures. In others the cellular elements retain the great perishability of the epithelium, and perish in the formation of the secretion. Let us take, for example, a sebaceous gland of the external integument, a small clustered structure. An acinus is shown in Fig. 123, A. It is covered by several cell layers. In the cavity (b) we meet with a fatty mass, which subsequently becomes free as sebum cutaneum. How has the latter been formed ? In the peripherical cells, those lying im- mediately against the wall of the gland vesicle, one already notices an increasing deposit of fat molecules. This is, therefore, the fatty degeneration which we have already mentioned at page 13. It causes the Fu;. 121. — Human liver cells. Fig. 122.— From a gas- tric mucous gland of the dog ; a, lower portion of the excretory duct ; />, commencement of the glandular canal. GLAND TISSUE. 133 retrogression of the tissue elements in a normal way here, as by a pathological process elsewhere. The gland cell swells with the increasing embedment of fat, and finally falls from its matrix. Suspended in the cavity of the acinus, it has now become a corpse. We meet, accordingly, in the Fig. 123. — A, the vesicle of a sebaceous gland ; a s the gland-cells resting on the wall ; £, those which have been cast off, containing fat and filling the cavity; B, the cells more highly mag- nified ; a, smaller ones, poorer in fat and belonging to the wall ; 6, larger ones, more abundantly filled with fat; c, a cell with larger fat drops joined together, and d one with a single drop of fat ; , e,/ y cells whose fat has partially escaped. sebum with these cells fatty degenerated to a high degree, with their fragments, their nuclei which have become free, and fat molecules with an albuminous connecting substance. This is the origin of the sebum cutaneum, a relatively unimpor- tant secretion. The lacteal gland consists of a group of enlarged sebaceous glands, destined for a higher performance. Even before the final period of pregnancy, the human organ forms the so-called colos- trum. We meet in the latter with globular cellular elements of 0.0151 to 0.0563 mm. in size (Fig. 124, b). These "colostrum corpuscles" are simi- lar to the detached, highly fatty, sebaceous follicle cells. Subsequently, soon after the delivery, the milk contains millions of the so- called milk globules (a). They are drops of fat which have become free, and are surrounded by a very thin shell of a coagulated albuminous body, which is usually Oo°* °Ofo Fig. 124. — Elemen- tary forms of hum in milk ; a, mf-k globule ; by colostrum corpuscle. 134 TWELFTH LECTURE. called caseine. Their size varies between 0.003 to 0.009 mm - The gland cells should now, with a far more energetic secre- tion in the acinus, have been early destroyed. A different view might, however, be entertained. The membraneless cells may have thrown out the elaborated secretion, as the crater of the volcano does the lava — only the cells, like the volcano, may persist. I regard this as indeed very plausible. We have just spoken of probably the most perishable gland elements, immediately after the discussion of more permanent elements. Let us now return to the latter for an instant, taking up the liver cells. One meets in them, from time to time, with brownish molecules and drops of fat. Both ap- pear subsequently in the bile ; the former is the " biliary coloring matter " (to repeat a crude expression of former days), the latter becomes " cholesterine." Therefore, even here, the gland cell once enclosed in its body the secretory substance which subsequently becomes free. Here the com- ing and going of the latter through the permanent cell body is not to be doubted. A still further confirmation of the persistence of many gland cells has been more recently obtained. Extraordinarily fine permanent canaliculi, "the gland capillaries " (first found in the liver), occur between the gland cells as the terminal offshoots of the excretory ducts. Our Fig. 125 represents such from the pancreas. We shall, later, refer to the matter more in detail. With the mcmbrana propria and the secretory cells we are, therefore, finished. Let us now refer to the capillary reticu- lum, the art and manner in which the in- dispensable blood current reaches the V^J^-X^Zl surface of the secreting organ. ?o f ry"i C nar'' ,finestsecre " We repeat what we said at page 96. The form of the tissue elements deter- mines the arrangement of the capillaries. With thin and long glandular tubes, such as stand close to GLAND TISSUE. '35 each other in the gastric-mucous membrane, the individual tubes occupy about the position of the transversely striated muscular filament (Fig. 91). The reticulum (Fig. 126) becomes similarly elongated ; only the rings around the gland apertures, together with anomalous arterial and venous brancheSr produce a considera- ble difference in the thing. Turning to the racemose glands, with the generally rounded form of the element, the small acinus, the capillary net-work must, as we have already remarked, correspond to the form of a fat lobule (Fig. 93). Our Fig. 127 represents the capillary arrangement of a larger lobular group of the pancreas. The figure might, with equal propriety, be used for the vascular arrangement of a conglomeration of the lobules of fat cells. The immense assimilation of glandular organs renders a considerable wealth of lymphatic passages, which are to re- store the superfluous transudation to the blood passage, very appreciable. A portion of these lymphatic passages have been discovered very recently. Smooth muscular fibres, which either invest the gland body or occur in the parieties of the excretory ducts, scarcely require a further physiologi- cal explanation. They are of great importance for the ex- pulsion ot the secretion. Concerning the gland nerves, this most obscure portion of the structurj of the organ in question, we shall speak later. The last which remains for discussion is the excretory duct. If we take a simple gland tube (Fig. 128), such as are con- Fig. 126 — The vascular net-work of the mu- cous membrane of the human stomach— semi- dia^ramatic. The (finer) arterial trunk di- vides into the elongated, capillary net-work, which passes over into the rounded reticulum of the, gland apertures, from which the vein (the wider, darker ves*el) arises. 136 TWELFTH LECTURE. tained in infinite numbers in the gastric mucous memb and examine a so-callqd " peptic-gastric gland " (it may it is true, be somewhat more complicated), we readily recognize from d to b the secre- tory cells. Over b we meet with a cylindri- cal epithelium, the same which covers the surface of the gastric mucous membrane. A further explanation is, therefore, super- fluous. Let us, furthermore, cast a glance back to our Fig. 122. The drawing represents a so- called "gastric-mucous gland." A long, rane, also, Fig. 127. — The vascular net work of the rabbit's pancreas. Fig. 128.— A lateral view oi' a gastric gland of the cat ; a. stomach cells : b, inner ; r, ex- ternal interca'ary por- tion ; d y the g'an'l tube, with both varieties of cells. excretory duct bears the same cylinder cells (a). It then divides into two caecal tubes. These (b) contain lower cubical elements, the suppliers of a tolerably unknown secre- tion. Let us examine a still earlier figure — our Fig. 120 — the small racemose glands. No doubt can prevail here concern- GLAND TISSUE. 1 37 ing the excretory duct. Its cell covering is not rarely different from that of the acini. The wall of the excretory canal is here of a connective-tis- sue nature. In larger, and the largest glands of a similar structure, the omitted duct acquires an increasing complica- tion. We shall later return to the particulars. Let us now take a cursory survey of the different glands of the human body. a. To the tubular group belong : the Bowman's glands in ■ the regio olfactoria of the organ of smell ; the tubes of the mucous membrane of the stomach, small and large intestine, which bear the names of the gastric juice glands, or peptic- gastric glands, or gastric-mucous and Lieberkiihnian tubes ; finally, the uterine glands. Then, as modified structures, as so-called convoluted glands, we have, finally, to mention the smaller and larger sudoriparous glands, together with the ce- ruminous glands of the ear. Very complicated tubular organs are, as we previously mentioned, the kindey and testicle. b. Among the racemose glands are included a host of our organs from the smallest to the largest dimensions. First belong here all the small glands of the mucous membranes of the body, then the so-called Brunner's glands of the duo- denum, the sebaceous glands of the skin, and the Meibomian of the eyelids. As larger and largest, the group includes : the lachrymal gland, the various salivary glands, the pancreas, the lacteal glands, then the Cowper's and Bartholinian glands of the sexual system ; and, furthermore, the prostate. Finally, according to their manner of origin, the lungs should also be included here. We shall subsequently have to refer more particularly to them, as well as to their prede- cessors. c. The closed gland capsules. We scarcely need to repeat that the ovarium forms the only gland of this kind in the hu- man body. Our organs, with slight exceptions (the primitive kidney and the generative glands), originate, in their cellular portions. 138 TWELFTH LECTURE. either from the upper or lower germinal layer, from the cor neous and intestinal gland layer of Remak. The membrana propria and capillary reticulum are aggregated productions of the middle layer, which produces so much. A previous figure, 41, the primary rudiment of a hair germ, passes as well for the glands of the external in- tegument as for those of the mucous membrane. When, by a continuous "ncrease of the cells, lateral buds branch off from the cellular cone as it grows downwards, there is formed at first a solid, slightly berry-shaped mass (Fig. 129). It finally becomes a complicated racemose system, which at last becomes hollow {a), and thereby constitutes the completed gland. With this we leave the glandular organs in general. The subsequent lectures will, however, carry us back to certain of them. Fl(j. 129. — Developing racemose gland : a, excretory duct, already permeable ; 6, solid gland bud ; c t membrana propria ; rf, surrounding connective tissue. THIRTEENTH LECTURE. THE DIGESTIVE APPARATUS WITH ITS GLANDS. The digestive apparatus, in its connective-tissue external layers and the muscular middle layers, is certainly of a rela- tively simple nature. The mucous membrane, however, with the immediately adjxcent loose connective tissue, and with all which is connected with it, presents an abundance of the most diversified structural relations. Let us therefore briefly examine the long canal work, with the varying constituents in its interior. The oral cavity contains the already described teeth (p. 73). as well as the tongue. In it open the salivary glands, large racemose organs, and, together with these, a number of smaller associates, the so-called mucous glands. From the vascular mucous membrane of the mouth project closely crowded papillas. It is covered by the stratified pave- ment epithelium spoken of at page 30. The latter may here acquire a thickness of 0.45 mm. The submucous connective tissue appears sometimes dense (gums), sometimes loose and extensible (the floor of the mouth). In it lie the bodies of the numer- ous small racemose glands. The secretion is mucus ; the cells form a layer of pale, cubical or low cylindrical elements (Fig. 130). They occur as labial, buc- cal, palatine and lingual glands. Among the salivary glands the submaxillary has recently undergone an accurate investigation (Pfliiger, Gianuzzi, Hei- Fic. 130. — Gland vesicles of the palatine gland of the rabbit ; a, rounded, &, an elon- gated acinus. 140 THIRTEENTH LECTURE. denhain). Its cells differ in the several animals. The former are granular in the rabbit. In the dog and cat, on the con- trary, we find a mucous gland. The cells (Fig. 131) here consist of two different structures. Firstly (a), we meet with large rounded elements, which are filled with a homogeneous mucous substance. Be- sides these, quite granular, smaller cells occur in the periphery of the gland vesicle (c). Pressed closely together, and indistinctly separated from each other, they form a sort of cres- cent (Gianuzzi). They subsequently change into those large mucous cells. The finest secretory capil- laries, after the manner of our Fig. 125, likewise make their appearance here, as also do the flat stellate cells of the membrana propria (see Fig. 118). The excretory ducts show cylinder cells (Fig. 131, d), with longi- tudinal striations beneath the nucleus. We have, finally, to mention a rounded capillary reticulum, and abundant lym- phatics around and between the lobules and lobes. The sublingual appears to be nearly related to the sub- maxillary gland. We cannot, however, yet leave the latter. As experimen- tal physiology teaches, the irritation of the chorda tympani produces a profuse watery secretion ; that of the sympa- thetic, on the contrary, a scanty quantity of a thick fluid substance. The continued irritation of the nerves, as Heidenhain ascer- tained, produces an important change in the contents of the acini (Fig. 132). Nearly all the large round cells (a) have, Fig. 131. — The submaxillary g'and of the dog ; fl, mucous cells : b, protoplasma cells ; c, crescent ; d, transverse section of an excretory duct, with the peculiar cylindrical epithelium. THE DIGESTIVE APPARATUS. 141 in the mean time, given off their mucine as a secretion. A granular protoplasmatic substance now fills the altered cell body. Fig. 132. — Submaxillary gland of the dog, wilh its contained cells ; a. changed by the strong irritation of the chorda ; b t those remaining unchanged (after Heidenhain). This was altogether the first difference which a quies- cent and active gland presented to the eye of the micros- copist. The parotid gland contains in its acinus (measuring 0.034 to 0.052 mm.), granular cubical cells (of 0.014 to 0.018 mm.), without any mucous metamorphosis. Fine secretory tubes have been met with between the latter. Here, again, the ex- cretory duct has ordinary cylinder cells. The tongue is an essentially muscular organ, with transverse- ly striated filaments crossing each other. The dorsum of the tongue has innumerable different papillae. Three forms have been distinguished here : the filiform (papillae filifonnes, s. conicse), the fungiform (p. fungiformes, s. clavatas), and, finally, the circumvallated (p. circumvallatse). To the latter have also been added the so-called papillae foliatae, which were early discovered, then forgotten, and recently more accurately in- vestigated. Both the latter organs contain the terminations of the gustatory nerves. Our organ is rich in racemose glands. We meet principally with mucous glands, with the contents rendered familiar to us by Fig. 130. In the vicinity of the p. circumvailata and the 142 THIRTEENTH LECTURE. p. foliata, quite similarly shaped glands appear, it is true, but they have different anomalous contents, with granular cloudy cells (Fig. 133). The same organs have been met with in great numbers in the nasal mucous membrane, and they have received the name of the " serous glands" (Heidenhain). The tissue of the mucous mem- brane commences at the posterior fourth of the tongue to undergo a lymphoid metamorphosis, in which fig. i 3 3.-Acini («, round. K ob- the pharynx may also participate. long) of a serous gland from the , Tr . . . , . i_ • j vicinity of a circumvoiuted papiiia of We thus nave demarcated lymphoid organs, the lingual follicles, the ton- sils, and the pharyngeal tonsils, discovered by Koelliker (compare p. 1 13). The pharynx, with its transversely striated muscles, has the same covering of stratified pavement epithelium as the oral cavity. The tough mucous membrane acquires papillae below. The upper portion is rich in mucous glands. The oesophagus also retains the old epithelial covering. The muscular coating consists of a thicker longitudinal ex- ternal layer and a thinner internal transverse layer, and, as it descends, shows a replacement of the voluntary transversely striated fibrous formation by the involuntary smooth tissue. The mucous membrane projects in longitudinal folds, and contains racemose mucous glands. We may touch upon these only cursorily. The stomach or ventriculus, on the contrary, requires a more careful discussion. Its serous covering, it is true, pre- sents nothing worthy of remark, neither do its smooth muscles, which consist of layers running in longitudinal, transverse, and oblique directions. But the mucous membrane, which is lined with cylinder cells 0.0226 to 0.0323 mm. high and 0.0045 to 0.0056 mm. broad, shows, on the contrary, an abundance of interesting and important things. Its surface is not smooth, but uneven. Either lower or THE DIGESTIVE APPARATUS. 143 higher isolated prominences (Fig. 134, a), are met with there, or projecting folds, which are united in crossing each other. The glands open only in the valleys, and never on a hill or a fold. Numerous differences of the gastric surfaces occur according to the variety of animal. In general, the cardial half of the stomach presents a thinner and more even mucous membrane than the pyloric portion. The mucous membrane may here, at last, acquire an elevation of 2 mm. An enormous quantity of tubular glands (Fig. 134, b) permeate the /^ v\y\J~\ mucous membrane. The massiveness of the latter is, therefore, in compar- ison to this embedment, but slight. We find an ordinary soft connective tissue (Fig. 135, a). Lymphoid meta- morphosis of the latter may, however, take place. The glandular tubes of the stomach have been divided into two differ- ent forms ; the so-called peptic- gastric glands and the gastric- mucous gland. The former constitute the more dis- seminated and more important glandular formations (Fig. 134)- They open in part singly (Fig. 128), in part by the conjunction of several tubes into a common excretory duct (Fig. 136, 1). In both cases the aperture appears in the transverse sec- tion to be rounded (a), and lined with the ordinary slender, high cylindrical epithelium of the gastric mucous membrane (Fig. 128, a, 136, a). Fig. 134. — Vertical section of the human gastric mucous mem- brane ; a t surface papillae ; £, glands. Fig. 135. — Transverse section through the gastric mucous membrane of the rabbit; a, tissue of the mucous membrane; &, trans- verse sections of empty and injected blood- vessels, c ; d, spaces for the glands. 144 THIRTEENTH LECTURE. The gland body itself appears as a sometimes smooth bor- dered, sometimes sirtuous tube. The membrana propria shows the familiar flattened stellate cells. Passing, now, from the outlet of the gland in a downward direction, we meet at b with- a new metamor- phosed cell formation, broader, lower and more granular. Further below, at c, we have two large gland cells (peptic cells). The latter are, however, first met with at d in their highest development. Here, lying on an uninterrupted series of smaller gland cells are isolated larger, gran- ular elements (Fig. 128, d), lodged in niche-like sinuosities of the mem- brana propria. The latter struc- tures are the "overlying cells" of Heidenhain, in contradistinction to his " chief cells." We have already learned how dif- ferent is the appearance presented by the quiescent and overworked submaxillary gland of the dog. Something similar — and we are again indebted to Heidenhain for the interesting fact — is shown by the peptic-gastric glands. In the fasting animal they appear smooth bordered, somewhat shrunken, and their chief cells are transparent. A few hours after a plentiful meal an essentially different appearance is met with. The peptic- gastric glands are now swollen, their walls are sinuous, their chief cells enlarged, granular and cloudy. At a later period they again shrink ; the chief cells, however, remain per- ceptibly clouded. Now which of the two varieties of cells supply the gastric juice, we do not yet know. We are inclined to conjecture that it is the peptic-gastric glands. Fig. 136.— 1, a compound peptic- gastric gland of the dog ; a, the wide aperture (stomach cell) with the cylinder epithelium ; 6, the division ; c. the isolated tubes lined with pep- tic cells ; tU theescaping contents ; 2, the aperture a in transverse section ; 3. transverse section through the in- dividual glands. THE DIGESTIVE APPARATUS. 145 The second glandular formation, the gastric mucous glands, were long since discovered in the hog. In the dog, cat, rabbit and Guinea-pig they occupy a large extent of the pyloric region ; in man, on the contrary, but a small zone here. They are, again, in part ramified, in part unramified tubes. One may also recognize here in the excretory duct (and it may acquire a very considerable length) the ordinary cylindrical epithelium of the gastric mucous -membrane (Fig. 122, a) The lower true portion of the gland shows, on the contrary, lower cubical cells (b) richer in fine granules. They become cloudy in acetic acid, and call to mind the " chief cells " of the peptic-gastric glands. Small racemose glandules appear in the human pyloric re- gion. Isolated lymphoid follicles form the lenticular glan- dules, familiar to us from p. 112. At the border of the mucous membrane, towards the sub- mucous tissue, there is a net work of smooth muscular fibres, the muscularis mucosae (p. 80). Thin strips pass up between the gland tubes. The arrangement of the vessels in the gastric mucous mem- brane (Fig. 126) is elegant and characteristic. Thin and slen- der arterial branches, rising up through the submucous tissue, terminate in a long-meshed capillary net-work, circumvolut- ing the gland tubes, and forming rings around the apertures of the latter. The transition into venous roots takes place on the surface only, and these rapidly unite into large de- scending veins. The latter form a broad-meshed reticulum of wider tubes beneath the mucous membrane. The lymphatic passages were recently discovered by an eminent Swedish investigator, Loven. Large net-works, situated in the submucous tissue, send upwards considerable cjecal canals, which pass between the glands and reach nearly to the gastric surface. The gastric juice, an acid fluid, contains a peculiar fermen- tative body, pepsine. The granules in the covering cells (and possibly in the chief cells) are this substance, which has been formed by the gland cells. The power of the secretion to 7 146 THIRTEENTH LECTURE. digest albumen must be left for discussion in another lec- ture. Let us pass to the small intestine. Its serous covering and the smooth muscles, forming a double layer, we here omit. The mucous membrane, on the con- trary, requires an accurate description, for its structure is more complicated than in the stomach. In the first place, we meet with innumerable large crescen- tic folds (increasing downwards in height), the valvulse con- niventes Kerkringii. The surface of the small intestine, be- sides, projects in millions of complicated papillae, the intes- tinal villi. In the mucous membrane we meet, furthermore, with an infinite number of small glandular tubes, the Lieber- kiihnian glands; and in the duodenum, with small racemose organs, the Brunonian glands. Finally, the small intestine contains solitary and aggregate (Peyerian) lymph follicles. The tissue of the mucous membrane of the small intestine also shows a muscularis mucosas, but it is thinner than in the ptomach, and then a reticu- lar connective substance containing numerous lym- phoid cells (Fig. 47, a). The villi (Fig. 137) — we have already mentioned them in a previous lecture — also consist of a similar tissue. Even the surface is distinctly fenestrated, although with narrower meshes. In the axis we find the chyle vessel (Fig. 95, d), single or multiple, in the latter case sometimes, connected in an arched and bridge-like manner, covered by thin slips of smooth muscle (c) derived from the muscularis mucosa;, and finally circum- voluted by a looped net-work of capillaries {b\ We are already familiar with this from what has preceded. Fig. 137. — Lieberkiihnian glands (/z) of the cat, with the intestinal villi [b) situated over them. THE DIGESTIVE APPARATUS. 147 That the whole intestinal canal is lined with cylindrical epi- thelium, was mentioned in the second lecture. We also de- scribed the peculiarity which the cylinder cells of the small intestines presented, the thickened seam, permeated by porous canals, of the free broad surface. We now turn to the glands. By far the more important formations are the Lieberkiihnian tubular glands (Fig. 137, a). They are infinitely numerous, and occupy not only the mu- cous membrane of the small, but also that of the large intes- tine. We are thus reminded of the gastric glands ; the capillary net-work is also the same. The Lieberkiihnian glands are smaller, however ; they are only 0.38 to 0.45 mm. long, and 0.056 to 0.09 mm. broad. Their membrana propria also appears more delicate ; the tube remains undivided, and is lined by a simple layer of cyl- indrical gland cells (Fig. 117,5). The opening occurs regu- larly in the narrow vales which are enclosed by the adjacent villi. They secrete the intestinal juice. The racemose or Brunonian glands (Fig. 138) of the small intestine are of far more subordinate importance. Theycom- FlG. 138. — A human Brunner's gland. mence, in man, just beyond the stomach, and form, in a crowded sequence, a regular glandular cushion embedded in the submucous tissue. They thus extend to about the en- 148 THIRTEENTH LECTURE. trance of the biliary duct, becoming more scanty furlhei downwards. The mammalia show numerous variations. The size varies in man from 0.25 to 2 mm. The acini ap- pear rounded, elongated, sometimes regularly tube-like (0.56 to 0. 14 mm.) The duct and gland body have the same cover- ing of low cylindrical, pale and irregular cells. If I am not mistaken, the Brunonian gland stands in the middle, between the" ordinary racemose mucous gland, the gastric-mucous gland and the serous gland. Concerning the secretion we know very little. Isolated lymphoid follicles (solitary glands) may occur throughout the entire small intestine. These, as well as the aggregated lymphoid follicles (the Peyer's plates) have already been mentioned in the eleventh lecture. We have already mentioned that the Lieberkiihnian tubu- lar glands have an elongated net-work of blood-vessels. From it arise, and to it return, the afferent* and efferent vessels of the intestinal villi, which form the looped net-work (Fig. 95, b). The lymph or chyle vessels of the intestinal villi, having descended into the mucous membrane, likewise form a net- work, very much more incom- plete it is true, of wider tubes. Our Fig. 109 [a, b, c, k, to the left) may represent this toler- ably. During the resorption, of the chyme, its fat, in a con- dition of the finest division, penetrates first the body of the cylindrical epithelium ; it then enters a wall-less passage Fig. 139. — The very slender intestinal villus pf a kid, killed during digestion, with- out epithelium, and with the lymphatic ves- sel filled with chlye, in the axis. through the reticular connective substance of the villi, and, at last, the csecal chyle canal (Fig. 139) occupying the axis of the latter. " Preformed passages " for this process of wandering have frequently been searched for, it is true, and they have often been thought to be found. THE DIGESTIVE APPARATUS. 149 - Fig. 140 — Glands of the lar^ na-s- tine of the rabbit. I )ue tube with cells ; the others drawn without cells. but subsequently nothing of all this was confirmed. These were simply microscopic observations such as should not be made, instituted for the purpose of filling up a gap in the present physiological knowledge at any price. The Lieberkuhnian tubes continue throughout the mu- cous membrane of the whole large intestine, but now receive, most superfluously, a new name, that of the glands of the large intes- tine (Fig. 140). They have not be- come changed in the least. The reticular connective sub- stance of the mucous membrane of the small intestine has, however, been further transformed into an ordinary connective tissue ; the reticular character is less pronounc- ed, and the number of lymphoid cells contained in the tissue has de- creased enormously. The intesti- nal villi of the small intestine have finally entirely disappeared. If the mucous membrane, as in the upper part of the rabbit's colon, still projects as papillae, the latter appear broader and as prominences of the ordinary mucous mem- brane permeated by tubular glands (Fig. 100). The colon presents isolated lymphoid follicles. In the vermiform process of man and the rabbit, on the contrary, there is an enormous Peyerian plate, as we remarked at page 114. The blood-vessels of the large intestine correspond with those of the stomach (Fig. 126) for an interchange. Lym- phatics have also been subsequently met with in the carni- vora and herbivora. Those of the upper colon of the rabbit are represented by our Fig. 100, g, f, e. In the anus the simple cylinder epithelium is sharply de- marcated from the modified epidermis. At the lower end of the intestine, the smooth and transversely striated muscles become intermixed, reminding us of the oesophagus. FOURTEENTH LECTURE. PANCREAS AND LIVER. We have still left the two largest glandular organs of the digestive apparatus, the pancreas and liver. We shall soon finish the pancreas ; the liver, on the contrary, requires a more accurate discussion, in consequence of its peculiarities. The pancreas is an enormous racemose structure. It re- minds one of the salivary glands. The rounded acini meas- ure 0.06 to 0.09 mm. The membrana propria is likewise said to have flat stellate cells. The rounded vascular net- work was represented in our Fig. 127. The lymphatics re- quire still more accurate investigation. The gland vesicles are lined with indistinctly separated, very granular cubical cells. In the adult rabbit the latter show fatty molecules in their interior, that is in the parts turned to- wards the lumen. The middle and external portions remain transparent. Between them appears the net work of finest secretory tubes, already familiar to us from Fig. 125 (Sa- viotti). The thin-walled excretory duct of the human pancreas contains no muscular elements. Below, it presents mucous glandules. It is covered by a low cylindrical epithelium. If followed, in animals, into the gland, these cells are found to become more and more flat in the branches. Finally, in the gland vesicles themselves, we meet with thoroughly flattened ele- ments, reminding us of the endothelia of the vessels. These are the so-called " centro-acinary '' cells (Langerhans), which are found widely extended, not only in the pancreas, but also in the parotid. The character of the gland cells in a quiescent and active condition requires further investigation. PANCREAS AND LIVER. IS1 Let us now turn to the liver. The liver — as its natural external surface, or that of an arti- ficial section teaches — consists of individual, crowded arese, the so-called hepatic islets or hepatic lobules. In many crea- tures, as the pig, the demarcation of the lobules is very dis- tinct. The borders of the lobules appear tolerably distinct in the human organ during the infantile period of life, but very indistinct, on the contrary, in the adult. Our liver' islets are as- sumed to measure, as a mean, 2.2 mm. A hepatic lobule (Fig. 141)- however, consists essentially of innumera- ble gland cells and, cross- ing them, an uncommon- ly complicated capillary net-work. The latter unite at the central point of the lobule to form an initial branch of the hepatic vein ; the limits are shown externally by the branches of the portal vein and the fine biliary branches. The liver cells have already been noticed at Fig. 121. These thick, obtuse-angled structures, whose mean measure- ment is 0.018 to 0.023 nim., contain nuclei of 0.006 to 0.007 mm., with nucleoli. The soft, granular cell body remains membraneless and endowed with a slow contractility (Leuc- kart). The brown molecules of the biliary coloring matter in the cell body, as well as the fatty embedments, we have already mentioned. "The latter occur in the suckling infant, in adults whose diet is rich, and also in fattened animals. They form the so-called fatty liver (Fig. 142). The cell sup- ports such an overloading with fat (c, d) relatively well. Fig. 141. — Hepatic lobule of a boy ten years old, with the transverse section of the central hepatic vein trunk. 152 FOURTEENTH LECTURE. With an altered manner of life, the unusual contents soon disappear again- In the lobule (Fig. 141) the cells lie crowded together in a radiated manner, forming simple rows. Reticular combinations gradually become more frequent externally. These are the so-called cellular trabecular and cellulo- trabecular reticula of our organ. Between the lobules we meet with in- £t™ie : cu£/kn w d topTf" terstitial connective tissue, sometimes rf, with large drops. on | y s ijghtly developed (man) , sometimes abundantly (pig). This connective tissue derives its origin, in part, from the investing membrane of the liver; it is, in part, the continuation of a connective-tissue sheath which sur- rounds the blood-vessels and biliary passages entering the porta hepatis (Glisson's capsule). The liver receives its blood from two unequally developed supply tubes, the wide portal vein and the narrow hepatic artery. The first forms, around the lobules, partly shorter or longer branches (Fig. 94), sometimes, however, nearly and actually assuming a ring-shaped arrangement (pig). These branches rapidly divide into the compact capillary net-work of 0.009 t0 0.0126 mm. wide tubes. They approach the cen- tre of the lobule in a radial manner to bury themselves in the commencing portion of the hepatic vein, which is situated at this point. The latter, like its larger trunks, has uncom- monly thin walls, and has coalesced externally with the parenchyma of the liver. The branches of the hepatic artery, running along with the portal vein and biliary ducts, form, in the first place, nu- tritious vessels for both the last mentioned parts, and then capsular capillaries ; finally, they penetrate the lobule itself. They either bury themselves here in the branches of the por- tal vein, or pass over into the peripheral portion of the capil- lary net-work. Both varieties of net-work, that of the hepatic cell tra- beculae and that of the blood-vessels, are most intimateh PANCREAS AND LIVER. 153 interwoven with each other, so that every space of the one meshwork is occupied by portions of the other. After suitable treatment, as Beale and Wagner found, thin sections of the hard- ened hepatic tissue show an uncommonly elegant reticu- lar tissue of a right delicate, homogeneous, nucleated, connective substance (Fig. 143, a). In the last period of foetal life, or in the new-born (Fig. 143), this consists distinctly, in places, of a double mem- brane. The one layer corresponds to the capillary walls (and shows here and there a combination of the flat, vascular cells — Eberth) ; the other, investing the hepatic cell-trabeculae, represents a finest membrana propria. Fig. 143. — Frame-work substance from the rab- bit's liver ; «, homogeneous membrane with nu- clei : b, thread-like strands of the latter ; e, sev- eral hepatic cells still retained . < sifftl IM& gggp ■i-MMkl-Wt c-?sA "^rl , N§| e— ^\ ■ Fig. 144.— Biliary capillaries of the rabbit's liver. 1. A part of the lobule : it, vena hepatica; £, branch of the portal vein ; c, biliary ducts ; d, capillaries. 2. The biliary capillaries (b) in their relation to the capillary blood-vessels (a). 3. The relation of the biliary capillaries to the hepatic cells ; a, capillaries ; b, hepatic cells ; c, biliary ducts ; rf, capillary blood-vessels. Great difficulty was encountered, during a long period, in the investigation of the finest biliary passages (Fig. 144). A 7* 154 FOURTEENTH LECTURE. reliable result was at last secured here by means of trouble- some injections* (Gerlach, Budge, Andrejevic, MacGillavry) The finer ramified system of the biliary passages may, it is true, be still readily recognized (Fig. 144, 1). They run with the branches of the portal vein (£), in the intervening spaces of adjacent hepatic lobules. From them arise fine branches which circumvolute the branch of the portal vein (c). They are continuous inwards with a marvelously delicate net-work of finest canals, the so-called biliary capillaries (d). The diameter of the latter is 0.0025 to 0.0018 mm. (rabbit). They surround the individual liver cells (3, b) with elegant cubical meshes (a), so that the cellular element comes into contact at one point or another of its surface with these finest tubules. We thus have, in addition to the two coarse net- works of the cellular trabeculae and capillary vessels, this third, finest one, of the biliary capillaries. They are also not wanting in the other classes of vertebrate animals. There is, nevertheless, considerable variation (Her- ing, Eberth). We now encounter the question : do the biliary capillaries possess a proper wall, or are they only the finest lacunar canals? Furthermore, what is their more exact relation to the hepatic cells ? I have not doubted that there was a special, although extremely thin wall, from the instant thatT began to study the biliary capillaries of the rabbit. One sees here, not only the artificially injected, but also the adjacent empty tubules (often to a considerable extent), regularly demarcated by sharp, straight lines. A lacunar system between contractile cells would otherwise scarcely present the regularity of the biliary net-work. We therefore coincide with Eberth and Koelliker in the assumption of a wall. The same is also shown by the cat's liver. * These may be made from the biliary passages in the fresh animal cadaver. This was the earlier procedure. An injection may also be made into the vein of the living animal of indigo sulphate of soda, which is toon (as in the kidney) secreted by the liver (Chizonszczewsky). PANCREAS AND LIVER. 155 Fig. J45. — Finest biliary passages of the rabbit's liver ; tf, blood-vessels ; b, hepatic cells ; c, biliary capillaries. Years ago, Andrejevic had already correctly asserted that the blood and biliary capillaries never touched each other, but rather that the body of a hepatic cell always lies between them as a separating structure. The livers of the amphibia and reptiles, and even of birds, show this most distinctly. Nevertheless, the more compli- cated relations of the mam- malial liver yield the same result (Fig. 145), although with more trouble, to the attentive observer. We see the blood-vessels (a) in part transversely, in part longitudinally. The biliary capillaries (c) are in repeated contact with the hepatic cells (b) ; but portions of the cell body always remain as intervening parts between these and the capillary vessels of the passage. Our figure teaches, furthermore, that biliary capillaries occur only at the contiguous surfaces of two cells. We shall, therefore, have to regard the extremely thin walls of the capillaries as the product of adjacent cells which has become hardened. The lymphatics run in the capsule of Glisson in the same manner as the portal vein, hepatic artery, and biliary ducts. Having entered the lobule, they invest the capillary blood- vessels (MacGillavry, Frey, Biesiadecky and Asp). The deli- cate external wall of these "perivascular" lymph passages is without doubt the thin membrana propria of the hepatic cell trabeculae. Let us, finally, look after the efferent biliary canals. These canals also show between the lobules a membrana propria covered with low cylinder cells. Later, the walls become connective tissue, the cells are higher and have a seam which is permeated by porous canals (p. 8). In the largest canals passing out from the hepatic paren- 156 FOURTEENTH LECTURE. chyma, there is an external fibrous membrane and an internal mucous membrane. In the gall bladder there are, in addition, smooth muscular fibres. The largest biliary canals have numerous excavations (probably reservoirs for bile), as well as racemose glandules. FIFTEENTH LECTURE. THE LUNGS. The lungs originate in the same manner as the racemose glands, but acquire an essentially different texture. Their efferent canal system requires an especial preliminary dis- cussion, on account of its peculiarity and complication. The cartilages of the larynx are hyaline, as the thyroid and cricoid cartilages. In certain parts of the arytenoid cartilages there is an elastic metamorphosis. The Wrisbergian and Santorinian cartilages, with the epiglottis, are pure reticular cartilage. The triticeal cartilages are formed of hyaline or connective-tissue cartilaginous substance. The ligaments of the larynx present a considerable wealth of elastic tissue. The lower true vocal cords are purely elastic. The muscles are transversely striated. The mucous membrane, rather compact and likewise not poor in elastic elements, shows embedments of lymphoid cells. It contains racemose, true mucous glands. Strongly stratified pavement epithelium covers the anterior surface of the epiglottis ; there are not so many layers in that covering the posterior surface as far as the base ; the same is also true of the lower vocal cords. Otherwise, we meet with slightly stratified ciliated epithelium, which descends far down into the lungs. The wind-pipe or trachea, with its system of branches, the bronchi, presents a fibrous tube, in the anterior wall of which are embedded half rings of hyaline cartilage (annuli carti- laginei). A deeper layer of transverse smooth muscles con- nects the terminal portions of the half rings posteriorly. In the mucous membrane we again meet with numerous mucous glandules. IJ8 FIFTEENTH LECTURE. In the lungs themselves the bronchi divide dichotomously again and again, and thus become finer and finer passages. The cartilaginous half rings disappear, simple lamellae appear- ing in their place. Their last remains are still seen in canals of 0.23 mm. The thin parietes have a simple ciliated epithe- lium of 0.0135 nam. in height. Mucous glandules continue far down, as also do the smooth muscles, which form regular rings round the bronchial ramifi- cations, and possibly till near the so-called pulmonary vesicles. At the end of the terminal bron- chial branches (Fig. 146, a) we now arrive at the true respiratory portion of our organ. We have, first, thin-walled (0.4 to 0.2 mm. wide) canaliculi, the £&%Z£Z?%&&%Z?£& alveolar passages (Schulze). ' vedaVca,;au d %*£%£&.""" " *'" Their acute-angled ramifications (c) are familiar. Communicating with them laterally and also terminally are short, conical hol- low structures (b), the primary pulmonary lobules or, as they are commonly called, the infundibula. As the gland lobule consists of the gland saccules or acini, so does the just mentioned infundibulum consist of similar structures, the pulmonary vesicles, pulmonary cells or alveoli. They are less isolated from each other, however, and to a certain extent present more diverticulations of their walls, which meet in common cavities. At a later period, indeed, there is not unfrequently an absorption of individual portions of the walls. Such expansions of the wall of the alveolar passage into pulmonary vesicles (c) are met with every- where. On making a section through the lung tissue, we meet with the alveoli in the form of rounded and oval spaces (Fig. 147, b, b). Their diameter varies from 0.1128 to 0.3760 mm., and increases with the age. The hermetic enclosure of the respiratory organs in the THE LUNGS. 1 59 thoracic cavity compels the pulmonary alveoli to maintain a certain expansion permanently. In consequence of their great distensibility, the lungs follow the expansion of the thorax. By means of their elastic power, and assisted by the muscles of their canals, they contract at each expiration, Fig. 147. — Transverse section through the pulmonary substance of a child nf nine months. A number of pulmonary cells, b, surrounded by the elastic fibrous net-work, which bound them in a trabecula-like manner, and, with the thin structureless membrane, forming their walls (a) ; d, por- tions of the capillary net-work with their vessels curved in a tendril-like manner, projecting into the cavities of the pulmnnary cells ; c, remains of the epithelium. as far as the thoracic walls permit. It is only when the tho- racic cavity is opened that the lungs with their alveoli com- pletely collapse. The parietes of the pulmonary vesicles, a continuation of the terminal canal system, is a very thin connective-tissue mem- brane. It is surrounded by elastic fibres, finer and coarser, sometimes single, sometimes aggregated in groups. The latter are met with in the interalveolar septa. The fundus of the pulmonary alveolus shows only the finest elements, measur- ing o.oon mm., in part more isolated, in part connected in a reticular manner. l6o FIFTEENTH LECTURE. The primary pulmonary lobules of the new-born — later the nature of the arrangement becomes more indistinct — united by connective-tissue intermediate substance, form larger or secondary lobules. The latter appear on the surface of the organ in the human adult as areae. measuring i to 2 mm. and more, demarcated by a black substance, and often appearing quite distinct. They form, at last, the large lobes. Their delineation belongs to descriptive anatomy. We have just mentioned the black substance in the inter- lobular connective tissue ; it may occur between and in the walls of the pulmonary vesicles, and even in the bodies of their epithelial cells, as we shall mention hereafter. This is the so-called black lung pigment. We have just used the epithet "so-called." In fact these substances are not melanine, the complicated, dark ferrugi- nous coloring matter of the organism. They have rather an extraneous origin ; they are carbon, breathed in in a finely divided condition, which is induced by our artificial life in enclosed places. Mammals living wild show nothing of this, but it is seen in their kin when domesticated by man. In human beings constantly surrounded by smoke and soot, or in laborers in coal mines, the lungs may at last become quite black. If we shut a dog up in a place in which there is a constant genera- tion of soot, a similar change of the respiratory organs takes place with relative rapidity. In a condition of the finest division, these particles of car- bon penetrate the epithelial cells, and from them enter the pulmonary tissue. A great portion of them here become permanently quiet. Others enter the lymphatics, and pass from these into the lymphoid bronchial glands. They also become fixed in the latter organs. This is the so-called mela- nosis of these structures. Let us now examine the vascular arrangement. By the continual division of the pulmonary artery, there arises a system of fine blood-vessels, which encircle the in- dividual pulmonary vesicles, and frequently combine into THE LUNGS. I6l Fig. 148. — A pulmonary alveolus of the calf ; a, larger blood-vessel*, which run in the alve- olar septa ; If, capillary net-work ; c, epithe- lial cells. incomplete or more complete rings (Fig. 148, a). From them arises an uncommonly close capillary net-work of tubes 0.0056 to O.0113 mm. wide, which are scarcely separated from the atmospheric air by the thin membrane of the alveolar walls (b). The respiratory in- terchange of gases takes place here. These capillaries appear elongated when the lung vesi- cles are strongly expanded. When less expanded they pro- ject, in a tendril-like manner, into the cavity, reminding us of a relative condition in the muscles. The pulmonary veins commence with small branches in the interalveolar septa. Gradually combining into larger trunks, they accompany the ramifications of the bronchia and the divisions of the pulmo- nary arteries. The bronchial arteries are regarded as the nutritive vessels of the respiratory organ, but there is no very sharp demar- cation between them and the respiratory pulmonary arteries. The former supply the walls of the larger blood-vessels, the adjacent lymphatic glands, the connective tissue between the pulmonary lobules and beneath the pleura. Finally, they form the capillary net-works of the various parietal layers of the efferent bronchial system ; but the most superficial net- work of the mucous membrane arises, in a peculiar manner, from the respiratory system of vessels. The bronchial veins appear to be quite peculiar. They are conjectured to be only the reflux vessels of the arterial branches from the larger bronchial ramifications, from the lymphatic glands and from the pleura nearest the hilus of the lungs. The venous roots from the walls of the finer bronchi pass, on the contrary, into the respiratory pulmonary veins. The lungs are rich in lymphatics, beneath the pleura as well 1 62 FIFTEENTH LECTURE. as in the bronchial system. Lymphatic lacuni also occur in the pulmonary vesicles, and their efferent vessels subsequently invest the blood-vessels (Wywodzoff). We have, finally, to mention the epithelial lining of the alveoli. This has occasioned much discussion. In the mam- malial and human embryo there is a continuous covering of flat, protoplasmatic, nucleated cells. A change occurs after birth, however, with the commencement of aerial respiration. Fig. 149. — The epithelium from the basis portion of an infundibulum, situated just beneath the pleura of the developed cat ; treated with nitrate of silver. Only a small contingent of our cells now retain their old characteristics (Fig. 149). The epithelial element, over the incurvations of the pulmonary vessels, and over all the other prominences, has become a much more considerable proto- plasmless and non-nucleated scale. SIXTEENTH LECTURE. THE KIDNEY, WITH THE URINARY PASSAGES. The structure of the mammalial kidney is extremely com- plicated. This bean-shaped organ is covered by a not very thick, but resistent, connective-tissue envelope. The blood- vessels and lymphatics pass in and out at the hilus, and the efferent canal, the ureter, also has its exit at this point. The kidney (Fig. 150), consists of two different layers, a cortical, and a medul- lary substance. The former (above, /"), appears to the naked eye dark and homo- geneous ; the latter (a, b), paler, displays a radiated fibrous arrangement. In most mammals it projects in a single point into the pelvis of the kidney (a). In man the medullary substance is divided into a num- ber of conical portions, with their bases turned towards the cortex and their points towards the hilus. These are the Malpighian or medullary pyramids. The columnse Bertini are de- pressions of the cortical substance between the latter portions of these cones. The cortex and medulla are, further- more, permeated by a connective-tissue frame-work. The elements of the cortex, as well as of the medulla, are long, glandular tubes, the so-called uriniferous canals or Bellinian tubes. In the medulla they divide frequently, and run in a radial direction (b). They continue through the Fig. 150. — Diagram of the mammalial kidney ; a, papilla ; b, straight uriniferous canals of the medulla ; c, so-called medullary rays of the cortex ; d, outermost cortical layer ; e, cortical pyramids, with the arte- ries connected with the glomeruli ; /, border layer. 1 64 SIXTEENTH LECTURE. cortex from point to point, in the form of straight bundles (c). They are here called medullary rays. Between them, al- though incompletely demarcated, remain considerable portions of the cortical substance (e), comparable to a truncated pyra- mid. These are the so-called cortical pyramids. In them run the glandular tubules, with the most manifold turnings, which finally encompass, with their knob- like dilatations, the Malpighian vascular coil or glomerulus (Fig. 96). The latter structures occur in this portion of the organ only. Let us now commence the discussion of the particulars with the most internal division, with the apices of the medul- lary pyramids, the renal papillae. Here, alone, in the form of 10 to 15 apertures, the efferent canal-work of this organ, which is so complicated in its structure, opens as a system of short canals (Fig. 151, a). Very soon afterwards they break up, by acute-angled ramifications, into branches of the first and second order (b, c), and this is repeated several times more. The whole thus acquires a brush-like appearance. The canals be- come narrowed, in consequence of this continual subdivision, from 0.3 and 0.2 to 0.05 mm. About 4 to 5 mm. from A'STmSSEi,'^ the a P ex of the P a P illa the P rocess of ™ a tla h tkr : g «, ki frun y k ( of m a divisi °n ceases, however; the straight t U h r ^ap=°x S of Ca the 'pyemia- % canals now maintain their diameter un- t^XlT a :£«ZZ^l changed for a long distance. rati^io V „ a ; C f U A r el a s P arec^ Between them-and this was dis- covered by Henle — occurs an additional system of much finer loop-shaped canals (d). In order to ' facilitate a further insight, let us give to that particular part THE KIDNEY AND URINARY PASSAGES. 165 of the tube which descends from the convoluted cortical por- tion, and the side of the loop which passes off from this, the name of the descending, and that portion which returns towards the surface of the organ the name of the ascending side. The former usually has the least, and the latter the greatest diameter. The number of the looped canals in- creases in proportion as we examine the cortical layer further upwards towards the medullary layer. The terminal trunk of the efferent canal-work is invested by the connective-tissue frame-work of the papillary apices, and is without a membrana propria. The latter gradually makes its appearance at the system of branches, and is more distinct as well as more compact at the looped canals. Low cylinder cells of' 0.03 to 0.02 mm. border the transverse section of the efferent canal system (Fig. 152, a). In the further system of branches the lining cells are still lower (down to 0.016 mm.) Let us now, for an instant, leave the efferent apparatus and examine the secretory portion of the kidney. We will now turn to the cortical layer of our organ and, first of all, examine more closely the so-called cortical pyramids (Fig. 150, e). In their axis is seen a branch of the renal artery, to which the glomeruli are attached by lateral branches, like the berries on the stem of the grape (Fig. 150, e\ Fig. 155)- A cortical pyramid, however — we repeat what was pre- viously said— consists, for the rest, entirely of convoluted uriniferous canals. They take their origin with a balloon- shaped portion which surrounds the glomerules, as a bag does a sponge. This is the Miiller's or Bowman's capsule. Its con- Fig. 152. — Trr.nsverse section through a re- nal pyramid of the new-born child ; a, collec- tive tubes with cylindrical epithelium ; I?, de- scending side of the looped canal with flat cells ; c, returning side of the loop with granu- lar cells ; d, transverse sections of vessels ; e t connective- tissue frame-work substance. 1 66 SIXTEENTH LECTURE. tracted transition into the uriniferous canals (the so-called neck) was discovered at a relatively recent period. Only the most external cortical portion of our organ (Hyrtl named it the cortex corticis) is without this peculiar vascular coil (Fig. 150, d\ Fig. 155, d). The inner surface of this capsule has a lining of large, flat, endothelial cells. The external surface of the glomerulus presents an invest- ment of smaller cells which are not so flat. I found them thus, formerly. According to Heidenhain, however, the lat- ter elements are likewise quite flat. In the convoluted uriniferous canals we meet with a clouded, granular, cubical epithelium, and the lumen is quite narrow. Following this glandular tubule downwards, we find it as- suming a straight and direct course. At first it still remains wide, and the gland cells are' unchanged. Then, having en- tered the medullary substance, it diminishes in width, exceed- ingly, and now becomes the narrow descending side of Henle's looped canal. A re- markable transformation of the epithelial lining has taken place at the same time ; quite thin, flat scales, appearing like vascular endothelium, now line the canal '(Fig. 152, £.) Following the loop further, we arrive at the ascending wider side. Its epithelium is again the old, clouded, glandular variety of the convoluted uriniferous canals, as we must maintain in contradistinction to Ludwig. The returning side finally passes over in the cortex — some- times deeper, sometimes quite near the surface — into an expanded, gut-like convoluted structure, the so-called " inter- Fjg. 153.— From the kidney of the pig (semi- diagramatic) ; /z, arterial branch; b, afferent vessels nf the glomerulus, c ; (i, vas efferens ; <*, breaking up (! )- Fromtheperiphery of the latter a rounded net- work of somewhat wider vessels extends to the con- voluted uriniferous canals of the cortical pyramids (Fig. 153,/; Fig. 155. J - )- The most external cor- tical layer, Hyrtl's cortex corticis, receives its blood from the efferent vessels of the uppermost glome- ruli and the terminal branches of the coil-bear- ing arteries (Fig. 155, d). Let us pass to the veins of the cortex. Stellate venous rootlets, the so- called stellulse Verheyenii (e), appear quite superfi- cially. Connected with these stars, there is then formed in the cortical pyramids a long venous trunk (/?), which lies in close apposition to the coil-bearing artery. Into its regular lateral branches open the rounded capil- lary net-work of the cor- tical pyramids. The vein, itself, sinks at the margin between the cortex and medulla, into the venous arched vessel which we mentioned above. Thus far all is settled. 8 Fig. 155. — The vascular arrangement of the kidney In vertical section; «,arterial branch at the margin between the cortex and medulla ; <£, coil-bearing artery ; c» vasa afferentia of the glomeruli ; d, capillary reticulum of the external cortical layer ; c, vein of this part ;f, elongated capillary net-work of the medullary rays ; g; rounded net-work around the conv luted uriniterous canals of the cortical pyramids ; h< venous branch of the cortex ; /, efferent vessels of the deepest glomeruli ; /<-, their capil- lary net-work ; /, venous tubes of the medulla; >«i capillary net-work of the papilla. 170 SIXTEENTH LECTURE. A variety of views prevail, however, concerning the vascular relations of the medulla. Elongated vascular tufts, which appear in the upper portion of the medullary substance, the so-called boundary layer (Fig. 150, /"), are called vasa recta (Fig. 151, /; 155, /& and I). They pass, sometimes further upwards, sometimes further downwards, in a looped or noose-like manner, into each other, and may be mistaken for the' looped canals of the urinary passages (Fig. 151, e). Our vasa recta then form an elegant net-work (Fig. 155, m) around the apertures of the uriniferous canals at the apex of the medullary pyramids. These vasa recta have frequently, if not predominantly, a venous character (/) ; they are continuations of the capillary net-work of the cortical pyramids. Then — and we regard this source of supply as the more important — the medullary vessels arise from the breaking up of the vasa efferentia of the deepest glomeruli (Fig. 155,0- Quite isolated arterial branches, which have left the coil- bearing arteries before the giving off of the glomerulus branches, are, according to our views, of little consequence, though many investigators have considered these so-called arteriole rectas to be of great importance. The combination of the vasa recta into venous roots (J) presents' a similar condition. They frequently have a tuft- like character. Their affluent tubes are the returning sides of the looped vessels and the effluent canals of the papillary apices. These venous roots empty in part into the lower terminal portion of the cortical veins, in part into the arched communications at the margin between the cortex and the medulla. We are familiar with the lymphatics of the dog's kidney (Ludwig and Zawarykin). They occupy the interstices of a connective tissue full of clefts, which is situated beneath the capsule, and from her,e are in communication with the capsu- lar passages, and then form in the cortical pyramids finer, deeper canals between the uriniferous canals, capsules of the THE KIDNE Y AND URINAR Y PASS A GES. i 7 1 glomeruli and blood-vessels. Later, in making the injection, the narrower passages of the medullary rays become filled, and at last the lymphatics of the medullary substance itself. The whole reminds us of the arrangement in the testicle (see be- low). True lymphatics with valves first appear, however, at the hilus. The question now arises, which of the two systems of ves- sels, that of the glomerulus or the net-work circumvoluting the uriniferous canals, secretes the urine ? This role has been assigned to the glomerulus, and only the signification of an absorbing arrangement ascribed to the capillary net-work of the uriniferous canals (Ludwig). According to another view (Bowman), however, the glomeruli secrete the water chiefly, and the cells of the uriniferous canals, as true gland cells, fur- nish the characteristic solid constituents of the urine, which are washed out by the water flowing past. A new, and as I can say correct, observation of Heidenhain's is of signifi- cance for this theory of Bowman's. Indigo sulphate of soda injected into the veins of a living mammal is not excreted by the glomeruli, but through the convoluted glandular canals of the cortical pyramids. Let us finally take a hasty glance at the passages which convey away the urine. The calices and pelvis of the kidney present a connective- tissue outer layer, a middle layer of crossed smooth muscles (especially in the pelvis of the kidney), then a mucous mem- brane with the pavement epithelium mentioned at p. 30. Mucous glands may also occur. The muscular coating is thicker in the ureter. An external layer shows longitudinal, and an inner layer transverse fibres. Further downwards, a third, innermost, longitudinal layer is added. The urinary bladder has a relative structure. The muscular layer, considerably thickened, consists of oblique and transverse reticularly connected bundles of fibres. The sphincter vesica; appears at the neck of the bladder as a thicker annular layer. The longitudinal layers of the detru- sor urinae run over he vertex and anterior wall of the organ. 172 SIXTEENTH LECTURE. The mucous membrane and epithelium remain the same. Simple mucous glandules are likewise met with. The female urinary canal, the urethra, presents a longitu- dinally folded mucous membrane with papillae. The mucous membrane is very vascular, and has numerous mucous gland- ules, the largest of which bear the name of Littre's glands. A strongly developed muscular layer consists of longitudi- nally and transversely arranged fibres. The epithelium is of the stratified flattened variety. AX 'A/vVW."vXVW^/v -1 Vo^ 3W ^ 2UU SEVENTEENTH LECTURE. THE FEMALE GENERATIVE GLANDS. — THE OVARY WITH THE EFFERENT APPARATUS. THE ovary, a peculiarly constructed organ, forms the most important portion of the female sexual apparatus. It has a flattened oval, occasionally bean-shaped form, and therefore has a hilus through which considerable blood-vessels and lymphatics enter and leave the organ. We may distinguish in the ovary a sort of medullary sub- stance, that is, a connective tissue, uncommonly vascular sub- stance or the vascular zone of Waldeyer; and then an invest- ing glandular layer, the parenchyma zone. The medullary substance begins at the hilus. Its large vascular canals remind us of the later-to-be-mentioned cav- ernous tissue of the urinary and sexual passages. It radi- ates outwards into a frame-work permeating the glandular cortical layer. At the surface of the organ the frame-work reunites into a more solid continuous substance (Fig. 156, b). The entire ovary is covered by a simple layer of low cylin- drical cells (a). This was formerly erroneously called a serous membrane, but now bears the name of the germinal epithe- lium, a designation the correctness of which we shall learn later. We have next to describe the glandular constituents of the ovary, which are by far the most important. Beneath the firmer connective-tissue border layer we meet with an almost non-vascular layer of youngest ovules, the cortical or primordial follicle zone (Fig. 156, c). We here discover the young ova, already represented in Fig. 5. They are small globular elements (0.0587 mm. large), with an elegant globular and vesicular nucleus (0.0226 mm.). 174 SEVENTEENTH LECTURE. The cell body is constituted by a membraneless protoplasma containing fat granules. Each of these ovules is surrounded by a corona of small nucleated cells. The whole is finally enveloped in connective tissue. These are the so-called pri- mordial follicles which, often occurring quite crowded here, present an enormous excess of egg-germs. Other primordial follicles (Fig. 5, 2) become larger ; the ovule, which has meanwhile also increased somewhat in size, appears to be surrounded by a thicker hyaline rind. The small investing cells now form a double row (a). In the further development, however, both the cell layers Fig. 156. — Ovary of the rabbit ; a, germinal epithelium (serosa) ". b, cortical or external fibrous layer ; c, youngest follicles ; rf, a somewhat more developed older one. are separated from each other ; there is thus formed a smaller cavity (Fig. 156, d) filled with a clear albuminous fluid. In the growing follicle, this cavity becomes larger and larger. The small cells increase and gradually form a strati- fied epithelium. The ovum lies at one point crowded against the wall, and surrounded and held by a heap of these cells. A developed vascular net-work has, in the meanwhile, also been formed in the follicular walls. THE FEMALE GENERATIVE APPARATUS. 175 The normal ovarium contains besides a small number of ripest gland capsules (12 to 20). These are the Graafian fol- licles (Fig. 157), discovered long ago by De Graaf. Their size is determined, in a measure, by the dimensions of the mam- malial ovum. In women they finally attain to 6 to 9 mm. Fig. 157. — Mature follicle ; a, ovum: epithelial stratum covering the same, &, and lining the- cavity, c ; d, connective-tissue wall ; ?, outer surface of the follicle. The parietes consist of a double layer, an inner one with a' close capillary net-work, and an outer one with the ramifica- tion of the larger blood-vessels. The wall itself (e, d) is unde- veloped connective tissue. We here again meet with the granular connective-tissue cells mentioned at page 54. They may surround the vessel like a mantle. The small epithelial cells of the follicles measure 0.0074 to O.O113 mm. (c). At one point, mostly at the bottom of the follicle (Schron, His), but occasionally also at the surface that is turned to- wards the germinal epithelium (Waldeyer), we meet with the mature ovum (a) surrounded by a thicker epithelial stratifica- tion (b). In the mammalial animal it remains uncommonly small, 0.2. to 0.3 mm. :n diameter. This explains why its discovery was I 7 6 SEVENTEENTH LECTURE. first made in 1827, by an investigator of great merit, K. E. von Baer. It appears scarcely conceivable to us ; for a sharp eye sees the ovule, removed from the ruptured follicle, as a white point, without a magnifying glass. The successor, however, stands on the shoulders of the predecessor. Let us tarry for an instant at this most important of all cells (Fig. 158), without which there would be no higher ani- mal world. Let us remove from its surface the cells, which have now become cylindrical, of the epithelial investment, and our at- tention will be first of all attracted by the thick (0.009 to 0.01 13 mm.), resistant hyaline capsule, the so- called zona pellucida or chorion (a). fig 158.— Mature ovum of ihe rabbit; It is an inwardly deposited pro- rt, zona pellucida : i, yolk ; c, germinal - vesicle ; d, germinal spot. duct of the surrounding smaller cells, and, seen with higher magnifying powers, is permeated by the finest radial passages, the so called porous canals. The cell-body is a thick, fluid, more or less cloudy mass. We perceive in it granules of albuminous matter, as well as small drops of fat. In many mammalial animals, the quanti- ty of the latter may become great, and the substance darker and darker. This cell body is call the yolk or vitellus. The cell nucleus (c) attracts our attention by its elegant globular form, bordered by the finest lines. It now lies con- centrically; its diameter is 0.0377 to 0.045 1 mm. It has received the name of the germinal, or Purkinje's vesicle. In it, and almost always single, we finally notice the nu- cleolus (d), a fat-like, glistening granule 0.0046 to 0.0068 mm. in size. It bears the name of the germinal, or Wagner's spot, the macula germinativa.* * We have just become familiar with quite ordinary things provided with special names. This nomenclature originated in a former epoch of embryology. Further- more, the follicular walls are called theca ; their epithelial lining has been denomi- nated the formatio or membrana granulosa, and the cellular substance surrounding the ovum the cumulus proligerus. THE FEMALE GENERATIVE APPARATUS. 177 The blood-vessels of the ovary pass, as we mentioned above, from the hilus into the medullary substance. They at once acquire such a development that the connective tissue forms a relatively scanty connecting substance. The outer surfaces of the veins coalesce with the latter tissue. The spindle cells of the connective tissue must be muscular, for the ovary is contractile (His, Frey). From the medulla numerous and elegant vascular expansions pass between the follicles of the cortex, circumvoluting them with the already described net- work. The cortical zone, alone, is very poor in blood-vessels, as we already know. A considerable wealth of lymphatics is also met with in the medullary substance. A net-work of the same also circum- volutes the follicles. The parovarium represents the remains of the embryonic primitive kidney or the Wolffian body. It consists of con- nective-tissue passages, lined with ciliated cells. The ovary also originated from this primitive kidney, and the permanent ordinary kidney from the efferent canal of the Fig 1 59. — The ovary of a human foetus of 32 weeks, in perpendicular section ; a, germinal epi- thelium ■ i, youngest ova cells (primordial ova) lying in this ; c, a growing connective-tissue trabe- cula; d, epithelial cells becoming buried ; e, youngest follicles ; /, ovum— and gcrmmal epithelial cells in groups : g, lymphoid cells. latter gland. Unfortunately, we cannot enter further into this subject. We merely mention that, according to Waldeyer, in the embryonic chicken, at an early period, at the inner side i 7 8 SEVENTEENTH LECTURE. of the primitive kidney, an epithelial thickening appears, into which the connective tissue of this organ sprouts in a hill-like form. The latter becomes the frame-work substance ; from the former originate the germinative epithelium, the epithelial cells of the Graafian follicle, and, as the favored daughters of the latter, the ova. This section of the development is represented by our Fig. 159, a copy from Waldeyer's excellent monograph. The first embryonic ovula, the "primitive ova," are, therefore, of epi- thelial origin. Pfliiger had, even before Waldeyer, acquired interesting conclusions concerning the ovaries of the creature after birth. From time to time, soon after birth, and then towards the period of parturition, in the adult mammalial animal, the old embryonic affinity reasserts itself. The germinal epithelium again proliferates downwards in a conical form, and is at last separated from the point of origin. Thus arise irregular, occasionally cord-like, and cy- lindrical masses. These are Pfluger's follicular chains. I have called them the egg strands (Fig. 160). In their axis we meet with certain of the epithe- lial cells which have grown to be ova. By constriction (2, a), new Graafian vesicles are formed. What becomes of the follicles of the ovary ? Before sexual maturity they appear to be frequently de- stroyed by fatty degeneration and also by colloid metamor- phosis (Slavjansky, Frey). During the period of propagation, Fig. 160. — Follicular chains from the ovary of the calf; i, with ova forming; s at a, showing constriction into Graafian vesicles. THE FEMALE GENERATIVE APPARATUS. 179 also, a similar destruction takes place in a portion of the follicles. Others, on the contrary, meet with a different fate. The ripest follicles, which have reached the surface of the ovary, become ruptured, naturally at the place of the least resist- ance, and, therefore, towards the surface. The follicular fluid with the 6vule leaves the organ through the ruptured outlet. The ruptured follicle is transformed into the so-called cor- pus luteum, that is — to express ourselves more intelligibly — it returns, at last, by a complicated process of cicatriza- tion, to a connective-tissue frame-work substance, leaving no trace. In the human female, the follicle normally ruptures at the menstrual period ; in mammalial animals at the period of rutting. The ovule, liberated from the ovary and received into the oviduct, there undergoes the familiar segmentation of the en- capsulated cell (p. 15). Without impregnation, however, this multiplying action is soon paralyzed. If the former takes place, the old life is merrily and energetically continued. The encapsulated ovum at last becomes an aggregation of numer- ous small cells. From these living building stones is con- structed the new animal body, somewhat as the architect builds his house with stones. But the latter, the lifeless ones, are brought from all directions, the former are the primitive offspring of a single cell, members of a living family. It is the difference between the living and the lifeless. The oviducts, Fallopian tubes, have, beneath the serous covering, longitudinal and transversely arranged smooth muscles. The mucous membrane is glandless,* and projects in a highly developed system of papillae and folds. The in- ner surface is covered by ciliated epithelium. During menstruation and pregnancy the womb or uterus undergoes extremely important anatomical transformations. There is scarcely any organ, except the ovary, perhaps, on * All attempts to discover nerves here have, thus far, been unsuccessful. !8 seventeenth lecture. which is so thoroughly impressed the stamp of a proliferating formative life as the uterus. Its fleshy substance is formed of longitudinal, transverse and oblique muscles. Developed in an annular form, it at last constitutes the sphincter uteri. The mucous membrane — its tissue reminds one of lymphoid connective substance — is lined with ciliated epithelium. Be- low, in the neck, commences the stratified flattened epithe- lium of the vagina. The surface of the mucous membrane is sometimes smooth (fundus and body), sometimes with trans- verse folds (upper portion of the cervix), sometimes projecting in papillae (terminal portion of the cervix). Tubular, frequently spiral uterine glands, which are sub- ject to considerable variation, occur in the fundus and body of the uterus. They have a lining of ciliated cylinder cells (Lott). Our glands disappear below. The uterus has a highly developed system of blood-ves- sels. The wide veins coalesce with the tissue of the latter, and gape in transverse sections. The lymphatic apparatus also acquires a great develop- ment, especially in the loose connective tissue of the mucous membrane, then in the muscular layer, and finally, in the subserous layer (Leopold). This is also in beautiful harmony with this proliferating formative life. The immense enlargement of the pregnant uterus consists in the first line, in an increase of the muscular tissue. The old mucous membrane is hereby disposed about the ovum as a so-called transient membrane, the decidua, while a new mucous membrane, destined to be a substitute, is meanwhile formed beneath. Still, much is here obscure, and, in certain groups of mammalial animals, we meet with great variations. In the vagina we find external annular, and internal longi- tudinal muscles. The mucous membrane shows numerous rugosities and folds, columnae rugarum. It has no glands, and is covered by stratified, flattened epithelium. The hymen is a vascular duplicature of the mucous mem brane. THE FEMALE GENERATIVE APPARATUS. 18I The clitoris lias a prepuce of mucous membrane tissue ; the female glans is also covered by such a membrane with numerous papillae. The corpora cavernosa and bulbi vesti- buli remind us of the same tissue in the male. The labia minora, nymphs, are folds of mucous mem- brane, containing no fat, but numerous papillae and sebaceous follicles. The labia majora are rich in fat, and have internally the characteristics of the mucous tissues, externally those of the corium. In the vestibulum and the ostium vaginas, numerous mucous glands occur. The glands of Duverney or Bartho- lini are larger organs of this kind. The lacteal glands are primarily of similar formation in the male and female body ; they do not become developed in the former, and in the latter only after a prolonged period of quiescence, and even then only when pregnancy commences. We recognize in the mammary gland an aggregation of in- dividual racemose glands, which open into numerous (18, 20 and more) canals, the so-called " lactiferous ducts." Examined in the earlier period of life, our organ ponsists merely of a ramified canal-work. It is hollow above ; below in its knob-like terminal portion, it is completely plugged by closely compressed cellular masses. The special gland- vesi- cles or acini destined for secreting are still wanting. This is the condition, during the days of childhood, of the male and female lacteal gland, though the latter gradually advances somewhat in its development. The entrance of puberty exerts no influence on the male organ, but a great one on that of the female. There is here a bud-like production of numerous terminal vesicles. As- sisted by a development of fat cells, they produce the curved elevation of the maturing female breast. In this manner the female gland is prepared for a possibly coming activity ; but it is only with pregnancy, and towards the end of the same, that the lacteal secreting apparatus acquires its complete de velopment. )82 SEVENTEENTH LECTURE. Let us now examine the organ at the height of its activity in the body of the nursing woman (Fig. 161). The gland vesicles, rounded or elongated (o. 1 128 to 0. 1872 mm.), are formed by a membrana propria with flat stellate cells. They have a simple lining of low cylinder cells (of 0. 01 13 mm.). Those finest se- cretory canals between the cells, which we have already mentioned at p. 134, have also been demon- strated here by means of injections. The excretory canal-work also has a cylindrical epithelium. How far the fatty secretion of our organ, the milk, depends upon the destruc- tion of the gland cell, or whether the latter structure does not simply express the produced or received fat substance from the membraneless, contractile cell-body — are questions which require more accurate investigation. In advanced life, the female mammary gland loses its secretory apparatus. It becomes reduced to the old canal- system of a long passed period of childhood (Langer). The colostrum (already mentioned at Fig. 124) contains, in addition to albuminous fat vesicles surrounded by a very thin envelope, gland cells and cell fragments, 0.0151 to 0.0564 mm. in size. The ordinary milk of a later period contains only the former elements, the so-called milk globules. The size of the latter varies from about O.0023 to 0.009 mm > Fig. r6i. — Gland-vesicles of a nurs- ing woman, with cells and capillaries. EIGHTEENTH LECTURE. THE MALE GENERATIVE GLANDS, THE TESTICLES WITH THE EFFERENT APPARATUS. The seminal gland or testicle represents in the male organ- ism that which the ovary does in the female body. We leave its coarser structure, for the greater part, to descriptive anatomy. A firm connective-tissue envelope, called the albuginea, invests our organ. Numerous and incomplete septa radiate from it into the interior, where they finally unite above into a thickened wedge-shaped mass, the corpus Highmori. The interior is thereby divided into conical lobules whose apices are turned towards the corpus Highmori. A testicle-lobule consists of an aggregation of uncommonly long convoluted canals or tubes. They present divisions and communications, and finally pass over into each other in the form of a loop, but never terminate in a cul-de-sac (Mihal- kovics). These tubules are called seminiferous canals. At the apex of the lobule, the seminiferous canal becomes united into a straight excretory duct (tubulus rectus) which, passing into the corpus Highmori, unites with others in a reticular manner and forms a further tubular system, the rete testis. From the latter continue nine to seventeen larger canals, the so-called vascula efferentia. They at first pursue a direct course, and thus perforate the albuginea; then, becoming narrow, they form with numerous convolutions several conical lobes, the so-called coni vasculosi ; the latter form the caput epididymis. The terminal canals gradually come together into a single one 0.3767 to 0.45 mm. in diameter. It forms, with numerous convolutions, the cauda epididymis. 1 84 EIGHTEENTH LECTURE. Further below, the efferent canal becomes straighter, and its diameter increases to 2 mm. It is now called the vas deferens. Not infrequently, a lateral csecal branch, the vas aberrans Halleri, has previously entered it. This is the coarser structure. Having become familiar with this compli- cated arrangement, let us investigate the histological texture. The seminiferous canals (Fig. 162) have about the same diameter throughout their entire length. Their diameter is, in most mammals, 0. 1 to 0.25 mm. They are re- markably large in the rat (0.4 mm.). In small animals the walls consist of a single layer of firmly cemented endothelial cells. In larger creatures, this inner layer is sur- rounded by others which show the same construction of flat nucleated scales, but are fenestrated (Mihalkovics). As we shall subsequently return to the parenchyma cells, we merely remark here that the efferent ductuli recti, deviating from these, have a different epithelial lining, namely, cylinder cells. In the rete testis there is no gland membrane; the cells are pavement shaped. Towards the end of the rete, how- ever, commences the cylinder epithelium of the epididymis. The quiescent semi- niferous canal is either entirely (Fig. 163, a, b), or, up to a narrow Fig. 163.— From the testicle of the calf ; a, seminiferous lumen, filled with canals seen in more oblique, b, in more transverse sections ; j t i 1 r, blood-vessels ; d, lymphatics. T O U n d e U polygonal Fig. 162. — Human semi niferous canal ; a, parietes , b. cells. THE MALE GENERATIVE GLANDS. 185 cells, measuring 0.0113 to 0.0142 mm. The peripheral ones present a radiated appearance. In man, their cell bodies may contain a yellowish pigment. A coagulated, originally thick fluid, albuminous substance between the spermatic cells has been erroneously regarded as a second cell-work. The connective-tissue frame-work substance of the organ is, as we have previously said, developed from the inner surface of the albuginea and the system of septa. In many creatures (man, dog, rabbit) fibrillated connective tissue prevails ; in others (rat, male cat, boar) it is much less developed. In the rabbit the connective-tissue bundles are invested by the first mentioned (Fig. 55, a) forms of cells (the thin, nucleated plates, with protoplasma in the centre, and a hyaline, cortical portion) ; there may even be regular, endothelial cell membranes spread out over the seminiferous canals and the blood-vessels. In the just mentioned second group of animals we find the granular connective-tissue cells (Fig. 55, b) in immense numbers, while in the first division they are more scanty, or are scarcely met with. These granular cells (generally rounded or polygonal, rarely having processes, rich in protoplasm, fat, and brownish pig- ment) remind one of the hepatic cell (Fig. 121). They have a strand or column-like arrangement. Very frequently the blood-vessels are here regularly ensheathed by such cell layers, as we have described them (p. 55) ' n connection with the vicinity of the vessels. The blood-vessels (Fig. 163, c) circumvolute the convoluted seminiferous canals in close apposition, with a long-meshed, tolerably wide capillary net-work. We find this net-work more strongly developed and rounded in the epididymis. The latter part, also, probably has a secretory glandular ac- tivity (Mihalkovics). Let us consider, finally, the lymph passages (d) ; for the gland tissue is entirely without lymphatic vessels. It was Ludwig and Tomsa who founded our knowledge of this sub- ject. Subsequent investigations, also a trifle of mine, have been added. 1 86 EIGHTEENTH LECTURE. The lymph passages keep in the spaces of the connective tissue, bounded by the membranous but fenestrated combina- tions of the flat connective-tissue cells. They form a copious reticular canal-work. In transverse sections of the seminiferous canals they form regular rings around the latter, with large expansions at the nodal points. A continued injection finally drives the mass through the spaces of the flattened cells, as far as the outer layers of the walls of the seminiferous canals. The solid inner layer of the latter alone prevents the further advance of the mass (Mihalkovics). Here and there a blood-vessel becomes en- sheathed by the lymph current, but this is not the rule. Larger lymph passages penetrate from the glandular por- tion into the septal system and from here, coalescing, pass beneath the albuginea. Having entered the latter, they be- come valved vessels, which unite with those of the epididy- mis. The final removal of the lymph takes place through the spermatic cord. The testicle arises, similar to the ovary, at the inner side of the Wolffian body. From its canal-work arises the epididy- mis (equivalent to the parovarium) ; the efferent canal of the primitive kidney, disappearing in the female, persists in the male generative apparatus, and becomes the vas deferens. The remainder must be left to the history of development. We have thus far considered only the quiescent gland. Let us now, however, examine the same at the height of its activity. Let us commence with its product, the semen, or sperm. It is by no means exclusively the product of the convoluted glandular canals of the testicle, but its fluid portions are cer- tainly also derived from the epididymis and the accessory glands, although its most important and characteristic ele- ments originate from the former source. The whitish, thickened fluid, spread out in a thin layer on the microscopic, glass slide, presents a remarkable appearance, which has been stared at for two hundred years, and was formerly very curiously explained. THE MALE GENERATIVE GLANDS. 187 Innumerable, lively moving, thread-like elements, the so- called seminal filaments, seminal animalcule, spermatozoa (Fig. 164) are here met with, suspended in a hyaline fluid. Their movement was, at an earlier epoch^ credulously accepted as a proof of an inde- v " v pendent animal life. The name of the seminal animalcule, spermatozoa, reminds one of that period. Nowadays we know that the motility of the seminal filaments is very nearly related to the ciliary motion (p. 35) ; we likewise know that the so-called " seminal animalcule " rep- resent tissue elements, cell derivatives. We are now no less familiar with the motley di- f; b- i6 4— Spo- J matozoaof t the versity of forms which these filaments present sh «j> ; . ' A middle piece; c, tail. in the animal kingdom. Let us confine ourselves to the class of mammalia. The filamentous, diminutive thing here shows a so-called head (a), then a somewhat thicker, thread-like, middle ap- pendage, the middle piece (b), and finally, extraordinarily thin, and becoming finer, the terminal piece or tail (c). There was formerly no distinction made between these fila- mentous portions. Whether this remarkable structure also has an internal complication is not determined, but is improbable. The head of the human seminal element appears as an oval disk, somewhat widened backwards, 0.0045 mm. long and about half as much in breadth, and' not more than 0.0013 to O.0018 mm. thick. The entire filament may have a length of 0.045 1 mm. ; but its terminal end is infinitely thin and difr ficult to recognize. In the fruitful copulation, the seminal filaments penetrate the zona pellucida of the ovum, conducted through the very fine porous canals of this envelope (Fig, 158, a), and pass into the yolk, that is, into the true ovum cell. They here finally disintegrate by fatty degeneration. The process of division which we have already mentioned i88 EIGHTEENTH LECTURE. at p. 14 may, indeed, commence without spermatozoa, and even in the mammalial animal ; but it soon ceases. When, however, the seminal elements have mingled their expiring body with the yolk, then (in an enigmatical manner, it is true), the multiplying process of the segmentation of the vi- tellus is continued, until at last innumerable building stones have been acquired, of which we have already spoken (p. 179). Whence comes the seminal filament ? For more than one generation this question has been very correctly answered : from the convoluted canals of the testi- cle. But the how has called forth the most diversified an- swers among the older investigators, their successors, as well as the present generation of histologics. The incipient, crude and bad methods of examination certainly led the pio- neers to the grossest delusions. That we at present understand the whole, I certainly doubt very much ; still we have made some progress. Let us listen, therefore, to the results of the most recent studies (Neumann, von Ebner, Mihalkovics). We have already mentioned (p. 185) that the most external gland-cell layer of the quiescent seminiferous canal presents a prismatic radiated form. This cell is the spermatozoa-producing structure. All the numerous inner cells of this glandular canal appear to have no future ; they form merely an indifferent redundant substance. When the seminal gland becomes active — in mammals this is only pe- riodically the case, generally once a year, in man in uninterrupted se- quence throughout the entire pro- creative epoch — when, therefore, the testicle is active, a remarkable metamorphosis occurs in these pris- matic parietal cells (Fig. 165, b). The epithelial cell-body grows inwards, that is towards the Fig. 165. — From the seminiferous canals of the rat ; a, parietes with the cell nuclei ; parietal cells and sperma- toblasts . c, the latter with small nar- row nuclear corpuscles ; d, inner cell layer. THE MALE GENERATIVE GLANDS. 189 axis of the glandular canal, into a pedicle or neck-like proto- plasma process. It might remind one of a rude and clumsy candelabrum — but the comparison is a lame one. These modifications of our peripherical cell layer have been appropriately named spermatoblasts (von Ebner). In each club-like projection there is formed a nucleus (c) — how, we do not know. It becomes the head of the seminal element. The protoplasma, further inwards, is changed into the filament or tail. Thus each of our spermatoblasts pro- duces a number (8 to 12) of seminal filaments. At last the latter are set free, and lie in the lumen of the convoluted canals of the testicle, the caudal end in the axis of the canal, and directed downwards (Fig. 166, 1, b, c, 2). Ova and spermatozoa are, there- fore, according to their origin, quite different things. The former repre- sent very highly developed cells ; the latter proceed from portions of a more simple cell body. Let us finally turn to the efferent apparatus. The vas deferens presents an exter- nal connective-tissue layer, a middle layer consisting of three strata of muscles, and, finally, a mucous mem- brane covered with cylinder cells. The latter acquires below a greater development. The seminal vesicles and ejacula- tory duct have a similar structure. The prostate presents a system of small racemose glands embedded in an abundance of connective tis- sue, which first acquire their com- plete development at the period of puberty. The epithelium has a double layer (Langerhans). The Cowper's glands likewise belong to the racemose for- FlG. 166. — Development of the rat's spermatozoa, i. Spermato- blast n, with head 6, and filament c. 2. Nearly mature semin;il fila- ment with adherent protoplasma re- mains. I9 o EIGHTEENTH LECTURE. mation. Their cells are cylindrical, but become lower in the efferent canal-work. The male urethra presents a pars prostatica, a consecutive membranous middle portion (pars membranacea), and a terminal division running through the penis (pars cavernosa). The latter portion is surrounded by a cavernous tissue (corpus spongiosum urethrse), which takes the shape of the glans an- teriorly. Two similar cavernous structures, the corpora cav- ernosa penis, are added. The mucous membrane of the urethra has at first flattened, and further downwards cylindrical cells. It is surrounded by loose connective tissue, which might be called cavernous in consequence of its great vascularity, and over this there are smooth muscles. Racemose glandules occur in the prostatic portion, as well as in the colliculus seminalis. The mucous membrane presents folds. In the middle and lower portions the muscular coating diminishes more and more. The mucous membrane of the lower portion contains excavations (lacunae Morgagnii) and small, undeveloped Littre's mucous glandules. Towards the orifice of the urethra stratified flattened epithe- lium again commences. The skin of the penis, thin and flaccid, has a loose subcuta- neous cellular tissue, free from fat, and permeated by smooth muscular fibres. An extensible connective tissue, free from fat, unites the two plates of the prepuce ; it also contains mus- cular elements. The thin skin of the glans has numerous papillae, which dis- appear in the epithelial covering ; the inner, mucous-mem- brane-like surface of the prepuce also shows such papillae. The Tyson's glands occur on the inner surface of the pre- puce, occasionally also on the glans, especially on the frenu- lum. They participate in a very subordinate manner in the formation of the fatty smegma praeputii. Let us also mention, in conclusion, the structure of the corpora cavernosa. These structures are surrounded by a firmer, elastic element, which is however poor in muscular elements, a so-called albuginea. It sends off innumerable THE MALE GENERATIVE GLANDS. 191 processes in an inward direction, which are sometimes larger sometimes smaller, in the form of trabecular and plates.- Con- nective tissue, elastic fibres and smooth muscular substance combined form the latter. This incomplete system of septa, as we must call it, is divided and interconnected in the most multifarious manner. We have, therefore, a system of spaces and cavities, remind- ing one of a bathing sponge, lined with vascular cells, des- tined to receive venous blood. Herein consists just the pecu- liarity of the so-called cavernous tissue. The various " cavernous bodies " present small subordinate structural peculiarities. We pass over these minutiae. Constantly filled with blood, they become periodically over- charged with the same, and cause the erection of the male or- gan. The cavernous bodies receive their blood supply to a slight extent from the arteria dorsalis penis, essentially from the arteria profunda?. These arterial branches, enclosed in the tissue of the septum, pass into the cavernous spaces, partly through a capillary net-work, partly with an intermediate opening (Langer). Corkscrew-like, crooked arterial branches, the so-called arteria? helicinae of J. Miiller, constitute artefacts (Bouget, Langer). The various venae emissariae serve for the removal of the blood from the caverni. Abundant lymphatic net-works are not wanting in the male urethra and the organ of copulation (Teichmann, Belajeff). The theory of the erection we leave to physiology. NINETEENTH LECTURE. NERVE TISSUE. We turn to the final and highest histological formation of the animal body : we refer to the nerve tissue. This has been included among the so-called " compound tissues," that is those which possess more than one element. And, in fact, we here meet with two such, namely, fibres and cells. The former bear the name of the nerve fibres, nerve tubes or primitive fibres ; the latter are called nerve cells or ganglion bodies. The human nerve fibres appear either as dark contoured medullated elements (Fig. 167) or as pale non-medullated ones (Fig. 172, b). Since the former constitute by far the most widely extended and impor- tant peripheral elements, let us begin our discussion with them. They are, like the non-medullated, for long distances unramified fila- ments, but of very unequal diameter* from 0.0226 to 0.0018 mm. and less. We distinguish, accordingly, broad or coarse nerve fibres (Fig. 167, a) and fine or narrow ones (c, d, e). Inter- mediately between these appear the nerve tubes of medium width (b). Let us commence our investigations of the structure with the coarse, medul- lated elements. Fresh and living, it appears like a thread of a homogeneous milk-glass-like substance. We recognize in it no further composition. 167. — Human nerve a, broad ; b, medium c. d. e, fine. NERVE TISSUE. 193 The nerve tube is, however, a marvelously changeable thing. Under our eyes, and against the will of the observer, it changes its original appearance most rapidly into a second, third cadaveric image. It is at present established that every broad nerve tube con- sists of three elements. It is invested by a, as a rule, very fine homogeneous con- nective-tissue envelope, the neurilemma, the Schwann's or primitive sheath (Fig. 169, b, 171, e). The latter contains, from point to point, an elongated nucleus. Occasionally the neu- rilemma appears considerably thickened (Fig. 171, c). In the axis, occupying a fifth to a fourth of the entire diameter, we recognize a pale cylindrical filament, formed of Fig. x68. — Human nerve fibres in various stages of coagulation. Fig. 169. — Various nerve fibres ; a, after treatment with absolute alcohol ; b, with collodion ; c t fibres of the lamprey ; rf, from the olfactory nerve of the calf; e and f, from the human brain. an albuminous substance. This is the axis cylinder, the sole essential portion of the nerve tube (Fig. 169, a, b, c, e.iyi, e). It is surrounded by the so-called nerve medulla or medullary sheath, a peculiar and very delicate combination of albumin- 9 194 NINETEENTH LECTURE. ous bodies, as well as lecithin and cerebrin. This investment originally conceals the axis cylinder. As soon as we isolate broad nerve tubes, we encounter the cadaveric form of the medullary sheath (Fig. 168). "They are now coagulated," is a customary expression of the histolo- gists. We meet with the most varying stages of coagulation, often close to each other, and even in the course of one and the same primitive tube. As a commencing stage, we discover on both sides a double contour, a sharp but dark external, and a closely applied finer border (Fig. 167, a, b, 168, b, above). Later, the double contours no longer run parallel with each other, and the inner one appears frequently interrupted (Fig. 168, b, below). The latter becomes constantly more and more irregular, and in the previously homogeneous axis por- tion, dark bordered, lumpy substances are formed (a, b). The process of coagulation may, it is true, be arrested at an earlier stage. The cortex then forms to a certain extent, a protective mantle around the axis portion. In other cases, the latter also does not escape its final destiny ; together with the cortex it is completely disintegrated into clots (c). It was a long-time before the just described structure of the nerve tubes could be agreed upon. The existence of the axis cylinder, especially, gave rise to heated debates. It is to-day a child's play to recognize the latter in any transverse section of a hardened peripheral nerve or — which amounts to the same — each primitive tube in a white column of the spinal cord (Fig. 170). The nerve tubes of medium size have a similar constitution. A similar structure — envelope, axis cylin- der and medullary sheath — is also perceived in the fine filaments of the nerve trunks. Pig. 170. — 1 r ans - vefseiy divided nerve The medullary sheath (Fig. 167, c, d) remains fibres from the posterior J \ o / > » / spinTcorf ' he human c l ear > an d simply demarcated, even with advanced post-mortem changes. Osmic acid, which rapidly blackens the medulla of the broad nerve NERVE TISSUE. 195 fibres, as it does other fatty substances, here acts much less thoroughly and more slowly . ; there must certainly, therefore, be a difference in the constitution of these two different fibrous substances. Our fine nerve tubes present an additional peculiarity. Every mistreatment, pressure, pulling or reagent to which it is subjected causes a certain displace- ment of the medulla, so that unnaturally thinned spaces interchange with rounded bulgings (e). The latter have been desig- nated as varicosities, and varicose nerve fibres are spoken of. Nothing of the kind exists during life. We here touch upon another unsettled question. Ranvier, at present the first histologist of France, called .attention to a familiar phenomenon, to constrictions which occur in the course of broad medullated (peripheral, but not central) fibres. Formerly, however, these con- strictions were always regarded as a product of the methods of preparation. Now, these constricted places (Fig. 171) are pretty regularly situated, arid be- tween every two, very nearly at half the distance, one meets with a nucleus of the sheath of Swann (a). It is thus in mammals, birds, and amphibia ; but in fishes the number of nuclei is greater between every two of these constric- tions. These Ranvier's "constriction rings," as the Germans have christened them, deserve — although we are at present far removed from an accurate knowledge of them — every consideration. The medullary sheath certainly isolates the axis cylinder ; but this medullary space permits the penetration of nutrient Fig. 171.— Nerve fibres of the frog; a, after treatment with picro carmine ; b, c, d, with osmic acid ; £, with nitrate of silver. 1 1)6 NINETEENTH LECTURE. constituents and the giving off of the products of decomposi- tion. Let us now pass to the pale non-medullated nerve fibres. Originally, in the fcetal period, all the primitive tubes of the entire nervous system were thus constituted. If we take one of the lowest fishes, the lamprey (petromyzon), we meet with this condition throughout its entire life (Fig. 169, c). A nucleated sheath invests the axis cylinder. Medullated nerve fibres are here entirely wanting. Let us turn, at a bound, to the highest animal being, to man. In us, the olfactory nerve, alone, consists throughout of pale, non-medullated fibres, as does in great part the sympathetic with its ramifications. These pale structures have been called Remak's fibres. They appear as delicate D.0038 to 0.0068 mm. wide, nucleated fila- ments (Fig. 172, b). Does what has been mentioned above, however, contain the entire structure of the nerve fibre ? We now encounter this diffi- cult question. It does not appear so ; nevertheless, we are once more at the limits of the microscopy of the present day. The axis cylinder, the best portion of the nerve tube, most probably consists of a bundle of extremely fine filaments. They (Fig. 173) appear to be embedded in a delicate granular substance. They have been called axis fibrillae (Waldeyer) or primitive fibrillae (Schultze). Here, also, the incitation was furnished by a bril- liant investigator, who has by no means been honored by his - cotemporaries in proportion to his merits, Remak, the founder of the modern history of development. Many years ago he saw this combination in the nerve fibres of the river- crab. Fig. 172. — A sympa- thetic nerve branch of a mamrnalial animal ; two dark bordered nerve fibres, it, With an excess of the Remak's formation, £. NERVE TISSUE. 197 Diagnostic weight has subsequently been laid on the finest varicosities of these primitive fibrillar (M. Schultze). We shall subsequently return to this. We are now, so far as it is at present possible, familiar with the fibres. Let ua turn to the cellular elements. They belong solely to the gray substance of the nervous system (the peripheral, as well as the cen- tral) ; the white substance consists through- out solely of nerve tubes. m m 1 ti .!<; Fig. 173.— Fibrillated arrangement of the axis cylinder ; a, a thick axis cylinder from the spinal cord of tho ox ; 6, nerve fibre from the brain of the torpedo. Fig. 174. "-Ganglion cells of the mamma- lia ; a, cells with connective-tissue envelope^ which are continued in fibres, d, d ; a, d cell without a nucleus ; b y two single nucleated ones ; and c s one with two nuclei ; b% a gan- glion b.idy witf.Ojt an envelope. We frequently encounter, in a very characteristic form, those cellular elements, the ganglion bodies (Fig. 174, B). It is one of the handsomest cell-forms which the organism pos- sesses. The dimensions of most of the globular, ovoid or pear-shaped elements lies between 0,0992 to 0.0451 and 0.0226 mm. In a very delicate granular, thickly gelatinous, generally colorless, occasionally brown or black pigmented mass, we meet with a globular, delicate walled nuclear vesicle, 0.0180 to 0.009 mm. in diameter. In it occurs, as a rule single, a dull glistening granule, the nucleolus, 0.0029 to 0.0045 mm - m s * ze * 198 NINETEENTH LECTURE. Our structure is surrounded by an envelope. It appears thick, a sort of nucleated connective tissue at the first glance ; however, the nuclei may have another signification, for, on the inner surface of the capsule, a lining of endothelial cells has subsequently been noticed. This envelope appears more simple and thinner around the ganglion cells of the lower vertebrates, fishes (Fig. 175) and amphibia. At the first, most cursory examination — and the older his- tologists, with their bad methods of investigation, arrived no further— all the peripheral ganglion cells appear to have no processes or, as a scholastic expression runs, are apolar. We have subsequently adopted an entirely different view ; apolar ganglion cells either do not occur at all, or only exceptionally as embryonic, arrested in their development, and possibly futureless ele- ments. About 1845, Koelliker, one of the most cele- brated histologists, dis- covered in the sympa- thetic of the vertebrates ganglion bodies which sent off from one of their ends a pale filament, which after a sometimes shorter, sometimes longer course, was enveloped in a me- dullary sheath, and be- came a nerve fibre (Fig. 175.4 In vertebrate creatures something of the kind has, it is true, been previously seen. These are the so-called unipolar ganglion cells. Soon after this, R. Wagner, Robin and Bidder, with R.-i Fig. 175.— From the peripheral nerve ganglion of a fish, godus lota ; a, b, bipolar ganglion "cells ; c, uni- polar ; rf, ?, abnormal forms. NERVE TISSUE. 1 99 chert, met with other conditions. They discovered the bi- polar cells. The spinal nerves arise by a double root; .an anterior, which passes over the spinal ganglion, and a posterior, which passes through the ganglion. Fig. 176.— Multipolar ganglion cell from the anterior horn of the spinal cordof the ox, with the axis cylinder -process (rt), and the branched protoplasma process, from which, at b t the finest filaments arise. As has been known since the days of Charles Bell, the former consists of motory, the latter of sensory filaments. 200 NINETEENTH LECTURE. On teasing out the spinal ganglion of a fish (the ray is most to be recommended) we recognize (Fig. 175) that each nerve fibre penetrates a ganglion cell, to again pass out at the other pole (a, b). Broad fibres connect with larger cells, narrow nerve tubes with smaller ones. The latter nerve fibres are probably sensory constituents of the sympathetic. Numerous individual, otherwise consti- tuted combinations occur, in addition to these, perhaps as anomalous products of development (d, e). Both varieties of ganglion cells show distinctly that their envelope passes over into the primitive sheath of the nerve fibre connected with them. As a third form, we have to mention the multipolar gan- glion cells. They were seen for the first time in the year 1838 (Purkinje). They are met with in man in the sympathetic ganglia, in the retina of the eye, and in the gray substance of the brain and spinal cord. In the so-called anterior cornu of the latter is found the elegant form of our Fig. 176. A membraneless cell body sends off a varying, often quite considerable number of delicate granular processes (b), which undergo repeated divisions and continual ramifications, until they at last disappear from view in the form of the finest fila- ments. The finest lateral filaments were regarded as primi- tive fibrillae of the axis cylinders (Deiters), but hardly with accuracy, for all is here obscure. Together with this system of processes — they have been , called protoplasma processes — we also meet with a long pro- cess, which is always single, and usually arises from the cell body, more rarely from the origin of another thick offshoot. It never ramifies, and is conspicuous from its sharper, homo- geneous appearance. This is the axis-cylinder process (a). Later it is invested by the medullary sheath, and becomes a nerve fibre. This has also, however, been recently doubted (Golgi). In the sympathetic of the frog Beale and Arnold met with an interesting, although not yet accurately determined struc- NERVE TISSUE. 201 ture of the cells (Fig. 177). From the interior of its rounded, or pear and kidney-shaped body passes a straight axis-cylin- der process (c), which subse- quently acquires a medullary sheath. From the surface of the cell arises, singly or doubly, with close spiral convolutions, an- other filament, which surrounds the straight axis cylinder with wider turns ; it may also run alongside of the latter (d), and subsequently leave iP(f), pass- ing further in a straight form. Whether these spiral fibres are elastic or — which we regard as more probable — are actually of a nervcus nature, is still unde- cided. Subsequent German in- vestigations have, unfortunately, not determined this. Finally, the fine, fibrillated formations, such as are pre- sented by the axis cylinder (p. 196), have also been most re- cently observed, continuing into the interior of the cell body, and more especially in the cortical portion of the latter. The finest fibrillae which stream in from the protoplasm a, as well as the axis-cylinder process, run sometimes divergently, some- times crossing each other. Fig. 177. — Ganglion cell from the sym- pathetic of the hyla or green tree-frog ; a, cell body ; b, sheath ; c, straight nerve fibre ; and d, spiral fibre ; continuation oi the former, e ; and of the latter, /. TWENTIETH LECTURE. THE ARRANGEMENT AND TERMINATION OF THE NERVE FIBRES. The spinal nerves and those of the brain appear white through the medullary sheaths of their tubular constituents ; the trunks of the sympathetic appear gray from the excess of non-medullated fibres. The former, at their exit from the central organ, become invested in a delicate connective-tissue envelope ; they are subsequently surrounded by an additional reinforcement of connective tissue, furnished by the dura mater. This affords together the nerve sheath, perineurium or neurilemma. This connective tissue penetrates, in a lamellar or sheath-like man- ner, between the bundles of nerve fibres, becoming, at the same time, looser and softer. Its modified boundary layer forms at last the primitive sheath of the nerve tube. A scanty, straight net-work of finest capillary vessels permeates the whole. Injections made from the lymph spaces likewise penetrate beneath the perineurium and between the nerve bundles (Key and Retzius). The primitive fibres run alongside of each other in the nerve trunk, undivided and indifferent. The nerve trunks usually send off their branches at an acute angle, the bundles of fibres bending away from the main path to the lateral. When anastomoses take place, groups of fibres pass, at the point of communication, from the one nerve to the other, or we have a double interchange of fibres. The perineurium becomes finer and finer in proportion as we proceed from the larger trunks to the finest systems of branches. Finally, it appears as a striated or more homo- geneous connective substance with rather stunted cells. ARRANGEMENT OF THE NERVE FIBRES. 203 The investigation of the peripheral termination of the nerve tubes — in the crude, incipient period they were erro- neously regarded as a noose or loop-shaped connection be- tween each two fibres — cost the histologists much trouble and labor, and even at the present day we are still far removed from a satisfactory scientific possession. We present only the most important facts, and leave numerous, in part very uncertain, minutiae to the more comprehensive text-books on this subject. Let us commence with the termination of the motory nerve fibres in the transversely striated muscle. If we follow the small nerve branches which have entered the latter, in suitable objects, for example, many quite thin membranous muscles of the frog, we meet with a few broad, double contoured nerve fibres, subsequently surrounded by a hyaline sheath. If the branch divides again, we not infre- quently perceive that something new comes over the nerve tube ; it becomes narrower, forming a Ranvier's constriction ring (p. 19S), and, at the same time, divides into branches, two as a rule. With the continued division of these smallest nerve trunks, this diminution of the nerve branches is con- tinued ; they divide into branches of a new order, and so on. The latter hereby become finer, but still retain the double contours for a distance ; at last they are bordered by a simple boundary line. In the lower vertebrates this ramification of the primitive tubes is very extensive. In fishes, the latter may finally divide into fifty and even one hundred branches. Reichert, many years ago, examined the so-called thoracic cutaneous muscle of the frog. It contains from 160 to 180 muscular filaments, but only from 7 to 10 nerve tubes pass in for their supply. While, therefore, in the lower vertebrates a motory primi- tive fibre supplies with its system of branches quite a number of transversely striated muscular filaments, the arrangement is different and higher in mammals (and even in reptiles and birds). The primitive fibre is much less divided ; the mis- 204 TWENTIETH LECTURE. propartion between the number of the nerve and muscular filaments is accordingly very much less. In regard to the termination, the lower vertebrates present a different condition from that of the higher. The termina- tion takes place regularly, however, in the interior of the muscular filament, beneath its sarcolemma. We consider only the mammalial muscle (Fig. 178). Fig. 178. — Two muscular filaments from the psoas of the Guinea-pig, with the nerve terminations : a, b, the primitive fibres and their continuation into the two terminal plates e.f: c, neurilemma with nuclei, d, d, and passing over into the sarcolemma, g, g; A, muscular nuclei. The nerve fibre (a, b), surrounded by an expanding nucle- ated primitive sheath (c, d), here passes to the muscular fila- ment. Its neurilemma becomes the sarcolemma (g). Beneath the latter, at the place of entrance, appears a nucleated, deli- cate molecular substance, a rounded or oval bent plate with nuclei (e,f), concave within, convex without. This (occur- ring only single in the mammalial muscle, and more towards the middle) is the terminal plate of Krause, Rouget and Engel- mann, or the nerve-mound of Kuehne. At f, we have the ARRANGEMENT OF THE NERVE FIBRES. 205 profile view ; at e, we see the structure from its broad external surface. Its size varies between 0.0399 to 0.0602 mm. ; the number of the nuclei from 4 to 20. The great delicacy and changeableness of the motory ter- minal plate impedes its further study considerably. Does the axis cylinder actually cease on spreading out into the former? Or, does the termination of the axis cylinder first occur in the interior of the terminal plate, so that the signification of some- thing like a cushion is to be ascribed to the latter? In the muscular filament of the lizard (Fig. 179) we obtain, under certain circumstances, a peculiar interesting appearance. In penetrating the terminal plate, the axis cylinder of the nerve fibre {b, c) divides and, rapidly losing its medulla, passes over by a continual ramification into a pale, obtusely branched, antler-like fig- ure^, d). The molecular nucleated substance is just beneath this ex- pansion. We are indebted to Kuehne for this observation. I have seen something similar by reexamination ; but we are once more at the limits of the present microscopy. Kuehne named this antler-like formation the true ter- minal plate. This is, according to our expe- rience, the present state of the matter. Others maintain deviating views, as most recently Arndt and Gehrlach. It is impossible for us to -enter here into a polemic, the more so as this lies at the limits of the present microscopic perception. Concerning the nerve termination in the muscles of the heart, only hypotheses exist at present. We have also no very satisfactory knowledge of the nerves of the smooth muscles. Many years ago various observers (Beale, Arnold, His, Fig. 179. — Muscular filament (a) the lizard : b, nerve fibre ; c, its branch with the peculiar terminal figure, , axis cylinder. 210 TWENTIETH LECTURE. Concerning the Pacinian capsules (Fig. 182) we have abun- dant and no longer to be doubted material. These structures have had a peculiar history. They have been known for more than one hundred and thirty years. They were described in 1741, in the doctor's dissertation of a certain Lehmann, having already been discovered by a professor Vater of that period. They were forgotten for nearly three genera- tions. They were rediscovered soon after 1830, without any presenti- ment of a predecessor, by Pacini of Pistoja and, almost simultane- ously, on the occasion of an ana- tomical concourse, by Parisian physicians. The attention of the German investigators was especially directed to our structure by the monographs of Henle and Koelliker, in the year 1844. As a student at that' time in Goettingen, I had already found them in the abdominal cavity of the cat, and had seen the entering nerve. Let us leave these historical reminiscenes, however, and pass to matters of fact. The Pacinian bodies appear as elliptic structures, measur- ing 1 to 2 mm. and more, sometimes more elongated, some- times more developed in width. Without the microscope, we perceive them to be tense, tolerably firm, semi-transpar- ent, and with white axial striations. They are regularly met with in the human body on the nerves of the palm of the hand and the sole of the foot, especially of the fingers and toes. Their total number varies Fig. 182. — Pacinian body from the mes- entery of the cat ; r )> which are also obliquely directed, adhere in three or fourfold rows to the outer pillars of this Cortian tunnel. Fur- ther outwards occur spindle-shaped elements, "supporting cells" of Hensen (z), and then, gradually becoming flattened, lower cubical epithelial cells. The supports of the inner and outer pillars lock into each other in a quite peculiar form. From this point is developed an extremely remarkable horizontally extended membrane, the lamina velamentosa of Deiters (/, /). It is impossible to describe here the marvelous reticular structure. Where do the primitive fibrillae of the cochlear nerves end ? Freed at last from the confinement of the lamina spiralis ossea, it passes between the inner pillars in the tunnel of the Cortian organ. They are said to have previously become partially, lost in the inner hair cells. They now terminate in the outer hair cells (w). Notwithstanding the infinite pains and labor bestowed on this subject, it still stands on a weak foundation. TWENTY-FOURTH LECTURE. THE ORGANS OF SENSE, CONTINUED. — THE EYE. We have still to mention the termination of the optic nerve. In doing this we must of course draw into the circle of our discussion the entire eye, that magnificent and won- derful organ which is so important for the physician. Never- theless, in consequence of its extremely complicated structure, we can only present a cursory incomplete description. The eyeball (Fig. 199) presents first an external capsular m M Fig. 199. — Transverse section of the eye ; a, sclerotica ; b, cornea ; c, conjunctiva ; //, circulus venosus iridis ; e, choroid, with the pigment layer of the retina ; f t ciliary muscle ; g; ciliary process ; /i, iris; i, optic nerve; z v , colliculus opticus; k, ora serrata retinae; /, crystalline lens; vi, tunica Descemetii; «, membrana limitans interna of the retina; 0, membrana hyaloidea ; $, canalis Petiti ; q, macula lutea. system ; the posterior, opaque, greater portion is formed by the sclerotic (a) } while the anterior, smaller, transparent seg- THE EYE. 247 ment (6) is constituted by the cornea. These membranes enclose a black stratum, the so-called uvea. It consists of the choroid (*?) with the ciliary processes (g) and, applied exter- nally to the latter, the ciliary muscle (/) and, finally, a more anterior ring-shaped disk, the iris (/*). The contents of the hollow ball are formed by the various light-refracting media. Even the cornea {b) participates in this action. Next to it comes the so-called humor aqueus, that is, the watery contents of the anterior and posterior chambers of the eye (in front of /). Then follows a firmer structure, the most important refracting body, the crystalline lens (/). The completion is formed by a large globular mass, having a concave impression in front, the vitreous body or humor vitreus (behind /). The greater portion of the latter is covered by the cup- shaped expansion of the optic nerve, the retina (i). It termi- nates anteriorly, according to the usual impression, in the region of the origin of the ciliary processes, with an undulated border, the so-called ora serrata (k). A very complicated system of vessels, springing almost exclusively from the arteria ophthalmica, supplies our organ with blood. Lymphatics are, naturally, also not wanting. The cornea, with its two homogeneous boundary layers, was mentioned at p. 56; the stratified pavement epithelium of the anterior surface at p. 31 ; the simple cell layer of the posterior at p. 29 ; the nerves at p. 207. We mentioned at that time the system of passages of the cornea, and ascribed fo them a sort of parietes. Differences of opinion prevail concerning this, however. The passages of this system of juice clefts (Fig. 200) may be artificially filled by the puncturing method, in successful cases, with the pres- ervation of their old shapes, in numerous others, however, distorted, with the appearance of wide misshapen canals. They have been not badly termed "rupture spaces." The circumstance is interesting that a successful injection of the juice-spaces finally leads to the lymphatics of the conjunctiva. The cellular contents of the canal-work has caused endless 248 TWENTY-FOURTH LECTURE. controversies ; not the lymph corpuscles wandering through them, but rather the "fixed" corneal cells (Fig. 200, to the left and below). They are stellate and water-wheel-like cells, the nucleus of which is always invested by some protoplasm, while the peripheral portions are metamorphosed into homo- 'WSMMM. mmm Fig. 200.— The human cornea impregnated with silver. The corneal corpuscles, that is, the system of juice-spaces, colorless. To the left, below, four metamorphosed parenchyma cells. geneous veil-like plates. The cells probably have a limited contractility. Their processes do not, according to our views, form any connected net-work. Hence, a portion of the juice- canals remain filled with fluid. All this is disputed by others, however. No one should here leave the decision with confi- dence to one reagent, such as gold, for instance. The sclerotica (p. 57) is a firm connective-tissue membrane, and consists of bundles arranged meridionally, with others crossing them in an equatorial direction. In front they pass continuously over into the modified hyaline connective tissue of the cornea. It also contains regular passages with lymph corpuscles and in part colorless, in part pigmented connective- tissue cells (Waldeyer). It appears to have nerves only at the corneal border. At the margin of both membranes, although belonging to the inner surface of the sclerotica, we meet with a complicated ring-shaped reservoir. This is the sinus Schlemmii (Fig. 199, d). It has been declared to be a venous reservoii THE EYE. 249 (Leber). Others regard it as a lymphatic passage (Schwalbe, Waldeyer). Posteriorly, the sclerotica passes over into the external sheath of the optic nerve, derived from the dura mater. This membrane is finally strengthened by the insertions of the ten- dinous bundles of the ocular muscles. The system of the uvea, with the exception of its most anterior portion, the iris, is characterized by very considerably developed vessels. The entire inner surface (and the posterior surface of the iris) is covered by the pigmented outer epithelium of the retina (p. 30). During a portion of the fcetal period, the latter extended much further forwards than it does at a more mature period. The greater portion of the uvea is formed by the posterior segment, the choroid. The thin membrane consists of sev- eral, not sharply demarcated, connective-tissue layers. We recognize a, an inner hyaline boundary layer, 0.0006 tc O.0008 mm. in thickness, thicker and more uneven in front ; b, a thin homogeneous ' layer, with extraordinarily developed stellate capillary net-works (choroidea capillaris) ; c, the choroid proper of the histologists, with stellate, very generally pigmented connective-tissue cells, and a great wealth of arte- rial, as well as venous vessels ; and, finally, d, a loose pig- mented connective tissue, which forms the connection with the inner surface of the sclerotica. It is called the lamina fusca, and also the supra-choroidea ; it forms a lymphatic space. The vascular net- work in the ciliary body, and in the ciliary processes which project inwards from the latter, is greatly developed. The substratum remains similar to that of the choroid, though the pigmented connective-tissue cells dis- appear. Externally to these processes we meet with a peculiar smooth muscular mass, the tensor choroidese, musculus ciliaris, or ligamentum ciliare of an older epoch (Fig. 199, /). The human ciliary muscle arises from the inner side of the u* 250 TWENTY-FOURTH LECTURE. boundary region of the cornea and sclerotica. Meridional bundles of the former radiate in a posterior direction into the ciliary body. Below and inwards occur interwoven filaments, and still further inwards, circular bundles (Mueller's ring muscle). We meet with colorless connective-tissue cells in the con- nective-tissue substratum of the iris of light eyes, and pig- mented cells in that of dark ones. Besides these, smooth muscular elements occur. Annular bundles (Fig. 1 201, a) Fig. 201. — Surface of the human iris ; a, the sphincter ; b, the dilator of the pupil. form the constrictor or sphincter of the pupil. From it pro- ceeds the dilator pupillze, an object of controversy of later years. Muscular bundles, which are at first separated, form more peripherically a connected radial layer of fibres (b). At the ciliary, that is the outer border, we finally meet with an an- nular muscular layer. This external or ciliary border of the iris gives rise at its anterior surface to another peculiar tissue, the ligamentum pectinatum iridis (Huek). We have already learned (p. 56) that the posterior surface of the cornea is covered by a hyaline membrane, the mem brana Descemetica or Demoursii. At its periphery, this posterior covering layer passes over into a peculiar reticular tissue (probably, in man, most intimately connected with the elastic tissue), which passes through the outer margin of the THE EYE. 251 anterior chamber of the eye. This is the ligamentum pectina- tum, which has just been mentioned. Its trabeculae are covered with epithelial cells. The anterior surface of the iris also has such a layer. An incompletely closed, ring-shaped canal, which is bounded by the trabeculae of this ligamentum, has been called the canalis Fontanae. Small ganglia of the ciliary nerves occur in the choroid. The ciliary muscle and the iris are more plentifully supplied with nerve fibres, but their manner of termination we do not yet know. Concerning the crystalline lens and the vitreous body in general, we refer to pages 78 and 45. There is one circum- stance which requires more special mention here. According to a widely disseminated acceptation, the hyaloid membrane (Fig. 199 in the vicinity of k), separates into two leaves, a posterior and an anterior, the so-called zonula Zinnii, which is impressed in a ruffle-like manner by the ciliary processes. Both continue on to the crystalline lens at its equatorial zone. The zonula Zinnii presents a peculiar pale and resistant sys- tem of fibres. A three-cornered annular sinus, bounded by both lamellae, bears the name of the canalis Petiti. Much is still obscure here, and the space is, after all, only an artefact (Merkel,, Mihalcovics). Let us now turn to the expansion of the optic nerve into the retina. Our membrane has its greatest thickness (0.38 to O.23 mm.) at the place of the entrance of the optic nerve. It becomes thinner (to about the half) towards the periphery. Passing beyond the equator (thinned to 0.09 mm.) it termi- nates as the so-called ora serrata (Fig. 199, k). Externally from the place of entrance of the optic nerve (?'), about 3 to 4 mm. removed from it, is the macula lutea, the seat of the most distinct vision (q). In its centre there is an excavation, the so-called fovea centralis. The retina, provided with numerous other elements, appears to be an extraordinarily complicated structure, and, at the same time, of extreme delicacy and variability. It has been the object of infinite research in older and more recent times ; TWENTY-FOURTH LECTURE. but, notwithstanding the labors of H. Mueller and M. Schultze, we are still exceedingly distant from a conclusion, as Schwal- be's most recent studies show. The retina (Fig. 202) is invested externally by the simple pigmented epithelial layer already familiar to us (p. 30). Then (1) we have the stratum of rods and cones ; thereupon follows the so-called external limiting mem- brane, the membrana limitans ex- terna (the transverse line between 1 and 2). Next comes the external granular laj'er (2), then the inter- granular layer (3). Thereupon fol- lows the inner granular layer (4), then the molecular stratum (5). Further inwards we meet with the stratum of the ganglion cells (6), thereupon the radial expansion of the optic nerve fibres (7). The termination is formed by the inter- nal limiting membrane, the mem- brana limitans interna (10). The layer of rods and cones, as well as the external granular layer, is called by Schwalbe the neuro-epithelial stratum, all the rest the cerebral stratum. In the structure of this thin and wonderfully complicated mem- brane we must, however, distinguish two different elements, connective tissue and nervous. Let us first take the former into account (Fig. 203, A), and commence at the inner surface. The membrana limitans interna (/), an apparently hyaline, O.OOii mm. thick layer, deserves mention as the first connec- tive-tissue boundary layer. In an inward direction (to- wards the vitreous body), smoothly demarcated, it passes over Fig. 202. — The human retina in ver- tical section : i. layer of the rods cones, demarcated below hy the mem- brana limitans externa ; 2,. the exter- nal granular layer ; 3, intergranular iayer ; 4, internal granular layer: 5. line granular layer ; 6, layer of gan- glion cells : 7. expansion of the optic nerve fibres : 8, Mueller's supporting fibres ; o, their transformation into the inner limiting membrane ; 10, the mem- brana limitans interna. THE EYE. 253 externally (towards the choroid), commencing with a triangu- lar expansion, and then diminishing into a connective-tissue radial fibre system (e), which is wanting only in the macula lutea. Fig. 203. — Diagramatic representation of the retina ; A, connective-tissue frame-work ; (7, mem- brana limitans externa ; e, radial or Muellerian supporting fibres with their nuclei, e* ; d, frame- work substance of the intergranular, and g. of the molecular layer ; /, membrana limitans in- terna ; B, nervous elements ; b. rods with outer and inner members ; c, cones with outer member and body ; l>\ rod, and c\ cone granule ; d, expansion of the cone fibre into the finest fibrillar in the intergranular layer ; /, granules of the inner granular layer ; g, confused mass of finest fibres in the molecular layer ; /4, ganglion cells ; /t\ their axis-cylinder processes ; i, \ayer of nerve fibres. These are the Mueller-'s supporting fibres (e). They in- c.ease more and more towards the anterior terminal portion. 2 54 TWENTY- FO UR TH LECTURE. Lateral branches of the latter lead to manifold communica- tions. In the molecular (g) and the intergranular layer (d) there is thus formed a very fine reticular frame-work, such as we are already familiar with in the gray substance of the cere- bro-spinal system (p. 220). Nuclei or cell equivalents occur occasionally in the system of supporting fibres, as in the external granular layer (e*). The supporting substance certainly extends as far as the base of the rod and cone layer (a). There is scarcely any doubt, however, that it extends still further as a delicate, homogeneous connecting substance. At the former locality it forms, as the membrana limitans externa, a fenestrated boundary layer, further outwards a connecting medium of the rods and cones. Having thus become familiar with the connective-tissue sub- stratum — it should by no means be genetically confounded with the ordinary connective tissue — let us pass to the ner- vous elements of the retina (£). Let us here select the re- versed course, and commence with the outer layer. This stratum is formed by the rods and cones. The whole layer is called the rod-layer, stratum bacillosum. They are terminal nerve cells, similar to those which we previously met with at the higher nerves of sense. Those of the retina, however, possess many peculiarities, and we have a more ac- curate knowledge of them than of their relatives. The cir- cumstance is also interesting that the rods and cones vary according to animal groups. Their dimensions are propor- tionate to that of the red blood cells. The rods, bacilli (B, b), are slender cylindrical structures. They consist (Mueller, Braun, Krause) regularly of two parts, an apparently homogeneous narrower so-called " outer mem- ber," which refracts the light more strongly, and a shorter ' ' inner member. " The latter appears paler, somewhat granu- lar, and of considerable diameter. In the lower vertebrate animals the retinal pigment forms regular sheaths around the outer member of the rods and cones. In mammals and man the pigment sheath is less developed. THE EYE. 255 The rods acquire their greatest length, 0.06 mm. and more, at the bottom of the retina. Further forwards they become shorter, towards the ora serrata they are only 0.0399 mm - high. Their diameter may be estimated at 0.0016 to 0.0018 mm. Downwards or inwards, beneath the membrana limitans externa, the rod becomes pointed, and runs out into an ex- traordinarily fine filament, a primitive nerve fibrilla (Fig. 203, B, Fig. 204, 1, 4, Fig. 205, 1, 3). The latter passes through the outer granular layer verti- cally (and also radially). A small cell, the so-called " rod granule " (Fig. 203, B, b\ Fig. 204, 1, 2, 3, Fig. 205, 3) is embedded in its course, sometimes higher up, sometimes further down- wards. This granule forms the single element of the outer granular layer. Still more complicated textural con- ditions have been observed in the rods (Fig. 204). At the border of the in- ner member towards the outer mem- ber, embedded in the former, a plano- convex body has been found w^th its plane base directed upwards (1, a, 2). " rod-ellipsoid " of Krause. Furthermore, as has been long known, the outer member breaks up into transverse plates (3). These discs may have a thickness of 0.0003 to 0.0004 mm. in man (Schultze). The outer member shows a longitudinal striation, caused by longitudinal, channel-like depressions, with longitudinal elevations springing up between them, like a fluted column (Fig. 204, I, 2, and Fig. 205, I a). Longitudinal striations have also been subsequently discovered on the inner members (Fig. 205, 1, and 3 b). In the axis of the rod a very fine filament, a primitive nerve fibrilla, is also said to have been noticed (Ritter). Fig. 264.-^-Finat structure of the rods ; I, from the chicken with the outer and inner mem- ber, as well as the cone'ellip- soid ; 2, from the frog : 3, the outer member of the -od uf a frng dividing into transverse discs ; 4. rod with granule from the Guinea-pig. This is the so-called 256 TWENTY-FOURTH LECTURE. Our present knowledge concerning the cones (Fig. 203, B, c, Fig. 205 2), is uncertain. In man, they have the form of a slen- der bottle. Their base rests on the membrana limitans externa. Upwards, the cone passes into a shorter, conical, infinitely changeable structure, the so- called cone rod (Fig. 203, B, above c, Fig. 205, 2 a). It is the equivalent of the external member of the rod, charac- terized by its great tendency to break up into transverse discs. The inner member, or the cone body (Fig. 205, 2 b), also shows the longitudinal striation, similar to the equivalent portion of the rod. At the base of the rod, immediately beneath the limitans externa, we meet with a cell-like body, the so- called cone granule (Fig. 203, B, C, Fig. 205, 2, below d). A broad cone filament (up to 0.0029 mm - m thickness) finally runs downward, passing through the outer granular layer (Fig. 203, below c'). It is a fascicu- lus of primitive fibrillae. Interesting local variations (Fig. 206) in regard to the num- ber of cones and rods occur in the human eye. In the macula lutea, the seat of the most distinct vision) we meet with cones alone, which have become extremely fine (1). In the vicinity the latter are still quite crowded, and are Fig. 205. — Fibrillated cover- ing of the rods and cones ; i, rods ; 2, cones of man ; a, outer ; i, inner member ; c, rod-filament ; d, limitans ex- terna ; 3, rod of the sheep. The fibrilhe project beyond the inner member; the outer mem- ber is wanting. Fig. 206. — The rod layer seen from without ; a, cones ; 6, cone rods ; c, ordinary rods ; I, from the macula lu- tea-: z, at the margin of the same : 3, from the centre of the retina. THE EYE. 257 surrounded by a single circle of rods (2). The further out- wards we proceed, the further we find the cones removed from each other, and the greater the number of rods situated between them (3). Apes, and the most of our domestic animals, present an analogous condition. Nocturnal animals, such as the cat, have only stunted cones ; bats, hedgehogs, moles, are entirely deprived of the latter elements. Birds, on the contrary, generally have an abundance of cones. In the chameleon and lizard there are no rods at all ; we find only cones, as in the human macula lutea. The rod appears to be the ter- minal apparatus, serving for the objective colorless vision, as the cone does for the color perception of the outer world (Schultze). The membrana limitans externa, the sieve-like fenestrated boundary structure, we are already familiar with. The rod apices pass downwards through small spaces, the cone gran- ules through larger ones. Finally, this membrane sends out- wards the already mentioned delicate homogeneous connect- ing substance between the rods and cones. The external granular layer, stratum granulosum externum, is already familiar to us so far as its connective-tissue frame- work is concerned. It (Fig. 203, B) consists of layers of small cells stratified over each other, a minimal body closely surrounding the nucleus. We distinguish here the larger higher cone granules (c'), measuring 0.009 to 0.012 mm., and the smaller rod granules, measuring 0.0045 to 0.0079 mm., situated more deeply. The latter alone present a peculiar, perhaps normal transverse striation (Fig. 204, 4). Thus far the connection of the retinal elements is clear. Now, however, on coming to the so-called intergranular layer, the stratum intergranulosum, this clearness is lost. There exists here a grievous defect of knowledge. Schultze, the excellent investigator whom we have thus far followed, asserted that the finest rod-fibrills;, having arrived at the intergranular stratum, formed very fine terminal knobs (Fig. 203, B, above d). This is decidedly not the case. The 258' TWENTY-FOUR TH LECTURE. filament simply bends into another plane, suddenly and at a considerable angle. I have convinced myself of this with certainty. The broad cone fibres divide at the same place into three very fine processes (above d). In the most delicate connective-tissue frame-work of the intergranular layer we meet with a confused mass of fine horizontally and obliquely disposed filaments (d), the con- tinuations of the rod and cone fibrillar. The inner granular layer— the stratum granulosum inter- num — contains, in the first place, as we already know (A, e'), connective-tissue nuclei or cellules of oval shape. Together with these appear layers of sharply demarcated, globular, nu- cleated cells (B,f), into the upper pole of which sinks a rather fine nervous filament, to again pass out at the lower pole, very much finer, and continuing further in a perpen- dicular direction. These nervous granules do not show any transverse striation. The molecular or fine granular layer, stratum moleculare (B,g), repeats, although with greater thickness, the fine con- nective-tissue spongy structure of the stratum intergranulo- sum. We again discover in it a confused mass of primitive fibrillar. Ascending fibres from the more deeply situated cells of the intergranular layer, having entered this confused mass, may be obseryed here and there ; following their course is not to be thought of. We have here, therefore, a new de- fect in our knowledge of the retina. We now arrive at the layer of the ganglion bodies, the stratum cellulosum (B, It). These occur stratified (in 10 to 6 layers) at the bottom of the retina, to gradually appear to- wards the periphery as a single layer, and with an increasing distance from each other. With the exception of the macula lutea, where the ganglion bodies are bipolar, they form fine multipolar cells of not inconsiderable size (up to 0.0377 mm.). Their protoplasma processes turn outwards, and finally disap- pear with their terminal branches in the maze of fibres of the molecular stratum ; their axis-cylinder process is directed in- THE EYE. 2S9 wards (//). It passes over into a nerve fibre of the optic nerve-fibre layer, the stratum fibrillosum (2). In order to comprehend the latter we must commence with the contents of the optic nerve. It has medullated nerve fibres, 0.0045 to 1.0014 mm. thick. Having entered the ball of the eye, their medullary sheath is lost, and they become pale axis cylinders.* Having advanced into the retina, our optic nerve fibres di- vide and reunite at acute angles into bundles, forming a nerve plexus. In proportion as we follow their further course for- wards, the fibre bundles become thinner and thinner, and the distance between them is constantly increased. At last we meet with only isolated axis cylinders. We have grounds for assuming that each optic-nerve fibre penetrates the body of a ganglion cell as an axis-cylinder process ; still we cannot prove this at the present time. The membrana limitans interna, of a connective-tissue na- ture, has been previously mentioned. The best portion of the retina, the yellow spot or macula lutea, requires a short mention. The connective-tissue frame-work substance, with the ex- ception of the limitans interna, is undeveloped. The nerve- fibre layer likewise disappears; the layer of the ganglion cells, still largely developed at the periphery, also disappears completely in the centre of the fovea. The molecular and inner granular layers also suffer the same fate. There re- mains, therefore, only the (exclusively occurring) cones with the stratum granulosum externum. The latter (Fig. 207) are no longer as of old. Their body has at last become narrowed to 0.0028 to 0.0033 mm. (Schultze) ; it has diminished to nearly the thinness of the rod, and the cone rod too. 001 to 0.0009 mm - The cone fibre appears to have participated but little in this thinning. The * It is remarkable that in individual human retinas the medullary sheath of the nerve tubes is preserved. In the dog the same not unfrequently occurs ; in rab- bits and hares it is even the rule. 260 TWENTY- FOURTH LECTURE. cone granule lies sometimes higher, sometimes deeper (a) ; we might say from necessity. We meet with still another condition. In the peripheral layers of the retina the cone fibre passes through our mem- brane in an ascending perpen- dicular direction. The latter now leaves this direction more and more, to pass obliquely out- wards and downwards (a). This induces beneath the outer gran- ular layer (that is the cone gran- ules), a quite peculiar appear- ance. Forwards, towards the ora serrata, the retina increases in thinness, and the nervous ele- ments diminish ; the connective tissue frame-work acquires the upper hand more and more; finally all the nervous elements have disappeared. By the ciliary portion of the retina is designated a system of cylindrical cells which lie on the zonula Zinnii beyond the ora serrata, and run as far as the iris, according to many even to the pupillary border of the latter. The blood-vessels of the retina, springing from the arteria centralis, form an elegant wide-meshed reticulum of very fine tubes. They occupy the inner portion of the retina, but pass outwards to the inner granular layer, and perhaps still fur- ther. The adventitia of the same surrounds the inner layer but loosely, leaving a lymphatic space. It is impossible for us to enter into the exceedingly com- Fig. 207. — Cones from the macula Iutea and fovea centralis of man ; v, " subvaginal " space between the in- ner and outer sheath of the optic nerve ; fi, ''per- ichoroideal" space connected with the Tenon's space by oblique passages. 262 TWENTY-FOURTH LECTURE. connection with the lymphatics of the nervous central organs,, injected from the subdural space of the brain (p. 231) an intermediate space located between the external and internal sheath of the optic nerve, the subvaginal space of Schwalbe (s b v), and from this they drove the injection mass into the perichoroideal space of Schwalbe. Schwalbe does not, how- ever, accept the latter communication. Injection masses may be forced beneath the inner sheath of the optic nerve, between the bundles of optic-nerve fibres, and this may be done from the subarachnoidal space of the brain (p. 231). The lymphatics of the retina invest its capillaries and veins, therefore, in a sheath-like manner. We return to the chambers of the eye, the central reservoir of the lymph of the anterior portion of the globe. What is the relation of its affluent passages ? In the first place a cleft system leads from the canal of Petit into the posterior, and thus into the anterior chamber of the eye. Wider and more important introductory passages open from the Fontana's space in the ligamentum pectinatum iridis, probably for the lymph of the iris and ciliary pro- cesses. Injection masses pass from the periphery of the membrane of Descemet into the canal of Schlemm (p. 248). Can a communication between the lymphatic and venous passages actually exist here, similar to that which Key and Retzius admitted, by the aid of the Pacchionian granulations for the membranes of the brain (p. 232) ? Leber, an observer who has rendered great service to the anatomy of the eye, has, it is true, disputed this, and he may be right. We have still to mention, briefly, the external, less import- ant appendices of the eyeball. The eyelids contain, embedded in the firm connective tis- sue of the tarsal cartilage, the so-called Meibomian glands, short sinuous tubes with fatty parenchyma cells, but without a membrana propria or muscular tissue in the excretory duct. Its secretion is the sebum palpebrale. THE EYE. 263 The conjunctiva presents a complete mucous membrane over the posterior surface of the eyelids and the anterior sur- face of the sclera ; only the stratified pavement epithelium remains over the cornea, the mucous membrane having become metamorphosed into corneal tissue. The conjunctival glands are of manifold species. In man and in certain mammals we meet with small mucous glandules, though the cells contain fat granules. Convoluted glands' (Fig. 119) occur at the periphery of the cornea in ruminating animals (Meissner). Simple culs-de-sac have been recognized in the hog, externally to the corneal periphery, towards the outer canthus of the eye (Manz). In the tarsal border of the human eye we meet with modified sudoriparous glands (Waldeyer). Concerning the trachoma glands, we have already commu- nicated all that was necessary (p. 1 13). In man there are probably no true lymphoid follicles (Waldeyer). The ter- minal bulbs of the conjunctiva have been mentioned at p. 209. The tear-gland, glandula lacrymalis, consists of an aggre- gation of single racemose glands. We are not yet familiar with the nerve terminations here. The efferent apparatus presents differences of structure in its different portions. We leave the description of them, like that of so many other things, to more comprehensive text-books. INDEX. Actnus of the glands, 130. Adventilia of the capillaries, see Vessels. Air cells, see Lungs. Alveoli of the lungs, 158. \.mceboid changes of form of the cells, 9. Anthracosis of the lungs, 160; of the bronchial glands, 160. Aquula Cotunnii (perilymph) of the audi- tory organs, see Auditory apparatus. Aquula vitrea auditiva (endolymph), see Auditory apparatus. Arachnoid, see Nerve centres. Arrectores pilorum, 81. Arterise heliciniE, 191. Arteries, 94. Arteriolse recta? of the kidney, 170. Articular cartilage, 44. Assimilation by the cell, II. Auditory organ, 240 ; external ear, 241 ; membrana tympani, 241 ; auditory ossicles, 241 ; Eustachian tube, 241 ; internal ear, 241 ; vestibule and semi- circular canals, 241 ; otoliths, 242 ; cochlea, 242 ; its structure, 242 ; Reissner's, or the cochlear canal, Corti's organ, termination of the coch- lear nerves, etc., 243. Auditory ossicles, see Auditory organ. Auerbach's plexus myentericus, 218. Axis canal of the spinal cord, 224. Axis cylinder, 193. Axis-cylinder process of the ganglion cells, 200. Axis fibrillar of the nerves, 196. Bacilli of the retina, see the Eye. Bartholinian glands, 181. Bathybius, 1. Becher cells, 5. Bellini's tubes, see Kidney. Biliary capillaries, see Liver. Biliary passages, see Liver. Bladder, see Urinary apparatus. Blood, 21 ; cells and plasma, 21 ; red blood corpuscles and lymphoid cells, 21 ; nature of the former, 22 ; differ- 12 ences of the same according to the groups of vertebrate animals, 23 ; lymphoid cells of the blood. 23 ; rela- tive number, 24; circulation of the blood, 24 ; fate of the lymphoid cells ; 25 ; genesis of the blood in the em- bryo. 26. Blood-vascular glands, 123 ; thyroid gland, 123; structure, 123; colloid formation. 124; suprarenal capsules, 124; cortical and medullary layer, 124; structure, 125; vessels and, ' nerves, 126 ; apophysis cerebri, 126 ; coccygeal gland, 126; ganglion inter- caroticum, 127. Blood-vessels, see Vascular system. Bone tissue, 60; kinds of bone, 60; medullary or Haversian canal, 60 ; Haversian and general lamellae, 61 ; canaliculi, 61 ; bone corpuscles or lacunas, 62 ; bone cells, 62 ; composi- tion of bone, 63; bone cartilage, 64; bone medulla, 64 ; osteogenesis, 64 ; cartilage marrow, 65 ; ossification points, 65 ; formation of bone at the expense of the cartilage tissue, 65 ; osteoblasts, 68; endochondral bones, 69 ; theory of apposition and expan-. sion, 69 ; Haversian spaces, 70; os- teoclasts, 70; periosteal bone forma- tion, 70; Sharpey's fibres, 71. Bowman'sglands of the olfactory region, see Olfactory organ. Brain, cerebrum and cerebellum, see Nerve centres. Bronchia, see Lungs, Bruch's trachoma follicles, 113, 263. Brunner's glands, 147. Buccal glandules, see Digestive appa- ratus. Bulbus olfactorious, see Olfactory appv. rat us. Canaliculi, see Bone tissue. Canalis cochlearis, see Auditory appara- tus. 266 INDEX. CanaHs Fontanae, see Eye. Canalis Petiti, see Eye. CanaHs Schlemmii, see Eye. CanaHs semi-circular of the ear, see Auditory apparatus. Capillaries, see Vessels. Carotid gland, 126. Cartilage, 42 ; hyaline, elastic (reticular) and connective-tissue cartilage, 42 ; cartilage cavities and cartilage cells, 43; cartilage capsules, 43; intercel- lular substance, 43 ; metamorphosis of fibres and calcification, 44 ; occur- rence of hyaline cartilage, 44 ; reticu- lar cartilage, 45 ; connective tissue, 45. Cartilage capsules, see Cartilage. Cartilage cell, see Cartilage. Cartilage medulla, see Bone. Cavernous bodies, see Sexual apparatus of the male. Cavernous passages of the lymphatic glands, see Lymphatic glands. Cells, 3 ; naked cells, 3 ; cell doctrine, 3 ; cell and cytode, 4 ; cell forms, 4, 5 ; globular, flattened and cylindrical forms, 5 ; spindle cells, 5 ; pioto- plasma, 5 ; transformation of the same, '5 ; nucleus, 6 ; nucleolus, 6 ; non-nuclear cells, 6 ; multinuclear cells (myeloplaxes), 7 ; cell envelope and capsule, 7 ; porous canals, 8 ; vital (amceboid) changes in form of the cell, 9 ; pus corpuscles, 9 ; nutrition and locomotion, 9; penetration of cells into cells, 10 ; ciliated or vibratory cells, 10; sensibility of cells, 11; assimilation, 11; duration of life, 12; kinds of death of the cell, 13; spon- taneous genesis, 14 ; processes of divi- sion, 14 ; endogenous cell formation, with mother and daughter cells, 15 ; intercellular substance, or tissue cement, 16; metamorphosis of the cells, and production of tissues, 17; metamorphosis of the intercellular sub- stance, 17 ; elastic fibres, 17 ; glands, 18 ; transversely striated muscular fila- ments, 19. Cerebellum, see Nerve centres. Cerebral ganglia, see Nerve centres. Cerebrin, 194. Cerebrum, see Nerve centres. Cerumen, see Auditory apparatus. Ceruminous glands, see Auditory appa- ratus. CI jrio-capillaris, see Eye. Chorion of the ovum, 176. Choroid, see Eye. Chyle, 26. Chyle vessels, 103, 1 16. Ciliary cells, see Epithelium. Ciliary motion, see Epithelium. Ciliary muscles, see Eye. Circulatory apparatus, see Vessels. Clitoris, see Sexual system of the female. Coagulation of the blood, 25. Coagulation of the nerve medulla, 194. Coccygeal gland, 126. Cochlea, see Auditory apparatus. Cochlear canal, see Auditory apparatus. Colloid, 124. Colloid metamorphosis of the thyroid cavities, 124 ; of the apophysis cere- bri, 126. Colostrum, see Sexual system of the female. Columns Bertini, see Kidneys. Columns of the spinal cord, see Nerve centres. Commissura anterior and posterior of the spinal cord, see Nerve centres. Commissures of the spinal cord, see Nerve centres. Conarium of the brain, see Nerve centres. Coni of the retina, see Eye. Coni vasculosi, see Sexual apparatus of the male. Conjunctiva, see Eye. Connective substance, 41. Connective substance, lymphoid and reticular, 45. Connective tissues, 51; fibrillae, bundles, elastic elements, 51 ; elastic sheaths, 53 ; cells of two different forms, 54 formless connective tissue, 56 ; formed 56 ; cornea, 56 ; tendons, 57 ; liga ments, 57 ; connective-tissue cartilage. 57 ; fibrous membranes, 57 ; serous, 5;; corium, 58; mucous membranes, 58 ; vascular membranes (pia mater plexus choroides, and choroid), 58 connective tissue vascular walls, 58 elastic structures, 58 ; pathological 59 ; embryonic conditions of the tissue, 59- Constituents of the body, 3. Contour, double, of the nerves, see Nerre tissue. Contractility of the living cell, 9. Convoluted glands, 130. Cornea, 56, 207, and see Eye. Corneal cells, 56, 248. Corneal corpuscles, 56, 248. Corneal nerves, 207. Corneal tubes, see Eye. Corneous layer of the epidermis, 33. INDEX. 267 Cornification of the pavement epithelium, see Epithelium. Cornu ammonis of the brain, see Nerve centres. Corpora cavernosa, igo. Corpora qnadrigemma of the brain, see Nerve centres. Corpus callosum, see Nerve centres Corpus ciliare, see Eye. Corpus epididymis, see Sexual apparatus of the male. Corpus Highmori, see Sexual apparatus of the male. Corpus luteum, see Sexual apparatus of the female. Corpus striatum of the brain, see Nerve centres. Corpus vitreum, see Eye. Cortex corticis of the kidney, see Kidney. Corti's cells, see Auditory apparatus. Corti's fibres, see Auditory apparatus. Corti's organ, see Auditory apparatus. Cowper's glands, see Sexual apparatus of the male. Crura cerebri and cerebelli of the brain, see Nerve centres. Cuticula of the hair, see Epithelium. Cytode, 2. Daughter cells, 15. Dehiscence of the ovarian follicles, see Sexual system of the female. Deiter's cells of the cochlea, see Auditory apparatus. Dental nerves, 214. Dentinal cells, 75. Dentinal tubes, etc., see Tooth tissue. Dentine, 73. Desquamation of the cells, 12. Digestive apparatus. 139; oral cavity, 139; mucous glands, 139; salivary glands, submaxillary and sublingual, 139 ; change of the gland cells, 140 ; parotid, 141 ; tongue with its various papillje, 141 ; serous glands of the tongue, 142; pharynx, 142; oesophagus, 142 ; stomach, 142 ; tubular glands. 143 ; frame-work of the mucous mem- brane, 143 ; peptic and gastric-mucous glands, 143 ; blood-vessels, 145 ; lymphatics, 145 ; small intestines, 146; intestinal villi and Lieberkiihnian glands, 146 ; Brunner's glands, 146 ; lymph or chyle passages, 148 ; absorp- tion of fat, 148 ; large intestine and its tubular glands, 149 ; lymphoid follicles of the intestines, 149 ; blood- vessels, 149; anus, 149. Dilator pupillae, see Eye. Discs of the transversely striated mus- cles, see Muscles. Division of the cells, 14. Ductus ejaculatorii of the testicle, 189. Dura maler, 57 and 231. Duverney's glands, 181. Ear, see Auditory apparatus. Egg germ, see Sexual organs of the fe- male. Egg-strands, see Sexual organs of the female. Elastic tissue, 52. Emigration of colored blood-cells through the walls of the vessels, 90; of lym- phoid cells, 90. Emigration of red, and colorless blood- cells, 90. Enamel germ, 76. Enamel of the teeth, 75 ; enamel prisms, 75 ; enamel cuticle, 75 ; transverse sec- tion, 75 ; genesis, 76. Enamel organ, 46, 76. Enamel prisms, etc., see Enamel. Endogenous cell formation, 15. Endothelium, 28. Engelmann's accessory discs of the trans- versely striated muscle, 85. Envelopes of the finer nerve trunks, 57, 202. Enveloping structures of the central nervous system, 231. Epidermis, see Epithelium. Epididymis, see Sexual apparatus of the male. Epithelium, 28 ; endothelium, 28 ; pave- ment, cylinder and ciliated epithelium, 28; cement substance, ,31 ; pigment- ed epithelium, 30; stratified, 30; stachel and riff cells 32 ; epidermis, 32 ; ciliary movement, 35 ; nail tis- sue, 36 ; nail cells, 37 ; hairs, 38 ; hair shaft and root, 38 ; root sheath, 38; cortex and medulla of the hair, 39 ; epidermis, 39 ; appearance of the hairs, lanugo hairs, 40. Erection, 19:. Eustachian tubes, see Auditory appara- tus. Eye, 246 ; parts of the eyeball, 247 ; cornea, 247 j sclerotic, 248 ; canalis Schlemmii, 249 ; choroid, 249 ; parts of the same, 249 ; ciliary body, 249 ; ciliary processes, 249 ; ciliary muscle, 249 ; iris, 250; sphincter and dilator of the pupil, 250 ; Hgamentum pectina turn iridis, 250 ; nerves of the iris, etc.. 268 INDEX. 251; crystalline lens, 251; vitreous body, 251 ; zonula Zinnii, 251 ; cana- lis Petiti, 251 ; retina, 251 ; arrange- ment, 252 ; macula lutea, 252 ; layers, 252 ; frame-work substance, 252 ; membrana H mi tans interna, 252 ; Mueller's fibres, 253; membrana limitans externa, 254 ; rods and cones, 254 ; external granular layer, 257 ; intergranular layer, 257 ; inner gran- ular layer, 258 ; molecular stratum, 258; layer of ganglion cells, 258; of nerve fibres, 259 ; macula lutea, 259 ; pais ciliaris, 260 ; lymphatics of the eye, 261 ; eye'i.ls, 262 ; glands of the conjunctiva, 262 ; lachrymal glands, 263. Eyeball, see Eye. Fallopian tube, see Sexual organs of the female. Fat tissue, 48 ; fat cells, 48 ; fat drops, 48 ; chemical constitution of the tat of the body, 49 ; cells losing their fat, 4q ; occurrence of fat tissue, 50 ; gen- esis, 50. Fatty degeneration, 13, 88. Fijre cell, contractile, see Muscular tissue. Fibro-cartilage, see Cartilage tissue. Fibro-reticular cartilage, sec Cartilage tissue. Follicles, Graafian, of the ovary, see Sexual organs of the female. Follicles, Malpighian, of the spleen, see the latter. Follicles of the lymphatic glands, see the latter. Follicular chains of the ovary, see Sexual organs of the female Follicular rudiments of the ovary, see Sexual organs of the female. Forked cells, see Gustatory apparatus. Formatio granulosa of the ovary, see Sexual organs of the female. Fovea centralis of the retina, see Eye. Gall-bladder, see Liver. Ganglia, see Nerve centres. Ganglion body, see .Nerve tissue. Ganglion cell layer of the retina, see Eye. Ganglion cells, see Nerve tissue. Gasiric glands, see Digestive apparatus, Gastric-mucous glands, see Digestive ap- paratus. Gastric-mucous membrane, see Digestive apparatus. Gegenbaur's osteoblasts, see Bone tis- sue. Gelatinous tissue and reticular connec- tive substance, 45 ; vitreous body, 46; reiicular connective substance, 47; lymphoid cells and modifications of the tissue, 47. General lamellae, see Bone tissue. Germinal plates, 28, etc. Germinal spot, see Ovum. Germinal vesicle, see Ovum. Giant cells, see Myeloplaxes. Gland capillaries, 134. Gland nerves, 208. Gland tissue, 128; definition, 128; con- stituents of the glands, 129 ; various forms of glands, 130; gland cells, 131 ; secretions, 132 ; vessels. 134 ; lymphaN ics, 135; nerves, 135 ; excretory ducts, 135 ; individual glands of thr body, 137 ; genesis, 138. Glands, mucous, 139. Glands, serous, 142. Glomerulus of the kidney, 98, 164. Goll's column of the spinal cord, see Nerve centres. Graafian follicles of the ovary, see Sexual organs of the female. Granular layer of the retina, see Eye. Growth of the cells, 11. Gustatory apparatus, 236 ; the various papilloe, 236; papilke circumvallatse and foliatje, 236 ; gustatory buds, 237 ; nerve termination, 23S ; gustatory cells, 238. Gustatory buds, Sie Gustatory appar- atus. Gustatory organ (tongue), sec Gustatory apparatus. Gustatory papilke of the tongue, see Gustatory appara us. Habenulae of the cochlea, see Auditory apparatus. H.emoglobin, 22. Hair bulb, see Epithelium. Hair sac, see Epithelium. Hair, see Epithelium Haversian canals, see Bone tissue. Haversian lamellae, see Bone tissue. Haversian spaces, see Bone tissue. Heart muscles, 86. Hemispheres of the cerebrum and cere- bellum, see Nerve centres. Henle's loops of the uriniferous canals, see Urinary apparatus. Mcnseu's middle "discs of the transversely striated muscles, 84. INDEX. 269 Hepatic lobules, see Liver. Hepatic vessels, see Liver, llilus-stioma of the lymphatic glands, toS. Histology, 3. Horn lajer, 2S. Horn layer of the epidermis, 32. Humor aqueus of the eye, see Eye. Humor vureus of the eye, see Eye. Hymen, see Sexual apparatus of the female. Hypophysis cerebri, 126. Infundibula of the lungs, see Lungs. Interglobular spacesof thedentinal tissue, see Teeth. Intestinal glands, see Glands, and Diges- tive organs. Intestinal villi, 104; and Digestive or- gans. Iris, see Eye. Iris nerves, see Eye. Keratine, 5. Kidney, 163 ; cortex and medulla, 163 ; Malpighian or medullary pyramids, 163 ; columnce Bertini, 163 ; uriniferous canals or Bellini's tubes, 163 ; medul- lary rays, 164; cortical pyramids, 164; glomerulus, 164; papillae renales, 164; looped canals, 164; excretory passages anil secretory portion of the kidney, 165 ; vascular arrangement of the cortical pyramids, 165 ; Mueller's or Bowman's capsule, 165 ; epithelial relations, 166; intercalary piece, 167; frame-work substance of the kidney, 16S ; blood and lymph vessels, 160 ; blood passages, 168 ; lymph passages, 170; urinary passages, 171; renal calices and pelvis, 171 ; ureter, 171; bladder, 171 ; female uretha, 172. Krause's transverse line of the muscles, see Muscular tissue. Labia, see Sexual organs of the female. Lachrymal gland, etc , see Eye. Lacunae, see Bone tissue. Lamellae of the bones, see Bone tissue. Lamina elastica of the cornea, see Eye. Lamina fusca of the choroid, see Eye. Lamina reticularis (velameniosaj, see Auditory apparatus. Lamina spiralis of the cochlea, see Audi- tory apparatus. Large intestine, see Digestive organs. Larynx, see Lungs. Lens tissue, 78 ; lens capsule. 78 ; .lens fibres, 78. Lentiform gastric glands, see Lymphoid organs. Leucaemia, 123. Lieberkuhnian glands, see Digestive apparatus. Ligaments, see Connective tissue. Ligaments, elastic, see Connective tis- sue. Ligamentum ciliare, see Eye. Ligamentum pectinatum iridis, see Eye. Ligamentum spirale of the cochlea, see Auditory apparatus. Lingual papillce, 141. Liquor folliculi, see Sexual apparatus of the female. Liver, 150; hepatic lobules, 151 ; Tiepa- tic cells, 151 ; fatty liver, 151 ; hepa- tic cell trabecule, 152; vessels, 152; frame-work, 153 ; biliary passages and biliary • capillaries, 154; lymphalics, 155- Lungs, 157 ; larynx, 157 ; trachea, 157 ; lungs, 158; alveolar passages and pul- monic lobules, 158 ; pulmonary vesi- cles, p. cells, alveoli, T58; structure, 159; black lung pigment, 160; ar- rangement of vessels, 160 ; pulmo- nary epithelium, 162. Lymph, 27. Lymph corpuscles, see Lymphoid cells. Lymph passages, 102 ; ductus thorau- cus, 102; lymphatics', 103; injection of the lymphalics, 103 ; arrangement of the same, .104; clefts, 106; juice canals or juice clefts, 107 ; lymphatic glands, 107 ; envelope, cortex and medulla, hilus-stroma, 108; follicles 10S ; septa and tenter-fibres, 109 ; -in- vestment spaces, 109 j lymph canals, no; blood-vessels, no. Lymph sheaths of the blood-vessels, see Vessels. Lymph vessels, see Lymph passages. Lymphatic glands, see Lymph passages. Lymphoid cells, 5, 9, 23, etc. Lymphoid follicles, see Lymphoid or- gans. Lymphoid organs, 112 ; lens-shaped glandules, solitary and Peyerian fol- licles, tonsils and trachoma glands, 112; structure of the tonsils, 113; trachoma glands in particular, 113; structure of the Peyerian plaques, 114; • spleen, 116; Malpighian corpuscles, and pulp, 1I7; vessels, 119; cells containing blood corpuscles, 122 ; 270 INDEX. leucaemia, 123 ; lymphatics, 123 ; blood -vascular glands, 123. Macula lutea of the retina, see Eye. Malpighian bodies of the spleen, see Lymphoid organs. Malpighian glomerulus, see Kidney. Malpighian pyramids of the kidney, see Kidney. Malpighian rete mucosum, see Epider- mis. Medulla, see Spinal cord and medulla oblongata. Medulla oblongata, see Nerve centres. Medulla of the nerves, see Nerve tissue. Medullary canals of the bones, see Bone tissue. Medullary substance of the lymphatic glands, kidney, etc., see the organs in question. Meibomian glands, see Eye. Melanin, 5, 30. Membrana Descemetica (Demourisiana), see Eye. Membrana hyaloidea, see Eye. Membrana Hmitans of the retina, see Eye. Membrana propria of the glands, see Glands. Membrana tympani, see Auditory ap- paratus. Membranes, fibrous, serous, etc., see Connective tissue. Middle germinal layer, 28. Milk, see Sexual organs of the female. Milk glands, see Sexual organs of the female. Milk globules, see Sexual organs of the female. Molecular movement (Rrunonian), 27. Mother cells, 15. Mucous corpuscles, see Lymphoid cells. Mucous membrane, see Connective tissue. Mucous tissue, 46. Mueller's capsule of the kidney, see Kid- ney. Mueller's supporting fibres of the retina, ■see Eye. Muscle nerves, 203. Muscles, see Muscular tissue. Muscular filaments, etc., see Muscular tissue. Mu:cular tissue, 79; smooth and trans- versely striated, 79 ; smooth muscles, contractile fibre cells. 80 ; their occur- rence, 80; transversely striated, 81; muscular filaments (fibres), Si ; sai- colemma and sarcous elements, Si ; fibrillae and discs, 83; transverse discs, ' 84 ; accessary discs, 85 ; interstitial granules, 85 ; heart muscle. 86 ; transverse section of the muscle, 86 ; connection with the tendons, 86 ; embryonic development, 87 ; increase, 88 ; fatty degeneration, 88. Myeloplaxes, 7. Nail tissue, 37. Nails, 36. Nasal cavities, see Olfactory apparatus. Nerve centres, 215; ganglia, 215; their structure, 215; sympathetic, 217; sympathetic ganglia, submucous and plexus myentericus, etc., 217, 218; spinal cord, 218 ; neuroglia, 220; nerve roots of spinal cord, 22 1 ; white substance of spinal cord, 222 ; medulla oblongata, 224 ; its several parts, 224; cerebellum, 227 ; its several parts, with the con ex, 227; cerebrum, 229; its several parts, 229 ; blood and lymph vessels, 231. Nerve fibres, etc., see Nerve tissue. Nerve plexuses, etc., see Nerves, ar- rangement of. Nerve sheath, 202. Nerve tissue, 192; nerve fibres and ganglion cells, 192 ; medullated and non-medullated nerve fibres, 192; broad and narrow medullated fibres, 192 ; primitive sheaths, 193 ; axis cylinders, 193 ; nerve medulla (med- ullary sheath), 193 ; coagulation of the medulla, 194; transverse section, 194; varicosities, 195; Ranvier's constriction rings, 195 ; pale (Re- mains), nerve fibres 196; axis or primitive fibrillas, 196 ; ganglion cells, 197 ; apolar ganglion cells, 19S ; origin of nerve fibres, 198 ; uni- and bipolar ganglion cells, 19S, 199; mul- tipolar ganglia, 200 ; protoplasma and axis-cylinder processes, 200. Nerve tubes, see Nerve tissue. Nerves, arrangement and termination of, 202; nerve sheath (neurilemma), 193, 202 ; nerve termination, 203 ; ter- minal plates of voluntary muscles, 204; nerves of the smooth muscles, 206 ; nerve termination in the cornea, C07 ; gland nerves, 208 ; terminal bulbs, 208 ; Pacinian corpuscles, 210 ; tactde bodies, 211 ; other nerve ter- minations, 213; Langerhans' cor- puscles, 213. INDEX. 271 Nerves, see Nerve tissue. Neurilemma (nerve sheath), 202. Neuroglia, see Nerve centres. Nipple, see Sexual apparatus of the fe- male. Nucleus dentatus cerebelli, see Cerebel- lum, Nucleus of the cell, 6. Nymphze, see Sexual organs of the fe- male. Odontoblasts, see Dentine. (Esophagus, see Digestive apparatus. Olfactory hairs, etc., see Olfactory ap- paratus. Olfactory nerve, see Olfactory organ. Olfactory organ, 238 ; regio olfactoria, 238 ; its structure, 238 ; olfactory cells, 239 ; termination of the same, 240. Optic nerve, see Eye. Ora serrata retinae, see Eye. Oral cavity, see Digestive apparatus. Ossification process, see Bone tissue. Osteoblasts, etc., see Bone tissue. Otoliths, see Auditory organ. Ovarian follicles, see Sexual organs of the female. Ovary, see Sexual organs of the female. Oviduct, see Sexual organs of the female. Ovulum, see Sexual organs of the female. Ovum, 5, 175. Ovum, primordial, see Sexual organs of the female. Pacchionian granulations, see Nerve cen- tres. Pacinian corpuscles, see Nerve termina- tions. Palatine glands, see Digestive appara- tus. Palpebrse, see Eye. Pancreas, 150; contents, 150; centro- acinary cells, 150. Panniculus adiposus, 49. Papilla foliata of the tongue, see Gusta- tory apparatus. Papilla spiralis (Corti's organ) of the cochlea, see Auditory apparatus. Papillae circumvallatae of the tongue, see Gustatory apparatus. Papilla; filiforrnes of the tongue, see Gus- tatory apparatus. Papilla; fungiformes, see Gustatory ap- paratus. Papillae.of the corium, 58, 212. Papillae renales, see Kidney. Parotid, see Digestive apparatus. Parovarium, see Sexual apparatus of the female. Pavement epithelium, see Epithelium. Pednnculi cerebri, see Nerve centres. Penicilli of the splenic arteries, see Spleen. Penis, see Sexual apparatus of the male. Peptic-gastric glands, see Stomach. Peptic-renic cells, see Stomach. Pericardium see Connective tissue. Perichondrium, see Connective tissue. < Perilymph (aqua Cotunnii), see Auditory apparatus. Perimysium, see Muscular tissue. Perineuria™, (nerve sheath), 262. Periosteum, see Connective tissue and Bones. Petit's canal, see Eye. Peyer's glands (follicles), see Lymphoid organs. Pharynx, see Digestive apparatus. Pia mater, see Connective tissue and Nerve centres. Pigment cells, see Epithelium and Con- nective tissue. Pigment epithelium of the retina, see Epithelium. Pineal gland of the brain, 230. Pleura, see Connective tissue. Plexus choroidei of the brain, see Nerve centres. Plexus myentericus, see Nerve tissue. Plexus of the nerves, see Nerve arrange- ment. Plica semilunaris, see Eye. Pons Varolii, see Nerve centres. Porous canals of the cells, 8. Primitive fibnllae of the connective tis- sue, muscles, and nerves, see these tis- sues. Primitive sheaths of muscles and nerves, see these tissues. Primordial kidney, see Kidney. Primordial ova, see Sexual organs of the female. Processus ciliaris of the eye, see Eye. Processus vermiformis, 1 14. Prostate, see Sexual organs of the male. Protamceba, 2. Protoplasma, 2, etc. Pulp of the spleen, see Lymphoid or- gans. Pulpa dentis (tooth germ), 74. Purkfnje's ganglion cells, see Central nervous system ; germinal vesicle of the ovum, see Sexual organs of the female. Pus corpuscles (lymphoid cells), 9. 272 INDEX. Pyramids of the kidney, see Kic'ney. Pyramids of the medulla oblongata, see Nerve centres. Regio olfactoria, see Olfactory apparatus. Reissner's membrane of the cochlea, see Auditory apparatus. Remak's nerve fibres, see Nerve tissue. Remak's studies on cell formation, 14. Renal papillae, etc., see Kidney. Respiratory organs, see Lungs. Rete Malpighii, see Epithelium. Rete testis, see Sexual organs of the male. Reticular cartilage, see Cartilage. Retina, see Eye. Retinal vessels, see Eye. Riff cells (stachel cells), see Epithelium. Rod corona fibres, see Nerve centres. Rods of the retina, see Eye. Salivary glands, see Digestive apparatus. Sarcolemma, see Muscular tissue. Sarcous element, see Muscular tissue. Scala media of the cochlea, see Auditory apparatus. Schlemm's canal, see Eye. Schneiderian membrane, see Olfactory apparatus. Schwann's cell doctrine, 14; Schwann's nerve sheath, see Nerve tissue. Sclerotic, see Eye. Sebaceous follicles, 236. Sebum cutaneum, 132, 236. Sebum formation of the glands of the skin, 132. Sebum palpebral, see Eye. Segmentation of the yolk, 179. Semen, see Sexual organs of the male. Seminal filaments, etc., see Sexual or- gans of the male. Sexual organs of the female ; ovary, 173 ; cortical and medullary substance of the same, 173 ; germinal epitheli- um, 173 ; cortical or zone of the pri- mordial follicle, 173; ripe Graafian follicle, 175 ; ovum with the chorion, yolk, germinal vesicle, and germinal spot, 176; blood and lymph vessels, 177 ; parovarium, 177 ; genesis, 178 ; follicle chains or ovum strands, 178 ; corpus luteum, 179 ; segmentation of the ovule, 179 ; oviduct, 179 ; uterus, 179 ; uterine glands, 180 ; blood and lymph passages of the uterus, 180 ; pregnancy, 180 ; vagina, 180 ; hymen, ciitoii.s, nymphae, and labia majura, 181 ; vestibule, entrance to the vagina, 181; lacteal glands, 181'; colostrufr and milk, 182. Sexual organs of the male ; testicle, 183 j corpus Highmori and seminal canals, 183; epididymis, etc., 183; vas defe- rens, 184 ; vas aberrans H alien, 1S4 ; structtue of the seminal canals, 184; blood and lymph vessels, 1.S5 ; genesis, 186; semirjal filaments, 1S7 ; copul 1- tion, 187; genesis, 188; spermato- blasts, 189; structure of the vas defe- rens, 189; seminal vesicles, ejaculatory ducts, prostate, other glands, 189 ; urethra, 190 ; corpora cavernosa, glans 190 ; colliculus seminalis, 190 ; Little's and Tyson's glands, 190 ; structure of the cavernous tissue, 190 ; erection, 191 ; vessels, 191. Sharpey's fibres of the bone, see Bone tissue. Sheath of the nerve fibres, see Nerve tissue. Skin, see Connective tissue, 58, and or- gans of sense, 234 ; tactile papillae, 234 ; blood-vessels and lymphatics, 234 ; glands, 235. Small intestine, see Digestive apparatus. Solitary glands of the intestinal canal, see Lymphoid organs. Sperm (semen), see Sexual organs of the male. Spermatozoa, see Sexual organs of the male. Sphincter pupillae, see Eye. Spinal cord, see Nerve centres. Spinal ganglia, see Nerve centres. Spiral fibres of the ganglion cells, see Nerve tissue. Spiral leaf of the cochlea, see Auditory apparatus. Spleen, see Lymphoid tissue. Splenic follicles, see Lymphoid organs. Splenic vessels, see Lymphoid organs. Spot, yellow, of the retina, see Visual apparatus. Stachel cells (riff cells), see Epithelium. Stellulae Verheyenii of the kidney, see Kidney. Stomach, see Digestive apparatus. Stomata of the vessels, see Blood and lymph vessels. Subarachnoidal spaces, see Nerve cen- tres. Subdural space, see Nerve centres. Sublingual glands, see Digestive appara- tus. Submaxillary gland, see Digestive ap- paratus. INDEX. 273 Submucous ganglion plexuses of the di- gestive organs, see Nerve centres Suprarenal capsule, see Blood -vascular glands. >\veat glands, see Gland tissue. Sympathetic nerve, see Nerve arrange- ment. Tactile bodies, see Nerve terminations. Tactile organs, 234. Teeth, 73 Tendons, see Connective tissue. Tensor choroidiae, see Eye. Terminal bulbs of the nervous system, 203 Terminal plates of the muscular nerves, see Nerve terminations. Terminal structures of the nerves, see Nerve terminations. Testicles, see Sexual apparatus of the male. Thalamus opticus, see Nerve centres, Theca of the ovary follicles, see Sexual organs of the female. Thymus, see Blood-vascular glands. Thyroid, see Blood-vascular glands. Tissue, 3 ; simple, 20; compound, 21. Tissue cement. 16. Tissue elements, 4. Tissues, division of the, 20. Tonsils, see Lymphoid organs. Tooth tissue, 73; dentine, 73; enamel and cement, 73; dentinal tubes, 73; cement, 74 ; interglobular spaces, 74 ; dentinal cells or odontoblasts, 75 ; genesis of the teeth, 76 ; tooth mound, enamel germ, tooth germ, 76 ; enamei organ, tooth sac, 77. Trachea, see Lungs. Trachoma glands, see Lymphoid organs and Eye. Tulwe Fallopii, see Sexual organs of the female. Tunica vasculosa of the eye, see Eye. Tympanum, etc., see Auditory appar- atus. Tyson's glands, see Sexual organs of the Ureter, see Kidney. Urethra, 172, 190. Urethra, female, see Urinary apparatus ; urethra, male, see Sexual organs of the male. Urinary apparatus, 163 ; kidneys, 163 ; cortex and medulla. 163 ; medullary pyramids, 163 ; columns Bertini, 163; uiiniferous canals (Bellini's tubes), 163 ; cortical pyramids and glomerulus, 164 ; papilla; renales, 164 ; looped canals, 164 ; their two sides, 165 ; Mueller's or Bowman's capsule ol the glomerulus, 1 165 ; course of the urini- ferous canals, intercalary portion, etc , 166 ; vascular arrangement, 16S ; cortex corticis, 169; vasa recta. 170; lymphatics, 170; theory of the urinary secretion according to Ludwig, Bow- man, 171 ; urinary canals, renal cali- ces and pelvis, 171 ; ureter, 171 ; urin- ary bladder, 171 ; female urethra, 172. Uterine glands, see Sexual organs of the female. Uterus, see Sexual organs of the female. Uvea of the eye, see Eye. Vagina, see Sexual organs of the fe- male. Varicosities of the nerves, see Nerve tis- sue. Vas aberrans Halleri of the testicle, see Sexual organs of the male. Vas afferens ami efferens of the lymph- atic glands, see Lymphatics. Vasa recta ol the kidney, see Kidney. Vascula efferentia of the testicle, see Sexual organs of the male. Vascular membranes, see Vessels and Connective tissue. Vascular tissue, see Vessels. Veins, see Vessels. Venae, inter, and intralobulares of the liver, see Liver. Vena? vorticosoe of the eye, see Eye. Venous plexus (plexus choroides), cf the brain, see Central organ of the nervous- system. Vesicular seminales, see Sexual organs of; the male. Vessels, blood, 16 ; arteries, veins and capillaries, 89 ; capillaries, 89 ; vascu- lar cells, 90; adventitia capillaris, 91 ; lymph sheath. 91 ; structure of the large arterial and venous trunks, 91 ; structure of the veins, 93; of the arteries, 94 ; valves, 95 ; capillary system, 95 ; capillary net-work, 96 ;. various forms of the same, 96 ; genesis in the embryo. 99. Vessels, lymphatic, 102; intestinal villi, 104 ; other localities, 105 ; lymphatic apertures, 106 ; juice canals and clefts, 107 ; lymphatic glands, 107 ; their structure, io3 ; cortex, medulla, fol- licles, medullary strands, septum sys- 2/4 INDEX. tern, investment space, 108, log ; lymphatics of the medulla, 1 10 ; ves- sels, no; lymph current, in. Vestibule of the ear, see Auditory ap- paratus. Visual apparatus, 2^6. Vitreous body, 45, and the Eye. Wandering of the cells, 10. Wolffian body, 177, 186. Yolk, see Ovum.