ALBERT R. MANN LIBRARY New York State Colleges OF Agriculture and Home Economics AT Cornell University Cornell University Library The original of tiiis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924003130527 HISTOLOGY By the same Author. EXPERIMENTAL PHYSIOLOGY : Practical Elementary Physiology of Muscle and Nerve and of the Vascular and Nervous gjstems. LONDON : LONGMANS, GREEN, & CO. TEXT-BOOK OF MICROSCOPIC ANATOMY. Containing over looo Illustrations and ^any Coloured Plates. LONDON: LONGMANS, GREEN, & CO. THE ENDOCRINE ORGANS. An Introduction to the Study of Internal Secretion. LONDON: LONGMANS, GREEN, & CO. A TEXT-BOOK OF PHYSIOLOGY FOR ADVANCED STUDENTS. BY BRITISH AUTHORS. In two Volumes. LONDON; HENRY FROWDE, HODDER \- STOUGHTON. A COURSE OF PRACTICAL HISTOLOGY. Containing Plain Directions for Individual Work in Histology. LONDON : TOHN MURRAY THE ESSENTIALS HISTOLOG-Y DESCRIPTIVE AND PRACTICAL FOR THE USE OF STUDENTS Sir EDWARD SJIARPEY-SCHAFER, F.R.S. PROPBBSOR OP PHYSIOLOGY IN THE UNIVERSITY OF BDINBUROH PORMBRLY JODRELL PROFESSOR OF PHYSIOLOOY IN UNIVBRSITY COLLEGE, LONDON ELEVENTH EDITION LEA k FEBIGIJH PHILADELPHIA AND NEW YORK BIBLIOGRAPHICAL NOTE First Edition, May 18S5 ; Secdiid Edition, January 1887 ; Third Edition, May 1892 ; Fourth Edition, April 1894 ; Fifth Edition, [une 1898 ; Sixth Edition, May 1902 ; Seventh Edition, JanuaT^ 1907 J Eighth Edition, September 1910 ; Ninth Edition, January 1914 ; Tenth Edition, June 1916 ; Eleventh Edition, July 1920. PEEFACE TO THE ELEVEN-TH EDITION. This book is written with the object of supplying the student with directions for the microscopic examination of the tissues. At the same time it is intended to serve as an Elementary Text-book of Histology ; comprising the Essential facts of the science, but omitting less important details. A more complete account will be found in larger works, such as the Author's Text^hook of Microscopic Anatomy, and the portions of Quain's Anatomy which deal with the nervous system g,nd the sense organs. For conveniently accompanying the work of a class of medical students, the book is divided into fifty lessons. Each of these may be supposed to occupy from one to three hours, according to the relative extent to which the preparations are made beforehand by the teacher, or during the lesson by the students. A few of the preparations cannot well be made in a class, but it has been thought inadvisable to injure the completeness of the work by omitting mention of them. Only those methods are recommended upon which experience has proved that dependence can be placed, but the directions given are for the most part easily capable of modification in accordance with the experience of different teachers. The author desires to acknowledge the assistance of Mr R. K. S. Lim, M.B.,.Ch.B., Lecturer on Histology in the University of Edinburgh, in the preparation of this edition. CONTENTS. INTRODUCTORY. PAQK Enumeration or the Tissues — General Structure of Animal Cells — Division of Cells , 1 LESSON I. Use of the Microscope — Examination, of Common Objects 26 LESSONS II. and III. Human- Blood - Corpuscles — Djivblopmbnt op Blood Corpuscles — Bone-Marrow 30 LESSON IV. Action of Reagents upon the Human Blood-Corpuscles 49 LESSON V. Blood-Corpuscles of Amphibia - - - 53 LESSON TI Am^ LESSON XVI. Tissues of the Nkrvouk System : Nbrve-Fibrf,s ^4- CONTENTS ix- LESSONS XVII. AND XVIII. PAGK Ti.ssuEs OP THE Nervous System {continued) : ISServe-Cblls — Ganglia — Pegeneration and Regeneration op Nerve-Fibres and Nerve- Cells — Neuroglia — Dbvelopmknt op Nerve-Cells and Nbrve- FlBRES - 157 LESSON XIX. Modes of Termination of Nerve-Fibres — Sensory Nerve-Endings — Motor Nerve-Endings 189 LESSON XX. The Larger Blood-Vessels 207 LESSON XXL The Smaller Blood-Vessels — Lymph- Vessels^NIioeoscopio Study of the Circulation — Development op Blood- and Lymph-Vessels — Serous Membranes 216 LESSON XXII. Lymph-Glands — Spleen— Tonsil— Thymus 232 LESSON XXIII. Suprarenal Capsules — Carotid and Coccygeal Glands — Thyroid Body — Parathyroids — Pituitary Body — Pineal Gland 250 LESSONS XXIV. and XXV. Skin -Nails — Hairs — Glands of the Skin — MaiImary Glands 264 LESSON XXVI. Heart 288 LESSON XXVII. Larynx — Trachea — Lungs 295 h •X CONTENTS LESSON XXVIIl. PASE Structure and Development of the Teeth 306 LESSON XXIX. ToNOUE AND Gustatory Organs — Mucous Membrane of the Mouth — Pharynx and ffisoPHAf*us 320 LESSON XXX. Salivary Glands 327 LESSON XXXI. Stomach 335 LESSONS XXXII. AND XXXIII. Small and Largb Intestine 344 LESSONS XXXIV. and XXXV. Liver — Pancreas 360 LESSON XXXVI. Kidney — Ureter and Bladder 374 LESSON XXXVII. Male Gbhebativb Organs 3,^- LESSON XXXVIII.^ Female Generative Organs ,q^ LESSONS XXXIX. and XL. Spinal Cord ^o-j CONTENTS LESSON XLI, I'AGK Medulla Oblongata 443 LESSONS XLII. AND XLIII. Pons: — Mesekcephalon — Thalamencbphalon 459 LESSONS XLIV. and XLV. Cbebbbllum and Cerebrum 485 LESSONS XL VI., XLVIL, and XLVIII. Eye 509 LESSONS XLIX. and L. Nose and Ear 535 APPENDIX. Methods - 551 INDEX 569 CORRIGENDA. p. 16. — Description of fig. 24, line 1. For to read into. P. 30. — Line 3 from bottom. For or readyb?-. P. 35. — Fig. 47. The letters A and B have been omitted. P. 37. — Line 6 from bottom. For adult read adults. P. 41. — Fig. 57. There are several mistakes in the lettering of this figure. P. 80, Sec. 2, line 2. — Omit acid heiore/uchsin. P. 159. — Description of fig. 211. For ventra read ventral. P. 169,. — liast line of small type. For affected read effected. P. 175. — Last line. For begin read begins. P. 194. — Line 1. For neuro fibrils read iietiro-fibrilK. THE ESSENTIALS OF HISTOLOGY INTRODUCTORY ENUMERATION OF THE TISSUES AND GENERAL STRUCTURE OF ANIMAL CELLS Animal Histology ^ is the science which treats of the minute structure of the tissues and organs of the animal body ; it is studied with the aid of the microscope, and is therefore also termed Microscopic Anatomy. Every part or organ of the body, when separated into minute fragments, or when examined in thin sections, is found to consist of certain textures or tissues, which differ in their arrangement in different organs, but each of which exhibits characteristic structural features. The following is a list of the principal tissues which compose the body : — 1. Epithelial. 2. Connective : Areolar, Fibrous, Elastic, Reticular, Lymphoid, Adipose, Cartilage, Bone. 3. Muscular : Voluntary or striated, Involuntary or plain, Cardiac. 4. Nervous. Some organs are formed of several of the above tissues, others contain only one or two. It is convenient to include such fluids as the hlood and lymph amongst the tissues, because they are studied in 'the same manner and contain cellular elements similar to those met with in some of the other tissues. All the tissues are, prior to differentiation, masses of cells (embryonic cells). In some tissues elements become developed which take the form of fibres. Thus the epithelial tissues are composed throughout life entirely of cells, only slightly modified in structure, and the nervous and muscular tissues are formed of cells which are greatly modified to form the char- acteristic fibres of those tissues. On the other hand, in the connective tissues an amorphous material becomes formed between the cells which is termed intercellular substance or ground-substance, and in this substance fibres make their appearance,, sometimes, as in the fibrous connective tissues, ^ From iffTos, a web or texture. 2 THE ESSENTIALS OF HISTOLOGY in so large an amount as to occupy the whole of the intercellular sub- stance, and greatly to preponderate over the cells. This ground substance, by virtue of its incorporating a certain amount of inorganic chlorides, has the property of becoming stained brown or black by nitrate of silver and subsequent exposure to light, in which case the cells, which remain unstained, look like white spaces (cell-spaces) in the ground-substance. When an epithelial tissue is similarly treated, the narrow interstices between the cells are also stained, from which it is concluded that a similar substance exists in small amount between the cells of this tissue. It has here been termed cement-substance, but it is better to apply to it the general term intercellular substance. The cells of a tissue are not always separate from one another, but are in many cases connected by bridges of the cell-substance, which pass across the intercellular spaces. This is especially the- case with the cells of the DlACJKAMS OE CE1,L-STKUCTURE. A, diagram of .1 cell the protoplasm of which appears sfcnicturelesa, but is occupied by vacuoles and granules. By diagram of a cell the protoplasm of which appears reticulated or apoh^e-like. p, protoplasm, consisting (in E) of hyaloplasm and a network of spongioplasm ; /(, nucleus; n', nucleolus. higher plants, but it has also been found to ocpur in many animal tissues ; e.g., in some varieties of epithelium and in cardiac and plain muscular tissue. Occasionally the connexion of the cells of a tissue is even closer, and lines of separation between them are faint or entirely aibsent. The term syncytium, is given to any such united mass of cells. Structure of Cells. — A cell is a minute portion of living substance (cyto- plasm) which is sometimes enclosed by a cell-membrane and always contains a specially differentiated part which is known as the nucleus. The cytoplasm of a cell (fig. i, p) is composed oi protoplasm,, which con- sists chemically of proteins or nucleoproteins, with which arc associated lecithin, a combination of fatty acid with glycerophosphoric acid, and cholesterol, a monatomic alcohol; these belong to the class of "lipoids," and have many of the physical characters of fats. The protoplasm tends during life to exhibit movements which are apparently spontaneous ; when the cell is unenclosed by a distinct membrane, a change in the shape, or even in the position of the cell, may be thereby produced. This is characteristically STRUCTURE OF THE CELL 3 shoWn in the movements of the unicellular organism known as the amoiba (fig. 2) ; hence the name amoeboid movement, by which it is generally 2 3 4 5 6 7 8 Fig. 2. — SncCESSivs changes exhibited by ak amohEa. (Verworn. ) ,^^^' Fig. 3.— Untouched photogbaph of living leucocyte of tbiton, showing BETICULAB APPEARANCE OF THE PROTOPLASM. Magnified ] 360 diameters. The photograph was taken in monochromatic light with Zeiss' 2 mm. apochromatic objective and a compensation eye-piece. The polymorph nuoleua also exhibits a reticular structure. designated.! The protoplasm often, but not always, contains a fine sponge- The amceboid phenomena of cells will be studied later (in the colourless corpuscles of blood). 4 THE ESSENTIALS OF HISTOLOGY wort, which takes under high powers of the microscope the appearance of a network (see diagram, fig. 1, B, and figs. 3 and 4), the remainder of the Fig. 4. — A livisi; leucooyte (white blood-coeposcle) of Salamandka macolata, SHOWING LACE-LIKE KETICULAR APPEARANCE OF ITS PROTOPLASM. Magnified 1200 diameters. Untouched photograph. An erythrocyte (red blood-corpusde) is included in the photograph. A film of the protoplasm of the leucocyte extends over its margin. Fio, .5.— Tbophospongium canai.,- I8ATI0N within A IJANCJLION CELL. (E. Holmgren.) Fig. 6. — Epitheluvm-cklls of salamander LAKVA, stained intra rilam with neu- tral red, .snowiNc the cell-gkancles (Fisohel.) Magnified 300 diameters. protoplasm being a clear substance which occupies the interstices of the spongework, and covers the surface or may project beyond the rest of the cell A granular appearance is often produced by the knots in the spongework^ which, when imperfectly observed, look like separate granules. The material STRUCTURE OF THE CELL 5 which forms the spongework is termed spongioplasm ; the clearer material ■which occupies its meshes is hyaloplasm. In other cases cell-protoplasm resembles an emulsion- rather than a spongework, being formed of a clear fluid (hyaloplasm), containing globules of a more highly refracting substance suspended in it. These conditions of protoplasm are analogous to the gel and sol conditions which are characteristic of colloid solutions (see p. 7). The protoplasm of some cells shows a differentiation into fibrils, which may be unconnected or may form a network within the cell. Certain cells exhibit a fine canalisation of their protoplasm (fig. .5) ; according to Pig. 7. — Cells from tfe testicle of the mousb in process of TRANSFORMATTorr INTO SPERMATOZOA. (Benda. ) The "mitochondria " are darkly stained and are seen in the successive stages {a to g) to be arranging: themselves so as to constitute the spiral filament of the spermatozoon (A). Holmgren the canaliculi are occupied by bcanching processes of other (nutrient) cells, which form what he has termed a " trophospongium." Besides globules of colloid material, which can only be seen with the ultramicroscope, protoplasm often includes granules of a protein nature (fig. 6), reacting variously to different stains. Those contained in some cells stain only with alkaline dyes (basiphil), those in others only with acid dyes {oxyphil), whilst some cells contain granules stain- ing with both basic and acid dyes (amphophil), and others, granules staining only with neutral dyes (neutrophil). Certain pf these granules have been regarded as essential constituents of the protoplasm (Altmann), being closely associated with what is, chemically, the most actjive part of the cell, the part, namely, in the neighbourhood of the nucleus ; indeed they appear to become formed in this part (if not actually from the nucleus) and from it to extend throughout the cell. When fibrils are formed in the protoplasm, they are 6 THE ESSENTIALS OF HISTOLOGY produced from the granules in question, to which the name mitochondria was given by Benda (fig. 7). The mitochondria are sometimes collected near the nucleus into a spherical mass which stains more deeply than the rest of the cytoplasm (fig. 8). To this body the term paranucleus has been applied. In many cells ■ other materials are included in the cytoplasm which are not factors in its constitution, such as pigment granules, fat globules, and vacuoles containing watery fluid, with or without glycogen or otbef substances in solution. Materials which are thus included in the protoplasm of a cell are either stored up for the nutrition of the cell itself, or are converted into substances which are eventually extruded from the cell in order to serve some purpose useful to the whole organism, or to be got rid of from the body. The term paraplasm is employed to denote any such materials within a cell. Paraplasm is often present in sufiicient quantity to reduce the cytoplasm to a relatively small amount, the bulk of the cell being occupied by other Fig. 8. — Pancreas cells of fbog, showing parantj- CLEtrS AND CHONDBOMITOME FIBRILS FORMED FROM MITO- CHONDRIA. (Matthews.) ~"l A \ > Fi(-. 9. — Photograph of leucocyte or triton, fixijd whimt in amceboid condi- tion BY JET OF STEAM DIRECTEO ON TO COVBR-CLAS'S, AND SUBSEQUENTLY STAINED WITH n^sMATOXYLiN. MagniHed 1360 diameters. Untouched photograph. The protoplasm shows an internal ffranular or reticular endopKosni and a clear exopla.sm. material, as when starch becomes collected wijthin \egetable cells or fat within the cells of adipose tissue. It is frequently the case that the paraplasm is confined mainly to the protoplasm in the neighbourhood of the nucleus, an external zone of the protoplasm being left clear. The two portions of protoplasm which are thus imperfectly differentiated from one another are termed respectively the endoplasm and the eavplasm,. They are exhibited in the amreba (fig. 2), and in the white blood-corpuscle (fig. 9). According to the view advocated .b}' Biitschli the apparent reticulum or spongioplasm of a cell is the optical effect of a soft honeycomb or froth-like STRUCTURE OF THE CELL 7 structure ; in other words, the meshes of the reticulum do not communicate , with one another as in a sponge, but are closed cavities as in a honeycomb. Biitschli finds indications of 'the same alveolar structure in all cells, including nerve-fibres and muscle-fibres, and has devised experiments with drops of froth made up of a mixture of oil and alkaline carbonate or sugar solution, which, when examined in water under the microscope, imitate very closely not only the structural appearance (fig. 10) but even the so-called spontaneous or amoeboid movements of actual protoplasm. It may be stated, however, that although it is a matter of difficulty to det&rmine whether a microscopic reticulum is a spongework or a honeycomb, it is probable that neither structure is essential to living substance, for the outermost layer of the cell- protoplasm, which is usually the moat active in exhibiting movements, often shows no indication of any structure. And further, it has been shown by Hardy that a colloid solution such as that whidi exists in protopla/sm may, under ' some circumstances, appear homogeneous and under others may separate out into two parts, one more solid the other more fluid, and after Fro. 10. — Comparison ot paoTOPLASM with oil and watek emulsion. ( Verworn, after Biitschlii j A^ protoplasm of Thalassicola. B, froth-like appearance of a mixture of oil and cane sugar. such separation may exhibit either a granular, a reticular, or a honeycomb structure, according to circumstances {gel and sol conditions of Graham i). Nor is a "froth" necessary for the imitation of amceboid movements, for similar movements, due to changes in surface tension, are exhibited by a simple oil drop or a drop of oil-clad albumen when brought in contact with solution of soap or an alkali (Berthold, Quincke). Indeed, drops of any fluid are subject to changes of surface tension when exposed to varying external influences, and these changes are invariably accompanied by alterations in form of the drop. It follows from such observations that the amoeboid movement of cells which used to be regarded as especially significant of the presence of life, is capable of being explained by known physical laws, and it is, therefore, superfluous to assume the possession of a special form of energy (" vital force ") to explain it. There are grounds for believing that a very fine pellicle covers the exterior of the protoplasm of all free cells, and that this pellicle is composed of a material which, although not soluble in water, is, permeable to watery fluids, and may also allow the passage of solids without rupture. Such a material might be furnished by the lipoids (Overton), which are, as we have seen, constant constituents of cell-protoplasm. It must, however, be stated that, although probable, it has not been proved that th«se substances are especially collected at the surface of protoplasm. It must further be borne in mind that either a sponge-like or honeycomb structure would have the efl'ect of producing a large number of " internal surfaces " within protoplasm, at all of which changes of surface tension and adsorption are liable to occur.? The essentially fluid nature ' Bayliss has shown that protoplasm is in the " .-iol " condition when amo-hoid and in the ' ' gel " condition when stimulated to contract. '^ Of. Bayliss, Principles of General Physiology. THE ESSENTIALS OF HISTOLOGY of amoeboid protoplasm is proved by the dancing (^rownian) movement of its granules ; this movement, which is of a physical nature, only occurs in fluids. Properties of living matter. — Living cells exhibit (1) irritahiUty or the property of responding to stimuli ; (2) meUxhoJic or chemical changes which I'esult in assimilation or the taking in of nutrient matter and converting it into living substance (anabolism), and disassimiliitiori, the property of breaking down such substance (katabolism) ; (3) reproduction resulting in the multiplication of individuals. Of these properties (2) and (3) are governed by the nucleus, and '(3) is usually initiated by the centrosome (see below). The irritability of the cell depends, however, mainly upon the cytoplasm. It is in consequence of this property that protoplasm reacts, sometimes by contraction, sometimes by relaxation, to mechanical, chemical, thermal, and electrical stimuli, and in the case of some cells {e.g. the pigment-cells and cones of the retina) to the stimulus of light. Jhe aniirV^oid movements_ of cells are also a manifestation of irritability, being produced and influenced by various external con- ditions and stimuli. Sometimes the result of a stimulus is to cause a cell or organism to move towards the source of excitation (attraction) ; in other cases the movement is in the reverse direc- tion (repulsion). The terms positive and negative chemotaxis, phototaxis, thermotaxis, thigmotaxis and the like, are used to indicate the nature of the effects produced by various formn of stimulation. Attraction-sphere and centrosome. — In some cells, as alrea'dy indicated, there are fine but distinct strife or fibrils (cytomitome) run- ning in definite directions. These are very commonly met with in fixed cells, such as various kinds of epithelium-cells, nerve-cells, and muscle-cells. But besides these permanent differentiations, which appear to be related to special functions, there are other fibril-like structures in the cell-protoplasm, associated wjth what is known as the centrosome (fig. 11). This consists of a minute particle {attraction-particle, centriole), usually situated near the nucleus, and staining darkly with iron- hsematoxylin, surrounded by a clear area {attraction-sphere), and from it radiate into the surrounding protoplasm a nunjber of fine varicose lines or threads, The attraction-sphere, with its central particle, was first noticed in the ovum and was supposed to be peculiar to the egg-cell, but it has now been recognised in very many kinds of cells, and is of nearly universal occur- rence in animal cells. The centrosome is frequently double, the twin-spheres being connected by a spindle-shaped system of, delicate fibrils {achromatic spindle) : this duplication invariably precedes the division of a cell into two. In some cells the oentrioles are multiple ; this is fioquently the caso with leucocytes and always with the giant-cells found in bone-u\arrow and elsewhere (figs. 12, 13). The cytoplasm surroimding the centriole, including the radiating flbres and the fibres of the spindle, is emisidered by some to be distinct in nature from the general protoplasm : it has l.i?en termed iirc/iopla.mt. No centriole has been found in the cells of the higher i)lants, although the anho- plasmic fibres are very well marked in tliem during cell-division. Fig. 11. — A CELL (WHITE ELOOD- CORPUSOLE) SHOWINIl ITS AT- TRACTION -SPHEEE. (M. Heidenhain.) In this, as in most, cases, the attrac- tion - sphere, a, lies near the nucleus, //. STRUCTURE OF THE CELL A cell-membrane is rarely distinct in animal cells. When present, it is usually formed by transformation of the external layer of the protoplasm; 1- i) Fig. 12. — Cells with irrbgitlar lobed nhclei and a giant-cell with annular NUCLEUS FROM RONE-MARROW OE %AEBiT. (M. Heidenhain. ) a, b, c, d, zones in the protoplasm. Fig. 13. — Multi-nucleated giant-cell from lymph gland of rabbit. (M. Heidenhain.) its chemical nature has not been sufficiently investigated. In plant-cells a membrane formed of cellulose is of common occurrence. lO THE ESSENTIALS OF HISTOLOGY The nucleus of the cell is a spherical, ovcSid, elongated, annular, or irregularly lobulated vesicle (figs. 1, 3, 5, 9, 11, 12), embedded in the protoplasm. Cells often have two nuclei, and occasionally several (flg. 13). The nucleus is bounded by a so-called membrane which encloses a clear substance {nuclear hyaloplasm, karyoplasm) (fig. 14) ; the whole of this substance is generally pervaded by an irregular network of fibres, some coarser, others finer {nuclear reticulum, karyom,itom.e) (figs. 14, 15). The membrane Fig. 14. — Nucleus op an beithelial CBLL OF salamander LARVA . (M. Heidenhain.) Magnified 2300 diameters. Fig. 15. — LyMPiiocYTE of triton^ SHOWING THE EBTICULAB STiiuOTUBE OF ITS NUCLEUS. Magnified 2000 diameters. Untouched photograph. The cell was fixed by steam, and after- wards stained with hiematoxylin. is formed by the same substance as^the reticulum, of which it constitutes the outermost layer. The knots of the reticulum are sometimes very distinct, and they then give an appearance of conspicuous granules within the nucleus {pseudonucleoli), not to be confounded with the highly refracting spherical particle known as the nucleolus, which is almost always present as a dis- tinct structure and is very conspicuous in sonje cases such as the ovum and nerve cells. Sometimes two true nucleoli are 'found in a nucleus (fig. 14). Occasionally the nucleolus has a vacuole-Iike globule in its interior. The material of the nucleolus, although basiphil, differs in its chemical and staining reactions from the nuclear reticulum. During cell-division it disappears. Whether it blends with the J^aryomitome fibres or becomes absorbed and removed is uncertain. The nucleoli may sotnetimes be seen to be bodily extruded from the nucleus into the protoplasm. The nuclear membrane and intra- nuclear fibres stain deeply with hwmatoxylin and with basic dyes* generally ; this propertv distinguishes them from the nuclear matrix, and they are accordingly spoken of as bani-clirr in the case of short straight chromosomes into small quadrangular masses (tetrads) (see fig. 26). DIVISION. OF CELLS 17 It ia further noteworthy that the generative cells which undergo the reduction- division above described exhibit either immediately (male) or a long while (fm ) Fm. 25. — Diagram of the changes occtTRRTNO in homotypioal mitosis. In A and B the eiffht chromosomes are united into pairs : in C, D, and E they are shown separating from one another, without any longitudinal cleavage. F, daughter nuclei each with only four chromosomes. Fig. 26. — Three stages of heterotypic al mitosi§ in spermatocyte op TRITON. (Moore.) a, geminal condition of chromosomes ; l>, gemini arranged in quadrate loops or tetrads ; c, separation of tetrads into the duplex chromosomes of the daughter nuclei, (female) before the final divisions a.remarkable series o,f changes in their nuclear chromatin ; the chromosomes first becoming distinct in place of forming a THE ESSENTIALS OF HISTOLOGY network, then entangled together at one side of the: nucleus (synaptic condition), and finally again becoming distinct, but now airanged in pairs (gemini) which later take various forms, such as double rods, loops, or rings as in heterotypical mitosis, but without necessarily forthwith proceeding to nuclear division (see fig. 27). The protoplasm of the cell divides soon after the formation of the diaster (fig. 21, m; fig. 23, 7). During division fine line^ are seen in the protoplasm radiating from the attraction-particles at the poles of the nucleus, whilst other lines form a spindle of ac/iroma, mi\iii}; bowl ; E, nii\pr ; ' F, needle for pricking finger. the cover-glass is touched by a needle, on account ef their tt-ndencv to stick to the glass, whilst the coloured coi'puscles are driven pasfby the cui'reiits set up ; (c) in the clear spaces, fibrin-filaments and blood-platelets. Sketch a roll of coloured corpuscles and one or two colourless corpuscles. Count the numbei' of colourless corpuscles in a field of the microscope. 2. To be made as in § 1, but the drop of blood is to lie mixed upon the slide with an equal amount of normal or isotonic saline' so that the icd corpuscles tend to be less massed together, aiid theii' peculiar shape is better disjilayed. ' A solution of sodium chloride containing from 7 "i to fl grammes to the litre or mammals, 6 grammes for the frog. Ringer's solution may also be used. This is made by adding to every 100 c^c. of normal saline O'024 gramme CaCl.. : 0'042 gramme KGl and O'l gramme NaHCO.,. STUDY OF THE HUMAN BLO'OD-UORPUSCLES 31 Sketcli a red corpuscle seen on the flat and another in profile (oi' optical section), Also a creiiated corpuscle. Measure with the scale (p. 27) ten red corpuscles, and from the result ascertain the average diameter of a corpuscle. Measure also the largest and the smallest you can find. 3. Make a preparation of blood as in § 1 and put it aside to coagulate, Keep the edges from drying by placing it in a moist chamber or by occasionally breathing upon it. After a few- minutes place a drop of 1 per cent, methyl violet at one edge of the cover and allow this to pass in and mix with the blood : it may be drawn through the preparation by applying a very small fragment of blotting paper to the opposite edge. The dye stains the nuclei of the white corpuscles, the blood-platelets* the network of fibrin-filaments, and the membranes of the red blood-corpusclos. 4. Place a small drop of blood on a slide, and at once invert it over the mouth of a bottle containing strong formol. After five minutes, gently wash with saline to remove blood-corpuscles, place a drop of 1 per cent, methyl violet solution on it for one minute, wash with water and cover. The blood-platelets are especi- ally well shown in this preparation. &; To fix and stain the coloured corpuscles : — Place upon a slide a drop of 1 per cent, osmic acid mixed with- an equal amount of saturated aqueous solution of eosin. Prick the finger, and mix the blood .directly with the coloured fluid, stirring them together with a needle. Cover the mixture and put aside for an hour, protected from evaporation ; then place a very small drop of glycerine and water at the edge of the cover- glass. When this has passed under, i.e. in about half an hour or more, fix the cover-class with gold size. 6. To study the granules of the colourless corpuscles and their reactions to different staining reagents, a film of blood is enclosed between two cover-glassep which are at once separated and the film on each quickly dried in the air. Or a«lide may be used instead of a cover-glass ; the drop of blood is placed close to the ground edge of one slide and this is drawn evenly over the middle of another. The film is fixed by im- mersion for a minute or two in methyl alcohol. It is then stained by (1) a 1 per cent, solution of eosin in rectified spirit (one minute), after which it is rinsed with water, and treated with (2) a 1 per cent, solution of methylene-blue in water (one minute). The film is again rinsed with water, rapidly dried, and mounted in dammar. Combined eosin-methylene-blue stains, such as Giemsa's or Jenner's or Leishman's, may also be em- ployed for films. These require only one operatioA (see Appendix). 7. Mount (in dammar) section^ of marrow from a long bone (rabbit) fixed with formol and stained with alcoholic eosin and methylene-blue. Observe the fat- cells, the siipporting reticular tissue, the proper marrow-cells in this tissue, the myeloplaxes and the erythroblasts. 8. Tease in salt solution or serum some of the red marrow from the rib of a recently killed animal. Observe and sketch the proper marrow-cells (myelocytes) and look for myeloplaxes (giant cells) and nucleated coloured blood-corpuscles (erythroblasts). 9. Make a film preparation of red marrow by sn^earing ^ little upon a cover- FiG. 42. — Pipette used for THE Thoma-Zeiss HjEma- CYTOMKTER. 32 THE. ESSENTIALS OF HISTOLOGY glaaH or slide, allowing it to dry quickly, and placing it in methyl alcohol. .After a fe-w minutes in thia, the preparation may be staitaed with alcoholic eoain and methylene-blue or by Leishman's stain in exactly the same way as a film prepara- tion of blood (see § 6), and mounted in dammar. 10. Enumeration of the blood-corpu.scles. This is done by some form of blood counter such as the hajniacytometer of Gowers, or the similar apparatus of Thoma. !) Fm. 43.— H;ivMArYT()METKK SI.IOE, KtlLED IM SQUARES FOR THE KNl'MERATTOX UI' Jil.OOD-CORPUSfLES. FiCi. 44. — DlAfiRAM OF A SiiCTION THROUGH THE H.tJSI.Vf VTO.VIETER SLIDE. m \Sl.SA^^ -f3-^ . o !?, O, q. ^Nj- oo 5—^ -■--«)■ <4C -%Ti V w- i^« & I o ^ S>. 9 -«ff- g» a m. i 3 Cl "^ JiL € S^ 10 ^ ^oo o -s w ^ c » ,<=? o *=>tical section ; c, in proiile ; v, a corpuscle with apparent vacuoles (probably parasitic organisms which are common in frog's blood-corpuscles) ; m, an amoeboid leucocyte ; n, nucleus of an erythrocyte, set free and contracted to the spherical form ; jfc, a lymphocyte ; p, a blood-platelet. Fig. 69. — Amphibian brythrocytes. Photographs. 450 diameters. A, from the frog. B, from the toad. Magnified but is brought clearly into view by the action of reagents, especially those of an acid nature. The action of reagents ijpon the red corpuscle of Amphibia is otherwise similar to that upon the mammalian corpuscle, water and hypotonic solutions causing it to swell into a globular form and then to become decolorised ; hypertonic solutions causing wrinkling of the envelope, BLOOD-CORPUSCLES OF AMPHIBIA Si and so on. As a first effect, water and certain other fluids may cause the hsemoglobin to retire from the envelope at the points where the fluid is passing through the membrane : a stellate appearance is thereby often produced. Boric acid causes thfe hsemoglobin of the newt's corpuscle to A B Fio. 70. — Ekythrooytes of lepidosiben labva, fixed with Flemming's SOLUTION AND STAINED WITH IRON-HiEMATOXYLlN. (T. H. Bryce. ) A, as seeu on the flat ; B, in section. In A the fibrils around the edge are visible as fine lines parallel to the margin of the corpuscle. In B their sections are seen as fine points just within the thinnest part of the edge. become partially or wholly collected around the nucleus, which may then be extruded along with it from the corpuscle. Immediately within the envelope, at the periphery of the amphibian erythrocyte, is a band of fine fibrils which are stained by gentian violet (Meves). As Bryce has shown, they can also be seen cut across in sections of the corpuscles, and may be stained with iron-hsematoxylin (fig. 70). Fig. 71. — A elood-platelet of Salamandea, and the changes which it UNDEE.WENT IMMEDIATELY AFTER WITHDRAWAL OF THE BLOOD FROM THE VESSELS. (F. Meves.) , Leucocytes. — The colourless corpuscles of Amphibia, although larger, are very similar to those of mammals. Like them, they are either wholly pale and finely granular, or enclose a number of very distinct granules of similar nature to those met with in mammals. These corpuscles vary much in size and in the activity of their amoeboid movements : those which have a multilobular nucleus (polymorphs) are usually the most active. Reagents have the same effect upon the amphibian leucocytes as on those of mammals. 56 THE ESSENTIALS OF HISTOLOGY Fkj. 72, — A iiLuou-i'ijATji]LiiT Of Salamandba, s^o\vl^*u its ikkegulak i'kojection.s AND FIBKINOUS FILAMJiNTS KADIATIM.; FKOM IT AJ(1> ATTACJiJSD TO ADJACENT blood-cokpislTjES. (F. Meves. ) Two erythrocytes, one free nucleus, and one polymorph leucocyte are included in the figure. Fill. 73. — Microscopic preparation of fkog's bloud showinc; the manner ik WHICH THE erythrocytes EECO.MK AIlRANOEn IN' ROSKTTED LINES OWINCJ TO THEIR EI.XATIDN BY THE COHTBACTIN(i THREADS FROM THE BLOOD-PLATELETS WHICH ARE AUULUTINATED AT CERTAIN i>oiNTS. Magnified 90 diameters. (J. Tait.) BLOOD-CORPUSCLES OF AMPHLBLA 57 The presence of glycogen may be demonstrated m them by its reaction with iodine solution (port- wine colour). Blood-platelets. — The blood-platelets or thrombocytes are much fewer in number than in mammals. They are of a spindle shape (fig. 68, p). They contain a nucleus-like body, and like the bloodr-platelets of mammals they show rapid changes as soon as the blood is drawn. Some of these changes are represented in figs. 71 and 72. The elongated corpuscle first contracts and becomes more globular, its nucleus changing similarly in shape. Irregular processes then begin , to be protruded from the corpuscle, and very soon fine threads are shot out radially in all directions. These become attached to those of other platelets,' or to any solid object which may be in the vicinity of the platelet. The filaments, which appear to be of a fibrinous nature, and may possibly be threads of fibrin, then begin to retract and drag upon the objects which are entangled by them. In • this manner a number of erythrocytes may be drawn together towards a common centre and assume a radial or resetted arrangement (fig. 73). Similar changes probably occur in the blood-platelets of mammalian blood after it is drawn. It is suggested by Tait that the attachment of the blood-platelets to a foreign or injured surface, as well as their entanglement and agglutination, may serve to plug small apertures in blood-vessels caused by injury, and thus aid in arresting haemorrhage. 58 THE ESSENTIALS OF HISTOLOGY LESSON VI. THE AMCEBOID PHENOMENA OF THE COLOURLESS BLOOD-CORPUSCLES. 1. Make a preparation of blood from the finger in tie usual way. Draw a briish just moistened with pure liquid paraffin around the edge of the cover-glass to prevent evaporation. Avoid an excess of paraffin. Place the preparation upon a " warm stage," and heat this to about the temperature, of the body (38° C). Bring a white corpuscle under observation with the high power, and watch the changes of Fio. 74. — Simple warming apparatus, complete, shown in opkration. shape which it undergoes. To become convinced of these alterations in form, make a series of outline sketches of the same corpuscle at intervals of a minute. The simplest form of warm stage is a copper plate of about the size of an ordinary slide, perforated in the centre and with a lopg tongue of the same metal projecting from the middle of one edge (fig. 74). Th^ copper plate rests upon the stage of the microscope, with a piece of asbestos or other non-conducting material between. The preparation is made upon an ordinary slide or on a long cover-glass, which is placed upon the warm stage and pressed into contact with it by the brass clips of the microscope. Heat is applied to the copper tongue by a small spirit- lamp flame; a greater or less amount is conducted to the warm stage and the superjacent preparation according to the point to which the flame is applied. To ascertain that the right temperature is got and maintained, put two pieces of solid paraffin, one melting at 35° C. (95° F.) and another at 38° C, (100° F.), one on either PHENOMENA OF COLOURLESS CORPUSCLES 59 side of the preparation. Tiie temperature must b'e such that the first piece is melted and remains so whilst the second remains unmelted.^ 2. Mount a drop of frog's or newt's blood diluted with an equal amount of salt solution, and examine it in the same manner upon the copper stage, at first cold, afterwards warm ; the temperature must, however, be kept below 30° C. Observe the effect of warmth in accelerating the amceboid movements of the pale corpuscles. Sketch one at intervals of a minute (a) in the cold, (6) whilst warmed. 3. Take some yeast which has been mixed with salt solution, and mix a very little of the yeast and salt solution with a fresh drop of newt's blood, slightly paraffining the edge of the cover-glass as before. Endeavour to observe the taking-in Fig. 75. — A polymorph leucocyte op tkiton fixed by ' steam in amieboid CONDITION AND STAINED WITH HEMATOXYLIN. Untouched photograph. Magnified 1360 diameters. Notice the homogeneous appearance of the protoplasm of the pseudopodia as compared with that of the body of the corpuscle. The nucleus is multilobed, the lobes being joined by threads of chromatin. . Its reticular structure is well shown. of the yeast-torulse by the white corpuscles. Sketch one or two corpuscles which have ingested torulse. Particles of carbon (Indian ink) or of vermilion may be used instead of yeast for this experiment. 4. To obtain a specimen with the white corpuscle? fixed in amreboid condition, a preparation of newt's blood mixed with salt solution is made, and set aside for ten minutes. By this time the corpuscles will be freely amceboid, and may show well-marked pseudopodia. To fix them in this condition let a jet of steaih from a tube attached to a boiling flask or kettle of water play for a second upon the cover-glass. The heat instantly kills the corpuscles, and they are fixed in the form they presented at the moment the steam was applied. They may now be stained by passing dilute hsematoxylin ^ under the cover-glass, the stain being followed by dilute glycerine. When this has diffused through the preparation (it must not be drawn under by filter paper), the cover may be cemented and the preparation kept. ' For exact work, an apparatus somewhat more complex than the above is required. For description of such apparatus, see the author's Course, of Practicai Histology. 2 The water used for the dilution of hsematoxylin solutions must always be distilled. 6o TH.E ESSENTIALS OF HISTOLOGY The amoeboid phenomena which are exhibited by the protoplasm of the colourless blood-corpuscles consist of spontaneous changes of form, produced by the throwing out of processes or pseudopodia 'in various directions. When first thrown out the pseudopodia are quite clear ; when a distinction into spongioplasni and hyaloplasm is apparent, the pseudopodia are at first com- posed only of the hyaloplasm, which flows out in any direction in which the surface tension is for the moment diminished (see p. 7). If the corpuscle is stimulated, either mechanically, as by tapping the cover-glass, or electrically, all pseudopodia are retracted, the corpuscles becoming spherical. A change of form caused by the protrusion of the pseudopodia may, when active, be Fig. 76. — An jsosihophil leucocyte of Salamamdra begikhino to adhjeke TO AN EKYTHBOGYTE. Perfectly fresh prepa.ratipn without addition of fluid. Untouched photograph. Magnified 600 diameters. Two other erythrocytes are included in the field. Notice that the nuclei in these have undergone a change of position within the corpuscle, showing that its contents must he completely fluid. followed by changes in place or actual locomotion (migration) of the corpuscle. When a pseudopodium, or the external surface of the protoplasm, comes in contact with any foreign body, the protoplasm tends to flow round and enwrap it; if it is small, it is drawn into the corpuscle; particles thus ingested may be conveyed by the corpuscle iti its movements from one place to another (fig. 78). This property plays an important part in many physiological and pathological processes. Thus cfells in the spleen resembling large leucocytes — the so-called splenic cells — take in blood-corpuscles, which become broken down within them j and pathogenic bacteria become taken fhto the protoplasm of certain leucocytes (on this account termed phagocytic), there to be destroyed (Metchnikoff). The phagocytic properties of the leucocytes become especially developed as the result of the action upon the bacteria of certain substances which are present to a variable extent in blood and are termed opsonins (Wright). They are also afi"ected by agents capable of acting upon lipoids ; which form, it is believed, a delicate surface film over PHENOMENA OF COLOURLESS CORPUSCLES 6i the protoplasm of amceboid cells. Hamburger, who makes this observation, points out that the beneficial action of certain medicinal remedies may be ^v y- I-- J7.iy#« *i '(?/ ■'""'nlililhiti' Fir;. 82. — Section thrgurii the deeper layers of a stratified EPiTHELinM, SHOWING EIBRILS, ,/', PASSING FROM CELL TO CELL ACROSS THE INTERCELLULAR SPACES. (Ranvier. ) and protoplasmic, and are separated from one another by a system of intercellular channels, which are bridged across by numerous fibrils passing from cell to cell (figs. 81, 82), giving the cells, when separated, the appearance of being beset with short spines (pricMe- cells). These "bridging fibrils" are not peculiar to stratified epithelium, but occur in many tissues. The deeper cells multiply by karyo- kinesis. The newly formed cells tend as they enlarge to push those superficial to them nearer to the surface, from which they are eventually thrown oif. As they approach the surface they become keratjnised, and in the case of the epidermis entirely lose their cellular appearance, which can, however, be in a measure restored by the action of alkalies (g 2). The castofif superficial cells of the stratified epithelium of the mouth, which are seen in abundance in the saliva (§ 1), ^are less altered than those of the epidermis, and the remains of a nucleus is still visible in them (fig. 83). Fig. 83. — Epitiielium-scales from the inside of tub mouth. (Sharpey. ) Magnified 260 dia- meters. EPITHELIUM 67 The stratified epithelium of the human skin (epidermis) shows many peculiarities ; these will be considered when the skin is treated of. The name transitional epithelium is given to a stratified epithelium con- ./ •V--'^ Fig. 84. — Epithelial cells pbom the bladder of the kabeit. Magnified .500 diameters. (Klein.) a, large flattened ceil from the superficial layer, with two miclfei and with strongly marked ridges and intervening depressions on its under surface ; 6, pear-shaped cell of the second layer adapted to a depression on one of the superficial cells. Pig. 85. — Pavement epithelium ob endothelium of a serous membrane. Nitrate of silver preparation. Carmine staining op nuclei. sisting of only three or four layers of cells. It occurs in the urinary bladder, the ureter, and the pelvis of th© kidney. The superficial cells (fig. 84, a) are large and flattened ; they often have two nuclei. Their free surface is covered with a cuticular stratum, and on their under surface they exhibit depressions, into which fit the larger ends of pyriform cells, which form the 6S THE ESSENTIALS OF HISTOLOGY next layer (fig. 84, b). Between the tapered ends of the pyriforin cells one or two layers of smaller polyhedral ' cells are found. The epithelium seems to be renewed by mitotic division of these deeper cells. It is possible that the superficial cells also multiply; it is stated that the division of their nuclei is amitotic (see fig. 19, p. 12). Simple scaly or pavement epithelium is found in the saccules of the lungs, in the ducts of the mammary glands, in the kidney (in the tubes of Henle, lining the capsules of the Malpighian body, and covering the glomeruli), and also lining the cavities of serous membranes (fig. 85), and the interior of the heart, blood-vessels, and lymphatics. When occurring on internal surfaces, such as those of the serous membranes, blood-vessels, and lymphatics, it is spoken of as endothelium or (sometimes) mesothelium. Kolossow showed that the cells of a serous epithelium are provided with a striated border consisting of what appears to be a fine pile of closely set hairs on their free surface, somewhat like that which is found on columnar cells. These hairlets rest on a thin homogeneous border. The latter appears to be a common feature of endothelium for it also occurs in the endothelium of the blood-vessels, but the pile of hairs is only found in the endothelia of Fig. 86. — Endothelium-cells op sekous membrane seen in profile ^^E\v, SIIOWINfJ I'EOTOPL.iSMIC BRIDGES STRElCIIlNO ACROSS THE INTERCELLl'LAE, SPACES. (M. Heidcnhain. ) serous membranes, at least in mammals. Kolosgow's statements have been confirmed by several other observers. In some amphibians cilia occur on parts of the peiitoneal epithelium (Klein). GLANDULAR EPITHELIUM AND SECRETING GLA^'DS. Glandular epithelium is the essential tissue of all the organs which are known as secreting glands. These are of two chief kinds. Those which are best known and which are termed externally secreting gla7ids are furnished with a duct which ramifies in all parts of the gland and by means of which the products of the secretory activity of the gland-cells are brought to a free surface. Such glands have been developed as involutions of the surface upon which they open, and their epithelium is tontinuous with that of this surface, and is in some cases, especially where the surface upon which the gland opens is covered with columnar epitheliuin, of a similar character to that epithelium. In other cases it is different in character from the epithelium of the surface, becoming altered as we trace the duct back into the recesses or alveoli of the gland, and it is in these that the characteristic glandular cells, which are generally polyhedral in shape, are found. Every such involution or ingrowth of epithelium to form a gland is, when first formed GLANDULAR EPITHELIUM 69 ■'"0 K>Joi^^ /;: Ip *. FiG. 87.— Various kikds of glands. I. Simple saccular gland from amphibian skin (Flemming). II. Simple tubular gland from intestine " (Flemming). III. A small racemose ^land with a simple duct, d, into which a number of irregularly tubular acini, a, open (Klem). IV. Part of a tubulo-racemose f^land with the acini unravelled (Flemming). V. Wax model of a smajl tubulo-racemose g-land fronl the epiglottis (Maziarski). . 70 THE ESSENTIALS OF HISTOLOGY of a simple character, shaped either like a flask or test-tube and filled with a solid mass of cells, but it presently becomes hoU'owed out, some of the cells being left as a lining to the connective-tissue membrane which bounds the involution. The gland may remain simple and unbranched {simple saccular and simple tubular glands, fig. 87, I. and II.), 6r it may branch again and again until a complicated structure, in some cases small, in others of con- siderable size, is produced (compound tubular and compound saccular (or racemose) glands) (fig. 87, TIT., TV., V.), instances of which are furnished by the kidneys and salivary glands respectively. The cells which furnish the Fig. 88.— Two cells from a cutaneous gland of salamander-lakva, SHOWING THE SECRETION GBANTLES. (Gurwltscll. ) The left-hand cell, which has two nuclei, is filled with granules. In the right-hand cell the granules are becoming swollen andodissolved. secretion of the gland and which line the secreting parts of the tubules of a tubular gland, or the alveolar enlargements (acftii) at the ends of the ducts of a racemose gland, are often partly or wholly filled with granules in the intervals of secretory activity ; these granules become discharged or dissolved .and pass into the secretion during activity. Secreting glands are always abundantly supplied with blood-vessels and generally also with nerves. The blood-vessels are brought to the alveoli in the connective tissue which holds . together the acini and groups of acini Oobules) of the gland ; the nerves are supplied partly to the blood-vessels and partly to the secreting epithelium cells. The liver differs from all other secreting glands in being composed of goljd masses of cells (hepatic lobules) instead of tubular acipi lined by GLANDULAR EPITHELIUM 71 epithelium. It exhibits also other important differences in the nature of its blood supply and the relation between the blood and the liver-cells. The other kind of secreting glands, known as the internally secreting or endocrine glands, are not furnished with ducts and were formerly classed with the spleen and lymphoid structures as ductless glands. But the true endocrine glands are, like the externally secreting organs, composed of epithelial cells, sometimes grouped in solid masses (as in the suprarenal), in other cases disposed around hollow vesicles (thyroid) which become filled with the material of the secretion. Since there is no duct in these glands the secretion is carried into the blood either directly by the blood-vessels of the gland or indirectly through the lymphatics. The detailed study of the glands and of other epithelial structures may be reserved until the organs in wjiich they occur are described, but columnar and ciliated epithelia will be dealt with in the next lesson. The hairs and nails and the enamel of the teeth are modified epithelial tissues. They will be described with the skin and mouth respectively. THE ESSENTFALS OF HESTOLOGY LESSON VIII. COLUMNAR AND CILIATED EPITHELIUM: ACTION OF CILIA. 1. Break up in dilute glycerine a .shred of epithelium from a minute piece of the nlucous menibrani' of intestine (frog) that has been treated with 1 per cent, osniic acid for some houvw, and has subsequently macerated in water for a few days. The cells easily separate on tapping the cover-glass. Measure and sketch one or two cells. The cover-glass may be at once fixed by gold size. 2. Prepare ciliated epithelium either from the oesophagus of the frog or from the trachea of a mammal. The tis.sue may either be treated with osmic acid like the last preparation, or macerated in chromic acid solution (1 to 2000 Ringer) for a few days. Measure in one or two of the cells {<() the length of the cell, {h) the length of the cilia, (c) the size of the nucleus. Sketch two or three cells. 3. Mount in sea-water one or two bars of the gill of the marine mu.ssel (fig. 89). Study the action of the large cilia. Now place the pre)mration upon the copper warm stage (see Lesson VI.) and oljserve the effect of gently raising the temperature. Fig. 89. — MrasEL (Mytimts kdtilis), from which one shell- v.m.ve (the rioht) AND THE COKRESPONDINd MANTLK-LOBE HAVE BEEN REAIOVEP. 6r, br, the expanded ^ills or branchi:n. which, owin^ to the Httle bars of which they are composed, present a striaterl aspect ; ^lil, mantle ; ?/(, cut adductor muscle ; i, mass of viscera ; the dark projection just below is the foot. Put this prepaiution aside, until the end of the lesson, liy which time many of the cilia will ha\e become languid. When this is the case pass a drop of dilute potash solution (1 part KH( t to 1000 of sea-water) undei' the cover-glass and obser\'e the effect. 4. Cement with sealing-wax ,i ]iiece of small glass tubing to a slide so that one end of the tube comes nearly to the centre of the, slide. To do this eft'ectually the slide must be heated and some sealing-\\'a\ melted on to it and allowed to cool. The glass tulx^ is then made liot and a)iplie(l to the slide, embedding itself as it does so in the sealing-wax. Apply a ring of modelling wa.\ or plasticine (half an inch in diameter and rising well above the glass tube) so as to include the end of the tube. Make a deep notch or a hole in the ring opjiosite the tube for the exit of gas. Place a drop of watei- within the ring (fig. 90). COLUMNAR EPITHELIUM 73 Put a bar from the gill upon a cover-glass in tiie least possible quantity of sea-water ; invert the cover-glass over the ring, and (with anothei' slide) press it gently and evenly down. The preparation now hajigs in a laoht chamber within which it can be studied through the cover-glass, and into which gases or vapours can be passed and their effects observed. The slide must bo soeuroly clamped to the stage of the microscope. Pass Q9c'^ Q Fid. 110. — A s.M.M.i. Li>i;m,E of .mhi-ose tissue. Magnified l?0 diameters. rr c, small atter\- anrl vein enterinji: the lobule. Fig. 111. — FoDR fat-cells in connective tissue. Magnified 400 diameterst Each cell is distended by the fat-globule, the oell-protoplasm forming a thin envelope to the globule. The nucleus lies at one side in a somewhat larger amount of protoplasm. The fat is stained with Sudan III., and appears dark in the photograph. (3) Mast-cells (Ehrlich), usually spheroidal or ovoidal in shape, filled with granules, which are deeply stained by gentian violet and by other basic aniline dyes. They are not everywhere common, but are numerous in parts where fat is being laid down (fig. 113). (4) Plasma-cells. These are characterised by their granular protoplasm, which is less basiphil than that THE CELLS OF AREOLAR TISSUE 87 of the mast-cells and their relatively small nucleus ; in shape, they are either rounded, angular, or elongated. Migratory leucocytes may also be seen here and there in areolar tissue (wander-cdls). Fig. 112. — The fat-cells, which have been stained with Sudan III., aee ^ DISTKIEUTED ALOHG THE COURSE OF A SMALL AKTERT AND VEIN. Fig. 113. — Deposition of fat in oonnbctjve-tissue cells. f, a cell with a few isolated fat-droplets in its protoplasm ; /', a cell with a single lar^e andseveral minute drops ; /", fusion of two large drops ; jr, granular mast-cell ; c.t., lamellar connective- tissue corpuscle ; c, network of capillaries. Pigment-cells. — In the middle coat of the eye in mammals, and in some parts of the skin, some of the connective-tissue cells are occupied by granules of pigment (pigment-ceMs). These are much more extensively' present in lower vertebrates, especially in Amphibia and fishes, where they exhibit changes which re.'iult in the pigment being at one time diffused over a considerable area and at another time restricted to the immediate neighbourhood of the nucleus. The changes thus produced cause alteration in the general colour and shade of the integument, when such pigment- THE ESSENTIALS OF HISTOLOGY ' cells are numerous, and serve the purpose of protective adaptation of the animals to their environment. The alterations are brought about through the nervous system. The connective-tissue cells occupy spaces of corresponding shape in the semi-fluid ground-substance, lying between the bundles of white fibres. In some parts the white bundles are developed to such an extent as to pervade aln(ost the whole of the ground-substance, and then the connective- tissue corpuscles become squeezed into the interstices, flattened lamellar expansions of the cell? extending between the» bundles, as in tendon (see next Lesson). The cells of areolar tissue come into intimate relation with the cells lining the lymphatic vessels and small blood-vessels. This connexion can best be seen in silvered preparations, where both the cells and the lymphatics are left white on the brown ground of stained intercellular substance ; this fact nm^^^^^ will be again referred to in speaking of the origin of the lymphatics. ADIPOSE TISSUE. Adipose tissue consists of vesicles filled with fat (figs. 110, 111) and collected into lobules, or into tracts which accompany the small blood-vessels. The vesicles are round or oval in shape, except where closely packed, when they become polyhedral from mutual compression. The fat-drop is con- tained within a delicate protoplasmic envelope (fig. J 11), which is thickened at one part, and here includes an oval flattened nucleus. The fat is stained black by osmic acid (fig. 114); a deep orange- red by Sudan III. ; and an intense red by Scharlach R. The vesicles are supported partly by filaments of areolar tissue, partly by a fine network of capillary blood-vessels. The fat when first formed in the embryo is deposited within large granular cells (fig. 115) of a spheroidal or polyhedral shape ; some authorities regard these cells as of a ^ecific nature, for they are in certain situations collected into gland-like masses abundantly supplied with blood-vessels, They gradually become transformed into fat-cells by the deposition of fat in the cell-protoplasm. Fat is, however, also laid down elsewhere in ordinary cells of connective tissue. In all cases the fat appears to be' produced by a transformation into droplets of fat of albuminous granules which the cells contain. . As the droplets increase in size they run together into a larger drop, which gradually fills the cell; swelling it out more and more Fig. 114. — Fat - cells prom YOUNO ANIMAL. (Ranvier.) Osmic acid preparation. The drops of fat are stained of an intense black, n, nucleus ; ;;, small gloliules of fat. RETICULAR TISSUE 89 so that eventually the cell-protoplasm appears merely as the envelope of the fat- vesicle. Fat-cells often contain lipoid globules as well as true fat, and it is possible that in its development the fat in the cell is always preceded by lipoid matter. Pat is found most abundantly in subcutaneous areolar tissue, and in some deeper parts, e.g. at the back of the peritoneum, around the. kidneys, under the Fin. 115. — Two STAGES of formation of adipose tissue. (H. Batty Shaw.) In A the tissue is formed of a gland-litte mass of cells, in some of whicli tlie cytoplasm is occupied by fat-globules (looking white in the sections). In B the fat fills many of the cells. Fig. 116. — Rbticulab tissue from a lymi-h-gIjAnd. Moderately magnified. tr, a trabecula of connective tissue ; r, 7^, reticular tissue, with more open meshes at r and denser at r*. epicardium, and in the mesentery and omentum. The yellow marrow of the bones is also principally composed of fat. There is no adipose tissue within the cavity of the cranium. S KBTICULAE TISSUE. In reticular tissue (figs. 116, 117, 118) the intercellular substance is largely replaced by lymph, and is traversed by a network of white fibres, the meshes of which vary in size, being very small and close in soine parts ; more open and like areolar tissue in other parts. There are few or no elastic fibres. The fibres are often enwrapped by flattened branched connective- go THE ESSENTIALS OF HISTOLOGY tissue cells, which may have to be removed to bring the fibres clearly into view, Chemical differences between the fibres of reticular tissue and those of ordinary areolar tissue have been described by Mall and others, but, according to Halliburton, it is doubtful if they are really different. Fig. 117.- ReticdIjAr tissue, more highly magnified. with the connective tissue of a showing the continuity of the retiforni tissue, r, t, trabeculum, tr. Microscopically the fibres of the two are indistinguishable : they are stained by the same reagents and occur in complete continuity with one another Fig, 118. — Reticulum or bone-marrow. (Enderlen.) (see figs. 116, 117, 119). Reticular tissue forms? a fine framework in many organs ; supporting the proper elements and extending into the interstices between the coarser connective-tissue bundles. It can be well shown by dissolving the cells of the tissue by tryptic digestion and subsequently staining the fibres forming the reticulum (p. 79, § 5). It Occurs in lymph- RETICULAR TISSUE 91 glands, in the spleen, liver, bone-marrow (fig. 118), mucous membranes, and many other ,parts. , Wherever it occurs it supports the cells of the organ, which are contained within its meshes. Fig. 119. — Lymphoid tissue of a lymph-gland. The fibres of the tissue have been stained. Their continuity with the connective-tissue trabeculsB is in this way well shown. Lymphoid or adenoid tissue is reticular tissue in which the meshes of the network are largely occupied by lymph-corpuscles (fig. 119). This is met with in the lymph-glands and in allied structures, such as the tonsils, lymphoid follicles, and Malpighian corpuscles of spleen. It will be described with those structures. 92 THE ESSENTIALS OF HISTOLOGY LESSON X. THE CONNECTIVE TISSUES {continued). 1. Tease out as finely as possible a small shred of elastic tissue (ligamentum nuchee of the ox or ligamentum subflavum of man) in glycerine and water, slightly tinged by magenta. Cover and cement the preparation. Note the large -well- defined fibres constantly branching and uniting with one another. Sketch a small part of the network. Note the existence of bundles of white fibres amongst the elastic fibres. 2. Examine a thin transverse section of ligameiitum nuchas which has been hardened in 2 per cent, solution of bichromate of potassium. The section is to be stained with hsematoxylin and eosin and mounted in dammar by the usual process, or left unstained and simply mounted in glycerine and water. Observe the grouping of the fibres and their angular shape. Frequently the angles are rounded. 3. Pinch oflf the end of the tail of a dead mouse or rat, draw out the long silk- like tendons and put them into salt solution. Take one of the threads, which should be nearly three inches long, and stretch it along a slide, letting the ends dry firmly to the glass but keeping the middle part wet. Put a short piece of fine hair on one side of this and cover in salt solution. Observe with a high power the fine wavy fibrillation of the tendon. Draw. Now run dilute acetic acid (0'75 per cent.) under the cover-glass ; watch the tendon where it is becoming swollen by the acid. Notice the oblong nucleated cells coming into view between the tendon- bundles. Sketch three or four cells in a row. Lastly, lift the cover-glass, wash away the acid with distilled water, place a drop of dilute hsematoxylin solution on the tendon, and leave the preparation until it is deeply stained ; then wash away the stain and mount the preparation in faintly acidulated dilute glycerine. 4.. Take another long piece of rat or mouse tail tendon, and after washing it in distilled water, stretch it upon a slide as before, fixing the ends by allowing them to dry on to the slide but keeping the middle wet. Put a drop of nitrate of silver solution (1 per cent.) on the middle, and leave it for five minutes. Then rinse off the silver nitrate with- distilled water, drain this off and expose the slide to direct sunlight. In a very few minutes the silvered part of the tendon will be brown. Draiii off the water, allow the preparation to dry completely and then mount in dammar. 5. Stain with magenta solution a thin section of ox tendon which has been hardened in 70 per cent, alcohol. The section may be cut by hand with a razor. Or the tissue may be hardened in 10 per cent, formol, soaked in gum and cut frozen. Mount in dilute glycerine and cement at once. 6. For studying the development of connective tissue, sections of the umbilical cord at different periods may be used. Fix with formol. Stain with Van Gieson and hsematoxylin. ELASTIC TISSUE. Elastic tissue is a variety of connective tissue in which the elastic fibres preponderate. It is found most characteristically in the ligamentum nuchse of quadrupeds and the ligamenta aubflava of the vertebras, but the connective tissue of other parts may also have a considerable development of elastic fibres. It occurs in an almost pure form in the walls of the air -tubes, and ELASTIC TISSUE 93 uniting the cartilages of the larynx. It also enters largely into the formation of the lungs and of the walls of the arteries. In the ligamentum nuchse most of the fibres are large (fig. 120). They often exhibit cross markings or even transverse clefts. When dragged Fig. 120. — Elastic fibkes from the ligamentum nuchas of the ox, showing transverse markings on the fiebbs. Fig. 121. — Cross section of elastic fibres from the ligamentum nucha; OF the ox. Photograph. 200 diameters. The angles of the fibres are mostly rounded, asunder, they break sharply across. They constantly branch and unite, so as to form a close network. In transverse section they appear angular, but usually the angles are rounded (fig. 121). They are separated into small groups or bundles by intervening areolar tissue. Elastic tissue does not always take the form of fibres, but may occur as membranes (e.g. in the blood-vessels). In areolar tissue the elastic fibres may be very fine, but their microscopic and chemical characters are always well marked (p. 82), 94 THE ESSENTIALS OF HISTOLOGY FIBROUS TISSUE. Fibrous tissue is almost wholly made up of bundles of white fibres running in a determinate direction. These agairi are collected into larger bundles, which give the fibrous appearance to the tissue. The bundles are Fig. 122. — Section or tendon, human. (Sobotta.) x 32. «, tendon-bundles ; 5, septa of areolar tissue ; i>, vessels. constantly uniting with one another in their course, although their com- ponent fibres remain perfectly distinct. The interspaces between the larger bundles ape occupied by areolar tissue (fig. 122, s; fig. 123, c, d, e) in which the blood-vessels and lymphatics of the fibrous tissue are conveyed. The interstices between the smallest bundles are occupied by rows of lamellar connective-tissue corpuscles {tendon-cells), FIBROUS TISSUE 95 which, from being squeezed up between three or more bundles, become flattened out in two or three directions. In transverse section the cells look Fig. 123. — Pabt or a lakgk tendom ik tkansvekse skction. More highly magnified.. te, areolar sheath of the tendon, with the fibres for the most part running transverselv ; but with two or three longitudinal bundles, b ; I. lymphatic cleft in the sheath ; immediately over it a blood-vessel is seen out across, and on the other side of the figure a small artery is shown cut longitudinally ; c, large septum of areolar tissue ; d, smaller septum ; e, still smaller septum. The irregularly stellate bodies are the tendon-cells in section. irregularly stellate (figs. 123, 124), but when seSen on the flat they appear lamellar (fig. 125, A; fig. 12G), and from this aspect their general shape is square or oblong. They lie, as before said, in rows between the tendon-bundles ; the nuclei of adjacent cells are placed opposite one another in pairs (fig. 126). The cell-spaces correspond in general figure and arrangement to the cells which occupy them (.fig. 125, B;. Fibrous tissue forms the tendons and ligaments, and also certain membranes, such as the dura Fig. 124. — Section of mater, the fibrous pericardium, the fascisB of the ''^'^'"°*' ^""^^ '^ff.Z ' . MOUSE. Magnified 150 limbs, the fibrous coverings of organs, etc. It diameters. is found wherever great strength, combined with ^he dark branched bodies are ° ° ' sections of the tendon-cells. flexibility, is concerned. It receives a few blood- vessels, disposed longitudinally for the most part, and contains many lymphatics. Both blood-vessels and lymphatics run in the areolar tissue which separates and surrounds the tendon-bundles. Tendons and ligaments 96 THE ESSENTIALS OF HISTOLOGY also receive nerve-fibres, many of which end in localised ramifications within fusiform enlargements of the tendon-bundles (organs of Golgi), while others terminate in end-bulbs or in simple Pacinian corpuscles. These will be described with the modes of ending of nerve-fibres. MINOR VAEIETIES OF CONNEOTiyE TISSUE. Basement- membranes {memhranoi proprim) are homogeneous-looking A g: ^^■SW-^Ejj O ^ Fig. 125. — Tendons of mouse tail; showing chains of cells between THE tendon-bundles. 175 diameters. A , stained with hematoxylin ; B, Bt»ined with silver nitrate, showing the cell-spaces. membranes, which are found forming the surface layer of the connective-tissue expansions in certain parts, especially where there is a covering of epithelium, Fig. 126. — Eight cells fbom the same tendon as bbpeesekted in fig. 125, A. Magnified 425 diameters. The dark lines on the surface of the cells are the optical sections of lamellar extensions directed towards or away from the observer. as on mucous membranes, in secreting glands, and elsewhere. They are sometimes formed of flattened connective-tissue cells joined together to form a membrane ; but in most cases {e.g. front of cornea, trachea) they are evidently formed not of cells, but of condensed ground-substance, and in yet other cases of elastic substance (back of cornea) ; the name basement- membrane is therefore used to denote structures of an entirely different nature. Jelly-like connective tissue, although occurring largely in the embryo, MINOR VARIETIES OF CONNECTIVE TISSUES 97 is found only in one situation in the adult — viz., forming tlie vitreous humour of the eye. It is composed mainly of soft, fluid or semi-fluid ground-substance, with cells scattered here and there through it, and with fibres which interlace throughout the tissue and confine the fluid of the ground-substance within their meshes ; thus 'conferring upon the tissue my 7 ■(*/ ^T.l Fig. 127. — Developing connective tissue in heart of ohiok-embryo of 48 HOURS. (Szily.) ■my, cells forming myocardium ; j, jelly formed of reticulum ^rith enclosed fluid ; e, endo- thelium (mesothelium) of heart ; hi, mesenchyme cells in jelly ; hi, blood-corpuscles. its jelly-like character. All embryonic connective tissue is at one period-of this jelly-like nature (see below). DEVELOPMENT OF CONNECTIVE TISSUE. Connective tissue is developed in and from certain cells of the mesoderm (mesenchyme) of the embryo. In those parts which are to form con- nective tissue, there may frequently be seen a clear space separating the cell-layers which are already formed, this clear space being sometimes permeated with fibres which appear to be produced from the cells bound- ing the space. Branching mesenchyme cells, which separate off from the bounding cells, are presently found forming & reticular syncytium within the clear space (fig. 127, m; fig. 128). In the meshes of this syncytium is a semi-fluid intercellular substance (ground-substance). The connec- tive-tissue fibres, both white and elastic, are deposited in this ground- substance. The elastic substance takes in the first instance the form of granules (fig. 129, g), which subsequently become connected together into 7 98 THE ESSENTIALS OF HISTOLOGY elastic fibres or laminae, as the case may be. The white fibres appear at first as single threads, which are ultimately collected into fine bundles. The bundles become gradually larger ; so that in some tissues the whole r^" or '6) -y^ f.:, (:■_. ) ^ ^ys* .'*». Fig. 128.— Cells of develoi'Ing i'(innei.'tive tissue (mesenchyme) united to FORM V syncytium. (From Prenant, Bouin, and Maillard.) No iibrey are as > et developed in the intercellular substance. ground substance is eventually pervaded by them, and the cells of the tissue become squeezed up into the intervals. Before any considerable development of fibres has taken place, the embryonic connective tissue ■/^i^<^ Fig. 129. -Development of elastic tissce hy dei'iisitiiin of fine i;ranules. (Ranvier.) g, fibres being formed of rows of " elastin " gfranules ; p, flat plate-like expansion of elastic substance formed by tbe fusion of " elastin " granules. has a jelly-like appearance; in this form it occurs in the umbilical cord, where it is known as the jelly of Wharton. There has been always a difference of opinion as to the origin of the fibres of connective tissue, some histologists holding that they are formed within the protoplasm of the cells, which gradually lose their cell-characters as fibres become developed within them ; others taking the \-iew that the fibres, both white and elastic, are extracellular* formations. While it is DEVELOPMENT OF CONNECTIVE TISSUE 99 certain that they are produced under the influence of the cells, there is distinct evidence that both kinds of fibres are deposited in ground-substance and not in cell-protoplasm, so that they are rathdr to be looked upon, like the ground-substance itself, as formed by ti process of secretion than by one of i J A // ¥■ ^"fe&p i ^^ Fig. 130.— Jelly of Wharton from umbilical cord of new- born child (Sobotta.) x280. f, conneetivc-tiseue fibres ; c, cells. direct cell-transformation. That this is the true account of the mode of their formation is shown by the manner in which they become developed in the ground-substance or matrix of hyaline cartilage, without any change in the form or structure of its cells being evident. Mall took the view that the intercellular oi' ground-substance i.s itself living matter, and regarded the whole structure, cells and ground-substance together, as constituting a continuum, the fibres being laid down by chemical transfor- mation in the ground-substance, which he termed ejcoplasm. loo THE ESSENTIALS OF HISTOLOGY LESSON XI. THE CONNECTIVE TISSUES {continued). \. Ctit two or three thin tangential slices uf the fresh cartilage of a joint, raount them in salt solution, and examine with the high power. Observe the form and grouping of the cells. Look at the thin edge of the section for spaces from which the cells have dropped out. Measure two or three cells and their nuclei, and sketch one or two groups. Now replace the salt solution by watei- and set the preparation aside for a little' while. On agairi examining it, many of the cai'tilage-cells will be, found to have shrunk within their containing capsules. 2. Make other sections of the cartilage (1) from rtear the middle, (2) from near the edge at the attachment of the synovial mepibraiie. Place the sections for two or three minutes in acetic acid (1 per cent.), wash them with water, and stain with dilute hsematoxylin solution. When stained mount in dilute glycerine and cement the cover-glass. In (2) look for branched cartilage-cells. 3. Study vertical sections of articular cartilage from an end of bone which has been fixed and decalcified, and mount the sections in glycerine and water, or, after staining with hsematoxylin, in dammai'. Sketch the arrangement of the cells in the differeiit layers. 4. Binse a fresh joint (from a sheep's foot) with distilled water ; drop 1 pei' rent, nitrate of silver solution over it ; after five min-utes wash away the nitrate of silver and expose in water to direct simlight. When browned, place in rectified spirit foi' half an houi' or more, and then with a lazor wetted with the same spirit cut thin sections from the surface and mount in dammar after passing through clove oil. The cells and cell-spaces show white in the brown ground-substance. .'j. To study the structure of synovial membrane mount other slices from the same silvered preparation of the joint (S 4) taken just beyond the limits of the articular cartilage. Also look for small fringed piojections of the membrane. Snip them off with scissors and mount as before. 6. The superficial flexor tendons of the foot (ox or sheep) lun in grooves formed by the deep flexors, and these grooves are Jined, and the tendons which ])ass through them are covered by vaginal synovial membranes. To show the structure of these treat one of the -superficial flexor tendons with silver nitrate in the manner recommended for the joint, § 4, and after hardening in 70 per cent, alcohol cut sections from the surface, pass through clove oil, and mount in dammar as befoi'e. CARTILAGE. Cartilage (gristle) is a translucent bluish-wliite tissue, firm, and at the same time elastic, and for the most part found in connexion with bones of the skeleton, most of which are in the embryo at first represented entirely by cartilage. Three chief varieties of cartilage are distinguished. In one, which is termed hyaline, the matrix or ground-substance is almost clear, and "free from obvious fibres; in the other two, which are termed Jibro- cartilat/e, the matrix is pervaded by connective-tissue fibres. When these are of the white variety, the tissue is irhitr fibro-cartUage ; when they are elastic fibres, it is gdloic or claatic fibro-cartilage,. CARTILAGE lOI The matrix immediately around the cartilage-cells is often marked off from the rest by a concentric line or lines, this part of the matrix, which is the latest formed, being known as the capsule of the eell. The cells, which lie in groups of two, four, eight, etc., in the matrix, are bluntly angular in form, the sides opposite to one another in the groups being generally flattened. The protoplasm is clear ; it may have droplets of fat ; and with a high power fine interlacing filaments and granules can be observed in it. Cartilage-cells also contain, as a rule, glycogen : this can be shown by staining with iodine. During life the protoplasm entirely iills the cavity or cell-space which it occupies in the matrix ; but after death, and in consequence of the action of water and some other agents, it tends to shrink away from the capsule. The nucleus is generally spherical and reticular (fig. 132). The disposition of the cells of cartilage in groups of two, four, eight, A BODE Fig. 1-31. — Plan of the multiplication of the cells of cabtilase. (Sharpey. ; A, cell in its capsule ; B, divided into two, each with a capsule ; C, primary capsule disappeared, secondary capsules coherent with matrix ; D, tertiary division ; E, secondary capsules dis- appeared, tertiary coherent with matrix. etc., is due to the fact, that these groups have originated from the division of a single cell first into two, and these again into two, and so on. The division of the cartilage-cell, like that of most other cells, is effected bj' karyokinesis. It would seem that the matrix is formed of successive portions, which are deposited around each cartilage-cell as the so-called " capsules " (fig. 131), each newly formed portion blending in its turn with the previously formed matrix, whilst a new capsule is formed within it. The more newly formed portions of matrix stain with hsematoxylin more deeply than the rest; in some cartilages this gives the appearance of rounded clumps of darkly stained matter surrounding each cell or cell-group (chondrin balls) (fig. 138). HYALINE CARTILAGE. Hyaline cartilage occurs principally in two situations — namely (1) cover- ing the ends of the bones in the joints, wherfe it is known as articular oa/rtilage; and (2) forming the rib-cartilages, where it is known as costal 102 THE ESSENTIALS OF HISTOLOGY cartilage. It also forms the cartilages of the nose, of the external auditory meatus (but not the pinna), most of those of the larynx, and the cartilages r^'^ % ® m ^^mMi ..■3':,..:i^i:^is>^!...;«'l3S.Aki,= ^ ■■91-z. WF' ^B «L^ >Jr^ .-_),-_, "-^ , ^1 .aSG"« ™„ -t^s. ¥, i ra^ s®S)© ' •>'0f. '? Ss «J^ 3B '" l^a @5) -.1?) ^ 9 So, a s'js Fif!. l;W, — VERTTf'AT. SECTION' 1 IF AKTICULAR I'ARTILAUE (.'OVEKINi; THE LOWER END IIP THE TiTjiA, Hi'MAN. Magnified about 30 diameters. a, cells and cell-groupie tlattened conformably with the surface ; b. eell-fi-roups irrcgulaily arratijjfed ; c, cell-grroupp disponed perpendicularly to the surface ; */, layer of calcified carti'la;;e ; <■■ Iione. with one another, Ijut these are of doubtful occui-reiice in vertebrate cartilage, although they unquestionably exist in the cartilage of cephalopods. #1. 1^ Va's^ Fig. 135. — Section oi- .hunt oe yoini; r.m!i;it. Jfagiiificd ."jO diameters. Notice the capsulaKligament uniting the ends of the bones and lined by the thin synovial membrane in which there are folds projecting slightly into the*edge of the joint. I04 THE ESSENTIALS OF HISTOLOGY AKTICULAK CARTILAGR The cells of articular cartilage are generally scattered in elongated groups throughout the matrix (fig. 134). The latter la free from obvious fibres, except at the extreme edge of the cartilage, where the connective-tissue iibres from the synovial membrane extend into it ; and here also the cartilage-cells are often branched, and oflfer transitions to the branched connective-tissue corpuscles of that membrane {transitional ca/rtilage, fig. 133). In vertical section (fig. 134) the deeper cell groups (o) are seen to be arranged vertically to the surface, the more super- ficial ones (a) parallel with the surface ; whilst in an intermediate zone the groups are irregularly disposed (6). In the deepest part of the cartilage, next to the bone, there is often a deposit of cal- careous salts in the matrix (calcijied cartilage, d). SYNOVIAL MEMBRANES. Ssmovial membranes are connective-tissue structures occurring in connection with articular cartilage (fig. 135) and in certain other movable parts, e.g. where a tendon glides within a fibrous sheath, and at the so-called bursse, such -as that which lies between the skin and the patella. Their cells are for the most part branched like connective-tissue cells', but in some places they resemble cartilage-cells, and where a synovial membrane is continuous with cartilage, transitions occur between them (transitioned). The synovial membranes are often compared with serous membranes. Like the latter they bound closed cavities* moistened with fluid, but they are not connected with the lymphatic system, nor is the glairy fluid (synovia) which moistens them of the nature of lymph. Moreover, •there is either no endothelial lining, or it occurs only in patches, in place of the continuous lining which we find in serous membranes. Long villus-like projections, simple (fig. 136) or compound — the so-called 'Haversian fringes — occur in some situations ; they contain a few cells, having the character of cartilage-cells, surrounded by cartilage- matrix. The fringes, probably serve to extend the surface for the secretion of synovia. The blood-vessels of synovial membranes are numerous; they approach close to the inner surface. They are well seen in preparations from an injected limb. Fio. 136.— iViLiiUS OF SYNOVIAL MEMBKANE. (Hammar. ) SYNOVIAL MEMBRANES 105 Besides the Haversian fringes and villi there are often larger folds of the membrane containing fat. The synovial membrane of a joint is never prolonged over the opposed surfaces of the articular cartilages, but ceases near the edge of these in the transitional zone already alluded to. The blood-vessels of the membrane terminate here in capillary loops. The nerves of synovial membranes end partly in peculiar end-bulbs in the substance of the membrane, partly in a fine terminal plexus close to the inner surface. Pacinian corpuscles are also found in some places. io6 THE ESSENTIALS OF HISTOLOGY LESSON XII. V THE CONNECTIVE TISSUES (continued). 1. Make transverse and tangential sections of a, rib-cartilage (young animal) which may either be fresh or may have been preserved (formol and spirit). Stain the sections with hieniatoxylin (if fresh, after treatment with acetic acid as in Lesson XI. § 2 ; or they may be placed for an hour in '5 per cent, osmic acid), and mount in glycerine. Sketch a part of a transverse section under a low power and a cell-group from one of the tangential sections under a high power. Notice especially the arrangement of the cells, somewhat concentric nea# the surface but radial near the centre. The costal cartilages tend as age advances to become ossified ; this occurs near the middle of their thickness in some animals, but in man when ossification occurs it is the superficial layer which is first invaded, 2. Make sections of the caiiilage of the external ear (pinna), either fresh or after hardening in alcohol. Mount in dilute glycerine faintly coloured with magenta or stain with orcein and mount in damjuar. The upper end of the arytenoid cartilage of the ox or calf may also be used to display the structure of clastic cartilage. Notice the lai'gc reticulating elastic fibres in the matrix. Notice also the isolated granules of elastin, and around each cartilage-cell an area of clear ground-substance. If the picparation is from the ear of the mouse or rat there is vciy little matrix and no elastic fibres, and the cells are almost in contact (parenchymatous cartilage). .3. Mount a section of the epiglottis in the same way. Notice the closer network of much finer elastic fibres in its cartilage. 4. Cut sections of white fibro - cartilage (intervertebral disk or semilunar cartilage of knee), which has been hardened in picric acid followed by spirit, or in spirit only. Stain the sections with dilute ha^matoxylin or picrocarmine. Mount in dilute glycerine. Observe the wavy fibres in the matrix, and the cartilage-cells, sometimes branched, lying in clear areas often concentrically stjiated. iSkeUh three or four cells and the adjoining fibrous matrix. COSTAL CAETILAOE. In the rib-cartilages (fig. 137) the matrix is not always as clear as in the cartilages of the Joints, and it more often happens that fibres become developed in it. The cells are generally larger than those of articular cartilage, and collected into larger groups (fig. 138). The matrix surrounding these stains more deeply than the rest with hsematoxylin (fig. 138): often this more deeply stained part is itself separated from the rest of the matrix by a less stained area. Near the circumference, and under the perichon- drium or fibrous covering of the cartilage, the cell-groups are flattened and parallel to the surface, but in the deeper parts they have a more irregular or a radial arrangement. The cells frequently contain fat globules. The cartilages of the larynx and windpipe and of the nose resemble the costal cartilages ; they will be further noticed when the organs M-here they occur are dealt with. ■YELLOW FIBRO-CARTILAGE to7 YELLOW FIBR0-CARTILA(JE. Elastic or yellow fibro cartilage occurs in only a few situations, viz. : — the cartilage of the external ear, that of the Eustachian tube, and in the \)f \'- fi^ '^? 1 Fio. 137. — Section of me-oartilage oe dale. High power. The matrix is indistinctly fibrous. Two or three empty cell-ap'aoes are seen in the section, the cells having dropped out in the course o1 preparation. Fig. 138. ^Section oe costal cartilage. Photograph. Magnified 240 diameters. The section shows several groups of cartilage-cells. Capsule ouUines are seen around the groups and also around the individual cells. The part around the cells and c^ll-g-roups is stained more than the rest of the matrix. cartilages of the epiglottis and of Santorini in the larynx. The matrix is everywhere pervaded, except immediately around the cells and cell-groups, with well-defined branching fibres, which unite with one another to form a io8 THE ESSENTIALS OF HISTOLOGY close network (fig. 139). These fibres resist the aption of acetic acid, and are stained deeply by magenta and orcein ; they are evidently elastic fibres. In cap Pig. 139. — Section of elastic cartilaoe of ear, human. (Sobotta.) x280. c, cartilage.cells ; cap, their caiisules ; in, clear matrix around ceI!sj^ld" cell-groups ; /", elastie fibres. *) Fifi. 140. — Skotion of arytenoid cartilage of calf \t .utnition of hyaline WITH ELASTIC PORTIONS. Magnified .50 diameters. , the ox they are very large, but smaller in man, especially in the cartilage of the epiglottis They appear to be developed, as with elastic tissue else- WHITE FIBRO-CARTILAGE 109 where (see p. 97), by the deposition of granules of el'astin in the matrix (fig. 141); the granules at first lie scattered, but afterwards become joined to form fibres. WHITE FIBEO-CAETILAGE. White fibre-cartilage is found wherever great strength combined with a certain amount of rigidity is required : thus we frequently find this form of flbro-cartilage joining bones together, as in the intervertebral disks and other symphyses. But in these cases the part in contact with the bone is always hyaline cartilage, which passes gradually into the fibro-cartilage forming the "St, AJ.. / A ' hi'' ■a" iJr^L. j:.2&^iaMi^ Fk;. 141.— Sbctiun ov elastic cartilagk (upper pabt of arytenoid uf. calf) STAINED WITH MAGENTA. Photograph. Magnified '200 diameters. The elastiii is seen partly in the form of a granular deposit, partly as finer and ooarser inter- coinnmnicating fibres. These are nowhere in contact with the uartilage-cells, which are surrounded by clear cartilage-matrix. At most parts of the section the cells have dropped out, but two or three are seen still in situ, > bulk of the symphysis. White fibro-eartilage is also found lining grooves in which tendons run, and it may be found in the tendons themselves. It is employed to deepen cup-shaped articular surfaces ; and in the case of the interarticular cartilages, such as those of the knee and lower jaw, to allow greater freedom of movement whilst diminishing the liability to dislocation. Under the microscope white fibro-cartilage looks very like fibrous tissue, but its cells are cartilage-cells, not tendon-cells (flgs. I42, 143). They are rounded or bluntly angular and surrounded by a concentrically striated area of non- fibrous cartilage-matrix. In some parts of the intervertebral disk some of the cells are branched ; these may perhaps be looked upon as transitional forms to connective-tissue corpuscles. I lO THE ESSENTIALS OF HISTOLOGY DEVELOPMENT OF CARTILAGE. Cartilage is formed in the embryo from mesenchyme similar to that which gives origin to other forms of connective tissue. Each cell forms a capsule around itself, and the blended capsules compose the first matrix. r^^js^ 1 •^*^'^©;-~:%^ .•=^*^\ '^y. ijKit '.ITi' ri-'-vtr Fig. 142. — Section of \\hite fibro-cartilage. Photograph. Magnified '200 diameters, The gi'ound-Bubstaiice is pervaded by wavy connective-tissue fibres. Fig. 143. — Whitk fihro-cartilage fkom an intkkvertebkai. disk, uumak. Highly magniiied. Tile concentric lines around tlie cells indicate tlie limits of deposit of successive capsules. One of the cells has a forked process which extends beyond the Jiyaline area surrounding the cell amongst the fibres of the general matrix. Cartilage sometimes remains in this condition throughout life ; it is then termed parenchymatous cartilage. This can be seen in the mouse's ear ; where also the cartilage-cells become filled with fat. Cartilage at first grows partly by interstitial expansion (accompanied by cell multiplication and by formation, around and between the cells, of intercellular substance), partly by apposition at the perichondrium, the connective tissue becoming here transformed into cartilage. At a later period of growth the increase DEVELOPMENT OF CARTILAGE in in size and change; in shape of cartilages are due ahnost entirely to the agency of the perichondrium. Embryonic cartilage is usually characterise'd by the cells being more sharply angular and irregujar ; in some cases they are branched, like those which occur at the junction of cartilage and synovial membrane in the adult. The cells ai-e also more closely packed, the matrix being in relatively less amount than in later life. Pibro-cartilage is developed at first in exactly the same manner as hyaline cartilage, but at a certain stage connective-tissue fibres, either elastic or white, become formed in the ground substance or matrix, and as they accumulate they impart their distinctive character to the tissue. The development of the elastic fibres is preceded by the deposition of granules of elastin in the matrix : these run together to form fibres as in the development of elastic tissue elsewhere (see p, 97). In some parts where white fibro-cartilage is found the tissue is at first entirely fibrous, like tendon or ligament, and the cartilage is a secondary formation. In such cases the cartilage-cells are probably formed by direct transformation from the tendon-cells. 112 THE ESSENTIALS OF HISTOLOGY LESSON XIII. THE CONNECTIVE TISSUES (continued). 1. In thin sections of hard bone made by grinding,' observe the Haversian canals, lamelte, lacunse, canaliouli, etc. Make sketches under low and high powers. 2. With iine forceps strip off a thiu shred frofli the superficial layers of a macerated bone which has been decalcified in 5 per cent, commercial sulphurous acid and afterwards washed with water for 24 hours. The decalcified bone may be kept in dilute alcohol. Mount the shred in water. Observe the fibrous structure of the lamellae. Look for perforating fibres or the. holes from which they have been dragged out. Sketch a small piece of the thin edge of a lamella. 3. Stain succesaively with dilute magenta and heematoxylin solution, or with methyl-blue and eosin, very thin sections of compact borie which has been fixed with iO per cent, formol (1 to 3 days) and then decalcified in sulphurous acid as above. Mount in dilute glycerine, cementing at once. Look for fibres of Sharpey piercing the circumferential lamellfe. The elastic pei'f orating fibres are darkly stained with magenta; Notice the stained nviclei of the bone-corpuscles in the lacunse. In thin sections the blood-^■essels and othei" structures in the Hnver-sian canals may be made out. 4. Mount in dammai' a section of a fcctal lower jaw which has been stained in bulk and embedded in paraffin.^ Find the part where the lower jaw-bone is becoming ossified, and carefully study the appearance which it presents. The bone is prolonged in the form of osteogenic fibres which are covered with osteoblasts. 5. Intramembi'anous ossification may also be studied in the pai'ietal bone of embryos preserved in MtlUer's fluid. A piece of the growing edge is scraped or .brushed free from its investing membranes and from, most of the cells which cover and conceal it, and is mounted in glycerine with oi' without previous staining witli carmalum or haematoxylin. B. Mount in dammar sections, longitudinal and transverse, of a foetal limb which lias been stained in bulk.^ The bones will be found; in diflFerent stages of ossifica- tion, those of the wrist or ankle and digits being least developed. Make sketches illustrating the three chief stages of endochondral ossification. Notice the peculiar terminal ossification of the third phalanx. STRUCTURE OF BOXi; Bone is a connective tissue in which the ground-substance is impregnated with salts of lime, chiefly phosphate, these salts constituting about two- thirds of the weight of the bone. When bonc.s are macerated this earthy matter prevents the putrefaction of the animal matter. When bones are calcined they lose one-third of their weight, owing to the destruction of the animal matter ; when steeped in acid the earthy salts ' are dissolved and ' Such a section should be purchased : it is ditiioult.to make without a proper lathe. - See Appendix for method of staining in bulk. In place of this sections may be stained by Mallory's method, which brings out the osteogenic fibres. STRUCTURE OF BONE i'3 only the animal matter is left. This, like areolar and fibrous tissue, is converted into gelatine by boiling. Bony tissue is eitliei' comparj, or rancfUnted. Compact bone is dense. ,2^1 Fig. 144. — Skction of a DECALCiPiBn human kadius. (Sobotta.) x48. p^ periosteum ; pi, periosteal bony lamellae ; p'l\ deeply seated lamellae between the Haversian systems ; H, Haversian systems ; tr, ti\ trabeculae of spongy substance ; m?, lamellaj bounding medullary spaces. almost like ivory ; cancellated is spongy with obvious interstices. The outer layers of all bones are compact, and the inner part is generally cancellated, but the shaft of a long bone is almost entirely made up of compact substance, except in and near the middle, which is hollow and filled with marrow. The .iWi 114 THE ESSENTIALS OF HISTOLOGY interstices of cancellated bone are also occupibd by marrow. Externally bones are covered except at the joints by a vascular fibrous membrane, the periosteum. True bone is always made up of lamellce, and these again are composed of fine fibres lying in a calcified ground-substance. Between the lamell» are branched cells, the bone-corpuscles, which lie in cell-spaces or lacunas. The ramified passages containing the cell-processes and uniting the lacunae are termed canaliculi. In cancellated bone the blood-vessels run in the interstices of the bone, KiG. 145. — Photograph or transverse section or compact eone, made by GRINDING, showing THREE HaVERSI.AN CANALS WITH THEIR CONCENTRIC LAMELLJS, AND ALSO INTER-HaVERSIAN BONY SUBSTANCE. Magnified 200 diameters. a, Haversian canal, filled with air and debris ; a', a very small canal ; 6, 6, junctions of Haversian systems ; 6', margin of Haversian system abutting on non-Haversian lamellffi ; e, c, c, lamellffl parallel to periosteum ; d, inter-Haversian bone with irregular lacume. surrounded and supported by the marrow. In compact bone they are con- tained in little canals— the Haversian canals — which everywhere pervade the bone. These canals average 005 mm. (^^^ inch*) in diameter, but some are much smaller, others much largpr than this. Their general direction is longitudinal, i.e. parallel with the long axis of the bone, but thej' are constantly united by transversely and obliquely running passages. In a section across the shaft of a long bone they are seen as small rounded or elongated holes (fig. 144). When the section has been made by grinding, the holes get filled up with air and debris; the air causes them to look black by transmitted light (p. 29) ; this is also the case with the lacuna3 and canaliculi (fig 145). Most STRUCTURE OF BONE "S of the lamellae in compact bone are disposed concentrically around the Haversian canals ; they are known as Haversian lamellse, and with the included canal, form what is known as a Haversian system. The lacunee of a Haversian system communicate both with one another and with the Haversian canal which they encircle, but not as a rule with the lacunas of adjacent Haversian systems. The angular interstices between the Haversian systems are generally occupied by bony substance which is not regularly lamellar (figs. 145, 146, d). Besides the concentric lamellas of the Haversian systems there are other lamellae both at the surface, immediately under- Fig. 146. — Longitpdinal seotion of oompact bone, showing Haversian systems- op lamella;, and inter-Havbrsian bone. Magnified 200 diameters. ff, Haversian canal out longitudinally ; i, junction of two Haversian systems of lamellx ; c, margin of Haversian system abutting upon inter-Haversian Ijone with irregular lacunae, d. neath the periosteum (fig. 144, pi), and throughout the thickness of compact bone, between the Haversian systems (fig. 145, c, c, c) which are arranged parallel with the surface ; these are known as periosteal lamellw. They are pierced here and there by simple canals for blood-vessels, the so- called Volkmann's canals, which are proceeding from the periosteum to Join the system of Haversian canals, and also by calcified bundles of white fibres and by elastic fibres prolonged from the periosteum. These are the perforating fibres of Sharpey (fig. 147). The lamellae of bone are fibrous in structure. This may be seen in shreds torn ofi" from the superficial layers of a decalcified bone. The fibres {decussating fibres of Sharpey, lamellafibres) often cross one another in adjacent lamellae, and in the Haversian systems they run in some lamellse ii6 THE ESSENTIALS OF HISTOLOGY Fk;. 147. — Transverse section of decalcified iipman tibia, from near THE surface of THE SHAFT. , \i, Haversian canals, with their ayatems of concentric lamellse ; in all the rest of the figure the lamellae are periosteal ; .-.■, s, ordinary perforating fibres of Sharpey ; e, e, elastic perforat- ing fibres. Drawn under a power of about ITid diameters. 6 /J Fro. 14S. — LamhiJ/;!! torn off from a dbcaloified iu'man partrtai. p.onf. AT SOME DEPTH FROM THE SURFACE. (I, lamells, showing decusaatiiigf fibres ; 6, 6, thicker part, \vhert> several lamellm are superposed ; c, c, perforating fibres ; the fibrils which compose them are not shown in the figure. Apertures through which perforating fibres had passed are seen, especiall.v in the lower part, a, of the figure. Magnitude as .^een under a power of 200 diameters, but not drawn to scale. (Sketched by Allen Thomson from a preparation by W. Sharpey.) STRUCTURE OF BONE 117 concentrically, in others parallel with the Haversian canal. In shreds of lamellje which have been peeled from the surface the perforating fibres may sometimes be seen projecting from the surface of the shred, having Ijeen torn out of the deeper lamellae (fig. 148, c, c). When tendons or ligaments are inserted into bone, their bundles of white fibres are prolonged into the bone as perforating fibres. The lacunae are occupied by nucleated corpuscles, which send branches along the canaliculi (fig. 149). They have a special lining layer different in chemical composition from the rest of the bone, being much more resistant to the action of strong chemical solvents such as hydrochloric acid (Neumann). The dentinal tubules of the teeth have a similar lining. Each Haversian canal contains one or two blood-capillaries and nervous Fig. 149. — A eoUk-cell isolatmd AMD HIGHLY MAGNiriBD. (Joseph. ) a, proper wall of the lacuna (Neumann's layer), where the corpuscle has shrunken awa.v from it. Fig. 150. —Section or a Haversian- CANAL, showing ITS CONTENTS. Highly magnified. II, small arterial capillary vessel ; u, large venous capillary ; n, pale nerve-fibres cut across ; ly cleft-like lymphatic vessel ; one of the cells forming its wkll communicates by fine branches with the branches of a bone-corpuscle. The substance in which the vessels run is connec- tive tissue with ramified cells ;' its finely granular appearance is probably due to the cross-section of fibrils. The canal is surrounded by ooncentri&lamellre. filaments, besides a little connective tissue ; the larger ones may include a few marrow-cells. There are also cleft-like lymphatics running with the blood-vessels, their cells being connected through canaliculi with branches from corpuscles within the neighbouring lacunae of the osseous substance (fig. 150). The periosteum may be studied either in torn-ofif shreds, or in preparations treated in situ with silver nitrate, or in stained sections from an unmacer- ated bone which has been decalcified. It is a fibrous membrane composed of two layers, the inner of which contains many elastic fibres. In the outer layer numerous blood-vessels ramify and send branches to the Haversian canals of the bone. The periosteum ministers to the nutrition of the bone, partly on account of the blood-vessels and lymphatics it contains, partly, especially ii8 THE ESSENTIALS OF HISTOLOGY in young animals, on account of the existence between it and the bone of a layer of osteoblasts or bone-forming cells, a remainder of those which originally produced the bone. It also serves to give attachment to muscular fibres. The marrow of bone has been already studied (pp. 45 to 47). •■'•MA Fig. 151. — Section of phalangeal bone of humak fcetus at the time of com- mencing OSSIFICATION. (From a preparation by F. A. Dixej.) The prepara- tion was stained in bulk with magenta. The drawing is made from a photograph, and is magnified about 75 diameters. The cartilaBe-cells in the centre are enlarged and are separated from one another by stained calcified matrix ; im, layer of bone deposited underneath* the periosteum ; o, layer of osteo- blasts by which the layer baa been formed. Some of the osteoblasts are already embedded in the new bone as bone-cells within laounse. The cartilaffe-cells are flattened and arranged in rows above and below the calcified centre. At the ends of the cartilage the cells are small and the groups are irregularly arranged ; the fibrous periosteum is not sharply marked off from the cartilage. DEVELOPMENT OF BONE. True bone is formed in all cases by ossification of connective tissue. Sometimes the bone is preceded by cartilage, which first becomes calcified, and is then invaded, and for the most part removed, by an embryonic connective tissue which re^deposits bony matter in the interior of the DEVELOPMENT OF BONE 119 cartilage. This is cartilaginous or endochondral ossification. At the same time layers of bone are being formed outside the cartilage by the periosteum {periosteal ossification). The whole bone thus formed is termed a cartilage- bone. Sometimes bone is not preceded by ca'rtilage, and then the only process which occurs is one corresponding to the periosteal ossification of the EiG. 152. — Section of part of ONE OF THE LIMB-BONES OF A FCETAL CAT, AT A MORE ADVANCED STAGE OF OSSIFI- CATION THAN THE BONE RE- PRESENTED IN FIG. 151, AND MORE HIGHLY MAGNIFIED. Drawn from a photograph. The calcification, of the cartilage- matrix has advanced from the centre, and is extending between the groupa of cartilage -cells, which are arranged in charaoterietic rows. The. subperiosteal bony deposit (im) has extended pari passu with the calcification of the cartilage - matrix. The cartilage- cells in the calcified part are mostly shrunken and stellate ; in some cases they have dropped out of the spaces. At ir and in two other places an irruption of the subperiosteal tissue, composed of ramified ■ cells with osteoblasts and growing blood-vessels, has penetrated the subperiosteal bony crust, and has begun to exca- vate marrow spaces ; p, fibrous layer of the periosteum ; o> layer of osteoblasts ; some of them are embedded in the osseous layer as bone - corpuscles in laQuns. The blood-vessels are occupied by blood- corpuscles. Beyond the line of ossific advance the periosteum m&y he noticed to be incurved. This incurvation is gradually moved on, the cartilage expanding beyond it until the head of the bone is reached, when it forms the perio- steal notch or groove represented in figs. 155 and 159. cartilage-bone ; the ossification is then known as membranous^ and the bone formed is a membrane-hone. Ossification in cartilage. — This may be described as occurring in three In the first stage the cells in the middle of the cartilage become enlarged and arranged in rows radiating from the centre* (fig. 151), and fine granules of calcareous matter are deposited here in the matrix. Simultaneously with this the osteoblasts underneath the periosteum deposit layers of fibrous material upon the surface of the cartilage, and this material also becomes I20 THE ESSENTIALS OF HISTOLOGY calcified (fig. 151, im). As the layers are formed, some of the osteoblasts (o) are included between them and become bone- corpuscles. Tn the second stage the vascular subperiosteal tissue eats its way through the newly formed layer of bone and into the centre of the calcified cartilage (fig. 152, ir). This is freely absorbed before^ it (figs. 153, 154), so that large spaces are produced which are occupied by embryonic connective tissue of a jelly-like character (fig. 158) including numerous osteoblasts and many i.^, ...u^ _, Cr»i J «ST•, I" Fk;. IftO.— Section of thio OSSIFICATION GROOVE IN THK HEAD OF A LONG BONE. c, cartilag-e^; p, periosteal tis.-iue witli osteogenic fibres and osteoblasts. This tissue occupies the "^^roove." / ^. ^^ '- "r . \ kl'^'/V'V'kX^'"?'" 'IV I* { t ^'i^i c V y J Fig. IfiO. — Section iiikouuh uppjiI^ end of tii.ia of a IIALF-uKu\^^ i.aldit. (A. Bidder.) Drawn und&r a magnifying power of 30 diameters. aj apophysis ; e, epiphysis ; d, diaphysis ; I, lig;amentum patellae ; c, cartilage of articular surface ; d, intermediate cartilage ; p, periosteum, with periosteal bone ; m, pad of synovial membrane. 126 THE ESSENTIALS OF HISTOLOGY VI V/ Fig. Ifil. — Past of the gro\vin(! edge of the developing parietal bone OE A FfETAL OAT, l\ INCH IjbNG. ftp, bone spicules, with some of the osteoblasts embedded in them, producing the lacunae ; of, osteo- genic fibres prolongring the spicules, with osteoblasts lout) between them and applied to them ; a, granular calcific deposit occurring in the ground-substance between the fibres ; c, calcareous deposit joining two adjacent spicules. ^oV.' cp ..--c'^^vv*"^-! -tw ' .-1' ;■ >A. T> i-i ^* i \ ^T^ i- 5^ Fig. lli'2.-.SJi;cTiu2i ui' ussiitvinu aiaxillakv iioiiii of iiuw-BORN rat (v. KorfiF.) 0, 0, osteoblasts ; b, bony substance with osteoblasts and osteogenic fibres ; b', growing border of ■ bone ; c, embryonic connective tissue, showing its fibres continuous with the osteogenic fibres ot the growing bprdcr. DEVELOPMENT OF BONE 127 fragments of bone may undergo regeneration even after removal of the periosteum, by the agency of osteoblasts in the marrow. Membranous ossification. — In this variety' of ossification (figs. 161, 162) the bone is not preceded by cartilage at all, and therefore no endo- chondral bone is formed, but the calcification occurs in an embryonic connective tissue which contains numerous osteoblasts and blood-vessels. The fibres of this tissue (osteogenic fibres) are collected into fine bundles, and become enclosed in a calcareous matrix, produced by the deposition of lime salts in the ground-substance of the connective tissue ; as the fibres grow, the calcification extends further and further, so that bony spicules are formed, which become thickened and run t'ogether to -form reticulated layers, leaving spaces filled with jelly-like connective tissue containing osteoblasts surrounding the blood-vessels. The osteogenic fibres are covered with osteoblasts, and as the bone forms,- some of these become left as bone-corpuscles - within lacunse. Thus in every particular the development of these bones resembles that of the subperiosteal layer of endochondral bone ; which is, therefore, also to be considered as an instance of mem- branous ossification, taking place on the surface of cartilage. Moreover, it is the same subperiosteal tissue which, in endochondral ossification, invades the calcified cartilage and after causing the absorption of marrow spaces within this, deposits true or secondary bone upon those parts of the calcified cartilage-matrix which have escaped absorption ; this muat also, therefore, be reckoned as developed according to the same .type. In fact, even in cartilaginous ossification, very little of the calcified cartilage- matrix eventually remains, for this is almost wholly absorbed ; being either replaced by true fibrous bone which has been formed by osteoblasts, or swept away to form the marrow cavity and other spaces in the bone. 128 THE ESSENTIALS OF HISTOLOGY LESSON XIV. STRUCTURE OF MUSCLE. 1 . Take a shred of muscle from a recently killed mammal, and on a dry slide carefully separate long pieces of muscle (single fibres if possible) and stretch them out, keeping them moist during the process by breathing on the slide. A drop of serum or mammalian Kinger's solution must be ready on the cover-glass, which is then (juickly inverted over the preparation. Study first with a low, then with a high power. Sketch all the appearances seen in a small piece of a fibre, focussing carefully the most superficial layers. Notice the oval nuclei immediately under the sarcolennua. Then allow a, little dilute acetic acid to I'un under tlie covei- glass and watch its effect. The acid may be followed by weak solution of magenta or by dilute hsematoxylin, and the preparation mounted in glycei'ine by adding a small drop of this at one edge of the cover-glass. i. Prepai'e frog's muscle in the same way, mounting in frog-Ringer. Notice the muscular substance shrinking away here and there from the sarcolemma, which then becomes distinctly visible. Sketch a piece of sarcolemma bridging across an interAal thus produced. The pi'eparation oan be stained with magenta and mounted in glycerine like the last. 3. Study stained longitudinal and transverse sections of muscle which has been hardened in alcohol or formol, mounting in dammar. Examine the sections first with a low and then with a high power. Sketch the appearances which are seen. Measure the diameter of some of the fibres. Sections of muscle-spindles may be searched for in the sections of muscle. 4. Place in 1 per cent, osmic acid a small shred of muscular ti.ssuo (mammal or crab)" which has been stretched upon a cork. Aft'er 24 hours, when it will be deeply stained, wash it in watei' and with needles break the filues up in glycerine as finely as possible. Cover and examine with a high power. f). Cut ott' the head of a garden beetle or wasp or water beetle, and bisect tlie trunk with scissors so as to expose the interior. Notice two kinds of muscular tissue, the one belonging to the legs greyish in colour, the other uttachetl to the wings yellowish. Preparations of both kinds of muscle are to be made in the same way as living mammalian muscle (§ 1). Mount them in a drop of white of egg. In both preparations the dark-looking air-tubes or tracheas form prominent objects ramifying amongst the fibres. Observe the structure of the two kinds of muscle so far as it can be made out in the fresh preparation. If the preparation is made quickly, waves of contraction may be observed passing along the fibres. 6. Make another preparation of the leg-muscles, mounting in dilute acetic acid. Alcohol-hardened muscle of insect or crab may be used for this purpose. Notice that the muscular substance swells and becomes clearer, whilst the sarcoplasm- network, with its appearance of lines and dots, comes more distinctly into view, 1 n a well-teased preparation made in acid, the fibres are frequently found breaking across into disks. Make careful drawings from this preparation. 7. Rollett's method. Cut off the head of an insect (wasp, small liectlo), bisect tlie trunk and place in 90 per cent, alcohol for 24 hours or longer. Then take a .Mniall piece ot each kind of rau.^clo, and place in strong glycerine overnight. Wash thoroughly witli water and ti'ansfer to 1 ]}cr cent, chloride of gold sohition : lea\e the pieces of muscle in this from 15 to ."JO minutes accoi-ding to size. l'''roih tlie gold solution they are transferred to formic acid (1 pai't of the sti'ong acid to .3 of water), and ke]it \\\ the dark for ^4 houi-s ; but they nuvy be kept longer without disadvantage. The nniscle is tlum teased in glycerine, Some STRUCTURE OF MUSCLE 129 of the fibres will be found after this process to have their sarooplasm darkly stained, and to show the appearance of a network both in longitudinal and transverse view : others, on the other hand, have the saroous elements of the fibrils or sarcostyles stained, whilst the sai'coplasm'has remained colourless. This preparation shows the sti'ucture of the fibi'ils of the wing-muscles far better than any other. 8. The structure of the fibrils can also be utudied in sections of wincr-muscles Fig. 163. Fig. 164. Fig. 165. Fig. 163. — Sabcolbmma of mammalian muscle, highly magnified. The fibre is represented afc a place where bhe muscular substance has become ruptured and has shrunk away, leaving the sarcolemma (with a nucleus adhering to it) clear. The fibre has been treated with serum acidulated with acetic acid. Fig. 164. — Muscular fibke of a mammal examined fkesh in serum, highly magnified, the sukface of the fibre being accurately focussed. The nuclei are seen on the fiat at the sufF?.cc of the fibre, and in profile towai-ds the edge. Fig. 165. — Portion of a medium-sized human muscular fibre, showing the intermediate line {Doeie's line) mentioned in the text. (Sharpey.) fixed with alcohol and stained by the iron-hsematoxylin method (see Appendix). This is more certain but does not give as good i*esults as a successful Eollett preparation. CKOSS-STKIATED OK VOLUNTARY MUSCLE. Voluntary muscle is composed of long cylindrical fibres, measuring on an average 05 mm. in diameter (j-^^ inch) in mammalian muscles, and often having a length of an inch or more. Many fibres are, however, much larger or smaller than the average. Each fibre has an extensible sheath, the sarcolemma, which encloses the contractile substance. The sarcolemma is seldom visible, unless the contained substance becomes broken (fig. 163t. A fibrillar structure has been described in the sarcolemma, but under ordinary circumstances it looks completely homogeneous. 130 THE ESSENTIALS OF HISTOLOGY The contractile substance is characterised by the alternHte dark and light stripes which run across the length of the fibre ; hence the name cross-striated muscle. On focussing, it can be seen that the stripes pass through the whole thickness of the fibre ; they may therefore be looked upon as representing alternate disks of dark and light substance. If the fibre is very carefully focussod, rows of apparent granule's are seen lying in or at the boundaries of the light streaks, and very fine longitudinal lines may, with a good microscope, be detected uniting the apparent granules. These fine lines, with their enlargements, the granules, are more conspicuous in the muscles of arthropods (fig. 169). They indicate divisions between the ."3 if, */. aiii .*m" Si ,/h m «■/ '■'^ ItJS. Fk;. lB(i. Fi.:. 11)7. Via. 166.-^8mall portion of a human musculak fibre tkased into small LONOiTDDiNAL FRAGMENTS. (Sharpey. ) Magnified about 8(J0 dianieteus. a, b, c, larger and smallei- gi'oupa of fibrils ; ti, ultimate fibrils. FKi. 167. — Small roivnoN of a muscle-fibre of craf, splittin<; ri> into piBBiLS. From a photograph. Magnified tiOO diameters. Fig. 168. — Suction dF a muscular fibre, SHOiviNO areas of Counhf.im. Three nuclei are seen lying close to tlie sarcolemma. longitudinal elements {fibrils or sarcostyhs) wJiich compose the fibre, and in preparations treated with dilute acid the lines appear to form part of a fine network, which pervades the muscle-substance, and serves to unite the granules both transversely and longitudinally (fig. 170). This network, which is sometimes very distinct in preparations of muscle treated with chloride of gold, is, however, a network in appearance only : in reality it is the optical expression of the interstitial substance which lies between the fibrils. This substance is termed sarcoplasm. The transverse section of a muscle shows the fibres to be nearly cylindrical in figure. Between the fibres is a certain amount of areolar tissue, which serves to support the blood-vessels and to unite the fibres into fasciculi ; the fasciculi are again united together by a larger amount of this intra-muscular connective tissue (endomysium). CROSS-STRIATED MUSCLE 131 On examining the transverse section of a fibre with a high power, it is seen to be subdivided everywhere into small angular fields, Cohnheim's areas (fig. 168), which are themselves finely dotted. The dots represent sections of the fibrils of which the fibres are composed, and into which they may be split after death (figs. 166, 167), especially after being hardened in certain reagents, e.g. cliromic acid or osmic acid. The areas represent groups of fibrils, and are usually polyhedral, but they may be elongated ; sometimes they are disposed radially, and occasionally concentrically with the circumference of the section. The interstitial substance or sarooplasm lies between the fibrils and can be made visible by treatment with dilute acid or by staining with chloride of gold (figs. 170, 171, 172). It is sometimes in relatively large amount, but in most muscular fibres is reduced to a very fine interstitium. An ill-defined clear line is sometimes seen running transversely across the fibre in the middle of each dark band. This' is termed Hensen's line. If instead of focussing the surface of the fibre it is observed in its depth, an appearance diiTerent from that shown in fig. 164 is frequently visible, namely, a fine dotted line {Dohie's line), bisecting each clear stripe (fig. 165). This appearance is often considered to represent a membrane {Krause's membrane), which subdivides the fibrils at regular intervals (see p. 133). But the membranes of the individual fibrils or s^fcostyles are rarely, if ever, visible in an intact mammalian fibre, and it is certain that the appearance known as Dobie's line in the middle of the clear stripe of the intact fibre is due to interference, caused by the light being transmitted between disks of different refrangibility. Haycraft has suggested that the cross-striation of voluntaiy muscle is due to refractive effects produced by a varicosity of the component fibrils ; he bases his view upon the fact that in impressions of the fibres made on soft collodion all the cross-striations which aie observed iu the fibre itself are reproduced. There is no doubt that a well-marked cross-striated appearance can be produced in homogeneous fibrils by regularly-occurring varicosities, and some of the appearances observed in muscle may, as Haycraft contends, be referred to this cause. But even when a fibre or fibril is stretched so that it exhibits no varicosities, the cross-striations are still perfectly distinct. Moreover, in view of the entirely difierent manner in which the substances of the dark and clear stripes behave to many staining reagents, and especially to chloride of gold when applied as directed in § 7, the fact being that very definite structural appearances can under these circumstances be made out, the homogeneity of the muscle-fibril cannot be admitted. This inference is strongly confirmed by the microchemical work of A. B. Macallum, who has shown that the potassium salts of the wing-muscle fibrils are accumulated in a portion only (the sarcous elements) of thefibril (fig. 177). Nuclei. — Besides sarcolemma and striated substance, a muscular fibre possesses a number of oval nuclei which have the usual structure of cell- nuclei ; their chromatin often has a spiral arrangement. Sometimes there is a little granular substance (protoplasm) at each pole of the nucleus ; each nucleus with the adjacent protoplasm has then been spoken of as a muscle- corpuscle. But the protoplasm which is adjacent to the nuclei is continuous with the sarcoplasm between the fibrils; both being the remains of the original undifferentiated protoplasm of the cells from which the muscular 13: THE ESSENTIALS OF HISTOLOGY fibres are developed. In mammalian muscle the nuclei usually lie immedi- ately under the sarcolemma (figs. 163, 164, 168), in frog's muscle they are Fig. 169. — LiviNd muscle of wateh-heetle (Dytisous marginaIjIs). Highly magnified. a, dim stripe ; 6» bright stripe ; c, line lines, with dot- like enlarffements upon them which represent the interfibrillar sareoplasm. Fig. 170. — Portion of leg-muscle of insect treated with dilute ACID. .S', saruoleinina ; i), dot-like enlargement of sarcoplasm ; K, Krause's membrane. The sarcous elements are dissolved or at least rendered invisible by the acid. Fig. 171. Fig. 172. Fig. 171. — TR.A.NSVERSB section of LEG-MUSCLJS fibre of an INSECT, STAINED WITH GOLD CHLORIDE. The sarcoplasm is here stained, and appears in the form of a network, in the meshes of which lie the sections of the fibrils. Notice the mottled appearance of the sections of the sarcostyles or fibrils, indicating a porous structure, as in the wing fibrils (see fig. 176). The central protoplasm (with a nvicleue) is also evident. (From a photograph.) Fig. 172. — Leg-muscle fihre of insect treated wjth dilute acid, showing A tendency to break across into disks. The sarcoplasm is in the form of fine lines. The ordinary dark stripes of the fibre have disappeared in the acid. A, a disk, seen partly in section and exhibiting the reticular arrangement of the sarcoplasm ; -B, longitudinal view of fibre. scattered throughout the thickness of the fibre, in the leg-muscles of insects they lie in the middle of the fibre (fig. 171). Some animals, c.//. the rabbit, have, besides muscles of the ordinary trpe of structure, which in this animal are pale in colour, others of a deep red colour. CROSS-STRTATED MUSCLE 133 These red muscles were found by Eanviei' to exhibit certain differences both in structure and function. One difference of structure is that the nuclei, which are numerous, are not, as in the ordinary type of niaaimalian fibre, confined to the surface, but are scattered throughout the thickness of the fibre. The fibres in question also contain more sarcoplasm than the ordinary fibres, and their blood- vessels have a peculiarity of structure which will be afterwards noticed. It has further been shown that in many other mammals,, amongst the ordinary fibres, are some in which the nuclei are distributed throvigh the thickness of the fibres : this is also the case, as we have seen, with all the muscular fibres of the frog. In muscles which are in constant activity, such as the diaphragm, and the dorsal fin-muscles of Hippocampus, the protoplasm (sarcoplasm) of the fibre is present in relatively large proportion ; this is also found to some extent in the wing-nuiscles of insects (see below). Muscles of insects. — In the muscles of insects the stripes are relatively broad, and the structure can be more " readily made out than in mammals. In the living fibres from the muscles which move ^ ..m...^^. .„„„ the legs, tjie sarcoplasm presents a strik- T^ i'-^ K ing appearance of fine longitudinal lines ■B«Bps^'w"W'y''^^«^f >[ 7 pith ,§ e traversing the muscle, and enlarging within the light stripes into rows of dots (figs. 169, 179). This is still better seen in fibres and portions of fibres which have been treated with dilute acid (figs. 170, 172). In sepa- rated disks, produced by the breaking across of muscle-fibres, the surfaces of the disks show a network: with polyhedral fci . u u.l»..i; meshes in sorne insects (fig. 172, A); formed of lines radiating from the centre Fi«. 173.— Leg-mhscle fibre of t i-V. flK ■ fVi INSECT, STAINED WITH GOLD ot tne nbre in ottiers. chloride by Roi.lett's method. The muscular fibres of the wings are k, line formed by membranes of .-,111 ,1 ii i! j.T_ Krause ; S.E., dark stripe formed considerably larger than those ot the by saroous elements. The sarcoplasm legs and contain a far greater amount H^e s^ithXr™' "' '°"^''"<""=" of sarcoplasm, in 'which the fibrils are embedded. When the fibre is broken up the fibrils are easily isolated, even in the fresh tissue, and they can then be readily studied. It can be seen even in the fresh fibril, but much more distinctly after staining, that each fibril — or sarcostyle, as it is often termed — is composed of alternate dark and light portions, which by juxtaposition in adjacent fibrils produce tlie cross-striated appearance of the fibre. Further, in the middle of each of the clear striae is a transverse septum, known as the membrane of Kraii,se ; the fibril is subdivided at regular intervals by these membranes into serial portions, termed sarcom.eres. Each sarcomere is occupied by a saroous element ; the sarcous elements by their juxtaposition in adjacent fibrils form the dark strise of the whole fibre. The sarcous element is really double, and in the stretched fibril separates into two at the line of Hensen (fig. 174, B). At each end of the sarcous element is clear substance (probably 134 THE ESSENTIALS OF HISTOLOGY fluid) separating it from the membrane of Krause : this clear substance is more evident the more the iibril is extended, but diminishes, even to complete disappearance, in the retracted (contracted) fibril (fig. 174, A). The cause of this change is explained if we study more minutely the structure of the sarcous element. For we find that each sarcous element is pervaded by longitudinal canals or pores, which are open in the direction of Kranse's Fig. 174. — Fibrils of the wing-muscles of a wasp, prepared by Kollett's METHOD. Highly magnified. A, a contracted flbvil. B, a contracted fibril, which has been forcibly stretched, causing each sarcous element to be separated into two parts at the line of Hensen. C, an uncontractea fibril, showing the porous structure of the sarcous elements. ^, an uncontracted fibril, ina^lified 2000 diameters. A, B, and were drawn by Mr R. Muir from the pre|.)aration with the taid of photographs ; i) is an untouched photograph. membranes, but closed at the middle of the sarcous element (figs. 174, C, D ; 175, 176). In the contracted muscle it can be seen that the clear part of the muscle-substance has nearly disappeared, the sarcous element is swollen and the sarcomere is shortened ; in the uncontracted muscle, on the other hand, the clear part occupies a considerable interval between the sarcous element and the membrane of Krause, the sarcbmere being lengthened and narrowed. This difference is well seen with certain methods of staining (fig. 174). The sarcous element does not lie free in the middle of the sarcomere, but is attached at either end to Krause's membrane by what look CROSS-STRIATED MUSCLE 13s like very fine lines, which may represent septa, running through the clear substance (fig. 176); on the other hand, Krause's membrane appears to be attached laterally to a fine membrane which limits the fibril externally. As already stated, the sarcous elements are set side by side in planes forming the dark stripes (sometimes called principal disks) of the striated- substance of ordinary muscle fibres. In the wing-muscles of insects, the fibrils are surrounded by a considerable amount ©f granular sarcoplasm, and the whole fibre is only very indistinctly cross striated, although each ---JL^__,. Fig. 175. — Isolated sakoous EI,EMKNTS OF A WING-MUSGliE, SHOWING THE TUBULAR OR POROUS STRUCTURE. Un- touched photograph. Mag- nified 870 diameters. At ft some are seen in profile ; at h on the flat. The two eircular bodies are fat-drops. S.E.- Fig. 17fi. — Diagram of a sarcomere in a MODERATELY EXTENDED CONDITION, A, AND IN A CONTRACTED CONDITION, B. K, K, membranes of Krause ; //, line or plane of Hansen ; S.-fc'., j^oriferous sarcous element. Fig. 177.*^Localisation of potassium in sarcous ele- ments of winu-musole of BEETLE. (A. B. Maoallum, ) a, resting ; &, contracted. individual fibril is markedly so. As already mentioned, the sarcous elements contain a large proportion of potassium salts (fig. 177). Sometimes in the ordinary (leg) muscles of arthropods what look like detached dot-like portions of the sarcous element are seen within the clear stripes, lying usually near Krause's membrane. The rows of such dots have been termed 'accessory disks. JVIoat muscles show no accessory disks, but the sarooplasm-enlarge- ments between the fibrils (lig. 170, D) are often mistaken for them. Muscles in polarised light. — When muscle-fibres are examined with polarised light between crossed nicols, the sarcous elements (which form the dark stripe) are seen to be doubly refracting (anisotropous), while the clear substance (forming the light stripe) is singly refracting (isotropous). In contracted parts of the muscle the (anisotropous) sarcous elements are seen to have increased in bulk, while the isotropous substance of the clear stripe has correspondingly diminished (fig. 178). lilerkel imagined that there is a reversal of the stftpes during contraction, i.e. a transference of the anisotropous substance of the dai-k stripe from Hensen's line to Krause's membrane, the place of the dark stripes thus becoming occupied by clear 136 THE ESSENTIALS OF HISTOLOGY material, that of tlie light stripes by dark. He further described this condition as being preceded by an intermediate stage in which the fibril shows homogeneity of shading. No doubt in the ordinary muscle-fibres of arthropods, when we observe the so-called "fixed " waves of contraction (fig. 17fi), there is often an apparent blurring of the cross-striation of the fibre just where the muscle is passing from extension to contraction, but this is explicable by the unequal pull of the contracted parts of the fibrils upon those which are not yet contracted. The contraction in each fibre starts from the nerve-ending, which is at one side of the fibre, and spreads first across the fibre and then tends to pass as a wave towards either end. The one side always has a start in the progress df this wave, and the fibrils must thus receive an unequal pull, so that they are shifted along one another and w Fig. 178. — Leg-muscle fibee of Chkysombla f^RULEA with (fixed) con- traction WAVE rllOTOGRAPHKT) UNDER POLARISING MICROSCOPK.' A. with uncrossed niool.'? ; B. ^^^th crossed nicols. the line of cross-striping is broken up. That no transference of anisotropous substance really occurs is at once clear from the appearance of the contracting fibre under polarised light (fig. 178, B), and the study of the isolated fibrils of wing-muscle gives no support to the theory of reversal, although it is widely held by German authors. That the apparent reversal is not real is also illustrated by fig. 179, which represents a leg -muscle fibre of an insect in process of contraction. The dark bands of the contraction -wave are seen to be really due to accumulations of sareoplasm. Owing to thi.s having a higher index of refraction than the rest of the muscle-substance these accumulations appear as dark lines which not only obscure the continuity of the fibrils, but by contrast cause the whole of the sarcomeres between them to appear light. Mechanism of contraction. — Comparing the stinicture of the sarcomere with certain kinds of protoplasm we find Doth diflerentiated to form a framework ■ I am indebted to the late Professor Engelraann for these two photographs. CROSS-STRFATED MUSCLE 137 (spongioplasm, substance of sarcous element) which encloses in its meshes or pores a cleai- fluid material (hyalojilasm, cleai' substance of sarcomere). In both the clear material or hyaloplasm, when the tissue is subjected to stimulation, passes into the pores of the porous matter or spongioplasm (contraction), whilst in the absence of such stimulation it tends to pass out from the spongioplasm (formation of pseudopodia, I'esting condition of muscle). The effect of stimulation appears in g^'T!"ImmMttt"i /i'll|lll(MWM"WI»*""'""' A Fio. 179. — Wave of contrac- tion PASSING over a LKfi- MtrSCLE FIBRE OF DYTISCUS. Highly magnified. both structures to be the pioduction of a change in surface tension (perhaps between the hyaloplasm and spongioplasm) which produces a movement of fluid. This change is demonstrably accompanied in muscle by a, difference in electric potential : probably such an electric change occurs in all protoplasm. The move- ments of cell-protoplasm and those of muscle are therefore in all likelihood brought about by similar means, although at first sight the structure of muscle is very dissimilar from that of protoplasm. As we have already noticed, the movements of cilia are also capable of being explained by assuming variations of surface tension in the protoplasm of the cells to which they-3,re attached. 138 THE ESSENTIALS OF HISTOLOGY LESSON XV. STRUCTURE OF MUSCLE (continued). 1. To study the connexion of muscle with tendon, a. frog is killed by destruction of the biain and spinal cord, and placed in about a litre of water raised to a temperature of 55° C. It is left in this for 15 minutes, the water gradually cooling. It is then easy to dissociate the muscular fibres in large numbers. To obsei've their attachment to the tendon-bundles a fine longitudinal' shred must be snipped off with scissors at the tendinous attachment, and dissociated upon a slide in a drop of Ringer. It will usually be found that the muscular substance is retracted from the end of the sarcolemma tube, which is firmly cemented to the tendon- bundle. The structure may be brought more distinctly into view by adding to the dissociated fibres a drop of a weak solution of iodine in salt solution or in . serum (iodised serum).' 2. The blood-vessels of muscle. These are studied in longitudinal and trans- verse sections or in flattened-out pieces of injected j^iuscle. It will be noticed that the capillaries are very numerous, and form a network with oblong meshes. In the red muscles of the rabbit, sinall dilatations are seen on the transverse vessels of the network. 3. The muscular tissue of the heart is studied in sections of that organ (see Lesson XXVII.) and also in teased preparations. To prepare the latter, place a small piece of heart-muscle in ."?.■? per cent, alcohol for a few days ; stain in picro- carmine or borax-carmine solution for some days ; tea.se in dilute glycerine. 4. Tear off a small shred of the circular muscular coat of a piece of dog's or cat's intestine which has been for 48 hours or more in 1 in 2000 chromic acid or in 33 per cent, alcohol. Hold the shred with forceps in a drop of water on the slide and fray it out with a needle. In this process many cells will be set free and can be seen with a low power. Remove the rest of the shred. The preparation may then be covered and examined with a high power. Sketch one of the cell.'i. Then allow a small drop of dilute nasmatoxylin solution to diffuse under the cover glass.; to be followed by a small drop of dilute glycerine. Sketch a cell after staining. Measui'C two or three cells and their nuclei. Sections of involuntary muscle will be seen and studied along with the \ iscera which possess muscular coats. CONNEXION WITH TENDON : BLOOD-VESSELS : DEVELOPMENT OF CROSS-STRIATED MUSCLE. Ending of muscle in tendon. — A small tendon-bundle passes to each muscular fibre and becomes firmly united with the sarcolemma which extends over the end of the fibre (fig. 180). Besides this attachment, a further connexion is established by the fact that the areolar tissue between the tendon-bundles is continuous with that which lies between the muscle- fibres. There is no actual continuity between contractile substance and tendon. ' This method is the one given by 'R&nvier (T mil !■ Techniqm). The musoleendings may also sometimes be well seen at the extremities of the tendons which are removed from the mouse's tail in the manner described in Lesson X. STRUCTURE OF MUSCLE 139 Blood-vessels of muscle. — The capillaries of muscular tissue are very numerous. They run, for the most part, longitudinally, with transverse branches, so as to form long oblong meshes (fig. 181). No blo6d-vessels ever penetrate the sarcolemma. In the red muscles of the rabbit, the transverse capillaries have small dilatations upon them (fig. 182). Associated with this and other peculiarities of structure (see p. 133), it is found that the red FiK. 180. — Teemin4,tion of a mus- cular pibke in tendon. (Ranvier.) m, aarcolemma ; s, the same membrane passing over the end of the fibre ; ^, extremity of muscular substance, c, retracted from the lower end of the sarcolemma-tube ; t, a tendon-bundle passing to be fixed to the sarcolemma. i- '.— _*- ■li-: Fir. 181. — Capillary vessels QF muscle : HCTMAN. muscles have a much slower rate of contractiori, and a much longer period of latency than the ordinary muscles. Lymph-vessels, although present in the connective-tissue sheath (peri- mysium) of a muscle, do not penetrate between the component fibres. The motor nerves of voluntary muscles pierce the sarcolemma and terniinate in ramified expansions known as endijolates or motor end-organs ; the sensory nerves end in groups of specially modified muscle-fibres known as muscle-spindles (see Lesson XIX.). Development. — Voluntary muscular fibres ai-e developed from embryonic cells of the mesoderm (muscle-plate cells), which become elongated, and their nuclei multiplied, so as to produce long slender, multi-nucleated I40 THE ESSENTIALS OF HISTOLOGY fusiform or cylindrical embryonic fibres. It is not quite certain whether, as has usually been supposed, the whole fibre is formed of a single enlarged cell, or whether it m.ay be produced by the joining together, end to end, of a number of cells of the muscle plate (or of more than one muscle-plate), so as to produce a syncytium, within -which the striated fibrils make their appearance. The cross-striations appear at first along one side of the em- bryonic fibre, the change gradually extending around the circumference and also penetrating towards the centre ; but the protoplasm both at the middle of the fibre, to which the nuclei are at first confined, and at the side opposite to that at which the differentiation began, remains for some time unaltered Fig. 182. — VASCtTLAR NKTWORK OF A RED MtrSCLK (SEMITENDINOStTS) OF THF. RABBIT. (Ranvier. ) ((, arteriole ; c, v, venules ; n, dilatation on transA'erse branch of capillaries. in character (fig. 183). Eventually the change in structure extends to these parts also, and the nuclei pass gradually to ocfiupy their ordinary position under the sarcolemma, which has by this time become formed. The sarco- lemma is believed to be produced, not by the muscle-fibre itself, but by the mesenchyme or connective-tissue cells between the fibres, but the question of its origin is not definitely settled. CARDIAC MUSCLE. The muscular substance of the heart is composed of transversely striated muscular fibres, which differ from those of voluntary muscle in the following particulars, viz.: — their striations are less distinct; they have no sarcolemma, although there is a thin superficial layer of non-fibrillated substance ; they branch and unite by their branches and also at the side with neighbouring CARDIAC MUSCLE 141 fibres, and their nuclei lie in the substance and often near the centre of the fibres. In man and many mammals the fibres are marked off by transverse septa into a series of short cylindrical cell-like portions (figs. 184, 185, 186) joined together end to end and side to side, each corresponding to one of the nuclei. The junctions of these portions may be seen in longitudinal sections of Fig. 183. — DisvjaiiOrmG MnscuLAB, fibres. A, elongated cell with two nuclei from foetal sheep. Striation is be^inninj^c in the protoplasm along one side of the cell. (Wilson Fox.) B, from human foetus of two months. (Ranvier.) ^, central protoplasm with several nuclei, n, scattered in it ; s, commencing garcolemma, with striated muscular substance developing immediately beneath it. C, from human fcetus of three months. (Ranvier.) The contractile substance, /, now almost encloses the unaltered protoplasm, g ; only one nucleus, n, is represented." appropriately stained fixed tissue ; they also come distinctly into view in sections of fresh tissue stained with nitrate of silver. The septa appear to be bridged across by fibrils, continued into the portions above and below the lines of junction (fig. 187). These apparelit septa have usually been regarded as intercellular spaces separating the constituent cells of the tissue fro'm one another. Some authorities, however, are inclined to regard the cardiac muscular tissue as originally forming a .syncytium, the cells being all 142 THE ESSENTIALS OF HISTOLOGY Fio. 184. — Muscular fibres i-kom THE HEART, MAIiNlKIED, SHOWINU THEIR CROSS-STRIDE, DIVISIONS, AND J UNCTIONS. (Schweigger-Seidel. ) The iiuulel and cross-lines are only repre- sented on the right-hand side of the iigiire. Fig. 185. — Six muscular fierb-cells FROM THE HEART. Magnified 425 diameters. a, line of junction tetween two cells ; h, c, branching of cells. (From a drawing by J. E. Neale*.) Fi(i. 186. — Portions of muscle-fibres from the adult HUMA^ heart. (v. Palczewska. ) In A one of the so-called septa' traverses the protoplasm which extends between the nuclei as well as the striated substanoe. A second incomplete septum is also shown. • In B a nucleus is seen at the .surface, and serves to render the investing membrane apjmrent. Notice the /.igzagging of the septa, an appearance which is not infrt'unent. CARDIAC MUSCLE 143 continuous both laterally and longitudinally, and the apparent intercellular lines being special differentiations appearing later. H, E. Jordan regards the septal lines as due to fixed localised contractions ; Martin Heidenhain considers that they represent portions of the fibres at which growth in length occurs (analogous to the suture-lines between the- flat bones of the cranium). As against these two views of the transverse s'epta, and in favour of that of Schweigger-Seidel, must be set the silver-staining of the supposed cell- junctions, and the fact that it is easily possible in some animals to separate the fibres after maceration into short uninucleated fragments (as in fig. 185), Schweigger-Seidel's view has been recently upheld by the observations of Fig. 187. — Pobtion of cardiac muscle exhibiting continuity of eibkils ACROSS JUNCTIONAL LINE. (Przewosky. ) Highly magnified. Fig. 188. — Section from heart or FIVK MbNTHS' EMBRYO : HUMAN. (G. Mapn.) V. Palczewska and Werner (working with Zimmermann), who have studied the subject in the heart of man and of various mammals. These observers point out, as had been previously done, that the short non-nucleated seg- ments often seen, which Heidenhain regards as fatal to the cell-theory of cardiac muscle, may be parts of cells lying in other planes of the myocardium, which are inserted between those belonging to the plane included in the longitudinal section. On the other hand, the continuity of the muscular fibrils within the masses of Purkinje's fibres under the endocardium in the sheep, the fibrils belonging to one cell being freely continued- into those of the! neighbouring cells (see fig. 399, p. 288), is in favour of the syncytial theory. Further, in many vertebrates, including some mammals, no cell- territories can be made out in the myocai'diuro. 144 THE ESSENTIALS OF HISTOLOGY The explanation of these differences appears to lie in the fact that in all animals the heart-muscle at a certain period of development (flg. 188) is formed of a syncytium of coalesced cells within which the contractile fibres Fig. 190. Fig. 191. Fig. 189. Fig. 189. — Musculae fibre-cell from the muscuur coat OF THE SMALL INTESTINE. Highly magnified. A complete cell, showing the nucleus with intranuclear network, and the longitudinal fibrillation of the cell-substance. Fii;. 190. — Portion of a plain muscle-cell, showiSg FIBRILS WITHIN ITS CYTOPLASM. Photograph. Magnified 450 diameters. ^ Fio. 191. — Plain aMusoLE-FiBRE, showing nucleus, oen- TRIOLE, AND CYTOPLASM w'lTII FIBRILS. (Lenhossik.) are developed, and only in some is a differentiation of the syncytium into cells later produced ; even here the lines of junction are bridged across by the muscle fibrils. It is usually stated that thepe is no sapoolenmia in cardiac uiiiscle-tiViies, but V. Palczewska and Werner describe and figure a membrane covering the cardiac cells which they regard iis eiiuivalent to the sarcolemma of voluntary muscle. PLAIN MUSCLE 145 NON-STllIATED, PLAIN OR INVOLUNTARY MUSCLE. Involuntary or plain muscular tissue is composed of elongated fusiform cells (figs. 189, 190), which vary much in length. In cross section they are usually angular, an appearance due to mutual compression (fig. 192). Each cell has an oval or rod-shaped nucleus, which shows the usual intranuclear network and commonly one or two nucleoli. There is a centriole — some- times double — close to the nucleus (fig. 191). The cell-substance is finely fibrillated, but does not exhibit cross-strise like voluntary muscle. There Fig. 192. — Transverse section or plain MUSCLE-PIBBES OF INTESTINE. Photo- graph. Magnified 400 diameters. Fig. 193. — Muscle-cells or intes- tine. (Szymonowioz.) Magni- fied 530 diameters. The fibres are represented in longitudinal section ; the interstices between them ar^ seen to be bridged across by fine fibrils, i, interstice ; n, nucleus. appears, as in cardiac muscle, to be a delicate external layer, probably a stratum of undiiFerentiated protoplasm, not a true sarcolemma. Next to this, in some smooth muscle, is a layer containing coarser fibrils (boundary fibrils of M. Heidenhain) (fig. 190). Frequently there are seen on in- voluntary fibres a series of somewhat irregularly placed transverse markings which appear as knot-like condensations of the cell-substance (fig. 190) staining somewhat differently from the rest of the cell. The nature of these is not well understood, but they are perhaps fixed contraction waves (C. M'Gill) ; the fibrils are enlarged as they run through the knots. The 146 THE ESSENTIALS OF HISTOLOGY intercellular substance is bridged across by filaments passing from cell to cell (fig. 193). Plain muscular tissue is found chiefly in the w^lls of hollow viscera ; thus it forma the muscular coat of the stomach and intestines, and occurs abundantly in the muscular coat of the gullet, although it is here intermixed with cross-striated muscle ; it is found also in the mucous membrane of the whole alimentary canal from the oesophagus downwards ; in the trachea and its ramifications-; in the urinary bladder and ureters ; in the uterus and Fallopian tubes ; in the prostate ; the spleen and lymphatic glands ; the muscle of Miiller in the orbit, and the ciliary muscle and iris. The walls of gland-ducts also contain it ; and the middle coat of the arteries, veins, and lymphatics is largely composed of this tissue. It occurs in the skin, both in the secreting parts of the sweat glands, and in small bundles attached to the hair-follicles ; in the scrotum it is found abundantly in the subcutaneous tissue (dartos), and it also occurs in the areola of the nipple. Development. ^According to the observations of C. M'Gill, the smooth muscle ' of the alimentary canal (pig) is developed from a syncytium of mesenchyme cells which suiTounds the entoderm. Some of these cells become elongated and spindle- shaped while retaining their inter-connexion. Myofibrils are developed in their protoplasm. These need not be confined to the limits of a single cell, but may extend over two or even a number of cells. The myofibrils are of two kinds, coarse and fine, varying in relative number in difl'erent parts. As stated above, an inter-connexion of the cells probably obtains even in the fully formed muscle, which thus retains something of its syncytial character. In certain situations smooth muscle is formed from ectoderm ; this is the case with the muscular tissue of the sweat glands (Ranvier) and that of the iris (Nussbaum, Szili). NER VE- FIB RES H7 LESSON XVI. THE TISSUES OF THE NERVOUS SYSTEM. 1. Tease a piece of freah nerve (vagus of mammal by preference) rapidly ; either in Ringer or by the method of semidesiccation, keeping the preparation moist by the breath, afterwards mounting in Ringer. Touch the fibres as little and obtain them as long and straight as possible. Study the myelinated fibres, carefully noticing all the structures that are visible — viz., nodes of Eanvier, nuclei of Fig. 194.— Ordinary white ob myelinated nervb-pibbbs, show- ing a sinuous outline and double CONTOURS. (Sharpey.) Fig. 195. — Fine myelinated nerve- fibres, parts of which have acquired a varicose aprbakance — probably the result of manip- ULATION. neurolemma, double contour of myelin sheath, segments, etc. Besides the ordinary fibres, some very fine myelinated fibres, and some non-myelinated, will be seen in this preparation. Measure the diameter of four fibres. Draw a short length of one or more very exactly. The preparation may then be stained by dilute magenta and gentian violet solution and preserved with dilute glycerine. 2. Separate (in dilute glycerine coloured by magenta and gentian violet) into its fibres a small piece of nerve (or of a nerve-root : this is much more easy to separate into its fibres) that has. been an hour ih 1 per cent, osmic acid and then transferred to water. The nerve should have _ been moderately stretched on a card before being placed in osmic acid. Keep the fibres as straight as possible and only touch them near their ends with the needles. Sketch two portions, of, ajbre under a high power, one showing a node of Eanvier and the THE ESSENTIALS OF HISTOLOGY Fici. 190. — Portions of two neeve- riBRES STAINED WITH OSMIO A(J1D, FROM A YOUNd ANIMAL. Diagram- matio. (From a sketch by J. E. Neale. ) R, R, nodes or aonstrictions of Rainier, with axis-cylinder paaaing throng*!!, a, neuro- lemma of the nerve ; c, opposite the middle of the segment, indicates the nucleus and protoplasm lyin^ between the neurolemma and the myelin sheath. In A the nodes are wider, and the intersegmental substance more apparent than in B. other a nucleus of the neurolemma. Look for pale fibres. Measure the length of a nei've segment between two nodes of Kanvier. 3. Mount in dammar sections of nerve fixed (a) with picric acid or formol followed by alcohol, (b) with oamic acid followed by" alcohol. The sections from picric and formol may be^ stained with hsematoxylin. The nerve should be laid out straight upon a piece of card before being placed in the fixing solution. Examine the sections first with a low and afterwards with a high power. Notice the lamellar structure of the perineurium, the varying size of the nerve- fibres, the axis- cylinder in the centre of each fibre, etc. Measure the diameter of four fibres. Sketch a small portion of a section. 4. Teased preparations and longitudinal sections from the peripheral portions of nerves cut 10 to 30 days before death. The nerves may be prepared yfiih osmic acid as in § 2. Notice the breaking up of the myelin of the sheath, varying in degree according to the length of time the lesion was made previous to death. In longi- tudinal sections of the central cut end of the nerve, prepared by Cajal's reduced silver method,' new fibres may be seen budding from the extremities of the fibres of the stump. STRUCTURE OF NEKVE-FIBRES. Nerve-fibres are of two kinds, myelin- ated and non-myelinated. The cerebro- spinal nerves and the white matter of the nerve-centres are composed of myelin- ated fibres ; the sympathetic nerves near their peripheral distribution are largely made up of non-myelinated fibres. The latter are also found in considerable numbers in the vagus. The myelinated, termed also medul- latp.d or white, fibres are characterised, as their name implies, by the presence of the so-called myelin sheath or tvhite sub- stance. This is a layer of soft substance, of a lipoid nature, which encircles the ' See Appendix. NER VE-FIBRES 149 essential part of a nerve-fibre, viz., the axis-cylinder. Outside the myelin sheath is a delicate but tough homogeneous membrane, the neAirolemma or Fig. 197. ^A small pabt of a myelinated i^ibbe. Photograph. Very highly magnified. The fibre looks in optical section like a tube— hence the ternj tubular formerly appbed to these fibres. Three partial breaches of continuity or clefts are seen in the myelin sheath, which at these places exhibits a tendency to split into laminae. Elsewhere the myelin sheath shows coagulation-appearances. At n is a nucleus belong-ing- to the neurolemma, embedded in protoplasm ; the outline of the nucleus itself is not focussed. Fig. 198. — Myelinated nekve-fieke, eresh, showing a node of Banvier. Photograph. Very highly magpified. The coapfulation of the substance of the myelin sheath is advanced, and the axis-cylinder is sliffbtly shrunken away from it, and is thus rendered distinctly visible. On the ri^ht the axis-cyhnder show^s a fibrillar appearance. Fig. 199. — Nekve-pibbbs ekom sciatic ^'•EBVB including, besides several okdinaky LARGE MYELIHATBD TOJBES, A HON-MYELINATED EIBBE AND A FINE MYELINATED fibre. Osmio preparation. Photograph. Magnified 300 diameters. nucleated sheath of Schwann, but this is not ptesent in all fibres, being abseht in those within the nerve-centres. The myelin sheath is composed of a highly refracting lipoid material (myelin), 'which gives a characteristic double contour and tubular appearance ISO THE ESSENTIALS OF HISTOLOGY to the nerve-fibre (fig., 194). It affords a continuous inve.stment to the axis-cylinder, except that, as was shown by RanVjier, in the peripheral nerve fibres it is interrupted at regular intervals. At these places the neurolemma appears to produce a constriction in the nerve-fibre (figs. 196, 198, 199, 200, 202), and the interruptions of the myelin sheath are accordingly known as the constrictions (Ranvier) or nodes, the latter term being applied from the Fig. 200. — Nekve-fibre ruEPABED with osmio acid. Photograph. Magnified about 500 diameters. A constriction of Ranvier is seen. The intervals between the m3'elin segments appear as clear oblique lines. resemblance which they bear to the nodes of a bamboo. It is, however, uncertain whether the constriction is entirely occupied by neurolemma or partly by a special band (constricting hand of Ranvier) ; if the latter, it is composed of a material which resembles intercellular substance in being stained with nitrate of silver (fig. 210). The segment of nerve between two successive nodes is termed an internode ; in the middle of each internode is Fig. 201. -Reticulum of nedrokebatin in' myelin sheath of NKRVK-FinRE. Photograph. Magnified 600 diameters. one of the nuclei of the neurolemma. Besides these interruptions of Ranvier the myelin sheath shows a variable number of oblique clefts (figs. 197, 200, 202), subdividing it into conico-oylindrical portions of variable length (myelin segments) ; there is reason to believe that the clefts are artificially produced. At the clefts there is an appearance of spiral fibres in the myelin sheath, especially after treatment of the nerve with certain reagents ; it is, however, probable that this appearance also does not represent a pre-existing structure. NER VE-FIBRES 151 A reticular appearance has been noticed in the myelin sheath {neurokeratin network of Kiihne, fig. 201), and can be readily seen in nerve-fibres fixed in alcohol and treated with ether, but it varies greatly in aspect, and is perhaps produced by the action of the reagents employed to show it. By other wm Fig. 202. — Longititdinal and transverse section of myelinated nekvk- FiBBE OF FKou (osMio ACID AND ACID fuchsin). (After Biedemiami. ) The longitudinal' section shows one node of Ranvier and two myelin clefts. The fibrillar structure of the axis-cylinder is shown in both longitudinal and transverse section. modes of fixation {e.g. picric acid) the • myelin sheath seems to have a rod-like structure (fig. 203); this again may be due to the manner in which certain of its constituents are coagulated by the reagent. Osmic acid stains the myelin sheath black (figs. 199, 200, 202, 204). The axis cylinder, which runs along the middle of the nerve-fibre, is a soft transparent thread which is con- tinuous from end to end of the fibre. On account of the peculiar refractive nature of the myelin sheath it is difficult to see the axis-cylinder in the fresh nerve except at the nodes, where it may be observed stretching across the interrup- tions in the myelin sheath ; it may also sometimes be seen projecting from a broken end of a nerve fibre. It is longi- tudinally striated, being made up of extremely fine fibrils (neurofibrils, fig. 202). They are seen isolated at the terminations of nerves as in the cornea and are also visible in the section of a nerve-fibre as fine dots (fig. 202), which sometimes appear to have' a clear centre (fig. 203), as if the fibrils were tubular. Staining with nitrate of silver produces a curious transversely striated appearance in the axis-cylinder (From'mann) (fig. 210, C); this is due to successive precipitations of chlorides, and does not indicate a pre-existing structure (A. B, Macallum). Myelinated nerve-fibres vary greatly in size (fig. 204), but ma^ be classified as large, intermediate, and very small. The largest are those which are passing to the skin and to the voluntary muscles; the smallest are those destined for viscera and blood-vessels constituting the pre-ganglionic FIVE 1000 Fig. 203. — Section across NEBVE-FIBRES. .'Magnified diameters. The nerve was hardened in picric acid and stained with picro-carmine. The radial striation of the myelin sheath is very apparent. In one fibre the rays are broken by shrinkage of the axis-cylinder. The fibrils of the axis-cylinder appear tubular. (From a photograph.) 152 THE ESSENTIALS OF HISTOLOGY Fia. 204.— Section of the sciatic nerve of a cat, showing the variatios3 IN SIZE OF ITS constituent FIBRES. Photograpli. Magnified 3(K) diameters. The nerve was fixed with osmic acid. FlO. 205. — NON-MYELINATED FIBRES FROM A TEASED PREPARATION OF VAGUS OF CAT FIXED WITH OSMIC ACID. Photograph. Magnified 300 diameters. About u, dozen iion-m.veliuated fibres are included in the photograph. Besides these one ordinary ni;i'elinated fibre and three tine ny-elinated fibres are seen. NER VE-FIBRES 153 autonomic nerves. As shown by Gaskell, the ventral roots of the last one or two cervical nerves, of all the thoracic, of the first and second lumbar, and of the second and third sacral nerves contain, bes,ides the ordinary large myelinated fibres, bundles of these very small fibres. Some of the cranial nerves (spinal acces- sory, vagus, glosso-pharyngeal, facial) contain similar very fine myelinated fibres, intermixed with the larger fibres. The term " autonomic '' was introduced by Langley to include both the fibres of the sympathetic system and the analogous fibres (parasympathetic) proceeding \ from the cranial and saci'al regions. All autonomic nerves consist (1) of fine myelinated "preganglionic fibres" arising in the central nervous system and end- ing in ganglia, and (2) of non-myelinated " post-gangli- onio. fibres" arising in the ganglia and passing thence to their peripheral distribution. Non-myelinated fibres. — Intermingled with the myelinated fibres there Fig. 206. — Section across non-mybi,inated fibres (PROM THE splenic NERVE OF THE OX). (Tuckett.) Fig. 207. — Section op part of sciatic nerve of man. Photographed from a preparation by H. Pringle. Magnified 60 diameters. A dozen or more funiculi of various sizes are inclurled in the photograph. The fat-cella in the - epineurium appear as clear spaces. may always, in peripheral nerves, be found a certain number of pale fibres devoid of the distinct double contour which is characteristic of the presence of a myelin sheath (fig. 205). These are the grey or non-myelinated fibres, also called, after their discoverer, fibres of Remajs,. They frequently branch, which the myelinated fibres rarely do except near their termination, IS4 THE ESSENTIALS OF HISTOLOGY and they are beset with numerous nuclei which have usually been regarded as belonging to a delicate sheath, although, as a matter of observation, both in longitudinal view and in cross section the nuclei appear to lie in the • substance of the fibres rather than at their surface. As just stated, all the autonomic nerves, when they approach their peripheral distribution, are chiefly made up of fibres of this nature (postganglionic fibres) ; but the preganglionic fibres, both of sympathetic and of other autonomic nerves, always possess a thin myelin sheath, and have the usual structure of myelinated fibres. ',7* , jf- 208. — Section of the oeevical sympathetic of *hk cat. Photographed from an osniic preparation made by R. Tsukaguohi. On the left a small portion of the vagus is seen. The vagiis and sympathetic in the neck of the cat run in separate perineural sheaths, but are united by epineorium. The vapus has, both moderately large and, fine myelinated fibres and also a considerable number of non-niyelinated fibres. The cervical sympathetic nerve is wholly composed of fine myelinated fibres derived from the thoracic anterior roots. But in this case the sympathetic includes a bundle of moderately large myelinated fibres derived from the vag^us higher up. Structure of the nerve -trunks. — In their course through the body the nerve;;fibresjtre^athereiuji_into round bundles ovjunicnli, and the funiculi are again united together to form the nerves met with in dissection (fig. 207). The connective tissue which connects the funiculi and invests the whole nerve, uniting it to neighbouring parts and con-veying to it blood-vessels, lymphatics, and even, nerve-fibres destined for its coats, is termed the epineurium ; it frequently contains fat-cells. That which ensheathes the funiculi is known as the perineurium. It has a distinctly lamellar structure, the lameillse being composed of connective tissue covered by flattened Fro NER VE-FIBRES 155 lO •b^* *^^^!^^ -a-^^. '^''■it-Sf^ y^'t. "lb Fa(?ws. Sympathetic. Fig. 209. — Section of vago -sympathetic nerve of dog including a portion of EACH NERVE. Photographed from an osmic - stained preparation made by R. Tsukaguehi. In the dog the vag-us and sympathetic in the neck are included in one perineural sheath : their fibres are only separated by a septum of endoneurium. The vaffus contains a cpnsiderable number of fine myelinated and of non-myelinated fibres, besides the ordinarj' myelinated fibres which are of intermediate size. The cervical sympathetic is wholly formed of fine myelinated fibres. endothelial cells (fig. 210, A). Between the lamellae are clefts for the con- veyance of lymph from the interior of the funiculus to the lymphatics 200 i Fig. 210. — Nerves stained with silver nitrate. (Ranvier.) In A, the epithelial-like layer of flattened cells belonging- to the sheath of Henle is stained. In A and B, the cross-like markings at the nodes are exhibited, tn C, a single fibre is shown more highly magnified, with Frommann's transverse markings of the axis-cylinder, a, constricting band ; m, myelin sheath ; cy, axis-cylinder. 1 56 THE ESSENTIALS OF HISTOLOGY of the epineurium. The delicate connective tissue which lies between the nerve-fibres of the funiculus is the endoneuriwm. Within it is conveyed the longitudinally arranged meshwork of blood-capillaries ; its interstices communicate with the lymph-clefts of the perineurium. All the branches of a nerve, and even single nerve-fibres which are passing to their distribution, are invested with a prolongation of the perineural sheath, known as the sheath of Hmile. The nerve trunks themselves receive sensory ijerve-fibres (nervi nervorum) which ramify chiefly in the epineurium and terminate within this in end- bulbs (Horsley). The degenerative processes which occur in cut nerve-fibres as well as the subsequent reparative processes are dependent on the nerve-cells from which the fibres take origin and will be dealt with after the structure of nerve-cells has been studied (see p. 174). NERVE-CELLS 157 ■ LESSONS XVII. AND XVIII. THE TISSUES OF THE NERVOUS SYSTEM (continued). 1. Put a small fragment of spinal ganglion of fi'og' or mammal into 1 per cent, osmio acid for a few hours. Place in water containing a morsel of thymol for a few days. Tease in dilute glycerine. Notice the spheroidal ganglion- cells ; their large nuclei and distinct nucleoli. Many of the cells may still be seen within their nucleated membranous sheath. Look for cells which still retain the axis-cylinder process and for T-shaped junctions of nerve-fibres with this. Fat- cells may be present in the periganglionic connective tissue. These will appear intensely black in osmic preparations. 2. Prepare in the same way a spinal ganglion or Gasserian ganglion of the ray. Notice the bipolar character of many of the cells. 3. Prepare a piece of sympathetic ganglion as in i5§ 1 and 2. If from the rabbit observe that many of the cells are bi-nucleated. Measure two or three cells in each of the above preparations. 4. Mount stained sections of ganglia, both spinal and sympathetic. These will serve to show the arrangement of the cells and fibres in the ganglion and the nucleated sheaths around the nerve-cells. The ganglia may be fixed and hardened in saturated solution of corrosive sublimate or of picric acid or in 10 per cent, formol. Tl^ey may either be stained in bulk or sections cut from paraflBn and stained on the slide. 5. Ehrlich's methylene-blue method, Golgi's silver chromate method, or Cajal's silver reduction method, especially the last named, are all useful for showing the connexions of ganglion-cells with nerve-fibres. See Appendix. 6. Take a small fragment of the grey matter from a piece of spinal cord of ox, or calf, or man, either fresh or after a few days' maceration in |- per cent, bichromate of potassium. Choose by preference a piece from the lumbar enlargement (ventral horn). Spread the fragment out with needles into an even film on a slide, and allow it to dry. Immerse in alcohol for a few minutes. Stain with methylene- blue. Einse with water, dry completely and mount in dammar. Notice the large branching cells, some with a mass of pigment n^ar the nucleus. Observe the fibrillation of the cell-processes. Many axis-cylinders of nerves will be seen in this preparation deprived wholly or partially of myelin sheath ; their fibrillar structure can then be well seen. Carefully sketch .these appearances. Similar preparations may be made from the grey matter of the cerebral cortex and cerebellar cortex. 7. Examine sections of spinal cord, medulla oblongata, and brain stained by methylene-blue by Nissl's method (see Appendix), to exhibit the angular particles within the nerve-cells. 8. Examine sections of parts of brain, spinal cord, and ganglia prepared by Cajal's method, to exhibit the neuro-fibrils in the cells and cell-processes. These preparations are best made from young animals. 9. Examine the nerve-cells and neuroglia-cells in sections from the spinal cord, cerebi'um, or cerebellum of a small animal, e.g. young rat or kitten, prepared by Golgi's method. The sections must be mounted in thick xylol balsam or dammar, on a cover-glass, dried rapidly on a warm plate, and fixed inverted over a glass (or card) ring on a slide. 158 THE ESSENTIALS OF HISTOLOGY 10. Kxamine sections of spinal cord (lumbar enlargenicjit) and corresponding spinal ganglia taken from an animal in which the* sciatic nerve was cut about three weeks before it was killed. The sections arte stained by Nissl's method. Most of the vcntiul hoi'n nei-ve-cells and the ganglion-cells on the side of the lesioii will exhibit chromatolysi.s (breaking down of the Nissl granules) which is charactei-istic of cells the axons of which have been seveied. The altered cells may be compared with the normal cells on the intact side. 7, 8, 9, and 10 may be deferred until the central nervous system is studied. STRUCTURE OF NERVE- CELLS. A nerve-cell or neurocyte consists of a cell-body and cell-processes. One of the processes is always a nerve-fibre or the axis-cylinder of a nerve-fibre. The cell-bodies always lie either in the grey matter of the nerve-centres, or in little groups on the course of certain of the peripheral nerves ; these groups often cause nodular enlargements of the nerves, known as ganglia. The most conspicuous ganglia are those found upon the dorsal or posterior roots of the spinal nerves, upon the roots of some of the cranial nerves, and upon the trunk and principal branches of the sympathetic. Minute ganglia are also found very numerously in connexion with the nerves which are supplied to glands and involuntary muscular tissue, as in the salivary glands, heart, alimentary canal, bladder, uterus, etc. Nerve-cells vary much in size antl nhapc ; many are large, some being among the largest cells met with in the body, but others are quite small. The cell-hodji or cyton (Sanger Brown) is usually erroneously termed the nerve-cell ; it is the part of the cell containing the nucleus. The latter is large and usually spherical and contains a very distinct nucleolus. All nerve- cells possess at least one process ; this is known as the axonov nturon (nerve- fibre procesa) ; it becomes either a nonmyelinated ncrvc-tibre or the axis- cylinder of a myelinated fibre. If other processes are present they are always branched almost from their coramencemetot at the ccll-bodv, and are therefore termed devdrons or dendrites. The cytoplasm is tibrillated ; the fibrils pass into all the processes, and are known as neuro-jibril s ; they are believed to be the actual conductors of nerve impulses. Their existence in the .axis-cylinder (jf the nerve fibre has already been noted (p. 151). The cell-bodies contain numerous mitochondria, which can be shown by intra rilam stains (Cowdry). The cytoplasm contains also peculiar an£;ular ransniis {Nissl yran III es) staining deeply with basic dyes such as methylene- blue ; the size, number, and arrangement of these granules vary greatly in different cells (fig. 211). The Nissl granules change in number and size with the physiological condition of the cell; thus it is found that nerve-cells which have been fatigued by prolonged activity (fig. 212), and also those the axis-cylinder process of which has been cut (fig, 211 C, anB NERVE-CELLS 159 B 'jfflW^- — -Af^4*ii-- ''iiiiiM^ [! a [■ FiG. 211. — NERVte-GteLLS, STAINEI> BY NiSSL'S MKTHOD. X 750. A, from ventra horn of spinal cord, monkey ; a, commencing- axon. B and C, from facial nucleus, dog. C, shows Nissl deg-eneration consequent on section of the facial nerve 15 days previous to death. n f„r.™ ..-.*:—'"- « ■-•- - - which g-ives origin to axon. i6o THE ESSENTIALS OF HISTOLOGY ^ Fig. 212. — Two motor nerve-cells from the dog. t*, normal ; b, after a period of prolonged activity. (Photographed from preparations by G. Mann.) fig. 213), show the Nissl granules becoming disintegrated ; they may even disappear for a time from the cell. A similar result is found to occur after iFlG. 213.— ChROMATOLYSIS of two MliRVE-tl';I,l,S OJ. SPIHAL CORD OF RABBIT, PRODUCED BY SEVERANCE OF MOTOR NERVE 15 DAYS PKEVIQITSLY. (Cajal.)' In A, the ehromatolysis is rather Ie:a advanced than in B. In Ijoth, the nucleus i« displaced to the periphery, et, axon ; 6, c, ohromatolysed cell-substance. NERVE-CELLS i6i the action of poisons which especially affect the nervous system. The Nissl granules of the nerve-cell appear to consist cliemically mainly of nucleoprotein. They contain organically combined iron (Macallum), Many nerve-cells have a clump of pigment granules (fig. 214), containing lecithin, at one side of the nucleus. This is especially marked in certain localities (locus cccruleus, locus niger), and is more frequent in man than in the lower animals. The pigment tends to increase in amount as age ad\'ances. As already stated, the cyton or body of every nerve-cell is traversed Fig. i I 72 4. — A NEKVE-CELL FROM THE UI'MAN SPIN.VL CORD. Bouin, and Maillard.) (From t^ axon ; r/, deiuli'ons ; n niii'leiii with nucleolus; p, iMi^^nien t.trranule.s. Prunant, by fine fibrils (neuro-fibrils) continuous with those in the axis-cylinder of the issuing nerve-fibre process and with similar fibrils in the dendritic processes. They were noticed by Max Schultze in vertebrates and were later described by Apathy in certain annelids. They can be seen without difficulty in all nerve-cells (fig. 215) by the employment of certain special methods of staining. The neuro-fibrils are said to present variations in thickness according to the condition of activity of the cell at the time of death. Most, if not all, nerve- cells show a delicate superficial reticulum (fig. 21^), described by Golgi, which, according to J. Turner, is an investment derived from neuroglia-cells. . Golgi has also described another network l62 THE ESSENTIALS OF HISTOLOGY of fibrils with somewhat larger meshos {deep refAciUum of Golgi) (fig. 217) in the deeper parts of the cell. The iiieaniiig of this network is not known. Although most distinct in nerve-cells it is not ecmfined to them, a similar network having been noticed in epithelial and other cells. Entirely distinct from the nerve fibrils is a system of fine canalicnli, which has been described liy E. Holmgren, permeating the cytoplasm of the i-'lli, -Jl.").— NkKN li-CiilJjS nr KITTKN (KHIIM TlIK ANTERIllK COKrORA i,iu.\iikii;k»iin.\) siiowinc NKURo-Fir.Kirs. (L'ajal.) II. ii\nii ; /., c ,/, Miriiilis iBU'l!. of lilt iiitiiirfllnlar.i.lfMi;, i.f Hl,l■il,^, cell-body in .i,ak CANfiLTOK-riELLS hf fish, (Holmgren. In A, tlie ni,\ elin stteath stops .stiort of the uc4Mjody ; in /j, it is fotitiiiuecl as a thin layer o\ er the ee]]-boil\ . yv'- Fid. 221. — SpinaTj oanomon-cells and fiekes of Ray showing the bipolar f'HAKACTER OF THE CELLS. Osnilc preparation. (Ranvier. ) t.l., lar^G myelinated filjres ; /.m., medium sized myelinated fibres; E, (-onstriction of Rainier; .'/, sheath of ganglion-ceil : «, fl, nuclei of sheath ; r/', snrtafte of nell ; n, its nueieus ; c.a.'., axis-cylinder process enterin^^ the cell ; a similar process is seeti enierj^ing at the opposite pole. The ni^'elin sheath of the ner\e-fihces is stained hlack by the osmic acid. In preparations made by Golgi's chromate of silver method the nerve- cells with all their processes are coloured black by a deposit of reduced silver, so that the processes can be traced for a considerable distance from the body of the cell, in fact in many instances as far as their remotest ramifications. It has been found by the employment of this method that the axis-cylinder i66 THE ESSENTIALS OF HISTOLOGY process is not always an unbranched process, a^was formerly supposed, but that it Usually gives off fine lateral Ijianches (coHatera/.s), which themselves tend to ramify in the adjacent iierve-substanee (fig. -!23, r). And although the main part of the process usually passes on and becomes the axis- cylinder of a long myelinated nerve-fibre {long-a.roned cell, fig. 223), this is not always the case, for in another type of nerve-Cfll within the nerve- centres (short-axoned cell, fig. 224), the axis-cj-linder process breaks up almost immediately into an arborescence, The long process of the first tj'pe Fli:. '2'2'2. -FF.RICET-IJ'f.Ml NF,['R(1-FIHRTI,S AKOI-Xn A T.ARi:E rVRAMiriAI. CUM. nv TIIIO III'MAN I'llKTKX IERRHRI. I am imlflitt'il to Dr .1. Tunirr fur llie drawing hero reproiluced. (which becomes the axis-cylinder of a long nerve-fil..re), although it may remain unbranched throughout its course, ultimately ends in almost every instance in a terminal ramification oi- arborescence ; and this wliether the ending is at the periphery or within tlie central nervous system itself. Synapses. — Each nerve-cell including all its processes is regarded as an automatically independent element or iifrve-unil, the neuron" of Waldeyer,^ and the connexion of one nerve-cell with another is believed to be effected through the medium of the terminal arborisation of (heir cell-processes. Such arborisations may interlace with one another, as in the olfactory glomeruli, in the retina, and in the sympathetic ganglia (fig. 225) ; or a terminal arborisation from one cell may embrace the body or the cell- ' Often erroneously spelt lumron. A neurone is exafctly the same as the nerve cell (cell-body with all its processes) ; the neuron is the nerve-ribre process (see p. 163). NER VE-CELLS 167 processes of another cell ; as with the cells of the spinal cord (fig. 226), the cells of the central acoustic nucleus in the pons and in many Flfi. '223. — A PYR.iMID.U, CKM, IIF THE CORTEX CETIEI'.RI OF THE R.IEBIT. CeLL (IF TYPE I. (IP GoUlI (WTTH LONO ,*XON). (Cajal. ) a, basal dendrons ; p, apical dendron ramifying near surface ; e, axon or nerve-fibre process ; c, its collaterals ; d, fibres 9f white matter of brain. 168 THE ESSENTIALS OF HTSTOLOGY other places. The term synapfn' (nr.nro-mjnapsi') is applied to these modes of junction. By them nerve cells are linked together into long chains Fic, 224. — Cem. (jf tyi-'f. ii. of (iuLi::, with short .won I!.\mifvim: t.n THE .\D.I.\CKXT i:RKV MATTER. (iOLGI AIETHUD. ((i'ajlll. ) '(, axon ; t1, ./, deiidrons, Fig. 225. — Synaptic connexions of sympathetic cells from the SUPERIOR CERVICAL GANGLION OF MAN. (Cajal.) The cells A, B show well-marked intracapsular dendrons ; C, Z>, synapses between dendrons out- side the cell-capsules ; E, a fibre, which is itself surrounded 'by a fine spirally wound fibril, passing to a cell and forming a synapse with the cell dendrons within the capsul'e ; a, a, axons ; b, c, d, e, ft extra-capsular dendrons. NE URONE- THEOR J ' 169 {neiirone-chains) ; the anatomical path, as above indicated, being interrupted at the synapses, althougli physiological changes (ner\'e impulses) are pro- pagated—stepping ovei', as it were, from one cell to the other at eacli synapse. Probably what really happens is a generation of new nervous impulses in the of the uf*rve-ecll is ki as the successive cells forming the chain. The doctrine, of the anatomical independence " neurone-theory." It is supported liy the appeai'iinces of chixmiatc of sil^ei' pi'eparations of nerve-cells, [n these the reduction of the silver is stricth' confined to single cells, which become stained with all their processes ; and these processes, when demonstrated bj' this method, are never found in continuity either with the processes or with the bodies of other nerve-cells. Moreover, man_y of the facts relat- ing to nerve-degeneration can be more readily interpreted by this theory than by one which assumes the existence of direct continuity between the neive-units. But it has been shown by Apathy that in annelids (the nervous system of which was formerly supposed to offer a typical example of isola-ted, linked " neurones "), fibiils are in fact continuous from cell to cell and are not interrupted at the synapses ; it is possible that the same may pi'ove true for A'ertebrates also, in which case the doctrine of independent units would I'eqniie modification. But there undoubtedly exists a physiological independence so far as the main- tenance of nutrition of the cell and its processes is concerned ; and there is also evidence that in the ti'ansmission of nerve impulses from one neui'one to anothei- a block always occui's at the synapses, causing a slight arrest or delay in the transmission. It is also noteworthy that neiwe impulses, so fai' as is known, pass a synapse in one direction only, never in the reverse direction. In motoi- oi' efferent nerve- cells this direction is always towards the cell- body by the dendrons and away fiom it by the axon, but in the sensoiy fibres the conduction both towai'ds and away from the cell-body is affected by the nerve-fllire processes. NEKYE-fiANIU.IA. In ganglia (figs. 227, 228) each cell-body has a nucleated sheath which is continuous with the neurolemma of the nerve-fibre which belongs to the cell. In spinal ganglia, and in many of the corresponding ganglia on the roots of the cranial nerves of mammals and of most other vertebrates, the cells have only one issuing process, the axon, neuron, or nerve-fibre process. This soon acquires a myelin sheath and then passes with a somewhat convoluted course to some little distance from the cell-body, where, still within the ganglion, it divides into two ; one fibre passing to the nerve- centre, and the other towards the periphery. The branching is T-shaped or Fio. 220. — Arborisation of col- laterals FROM THE DORSAL ROOT-riBRES AROUND CELLS IX THE DOR.SAL HORN OF OREY MATTER. (Cajal.) A, fibres of dorsal coliiiim deri\'ed from dorsal root ; /j. collaterals ; C, D, nerve-cells in grey matter sur- rounded by the arborisations of the collaterals ; E, an arborisation shown separately. I70 THE ESSENTIALS OF HISTOLOGY Y-shaped, and always occurs at a node of Ranvier (figs. 229, 230). The neuro-fibrils of the contral and peripheral branches retain their' individuality /^ (_ "^^o^fej^^" ""'^^^J^s^ gg^ ~..^*of cell-liodifs, with Hhrfs jwsslntr from them, to iiiiiti' \\'ith tlu' loiit^^itiKlitiall; loiirHiii^f n('r\ c Hlirt's ii\ T-slia]ie'l jniit'tions. Fid 2-2.S —From \ section of doc's sfinai, oani;i,iiin-, shuwino dikfkkknt TYi'F.s OF I'FLI.S. I 'hot. )grapli. Magniticd 240 (liametris. ■s. seen in wonie of tlu' rrll-iioiliL's is thv iiiai-v of orii,Mn .,f tlu I' slirnnli ;i\va\ from tlu' niii-]i'ati.nl oa|.>^ult^ Nolic- tile smailct ntrustiut;^ witii the larjict ami oleurcr uull.s. . r patoh, flx'L- of NissI yram 1. S f .jfllioofll-ho.lioslii mor.-.larl
  • , it is limited to the axon. a, //, i\ (I, afferent fibres. Via. 2^2. — CEREP.RO-sriNAT. iiANci.KiN-rKi.i.s. (Caial.) (/, /), intrae.ajwnlai- proi-esses, with kiioblieil e\treiiiit iew. several parts forming at first a plexus close to the cell, oventuallv joining to produce a single axon, According to Cajal this multiple condition tends to become accentuated with age (fig. 233). Two chief varieties of cell occur in the spinal ganglia, one large and clear, the other small and staining almost uniformly dark (figs. 228, 230). According to Rawson, the latter give origin to non-myelinated .sensol y nerve-fibres. The cell-body of the spinal ganglion-cell is sometimes invested by ramifications of a fine nerve"- GANGLIA 173 (ibre (tig. 2.31), dfiived either frijin oiib uf the ntlier cells (.f the shiiic gungli'iii ui from ii cell in a iieighboui'iiig syiiipatlietie jj;iiigli(in. Similar liliies, fnrniiiig pfrieellular ijlexii.ses, al«(i occiii' in sympathetic ganglia ("tig. 237). (f /u / :^-;, ,0 '.-^."V.% '-^.,- Fk;. 233. — SKNTM5 type of CEKJSBK0-S1'I:. issuiiiK from rell . n , n , luii lei on tihi Fig. 236.— Two sympathetic gangliojj-uklls, man. (Cajal.) u,, ((, axon ; &, c, intrauapsular proucsse^ ; EATi[. (Cajal.) A, dnwii-fi^rowth of tKin-niyrliiial.cd liltrcw from the old axons; istat- kxd of a m'.kvk (itt "s days hkkokk int:ATii. (Cajal.) Axis c\ liiider sprouts wliich lia\ e Lfrown down Iroiii the ci'iitral cut end of a nor\ c into the oldishcatlis of the nerve-lihres ; nnelJn drops iire St ill \ isihle within the old slieath:^. '[■\\o <^t tlie lU'W filiri'S are interstitial (not ill ol\\iiij:;- iii a new 1,\ formed nucleated proli-iplasiuic strand, h, h. Two of the down-growing fibres (a, a) show enlarged ends ; c, a neuro-fibril with bulbous enlargement ; c, two neuro-fibrils growing down within an old sheath ; to the left of it, an old sheath without new fibres. for the down-growing axons. If the new fibres succeed in entering these sheaiths of the old fibres they grow down in them to their destination, and the NER VE-REGENEKATWN 179 continuity and conducting power of the nerve become idtiiiiately restored. This may not happen for three months or morej according to the lengtli of nerve cut out and the nature of the severance, although tlie process of down- growth begins within a few liours of the injury. iSome investigators have attempted to show that regeneration may take place independently in the peripheral part of the cut nerve. There is, liowever, no regeneration of miim Flli. 241. — L0>;(I1TI'I)1N.\L SWTIDN IIF TJIK rKRirUKPlAL MART OF A XERVE (CERVlrAL SYMPATHETIC (It' e,\T) WHICH W.\S (TT 4'2 DAYS KEFORK DEATH. (Tsukaguehi. ) Magnified 200 diameters. Notice the nunitrous loJif^itudinally arrani^'ed nuclei which are eiiihertflpfl in prot.npla,smic strands. Into some of these strands nenro-fibrils from the central stump ha\e alrearly made their \va.\ . axons in the peripheral cut end, although certain changes take place there, e.g. the multiplication of nuclei and their regular arrangement in long protoplasmic strands (occupying the old sheaths) into which the new fibres grow (fig. 241). But there is no actual union of the down-growing fibres of the central stump with others formed independently in the peripheral severed trunk, and of course no union with the old axis-cylinders, which have wholly disappeared, i8o THE ESSENTIALS OF HISTOLOGY The protoplasiiiic strands just mentioned were' first described by Eiingner, and are known liy liis name. Boeke has shown that^even when the regeneiating fibres grow not into but between tlie strands of Biingner they are invarialtly en- closed within the protoplasm of cells and maintain an intracellular position even to their remotest end. The cells which thus direct and proliably minister to the nutrition of the growing nerve-fibres are termed by Boeke " conducting cells." Such cells, piol)ably me.senchyniic or connective-tis.sue cells, are even found enclo.sing the growing axis-cyliTideis in tlie .scar-tissne wliich separates the ends of the cut neive. The adAancing a.xis-cylinders are usually terminated Ijy a Ijulbous swelling similar to that which characterises the growing Hl')res of the emluyonie nerves (p. 183), and they may also exhibit lateral ramifications. Even when the cut central stump is turned backwards and fixed amongst the muscles or mider the skin, a certain number of newly-budded fibres may find their way from it into the degenerated periplieral part of tlie nerve. When the \uiion is effected between the cut ends of an ordinary mixed nerve, sensory fibres ultimately Hnd their way to the sensory structures in which the original fibres terminated and motor fibres tn tlie end-plates on tlie mu.scle- tibres ; these having for the mo.st jjart remained as small collections of sarcoplasm with nnmei'ons muscle nuclei, althougli having lost tlie terminal ramifications of the axis-cylinder and the nuclei which belonged to it^ — the endings of the neive- fibres, with their network of nenro-fibril.s, being eventuall}' re-established. It is possible, however, to effect a connexion between dissimilar nerves as for example between the motor (hy))oglo.ssus) and scn.sory (lingual) nerves of the tongue. Uoeke has shown tliat in tliis ca.se (hyjioglossus and lingualis) the hyijoglossus fibres will grow down into the peiipheial degeuei-ated pait of the lingualis and will form sensory endings in the mucous membrane, and the lingualis fibres will grow down into the peripheral degeneiated ]iart of the hypoglossus and form motor endings in the muscular hbres. ft is a]so pos.siljle, as Langley and Andei'son showed, to cause the cut central end of the eci'vieal vagus to unite with the cut ]]eripheral end of the cei'vical sympathetic : in this case the regenerating llbies of the sagns pass into and end within the su])eiioi' cervical gaiigli»'ii. If from any cause regeneration fail to establish itself, the central end of the cut fibre and the cell-body from which it takes origin undergo slow atrophic changes resulting from disuse. These atrophic changes may ultimately extend to other links in the cell-chain, e.specially in young animals ; so that even remote cells in the same physiological path may eventually become atrophied (y. Gudden's atrophy, recurrent atrophy). No effective regeneration of cut nerve-fibres is ever seen in the brain or spinal cord, although the process of degeneration of all the fibres which are cut off from their cell-bodies occurs in the same manner as at the periphery and Nissl degeneration also takes place in the cell-bodies. Both in the nerve- centres and the peripheral nerves (if regeneration fail to occur in the latter), the place of the degenerated nerve-fibres becomes eventually occupied by strands of fine fibres, not unlike the fibres of cicatricial tissue. These strands stain deeply with carmine and remain unstained by osmic acid and by the Weigert-Pal method, and are thus differentiated from the surrounding normal myelinated nerves. NEUROGLIA. Besides the nerve-cells and nerve-fibres there occurs in the brain and spinal cord a peculiar tissue which has been termed the neuroglia. It is composed of cells and fibres, the latter being prolonged from fipd through NEUROGLIA i8i the cells. Of the nouroglia-elemeiits some are radially disposed. These start from the lining layer of the central canal of the spinal cord and the ventricles of the brain, being derivatives of the ciliated epithelium-cells lining those cavities. They course in a radial direction, .slightly diverging and constantly branching as they proceed towards the surface of the organ, where they end in enlargements attached to the pia mater. Radial neuroglia- colls and fibres are seen in the embryo before the nervous elements are fully developed (fig. 212) ; the neuroglia-cells when; first distinct form a kind of spongework (fig. 247). Fig. 242. — Section of sfinal cokd of umbkyu chick, showing neurogli.4- fibres prolonged from the efithelium of the central canal. (cajal. ) f7, dnrsal ; /', ventral .surface ; <;, centra] canal from which the neiiroglia-cells and fibres are seen to radiate to the periphery of the cord. Some detached neurog^lia-cells are al.50 represented. Neuroglia-fibres are contained within prolongations or cell-processes of branching neuroglia-cells {glia-ceUs). These cells are usually stellate in shape (fig. 244:), and their processes pass as neuroglia-fibres between the nerve- cells and ncrvc-flbre,g, which they aid in supporting (fig. 243). There appear to be two kinds of these neuroglia-cells differing from one another in the character .of their processes (Andriezen). In the one kind the processes branch repeatedly {arborescent cells) ; in the other kind they remain un- branched from their origin in the cell-body to their termination {spider-cells) (fig. 245, A and B). DEVELOPMENT OP NERVE-CELLS A.ND NEEVE-FIBKES. All nerve-cells in the body are developed from the cells of the neural groove and neural crest of the early embryo ; the neural groove closing to form the neural canal (fig. 246), the cells of which form the spinal cord and brain, and the neural crest giving off at intervals sprouts which become the 182 THE ESSENTIALS OF HISTOLOGY VUi. 243. — TRA>SA'l';KtSJ': yLl-jHiN iW \VHTTE MATTEK oK STINAT- CHKI), suowim; NKRVK-FiiiKES CUT ACKosy \^u ^; Euuu(; LI a-fihres amoncst TiiJ^M. (Ranvier. ) t, :i ni.\ t'liiiaLuil i ■■lilii'c ; c, iLa axis-cyliiuler ; /'. a small Hhrt ; n, ncuro^^Hia i-oll-liodv ; a, a, ntairo^dia-librc's ; tt', oUicrs uub across. Fk;. -i44.^-NEUROGLiA-<-'ELr FROM si'iNAi. CORD. (Raiivier.) Isolated aftur maceration in S.'i per ccul, alcohol. DEVELOPMENT OF NERVE-CELLS AND -FLRRES 183 germs of the spiiiiil ganglia. The cells which line the neural canal are at first all long columnar cells, but amongst those, and probably produced liy cell-division from some of them (fig. 247, (j ; fig. l!50, a), rounded cells, neurohlastg, make their ajipearance, the remaining elongated cells formiiig the sjMiig lob/ ants. iSoon from each neuroblast a process begins to grow out FlC. 245. — NEUKOLiLIA-Ci^LLS. lls, ,~ , '.i rmiTKk'il "[ffniiiiKU odls" in pmrcss of division to form iiL-iJ-olilasls ; ,i, a iiciirolilasl. Fti;. '248. — Nf,|!Kiii;i,,\sts KKoji ,\ I'lii kmukvk, minwiMi thkki; .stm:es ok iiKVKi.iii'MKXT. ((imwitsi li, after iScdtt. ) Vliglily iiiagiiifieil. Harrison }ias directly observed the outgrowth of the axon processes of the neuroblasts of the amphibian larva in isolated neuroblasts examined in serum under the microscope. The growth of nerve-fibresi can also be observed at the ends of the developing in'i\e-fibres in the tail of the tadpole (fig. 252). In this case, as in all others within the body, the growing fibres are not free but are DEVELOPMENT OF NERVE-CELLS AND -FIBRES 185 Fkj. 250. Fid. 249. — Section of ,spi,\ai, cord of crncK of third day of in(;ifi!Ation. (Cajal.) A, ventral root-fibres formed by outj^'rowths of motor neuroblasts, c, e ; JJ, dorsal root-fibres formed by ingrowths of bipolar sensory neuroblasts, O, in j^aiiylion rudiment ; a, early neuro- blasts ; b, neuroblast {^fivin^ rise to a commissural nerve-fibre, d ; h, i, enlarj^ed ends of jjrowiny axons ; e, e, neuroblasts of which the dendrons arc bey;inning" to appear. Fii;. 250. — Section of part of neural canal oy chick of two ano a half days. (Cajal.) A, germinal layer containing' spherical neurobla.'its, a, b, c (a neuro-fibril has already begun to ^'■ro\\- out from a); B, neuroblasts in a bipolar stage; d, enlarged end of growing axon ; e, another growing tangentiall^'. FlO. 251. — NEUROliLASTS FROM THE SIGNAL CORD OF A THIRD-DAY CHICK EMBRYO. (Cajal.) A, three neuroblasts, stained by Cajal's reduced silver method, lowing a network of neuro-fibrils in the cell-body ; a, a bipolar cell. B, a neuroblast stained by the method of Golgi, showing^ the incremental cone, c. 1 86 THE ESSENTIALS OF HISTOLOGY Fii;. 2."i-!.— (iKiiwiM; m-;kvk-fii;ke.s in tajl df t,\I'1-i.>l±;. (KoUikBi.) Tlie iiei-M.'-lilin-s, which are non-inM/liiiatcd, are (.'Vowint' into fgontfatdl niideatwl fells, which probahlj represent the " eonrliictinu cells "Jil Koeke. Fig, 253. — Spinal and sympathetic ganglia aAd part of spinal cokd OF CHICK OF SEVENTEENTH DAY OF INCUBATION. (Cajal.) , ventro-laterai part of spinal cord with d, a motor nerve.cell ; the fibres of the ventral root are seen emerging and passing to B (the connexion appears interrupted in the section) ; C, posterior root formed of fibres whioh have grown from the ganglion-oells in D, spinal ganglion ; K, mixed spinal nerve ; F, sympathetic ganglion ; a, a, axons of sympathetic cells, passing t^o join the spinal nerve : b, dendrons of these oellsi e, axons passing to.the sym^iathetic cord ; h, cells of spinal ganglion still bipolar ; i, i, bipolar cells becoming transformed mto unipolar ; ], unipolar cell with T-Junction ; f, section of artery ; g, body of vertebra. DEVELOPMENT OF NERVB-CELL^ AND -FIBRES 187 enclosed in elongated nucleated cells, which probably represent the " conducting cells " of Boeke (see p. 180). The sprouts from the neural crest contain the neuroblasts from which the dorsal root-fibres are developed. Axons grow out from these neuro- blasts in two directions, so that the cells become bipolar (figs. 249, 253). One set of processes, forming the dorsal root-fibres, grows into the dorsal portion of the neural canal ; these fibres ramify in the developing grey matter; the other set, containing the afferent fibres of the spinal nerves, remains Fig. 254. — Si'inal ganglxon-cells or bmbkyo at pekiod of transition from BIPOLAR to nNIPOLAR CELLS. (Cajal.) The preparation has been stained to show the neuro-fibrils. A, B, unipolar cells ; C, D, F, G, transitional forms ; B, E, bipolar cells ; H, small cell with neuro-flbrils incompletely developed, outside the canal and grows towards the developing ventral roots, eventually mingling with them to form the mixed nerves. As development proceeds, the bipolar ganglion cells become gradually transformed in most vertebrates, by a shifting of the two axons, into unipolar cells (fig. 253, h, i, j ; fig. 254 ) ; but in some fishes the cells remain permanently bipolar (fig. 220). This is also the case with the ganglion-cells of the eighth cranial nerve (ganglion of Scarpa and ganglion of the cochlea) in all vertebrates. The ganglia on the sympathetic and on other peripheral nerves are developed from small masses of neuroblast cells which have wandered along 1 88 THE ESSENTIALS OF HISTOLOGY the course of the out-growing nerve-fibres; they give origin to axons and ilendrons much in the same way as do the neuroblasts within the central nervous system. The manner in which the myeHn sheath and neurolemma of the nerve- fibres are formed is not fully understood. It is probable that the myelin at any rate is formed by the axis-cylinder itself, whilst the neurolemma with its nuclei is derived from cells {lemma! cells) which have wandered out from the neural ectoderm along with the outgrowths from the neuroblasts and accompany them in their progress to the tissues. It is however possible that the lemmal cells are of mesodermic origin. Development of neuroglia. — The neuroglia is developed from the spongio- blasts of the neural canal. Tliese, in place of giving off an axon and dendrons like the neuroblasts, send out a number of fine processes in all directions from the cell-body ; in these the fibres of the neuroglia are formed. It is held by some authorities that the neuroglia has a double origin, some of the cells — those with unbranched processes — being developed from ectoderm and the others from mesoderm. NERVE-ENDINGS 189 LESSON XIX. MODES OF TERMINATION OF NERVE-FIBRES. 1. Shell out a Pacinian corpuscle from a- piece of cat's mesentery, which may either be fresh or may have been kept foi' two or three days in -j^ per cent, chromic acid or in .5 per cent, formol. Clear it as much as possible of adhering fat, but be careful not to prick or otherwise injure the corpuscle itself. Mount in water or saline with a thick hair to prevent crushing with the cover-glass. Sketch the corpuscle under a low power, and afterwards draw under a high power the part of the core where the nerve enters and the part where it terminates. Notice the fibrous structure of the lamellar tunics of the corpuscle and the oval nuclei belong- ing to flattened endothelial cells which cover the tunics. The distinct lines, which when seen in the fresh corpuscles are generally takeil for the tunics, are really the optical sections of these flattened cells. 2. Pacinian coi'puscles may also be observed in* sections of the skin (in the subcutaneous tissue). Tactile corpuscles may be seen in the papillae of the palmar surface of the hand and fingers. Their study may be reserved until the skin is dealt with. .3. Dissect off a small portion of conjunctiva from the fresh eye of a calf or oth'er animal. Spread it out on a slide with the undei' surface uppermost, and place upon it a drop of 1 per 1000 methylene-blue solution. Watch the preparation with a low power until the nerve-fibres come into view, then cover the preparation and trace them with the high power. They will be seen to terminate in end-bulbs. Somewhat similar endings can be shown in the same manner in a piece of parietal peritoneum stripped off, laid out flat upon a slide and mounted in methylene-blue solution, 4. Study the corpuscles of Grandry and of Herbst in sections of the skin covering the duck's bill. 5. Mount in glycerine sections of a rabbit's cornea which has been stained with chloride of gold by Klein's method (see Appendix). The sections should be 9ut by the freezing method. Notice the arrangement in plexuses of the darkly- stained nerve-fibres and fibrils, (1) in the connective-tissue substance, (2) under the epithelium, and (3) between the epithelial cells. Make one or two sketches showing the arrangement of the fibrils. 6. Spread out a small piece of muscle which has been stained with chloride of gold by Lowit'a method, and examine it with a low power to find the nerve-fibres crossing the muscular fibres and distributed to them. Occasionally nerve-fibres which end in muscle-spindles may be observed. The pieces of muscle are advantageously thinned out for observation by pressure upon the cover-glass : they should not be too much separated. Search thoroughly for the close terminal ramifications (end-plates) of the axis-cylinders immediately within the sarcolemma. The motor endings are most readily shown in the muscles of reptiles such as snakes and lizards. These nerve-endings as well as others elsewhere can also be displayed in preparations made by other methods (see Appendix)., SENSORY NERVE-ENDINGS. Nerve-fibres which are distributed to sensory parts end either in special organs or in free terminal ramifications. Within the special organs the actual nerve-ending is also generally ramified. I go THE ESSENTIALS OF HISTOLOGY Nerve-endings in special connective-tissue organs. — Thi-ee chief kinds of these special orifaiis are usually desciilifd, rcpresi'nted in man by I'dcinian corpHsde.t, tarli.fe corpiixdes, and cikUjuIIis. The type is the same in all : a lamellated connective' tissue capsule enclosing a core of a soft material whicli appears to be mainly composed of nucleated protoplasmic cells. The capsule is an expansion of the peiineurium of the neive, and the core an expansion of the endoneurium of the nerve. Within the core the axis- Fic. 2.56. FlO. •i.j.'l. — Ta('TII,K ( IIKITSI'T.K WITHIN A I'AI'II.I.A (IK THE SKIN .IF THE HASP, STA1NE]> WITH I'HEIIItlDE IIP CIIMI. ( I lamicr. ) y(. Two lIPIAf^ ("iriiii.4cli> ; a, a. xlili.k-rs ^^ill,i,, I) it'natinns iif rile ;l\i> <-■ '-"il" Flo. '2r>6. SE( TION DK .\ TACTII.!'; I nulMSCI.l:, SHnwINi; THE rEI.l.'-i It lAll'i vSiINi : THE ClHiH AMI THE E.V ^n KI( 'ATIO\ 1 (iK 'IHE \\IH-( '\- 1 ,1 N liEK AMI1M:ST THEM, ENDING IN KrilUII.I.ATEH EM.VUOEMEXTS. (Vail (U' W'llle.) a, ;iNis-i'\ liiidfi' ; /', (Ml 1-^1 lie 111 ciiriMi^ili' ; c. ;i npiA !■ liTiiniiiit inn niilsiile tin- i-orim-^L-le. cylinder terminates either simply or by an arborescence. The variations which occur are chiell}' due to the comjilexity of this arborescence and that of the capsule, which is simplest in the ciid-buUis and most complex in the Pacinian corpuscles. In the tactile corpuscles and end bulbs the perineural connective-tissue sheath of the myelinated fibre expands to form a bulbous enlargement, which is cylindrical or spheroidal in end-bulbs and ellipsoidal in tactile corpuscles. In both kinds of end-organ as the nerve- fibre enters (in the tactile corpuscle this only happens when it has reached the distal extremity after having wound spirally once or twice round the corpuscle) it loses its sheaths and is prolonged as an axis-cylinder only. NER VE-ENDINGS 191 This generally soon ramifies and its branches terminate after either a straight or a convoluted course within the organ ; but it sometimes remains almost unbranched (see figs. 255 to 260). Fiu. 257. — End-bulbs at the tjskm[natioks of nekves in the human COHJUNUTIVA, AS SEEN WITH A LENS. (LongWOrth.) FlG. 258. — A MYELINATED HOMAN rBRITONEUM. power. FIBRE TERMINATING IN SEVERAL END-BULBS IN (A. S. Uogiel.) Methylene-blue preparation. THE Low Tactile oorpuacles occur in some of the papillaa of the skin of the hand and foot, in sections of which they will be studied (see fig. 367). End-bulbs are found in the conjunctiva of the eye, where in most animals they have a cylindrical or oblong shape, but in man they are spheroidal (fig. 257). They have also been found in papillae of the lips and tongue, in serous membranes, in tendons and aponeui'oses, and in the epineurium of the nerve-trunks ; and somewhat similar 192 THE ESSENTIALS OF HISTOLOGY b \ "h Fni. 259.- -End-hut. lis kkum tiik iir.M.\iN rKKiTuMirw. (Doyiel.) Mure highly mtigniiitd. Metliyleue-blue iirepanitinn. a, iti> dinatod filjt'f ; /', mn-loatc'd lantcllatcil capsule of t'Tid-hiillj ; r. iion-iii_\ olinatfd tihrPR, jifoitahl.v dt^stiiifd lor tlu' oapillarics which siiiround tin- cnd-liulli^. Fill. 260. — End-iuimi from the central tendun of the dupiiracm of the doc. (Dogiel.) Showing bcsidcM tlic main myelinated fibre terminating by an arboresocnee within the core, a second very tine myelinated Hbre, forming a * more delicate arboresocnee around the ending of the main Hliic in the ontcr part of the core. Methylenc-blne preparation. Fio. 201. — End-bulb from the glams PENIS, SHOWING TKBMINATION OF AXIS- CYLINDEB. Methylene-blue prepara- tion. (Dogiel. ) ii, myelinatecl rierve-ftbre ; ,6, slienth qE end-bulb. Fig. 262. — Grandey corpuscles from TiiK duck's tongue. (Izquierdo.) A, composed of three cells, with two interposed disks, into which the axis-cylinder of the nerve, », is observed to pass ; in B there is but one tJinUlp dial; enoloBed between two tactile cells. NER VE-ENDINGS 193 sensory end-organs {genital cwp^isclei) also occur in the integument of the penis and clitoris (tig. 261). Similai' bodies of lai'ger size are also met with in the neighbourhood of the joints (artioihir mrpvKi^hs). In the skin covering the duck'^ Fig. 263. — Maonjpied view of a pacinian body j?kom the cat's mesentery. (Ranvier. ) 71, stalk of corpuscle with nerve-fibrCj enclosed in slieatli of Henle, passing to tlie corpuscle ; n, its continuation through the core, m, as axis-cylinder only; a, its terminal arborisation; c, d, sections of endothelial cells of tunics, often mistaken for the tunics themselves ; /, channel througfh the tunics which expands into the core of the corpjiscle. bill, a simple form of end-Organ {corpuscle of Oraiidry, fig. 262) occurs, consisting of two or more cells arranged in rows within a capsule, with the axis-cylinder terminating in flattened expansions {tactile dish) between the cells. These so-called tactile disks are composed like the terminations of axis- cylinders 13 194 THE ESSENTIALS OF HISTOLOGY everywhere of neuro fibrils which in the disk are arranged in a close network. FTeringa, woikiiig wit,li Boelai, haa shown that this network is prolonged into the protoplasm of the cells which bound the disks, so that the actual ending of the axis-cylinder is intracellular. It is not irnproliahile that this will prove true for many other instances of sensory nerve-termination ; it has long been known to lie the case with motor nerve-endings. The Pacinian corpuscles (figs. 263, 2fi+) are larger and have a more complex structure than the tactile corpuscles and end-Lulbs. They are composed of a number of concentric coats arranged like the layers of an ml ! ///A -^ ' '■ — - '^"*> "XVv^A \\ \ ~^ \ Fk;. 204. — Section ok rACTNiAX roRPUscLfe, (Szymonowicz.) c, one of tlie Ka,\eis of ondoMu'lial ruUs ; 71, micleti^ of endothelial rell. It is seen that tlie tnnios !ire \'er\ closei\ paelird aronnd tlie rore, in the niiildle ot which the a\i^-cyhnder is ont across. onion, and enclosing the prolonged end of a nerve-fibre. A single myelinated nerve-fibre goes to each Pacinian corpuscle, encircled by a prolongation of the perineurium {sheath af llcnle), and within this by endoneurium ; when it reaches the corpuscle, of which it appears to form the stalk, the lanielhv of the perineurium expand into the tunics of the capsule. The nerve passes on, piercing the tunics, surrounded by endoneurium, and still provided with myelin sheath, to reach the central part of the corpuscle. Here the endoneurium is prolonged to form a core of cylindrical shape, along the middle of which the nerve-fibre, now deprived, of its myelin sheath and neurolemma, passes in a straight course as a simple axis-cylinder (figs. 263, n'; 265) to terminate at the farther end of the core, either in an arborisation or in a bulbous enlargement. In its course through the core it may give NER VE-ENDINGS 195 off lateral ramifications, which penetrate to all parts of the core, and them- selves end in fine branches. Occasionally the axis-cylinder passes completely through one Pacinian corpuscle, reacquires its sheaths, and eventually ends in another corpuscle. Besides the myelinated fibre, which is always very conspicuous, it has been shown that both the Pacinian and Herbst corpuscles (see below) receive a fine non-myelinated nerve-fibre which arborises over the outer sui'face of the core. A similar arrangement also obtains in Grandry's corpuscles, where the tactile cells are surrounded with such an arborisation (Hogiel and others). Pic. 265. Fig. 266. Fig. 265. — Part of pacinian body, showing the nerve-mbbe entering the CORE. From an osmic acid preparation. ?7i5, entering nerve-fibfe, the myelin sheath of which is stained darkly, and ends abruptly at the core, c ; p«, prolongation of neurolemma passing towards the outer part of the core ; cf, axis- cylinder passings through the core as the central fibre; e, some of the inner tunics of- the corpuscle, enlarged where they abutiagainst the canal through* which the nerve-fibre passes — the dots within them are sections of the fibres of which they are composed ; n, nuclei of the tunics ; 71', nuclei of the endoneurium-cells, continued into the outer part of the core. Fig. 266.- -Pacinian corpuscle from the cat, stained with silver nitrate. (Drawn by G. 0. Henderson. ) The tunics of the capsules are composed of connective tissue, the fibres of which for the most part run circularly. They are covered on both surfaces with a layer of flattened endothelial (jells (fig. 266), and here and there cleft-like lymph-spaces can be seen between them like those between the layers of the perineurium (see p. 155). • A simple form of Pacinian corpuscle with fewer tunics and a core, formed of regularly arranged cells is found in birds {oorpVsSelas of Herbst, fig. 267). Pacinian corpuscles occur in many situations, especially in the deeper layers of the skin of the hands and feet and penis, in the periosteum of bones, especially in 1 96 THE ESSENTIALS OF HISTOLOGY the iieiuhlKiuiliiHjd of tciidoUK and ligaiiieiits, in tile connective tissue at the back of the alxlonien and (in the cat) very nnnierouHly in tlie mesentery, where they are nuwt eauily got foi' ol.iservation. Althiiuo-h most of the nerve-endings in connective-tissue structures are Fii;. 267. — Hekust ouKrusfLK of duck. (Sobotta. ) x 380. II. iinelinated iierve-tibre ; a, its axis-i;.vliiider, teriijiimting in an enlargement at end of (ore; (;, nuclei uf cells of core : /, nuclei of cells nf outer tunics ; t , inner tunics. Fid. '268. TkRMINAI, ARUORTSATToN FKIIHI TIIK IXTKRMrSCT'LAR f'ONNECTIVE-TISSrK OF TIIK RKI'TUS AllDOMIMS OF TIIF, KAIirlT. iMf.TII YI,KNK-1!IATK rRKrARATIOX. (l)ogiel.) enclosed within lamellated capsules, nerves are found to end in some situations in arborisations between bundles of connective-tissue fibres. This has been shown by Dogiel to occur in intermuscular connective-tissue septa (fig-. 268) ; and in serous membranes (fig. 269) ; in the latter such arborisations may be quite superficial and placed just below the endothelium. Organs of Rlifllni — These, which resemble long cylindrical end-bulbs, aie NER VE-ENDJNGS 197 connective-tissue bundles, within which the axis-oyUnders of the nerves ramify, ending in flattened expansions (fig. 270). They occur fairly numer- '■■,' -/^Yv;.., .,^; ';^* '• ^-iii -*•«.' V ^^ 0. r* > >«.-- Fig. 269. — Tkrminal arbokihation trom the supkkficial layer of the PKRITONKUM OF THE RABBIT. METHYtENK-ELHE PREPARATION. (Dogiel.) d, myelinated fibre ; b, fibre conneefcing the arborisation with another one not here represented. Fia. 270. — An organ ov Rufwni from the subcutaneous tissue. (Ruffini. 71, entering nerve-fibres ; a, a, ending of their axons ; c, c, uapsule of organ ; c', eore. F Fig. 271. — Organ of Golui-Mazzoni from subcutaneous tissue. (Rufhni. • The organ resembles an end-bulb in general structure. ously in the subcutaneous tissues of the finger. Other bulb-like organs, spheroids,!, oval, or cylindrical in form, have been described by Ruflfini igS THE ESSENTIALS OF HISTOLOGY under the name of Golgi-Mazzoni corpuscles (fig. 271); they appear to be varieties of the end-bull). They also occur in the Kubcutaneous tissue of the pulp of the finger ami in tendons. Organs of Golgi. — A special mode of nerve-ending is met with in many hi 1 f>-:z,^'^'^i-f^J^ -^_- < V Fig. 272. — Orh.vn hf (hiLci fkh.m the utm.w tk.ndu ai HiLi.iS. Chluride (IK i;i)J,II i'REF.\K..\TIIIN. (CiaCCM). ) in, iiRiseular fibres ; /, tetidoii-bundles ; G, Gol^^i's oit,';iu ; n, tA\u ml'ia L'-librey |j;is^iii^' Lo iL. tendons, near the points of attachment of the muscular fibres. The tendon- bundles become somewhat enlarged and split into smaller fasciculi, and the nerve-fibres — one, two, or even more in number — pass to the enlarged parts and penetrating between the fasciculi lose their myelin sheaths, while the axia-cylinders end in a terminal arborisation, beset with irregular varicosities. The structure (figs. 272, 273) is enclosed within a fibrous capsule continuous with the areolar tissue covering the bundles of the tendon ; and between the NER VE-ENDINOS 199 cafsule and the organ proper is a lymph-space, similar to that which is found in the muscle-spindle (see p. 201). Free nerve-endings. — When sensory nerve-fibres terminate in epithelium, they generally branch once or twice in the subepithelial connective tissue on Fig. 274. — Vertical section of coknea stained with chloride of GOLD. (Banvier. ) n, r, primary plexus in connective tissue of cornea ; a, branch passing to subepithelial plexus, s ; p, intra-epithelial plexus ; b, terminations of fibrils. nearing their termination. The sheaths of the fibres then successively become lost, first the connective tissue or perineural sheath, then the myelin sheath, and lastly the neurolemma, thfe axis-cylinder being alone continued as a bundle of neuro-fibrils. This branches, and interlacing with the ramifications of the axis-cylinders of neighbouring nerve-fibres Fi«. 275. — Intba-bpithelial nerve-tekminations in the larynx. GoLGi METHOD. (G. Retzius. ) On the left the epithelium is stratified and on the right ciliated columnar. n, nerve-flbres in corium. forms a primary plexus. From the primary plexus smaller branches come off, and form a secondary ple.xus nearer the surface, generally immediately under the epithelium if the endihg is in a membrane covered by that tissue. Finally, from the secondary plexus nerve-fibrils proceed and terminate by ramifying amongst the tissue cells (figs. 274, 275), the actual ending being generally in free varicose .fibrils. This mode of 200 THE ESSENTIALS OF HISTOLOGY ending is characteristically seen in the cornea of the eye, hut can also be rendered evident in other cpithelia. '. { fy & ' Fic. ^70. /* » '.-\ •'' / .- Fr.4. -277. I'm. 270.— E.M'iN*; "k .nj.;kv±; in taitile disks ix tiik i'i«;'s snuut. (Haiivier.) n, Diyeliiiated fihj-c ; m, t.fi-minal disks or menisci ; «, cells of the Malpijjfhiati layer of the epidtrmia ; a, f^omcwhat. inodified <^eU to which a tactile diwk is apjilied. Fii;. 277. — Section "F [\iuscle-spindlk. (Sotiutla.) Magnified 40 diameters, .^^, sheath of s]iind]e ; in, intrafusal tmisclu-tibrey ; )i, ]ier\'e-tlbrGs ; M, ordinary uiusclf-fil>re^. Fig. 278. — Ending of nervk-fibrks in muscle-spindle. (Ruffini.) Three intrafusal muscle-flbres are shown, n, nerve-fibres entering spindle; a, axis -cylinders terminating around and between the inbrafusftl fibres in ring-like, spiral, and irregularly ramified endings. * NER VE-ENDINGS 201 In some situations the nerve-fibrils within a stratified epithelium ter- minate in flattened or cresoentic ex- pansions which lie in the interstices of the deeper epithelium cells, to some of which they are applied. These expansions are known as tactile disks ; they are characteristically developed in the skin of the pig's snout (fig. 276), and are also found in the outer root sheath of hairs and in the deeper part of the epidermis in various situations. With appropriate treat- ment it may be shown that they consist of a fine network of neuro-fibrils. Sensory nerves of muscles. — The sensory nerves of muscles end in peculiar organs which were termed by Kiihne muscle-spindles. Their struc- ture has been specially investigated by Ruflani, Huber, and Dogiel, and also by Sherrington. Sherrington has shown that the large myelinated nerves which they receive (about three or four such fibres entering each spindle not far from its equator) are derived from the dorsal root-ganglia. The muscle-spindle is a fusiform body, from 0'75 to 4 mm. 'long, and from 0'08 to 0'2 mm. in diameter; it lies parallel with the general direction of the fibres of a muscle (figs. 277, 280); It consists of a lamellated connective- tissue sheath externally, within which is a bundle (intrafusal bundle) of from two to twelve peculiar muscle-fibres. These with some connective tissue and the nerve-fibres form an axial mass ; between the axial bundle and the sheath is a lymphatic periaxial sp&ce, bridged across by connective-tissue cells and fibres. The intrafusal muScle- fibres are somewhat like embryonic fibres in appearance, being smaller Fig. 279. — NERVE-icNmNos upon the INTRAFUSAL MUSCLE-FIBRES OF A MUSCLE-SPINDLE OF THE RABBIT ; MODERATELY MAUNlFIflD. METHYLENE- BLUE PREPARATION. (Dogiel.) », larg-e myelinated fibre coming off from ' ' spindle " nerve and passing to end in an annulo-spiral termination on and between the intrafusal fibres ; &, a fine myelinated fibre coming off from the same st^m and dividing. Its branches, c, pass !.u wards ' the ends of the muscle-fibres and- termi- ._ : :; in a number of small localised arborisations. 202 THE ESSENTIALS OF HISTOLOGY than the ordinary fibres of the muscle and having a relatively large number (jf nuclei with surrounding protoplasm, as in the red variety of muscle. At the proximal end of the spindle they ai'e usually only two I il ^ ;:, I Flu. 280. — Dl,V(iK.\MM.\TIC UEI'UESKNT.VTION liF .\ .M PSCLE-SFIN lll.K IN SlTl'. (Modilied from Bockc. ) Drawn by R. K. S. Lim, 7/1, //', oriliiiiily tilircs of Die muscle ; 7/1', buTidIc of intrafusal fibres ; /(, sensovv iier\ u entcrinj^ spiiulk' iiuri passing' to t(_^rniinato in aMTUilo.s]>iral i-ndin^'s around its nuist'le-liliros. or three in number, but they often become cleft aa they pass through it ; at the distal end they may terminate in tendon bundles. The nerve- fibres which pass to the spindle are mostly of large size ; they divide after reaching the intrafusal bundle, but retain thei^ myelin sheath for a time, although eventually terminating as axis-cylinders, which wind in a spiral NER VE-EN DINGS 203 manner between and around the intrafusal muacle-fibres (figs. 278, 279, 280), which -they .clasp by flattened encirclirig branches {annulo-spiral FkJ. 281. — SiSNSUKl' NiSKVJi TiiKMlNATliNU I.N' AKKUKLSATIOSS AKOlIiNI) THE EKLis OF MusuLJi-riCKiSH. (Ceocherelli. ) 1 SfiMffdMr?^ Fiti. 282. — NEIlVE-liJMDINLI IN I'EKSH ML'SCULAIt I'lBEES UlT LIZARD [LaCerCa viridis). (Kiihne. ) A, end-plate seen edgeways ; B, from the surface ; «, g, sarcojemma ; ^, p, expansion' of axis- cylinder. In B the expansion of the axis-cylinder appears as a clear network branching from divisions of the myelinated fibre. endings). , Other, much finer, myelinated fibres pass to the spindle and terminate in neighbouring parts of the intrafusal bundles in flower-liko or platerlike expansions (fig. 279). According to some observers these fine fibres are prolonged from the annulo-spiral endings of the coarser fibres ; 204 THE ESSENTIALS OF HISTOLOGY but Dogiel wfcates that they run independently to the intrafusal bundle. No motor nerve-fibres appear to pass into the spindles, unless the fine fibres above mentioned are to bo so regarded, nor do the muscle-fibres of the spindle undergo atrophy on section of the motor nerve-roots, as is the case eventually with the ordinary muaele-fibres. It is not uncommon to find two or three spindles near one another or even enclosed in a common sheath. Aijotlier kind nf ending of .sensory liljrfs iii muscle lias been de.scnbed in the foi-ULof an arbori.sation nf nerve-filii-iis aniund the ends of the muscle-fibres which are inseited into tendon (tig. i81). Fic. 288. -Motor nervk-kmunos in the ..\r!i>oMiN.^E muscles oe .\ k.\t. GiiLiJ I'RKPAK.VTniN. MagniHecl 170 diiiincters. (S7.ymuno\\iez. ) ENOINi; UF iMOTOR-NEia'ES. The motor-nerves to muscles terminate in fine ramifications of the axi.s- cylinder. In cross-striated (voluntary) nmscles the ramification is localised in special organs termed motor end-urgaus, or, less correctly, rnd-j>/ate.f. In cross-striated muscles, the nerves, which are large and myelinated, terminate, as is just stated, in special end-organs (figs. 282 to 285). A myelinated fibre will branch two or three times before ending, and then each branch passes straight to about the middle of' a muscular fibre. Having reached this, the neurolemma of the nerve-fibre is continued into the sarco- lomma of the muscle, the myelin sheath stops short, and the axis-cylinder ends in a close terminal ramificatioii with varicose expansions upon its branches. This ramification is embedded in a layer of granular sarcoplasm (sole) (fig. 284, b), which is collected into a small mass at the place of nerve- ending. Embedded in this mass of sarcoplasm are two kinds of nuclei ; one oval in shape resembling the muscle-nuclei generally; the other circular NER VE-ENDINGS 205 and more closely connected with the expanded aijd branched ending of the axis-cylinder. When a motor-nerve is cut and undergoes degeneration these last become atrophied and disappear, but the sole and the nuclei which more properly belong to it remain ; and if the nerve undergoes regeneration a new axis-cylinder eventually finds its way to it and develops again a ramification with the usual fibrillar network. In some cases the ramification of the axis- cylinder is restricted to a small portion of the muscular fibre, and forms with the granular bed a slight prominence {eminence of Doyere). This is the case in insects and mammals. In lizards the ramification is rather more extended than in mammals, whilst in the frog it is spread over a con- siderable length of the fibre. The ramifica- tion always shows a fibrillar structure, when appropriately fixed and stained (fig. 285). In mammals there appears to be only one end-plate to each fibre; in reptiles there may be several. The end-plate is covered, ex- ternally to the sarcolemma, by an expansion of the sheath of Henle of the nerve-fibre. This expansion has been termed telolemma. Besides the myelinated nerve-fibre with it. nuclei, anil, cspeciall\ near I he nuiscular coat, a Tonnhei "i clastic fibres cut across. ;.'■' * / ^ "■■"^ ^■■'' .■ ■ ' ■■■' i,-' •"" -L l^-*.--. ■■'-' • -^^ 1\f, •^■' ..^-iS";^.?^, ^^.."^ ^" r ..vw.. -;.j;;t-' Fig. 290. — Skction of benal aetkry stained \\;ith oiu'Kin to show the DISTRIBUTION OF THK ELASTIC TISSUE. Magnified '200 dianieli'i's. Photograph, li, inner coat; h^ niiddle coat; o, aiiventitia. THE LARGER BLOOD-VESSELS 209 An artery is usually described as being composed of three coats, an inner or elastic, a middle or muscular, and an external or areolar (figs. 288, 289, 290). It is, however, more correct to describe the wall of an artery as being mainly composed of muscular and elastic tissue, lined internally by a pavement epithelium {endothelium), and strengthened externally by a layer of connective tissue {adventitia). The inner coat {tunica intima) is lined by a thin layer of pavement Fig. 292. — Elastic network of ARTERY. (Toldt. ) Fis. 291. — Epithelial layer lining THE POSTEBIOR TIBIAL ARTERY. 250 diameters. Fig. 293. — Portion of fenestrated MEMBRANE OF HeNLE FROM AN ARTERY. (Toldt. ) epithelium {endothelium) the cells of which are somewhat elongated in the direction of the axis of the vessel (fig. 291), and form a smooth lining to the tube. After death they become easily detached. The endothelium is the essential layer in all blood-vessels. /It is always the first part to be developed, and in some it remains as the only layer of the vessel. This is the case with all true capillaries and with certain veins, and also with the lacunar spaces or sinusoids, which, as Minot has pointed out, take the place of capillaries in certain parts {e.g. in the liver, the medulla of the suprarenal capsules and the Wolffian body of the embryo) ; it is also true of the sinuses of erectile tissue, as well as the sinus-like blood-vessels which are met with in invertebrates. In some structures the endothelial layer of the blood-vessels is imperfect, viz. : in the capillaries and blood-sinuses of the spleen, the placental mucous membrane of the pregnant uterus, the sinusoids (capillaries) of the liver and probably the 2IO THE ESSENTIALS OF HISTOLOGY sinus-like caiiillai i(« of lionc-iuai row ; in certain of these places the blood finds its way into tin- inteistices of the organ and into direct gontact with the tissue-cells. Tlio en;('nKs of tuk UFNAI. AnTKKV. (Manu.) Flo. 'i'.i.'). - iSruKxnoTUK- I.VAL l..\YFK OF AKTKKV STAiNKU wiTu sir\i;u XITRATK. some ar'tcries there is a layer of fine connective tissue intervening between the endothelium and the fonestriited membrane {subeiidot/ielinl laijer) (tig. 295). The middle cual {Luaica madia) consists mainly of ciroulaidy disposed plain muscular fibres, but it is also pervaded iii most arteries by a network of elastic fibres connected with the feiiestrated membrane of the inner coat and sometimes almost as much developed as the muscular tissue itself. This is especially the case with the largest arteries, such as the aorta and carotid and its inunediate branches, whereas in the smaller arteries THE LARGER BLOOD-VESSELS 211 Fig. 296. — Muscle-cells or ARTERY. (KoUiker. ) d,, nucleus. Fig. 297. — Muscle-cells from superior thyroid artery. 340 diameters. intima media adventitia Fig. 298. —Section oe the lingual artery. (Grunstein.) u, endothelium and subendothelial layer of inner coat ; b, its elastic layer ; c, c, d, innermost and outermost layers of middle coat, with elastic iibrea passing obliquely to join the elastic layers which bound that coat ; e, innermost part of outer coat or adventitia, showin? many elastic fibres cut across ; f, outer part of adventitia. o j v 212 THE ESSENTIALS OF HISTOLOGY of the limbs the middle coat is composed almost purely of muscular tissue. The muscular fibres are comparatively short, with long rod-shaped nuclei (fig. 296) ; they are often irregular in shape (as in fig. 297), especially if the middle coat contains much elastic tissue. The outer coat is formed of connective tissue with a good many elastic fibres, especially next to the middle coat (figs. 290, 298). The strength of an artery depends largely upon this coat ; it is far less easily cut or torn than the other coats, and it serves to resist undue expansion of the vessel. Its outer limit is not sharply marked, for it tends to blend with the surrounding connective tissue ; hence it has been termed tunica adventitia. Fig. 299. — Section of TnoRACio aorta as seen under a low power. (Toldt.) a, the inner coat consisting of three layers, viz. : 1. Endothelium seen as a fine line. 2. Sub- endothelial layer. 3. Elastic layer. In the outer part of the inner coat, at its junction with the middle, a layer of longitudinal muscular fibres is represented as cut across. 6, middle coat with alternating layers of muscle and elastic tissue ; c, outei'^coat with two vasa vasorum. Variations in different arteries.— The aorta (4gs. 299, 300) differs in some respects in structure from an ordinary artery. Its inner coat contains a consider- able thickness of subendothelial connective tissue, and its elastic tissue is chiefly composed of fine iibres, not especially marked off from those of the middle coat, so that the inner and middle coats appear blended with one another. On the other hand, there is a very great development of elastic tissue in the middle coat, forming membranous layers which alternate with layers of the muscular tissue. A good deal of connective tissue also takes part in the formation of the middle coat, making it unusually strong. The middle coat constitutes almost the entire thickness of the wall, the inner and outer coats being thin. Apart from the relative amount of plastic tissue which has been already referred to, the variations which occur in the arterial system have reference chiefly to the development and arrangement of tlie muscular tissue. Thus in many of the larger arteries there are a few longitudinal muscular fibres at the inner boundary of the middle coat, and in some arteries amongst the circular fibres of the middle coat. This is the case in the aorta. In the part of the umbilical arteries within the umbilical cord there is a complete layei' of longitudinal fibres internal to the circular fibres and another external to them, whilst the amount of elastic tissue is very small. Longitudinal fibres are also present in some other THE LARGER BLOOD-VESSELS 213 arteries (iliac, superior mesenteric, splenic, renal, etc.), external to the circular fibres, and therefore in the outer coat of the artery. mlima media ( adventitia ' Fig. 300. — Section of acuta mobb magnified. (Griinstein. ) u, endothelial and subendothelial layers of inner coat ; b, c, outer layer of inner coat containing many fine elastic fibres ; d, e, parts of outer coat. The veins on the whole resemble the arteries in structure, but they exhibit certain differences. In the internal coat (fig. 301 a, h) the same layers may be present, but the elastic tissue is Jess developed, and may be 214 THE ESSENTIALS OF HISTOLOGY quite inconspicuous ; it seldom takes the form of a complete uiembrane. The ondothelium-cclls are less elongated than t;^osc of the arteries. The middle coat (r) contains less elastic tissue and also much less muscular tissue, being partly occupied by bundles of white connective-tissue fibres. These are continuous with those of the e.xternal coat (dj, which is relatively better developed in the veins than in the artei-ies, so that, although thinner, their walls are often stronger. Many of the veins are provided with va/vrs, which are crescentic f(jlds of the internal coat strengthened by a little fibrous tissue : a few muscular fibres may be found in the valve near its attachment. The layer of the .:-<^fk^' -.b '/',',. ' .'->•'•<-- ^_. --"-. •, V _:':-- -:-..^..::£;^''- Flc. olll.- Tk \NS\KKSK Si:i'TION III'- I'AliT UK THE W.M.Tj UK ON K OF THK 1'(isti>;kiui; tii;iai, veins (m.\n). Atiout 200 diauK'ters. .-inlitthclial, mill />, subonilotliflial l;i> lts of iTiiiLi' L-nal ; t\ niiiUlle mat (.■onsistiti^ of irrfi;rular la,\ fr.s 111' niiiMailar ti.ssiie, alteniatin^' witli i:(>iiiRa-ti\L' tiriPiU', and iia^siii^ sonu'what j^afiiially into lliL' oiitLi- (.■oniiuL-ti\ c-tissut coat, d. inner coat is rather thicker and the endotheliuni-cells are more elongated on the side which is subject to friction from the current of blood than on that which is turned towards the wall of the vessel. Variations in diflferent veins. Tlic \cins i.f iliitlrciu ]«uts \ary lonsidfiuhly in stiucttne. In man}' veins liiiigitubserM' the lyni])hatic plexus under a low power ; sketch a. portion of the network. If the peritoneal surface is foctissed, the endothelium which covers that surface will be seen, and opposite the clefts between the radially disposed tendon-bundles stomata may be looked for in this endothelium. 4. Examine sections of the thoracic duct. These are made in the .same way aa aeetioiis of the blood-vessels, 5. Stomata. — Open the abdomen of a freshly killed frog, preferably a male, and remove the abdominal viscera, taking care not to injure the membrane at the back of the abdomen, which lies between and at the sides of the kidneys and separates the peritoneal cavity from the cixlcniu lymphaiica niatjua, a large lymph-s])ace in which the aorta and vena ea\a are contained. Cut out one kidney, along with as much as possible of the membrane which lies between the kidney and abdominal wall ; rinse with distilled water ; itnd place in a watch-glass THE SMALLER BLOOD-VESSELS 217 of 1 per cent, silver nitrate for one minute. Einse again in distilled water and expose in tap water to -the light. When slightly browned snip off a portion of the thin membranous septum, float it flat on a slide, drain off the superfluous water and allow it to dry ; then add a drop of dammar and cover the preparation. Before the preparation is dried upon the slide it may be stained with magenta and gentian-violet solution, washed with distilled water and then allowed to dry. If this is done the nuclei of the cells are shown. 6. Kill a frog by destroying the brain and study the circulation of the blood in the mesentery. It can also be studied in the web of the frog^ foot, in the lung and tongue of the frog or toad and in the tail of the' tadpole or of any small fish. For observing the phenomena attending commencing inflammation and the emigration of leucocytes from the vessels, the mesentery is the most convenient Fig. 303. -Method or studying the cntcniiATioK in the feog's MUSENTEKY. (Ranvier.) L, cork or glass plate ; E, perforated cork, the aperture in which is closed by a circular ^lass cover (not too thin) ; M, mesentery laid over the glass cover ; I, intestine. The brain is destroyed and the animal then immobilised with curari. object. The decerebrate frog can be immobilised with curari or by placing it in water in which chloroform or ether has been shaken up : a lateral incision is then made in the abdominal wall, a loop of intestine drawn out;, and laid over a ring of cork which is fixed to a glass or cork plate (fig. 303). The membrane must be kept wet with Ringer's solution.^ ' 7. The arrangement of the blood-vessels in the various tissues and organs is studied in injected preparations (see Appendix for methods of injection). THE SMALLER BLOOD-VESSELS. The coats of the small arteries and veins are much simpler in structure than those of th^ larger vessels, but they contain at first all the same elements. Thus there is a lining endothelium and an elastic layer, the two ^ For details of the methods used in studying the circulation in different parts, see the author's Course of Practical. Histology. 2l8 THE ESSENTIALS OF HISTOLOGY together foiiiiing an hvner coal ; a middle coat of circularly disposed plain muscular tissue; and an advevlUia. The same differences are found between the smaller arteries and veins as with the larger, the walls of the veins being thinner and containing far less muscular tissue (fig. 304), and the lining epithelium-cells, much elongated in both vessels, being far longer and narrower in the small arteries than in the corresponding veins (fig. 305). In the smallest vessels it will be found that the elastic layer has entirely disappeared in the veins, and that the muscular tissue is considerably reduced in thickness in both kinds of vessel. Indeed, it is soon represented by but a single layer of cells, and these eventually no longer form a complete layer. By this time, also, the outer coat as well as the elastic layer of the inner coat have disappeared both from arteries _ and veins. The vessels are «^=^-4^i Fk;. 304. — Tu.\Ns\'j!i:sK sectiiin' of a small autkuv and \ ein'. ' Mamififd li.XI diaiiiuters. reduced, therefore, to tlie condition of a tube formed of end<>thelium-cells, with a partial covering of circularly disposed muscle-cells. Even in the smallest vessels which are not capillaries the differences between arteries and veins are still manifested, These difl'crences may be recapitulated as follows; The veins are larger than the corresponding arteries; they lirauch at less acute angles ; their muscle-cells are fewer, and their enduthelium-cells less elongated ; the elastic layer of the inner ci.iat is always less marked, and disappears sooner as the vessels become smaller. Capillary vessels. — When traced to their smallest brandies the arteries and veius are eventually seen to be uoutiuued iuto a. uetwork uf the {jmalle&t blood-vessels or capillaries. The walls of these are composed only of flattened epithelium-cells (fig. 306) continuous with those that lirte the arteries and veins ; these cells can be exhibited by staining a tissue with nitrate of silver. The cell-outlines are not shown in developing capillaries ; in these, silver nitrate shows no elective staining. This is the case also in the adult with THE CAPILLARY BLOOD-VESSELS 219 the Capillaries of the villi, those of the choroid coat of the eye (Eberth), and those of the kidney-glomeruli (Ranvier) : in all these places the walls are formed of a syncytium. The capillaries vary somewhat in size and in the closeness of their Fig. 30.5. — A small abtery, A, and vein, V, fboh ^he subcutaneous connective TISSUE OF THE BAT, TREATED WITH NITRATE OE SILVER. 175 diameters. a, a, endothelial-cells with b, h, their nuclei ; m,, m, transverse markings due to staining of intercellular substance between the muscular fibre-cells*; c, c, nuclei of connective-tissue corpuscles attached to exterior of vessel. meshes; their arrangement in different parts, which is mainly determined by tie disposition of the tissue-elements, may best be studied in injected preparations, and will be described when the structure of the several organs is considered. Usually the arterioles pass gradually into the capillary network and the capillaries unite to form small veins which, on receiving others, gradually increase 220 THE ESSENTIALS OF HISTOLOGY in sizu. But in uuituin situations the uirangenmnt is different. Tlius in the sjjleen the artoiial capillaries have inipeifect walls and the blood jjasses into the interstices of the spongy tissue of the organ, from which it is collected by_^ sinus-like veins which also have incomplete walls. In erectile tissue the arterioles open, without the medium of capil- lai-ies, into lai'ge eavei-nous spaces bounded by (ibrous and plain muscular ti.ssues and lined by endothelium : the veins lead out of these spaces, so that there ai'e no true cajiillaries, except such as are distributed to the tissues which form the walls of the spaces. In the sympathetic ganglia, us shown by Eanvier (tig. 307), the capillaries open abiuptly into laige .sinus-like venules. And in the livei' and a few other organs, as will presently lie ex]ilained, the con- nexion between atferent and eH'erent vessels is effected, not by true capillaries, but bj' sinus- like spaces between the tissue-elements, the "sinusoids" of Minot. (See pp. 209, 22.3.) X'KSSELS or THE (After In the transparent parts of animals, the blood may be seen flowing through the capillary network from the arteries into the veins (fig. 308). The current is very rapid in the small arteries, somewhat less rapid in the veins, slowest in the capillaries. The flow in any vessel is V Fm. autj.— Cai'Ii.lauy FROM THK ULAJiDEH CAT, MAONiriELI. Chrzonszczewsky. ) The outlines of Uie cells are stained by nitrate of silver. ^AAkUAH fU Fio. 307. — Vessels in a sympathetic ganglion of the rabbit injected. (Ranvier. ) lif arterioles ; b, c, capillaries ; K, sinus-like veins. fastest in the centre, slowest nearest the wall (inert layer). In this layer the leucocytes are carried along and they may be observed — especially where FLOW OF BLOOD IN VESSELS 221 there is commencing* iniiammation of the part, as in the mesentery in con- sequence of exposure — to adhere to the inner surface of the blood-vessel, and here and there to pass through the coats of the small vessels and appear as migratory cells in the surrounding connective tissue (fig. 309). The Fig. 308. — Blood-vessels in THE WEB OF THE FEOG'S FOC^ SHOWING AN ARTERIOLE CGMMUNICATINQ THROUGH THE CAPILLARY NETWORK WITH A VENULE. (Allen, Thomson.) Fio. 309. — Blood plowing through a small vein of THE EKOO'S MESENTERY. The mesentery had heen exposed for a short time, so that there was oommencin^ inflammation and many of the white corpuscles are observed sticking to the aide of the vessel and even passing through the vascular wall, a, central rapid layer containing the coloured corpuscles ; 6, outer slower layer (mert layer) containing the white corpuscles. blood-plateletB are also to be seen in the inert layer, and if the vessel is in- jured or the part is inflamed, tend to adhere to the wall and to one another. Fig. 310.— a living capillary vessel. (Sieinach.) Aj as seen previous to excitation. B, contracted condition resulting from strong excitation. Contractility of capillaries. — As was first shown by Strieker, the cells which form the walls of the capillaries appear to possess contractility, for it is found that when these vessels are directly stimulated — even after isolation — they diminish in calibre even to complete extinction of the lumen (iig. 310). Vessels and nerves of blood-vessels. — The larger arteries and veins possess blood-vessels {vasa vasorum) and lymphatics, both of which ramify chiefly in the external coat. Nerves are distributed to the muscular tissue of the middle coat, after forming a plexus in the outer coat. Most of the nerves are nonmyelinated. 322 THE ESSENTIALS OF HISTOLOGY But there .ire n certain iiiiinlier of myelinated fibres intermingled with the non- iiiyelinatcd and jias.siiig td end in localised arborescpnces partly in the a.dventitia, partly in the iiitinia. These myelinated liljies are drJubtless afferent ; the majority of the non-myelinated ai-e ]))u)ial)ly efferent and dei-ived from the sympathetic (vaso-motors). In the aoita nf man and in some of the larger aninjals Pacinian corpuscles aie here and theie met with in the adventitia. The capillary vessels also receive non-myelinated nerve-libies which have Jinclei upon them (fig. 311), and form a fine plexus of fibrils in close contact with the cndotheliinn-cells of which the walls of these vessels are composed. DEVELOTMENT OF I'.LOOD-VESSELS. The heart and blood-vesseLs .show themselves very early. They are always developed in connective tissue or in the mesenchyme which precedes FtO. 311. — l^^NDINC OI'^ NET:A"K-FTr.Hll,S ON OA I'lT.T.Aia \J';SSII.S. (Dns^ifl.) Fic. 312. — Isolated CArii.LARv network formed iiy thio junctioh ok a hollowed- OUT SYNCYTIUM, CONTAININtl COLOURED BLOOD-CORPUSOl.ES IN A (T.EAR FLUID, c, a hollow cell the cavit.v ot whloh does not .yet communicate with the network ; », p, pointed prooesees, extendinj,' in dilTcront directions for union with neighbouring capillaries. SINUSOID VESSELS 223 it, the first vessels Being found in the vascular area which surrounds the early embryo. Their development may be studied in the embryo chick or mammal, in the omentum of the new-born rabbit, and in the serous membranes and subcutaneous connective tissue of foetal animals. The cells which are to form the vessels (vasoformative cells) branch and unite with one another to form a syncytium, and cavities form in this and extend into the branches. In the meantime the nuclei multiply and become distributed along the branches, cell-areas being at - a later stage marked out around the nuclei. In this way intercommunicating vessels— capillaries in which blood-corpuscles may have become also developed (see p. 42) — are produced (fig. 312). These presently become connectfed with previously formed vessels, which extend themselves by sending out sprouts, at first solid, and afterwards hollowed out. Even the larger blood-vessels appear to be developed in the same way as the capillaries, in so far that the epithelium is first formed, and the muscular and other tissues are subsequently added ; but whether they are produced as clefts in the mesoblastic tissue, which become bounded by flattened cells, or whether aS a hollowed-out syncytium, has not been definitely ascertained. Some authors consider that new blood-vessels are exclusively formed by sprouts from pre-existing vessels, and regard the appearances above described as being due to retrogressive development of an already formed' vascular network (see p. 45). SINUSOID VESSELS. ! These are sinus-like blood-spaces between the cells of certain tissues (Minot). They may when fully developed bear a superficial resemblance YCL Jrv V Ar Fig. 313. — Diagram to illustrate the developmbkt or blood-capillaries (right side), and sinusoids (left side) respectively. (F. T. Lewis.) /nt, intestinal entoderm with out^owth on the left to form the liver and gall-bladder, and on the right to form the pancreas. V.C.I., vena cava inferior ; V.P., vena portJe ; V, vein, and Ar, artery supplying pancreas. It is seen that the sinusoids or apparent capillaries of the liver are formed hy the breaking up of a large blood-spaoe into channels by the growth into it of cell-columns derived from the hepatic outgrowth of the entoderm. to blood-capillaries, but differ essentially from these in their mode of develop- ment, as well as in their relationship to the connective tissue, and to the tissue elements of the organs in which they occur. For, whereas capillary blood-vessels are developed amongst and between the tissue-elements and are connected with or grow from neighbouring capillaries which are them- 224 THE ESSENTIALS OF HISTOLOGY solves surrounded hy areolar tissue, sinusoids make their first appearance in the form of comparatively large blood-spaces connected with the venous, / IS). !v ,^ '-'M-'-^:M.. Tfi' '■< Ir h.c. ;^ ,.- - W S\ If ;;' 'Si?'" FlO. 314.— DeVKI.OPTNO LTVEB of CTIICK, to show how the hepatic THAr.ECrL-E ENCROACH (IN THE TJUTTNA OF THE SINUS-T.IliE VEINS ANll BKEAK THEM UP ULTIMATELY INTO THE CM'II, LA KV-I,I K E CHANNELS C \LLED SIN CSOIIiS. (Minot.) ( h.c, hepatic trahecul.'i? ; .SV, sinusoids. i-^V--'";.' .1\I*1. I? x3 00 '- ' " ;^'- . ' '. Fic. 315. — Liver of embryo chick of eleven hays. (Minot.) A.C., )ic]>ati(' t.rnliL'fnhi' ; .S/, siiuisnids, or it may be with the arterial, system. Into the^e spaces, the walls of which are formed only of a single layer of endothelial cells, the tissue-elements of the developing organ (Wolffian body, liver, suprarenals, etc.) grow, invaginating the thin wall and forming cell-trab§cul8e within the sinus (fig. 313), so that the cells of the organ are brought directl}' into contact with the invaginated endothelium, and are only separated by this from the blood LYMPH-VESSELS 225 contained within the sinus. But the connexion may be yet closer than this, for, as happens in the liver, the invaginated endothelium may become defective, so that the blood within the sinus is in actual contact with the cells of the organ, flowing in the irregular interstices between them. As development proceeds these interstices come to resemble blood-capillaries in '■^n Fxu. 316. — Section of moder.U'B-sized lymphatic. (Evans.) c, c, capillary vess'els distributed to the inui?cular coat (tunica media). size and general arrangement ; but the resemblance is superficial, and the intimate relationship between the blood and the tissue-elements, which arc both enclosed within the original sinus, is usually maintained. .LYMPHATICS OR LYMPH-VESSELS. To the lymphatic systpm belong not only the lymj/h-vessels and lyniph- glands, but also the cavities of the serous membranes, which are moistened IK 226 THE ESSENTIALS OF HISTOLOGY with lympli iiiiil are in ojien (■ommiinii.'ation with lymph vessels which run in their parietes. The laiger lymph-vessels soinewhat resemble the \eins in structure >>-^rt*^ 11*, I L^-iW^A^%?i^, ^v 'm 'W hn c ^<. r">'-^ i'ui. 317. -Srn-;A\ A],vri.Al; IIIHTATiuN m a ].\MniATlr UF THt mksentekv (IF A fAT: silvi;k mt!:ati-: rkFi' akatiun. (Kanvier.) ('', ilTeL,'ul;ii' arraiii,'(.'iHfiit of iiiusck' at tlit dilatation. ))i, (jin.Ailar riiU!i(.'le-tiln'us Fr:. .'ilS.— a smaj.j. L'.MiT (IF Till'; L>- \i r 1 1 A'n(.' ri.ii.^xi.s m- I'lii.: ri.Ki k.m. i .vvru (IF THE DuriiKACM. iM;igiiiti(-'d 11(1 (luini(.'ti.i's. (Kauvifr. ) ^1 lylUphatititi with (jhui'aulmi&uu miduUmiiuui ', o, ui^U-ai>aut» ot iAlv voutlculivt: Lisaue here and thove abutting against the lymphatic. (fig. 316), except that their coats are much thinner and valves much more numerous. In lymphatics of smaller size, which in the fresh condition have a clear, perfectly transparent appearance and a very thin wall, the latter is formed, first, by a lining of pavement-epithelium cells (lymphatic LYMPH-VESSELS 227 endothelium), which are elongated in the direction of the axis of the vessel ; and, secondly, by a layer of circularly and obliquely disposed muscular fibres (fig. 317). In the smallest vessels (so-called lymph-capillaries, which are generally considerably larger than the blood-capillaries), there is nothing but the endothelium remaining, and the cells of this are frequently not more elongated in one direction than in another, but have a characteristic wavy outline (fig. 318). The lymphatics receive numerous nerve-fibres, which are non-myelinated, Fic. 319. —Nerves of a lymphatic vessel, shown by methylene-blue. (Dogiel.) cf, t*, non-myelinated fibres passing: to the vessel ; &, part of their terminal ramification. and end in a ramification of the finest fibrils, distributed to the coats of the vessels (fig. 319). Lymphatics begin either in the form of plexuses, as in membranes (fig. 320), or of lacunar interstices, as in some of the viscera : transitions occur between the two. In order to show their structure, it is usual to stain a tissue with nitrate of silver ; for exhibiting their distribution they may be injected by sticking the nozzle of a very fine injecting cannula into any organ which contains them, and forcing coloured fluid under gentle pressure into the interstices of the connective tissue. 228 THE ESSENTIALS OF HISTOLOGY 111 silver preparations it may be observed, that the lymphatics always appear in the form of clear channels in the stained ground-substance of the connecti\e tissue, and that their walls are in clb.se connexion with the cells and cell spaces of that tissue (hi;. 320). But except in the case of the serous membranes, no open comnmnication is observable between the lymph-vessels and the interstices of the connective tissue, although from Yk. 320. , efferent lyiii surroun -OrIHIN of I.YMPH-VKSSELS in CllNMOCTIVE TISSUE, SUO\\> l;V THE NITRATE OF SILVER ^lETHuD. (v. ReSklinghauseH. ) ihatic \essel ; (/, plexus of oriy-iii ; h, rontleU of the plexus. LOniieLted with ^elU of the ing connective tissue (seen as white i.-eil-spaces. c/in the lirown irrouiui-substaiirel the readiness with which they can be injected from the latter there must be a ready means of passage of the interstitial lymph into the commenciu" lymphatics. Development.— The lymphatic vessels were described by Klein, and later by Retterer, as being developed from hollowed-out cells iu" the same manner as the blood-vessels ; by Gulland as becoming formed at the periphery as clefts in the connective tissue, subsequently establishing connexion with the venous system. But the investigations of Ranvier, recently coniiimed by Miss Sabin, Lewis, and others, have shown that the lymphatic trunks grow out at certain places from the venous system, and gradually spread'from these spots to all parts of the -embryo. SEROUS MEMBRANES 229 SEROUS MEMBRANKS. , Tlie serous membranes, wliich may be conveniently studied in connexion with the lymphatic system, are delicate membranes of connective tissue Fig. 321. — Lymphatic plexus of central tendon oe diaphragm of RABBIT, PLEURAL SIDE. (Klein.) ' a, larefer vessels with lanceolate cells and numerous valves ; &, c, lymph-capillaries with wavy-bordered cells. The cell-spaces of the connective tissue are not represented in this ligrure. which surround and line the internal cavities of the body, and are reflected over many of the thoracic and abdominal viscera ; in passing to these they form folds (such as the mesentery), within which blood-vessels, lymphatics, and nerves are conducted to the viscera. 230 THE ESSENTIALS OF HISTOLOGY The, iniior surface is lined by a eontiiiuou.s la^'er of 'jiari'iiieiit-epillifilium (f.fii/iithdi/iuit) (II-'. ;!2l'), wliicli is xt-ry ilistinct in nitrate of siKer prepara- tions, Tiiis endotlieliiiin lias a special struetuie, in the f"rrii of a vertieally striated free bonier (see, \t. (i^). The cells arc cnnnected hy intercellular bridues (fig. -'ll!.'"!). Tn some places there are apertures in the epithelium FlC. .S22. — iSKKOCS li> ImrHI'J.Il'.M FnC]\l TKl-lTCNEVr SUKr \l 1", riF r'lArHl:.\CM. XiThi.'Vn'; CI- sirvi:]: i->;i:]'.\i;.\ iicn. (Ivlciii.) "..lar^rrr; /(, ^nu'illoi rv]]^. t'.ctWLH'ii riit- larlcr ar.' ^cm s-mnll ivn-unilar ^pai-e-: (].^;cni(ln-^rninatay which lead directly into subjacent lymphatic \esscls. These apertures are called stonia/ii, and are sometimes sui'rounded hy special cells (fii;-. "'l-l). Thev are numernns u}H)n tla^ perilr.meal surface nf the diapliragni, but are F[c. ',]2'^. — KNnnTrTi':rii M-{ I'.ri.s nr si.i.ui s Mr.MruvNV si.ia tn i i.cni.i-. \if\\. sUdWiNc ritiiTiirnsMic r.):i iii:i:s sTUKTiiiiNu. Aciiuss TlIK iNTKUi'Kri rr vk si'ACKs. (M. Heidcnhaui. ) present in most serous menduanes. They are no\vber(> b(^ttei' studied oi' more easily seen than in the peritoneal membrane at the back of the abdominal cavity in the frog. This membrane lies between and at the sides of the kidneys, and serves to separate the peritoneal cavity from the large lymph -space just behind it. If the membrane is prepar-ed by the nitrate of silver method, both the stomata and the cells which bound them are shown. SERO[lS MEiMRRAnES 231 The endothelium of the serous membrane rests upon a homogeneous basement-membrane, which is especially well marled in the serous membranes of man. The rest of the thickness of the membrane is composed of connective tissue, with a network of fine elastic fibres near the inner surface (fig. 325). FlO. 324. — EnDOTHELITJM from the FOSTKKIOR part or the FKOU'S fEBlTOHJSUM, SHIIWING THREE STOMAT.V LEADIi^li INTO THE filSTERNA JAMfHATICA MAUNA. (After Ludwig and Schweigger-Seidel.) Fici. ."ias. — Section of pleura (Favaro. ) Magnified 270 diameters. e, enrlothelium ; m, substance of membrane with numerous elastic fibres ; /*, sub-pleural layer ; ?, I,yinph-vessel. Development. — The serous cavities are originally formed in the embryo as a cleft in the mesoderm (pleuro-peritoncal split, ooelom) which becomes lined with endothelium, and, later, becomes separated into peritoneum, pleura, and pericardium. Outside the endothelium .the crelomic wall eventually becomes differentiated into the tissues of the serous membrane. 232 THE ESSENTIALS OF HISTOLOGY LESSON XXII. LYMPH-GLANDS, SPLEEN, TONSILS, THYMUS. I. Skc'J'ion's (if a l_yiii|jli-glniiil wliirli lias lii-i'ii liardeiied in foiuifil or other fixative, stained in Vmlk, and eniliedded in paniftin. Or tlie sections nia^' lie stained witli li;ei]iatnxylin and eosin. Notirc (I \ the tilii-ons and nmsiulai eajisule, with trahernbe extending inwards from it through tlie cortex and anastomosing witli one another in tlie ini-diilia, (2) the dense lymphoid tissue (adenoid ti.ssue of some authors) forming large masses in the cortex (cortical nodules) and rounded cords in the medulla. Notice also the clearer chjinnel or lynijili-sinus wliich everywhere intervenes lietweeii the tilirous tissue and the lymphoid tissue. ( lliservc the line Hlire.s and liranehed cells which Tiridge across this channel. IMake a. geni'nil sketch under a low jiower of i,, portion of the cortex together with the ailjoining part of the mechilla, and under a high |iower drawings of small portions of coiicN and meihdla. TIk^ retifiu'iii tissue of the lymph-glands has already lieen studied (pp. 89 to y] ). 1. Sections of a haemal lymph-gland. ^Fhese may he readily found in the neek of (he o.x, in the neighlioiirliood of tin: large lilood-\esse|s. Stain with luematoxylin and eosin or with alcoholic eosin and methylene-lilue. Notice that the channels around the Iviiijihoid nodules lor only some of them) contain lilood instead of lymph. 3. Sections of the s|ileeii liardeueil in Miiller's fluid or formol and stained with alcoholic eosin and methylenc-bliie or lueniatoxylin. Notice the traViecuhe e.xtemling into the snlistanci' of the organ from the cap.sule. Notice also that the glandular sulistauce is of two kinds, (1) lymphoid ttesue accunudated around the small arto'ies and here and there mas.sed to form lifinphoid nodiili'.i — the Malpighian corpuscles and (2) a. tissue — the red pulp — consisting;- of a retic-ulum of lilirils and liranchiug cells : tliis tissue cmtains lih.iod in its inlerstii'es. (Sketch ]iart of a section under a, low power and a small portion of the pul|i under a higli power. 4. In sec-tions of tonsil |.ire|iaied similarly to tlio.se of the lyiuph-gland, notice the large amount of lym|ihoid tissue, partly collected into nodules. Observe also that the stiatitied epithelium, which covers the mucous memhrane here as elsewhere ill the mouth, is inliltiated with lyni]ih-corpiiscle.s. The tonsil is lieset with pit- like recesses, ^\'ith mucus-secreting .glands opening into the ]">its. T). Lymphoid nodules of mucous membranes. In other mucou.s membranes besides tliat of the back of the mouth and pharynx, collections of lymphoid tissue occur which resemble those of the tonsils; such uodides form the solitary glands of the stomach and intestines and the agminated glands of the small intestine, and are also found in the trachea and bromliial tubes ami in the ieso]ihagus. They will be stiidii'd lati'r in sections of those, parts. (I. Sections of the thymus gland of an infant or young animal. Notice that the massea uf lymphoid {i) tissue which form the lobules of the ffland are separated by septa of connective tissue, and that the lobules show a distinction into two parts, cortex and medulla. There are no lymph-paths within the lobules. Observe the diffeienoes of structure of the cortex and medulla, and especially notice the concentric corpuscles in the medulla. Make a sketch of one of the lobules under a low power and of a small part of the medulla under' a high power, including one or two concentric corpuscles. Measure the latter. L YMPH-GLANDS 233 LVMPir-GLANDS. Structure of a lymph-gland. — A lymph-gland (lymphatic gland) is com- posed of a framework of fibrous and plain muscular tissue, which encloses and supports the proper glandular substance, but is everywhere separated from it by a sinus-like channel, bridged across by cells and fibres, which is known as the lymph-channel. The framework consists of an envelope or capsule of fibrous tissue (fig. 326, 0), and of irab^oulm (tr), composed of the same tissue, which pass at intervals inwards from the capsule, and after traversing the cortex of the gland, divide and reunite with one another to form a network of fibrous bands. At one part of the gland there is usually a.l. Fig. 326. — Diagkam of a section of lymph-gland. (Sharpey. ) , afferent, e.L, efferent lymphatics ; C, nodules of cortical substance ; M, reticulating cords of medullary substance; l.h,, lymphoid tissue; I.e., lymph-sihus ; c, capsule sending trabeculBC, tr, into the substance of the gland. a depression (hilus), and at the bottom of this the medulla comes to the surface and its fibrous bands are continuous witlj the capsule. Both capsule and trabeculse contain plain muscular tissue. The proper glandular substance (l.h.) is composed of a fine reticulum with the meshes thickly occupied by lymph-corpuscles (lymphoid or adenoid tissue). It occupies all the interstices of the gland, forming comparatively large rounded masses in the cortex (lymphoid nodules, C), which may be two or three deep, and smaller reticulating cord-like masses (lymphoid cords, M) in the medulla. The lymph-channel is bridged across by fibres derived from the capsule and trabeculas, which pass to the lymphoid tissue and merge into its 234 THE ESSENTIALS OF HISTOLOGY reticiiliii-n (figs. 327, 32^), The fibres are often largely ooncealed by branch- ing Cells, wliieh wcie indeed at une time thought to constitute the leticuluni. Tn some animals ('.!i-^imis : ?',/>, i raln^iMil:!- ; (7, r/, (-■at>illar\ liIorn|.\e^seI-i. glands at the root of the lung to contain carlxm particles -which have been inhaled in the form of soot. The branched cells which cover the reticulum are continued over the trabeculic, and at the entrance and exit of thr lymphatics are continuous with the endothelium cells of these vessels. They represent therefore a lymphatic endothelium bounding the lymph-spaces, but like the corresponding endothelium of the small veins of the spleen the}- have become branclied and form part of the supporting reticulum of the- organ. The phagocytic function of the branched cells of the medulla is shared by certain large cells which are sometimes foimd lying loose in the lymph channel and are probably derived from the branched cells. These cells resemble the large phago.cytes found in the pulp of the spleen. Giant-cells with lobed or multiple nuclei are also occasionally seen. LYMPH-GLANDS 235 Afferent lymph-vessels (fig, .'^26, a.?.) enter the lymph-sinuses of the cortex after ramifying in the capsule, and the lymph is conveyed slowly along the channels of the cortical and medullary part towards the hilus, taking up lymph-corpuscles in its passage. At the hilus it is gathered up by an efferent vessel or vessels («.Z.) taking -origin in the lymph-sinuses of the medulla. The out-going lymphatics always contain many more lymph-corpuscles than those which enter the gland, for lymph-corpuscles are constantly being Fi«. .328. — Section of medulla of lymph-gland of dog showing reticular TISSUE IN THE LYMPH-CHANNEL EXTENDING BETWEEN THE LYMPHOID CORDS AND TRABECULE-;. Magnified 200 diameters. (From », preparation by M. Heidenhain. ) formed by karyokinetio div.ision of the pre-existing cells in the glandular substance, especially in the centre of each cortical nodule (^germ-centre of Flemming) ; they gradually find their way through the close reticulum of the lymphoid tissue into the lymph-channels. The leucocytes of the germ-centres frequently ,^how, in sections, peculiar darkly coloured bodies — the stainahle bodies of Flemming — the nature of which has not been determined. ^An artery passes into each gland at the hilus ; its branches are conveyed at first along the fibrous cords, but soon become surrounded by the lymphoid tissue, in which they break up into capillaries (fig. 327, d). The blood is returned by small veins, which are conducted along the fibrous trabeculse, joining to form large vessels which eventually emerge at the hilus. 236 THE ESSENTIALS OF HISTOLOGY Tn some lymph-glands tlii> filji'ous tvaljocul;r> aro vi^vy sliglitlv .'ht) ; .n, cortiiTal .•^inus ; t, traliecula^; '■, \eiit; /, effi-fem l\ niph.\esst?ls, ai'conip.anyinp and |)artl>- surrouridin^r l)]on(l-\e«sol.s. hi. Nerve-fibres pass to lymph-glands : they appear to be distributed chiefl}- as nonmyelinated fibres to the plain mu.scular tissue of the blood-vessels and trabeoula-. Haemal lymph glands. — Tn many animals a certain number of lymph- glands are observable which have a red colour. Some of these on section show that what corresponds to the peripheral lymph-chauuel iu ordiuary lymph-glands is in them occupied by blood. Others have the greater part of the interior occupied by large sinuses filled with blood ; while other parts show the ordinary structure of a lymph-gland. The names hwinal glands and ha'mal lymph-glands (Robertson) have been given respectively to these structures. The blood passes into the sinuses from arterial capillaries, which • i HAEMAL GLANDS 237 Fig. 330. — Section or a lUiMAL lymph-gland. A, niagniiied 50 diameters ; B, magnified 350 diameters. c, capsule with plain inuscle-fihres ; ()•, fine trabecule passing in' from capsule ; hi, blood-sinuKes full of blood-corpuscles ; other red corpuscles are seen in the interstices of the lymphoid tissue, It ; ly, lymph-sinuses ; eo, eosinophil-cells amongst the lymphdcytes of the lymphoid tissue. 238 THE ESSENTIALS OF HISTOLOGY appear, as in the s|j]een, tu o|ien into fclic tissue interstices, from which at othoi' parts small veins arise in like manner. Like the spleen these htemal Ljlands siiow nunierous large phagocytes which contain reil blood i;orpuscles in \arioiis stages of transformation into pigment. iSome h.'Bmal glands are said to have )io lymph-channels, hut to Ije purely blood-glands: in that case tliey may be considered to represent acces8*)ry spleens. ()riliiinrv l\i]ipli-_ul;nids ;in' i/cuiKned tn iiianiiiials, but V'iiK-ent and llai'i'isiin lia\ f t'lund liajiiial 1} uipli-glauds in bird.s. 'I'l" ml" K- ' &'■ .-■■■.* ;■ ' - ' '' ' ^ ..-*», > , « -W Yi^^i^L^^ FlO. 331. — SeCTIii.S UK SI'LEEN, SOMEWHAT MAGNIFIED. (G. Mann.) The .section was btaiTje'l, and the Malpighian coflHlseles therefoie appear darker than (he pull>. whereas, in the fi-esli spleen, the.f are g:re,\ish white in a red^pulp. Tlie \enony ^innse- sliow av elear spaces. T)ie larger \ eins are contained in tile I ratieenliv. THE Sl'LEEN. The spleen is the largest of the so-called ductless glands. It appears to be functionally connected with the blood, white blood-corpuscles beinu' formed and coloured blood-corpuscles being submitteil to destruction within it. Like the lymph-glands, the spleen is invested ^^■ith a hbrous and muscular capsule (fig. 332), which is, however, stronger a,ud has far more plain muscular tissue than that of the lymph-glands ; outside the capsule is a covering derived from the peritoneum. The capsule sends bands or trabeoulae into the organ ; these join with a network of similar trabeculae which pass into the gland at the hilus along with the blood-vessels. In the interstices of the framework thus constituted lies a soft pulpy substance THE SPLEEN 239 containing a large amount of blood, and therefore of a deep red colour, dotted within which are here and there to be seen small round bodies, whiter than the pulp in the fresh organ but darker in stained sections, the Malpighian corpuscles. These are composed of lymphoid tissue gathered up into globular or cylindrical masses enveloping the smaller arteries, whilst the red pulp surrounding them, which forms the .bulk of the organ, is composed (Oarlier) of a close network of connective-tissue fibrils (fig. 333), partly covered by flattened and branched cells (figs. 334, 335). -^^• '^ ■» -J*,-" re \\ .'..-"Si Fig. 332. — Vertical section of a portion of the monkey's spleen, as seen with a low power. Part of the capsule, two trabeculse and two Malpighian corpuscles are represented. Passing into the pulp and communicating with its interstices are capillary blood-vessels which are connected with the terminations of the arteries ; whilst in other parts venous channels — characterised in the \ human, spleen by an encirclement of retioulum-fibres (fig. 335), and by the presence of a layer of highly characteristic, comparatively thick and prominent endo- thelium-cells — course through the pulp and bring the blood which has passed into its interstices from the arterial capillaries towards the larger veins of the organ, which run in the trabeculse and are by them conducted to the hilus. The arteries, which are also at first conducted from the hilus along the trabecules into the interior of the organ, presently leave the 240 THE ESSENTIALS OF HISTOLOGY Frc. 833. — Keticuh'm of splekx, (iolci wetikhp. Low power, {(ijipel.) t(. Mal]ii;;hiari t:or]'u^c-le ; h, part of its reticutuiii ; .-. oondenyed rutiruluiii at ity niar;,'-ii] ; if, more open tissui- next to this:: e. wall of arteriole: f.f. cajiiJIarirs of .Malpi^'-hiaii corimsL-le ; ,'/. i-eLi''iiluTn of aiierinle e.\i)aiirli[i}.'- into tliat r.f the Slalpivjhian i:-orpnsi-le. '0 ^ cj^^^xf ■ ■ . ir^-^^^^i ■"' }t\ Fifj. 334. SiMAiA VEINS OF srj.Ki:N-i'M,r wixir retici'i.ak tissi'k : ulman High power. (Huycr.) The \i.'iiisJ, uliiL'li arc iii\ ustt'ii li.\ ciicircliii;,' litn-os, show t^ix^K in their ^Mills. whL-rcli.v tlu\\ connnuiiM-atf with the intursticcB of tht' pulp. THE SPLEEN 241 trabeculfe, and their external coat becomes gradually converted into a thick slieath of lymphoid tissue whicj:i invests them in the remainder of their course, and in places becomes swollen into the Malpighian corpuscles already mentioned. The small arteries distribute a few capillaries to the Malpighian Fio. 335. — Venous sinuses of splekn-pulp (monkey), showing the enciecling PIBBE^IN THEIE WALLS WHICH AEE DERIVKD FROM CELLS OF THE RETICULUM AND ARE ATTACHED TO LONGITUDINAL FIBRES WHICH BELONG TO THE ENDO- THELIUM or THE SINUSES. (S. Mollior. ) High power. corpuscles, and then break up into pencils of capillary vessels which open into the interstices of the pulp. The Malpighian corpuscles frequently but not always show a clearer central nodule or germ-oentre, characterised by the presence of numerous karyokinetic figures ; and the " stainable bodies " of Flemming, which have been noticed under lymph-glands, are also seen in their cells. The special cellular elements of the spleen-pjilp are of three kinds, viz., 16 242 THE ESSENTIALS OF HISTOLOGY (1) lai'se, amo'bdiil pliagcicytic Kp/e»M e^//s» (ftg. .T.IC;, r7), (2) ijv tut cell f (iv^. yil), (•"!) branched reticvhim cf/h which assist in forming the sponge- work (fig. '■)■»'>, '■). Tn additicjn to these the pulp contains all the corpuscular elements of blood. The phagocytic cells are frequently found to contain coloured blood-corpuscles in their interior in various stages of transformation into pigment. These cells occur both in the interstices of the pulp and iu the venous sinuses and \eins, where they are often full of erythrocytes < '■■! % $ I<'tC. ?,?,(i. — TlIlN SKCTTON or Sn.KHN-ITI.r (IF Cllll.n, nillllLV M.\i;NIFIKh, SHOW IXC THE MOIIF. OF OKICIX OF A S^^\l,^ \KIN IN THF INTFRSTIlKS (IF 'IIIF ITI.r. AragiiifieiJ 400 (]iaiii(=tcrs. a, lilood in jmlp ; a\ Iilooii in vt'iii ; h, iiiia;,'n(*\ te in \ cin : ■■, InMnrlu'il cell of imlp ; (/, |ili;i^oc>'tic siilenic cell. (lig. 3-H)). The giant-cells are most frequeut in young animals. The branched cells of the spongework are probably of the same nature as the endothelium-cells of the terminal capillaries and \eins of the pulp. They are connected by branches with one another and with the endothelium-cells o£ the vessels. The phagocytic spleen-cells are perhaps budded off from them. Nucleated coloured corpuscles are found in the embryo, and occasionally after birth, in the spleen-pulp. The blood .of the splenic vein is at all times relatively rich in leucocytes. THE SPLEEN 243 The lymphatics of the spleen run partly in the trabeculse and capsule, and partly in the lymphoid tissue ensheathing the arteries. They join to form larger vessels which emerge together at the hilus. There are no lymphatics in the spleen-pulp itself. The nerves, which are numerous and mostly non-myelinated, are dis- tributed to the muscular tissue of the arteries and to that in the capsule and trabeculse. Mall finds the distribution of the trabecute and of the blood-vessels within the spleen to indicate a differentiation of the pulp into divisions (spleen-lobules) each of which has its own arteriole and venule, and in which the pulp is arranged in columns or cords surrounded by venous spaces. It must, however, be understood thaA there is nothing of the nature of partitions separating such lobules ; to all appearance the pulp is in continuity throughout the organ. Fig. 337. — A multinucleated giant-oell from the SPLEEN of a kitten. Magnified 400 diameters. THE TONSILS AND OTHER LYMPHOID STKUCTUEES. The tonsils are two masses of lymphoid tissue placed one on each side of the pharynx, into which they project. They are covered on the free surface with the stratified epithelium of the m^ucous membrane, and this Burface is pitted with apertures which lead in^o recesses or crypts in the substance of the.organ (iig. 338). These recesses are all lined by a prolonga- tion of the stratified epithelium of the surface and into them the ducts of numerous small mucous glands open. The tonsils are composed of lymphoid tissue, which, besides being diffused over the whole organ, is at intervals aggregated into nodules, in which the lymph-cells are more closely arranged than elsewhere. In the clear centre {germ-centre) of these nodules active multiplication of the lymph-cells occurs and i§, in fact, the cause of the formation of such nodules ; as in the other organs (spleen, lymph-glands) in which lymphoid tissue occurs. The epithelium, which covers the tonsils is 244 THE ESSENTIALS OF HISTOLOGY iiifiltratefl witli lympli-corpu.selfM (figs. ■''i^-iS, JC^Q), many of whicli wander out on to tlie freo surface, and Ijcconie mingled with tlie saliva as salivary corpuscles. The lymplioid tissue of the tonsils has numerous Ijlood-vessels ; it also contains lymphatic \essels. The mucous memhrane of the neighbouring part of the phar3'nx, that of the hack of the tongue, and that of the upper part of the pharynx, near the orifices of the Eustachian tuhes and behind the; posterior nares, shows crypts ,»■ i i P 1, ■.^ s Fii:. 3.'iS.— SucTiiiN oFTONsn, ; titmaw Maniiiliod Til) (liaim-trvs. (Pli.ii.>L;'vay>hrtl fiuiii a pveparixtion In I'rof. M.^flridnilmin. ) fi, fi, )iiKln]c.s or ;;evni-i'eiiires ; h, a rci-rss liiieil lt\ siratitk'd cjiitlirliimi w iL-iii-of-yt.c^. OpiiOHitc b, a niaMs of lfucoM_\ ti'H w liicll ha\ o t^sc'ai>0(l into tin 1 i< inTmcatoil 1>\ ily of llu> rei-i".-i. and ]iiassos of lymphoid or adenoid tissue similar in structure to those of the tonsils. Lymphoid tissues occurs in various nthor jiarts of the body in addition to the lymph glands and tonsils, although it uury not, as in these structures, constitute the bulk of the organ. Thus it is found in many mucous membranes, such as those of the alimentary and the respiratory tracts, both in a diffuse form and also collected into nodular masses which are like the cortical nodules of a lymph-gland, and may, like these, be partially sur- rounded by a lymph-sinus.- In the intestine such nodules constitute the so-called solitary glands and Peyer's vatchcs. Tn the vermiform appendix LYMPHOID riSS.UE 24S the mucous membrane is thickly beset with similar nodules. The lymphatics of the mucous membrane form plexuses of sinus-like vessels which partly enclose tlie nodules (fig. 34U). In the spleen,, as we have seen, a large amount of lymphoid tissue is found ensheathing the smaller arteries, Fig. 339. — Bart, of a section or kaeeit's tonsil showikg isfiltkation THE epithelium BY LEUCOCTTES. Photograph. Moderately magnified. ^^^>' Fiu. 340. —Lymphatics or A Peyek's patch, injected with silvee nitrate. (Kolliker. ) Magnified 85 diameters. /", a- lymphoid nodule or follicle ; /', its base, resting upoTi the muscular coat, m ; svi, submucosa ; I, lymph-vessels ; s, sinus-like enlargement of lymph-vessel surrounding follicle. expanded here and there into the nodular masses known as Malpighian corpuscles. Lymphoid tissue also occurs in considerable amount in the serous membranes, especially in young animals; in the adult it is here largely replaced by adipose tissue. Development of lymphoid tissue. — Lymph-glands are developed in connexion with plexuses of lymph-vessels, an accumulation of retifoi'm tissue and lymph-cells 246 THE ESSENTIALS OF HISTOLOGY taking place, according to Klein, either exteinal tu and around the lymphatics (perilym/phatii- foniiatiiiii) ; or some of the lymphatics ;are dilated into a sinus or sinuses, and the foiniation of the lymphoid tissue occurs within it (I'lidnii/iiiplaitii; . foriiiatioii.) (fig. .341, A and B). When there is a development of lyniphoid tissue outside the lymphatic \ essels this may form a cou.siderable accumulation before tlie formation of lymph-paths apjjears within the tissue, Blood-ve.s.sels are eaily develdped amongst the hniphatic plexuses, and by the.se, according to (iulland, the first lymph-corpuscles of the lymphoid tissue are brought to the gland. The marginal sinus is ]jroduced by the fusion of a numtier of lymph -\es.sels which surruund the conjmencing acciimulatiun of lyfujjhoid tissue, while in the ■ situation of the futuie hilus other lymph-vessels grow into the glandular substance and form chaunels which subdivide it up into cords iand nodules iKliug). The blanched cells of the lymph-path are derived from the lymphatic endothelium. ; LYMPHOID NODn.ES FROM THE OMENTUM. (Klein.) riNK.\->'IO ! A, perilvmphati'.- nodule ; a, ]\niphatic: -•, its endothelium ; r, \\\\\\A-\-yo\-\m^>-]>^^: l>, accuinulation of lymjihoid tissue on one side of it : d, blood-capill.iries within this. B, eii(IoIyni])hati(.- nodule consisting of an enlar|^ed l.\ ni|>hatic \essel, '/. uitliin \vliiili is a oapidarx network, c, c, an arter.\", b, and a \ein, 0; f, I\niphoid' tissue witliin rlie 1,\ niphatie, its branched eells liein;; joined to and derived from the l\nii>hatie endothejinni, l\ The aiillary glands were fiuind by .Stiles to increase in number and size tiuring lactation, diminishing again after lactation has ceased! In the developing tonsils GuUand occasionally found nests of epithelial cells iletachcd frcun the surface e|jithelium, somewhat like those found permanently in the thymus. THYMUS. The thymus gland is an organ which normally in man is found in a fully developed condition only in the ftvtus and young child. It is composed of a number of lobules (fig. 342) varying in size, separated from one another by septa of connective tissue, along which the blood-vessels pass to and from the lobules. Each lobule shows plainly, when examined with a low power, a distinction into an outer cortical and an inner medullary portion. The cortical part of the lobule is imperfectly divided into nodules by trabeculsB of connective tissue. It is superficially similar in structure to the lymphoid tissue of the lymph-glands and tonsils, with which it also THE THYMUS 247 agrees in exhibiting numerous indications of mitotic cell-division, but without definite germ-centvea. Besides lymph-corpuscles it contains a number of peculiar granular cells. , The medulla is more open in its texture ; Fiij. 342. — Section of pakt of loeulk of TiirMUS of child. Photograph. Magnified 60 diameters. (J, cortex ; m, medulla ; &, &, blood-vessels in connective-tissue trabeculae. Fig. 343. — Medulla of thymus of a child. Photograph. Magnified 300 diameters. The small darkly stained cells are lymphocytes. The section includes two concentric corpuscles and some blood-vessels full of corpuscles. - 248 THE ESSENTIALS OF HISTOLOGY its reticulum is formed by l.irge, transparent, hrancherl cells (fig. 344), massed together in places and then resembling an ejiitlielium. The medulla contains fewer lyinph-eoipuscles than the roi'tex ; hence it has a clearer aspect, tjonnective-tissue fibres are not wliolly absent from it. Within the medulla, but nevei' in the cortex, are found peculiar concentrii.-ally laminated bodies (concenlric rorpusdes of llassal, figs. .'.Ji-^, 345_). These are "nests" of flattened epithelial-cells arranged concentrically around one or more central cells ; these last having often undergone a degenerative pro- cess. Sometimes the corpuscles are compoimd, two or three being grouped sV,_, ^^ '^ ■^^^ ■®' --■'"■ ■ ;:% 4g5 m^ :.^ ^&1S/; ..-.,&iP., ^^^^KT;, -.^j^^iSi •; '):J^' ^--^.';> t% ' ->iiM JSDl -:li VlO. .■-)44. -|SK(■TI^^ (IK MKIiri.LA III'- TII'i'M I'S, ,SMU\\ INl, lU;AN(HI-:it IKLI.S IdKMlM; V KETICUrUM WITH \ IKRT.MN MM1;K1; UK LVllKUUIli IKI.I.S 1> ITS MKSIIKS. (Hamniar.) together and similarly enclosed by flattened cells. They represent part .of the remains of an epithelial tube, which forms the thymus i-udiment of the early embryo and is derived from one of the branchial clefts. According to the observations of llammar the reticulum of the gland is also derived from this epithelium. Stohr lielicved the Ivuiphoid cells of the gland to have a similar origin, but there are good reasons for thinking that this is not the case. Nucleated red blood-corpuscles (erythroblasts), similar to those seen in red marrow, have been described in the thymus (J. SchafFer). Occasionally cysts lined by ciliated epithelium are found (fig. 345, c). In some animals isolated cross-striated muscle-cells are seen in the medulla. Multi- nucleated giant-cells have also been described in it (H. Watney). The lobules, their cortex especially, are abundantly supplied with capillary THE THYMUS 249 blood-vessels. In man the arteries penetrate to the junction of cortex and medulla, and then give off most of their capillaries radiating outwardly into the cortical nodules ; some vessels pass inwards to supply the .medulla. Veins pass away both from the surface of the lobules and to a less extent directly from the medulla. The mode of distribution of the lymphatics has not been definitely ascertained ; none are seen within the lobules. Never- theless, large lymphatic vessels, containing many lymphocytes, issue from 4^. ^' Jo Fl(i. 345. — A C'lJNCKNTRIC CORPOSULE OF THYMUS WITH I'AKT OF THE ADJOINING RETiciTLDM. (HaMimar. ) c, a small ciliated u\ st. the interstitial connective tissue of the organ, but in what way they are related to the lobules has not been ascertained. The medullary substance is continuous throughout the gland, adjacent lobules being interconnected by their medulla. In the human subject the thymus gland undergoes after childhood a process of retrogression, its lobules ceasing to grow and becoming sur- rounded and concealed by a quantity of adipose tissue which develops in the interstitial connective tissue of the gland. Eventually the lobules atrophy, so that in advanced age very little of the gland remains. In exceptional cases this retrogressive or involution process does not occur. In these subjects there is usually also a more pronounced development of the lymphoid tissue of the body generally; the. condition is denoted by the expression status lymphaticus. 250 THE ESSENTIALS OF RISTOLOGY LESSON XXIII. SUPRARENAL CAPSULES, THYROID, PARA- THYROIDS, PITUITARY, AND PINEAL. I. iSki";'iux.s arross a supiui'enal capsule hardened iii,()'5 per cent, chromic acid «iiliitioii. In sections of such a gland, not otherwise stained, notice the deep brown coloration of the medulla (action of chromic acid on adrenalin). Other .seclions may be .stained with eosin and l]:cmatoxylin or by the iron-hfematoxyliii method. Notice the genera) arrangement and extent of the cortical and medullary paits of the organ, and make a general .sketch under a low ]X)wer. After- wards sketch carefullV under a liigh power a grr^up of cells from each part oi^ the organ. 2, Cramer'-s ineth\ smiiniit. of ),i(]iii.'v. THE SUPRARENAL CA]'BULES. The suprarenal capsules (adrenals) and the other organs enumerated above belong to the class of bodies known as internally secreting or endo- crine glands. A section through the fresh suprarenal (fig, 316) shows a THE SUPRARENALS 251 cortex which is striated vertically to the surface, of a yellowish colour, and a medulla which is soft and highly vascular, of a dark red colour. The whole organ is invested by a fibrous capsule which sends septa inwards through the cortical substance (fig. 347, a), subdividing this for the most part into columnar groups of cells {zona fasciculata, c). Immediately under- neath the capsule, however, the groups are more rounded, and the cells tend Fio. 347. — Vertical section of cortex of strpKAKisNAL or dog. (]5uhm and V. Davidoffi) Magnified about 150 diameters. / «, fibrous capsule ; b, zona glomerulosa ; c, zona fasciculata ; d, zona reticularis. to assume a columnar form {zona glomerulosa, h), whilst next to the medulla they have a reticular arrangement {zona reticularis, d). The cells which form the cortical substance are, for the most part, polyhedral in form; each contains a clear round nucleus, and numerous yellowish lipoid globules in the protoplasm. No arteries and veins penetrate between the cells; but the blood-vessels of the cortex run in the fibrous septa between the cell - columns, which they surround with a capillary 252 THE ESSENTIALS OF HISTOLOGY notwoik. In the zona retitiularis tbe capillaiies' widen out and occupy sinus- like .spaces Ijctween the celhculumns (fig. 347, AKIS AMI MEDUU..A. Magnified 150 diameters. THE SUPRARENALS 253 the septa above mentioned and communicate with fine canaliculi between the cells of the cortex. Deposits of yellow granules may sometimes be seen in the connective tissue of the cortex : their Significance is unknown. The cells of the medulla (figs. 348, 349) are more irregularly disposed than those of the cortex. They are supported by a network of elastic fibres. They lie in very -close relation to the large capillary blood-spaces (sinusoids) which pervade the medulla, and they probably pour a secretion directly into the blood. Their protoplasm is granular; in some animals it contains a brownish pigment, but in man the dark red colour of the medulla in the fresh gland is due to the blood contained in the large sinusoid spaces by Fin. 350. — Section of PABAOANur.tON from a nkw-born riiiLD. (Zuckerkandl. ) which it is pervaded, which receive the blood after it has traversed the capillaries of the cortex. A few arterioles pass straight to the medulla through the cortex. One large vein usually passes out at the hilus in the anterior surface of the gland. Investing the larger veins are longitudinal bundles of plain muscular fibres; but many of the veins have only an endothelium. Numerous nerves, after traversing the cortical substance, are distributed throughout the medulla, where they form a close plexus provided here and there with ganglion-cells. The cells of the medulla are characterised by staining brown by chromic acid and its salts, provided the organ is fresh (chromaph.il or chromajjlrt reaction). A similar staining is found to occur in some of the cells of small glandular bodies {chromapMl bodies, paraganglia) (fig. 350) which occur irregularly at the back of the abdomen, being especially frequent near the lower end of the aorta. A certain number of such cells 254 THE ESSENTIALS OF HISTOLOGY are also found in syiiipalJietic gaiii^lia (Kolin). This cbroiiiaphil reaction depends on tlie pre.seni/e of adrenalin in the cells where it occurs. Development. 'I'lit- infilnlla, nf tin- .supiaiBHal is (levi-lopcd fi oiii cells wbii;li )ifix>iiie detached fidiii tlie nidinients nf the sjuipathetic ganglia, and are therefni'e of iieuro-ertddeiiiial origin. The i.'ort.e.x ts developed from mesodei'ni. CAROTIII ANII I'OCX'VliEAL (ILANDS. These are minute glandular organs without -ducts, lying respectively at the bifurcation of the carotid artery and in front of the apex of the coccyx. 1 f^rm^. Fic. 351.— A I'l.iTMr on i F.i.t.-r.AT.i, from tuk cAROTTn ni,\Nr>, ismkitfo. (Schaper.) n.arlfl-iolp; p, venules ; e, simis.like capilLan witliiii nodule ; yK frroiiii ot .'laiid-rell, ■ ,■ bnnn.lnr\ nl iioilnle surrounded bi Ivinph si..i,>e ; ,/, inter.nodular eonneetive^issu,. of triaiid. They are composed of polyhedral cells (figs. 351 and .^ol'), with numerous blood-capillaries between them. In the carotid gland the cells are collected into spheroidal clumps, in the coccygeal gland into irregular nodules. The blood-vessels have a sinus-like character. Amongst the cells at least in the carotid gland, are some which stai^ dark brown with chromic acid like those of the medulla of the suprarenal capsules. THE THYKOID BODY. The thyroid body consists of a framework of connective tissue enclosing numerous spherical or oval vesicles (figs 353, 355) which are lined with cubical epithelium-cells ; these cells often contain granules of a fatty THE THYROID 255 character. The cavities of the veaicles are usually occupied by a peculiar viscid liquid (colloid). This is coagulated by alcohol and then becomes stained with dyes. The colloid of the thyroid is unique in the fact that it contains organically combined iodine. Colloid has been found in the lymphatics of the gland, and may sometimes be detected also in the interstices of the connective tissue. The amount of colloid accumulated in the vesicles at any one time varies considerably in different individuals ; the circumstances which influence its variations are not under- stood. There is frequently to be found in connexion with the thyroid and gener- ally embedded in its substance a small mass of tissue which resembles the thymus in structure, and, like it, contains concentric corpuscles. The blood-vessels of the thyroid are large and numerous in proportion to Flo. 353. — Section of thyroid of cat. Magnified 400 diameters. The vesicles are occupied by colloid, which has partly shrunk away from the epithelium. Some of the vesicles are cut tangentially and show only small sectors. the size of the organ. The capillaries form close plexuses round the vesicles (fig. 354), and even extend between the lining epithelium-cells. 256 THE ESSENTIALS OF HISTOLOGY In pndrmir- jroitre nilloid accinnnlntRF! in lieriiiiie j^neatly enlarged so that the gland fi llipre Is reason to believe that t}ie organ is in niie goiti'o on tlie other hand, where there is not accompanied by acc\inndation of colloid enlarged but become inegular in shape. In evidence of increase of activity, accompanied Development. — The thyroid is formed, 1 growth from the buccal epithelium which may with the month is severed, and the now lira into isolated vesicles. laT-ge qnaptity in the vesicles, whicli iiiiis a distinct tumour : ne\crtheless an inactive condition. In exuphthal- d.so enlargement of the organ, this i.s in tlie vesicles, which are not much this form of goitre the gland shows by arterial dilatation, ike an ordinary gland, b}' a solid ont- become.hollowed ; later, the connexion nched outgrowth becomes liroken up J'AI(A'J'in'i:01I)S. In close proximity to or embedded in the substance of the thyroid are always to be found four very small glandular organ.sof different structure from the thyroid proper (fig. 35."^). These bodies are formed of masses or columns of epithelium cells (fig. .3-56), some of which are much larger than the i-est and are iilled with oxyphil granules (Welsh). Numerous sinus-like blood -channels run Ijetween the columns and come into clo.se relationship with the cells. Here and there a vesicle filled with a material resembling colloid may be seen amongst the cells, and after removal of the thyroid it has been stated that the parathyroids undergo hypertrophy, and de- velop a vesicular structure like that of the thyroid, but this statement is doubtful. At any rate, in cases of mj'xoedema in the human subject, an aflfection characterised by atrophy of the thjjroid, no such hypertrophy of the parathyroid^ takes place. The colloid in the parathyroid, wdien it occurs, is not of the same chemical nature as that in the vesicles of the thyroid for it contains no iodine. Development. — The parathyroids are developed, liki> the thymus, as e|nthelial ri\itgio\vths from certain branchial clefts of the embryo : but they never become converted into lymphoid tissue and are solid from the first. They lose all connexion with the clefts from which they arise, but retain their epithelial structure, although becoming vascnlarised. Fic. .S.')4. Vessels of tiiv- K.rnn of ooi; tx.ieoted. THK ri'l'IHTAUY ROUY; The pituitary body {hypophysis cerebri) (fig. 357) is a small solid mass, in man about the size of the kernel of a nut, lying in the sella turcica, and connected ■with the third ventricle by the infundibulum. ' It consists partly of epithelium forrriing the pars anterior and pars intermedia, partly of nervous tissue, the pars nervosa. The epithelium is originally developed as a hollow protrusion THE PARATHYROIDS 257 ^o — Sr Ti N r rH\ir ir v pi \thii t \ : Macrnificd oU ditLmetctb. < if Fi Tlie \esicles of the thyroid are filled witli colloid. The parathyroid ifl patTly embedded in the thyroid. nil fjlfj^^^ I ^t^^:"^ > %^^-^ W'' , "^ '- ^M^^^^'^'s'i"^'^:'^ «? ■>,*■' *• «4*' *f 1. I (??t *«■ «■« ^^■•^' «ili v#'- #Sj sT- Fig. 356. — Section of human pakathyroid. Magnified 400 diameters. (Pliotographed from a preparation by M. Kojima. ) of the buccal epithelium. The nervous part is developed in connexion with another hollow outgrowth from the neural ectoderm. The epithelial part consiata at an early stage of a number of tubtfles, lined by epithelium and 258 THE ESSENTIALS OF HISTOLOGY united by connective tissue, but the lumen of the tubules has become obliterated in the adult, and their place is taken by solid cell-masses. Between the pars anterior and pars intermedia there is usually a cleft-like space containing glairy fluid. It is easy to separate the gland into two portions at this cleft : the posterior portion is tJhen composed of pars inter- media and pars nervosa. An extension of the epithelium portion of the gland over the. tuber cinereum, which is developed later than the rest, has been termed by Tilney pars tuheralis. The pwrs anterior is the largest and most vascular part of the organ. Its capillaries have a sinus-like character and occur in large numbers amongst the cells (fig. 359), many of which are set closely round the blood channels. Fig. 357. — Sagittal section through base o? brain and pituitary BODY OF OAT. Photograpli. (P. T. Herring.) Magnified. In photographs of injected preparations it appears almost black on account of the number of these vessels (fig. 358). The pars tuberalis is also very vascular. The cells of the pars anterior are of two kinds, clear and granular, varying in relative amount in different glands ; the variations being perhaps related to the functional condition of the organ. The granules are generally oxyphil, and stain with eosin, but there are many cells containing basiphil granules : the oxyphil cells become much larger and more numerous durin" pregnancy. Occasionally the cells of the pars anterior are set round closed vesicles containing colloid, but such vesicles are far more common in the pars intermedia. They are very conspicuous after thyroidectomy, and also in myxoedema (Hale- White). The pars intermedia is less vascular than the pars anterior, but more so than the pars nervosa, around which it extends in some animals {e.g. cat). Its cells which are clear, without obvious granules, are here and there set round colloid-containing vesicles (fig. 360). At the margins of THE PITUITARY 259 the cleft which separates them in the middle of the gland the junction between pars intermedia and pars anterior is not sharply defined. On the other hand the pars intermedia is well marked ofif from the pars nervosa, except in certain places. At those places its cells are continued into the pars nervosa,- either singly or in groups, and there undergo a peculiar degeneration resulting in the formation of hyaline or granular "colloid" substance, which when formed passes through the tissue of the pars nervosa (fig. 361), and is eventually set free in the extension of the third ventricle / WW^^i-^ Fig. .S58. — Base of brain and pituitaky of oat : injected. Photograph. (P. T. Herring.) Magnified, (t, chiasma ; &, pars tuberalis ; c, ventricle ; d, anterior lobe ; e, an extension of pars intermedia ; -/, posterior lobe (para intermedia and pars nervosa) separated from anterior lobe by cleft ; fif, artery entering posterior lobe ; A, vein leaving; it. which projects downwards into the neck of the organ (Herring). This colloid is increased after thyroidectomy, but is' not identical with that of the thyroid for it contains no iodine (Simpson and Hunter). It apparently becomes dissolved in the cerebro-spinal fluid, and under favourable cir- cumstances may be detected in that fluid by physiological tests. The fars nervosa of the pituitary body, in spite of its designation, contains in the adult no cells of distinctly nervous character, but is mainly formed of neuroglia elements and of ependyma fibres (fig. 361). It has far fewer blood-vessels than the epithelial parts. It receives a certain number of nerve-fibres which arise from large cells in the grey matter just behind 26o THE ESSENTIALS OF HISTOLOGY the optic chiasraa. Some of these fibres penetrate into the glandular substance of the pars intermedia and pars anterior. Between its elements Fig. 3i">9. — SEfTiox of paes aktkriok of pitditaky', hitman. Photograph. Magnified 300 diameters'. The blood-veRsels are seen iis liiyhter-lookinff channels bet\veen*the darkly-stained cell groujia. Fig, 360. — Sectiun of pituitary of i.vr passim: TiiKiiniit the intra- olandulak ci^eft, Magnified_200 diameteps. (Photographed from a preparation by M. Kojima, ) a, pars anterior with numerous large sinus-like capillaries (s».'cn as clear spaces) ; b, cleft ; c, pars intermedia allowing several vesicles (these are not always present) ; rf, pars nervosa. the hyaline and granular masses of colloid are seen on their way towards the infundibulum as just noted. , THE piruri'ARY 201 -a? •^^ .■sa* ^ ,& *T 4r -''^, k'^ •^'■^' e<-"" ^ .<.^^--. Uu,^!:r^:-'J — d Fig. 361. — Section of pahs hbbvosa of pitoixary of cat hear the neck of THE GLAND. (P. T. Herring.) • a, ependyma cells lining an extension ol the intundibulum into the gland ; b, hyaline masses of colloid within this extension ; c, ependyma fibres of pars n*evvosa d, e, hyaline and granular colloid passing between these fibres towards the infundibulifm. !, — Sagittal siction Of fineal of cat. Magnified 30 diameters. (Photographed from a preparation by M. Kojima.) 262 THE ESSENTIALS OF HISTOLOGY PINEAL GLAND. The pineal gland {epiphysis cerebri) (fig. 362) is developed as an invagina- tion from the roof of the third ventricle. In the adult it appears as a small reddish body, rounded or conical, attached by a short stalk just above the Fig. 363. — Section of pineai, of new-born child showing loosely arrangbd UJSLL-TRABECUL*; WITH LAKRE BLOOD-VESSELS BETWEEN THEM. The veSSels are full of blood-corpuacles which have come out dark in the photograph. Magnified 400 diameters. Fig. Se-l.— Section of ox pinkai, showing the cel[,s mdch diminished in kdmber WITH MUCH INTERCELLULAli TISSUE RESEMBLING NEUROGLIA. Magnified 300 diameters. (Photographed from a, ureparation \y E. Beard.) THE PINEAL 263 entrance of the aqueduct of Sylvius into the third ventricle and lying in the groove between the anterior pair of corpora quadrigemina. It is about half the size of the pituitary body. The structure of the pineal is best studied in the young subject, for as age advances its distinctive cells become less numerous. A number of calcareous nodules are then found within it, knov^cn as corpora, amylacea (brain sand) : these are, however, not special to the pineal but occur in the pia mater and its extensions in various parts of the nervous system. The gland shows in section masses or trabeculse of cells with large sinus- like blood-vessels between them (fig. 363) : whilst neuroglia cells and fibres are present in abundance in the intertrabecular tissue and also between the gland-cells. The cells are of two kinds. The majority hav6 oval nuclei and fine oxyphil granules ; in the remainder the nuclei are spherical and the granules basiphil. Cells with large oxyphil granules such as frequently occur in the pituitary are not seen in the pineal, nor are vesicles containing colloid observed. After puberty the gland undergoes retrogressive changes. These consist chiefly in diminution in number of the epithelial cells and increase in amount of the supporting connective tissue and neuroglia (fig. 364). 264 THE ESSENTIALS OF HISTOLOGY LESSONS XXIV. AND XXV. THE SKIN, 1. Sections of skin from the palmar surface of a finger. The skin is hardened in pieric acid or formol, followed by alcohol. The seotions are made vertically to the surface, and should extend down as. far as the subcutaneous tissue. Notice the layers of the epidermis and their different behaviour to staining fluids. Notice also the papillas projecting from the oorium into the epidermis and look for tactile corpuscles within them. In very thin parts of the sections the fine intercellular channels in the deeper parts of the epithelium (see Lesson VII.) may be seen with a high power. The convoluted tubes of the sweat glands are visible here and there in the deeper parts of the coriuni, and in thick sections the corkscrew-like channels by which the sweat is conducted through the epidermis may also be observed. Make a sketch showing the general structure under a low power, and Fig. 365. M d M" M' M dM" -Section of skin of heet,. (BlAschko.) ep, epidermis, showing ridfifes cut abross ; c, cutis vera ; d, d, ducts of sweat glands ; d', d', their openings at the surface of the papillary ridge ; M, Malpighian h\ i-r of epidermis thickened opposite the ridges, where it dips down into the cutis I'era (at M\ J/'i), leaving papillary prominences of the cutis between. other sketches to exhibit the most impoi'tant details under a high power. Measure the thickness of the epidermis and the length of the papillaB. 2. Sections of the skin of the scalp («) vertical to the surface and parallel' to the slope of the hair-follicles, and (h) parallel to the surfa'ce, and across the hair-follicles. Stain and mount in the same way as the last preparation. 3. Examine the structure of hairs from different pai'ts of the body, from different individuals, and, if possible, from different races. Compare with hairs of various domestic oi- other animals. The hairs may be mounted dry. 4. Vertical sections of the nail and nail-bed. To cut such hard structures as the nail it is best, after fixing with picric acid or formol followed by 75 per cent, alcohol, to soak the tissue in strong gum aiubic foi; a few days, then place it in an appropriate position upon a cork or upon the object carrier of a microtome, and plunge the whole into 70 per cent, alcohol. This renders the gum hard, and enables sections to be cut of sufficient fineness. A plane iron should be used with the microtome (Cathcart'.s), since the hardness of the nail will turn the ed^'e of a razor. To remove the gum the sections are placed in water for a few hours ; they may then be stained and mounted. Notice the ridges (not papill.T) of the corium. THE SKIN 265 yrojeuting into the epideiiiiis. Observe tlie distinction of the epidermis into Malpighian layer and nail proper. 5. Mount a section from a yjoi'tion of sl ^.^f Aft a- ■■'.'.' c'- ■ y ti*^- S' 'i- -mS ' r I. irele iiiucosuni. j cutis \ era. Fig. 367. — Vertical section thkough the skin of the palm.ib side of the finger, showini; two ob three papill.3i: and the deeper layers of the EPIDERMIS. Magnified about 200 diameters. One of the papillae contains a tactile corpuscle ; the others blood-vessels. The akin is composed of two parts, epidermis and ciitis vera (figs. 365, 366), The epidermis, or scarf skin, is a stratified epithelium (fig. 367). It is composed of a number of layers of cells, the deeper of which are soft and protoplasmic, and form the rete ■mucosum of M£(,lpighi, whilst the superficial layers are hard and horny, this horny portion sometimes constituting the greater part of the thickness of the epidermis. The deepest cells of the rete mucosum, which are Set on the surface of the cutis vera, are columnar in shape. In the coloured races of mankind these cells contain pigment granules. In the layers immediately above them the cells are polyhedral. THE SKIN 267 Between all these cells of the rete mucosum there are fine intercellular clefts separating the cells from one another, but bridged across by fibres which pass from cell to cell (fig. 368), and also through the substance of the cells (fig. 369) (Ranvier, Delepine). The intercellular channels serve for the passage of lymph; within them lymph-corpuscles may occasionally be found, having an irregularly stellate figure from becoming shaped to the interstices. The superficial layer of the rete mucosum is formed of somewhat flattened cells filled with granules or droplets of a material (eleidin) staining deeply Fig. 368. — Section (ir epidermis uf cat's fuot shuwini; intekcellulak CHANNELS, WITH EKIBMNO TIERILS. (KoloSSOW.) with carmine and hematoxylin. These cells form an irregular layer termed stratum granulosum (figs. 366, 367, 370, c). TMs is not sharply marked off from the rete mucosum next to it, for many of the cells of this show similar ■graniiles, although they less completely fill the cells. Superficial to the stratum granulosum is a layer in which the cell-outlines are indistinct and the cells contain flakes or larger droplets of a hyaline material (kerato- hyalin), staining less intensely than the granules in the last layer, and tending to run together (fig. 370, 6). This layer has a clear appearance in section, and is known as the stratum lucidujn. Immediately superficial to the stratum lucidum is the horny part (stratum corneum) of the epidermis. It is composed of a number of layers of epithelium-cells, the nuclei of which are no longer visible. These cells, near the surface, take the form of thin horny scales which eventually become detached (fig. 371, s). In certain 268 THE ESSENTIALS OF HISTOLOGY parts which have a thick epidermis and are not covered with hair (e.g. the palms and soles), the superficial part of the epidermis is a layer mainly formed # %:. I 1 ^ ^^ ■^l^ w^ y- -y '5i«» V 1 ~7 m Fig. 369. — Section through the deeper l.iverS' of a stratified EriTHELiuM, SHOWING FIBRILS, /, PASSING FROM CELL TO CELL ACROSS THE INTERCELLULAR SPACES. (Eanvier.) , Fig. 370. — Portion of ei'Idermis fjioh a suction of the skin of tub FINGER, COLOURED WITH PICROCARMINE. (Raiivior. ) (fc, stratum corneiim ; 6, stratum lucidum with HaUe.s of keratb-hyalin ; c, stratum ^ranulosum the cells filled with drops of eleidin ; ,d its matrix. Magnified aboub 10 diameters. a, root of nail ; b, Malpighian layer of matrix ; c, ridges in cutis of nail-bed ; d, epitrichial laj-er of epidennis ; e, eponyohium ; /, bone (terminal phalanx) of finger 272 THE ESSENTIALS OF HISTOLOGY glands, and the sweat glands. They are all developed as thickenings and downgrowths of the Malpighian layer of the epidermis. THE NAILS. The nails are thickenings of the deeper papt of the stratum comeum developed over a specially modified portion of the skin (fig. 374), which is known as the he.d of the nail, the depression at the posterior part of the nail- bed from which the root of the nail grows beirig known as the nail groov. The part of the bed occupying the proximal portion of the groove is termed Pig. .S75. — Teassversk section .4Ckoss nail takkn near one kdgr. Magnified 50 diameters. The apparent papillcB are really sections of ridges or laminre o( the cutis vera projecting into the Malpighian layer of the nail. the nail-matrix, since it is from this part that the growth of the nail proceeds. The distal part of the nail forms the free border, and is the thickest part of the body of the nail. The substance of the nail is composed of clear horny cells, somewhat like the cells of the stratum lucidum of the rest of the epidermis. Each contains the remains of a nucleus. The nail proper rests immediately upon a Malpighian layer similar to that found in the epidermis generally, but destitute of a dgfined stratum granulosum. Nevertheless, the more superficial cells of the lefee mucosum contain a large number of special granules ; these appear to represent those of the stratum granulosum of the epidermis, These granules are, however, not composed of eleidin, but of a material (onychogenic substance, Ranvier) which stains brown instead of red with carmine ; a similar material occurs in the cells THE NAILS 273 which form the fibrous substanae and cuticula of the hairs. The cutis of the nail-bed is beset with longitudinal ridges instead of the papillae which are present over the rest of the skin ; these ridges, like the rest of the superficial part of the cutis, are extremely vascular. Fig. 376. — Section through end or tingbk of hdhan eme'eyo at the time OE THE commencement OF FORMATION OE THE NAIL. (KoUiker.) Notice the ossification of the terminal phalanx beginning at the tip of the cartilage. In the thickened epidermis over this the commencing nail is seen as a dark line. The nail-bed also receives many nerve-fibres. The deeper of these end in Pacinian corpuscles, whilst others ramify in the ridges of the cutis, and some penetrate amongst the epithelium-cells of the Malpighian layer. '"'Jr^i'gr''^ "^ \ ?■ '■'"S'Ssfi'^ ?S,iW w>: ■:-■ ■ K;i3n;,^'dJ \:f.pfr:, .s-i,r.;Si, jiyA-Lir.; a\'D-\*^- Ssfefiiisiis'iisiife^iiis^ ='i_j _:J,,.J w Fig. 377.^Fiest appeakance of nail substance in the form of granules of onychogenic material in some op the cells covering the nail-bed. (KoUiker.) Development. — The nails show in the foetus at about the third month (fig. 376), a groove being formed at this time in the corium, and the nail rudiment appearing in it as a development of onychogenic substance in some of the cells of the epithelium which lies over the bed (fig. 377). It becomes free, in the sixth month, its free end being at first thin, but as it grows forward over the bed it receives additions on its under surface — at least in the posterior part of the bed — so that after a time the distal end becomes thicker. The epitrichial layer of the cuticle which originally covered the developing nail becomes detached aften the fifth* month, and, after 18 274 THE ESSENTIALS OF HISTOLOGY birth, only remains as the narrow border (jf free cuticle {eponychium) which overlies the root. HAIKS. The hairs are growths of the epidermis, developed in deep pits — the hair-follicles — which extend downwards into the thickness of the corium, or even into the subcutaneous tissue. The hair grows from the bottom of the follicle, the part which lies within the follicle being known as the root. ' The substance of a hair is mainly composed of a pigmented, horny,! fibrous material (fig. 378, /), which can be separated by the action of sul- phuric acid into long tapering fibrillated cells, the nuclei of which are still visible. The fibrous substance of the hair is covered by a layer of delicate imbricated scales, termed the hair cuticle (c). In many hairs, but not in all, the centre is occupied by an axial substance (medulla, to), formed of angular cells which contain granules of eleidin, and frequently have a dark appearance from the presence of minute air-bubbles. The latter may also occur in interstices in the fibrous substance. When air is present, the hair looks dark by transmitted, white by reflected light. The root has the same structure as the body of the hair, except at its deep extremity, which is enlarged to form the hair- bulb; this enlargement is composed mainly of soft, growing cells, and fits over a vascular papilla, which projects up into the bottom of the follicle (fig. 381). Structure of hair-follicle (figs. 379 to 382).— The follicle, like the skin itself, of which it is a recess, is composed of two parts : one epithelial, the other connective tissue. The epithelial or epidermic part of the follicle closely invests the hair-root, and is often in great part dragged out with it ; hence it is known as the root-sheath. It consists of an outer layer of soft columnar and polyhedral cells, like the Malpighian layer of the epidermis, but without stratum granulosum — the outer root-sheath ; and of an inner, thinner, horny stratum next to the hair — the inner root-sheath. The inner ropt-sheath itself consists of three layers, the outermost being composed of horny, fibrous, oblong cells the nuclei of which are obscure and difficult to make out (Senle's layer), the next of polyhedral nucleated cells containing elSidin (Huxley's layer), and the third — the cufiale of the root-sheath — a layer of downwardly imbricated scales, which fit over the upwardly imbricated scales of the hair itself. In the more superficial part of the hair-follicle the layers of Huxley and Henleare indistinguishable, the cells of bothbeing clear and keratinised; Fig. 378. — Piece of human hair. Magnified. A, seen from the aurface ; B. in optictil sectiou ; c, cuticle ; /, iibrous sub- stance ; «t, medulla, the air having been expelled by Canada balsam. THE HAIRS 275 even lower down where distinguishable they show a tendency to dovetail into one another. At the bottom of the follicle no differentiation into layers ^ It' 0] tl s c3 a,| -5 -+< -H if -2 tg i« &,"-§ S oT^ "3 *» —5 c3 I s i^ o «j CSi 02 ■^^iT f5 "■s .4 fl h p » _< s§ ■^ « a ?.| 3 m 'X, < rt IS S D e^ M f'S ta I- g o Izi -^ % o S o 3 & 3 .^ D H ■* & oc ,'6 1 '« ._ 1 .-d oi £* t- '5 '^ CO ^.S Sp 3 " £ f<"- can be made out in the root-sheath, which is here formed by a uniform mass of soft cells surrounding the papilla. In the greater extent of he follicle the outer root-sheath is several layei-s 276 THE ESSENTIALS OF HISTOLOGY deep; but as the bottom of the follicle is approached it becomes thinner, and is finally reduced to a single stratum of cells which, in the papillary part, becomes flattened out into a very thin layer (fig. 380, I.). The connective tissue or dermic part of the hair-follicle is composed II "■^51^^ "v hij ■,_». /■.>P' '.'-'".V-.. ,iaia,^:,,-i.^'--'-|iL"-^-*^--' Firi. 391. — Sectton op oKuuMiNons gland of the externat, ear. Photograph. f1, iluct of gland ; it has a spii-al course and is therefore ml several times ; it is partly filled with cerumen ; gl, secretingf tubules of gland ; a, extremity of a tubule of a sebaceous gland which extended as far as the base of the ceruminous gland. GLANDS OF THE SKIN 28s which begins within the gland and usually makes several convolutions before leaving the gland to traverse the cutis vera. The duct has an epithelium consisting of two or three layers of cells, within which is a well-marked cuticular lining, but there is no muscular layer. The passage through the epidermis has no proper wall, but is merely a channel excavated between the epithelium-cells. Very large sweat glands occur in the axilla. The sweat glands receive nerve-fibres, and each gland has a special cluster of capillary blood-vessels. The ceruminous glands of the ear (fig. 391) are modified sweat glands. The secretion is of a sebaceous nature, instead of being watery like that of the ordinary sweat glands. The ceruminous glands are closely associated with large sebaceous glands (fig. 392). Fia. 392. — Section siiowino the duct of a ceruminous gland AoooMi'ANiED BY THE SECBETING TUBULES OE LARGE SEBACEOUS QL.VNDS. Photograph. Development. — The sweat glands are developed, like the hairs, as down- growths of the Malpighian layer of the epidermis into the coiium. They are distinguishable from the hair-germs by the fact that the cells of the outermost layer are not columnar in shape, but spheroidal or polyhedral. The sweat-gland germs which are thus formed become eventually coiled up at their extremities and converted into hollow tubes. The muscular fibres of the tubes as well as the secreting epithelium-cells are ectodermic structures. THE MAMMARY GLANDS. The mammary glands are compound racemose glands which open by numei'ous ducts upon the apex of the nipple. The ducts are dilated into small reservoirs just before reaching the nipple (fig. 393). If traced back- wards, they are found to commence in groups pf saccular alveoli (fig. 394). 286 THE ESSENTIALS OF HISTOLOGY Fk;. 393. — A mammaky ulabd dissbctbu to show the ducts dilated into KESEBVOIKS BEFOKB OPENINl-i Ui'OB THE MIFFLE. ^A itH^S'"? I ('^ 11- (iif Fig. 407. — Mucous membrane op larVnx. (Merkel.) , g, a y:oblet-celI among^st the c-lliated C'liitheliiim-cella ; h, basement-membrane ; ly lymiihoirl tis;fluo ; r, elastic filires, eut across. 1(f, eolunuiar eiliated eiiithetiuni. Fic. 41U.— Section of fakt of \ iiuonchiai, tihe. Magnified '2110 diameu-rs. It, ciliated epithelium ; b, basement-membrane ; c, superfloiol. part of muedus membrane, with fine elastic fifwes ; d, deeper part with numerous coarser fibres ; e, plain muscle of broncliu.s • /, duct of gland passing througli mucous membrane. The section is slightly oblique. Lymphoid tissue is 'especially abundant in the mucous membrane of the ventricle of Morgagni (fig. 408, d). A large number of mucous glands open into this cavity amd into that of the sacculus which communicates with it. THE LUNGS 299 The cartilages of the trachea, as well as the thyroid, cricoid, and arytenoid cartilages of the larynx, are hyaline ; all these are liable to ossify as age advances. The epiglottis and the cartilages of Santorini and of Wrisberg' are composed of elastic flbro-cartilage. This is also the case with the uppermost part of the arytenoid and the tip of the vocal process of the same cartilage. THE LUNGS. The lungs are formed by the ramificatioiis of the hrmichial tubes and their terminal expansions ; these form groups or lobules of sacculated r>;is?^J:^^..^-LA:N Fig. 411. — Section of luns, dog, showing a moderate sized bbonchial tube WITH THE BRANCH OF THE PULMONARY ARTERY ACCOMPANYING IT. Photograph. Magnified 50 diameters. Some of the adja(?eT)t pulmonary tissue is included in the section, and presents a characteristic appearance. dilatations {air-sacs, infundibula), beset everywhere with small irregularly hemispherical bulgings, known as the pulmonary alveoli or air-cells. The bronchial tubes (figs. 409 to 413) are* lined (except the terminal bronchi) by ciliated epithelium resting on a basement-membrane. External to this is the corium of the mucous membrane, containing a large number of longitudinal elastic fibres and some lymphoid, tissue. Outside this again is a complete layer of plain muscular fibres encircling the tube. Next comes a loose fibrous layer in which, in the large and medium sized tubes (figs. 409, 412), small plates of cartilage are embedded. Mucous glands are also present in this tissue. 300 THE ESSENTIALS OF HISTOLOGY The extremities of the small bronchial tubes expand into respiratory bronchioles ; these give off as braaches the alveolar passages. The walls of both are beset with alveoli (fig. 414). The alveolar passages lead into irregularly spherical alveolated dilatations (atria) with which a number of blind and often funnel-shaped diverticula completely covered with alveoli communicate ; these are the infundihula or air-sacs (Waters). The arrange- Fig. 412. — Part or the section shown in the preceding riotrRE maonitied 200 DIAMKTEIJS. In the bronchial tube, the epithelium, the circular muscular fibres, parts of mucous glands and two small pieces of cartilage can be seen. The corrugations of the mucous membrane are caused by post-mortem oontraution of the circular muscle. ment of the parts, according to the investigations of W. S. Miller, is as follows (fig. 415): Two or more air-sacs, or grodps of alveoli, open from a common chamber [atrium), and three to six atria are connected with the ending of an alveolar passage. The latter lead out of the respiratory bronchioles, which are expanded continuations of the smallest bronchial tubes. The epithelium changes in character as we trace the small bronchi into the respiratory bronchioles ; from columnar and ciliated it becomes cubical and non-ciliated, and there are patches of the respiratory epithelium (see THE LUNGS 301 below) not only in the alveoli which occur scattered over the respiratory bronchioles but also elsewhere in the wall of the latter. The plain muscular tissue of the Small bronchi is continued as a distinct layer on the walls of the respiratory bronchioles, but not on those of the alveolar passages and atria, although some muscle-cells occur round the mouths of the atria and even of the alveoli. The alveoli are lined by large, irregular, flattened cells (fig. 416), which form an extremely delicate layer {Respiratory epithelium), separating the blood-capillaries from the air within the alveoli. Amongst the flattened cells are here and there groups of smaller and thicker (cubical) epitheliurji-cells. '4\ k ^,:- Hf--:-^, B:^.MtiiM^^^^.^$ *«&%. ■% Fig. 413. — Section of a small bronchial TUBEi and adjoining alveoli, RABBIT. X 300. Photograph. The tissue on the left is infiltrated with lymph (cedematous). The capillary network of the alveoli is very close, (fig. 417), and the capillary vessels of adjoining alveoli are in complete continuity, the vessels passing first to one side and then to the other of the septa which separate the adjacent alveoli. Outside the epithelium a thin layer of connective tissue (basement-membrane ?) forms the wall of each alveolus. Elastic fibres are numerous around the mouths of the alveoli ; a certain number course over the wall of each alveolus (fig. 418). Blood-vessels. — Branches of tlje pulmonary artery accompany the bronchial tubes to be distributed to the capillary networks upon the alveoli ; from these networks the blood is returned by the pulmonary veins. An arteriole runs with each terminal bronchiole, and, dividing into as many branches as there are atria (fig. 415), is distributed to the capillary networks 302 THE ESSENTIALS OF HISTOLOGY Fia. 414.— Gelatine casts from lung of young cat. Photographed by reflected LIGHT. Magnified 75 diameters. The figure shows (from left to right) ; (a) a respiratory bronchiole, its wall partly beset with alveoli ; {b) part of a terminal group of alveoli ; (c) two or three terminal groups of alveoli (infundibula or air-sacs), still connected with their common atrium. Fiti. 415.— Diagram of the ending of a broni jual tube. (W. S. Miller.) B, terminal bronchiole ; \, vestibule ; A, atrium ; S, air-sac of infundibulum ; C, air-cell or alveolus ; P, ending of pulmonary arteriole ; T, commencement of pulmonary venule. of all the aiv-cells with which the bronchiole is connected (Miller). From these networks one or two venules collect the blood, usually coursing (indepen- dently of the arteriole) on the outer border of the group of infundibula, and THE LUNGS 303 Fig. 416. — Section of pakt of cat's lung, stained with nitrate of SILVER. {Klein'. ) Highly magnified. Both the cubical and the large flattened cells of the alveoli are shown. In the middle is a section of a small bronchial tube, with a patch of cubical epithelium-cells at one side. Pio. 417- — Section or injected lung, human, including several CONTIGUOUS ALVEOLI. Magnified 300 diameters. Photograph. unite with other venules to form efferent veins. The venules of the super- ficial lobules are connected with a vascular network at the surface of the lun" underneath the pleura. This network is also supplied from the 304 THE ESSENTIALS OF HISTOLOGY bronchial arteries. The veins, pursuing a separate course through the tissue of the lung, join with others to form larger vessels which pass to the root of the lung. Branches from the bronchial arteries are distributed to the walls of the bronchial tubes, and to the connective tissue of the lung, including that of the pleura. Bronchial veins accompany the bronchial arteries to the larger tubes, but most of the blood brought to the lungs by the bronchial arteries is returned by the pulmonary veins. Connective tissue intervenes everywhere in small quantity between the infundibula (interstitial tissue), and forms a distinct layer, containing much. elastic tissue, covering the surface of the lung underneath the serous membrane (subserous tissue). In Hici. 418.- -Elastic fibres of Lnuij, stained with orcein. diameters. Photograph. Magnified 200 some animals (e.g. guinea-pig) the subserous layei* contains plain muscular tissue, which is especially developed near the lung-apex ; it has not been detected in man. The lympliatics of the lung accompany the bronchial tubes, the branches of the pulmonary artery, and the branches of the pulmonary vein ; they also form a network in the pleura. The atria and air-sacs have no lymphatics in their walls (Miller). The bronchial lymphatics are less super- ficial than the corresponding blood-vessels. The larger tubes have two plexuses ; one within, the other outside the cartilages. The smaller ha^■e only one set. The lymphatics of the bronchi are connected with those of the arteries and veins by lateral branches curving off at the divarications of the tubes ; at these points there ie usually ah* accumulation of lymphoid tissue. The larger arteries and veins have two accompanying lymphatics, THE LUNGS 305 the smaller only one, All the lymphatics tend towards the hilus, and enter lymphatic glands at the root of the lung. Those in the pleura have been said to communicate, by means of stomata between the epithelial-cells of. the serous membrane, with the cavity of the pleura ; this connexion is denied by Miller. The. lymphatics of the pleura are furnished with numerous valves. The pleura which covers the surface of the luns has the usual structure *■ — ._ f ^""^' " " T?^ 1, .,- -^^ -,'tt-^ 1 T-^ c'T- -^''- ''c : _' , " ' — ' ^c.-^ > ^' ^- J '. -.IB 1- '•* 1 c J ^ f-' f* 7 / t »*. . ♦».. ^ i-V^ / / S ^. -^ -. ^^' ^'J ( , r' J V" ^—'r . - - . ' k , '.*"^ ' i / ' "' x> \' Ht' _ * fe*^ fp . *^ .1 ^-^^v ' \4 •. ■• ' , . , J . - J ' 4^>/'j "*** . 4 " 1 J '^^ '"""^ ' C ' '^ ' ' ' _ -% / ^t* -r J mi 'l^ \ r 1'"^ V .' '''*"'' ^ » - ^ ^..»»» Fig, 419. — Section of developing lung (pig) showing the oland-like charactek OF the growing bronchial tubes and alveoli. (J. M. Flint.) Magnified 70 diameters. a, interstitial embryonic connective tissue ; b, bronchiaj tube ; c, alveoli ; I, lymph-clefts ; Py pleura. of a serous membrane (fig. 325, p: 2.31). As already mentioned, it is provided with a special network of blood-vessels, supplied partly from the pulmonary vessels of the superficial lobules, partly from the bronchial arteries. The lung is developed in the same manner as a secreting gland (fig. 419), to which, up to a certain period of formation, it bears a close resemblance. Its alveoli correspond with the secreting alveoli of a racemose gland, and the cells lining them are, prior to the introduction -of air, of some thickness and of protoplasmic nature. It is only after the organ li.is come into use for respiration that they acquire the thin, flattened appearance which moat of them pre.sent in the adult lung. 3o6 THE ESSENTIALS OF HISTOLOGY LESSON XXVIII. STRUCTURE AND DEVELOPMENT OF THE TEETH, 1 . Study first with the low power and afterwards with the high power a longi- tudinal section of a human tooth which has been prepared by grinding. It is better to purchase this specimen, for the process of preparation is difficult and FiQ. 420.— Vertical section op \ tooth in. situ. (Waldeyer.) c is placed in the pulp-oavity, opposite tlie cervix or necis ot tile tooth ; the part above is the crown, that below is the root (fang). 1, enamel with radial and concentric markinRs • • dentine with tubules and incremental lines ; 3, uement or crusta petrosa, with bone corpuscles • li, dental periosteum ; !>, bone of lower Jaw. ' THE TEETH 307 tedious without the aid of special apparatus. Examine carefully the enamel, the dentine, and the cement. The dark appearance of the dentinal tubules is due to 1' I Fi(i. 421. — Section of moi.ar tooth. (Sobotta. ) ■< 8. E, enamel ; D, dentine ; C, cement ; P, pulp-cavity. their containing air in the dried specimen. Mea.sure the diameter of the enamel prisms and of some of the dentinal tubules. Make sketches from each of the tissues, 3o8 THE ESSENTIALS OF HISTOLOGY 2. Section of a tooth in situ, which has been decalcified after fixation, and stained. In this section the mode of implantation of a tooth, as well as the structure of the pulp, can be made out. Make a general sketch under a low **■ **,* * Fig. 422.- -Cboss-seotion of boot of o.^nine tootii,, uctm.vn'. (Sobotta.) D, dentine ; O, its granular layer ; C, cement*; P, pulp-cavity. x25. power, and under a high power draw a small piece of the pulp showing the processes of the odontoblasts extending into the dentinal .tubules. Preparations with the soft parts in xitn can also be matle without decalcificjition. After fixation of the soft parts and staining of tissues in bulk the specimen is dehydrated with absolute alcohol and impregnated with xylol followed by Canada balsam. This is allowed to become hard, after which sections can be cut from it with a fine saw, and subsequently ground until transparent, when they are mounted in Canada balsam. This method needs special apparatus and skill. 3. The development of the teeth and the formation of their tissues are studied in sections made aoious the snout and lower jaw of fu'tal and young animals. Either the preparations are stained in bulk or the individual sections u\ay be stained, THE TEETH 309 STRUCTUKB OF THE TEETH.^ A tooth consists in man of three calcified tissues ; enamel, which is of epithelial origin, dentine, and cement or crusta petrosa. The dentine forms the main substance of a tooth, the enamel covers the crown, and the cement is a layer of bone which invests the root (figs. 420 to 422). Enamel is formed of elongated hexagonal prisms (flgs. 423, 424) often with rounded angles : they are set vertically, of with a slight curvature, upon the surface of the dentine. The prisms are separated by an inter-prismatic substance which is also calcified, and are connected with one another laterally by numerous bridges which pass across this substance (Leon Williams). They are marked at tolerably regular intervals with slight transverse shadings producing an indistinct cross - striated appearance (fig. 425); The cross - striation appears to be due to the manner in which the calcific matter has been deposited in successive layers and is often accentuated by slight varicosities upon the prisms. Sometimes coloured lines run through the enamel across the direction of its prisms. ' The enamel prisms have when first laid down a fibrous structure, but this becomes obscured after their calcification is complete, although it can occasionally be made out (fig. 425). The enamel of the fully formed tooth contains only an ex- tremely minut^ proportion of animal matter (C. Tomes, Lovatt Evans) ; practically it is wholly composed of earthy matter, chiefly phosphate of lime, with some carbonate. The enamel of unworn teeth is covered by a vepy thin membrane of a horny nature. This membrftne is perhaps the remains of the layer of cells which pro- duced the enamel. It is known aja ffasmyth's membrane or the cuticle of the enamel. Dentine is constituted of a hard dense substance like bone, but contain- ing no Haversian canals or lacunse. It is pierced everywhere by fine wavy or spirally coursing canaliculi {dentine tubules, fig. 426), radiating outwards from a central cavity which, during life, contains the pulp. The tubules branch at acute angles as they pass outwards ; the resulting tubules become gradually finer towards the periphery of thedentine. The main tubules give off along their whole course very numerous lateral branches which extend for ^ For detailed information on the subject of dental structure and development see J. Howard Mummery, "The Microscopic Anatomy of the Teeth," London, 1919. Fio. 423. — Section through the ENAMEL OE A TOOTH. Magnified 200 diameters. (Rauber. ) *, projection of dentine, showing some of its tubules ; b, penetrating into the enamel ; c, c, enamel fibres cut longi- tudinally ; d, d, prisms out trans- versely ; e, cuticle of the enamel. 3to THE ESSENTIALS OP H'lSTOLOGY a considerable distance in the dentine, and as they proceed become of almost immeasurable fineness (Mummery). To exhibit the finest ramuscles special methods of staining are required. A Fig. 424. — Enamel prisms. Magnified 350 diameters. (KoUiker. ) A, Fragments and single fibres of enamel, isolated by the action of hydrochloric acid. B, Surface of a small fragment of enamel, showing the hexagonal ends of the fibres. Fig. 425. — Section of en.^mel taken along the dikection of the prisms. Magnified about 900 diameters. {Photographed from a preparation by Leon Williams. ) The prisms show both a cross-striated appearance and longitudinal fibrillation. The tubules have a proper wall of their own*, which can be isolated by steeping a section of tooth in strong hydrochloric acid. In the living tooth they are occupied by protoplasmic fibres (Tomes' dentinal processes), pro- longed from the superficial cells (odontoblasts) of. the pulp. THE TEETH 3" The intertubular substance appears for the most part homogeneous, but it can be shown to have a fibrous structure (see p. 313). Indications of the fact that its calcareous matter was deposited in the form of globules can be seen in various parts. This is particularly the case in places where the globular deposit was imperfect ; the spaces (interglobular spaces) left between Fiu. 426. Fig. 427. Fig. 426. — Section of tang of tooth, PAB.UiBL with dentine tuuules. Magnified 300 diametei-s . (Waldeycr. ) It cement, with large bone laounce and indications of lamellsB ; S, granular layer of Purkinje (interglobular spaces) ; 3, dentine tubules. Fig. 427. — Section acjeoss dentine tobules. Magnified 300 diameters. (Fraenokel. ) a, cut across ; h, cut obliquely. the globules then produce the appearance of irregular cavities in sections of macerated tooth prepared by grinding and mounted dry. Under these con- ditions the cavities are occupied by air only, for the uncalcified animal matter has been destroyed in the process of maceration. Such interglobular spaces are most common near the surface of the dentine immediately within the crusta petrosa, where they give a granular effect to the section (granular layer, fig. 426, 2, and fig. 422, g). But they are also well seen in the course of certain lines or clefts seen traversing the dentine across the direction of the 312- THE ESSENTIALS OF HISTOLOGY Fig. 428. — A small portion or destine with interglobular spaces. Magnified 350 diameters. (Kolliker. ) d, portion of incremenUl line formed by the interglobular spaces, which are here filled up by the transparent mounting materia!. , , „ *,':■;;'■■• I -J ■■if Fig. 429.— Pbkpaeatio:s feom a decalci]?ied specimen of tooth stained by silver NITRATE AND PYRIDIN. (J. Ho\vard Mummery.) Magnified 600 diameters. p, pulp in which are seen many line neuro-fibrils. Moat of these are directed towards the dentine. At )• is the plexus of ■ Rasohkow whenoe fibrils are passing between the odontoblasts to the marginal plexus, tn \ some are traceable with the processes of the odontoblasts into the odontogenic «one, « ; d, calcified dentine ; b, 6, blood-vessels. THE TEETH 313 tubules {incremental lines, fig. 420, one such shown magnified in fig. 428), and such interglobular spaces, which are larger than those at the periphery of the dentine, may in the unmacerated tooth be seen to have the dentinal tubules passing through them. After decalcification the dentine can be separated into lamellse along these incremental lines. N Other lines, more numerous than the incremental lines, are sometimes seen I'unning across the dentine concentrically with its surface. These appear to have been produced by a physical cause, viz., the intermittent diffusion and deposition of calcareous substance in the animal matter formed by the odontoblasts. The animal njatter of dentine resembles bone and the connective tissues generally in having its ground-substance pervaded by fibres which yield gelatine on boiling. These fibres, which have been especially investigated by v. Ebner and Howard Mummery, are difficult of demonstration in the Fig. 430. — Pieparatiuii hy J. H. Mummery, .showing nerve-Jibrils passing into dentine. fully calcified dentine ; but in developing dentine and in dentine which is attacked by caries, they are more easily shown. They run for the most part parallel with the surface. The pulp (fig. 429) consists of a soft, souiewhat jelly-like, connective tissue containing branched cells, a network of blood-vessels most numerous near the dentine, lymph-vessels, and many nerve-fibres, for the most part myelinated but some non-myelinated, which pass into the pulp-cavity along with the blood-vessels by a minute canal at the apex of the fang. The superficial cells of the pulp form an almost, continuous layer, like an epithelium (fig. 429). They are known as odontoblasts, from having been concerned in the formation of the dentine, but, until calcification commences. 314 THE ESSENTIALS OF HISTOLOGY Fil;. 431. A. Section across the uppek jaw of a tietal sheep, 3 cm. long. (Waldeyer.) 1, common dental lamina dipping down into the nnicous membrane where it is half surrounded by a horseshoe-shaped more dense-looliing tissue, the ^erca of the dentine and dental sac ; J, palatine process of the maxilla. B, Section from rasTAL calf similar to that shown in A, mvi passing THKOUUH one OF THE SPECIAL DENTAL UERMS, HERE BECOMING FLASK- SHAPED. (Rose. ) a, epithelium of mouth, thickened at 6, above special dental germ ; c, papilla ; rf, special dental germ ; e, enamel epithelium ; /, dental sac, C AND D. Sections at later stages than A and B, the papilla havinc BECOME FORMED AND HAVINO BECOME PARTLY SURROUNDED BY THE EPI- THELIAL GERM. (Kolliker.) c, epithelium of gum, sketchedin outline ; /, neck of dental germ ; ./*, enamel organ ; e, ity deeper columnar ceUs ; e', projections into the corium ; p, papilla ; s, dental sac forming. In D, the dental germ {fp) of the corresponding permanent tooth is seen. they are not very diiferent in appearance from the other cells of the pulp, with which they appear to be connected by branched processes from their bases. At the side next the dentine they become, as it were, spun out into THE TEETH 315 the dentinal processes of Tomes, The nerve-fibres lose their myelin sheaths a short distance from the odontoblasts and the axis-cylinders form an inter- laceojent known as the plexus of Haschkow, near the bases of the odontoblasts ; from this plexus numerous fibrils pass between the odontoblasts and join another very fine plexus which lies between them and the dentine, the marginal plexus of Mummery. FrOm the nerves of the pulp fibrils pass to the dentine and, as Mummery has shown, enter the dentine tubules along with the processes of the odontoblasts (fig. 430) ; they pass along the tubules as excessively fine beaded fibrils, to end in arborisations at the surface of the dentine beneath the enamel and cement. Here and there a fibril may even pass a certain distance between the enamel prisms. Mummery has further described, in connexion with the plexus of Kaschkow, a layer close to the odontoblasts consisting of stellate cells, which he regards as sensory peripheral nerve-cells, and which, on the one hand, form synapses with branches of the nerve-fibres passing to the plexus in question, and on the other hand send fibres (axons) into the dentine tubules. It is, however, difficult to regard these as sensory cells and sensory nerves ; their mode of distribution, if they are really of a nervous nature, would seem to connect them rather with the autonomic nervous system. As age advances nodules of dentine may be formed in the interior of the pulp. Such nodules sometimes enclose blood-vessels, and^ thus give to this secondary dentine an appearance resembling bone. It has been on that account termed The crusta petrosa or' cement (figs. 422, 426) is a layer of lamellated bone which covers the dentine below the enamel. Except in situations where it is very thin it exhibits lacunae and canaliculi, but there are no Haversian canals in normal human teeth. It is covered with periosteum (dental periosteum), which also lines the socket. The fibrous bundles of this periosteum extend on the one side into the crusta petrosa, on the other into the bony wall, of the socket for the tooth, and thus serve to fix the tooth very securely. DEVELOPMENT OF THE TEETH. The development of the teeth has a gener,al similarity to that of the hairs. The first change w:hich foreshadows their development takes the form of a continuous thickening of the- epithelium along the line of the gum ; this thickening grows into the corium of the mucous membrane to form the com,mon denial germ or lamina (fig. 431, A). At regular intervals there is a further thickening and growth from the common germ into the tissue of the mucous imembrane, each of these special rudiments, which are ten in number, swelling out below into a flask-shaped mass of cells, the special dental germ (fig. 431, B) of a milk-tooth. The intermediate parts of the dental lamina long remain, forming a common epithelial strand uniting the several special dental germs to one another, and to the epithelium covering the gum (fig. 431, C, T>,/). A vascular pajoi^Zct is continued from the corium into .the bottom of each special germ (fig. 431, C, D, p) ; this papilla has the shape of the crown of the future tooth. Each special dental germ, with its 3i6 THE ESSENTIALS OF H'JSTOLOGY included papilla, presently becomesalmost entirely cut off from the epithelium of the mouth, and surrounded by a vascular membrane — the dental sac. The papilla becomes transformed into the dentine arid pulp of the future tooth, and the enamel is deposited upon its surface by the epithelial-cells of the dental germ. The root of the tooth, with its covering of cement, is formed at a later period, when the tooth is beginning to- grow up through the gum, by a gradual elongation of the base of the papilla. As shown first by O. Hertwig, and later by v. Brunn, there is a down-growth of epithelium either from the lower part of the enamel germ, or, rather, according to Mummery's observations, from other epithelial-cells, which lie outside the enamel organ and are probably of similar origin. This down-growth, which is termed the 'I J '^'^^^ e od e' SP'" IK \ "ttj.^ * Fii:. 4.32. — Sbution of a developing incisor tooth of a human embryo. (Rose.) The section also includes the tiERM of the adjacent tooth. UK, rtental papilla : 0(?, odontoblasts ; h, bone of jaw ; f, e\ outef and inner layers of enamel organ ; SP, enamel pulp; d./., dental furrow; .c, remains of common dental ^rm or lamina; n, neck or bridge of cells connecting this with the enamel organ ; m.e., mouth-epithelium ; c", enamel organ of adjacent tooth-germ ; ;■, reserve germ of permanent tooth. epithelial sheath, determines the form of the root and the formation of dentine in it, for it is always present where dentine is to be laid down. After completion of the dentine it becomes attenuated and broken up, and is evehtually for the most part absorbed. Formation of the enamel. — Before the enamel appears, the dental germ undergoes a peculiar transformation of its previbusly polyhedral epithelium- cells into four layers of modified cells (fig. 432). The itinermost is a layer of columnar cells (amelohlasts or adamantohldsts (fig. 433, a), internal epithelium), immediately covering the surface of the dentine. The amelohlasts form the enamel prisms : the latter are preceded by a fibrous formation (fig. 434,/) followed by a deposition of calcareous salts in the form of small globules. Such globules are always formed when lime salts are deposited TOO TH-DE VEL0PM.EN7 317 in colloidal solutions (Rainy, Harting), These changes take place altogether external to the formative cells or ameloblasts ; indeed according to some there is a fine homogeneous membrane between the ameloblasts and the forming enamel. This, if present, is probably of the nature of an "osmotic membrane '' : it is termed by L. Williams the inner ameloblastic membrane (membrana preformativa of Huxley). But processes from the ameloblasts Fio, 433. Fig. 434. Fig. 433. — Section showing the structure of the part or the enamel ORGAN WHICH LIES NEXT TO THE DENTINE. (RoSe. ) d, dentine ; e, newly formed enamel stained black by osmic acid ; T, Tomes' processes from the ameloblasts, a ; 8tr. int., stratum intermedium of enamel organ ; p, branched cells of enamel pulp. Fig. 434. — Developing enamel showing ameloblasts and the eibrods substance produced by these cells, which eorms the basis oe the enamel prisms. (Leon Williams.) a, portions of the ameloblasts ; /, fibrous basis of enamel prisms ; p, calcified part of enamel. appear to penetrate this membrane and to be attached to the forming enamel- prisms (Tomes^ enamel processes, fig. 433, T). These processes are fibrillated. The outermost cells form a single layer of cubical or polyhedral epithelium (external epithelium,) (fig. 432, e). All the other cells of the dental germ become transformed into branching corpuscles (fig. 432, SF ; fig. 433, p) inter-communicating by their processes, and thus forming a network. But between the ameloblasts and the reticulum of branched cells of the so-called enamel pulp is a stratum of polyhedral cells (stratum, inter- ■ medium). Both these and the cells of the external epithelium merge into the reticulum, which seems to be formed by a modification of them ; or rather of a mass of cells representing a second or outer, stratum of the enamel germ as distinguished from the stratum which develops into ameloblasts. When calcification is about to begin the ameloblasts become separated from the stratum intermedium by another fine homogeneous membrane, the outer ameloblastic membrane of L. Williams. The whole dental epithelial germ, 3i8 THE ESSENTIALS OF HISTOLOGY thus modified, is known as the enamel organ. The reticulum disappears in the later stages of enamel formation. The enamel organ contains no blood-vessels, although they are richly distributed in the developing connective tissue covering it. Fiii. 435. — Part of a .section of developino tootit of pio. (v. Korff.) a, araeloblasts ; (7, fibres of the first, formed layer of dentine ; od, odontoblasts ; p, pulp. The fibres of the pulp are seen to be in continuity with' those which enter into the formation of the dentine. Fic. 436. — Pakt op skction or developing TooTk op youno rat, showino THE MODE OP DEPOSITION OP THE DENTINE. Highly magnified. It, outer layer of fully calcified dentine ; li, uncalcifled matrix,»wiUi a tew nodules of calcareous matter ; e, odontoblasts with processes extending into the dentine ; rf, p\ilp. The section is stained, the uncalcifled matrix being coloured, but not the calcified part. Formation of the dentine. — This is formed by calcification at the surface of the papilla. There is here found a well-marked layer of odontoblasts (fig. 435, od ; fig. 436, c). These produce a layer of fibrillated dentinal matrix which forms a sort of cap to the papilla, and soon becomes calcified by the deposition of globules of calcareous matter. Processes of the odonto- TOOTH-DE VELOPMENT 319 blasts remain in the dentine as it is forming ; in this way the dentine tubules originate. Most of their finer branches are formed later, as in the case of the canaliculi of bone, no doubt by an extension of their proto- plasmic contents. Such extension may even penetrate between the enamel- prisms. In marsupials this occurs to an unusual extent, giving it the appearance of being pervaded by tubules (Mummery). Subsequently a second layer of dentine is formed within the first by a repetition of the same process (fig. 436), and others succeed this so that the papilla gradually becomes calcified. A part, however, remains unaltered in the centre of the tooth, and with its covering of odontoblasts forms the pulp. The ten milk-teeth are produced in each jaw in the manner described. These, however, become lost within a few years after birth, and are replaced by permanent teeth in much the same way that a new succession of hairs occurs. A small outgrowth takes place at an early period from the dental germ close to each of the milk-teeth (fig. 431, D, fy) ; this eventually becomes the germ of the corresponding permanent tooth. It gradually enlarges, acquires a papilla, forms an enamel organ : in short, passes through the same phases of development as the germ of the milk-tooth ; and when the milk tooth drops out of the jaw in consequence of the absorption of its roots (by osteoclasts) the permanent tooth grows up into its place. There are six permanent teeth in each jaw which do not succeed milk- teeth ; these are the permanent molars. They are developed from an extension backwards on each side of the jaw of the original epithelial thickening or common dental germ and by the down-growth from this into the corium of three successive special germs at comparatively long intervals of time. From these special germs the tissues df the permanent molars be- come formed in a manner exactly similar to that in which the milk-teeth are developed. 320 THE ESSENTIALS OF HISTOLOGY LESSON XXIX. THE TONGUE AND THE GUSTATORY ORGANS. THE MUCOUS MEMBRANE OF THE MOUTH. THE PHARYNX AND (ESOPHAGUS. 1. Sections of the tongue (man, monkey) vertical to the surface, stained with haematoxylin and eosin. The sections should be taken from different parts and include all three kinds of papillae. 2. Sections of injected tongue. .3. Sections of the papilla foliata of the rabbit, stained with hiematoxylin and eosin : these show taste-buds in nitn. The cells composing the taste-buds are studied by teasing osmic pieparationa of the papilla foliata. The nerve endings ai'e seen in sections of papillae foliatae which have been treated by Ciolgi's osmic-bichromate-silver method (see Appendix). 4. Sections of the pharynx and of the n'sophagns stained with hfematoxylin and eosiii. THE TONGUE. The tongue is mainly composed of cross-striated muscular fibres, running some longitudinally, others transversely. It is covered by a mucous membrane ; the epithelium, like that of the rest of the mouth, is stratified, and conceals microscopic papillae (fig. 437) like those of the skin. Besides these microscopic projections, the upper surface of the organ is covered with large papillae, which give it a rough appearance. They are termed the lingual papillce, and are of three kinds ; (1) About twelve or thirteen comparatively large circular projections, each of which is surrounded by a narrow groove (fossa), external to which the mucous membrane is raised above the general level (vallum). These papillse lie in a V-shaped line with the apex of the V towards the back of the tongue ; they receive filaments of the glosso- pharyngeal nerve, and have taste-buds in the epithelium which covers their .sides, and (in man but ndt in most mammals) in that of the side of the vallum. They are known as the circumvallate papillce (figs. 438, 441). (2) All the rest of the papillary surface of the tongue is covered by con ical papiUn, so named from the conical pointed cap of epithelium, which is borne by each ; sometimes this cap is fringed with fine epithelial filaments, when they are termed filiform (fig. 439). In the cat tribe the conical papillae are claw- shaped or recurved : they are hard and horny, and in the process of licking they produce the effect of scraping. (3) Scattered here and there amongst the conical papillw are larger papillre, the fungiform (fig. 440). These are very vascular, and have a redder appearance than the rest ; they lie partlv THE TONGUE 321 Kir. 437. — Sei'tion (pf MUCOUS JlISMBIlANIi OF MOUTH, SlIOWINa THREE MlCIlOSCOriC I'Al'lEJj.E AND STIIA- TIFIED El'ITIlEEIIIll. The liLddD-VEKSEI.S HAVE liEEN IX.IECTEll. (Tolclt.) Fi<;. 438. — hECTHi^f of circumvallatb papilj.a, HiiMAK. The i!iGui;E inceuoes une side of THE PAPILLA AND THE ADJOININO PART OF THE VALLUM. Magnified 150 diameters. (Heitzmann.) i', eiJitheliuiii ; Q, ta.'ite-l.ud ; C, coriuiii with injected Ijlood-vt'sscls ; M, yliiiid with duct. Fig. 439. — Section of two filifokm PAP1LL.S}, HUMAN". (Heitzmann. ) .&,. epithelium ; C, coi-ium ; i, lymphoid tissue ; if, musoular fibres of tongue. FiH. 440. — Section of fungiform papilla, HUMAN. (Heitzmann.) Letters as in previous figjire. embedded in little depressions of the mucous membrane. They _have a certain number of taste-buds in their epithelium and receive branches from one or other of the taste-nerves. 322 THE ESSENTIALS OF ITISTOLOGY Small tubular glands may be seen between the superficial muscular fibres sending their ducts to the surface. Most of these glands secrete mucus, but those which open into the trenches of the circumvallate papillae, and a few others elsewhere, yield an albuminous secretion {serous glands of tongue, glands of Ebner). The mucous membrane at the back of the tongue contains a large amount SfS* '^»' ^Wi'^^^^^ ^my^^W! Fi 441 — SB0TIO^ of circdma ^llatl papili 4 of monkiiy Photogiaph Magnified 50 diameters. Notice the irregularly pajiillated, flat surface of the papilla : tKe deep trench surrounding it : the tajjte-buds in the epithelium at the sides of the papilla, but none on the opposite side of the trench : the serous glands below it (the duct of one of these is seen opening into the bottom of the trench). of lymphoid tissue, continuous with that of the* tonsils (p. 243) and having a similar arrangement and structure. TASTE-BUDS. The minute gustatory organs, known as taste-buds or taste-bulbs, may be seen in sections which pass through the papillae vallatse or the papillse fungiformes ; they are also present here and there in the epithelium of the general mucous membrane of the tongue, especially at the back and sides, and some are found upon the under surface of the soft palate, and on the posterior surface of the epiglottis. But they are most easily studied in the papillae foliatse of the rabbit (fig. 442), two small oval areas lying on each side of the back of the tongue, and marked transversely with a number of ridges or laminse with intervening trenches. Sections across the laminfe TASTE-BUDS 323 show numerous taste-buds embedded iii the thick epithelium which clothes their sides (fig. 443). Fig. 442. — Tongue of raerit, showing the situation of the PArru.a'; foliat;!';, p. 1^ Fig. 443. — Vektioal section of fapu,t,A foliata of the rarett, passing ACROSS THE LAMINA. (Ranviei'. ) p, central lamina formed of cerium ; v, section of a vein, which traverses the lamina ; p', lateral lamina in which the nerve-fibres run ; g, taste-bud ; n, sections of nerve-bundles ; a, serous gland. %^> 0. (S' ■ .-- r"' ^" %■ "Mi '^il m^ rh0 ep Fii!. 444. — A TASTE- BUD within the stratified epithelium op the tongue , (Sobotta.) Magnified 600 Jia'meters. fj, gustatory cells ; «, sustentacular cells ; ejv, epithelium vji, gustatory pore ; h, liairiets. 324 THE ESSENTIALS OF HISTOLOGY The taste-buds are ovoid clusters of epithelium-cells which lie in cavities in the stratified epithelium (fig. 444). The base of the taste-bud rests upon Fig. 445. — VAKions cells from tastk-hud of rabbit. (Engelmann.) fiOO diameters. a, four gustatory ceUs from central part ; i, one susteiitacullir cell, and two gustator.1 cells, in connexion ; c, three austentacular cells. the corium of the mucous membrane, and receives a branch of the glosso- pharyngeal nerve ; the apex is narrow and communicates with the cavity of the mouth by a sihall pore in the superficial epithelium {gustatory pore, fig. 444, p). The cells which compose the taste-bud are of two kinds, viz. . 1. The r/ustatory cells (fig. 445, a). These are: delicate fusiform or bipolar cells composed of cell-body or nucleated enlarge- ment and of two processes, one distal, the other proximal. Of these the distal is nearly straight, and passes towards the apex of the taste-bud, where it terminates in a small, highly refracting oilium-like appendage (taste-hairlet), which projects into the gustatory pore above mentioned; the cell body does not itself quite reach the pore. The proximal process is more delicate than the other, and is often branched and varicose. The nerve-fibres to the taste-bud (fig. 446) terminate in ramifications amongst these cells (G. Ret^ius). 2. The sustentacular cells (fig. 445, o). These are elongated cells, mostly flattened, and pointed at their ends ; they lie between the gustatory cells, which thev thus appear to support, and in addition they form a sort of envelope or covering to the taste-bud. Between the cells of the taste-bud lymph-corpuscles are often seen, having probably ^ wandered hither from the subjacent mucous membrane. Connective-tissue Fig. 446. — Nerve-endiscs is TASTE-BUDS. (G. Retzius. ) 7/., nerve-fibres; b. t.a^te-buds in outline ; /, ending of fibrils with- in t»ste-V)ud ; p^ ending in epi- thelium between taste-buds ; x, sulcus of papilla foliata into which the gustatory pores open. MOUTH AND PHARYNX 32s fibrils penetrate between the taste-bud and the stratified epithelium in which it is embedded (Drasch). According to M. Heidenliain no sharp distinction, can be drawn between gustatory and sustentacular cells, but all giades of transition are found. MOUTH, PHARYN.X AND fESOPHAGUS. The mucous membrane of the mouth, is lined by a stratified epithelium (fig, 447) into which vascular, and, in some parts, nerve-containing papillse of the corium project. The corium is formed of connective tissue and contains within and beneath it a large number of small secretory glands (buccal glands). Most of these secrete mucus, but some are of the mixed type (see under Salivary Glands, in next Lesson) : this is the case, for example, with the :^'.: & A It ^ 1^ '•jt-fj - Fio. 447. — Suction or the stratified epithelium of the fauces of the KABBIT. Photograph. ' Magnified 240 diameters. glands of the lips. The ducts of the buccal glands open everywhere upon the surface of the membrane ; the large ducts belonging to the salivary glands also open into the mouth. The pharynx is composed of a fibrous memirane which is encircled by striated muscles (the constrictors), and lined by mucQus membrane with which the fibrous membrane is connected by areolar tissue. The mucous membrane is covered on its inner surface over the upper part of the pharynx with ciliated epithelium; this is continuous above and in front with that of the nostrils, and through the Eustachian tube with that of the tympanum. Below the level of the soft palate the epithelium is stratified like that of the mouth and gullet, into which it passes. In certain parts the mucous membrane contains a large amount of lymphoid tissuej and everywhere numerous mucous glands open on its surface. 326 THE ESSENTIALS OF HISTOLOGY The oesopliagus or gullet, which passes from the pharynx to the stomach, consists of an outer fibrous or areolar covering, a muscular coat, a lining mucous membrane, and intervening connective tissue forming the submucous or areolar coat (fig. 448). The muscular coat is composed of striated muscle in about its upper third only, the rest being of the plain variety. There are two layers of the muscular coat — an outer layer, in which the bundles of fibres run longitudinally, and an inner,- in which they have a circular arrangement. The mucous membrane is' lined by^ a stratified epithelium, into which papillae from the corium project. The corium is formed of areolar tissue ; its limits are marked externally by- a narrow layer of longi- tudinally disposed plain muscular fibres, the muscularis mucosce. This is separ- ated from the proper muscular coat by the areplar coat, which contains the larger branches of the blood-vessels and lymphatics, and also the mucous glands of the membrane. The ducts of these glands are large and usually pass through a nodule of lymphoid tissue, lymph-cells from which infiltrate the epithelium of the duct and may pass out into its lumen. Besides these mucous glands, there are met with both at the upper or laryngeal part of the oesophagus and at the lower or gastric end a certain number of small tubulo-racemose glands of a different character. They are confined to the mucous membrane, not penetrating the muscularis mucosae, and their ducts open upon and not between the papillae of the mucous membrane. They closely resemble the tubulo-racemose cardiac glands of the stomach (see fig. 466, p. 337), and it is usually found that the epithelium of the surface in the immediate neighbourhood of their ducts is similar to that lining the stomach. There are two ganglionated nerve-plexuses in the ffisophagus, one in the muscular coat and one in the submucous coat; they resemble in position and structure those of the intestine. Fifi. 448. — Section oi' the human (ESOPHAGUS. (V. Horsley.) The section is transverse, and from near the middle of the g^uUet. a, fibrous covering ; 6, divided fibres of the longitudinal mus- cular coat ; c, transverse muscular fibres ; d, submucous or areolar layer ; f , mus- cularis mucosae ; /, mucous membrane with papilla3 ; ,(/, laminated epithelial lining ; h, mucous gland ; i, gland duct ; w', striated muscular fibres in section. THE SALIVARY GLANDS 327 LESSON XXX. THE SALIVARY GLANDS. 1. Section of submaxillary gland (dog). The gland may be hardened in alcohol or formol followed by alcohol and stained with hsematoiylin-eosin, with iron- hsematoxylin or with alcoholic eosin and methylene-blue. Notice the acini filled with clear (mucus-secreting) cells, the nuclei of which usually lie near the basement- membrane. Notice here and there, outside the clear cells, demilunes or crescents of small darkly stained granular- looking (serous) cells. Observe also the sections of the ducts with their striated columnar epithelium. If possible find a place where one of the ducts is passing into the alveoli. Sketch under a high power. 2. Study sections of parotid and sublingual glands prepared in a siniilar way, and notice the diflferences between the three glands. 3. Examine small pieces of both submaxillary and parotid gland of the dog or cat fresh in 2 per cent, salt solution. In the submaxillary gland notice that the alveolar cells are swollen out with large granules or droplets of mucigeii, which swell up in water to form laige clear vacuoles. Dilute acids and alkalies produce a similar change, but more rapidly. The cells of the parotid gland are also filled with granules, but they are smaller. Their granules are swollen up and dissolved by dilute acids a,nd alkalies. Make a sketch from each preparation under a high power. The granules are not seen in preparations that have been in alcohol, but osmio acid preserves them moderately well ; they are well seen in sections from picric acid hardened glands. 4. To study the changes which the alveolar celjs undergo during secretion, pilocarpine is administered to an animal in sufficient amount to produce copious salivation ; after half an hour the animal is killed and its salivary glands are examined as in § 3. The salivary glands may be looked upon as typical of secreting glands in general. They are composed of a number of lobules bound together loosely by connective tissue. Each small lobule is formed of a group of irregularly saccular or tubular alveoli or acini from which a small duct passes, and this unites with others to form larger ducts. A main duct eventually leaves the gland to open upon the inside of the mouth. The alveoli are enclosed by a basement-membrane, which has flattened branched cells on its inner surface, next to the epithelium (fig. 449). The membrane may be shown by teasing the fresh gland substance in water (Langley). This basement-membrane is continued along the ducts. 'Within it is the epithelium, which in the alveoli is cQmposed of polyhedral cells, looking wedge-shaped in section (fig. 450, a), but in the ducts is regularly columnar, except in that part of the duct which immediately opens into the alveoli (junctional part) ; in this it is flattened (d). The columnar epithelium of the ducts is peculiar, in that the cells, which are granular, are not sharply marked off from one another and show a distinction into two unequal zones, an outer, larger zone, with the granules arranged in a striated mariner 328 THE ESSENTIALS OF HISTOLOGY . perpendicular to the basement-membrane, and an inner, smaller one (fig. 450, d, and fig. 459). The larger ducts are lined by non-granular cubical or short columnar epithelium, which may show more than one layer of cells. Fii:. 44!l. — MEirriRANA T'Roi^ria oy two ai.veoli. (v. Ebner.) Magnilied 600 diameters. Tlie previa r;U ion wa~ from a iini':ous <:land of rlie i-al>lii(.._ The cells of tlie alveoli differ according to the substance tlicy secrete In alveoli which secrete nniciis, such as those of most of the smaller glands which open on the uiucoiis membrane of the mouth, and contrilnite {n the s Fig. 450.— Section of the suemaxillary gi^vnd of the dog, showing THE ooMMBNCF.MUNT OP A DUCT IN THE ALVEOLI. Magnified 425 diameters. ti, one of the alveoli, several of which are in the section shown gtoTiperi around the nommencement of the duct, d' ; a', an alveolus, not opened by the section ; \ basement-membrane in section ; c, interstitial connective tissue of the gland ; d, section of :), duct which has passed away from the ahcoli, and is now lined with characteristically strialed columnar cells; ,s', crescentic group of darkly stained cells at the periplicrx- of an aiveolus.! production of saliva (fig. 451), antl some of the alveoli of the submaxillary and sublingual gland.s, the cells, if examined in normal saline solution or after hardening with alcohol, are clear and swollen. But if examined rapidlv in serum, or in solutions of salt of from 2 to 5 ppr cent., they are often seen THE SALIVARY GLANDS 329 to be occupied by large and distinct granules (fig. 452, a) (Langley) which become swollen up under the influence of dilute acid (6). These granules can Fio. 451. — Section of a mucous salivary gland (pnb of the small glands OF THE BUCCAL MUCOUS memeeane). Photograph. Magnified 200 diameters. In the middle ol the figure is seen the section of a duct. also be rendered visible by certain methods of staining. Granules are not present as such in all mucus-seoreting cells, but in many have become 5 w ^,' Fio. 452. — Mucous cells fkom -fresh submaxillary glands op the doo. (Langley.) a, from a resting or loaded gland ; &, from a gland which has been secretingr for some time ; a', 6', similar cells which have been treated with dilute acid. blended together and transformed into a substance which is known as mucigen which distends the cell. The mucigen is dissolved out and discharged as mucus into the lumen of the alveolus and into the ducts, when the gland 330 THE ESSENTIALS OF HISTOLOGY is stimulated to activity. After such discharge, the cells, instead of having a clear appearance, look finely granular, and are much smaller ; they also stain more deeply with hsematoxylin (compare figs. 453 and 454). These cells are known as mucona relh. But in most mucous alveoli certain of the cells do FiC. 4ri.'J, — SEr-TION OF A IJOO'S Rl'BMAXILLARV, AFTEK A PROLOXflED I'EiaOn (IK REST. (Ranvier.) ;, lunien of ah eoliis ; r/, mucus-se'-relini: eells ; c, r'l-CNeenc, formed of .^llimiiinoiis cells. not contain mucigen, but su}h11 albuminous granules : these cells often form groups which lie next to the basement-membrane (figs. 45:!, c, and 4.")5). These groups are the so-called crescents of G'uinu-r.i ; their constituent- cells arc knciwn as riiargiiml or senms e<4Js. Special diverticula pas.s from the 7-T3y L Fm. 454. — Submaxillary of docj, after a PERiop or activity. (Ranvier.) The mucus-secreting cells, g, have discharged their secretion, and are smaller and stain better ; the albuminous cells of the crcseent.s, f, af q enlarj^ed. lumen of the alveoli between the mucous cells tp penetrate to the crescents and to branch amongst and within their constitpent-cells; these diverticula are best shown by the Golgi method of staining (fig. 456; and also fig. 463). The serous cells are characteristic of purely serous alveoli (fig. 455), in which none of the celh secrete mucus, but watery or albuminous saliva. In these when the gland has been long at rest the cells are filled with granules, which THE SALIVARY GLANDS 331 do not swell with water nor form mucin ; they appear to be of protein nature, and probably yield to the secretion of the gland its ferment (ptyalin) and its Fig. 455. — Section of human suBLiNGnAL. Magnified 200 diameters. (Photographed from a preparation by Prof. M. Heidenhain.) Most of the alveoli shown in the figure are serous, but some are mixed, containing chiefly mucous cells but also crescentic groups of serous cells. Fig. 456. — Alveoli of human sublingual gland pkbpaked by GoLOi METHOD. (E. Muller.) I, lumen stained, with lateral diverticula passing between and into mucus- secreting cells ; ft, longer diverticula penetrating into the " crescent " cells. albumin. The granular substance within the cell is not the ferment, but the ferment is formed from it when the secretion is poured out. Hence it has been termed zymogen (mother of ferment). As Langley showed, the outer part of each cell becomes clear and free from granules after secretion 332 ! THE ESSENTIALS OF HISTOLOGY (fig. 457). Sometimes the change is found to occur in some cells and not in others (fig. 458). Kid. 4r>7. Aim. hi Of \ sErtoiis (iland. A, .at rest, B, afteii a siioiiT period ll^- AITIX [TV. U, AFTEll A I'Udl.ClNI ;KI> I'ERIIII) UK Af'TIVITV. (TjaiigleV.) (n A and H the liiwlei aie olisinrtMl ])\ thf t;rriiniU-s of ;:> nio^^en. Fid'. 4.58.— .Sl'BMA.MLI.AKY (idAND OF KAEBIT. (E. WiiUer.) Tlie c-ell«, wliioh are all serous, are in diffprent functional states, as indii.'atei:l l.\ the condition and stuininj: of the {.'ranules. a, celt filled with d.arkl> stained granules : /'-, clear cell : c. secretorc canaliculi penetratinj,^ into the cells. Fi(d 459. — Cells from duct of i'arotid. A, prior to secretion ; B, after secretion (Mislawski and Sniirnow). The.cells lining the diicta of the ordinary glands iue also occupied by granules •which are found to alter in iiiunber and size with varying states of secretion (fig. 459). THE SALIVARY GLANDS 333 In nearly all aiiiuuils thr pai'(jti(l glands arc e(iin|josud of purely Hcruus aheoli ; ill man and most animals tlie submaxillary and sublingual glands liave not only both serous and mucous alveoli (tigs. 4.^iri, 4fiO), but also "mixed" alveoli, /.c. alveoli ^ ^ ^FV^Tlf^r^- Flo, JOO- — f^Kl.TION OF PAKT OF THE HCMAN ST I'.MAX ILLAKV OLANI). (R. Heidbiiliaiii. ) To the right of the fiL^^ure is a group of miii-oiw and mixed alxGoli ; to tlie left a L;i-oiip of serous alveoli. containing both sei'ous and mucous cells. The detached anterior yjart of the sublingual gland, which in man is comparatively small, has ]iui'cly mucous alveoli. Fig. 461. — ii-LVEOLi from mucois POETION OF THE HUMAN SUBMAXIL- LARY GLAND, PARTLY UNKAVELLFD. (Peiser. ) Fjo. 4(ji2. — Alveoli from serous PORTION OP THE HUMAN SUBMAXIL- LARY OLAND, PARTLY UNRAVELLED. (reiser.:). When the glands are unravelled and examined with the microscope it is found that the mucous and serous alveoli are somewhat different in shape, the mucous alveoli being larger, more uniform in shape, and linked on to the ducts by shorter and wider intermediate or jupctional portions (compare fig. 461, which is from a mucous part of the hu,man submaxillary, with fig. 462 from a serous part). 334 THE ESSENTIALS OF BlSTOLOGY The largest ducts have a wall of connective tissue outside the basement- membrane, and also a few plain muscle-cella. The blood-vessels of the gland form a capillary network around each alveolus. The lymphatics commence in the form of lacunar vessels in the areolar tissue between the alveoli. Lymph-nodules are occasionally found in the interstitial connective tissue. The nerve-fibres of the gland, derived in the case of the lurger salivary glands both from cerebrospinal nerves and sym- pathetic, pass through ganglia before proceeding to their distribution. They ramify as fine varicose fibrils amongst the alveolar cells (fig, 463) ; many are distributed to the blood-vessels. SUB- DOG. Fid. 463. — Alveoli of the MAXILLARY GLAND OF THE (G. Retzius.) Golgi method. The extensions of the himen into the crescents of Gianuzzi are shown, and also the endings of nerve. fibrils amongst the cells of the alveoli. Development. — The salivary glands are developed as buds from the epithelium of the buccal cavity, at first solid but gradually becominf; hollowed out. To begin with they are simple, but undergo ramification as they extend into the mucous membrane and submucous tissue. THE STOMACH 333 LESSON XXXI, THE STOMACH. 1. Veetical longitudinal sections through the caidia, including the lower end of the iiesophagus and the adjacent cardiac portion of the stomach. These are intended to show the abrupt transition of the stratified epithelium of the cesophagus into the columnar epithelium of the stomach, and also the character of the gastric and cesophageal glands in the immediate neighbourhood of the cardia. The sections may be stained with haematoxylin and eosin or alcoholic eosin and methylene-blue. 2. Sections of the fundus of the stomach cut perpendicularly to the surface of the mucous membrane. In these sections the general arrangement of the ooats of the stomach is studied. Sketches are to be made under a low power illustrating this arrangement, and under a high power showing the structure of the glands. Measure the whole thickness of the mucous membrane, the thickness of the muscular coat, the size of the columnar epithelium-cells of the surface, and that of the cells in the deepei- parts of the glands. 3. Sections of the mucous membrane of the fundus, cut parallel to the surface. These sections will show better than the others the arrangement of the cells in the glands. 4. Vertical sections of the mucous membrane from the pyloric region of the stomach. In a section taken longitudinally through the pylorus, the transition of the gastric glands into the glands of Briinner of the duodenum will be made manifest. Make a sketch under a low power of one of the pyloric glands in its whole length, filling up some of the details with the high power. 5. Study the arrangement of the blood-vessels in vertical sections of the wall of a stomach the vessels of which have been injected.. The wall of the stomach consists of four coats, which, enumerated from without in, are as follows, viz. : serous, muscular, areolar or submucous, and mucous m,emhrane (fig. 464). The serous coat is a layer derived from the peritoneum. It is deficient along the lines of the lesser and greater curvatures. The muscula/r coat consists of three layers of plain muscular fibres. Of these the bundles of the outer layer run longitudinally, those of the middle layer circularly, and those of the inner layer obliquely. The longitudinal and circular bundles become thicker and stronger towards the pylorus ; at the pylorus itself the circular layer is greatly tKiokened to form a sphincter muscle. The oblique fibres are only present over the fundus. The areolar or subm,ucous coat is a layer of areolar tissue, serving to unite the mucous membrane loosely to the muscular coat ; in it ramify the larger branches of the blood-vessels and lymphatics. 336 THE ESSENTIALS OF HISTOLOGY The mucous membrane is in man a soft thick layer, generally corrugated in the empty condition of the organ. Its iriner surface is covered by columnar cells, all of which secrete mucus. They are prolonged into the ducts of the glands, but when these divide to form the tubules the cells become shorter, and lose their mucus-secreting character, although an occasional cell of the same character may be seen lower down. On the other hand, both oxyntic and central cells are sometimes seen between the columnar epithelium cells df the ducts. Where the oesophagus passes into the stomach the stratified epithelium lining the gullet gives place abruptly to the columnar epithelium of the stomach (fig. 465). In some animals {e.g. rat) the stratified epithelium of the oesophagus is continued over gastric or less extensive tract of always the ends by I 1 1 a more mucous membrane, but it similar sharply defined line. The thickness of the gastric mucous membrane is due to the fact that it is largely made up of long tubular glands opening upon the inner surfape ; but, as in all hollow viscera, the thickness depends to a large extent upon the state of distension. Between the glands the mucous membrane is formed of reticular tissue with some lymph-cells and many basiphil connective-tissue cells in the meshes. Externally the mucous membrane is bounded by the m,uscularis mucosce, con- sisting of an outer longitudinal and an inner circular layer of plain muscular fibres. The inner layer sends strands of muscle towards the surface betwfeen the glands. Gastric glands. — These are formed of a basement-membrane lined with epithelium. Each gland consists of secreting tubules, from one to four in number, opening at the surface into a larger tube, the duct of the gland. The duct is in all cases lined by mucus-secreting epithelium of the same character as that which covers the inner surface of the mucous membrane, but the epithelium of the secreting tubules is different from this, and also differs somewhat in the glands of different regions, of the organ. The follow- ing varieties of gastric glands are met with : — Glands of the cardia. — These are comparatively few in number. They Fig. 464. — Diagram of section through the coats of the STOMACH. (Mall. ) m, mucous membrane ; e, epithelium ; rf, orifice of gland duct; m.ui., mus- oularis mucosse; s-m,., submucosa; cm,, circular muscular laytr ; l.iii., ion^iUidinal mu.scTilar layer ; s, serous coat. 5.'iS? THE STOMACH 337 _^ - ■ - - ''*W^^<."'■■''"'1 r > - ^«^^ » \ « t i» li aph. Magnified 200 diameters. era ?', •i:rt // ^^^-J«i^"'r^^»l5*'«^^'5s-t-^i i-;C^^fer 338 THE ESSENTIALS OF H'lSTOLOGY are usually found only close to the oesophageal opening (cardia) and are of two kinds ; (a) simple tubules, similar in their general structure to the crypts of Lieberkiihn of the intestine, antl (6) small tubulo-racemose glands /i?>.. -»-.■'<•, "? '. \ o :;- r^&^ 'j, \ 1.--'"' '-■~^:\. ■». ' -&; c M l'l';'t'?!l.V. i ' Fig. 467.-— Sections of the mucous membrane of the fundus of the dog's stomach passing with a slight obliquity across the bong axis of the glands. vl, Section close to but not quite parallel with the surface, including on the left the gland ducts and on the right tho commencing gland tubules. Notice the rounded oxyntic or acid-forming cells ot the glands. They already begin to appear between the columnar cells of the ducts. 5, Deeper part ot the same section, showing the lumina of, the gland tubules surrounded by principal or pepsin-yielding cells, with the oxyntic cells altogether outside them. THE STOMACH 339 (fig. 466). The latter are commonest in man ; the former occur in consider- able number in certain animals. The secreting tubules of the racemose glands are lined by cells which are granular in appearance and of a short columnar form, and of the same nature throughout the length of the tubule, except near the orifice (duct), where they give place to columnar mucus- secreting cells. Glands of the fundus (figs. 464, 467, 468, 469). — In these glands the tubules are usually relatively long and the duct short. The epithelium of the tubules is composed of two sets of cells, termed from their relative position in the tubules the central and the parietal cells. Central cells. — These are of two types. 1. Those of the first type, which are the best known, are not stained .with hsematoxylin, although in aniline - stained sections their cytoplasm is strongly basiphil. The nucleus is spherical and is generally near the middle of the cell. In the fresh resting gland and with certain methods of fixation, the cytoplasm is seen to contain distinct granules (zymogen) most numerous near the inner zone (fig. 468). After a period of secretory activity the granules diminish in number, and the clear outer zone encroaches upon the granular inner zone (Langley), as in the analogous cases of the pancreas and parotid glands. It is believed that the granules in question contain pepsinogen, which is converted into pepsin when discharged. These cells (of the first type) may therefore be appropriately termed the peptic cells of the fundic glands. 2. The central cells of the second type (fig. 469, B, m) are quite different in appear- ance and staining reactions from those just described. They are larger and clearer and are stained blue by Mallory, like mucin-containing cells ; whereas the cytoplasm of the peptic cell is coloured yellowish brown by that reagent. They occur either in a scattered form wedged m between the other cells, or there may be a number together, occupying a considerable length of 'a tubule (as in fig. 469, B, m). The cytoplasm has no obvious granules : the nucleus is either flattened against or wedged into the attached end of the cell. For this second type of central cell the name mucoid cell is suggested. i ^ I am indebted to X)r Lim for the above description of the two types of central cell. Fig. 468. — A ruNDUS gland OF SIMPLE FORM FROM THE bat's stomach. Osniic aqid preparation. (Langley. ) c, columnar epithelium of the surface ; ?i, neck of the gland with central and i^arietal cells ; /, base occupied only by principal or central cells, which exhibit the granules accumu- lated towards the lumen of the gland. 340 THE ESSENTIALS OF HISTOLOGY' Parietal cells. — Scattereji along the tubule, lying between the central cells and the basementmembrane, are a number of large spheroidal or ovoidal cells. These are the pwrietal cells ; also known as oxyntic, having been so named by Langley because they are believed to produce the acid of the gastric secretion. Each of these cells is penetrated by a network of minute passages, communi- cating with the lumen of the gland by a fine caila], which passes between the aft. -'i' -..«:• -^ :!i!'iifi:'%.k:>-^& '^'-^]V ''.■V'-"> • .V-^'y '- : '■' *■;■, ';■ ". : ■•'"' ■-. ..>:, -' ',;"'■ 6 '-•!, » " . '■ -/;■■'. "t . •.:'■'.' ■:->*52'> '■■Pi ' ' M *'i'A-' Fig. 469. — Photographs of a vertical section or the mucous jiembbanb of the FUNnUS of the cat's stomach, showing the ULAHDS r\T IA1NGITUPIM.UJA'. (From preparations by R. K. !S. Lira.) A, magnified V5 diameters ; 7nin., muscularismuoosro. B, a portion of A mapnifled 400 diameters. p, a g:Iand containing ''peptic" cells; ifi, a gland containing "mucoid" cells; both show oxyntic cells on the outside. central cells (fig. 470). They are sometimes present in the neck of the gland or even at the surface of the stomach ; in these places they are wedged in between, the ordinary epithelium-cells (fig. 467, A). (3) Glands of the pyloric canal (fig. 471). — In the glands of the pyloric canal the ducts are much longer than those of the fundus glands, and the secreting tubules possess cells of only one kind.i These appear to correspond ' In man it ia, however, only quite near the pylorus that parietal cells are altogether absent. They have been oooasionally seen in Briinner's glands of the duodenum. THE STOMACH 341 with the "mucoid" cells of the fundus glands which have been above described as possessing flattened basal nuclei (p. 339). They have an indistinctly granular appearance and are said to yield pepsin to the gastric juice ; but are quite diiferent from the " peptic " cells of the fundus glands. They are also quite unlike the epithelium of the surface and ducts, which is formed, as Fig. 470. Fig. 471. Fig. 470.— Pakt of tdeule of a fundus gland, with thb lumen and sbcretoby CANALICULI STAINED BLACK ; THE GLAND-CELLS AKE ALSO SHOWN. (Zimmerraann. ) c, central cells ; ^, parietal or oxyntic cells ; I, lumen of tubule prolonged into arborescent canaliculi which penetrate into the parietal cells. Fig. 471.— PyLOKio glands, from a section of the hjjman stomach. (Photograpiied from a preparation by Prof. Martin Heidenhain. ) Magnified 60 diameters. elsewhere, of long tapering cells, the outer part of which is filled with mucigen, and the nuclei of which are ovoid and centrally situated. At the pylorus itself the gastric glands, which are of the same type as those of the pylorus canal, become considerably lengthened and enlarged, and are continued into the submucous tissue, the muscularis mucosse being here deficient ; they thus present transitions to the glands of Briinner, which lie in the subniucous tissue of the duodenum (fig. 472). Scattered amongst the ordinary secreting cells of the pyloric glands, cells are seen here and there which stain with hsematoxylin more deeply than the rest, and perhaps have a different function (Stohr). • 342 THE ESSENTIALS OF HISTOLOGY m^s^ &&"^ !:^f ii » € Fig, 472. — Sjsction through the pylorus, iNCTiOTJiNfi the commencement OF THE nuoDENUM. (Klein.) V, villi of duodenum ; b, apex of a lymphoid nodule ; c, crypts of LieberkOhn ; s, secreting tubules of Rriinner's gflands; d, dunta of pyloric glands of the^ stomach ; ff, tubes of these glands in mucous membrane ; t, deeper lying tubes in submucosa, corresponding to secreting tubules of Brunner's glands of duodenum ; 7ii, muscularis mycosDB. Fii;. 473.^Plan okthe blood- vessels OF THE STOMACH. (Modified from Brinton.) a, small arteries passing to break up into the fine capillary network, a, between the glands ; h, coarser capillary network around the mouths of, the glands; c, c, veins passing vertically downwards from the superficial network ; e, larger vei3sels in the submucosa. Fig. 47'1.^Ly]\!I'iiath.'s of the ih'man oastkic MUCOUS MKMliRANE, IN.IECTED. (C\ Lovrn. ) The tubules are only faintly indicated: a, muscularis inncniiH! ; 6, plexus of line \'cs>!t'ls at base of glands (!, plexus of larger valved lymphatics in submucosa. THE STOMACH 343 The blood-vessels of the stomach are very numerous ; they pass to the organ along its curvatures. The arteries traverse the muscular coat, giving off branches to the capillary network of the muscular tissue ; they then ramify in the submucous coat. From the arterial branches here, small tortuous arterioles pierce the muscularis mucosre, and break up into capillaries near the bases of the glands (fig. 473). The capillary network extends between the glands to the surface, close to whieh it terminates in a plexus of relatively large venous capillaries which encircle the mouths of the glands. From this plexus straight venous radicles pass through the mucous membrane, pierce the muscularis mucos8e,.and Join a plexus of veins in the submucous coat. From these veins blood is carried away from the stomach by efferent veins, which accompany the entering arteries. The lymphatics (fig. 474) arise in the mucous membrane by a plexus of large vessels dilated at intervals, and looking in sections like clefts in the interglandular tissue. From this plexus the lymph is carried into large valved vessels in the submucous coat, and, from these, efferent vessels I'un through the muscular coat to reach the serous membrane, underneath which they pass away from the organ. The muscular coat has its own network of lymphatic vessels. These lie between the two principal layers ; their lymph is poured into the efferent lymphatics of the organ. The nerves have the same general arrangement and mode of distribution as those of the intestine (see next Lesson). They are mostly derived from the vagus, but branches of the sympathetic also pass to the organ. 344 THE ESSENTIALS OF HISTOLOGY LESSONS XXXII. AND XXXIII. THE SMALL AND LARGE INTESTINE. ]. Sections of the duodenum, jejunum, and ileum, vertical to the surface. The three parts of the intestine may be embedded in the same paraffin block, and the sections stained and mounted together. Choose a, part of the duodenum not far from the pylorus and a part of the ileum which includes a Beyer's patch. Observe the nodules of lymphoid tissue which constitute the patch and which extend into the submucous tissue. Notice the lymphoid cells in the superjacent epithelium. Notice also the sinus-like lymphatic or lacteal vessel which encircles the base of each nodule. In the duodenum study the glands of Briinner in the submucous tissue. Make a general sketch of each section under a low power and draw a villus under the high power. The general arrangement and structure of the intestinal wall is to be studied in these sections. The portions of intestine should be fixed in 10 to 20 per cent, neutral formol. It is best to distend them slightly with this fluid, and when fixed to cut them open and to place them in a large amount of the fixative. (This applies not only to the small intestine but to all the hollow viscera.) 2,. Sections parallel to the surface of the intestine, and therefore across the long axis of the villi and glands of the mucous membrane. In order to keep the sections of the villi together so that they are not lost in the piounting, it is necessary either to embed in celloidin or, if (paraffin is used, to employ an adhesive method of mounting. Sketch a villus and some of the crypts of Lieberkiihn. 3. To study the process of fat-absorption, kill a frog two or three days after feeding with bacon fat. Slightly distend a short length of intestine with a mixtui-e of 2 parts Miiller's fluid and 1 part osmio acid solution (1 per cent.), and put the piece into a fairly large quantity of the same mixture. Also place a very small shred of the fresh mucous membrane into 0'5 per cent, osmic acid solution. After forty-eight hours teased preparations may be made from this preparation, in the same manner as directed in Lesson VIII., § 1. The piece in Miiller and osmic acid is left for ten days or more in the fluid. Sections are then made by the freezing method and mounted in glycerine (or from paraffin and mounted in dammar). 4. Sections of small intestine the blood-vessels of which have been injected. Sketch the arrangement of the vessels of a villus. D. Stain a piece of intestine of a rabbit or guinea pig with chloride of gold. It should be distended with a 1 per cent, solution, and then placed in a larger quantity ; after half an hour it may be cut open, washed with water and placed in a large amount of water faintly acidulated with acetic acid and exposed to sunlight. When stained tear ofi' broad strips of the longitudinal muscular coat, and mount them in glycerine. It will generally be found that portions of the nervous plexus of Auerbach remain adherent to the strips ; the plexus can in this way be studied. From the remainder of the piece of intestine tear, off with forceps the fibres of the circular muscular layer on the one side, and the mucous membrane on the other side, so as to leave only the submucous tissue and the muscularis mucosse, which is to be mounted flat in glycerine ; it contains the plexus of Meissner. Sketch a small portion of each plexus under a high power. The plexuses can also be shown by the methylene-blue method and by the reduced silver method of Cajal (see Appendix). 6. Sections of the large intestine, perpendicular to the surface. Sketch under a low power. gsnu. THE INTESTINE .-mi 345 Fig. 475. — Diagram or section of alimentary tube. (Sobotta.) Ly lumen ; glvti^ glands of mucous membrane ; &'^, epithelium^ gls, glands in submucosa ; ■mm, muscularis mucosa ; sm, submucous coat ; rjft, circular muscular layer ; lin, longitudinal muscular layer ; s, serous coat ; &s, mesentery ; Q^ny, ffanglion of plexus myentericus ; .f/sm, ganglion of plexus submucosus. Fig. 4-76. — Aubrbach's plexus, from the muscular coat of the intestine. (Cadiat.) 346 THE ESSENTIALS OF HISTOLOGY Fig. 477.— Meissner's plexus I'bom tue suejiucous coat. (Cadiat). a, j?ailglion ; h, h, nervous cords ; c, a blood-vessel ; d, an entering: sympathetic nerve. Fig. 478. — Nerves op the mucous membrane or the ssiali, intbstijsie. (Cajal.) Ji/, part of Meissner's plexus ; n-f, smnll f^'Is nnd iiprvp.filirn« in f.hp tissiin nf tho raucous m THE INTESTINE 347 7. Sections of the mucous membrane of the large intestine parallel to the surface, and therefore across the glands. Sketch some of the glands and the inter- glandular tissue under a high power. 8. The arrangement of the blood-vessels of the large intestine is studied in sections of the injected organ. Fig. 479. — Typical NEuvB-CELiiS fkom entekic ganglia. (Dogiel. ) At cell with numerous minute ramiiied dendrons ; B, cell with numerous almost unbranched axon-like dendrons ; aa, axons ; pz, dendrons. 348 THE ESSENTIALS OF HISTOLOGY THE SMALL INTESTINE. The wall of the small intestine consists of four coats (fig. 475). The serous coat is complete except over part of the duodenum. It leaves If/-'-, LieberkuUi. musculdfitf itvucotiai. St layer 0/ cdrculat' rnuscutar ItOi-tib. i nit' ntmncutar layer. lon. Fig. 481. — A crypt of Liebeekuhn from the human intestine, (Flemming.) Fio. 482. — Section of the ileum thkouoh a lymphoid nodule. (Cadiat.) u, middle of the nodule with the lymphoid tissue partly fallen away from the section ; &, epithelium of the intestine ; c, villi ; the epithelium is broken away ; d, crypts of Lieberkiihn ; c, /, musoularis roucosffl. muscular fibres of the mucous membrane, but also to the glands and villi (fig. 478). These " enteric " ganglionated plexuses contain two kinds of nerve-oell (fig. 479). One kind has a number of much branched dendrons and an unbranched process recognisable as the axon ; the other kind is characterised by the presence of a number of processes very little branched and hardly distinguishable from one another. This last type of cell is the only one found in Meissner's plexus. The mucous membrane is bounded next toi the submucous coat by a double layer of plain muscular fibres (muscularis mucosae). Bundles from this pass inwards through the membrane towards the inner surface and penetrate also into the villi. The • mucous membrane proper is pervaded 350 THE ESSENTIALS OFTFISTOLOGY with simple tubular glands — the crypts of Liehefkuhn (figs. 480, 481, 483) — which are lined throughout by a columnar epithelium, with scattered goblet- ) Ui. itf^l i^Al^l If Li^berkiihv. Ill ""'-«- . - i'l ^ J. f-^ u i ■^i' Sf'^l <% ^si^eiV^^ rjlands of JBriLntier Ag, m mbmucosa. longitvdijial muscular lay f>i\ \\' . ^', .' ■". J ; - ~ --'■ L ^^ ■- ^^-1 s:&rnv^ Coat. Fig. 483.— Section of duodenum of cat, showing Brunnkr's glands. Magnified about 60 diameters. cellsi like that which covers the general surface, and the villi. At the fundus of each crypt are a few cells containing well-marked granules (Paneth). The cells of the glands may show evidences of karyokinesis. It , has been stated that the epithelium of the general surface becomes regenerated THE SMALL INTESTINE 351 mi •ir 3*? Fig. 484. — Longitudinal section of a villus : cat. Magnified 200 diameters. (Pljotographed from a preparation by Prof. Martin Heidenhain. ) At one part the lacteal is cut longitudinally. Some leucocytes are seen within it : others are observable between the cohnnnar epitheliimi-cells of the surface and many occupy the interstices of the reticular tissue. Fig. 485.— Pakt of the wall of the villus shown in fig. 484. Magnified 400 diameters. c, columnar epithelium-cells ; leucocytes are seen between them ; sir, their-striated border ; 2, lymphoid tissue of villus. One or two goblet-cells are seen between the columnar cells. from them (Bizzozero). The mucous membrane between the glands is mainly composed of reticular tissue, with numerous lymph-cells; the latter are aggregated here and there into nodules of lymj5hoid tissue. These nodules 352 \ THE ESSENTIALS OF HISTOLOGY y~^. -f ''^^r'f^ e r^ i/''»'fr^'^"^'-^^ iTf^-^ la -At^ t-tfp:^ Fig. 486. — Oi'tical section oe a villus froim a rat killed three hours after feeding with bread and water. The columnar e]iitheliuni shows numerous ]\ niph-corpust-les between the rells ; I, lacteal, containing lymph-corpuscles ; c, some partly disintegrated. X. 'a' .';.'.■ *'^ 'A ij Fill. 487. — TuAnsVEKSE SECTioi; OF A VILLUS OF pi«. (Trautniaiui. ) ii, epithelium ; a', striated border ; o", goblet-oell ; 6, lymphoid tissue ; c, small central lacteal ; e, plain muBcle-flbres cut transversely ; f, section of arteriole. THE SMALL INTESTINE 353 constitute when they occur singly the so-called solitary glands of the intestine (fig. 482), and when agglomerated form the agminated glands or patches of Peyer (fig. 491). The latter occur chiefly in the ileum. The glands of Briinner, which have been alfeady noticed (p. 341), occur in the duodenum. They are small tubulo-racemose glands, situated in the submucosa (fig. 483); they send their ducts to the inner surface Fig. 488. — Lacteal within villus-like fold op the mucous membkane of SMALL IHTESTINE OF FROG. Magnified 200 diameters. The la<5teal is distended with chyle in which several leucocytes in various stages of disintegration are seen. of the raucous membrane either between the crypts of Lieberkiihn or into them. The villi with which the whole of the inner surface of the small intestine is closely beset are clavate or finger-shaped projections of the mucous membrane, and are composed, like that, of reticular tissue covered with columnar epithelium (figs. 484 to 488). The characters of this epithelium have already been described (Lesson VIII.). Between and at the base of the epithelium-cells many lymph-corpuscles occur', as well as in the meshes of the reticular tissue. The epithelium rests upon a basement-membrane. 354 THE ESSENTIALS OF HISTOLOGY In the middle of the villus is a lymphatic or lacteal vessel which may be somewhat enlarged near its commencement ; the enlargement is replaced in some animals by a network of vessels. Surrounding the lacteal are small bundles of plain muscular tissue prolonged from the muscularis mucosae. Fig. 489. — Small intestine (vertical transvekse section), with the BLOOD-VESSELS INJECTED. (Heitznianii. ) r, a villus ; (3, glands of Lieberki'ihn ; J!/, muscularis mucosae ; A , areolar coat ; i?, circular muscular coat ; L, longitudinal muscular coat ; P, peritoneal coat. The network of blood-capillaries (figs. 489, 490) lies for the most part quite near the surface under the basement-membrane ; it is supplied with blood by a small artery which joins the capillary network at the base of the villus ; the corresponding vein generally arises near the free end of the villus. The lymphatics (lacteals) of the mucous membrane (fig. 491), after receiving the central lacteals of the villi, pour their contents into a plexus of large valved lymphatics which lie in the submucous tissue and form ABSORPTION FROM INTESTINE 355 sinuses around the bases of the lymphoid nodules (fig. 340, p. 245). From the submucous tissue efferent vessels pass through the muscular coat, receiving the lymph from an intramuscular plexus of lymphatics, and are conveyed away between the layers of the mesentery. Absorption of fat. — In order to study the process of fat transference in the intestine, it is convenient to stain the fat with osmic acid, which colours it black. It can then be observed that in animals which have been fed with food containing fat, particles of fat are present (1) in comparatively large globules in the outer part of the columnar epithelium-cells, but in the form Fio. 490.— Villus of kat with BLOon-vEssBLS injected. Photograph. Magnified 210 dianietCTs. of much smaller globules in their deeper part (in the free border of the cell fat is entirely absent) ; (2) in fine granules in the interstitial tissue of the villus, but here often confined to the amoeboid leucocytes, which abound in this tissue] (3) in fine granules within the central lacteal of the villus. The leucocytes are present not only in the reticular tissue of the villus, but also in considerable numbers between and at the bfise of the epithelium-cells (figs. 485, 486) ; and they can also be seen in thin sections from bichromate osmic preparations within the commencing lacteal ; in the last situation they are undergoing disintegration (figs. 486, 488, 492). Since the leucocytes are amoeboid, it is probable from these facts that the mechanism of fat-absorption consists of the following processes — viz. 356 THE ESSENTIALS OF HISTOLOGY (1) formation of fat in the columnar epithelium-cells of the surface; (2) ejection of fat-granules from the epithelium into the intercellular Fig. 491. — Vertical section of a portion of a Peyrr's patch with the LACTEAL VESSELS INJECTED. Magnified 32 diameters. (Frey.) The specimen is from the lower part of the ileum ; a, villi, wittf their lacteals left white ; 6, some of the tubular glands ; c, the muscular layer of the mucous memhrane ; d, cupola or projecting Eart of nodule ; e, central part ; /, reticulated lacteal vessels occupying the lymphoid tissue etween the nodules, joined above by the lacteals from the villi and mucous surface, and passing below into g, the sinus-like lacteals under the nodules, which again pass into the large efferent lacteals, g' ; i, part of the muscular coat. Fig. 492.— Section op the villus of a rat killed during fat-absorption. ep, epithelium ; 8ir, striated border ; c, leucocytes ; o', leucocytes in the epithelium ; i, central lacteal containing chyle and disintegrating leucocytes. ABSORPTION FROM INTESTINE 357 spaces ; (3) ingestion of fat by leucocytes, these taking it up after it has passed out of the epithelium-cells ; (4) migration of leucocytes carrying fat-particles through the tissue of the villus and into the central lacteal ; (5) disintegration and solution of th^ immi- grated leucocytes, with setting free of their contents. Fat-particles are never seen in the striated border of the columnar cell. The fat of the food first becomes saponified by the action of the digestive juices, and reaches the epithelium-cell in the form of dissolved soap ; the fat which is seen and stained by osmic acid within the cells has become re-formed by a pro- cess of synthesis. In young sucking animals (puppy, kitten) the fat which is undergoing ab- sorption is sometimes seen not only in epithelium-cells and leucocytes, but also in the form of streaks, stained black by osmic acid, in the interstices of the reticular tissue of the villi. The migration of leucocytes into the lacteals of the villi is not a special Fig. 493. — Mu^^v-u-^^^ - 5 »3 -• '^ia>a^ Fib. 507. — Sections of the wall, oj the gam^-bIiAddbr. (Sommer.) A, Under a low magnifying power, a, muscular coat ; &, a fold of mucous membrane ; c, columnar epithelium ; d, portion represented in B more highly magnified. B, Magnified portion of epithelium and subjacent corium. e, striated border ; /, mucigen granules in cells ; g, blood-capillaries. The gall-bladder is in its general structure similar to the larger bile-ducts. It is lined by columnar epithelium similar to that of the small intestine ; outside this its wall is formed of fibrous and muscular tissue. The mucous membrane is thrown into permanent reticulating folds (fig. 507), which become larger and more numerous near the neck of the gall-bladder. The lymphatics of. the liver were described (by MacGillivray) as com- mencing as perivascular lymphatic spaces enclosing the capillaries of the lobules. But this cannot be the case, since there is np space between the liver cells and the blood in the sinusoid capillaries. There are, however, numerous lymph-vessels accompanying the interlobular branches of the portal vein, and others, less numerous, accompaijying the tributaries of the hepatic veins, but so far as can be ascertained no direct communication exists between the two sets of lymphatics within the lobules, although they communicate freely both at the periphery of the lobules and near their exit from the liver (Herring and Simpson). Most of the liver lymph passes away by the portal lymphatics. ^ For more detailed information on the plasmatic oanaliouli and the lymph- vessels of the liver consult Herring and Simpson in Proc. Hoy. Soc, B., Vol. 78, 1906. THE. PANCREAS 369 The nerves of the liver are chiefly non-myelinated. They reach the organ through the sympathetic. They are distributed both to the blood- vessels and to the liver-cells. The mode of development of the liver has already been mentioned in connexion with the formation of its sinusoid vessels (pp. 223 to 225). THE PANCREAS. The pancreas is a tubulo-racemose gland, resembling the serous salivary glands so far as its general structure is concerned, but differing from thenj in the fact that the alveoli are longer and more tubular in character. Moreover, t&S>) 1 ■ii ^1 /'' ^ '-'*'*^.^#' Fit;. oOy. — An iblet ot' LaiNukkmans i-N i'Ai.ciiEAs us Dui.. Magiulied 300 diameters. [Fig, 510. — Past or an alveolus of the kabbit'S pancreas. A, at kest ; B, aftbb active secketion. (From Foster, after Kflhne and Lea.) ((, the inner granular zone, which in A ig larger and more closely studded with granules than in B, in which the granules ore fewer ; b, the outer transparent zone, small in -4, larger in B, and in the latter marked with faint stria) ; o, the lumen, very obvious in B, but indistinct in A \ d, indentation at the junotipn of two cells, only distinct in B, 508, 509, 510, A, 511). After a period of activity the clear part of the cell becomes larger, and the granular part smaller (fig. 510, li ; fig. 512). In htematoxylin-stained sections the outer part is coloured more deeply than the inner (fig. 509), In sections stained by Mallory (see Appendix) the granules of the inner zone are coloured intensely red, and stand out black in photo- THE PANCREAS 371 graphs. The granules are always most abundant in the alveoli immediately surrounding the islets (Kojima), Pancreas-cells frequently exhibit a rounded mass of mitochondria near the nucleus, ■which is known as the paranucleus (see fig. 8) : it is probably .Fig. 511. — Alveoli of dog's pancreas, cells loaded: osmio pbepakatiok. (Babkin, Bubasokin, and Sea^witsch.) related to the secretory activity of the cells. A paranucleus is not peculiar to the pancreas, although often better marked in that organ than elsewhere. Under normal circumstances the pancreas-cells never exhibit karyokinesis or show any evidence of multiplication. But in rats fed with thyroid gland in Fig. 512. — Alveoli or dog's pancreas after a p'eriod of activity produced BY application of acid to mucous membrane of duodenum. {Babkin, Rubasckin, and Ssawitsch.) addition to their ordinary food numerous mitoses can be seen throughout the gland, indicating rapid cell-division (Kojima). In the centre of each acinus there may genwally be seen a few spindle- shaped cells (centro-acinar cells of Langerhans— »fig. 508, d). The nature of these has not been definitely determined ; they appear to be continued from 372 THE ESSENTIALS OF HISTOLOGY the cells which line the smallest ducts (fig. 508, e). Sometimes they are more conspicuous, and fill the parts of the alveoli which are nearest to the duct ; in these cases the mass of cells which they form is liable to be mistaken for a Langerhans' islet. Diverticula from the lumen of the alveolus penetrate between the alveolar cells (fig. 513) as in serous glands generally. The islets ' •■■ ■•,•'. ■ ^ ElG. 513. — A D0CT OF THE PANCBEAS WITH LATERAL DIVEETIO0LA INTO THE ALVEOLI : GoLOi METHOD. {E. MiiUer. ) In A the duct is shown cut lon^tudinally and giving: off ductules, m, to the alveoli, where they extend between the cells, (. In B the details of their tel'mination are shown more highly magnified. are wholly unconnected with the ducts, although originally developed from them. Blood-Tessels. — Like all secreting glands the pancreas is very vascular. Each alveolus has a network of capillaries closely surrounding it, but always outside its basement-membrane. The capillaries of the islets are large and irregular and resemble sinusoids (fig. 514). Nerves. — The pancreas has many nerves, with numerous small nerve-cells distributed upon their course ; the nerve-fibrils end by ramifying amongst the cells of the alveoli, as in the salivary glands. In the cat, which has THE PANCREAS 373 Pacinian bodies in its mesentery, these terminal organs are also found numerously in the substance of the pancreas, but this is a mere accident, resulting from the fact that the pancreas in the cat — as in many other animals — has a thin extension between the layers of the mesentery, and the last-named membrane always in the cat contg,ins Pacinian corpuscles. Fig. 514. — Injection of blood-vessels of ah (Kiihne and Lea. ) 'I^LET" OF THE PANCREAS. Development. — The pancreas is fornjed from an outgrowth (at first solid, afterwards becoming hollowed) of the entoderm of the small intestine much in the same way that the salivary glands are developed from the ectoderm of the mouth. The islets of Langerhans make their appearance as buds from the developing ducts, but they remain solid and do not acquire a lumen like alveoli ; their oonnesion with the ducts becomes lost and they become isolated in the midst of the glandular substance of the organ. 374 THE ESSENTIALS OF HISTOLOGY LESSON XXXVI. THE KIDNEY, URETER, AND BLADDER. 1. Sections passing through the whole kidney of a small mammal, such as a mouse or rat. These sections show the general arrangement of the organ and the dis- position of the tubules and Malpighian corpuscles. 2. Thin formol -fixed sections of the human kidney, if it can be obtained perfectly normal ; or failing this, of the kidney of the dog or cat, may next be studied. Some of the sections should be cut parallel with the rays of the medulla; others across their direction. The' characters of the epithelium of the several parts of the uriniferous tubules and the structure of the glomeruli are to be made out in t^ese sections. 3. Separate portions of the uiiniferous tubules may be studied in teased preparations from a kidney which has been maceiuted in strong hydrochloric acid for a few hours. This renders it possible to unravel the tubules for some distance. 4. Thick sections of a kidney in which the blood-vessels have been injected. Examine these with a low power of the microscope. Follow the course of the arteries of the cortex sending their branches to the glomeruli, and observe the pencils of capillaries which run from the deeper glomeruli between the straight uriniferous tubules of the bo'undary zone. Notice the efi^ereht Vessels from the rest of the glomeruli breaking up into the network of capillaries* distributed to the convoluted tubules. 5. Section across the lower part of the ureter and another across the upper part near the pelvis of the kidney. 6. Section of the urinary bladder vertical to the surface. The organ should be moderately distended by the fixative. In the sections of the ureter and of the urinary bladder, notice the transitional epithelium resting on a mucous membrane composed of areolar tissue, without glands in most animals ; also the muscular coat outside the mucous membrane. In the ureter there is a^laj'er of connective tissue outside the muscular coat, and at the upper part of the bladder a layer of serous membrane covering the muscular tissue. The kidney is a compound tubular gland. To the naked eye it appeai-s formed of two portions — a cortical and a medullary (fig. 515). The latter is subdivided in man into about twelve conical portions (pyramids of Malpiyhi), the base (boundary zone) of each being surrounded by cortical substance, while the apex projects in the form of a papilla into the dilated commence- ment of the ureter (pelvis of the kidney).^ B(5th cortex and medulla are composed entirely of tubules — the uriniferous tubules — which have a straight direction in the medulla and a contorted arrangetoent in the cortex ; but groups of straight tubules also pass from the medulla through the thickness of the cortex as the so-called medullary rays (figs. 515, 516). ' In many animals (R.g. dog, cat, rabbit, monkey) the whole kidney is formed of only a single pyramid ; in others the pyramids are even more numerous than in man. In some animals the pyramids form distinct portions^ of kidney substance united by connective tissue. THE KIDNEY 375 Fig. 515. — Diagram op the course or the tubules ik a unipybamidal ICIDNET, SUCH AS THAT OF THE RABBIT. (Toldt.) fi, Malpighian tiodiea ; b, first convoluted tubule ; c, rf, Irfoped tube of Henle ; e, second convoluted tubule ; /, collecting tube ; j7, ducts of Bellini. begin The urinifetous tubules .dilatations, each enclosing a tuft or glomerulus of convoluted capillary blood-vessels (corpuscles of Mal- piffhi), the dilated commencement of the tubule being known as the capsule (fig. 519, M). The glomer- ulus is lobulated (figs. 517, 518); the lobules being united by the branches of the afferent and efferent vessels ; it is covered by a flattened epithelium reflected from that lining the capsule ; this epithelium dips in between the lobules. The glomeruli near the medulla are larger than the rest and have more lobules. The capillary-wall in all the glomeruli is a syncytium, show- i ing no cell-outlines in silver pre- pacations (Drasch). The tubule leaves the capsule by a neck (fig. 519, n) which is, however, rarely narrower than the rest in the cortical part of the organ in • \ I'lU,, Fig. 516.— Section through part of a dog's kidney. (Ludwig.) , papillary^ and /?, boundary zones of the medulla ; r, cortical layer ; h, bundles of tubules in the boundary layer, separated by spaces, b, oontp.ininff bunches of vessels (not here represented), and prolong-ed into the cortex as the medullary rays, m ; c, intervals of cortex, composed chiefly of con- voluted tubulea, with irregular rows of glomeruli, between the medullary rays. of the tubule in mammals. In some 376 THE ESSENTIALS OF HISTOLOGY F[G. 317. — A Malpighian corpuscle from the kidney of the monkey. (Szymonowicz. ) Magnified 350 diameters. a, a, sections of convoluted tubules ; a', commencement of convoluted tube from capsule ; b, capsule ; c, afferent and efferent vessels of glomerulus. animals (e.g. frog) the neck is long, and has ciliated epithelium. The tubule is at first convoluted (first or distal convoluted tubule). It then becomes nearly straight or slightly spiral only (spiral tubule) and rapidly narrowing passes down into the medulla towards the dilated com- mencement of the ureter as the descending limb of the looped tubule of Henle. It does not at once, however, open directly into the pelvis" of the kidney, but before reaching the end of the papilla it turns round in the form of a loop (loop of Henle), and passes upwards again towards the cortex, parallel with its former course, and larger than before (ascending limb of looped tubule, of Henle). Arrived at the Fio. 518.— Model of a glomerulos. (Johnston,) a, afferent ; e, efferent blood-vessel. THE KIDNEY Z77 cortex it approaches close to the capsule from which the tubule took origin, but at a point opposite to the origin, viz., near the aiferent and Fig. 519. — Plan of the arrange- ment OF THE URINIFEROUS TUBULES. (Huber.) M, Malpig-hian corpuscles ; v, point of entrance of vessels of g^Iomerulus ; n, neok ; d.e.^ distal convoluted tubule, which arises from the Malpighian corpuscle ; e, spiral tubule into which it is continued ; d, narrow descending' limb of loop of Henle ; S, loop of Henle (this is sometimes formed by the narrow part of the looped tubule, but is here represented as formed by the wider part) ; a, wider ascending limb of loop of Henle ; this passes back to the neighbourhood of the' same Malpigrhian corpuscle, often becoming irreg:ular and zigzag- at its upper end. Here it becomes continuous with the proximal convoluted tubule, p.c, which ■i^ventually passes into the junctional tubule, j, by which it is connected with a collecting tubule, c. B, duct of BelHni, receiving a number of con- joined collecting tubules and opening at a papilla. > (I.e. eiferent vessels of the glomerulus (Golgi). It then becomes larger and irregularly zigzag {zigzag or irregular tubule), and again somewhat convoluted {second or proximal convoluted tubule). Eventually it straightens out again and narrowing into a small vessel {junctional ttibule)^ join^ a straight or collecting tubule. The last-named unites with others to form larger collecting 378 THE ESSENTIALS OF HISTOLOGY tubes which pass through the medullary substance of the kidney to open at the papilla as the ducts of Bellini (fig. 520). The tubules are throughout ' bounded by a basement-membrane, which is lined by epithelium ; the characters of the epithelium-cells vary in the \i%i/jViv- Pio. 520. — Longitudinal section through a papilla of the kidney, sho\vi>'i: ITS projection at one or THE CALICES OF THE KIDNEY -PELVIS. (Disse.) The ducts of Bellini are seen cut obliquely ; the smaller tubules are looped tubules of Hbnle ; a, epithelium covering papilla. ; !», epithelium lining calix ; c, cavit.v of calix ; d, connective tissue. different parts of a tubule. In the. capsule (fig. 517), the epithelium is flattened and is reflected over the glomerulus. In some animals (e.g. mouse) the granular epithelium of the convoluted tube is prolonged a little way into the capsule. In the distal convoluted and spiral tubules the epithelium is thick, and the cells are markedly granular, withi a tendency for the basiphil granules (mitochondria) to be arranged in lo,ngitudinal rows as in the THE KIDNEY 379 cells of the salivary ducts (rodded or fibrillar appearance, fig. 522). The granules near the lumen are not so arranged and are eosinophil. The cells often exhibit a brush of cilium-like processes projecting into the lumen (fig. 522), but these are not vibratile. In the najrrow descending limb of the looped tubules, and sometimes in the loop itself, the cells are clear and Fig. 521. — Part of a section through the cortex of a human kidney, the BLOOD-VESSELS OF WHICH HAVE BEEN INJECTED. (Disse.) gl., a glomerulus ; m.r., section of a myelin ray. flattened (fig. 523), and leave a relatively large lumen; but usually in the loop and always in the ascending limb they again acquire a granular or fibrillar structure and may nearly fill the lumeil. The arrangement of the cell-granules in lines perpendicular to the basement-membrane is still more marked in the zigzag tubules, and a similar structure is present also in the proximal convoluted tubules, into which these pass. On the other hand, the junctional tubule has a larger lumen and in it the granular striated epithelium 38o THE ESSENTIALS OF HISTOLOGY gives place to clear flattened cells. The collecting tubes have also a very distinct lumen and are lined by clear cubical or columnar epithelium-cells (fig. .527, a). The following gives a tabular view of the parts which compose a uriniferous tubule, and the nature of the epithelium in each part : — Portion of Tubule. Natokb of Epithkuum. Position of Tubulb. Oapaule - Flattened, reflected over glomer- Labyrinth of cortex.' ulus, where its cells are said to form a syncytium Distal convoluted tubule Cubical, granular, with appear- ance of fibrillation (" rodded "), the cells interlocking Labyrinth of cortex. Spiral tubule Like the last Medullary ray of cortex. Descending limb of Clear flattened cells Boundary zone and looped tubule partly papillary , zone of mec\ulla. Loop of Henle Like the last (or may be like the Papillary zone of ascending limb) medulla. Ascending limb of Cubical, granular ; the cells some- Medulla, and medul- looped tubule times imbricated lary ray of cortex. Zigzag tubule Cells strongly "rodded"; vary- ing height, lumen small Labyrinth of cortex. Proximal convoluted Similar to distal convoluted tube, Labyrinth of cortex. tubule but cells are longer, with larger nuclei, and they have a more refractive aspect .Junctional tubule - Clear flattened and cubical cells Labyrinth, passing to medullary raj'. Straight or collecting Clear cubical and columnar cells Medullary ray and tubule medulla. Duct of Bellini Clear columnar cells becoming Opens at apex of cubical near the mouth. papilla. Fto. 522. — Skition of a convoluted TURrLE OF THE RABBIT's KIDNBY, SHOWING THE STRnCTURB OF THB EPITHELIUM. (Szymonowicz.) Mag- nified 11 00 diameters. Blood-vessels.^ — The renal artery divides into branches on entering the organ, and these branches pass towards the cortex, forming arched vessels between the cortex and the medulla (fig. 524, a). The branches of the renal vein which are similarly placed are more distinctly arched {g). From the arterial arches vessel? pass through the cortex {cortical or irbterlobtdar arteries, 6), and give oflf at intervals (in some animals from one side only) small arterioles {afferent vessds of the glomeruli), each of which enters the dilated commencement of a uriniferous tubule, within which its capillaries form a glomerulus. From the The part of the cortex between and surrounding the medullary rays is so named. THE KIDNEY' 381 glomerulus a somewHat smaller efferent vessel passes out, and this at once again breaks up into capillaries, which are distributed amongst the tubules of the cortex (e). Their blood is collected by veins which run parallel with the cortical arteries but not in juxtaposition with them. These veins join the venous arches between the cortex and the medulla. They receive blood from certain other veins which arise by radicles having a somewhat stellate arrangement near the capsule (penK stellulm, j). The medulla derives its blood-supply both from special ofl'sets of the arterial arches, which immediately break up into pencils of fine straight arterioles running in groups between the straight tubules of the medulla, and from the efferent vessels of the glomeruli which are near'the medulla. Fig. 523i — Passage or tke spibai, coistikuatiojs of a distal convoluted tubule INTO the descending LIME OF LOOPED TUBULE 0¥ HeNLE. (Disse.) The bend is accidental. i', end of spiral tubule ; d, narrow descending limb of looped tubule of Henle. These vessels supply a capillary network with elongated meshes which pervades the medulla (iig. 524, /), and which terminates in a plexus of somewhat larger venous capillaries in the papilla. From these capillaries the venules of the medulla collect the blood, and pass, accompanying the straight arterioles, into the venous arches between the cortex and medulla. The groups of small arteries and veins {vasa recta) in the part of the medulla nearest to the cortex alternate with groups of the uriniferous tubules ; this arrangement confers a striated aspect upon that part of the medulla (boundary zone, fig. 516, g). In some animals most of the blood-supply of the medulla comes from the efferent vessels of the deep glomeruli. Between the uriniferous tubules, and supporting the blood-vessels, is a 382 THE ESSENTIALS OF HISTOLOGY variable amount of connective tissue, greatest in quantity in the papillae (fig. 527) ; it contains cleft-like lymphatics. Nerve-fibrils ramify amongst the epithelium-cells of the tubules (fig. 528), but most of the nerves to the kidney are distributed to its blood-vessels. Fig. 524. — Vascular sdpply of kidney. (Cadiat.) c(, part of arterial arch ; 6, interlobular artery ; c, glomerulus ; d^ Cerent vessel passing to medulla ; e, capillaries of cortex ; /, capillaries of medulla ; g, venous MCh ; h, straight veins of medulla ; ^, vena stellula ; t, interlobular vein. Development of the uriniferous tubules. — The ducts of Bellini and the collecting tubules are derived as hollow sprouts from the enlarged upper end of the ureter, which in its turn is formed as a bud from the Wolffian duct of the embryo. The rest of the uriniferous tubule, including the Malpighian corpuscle, is formed from a hollow S-shaped island of cells which become differentiated in the mesoderm near the blind end of a collecting tubule. The lower part of the S forms a spoon-shaped structure, within the bowl of which the vessels of the glomeruli are developed ; the sides of the bowl then grow round and completely THE KIDNEY 383 Fig. 525. — From an injected kidney. (Prenant and Bouin. ) Cortical arteriole on the left g'i\ ing off an afferent vessel to the glomerulus. From this a (smaller) efferent vessel oomes off and joinalihe capillaries surcounding the tubules. Fig. 526.— a GLOMERUiiUS from ^he part of the o®rtex of the horses kidkey NEAREST THE MEDULLA* INJECTED. (Bowman.) Magnified 70 diameters, a cortical artery ; c^. afferent vessel of glomenihis ; mm, glomerulus ; ej?, efferent vessel breaking up ' into a pencil of capillaries, 6, which pass down between the tubules of the medulla. 384 THE ESSENTIALS OF HISTOLOGY enclose them. The upper part of the S forms a convoluted tubule which before long makes connexion with the previously blind end of the forked collecting 'r'^'' Fig. 527. — Section across x papilla or the kidney. (Cadiat.) a, large collecting tubes (ducts of Eellini) ; &, c, d, tubules of Henle ; e, arterial capillaries ; /, venous capillaries packed with blood-corpuscles. tubule. At first there is no sign of the looped tubule, but this presently grows down from the convoluted tubule, very much as if a part of this tube had been Fig. 62S. — NtKVE-ilBHILS ending UVEK OAJ'LLLARV ULuuU-VESSKLS AM> AMONIiST THE EPITHELIUM-CELLS OF A CONVOLUTED TUBE OF THE FROG's KIDNEY. (Smirnow.) drawn out towards the papilla. The several stages of formation of the uriiiiferous tubule are shown in the diagrams marked 1 to 5 in fig. 5l'9. These diagrams exhibit nine stages of development of the tubules, since in every one, except diagram 3, an earlier stage is represented upon the left-hand side, and a later upon the right-hand side. THE URETER AND BLADDER 3«5 Fir. 529.— Five diagkams to illustrate the mode of development or the UKINIFEROUS TUBULES AND THE GLOMERULI.. (Hllber. ) THE URETER AND BLADDER. The ureter (fig. 530) is a muscular tube lined by mucous membrane. The muscular coat consists of two layers of plain muscular tissue, an outer circular, and an inner longitudinal. In the lower part there are some longitudinal bundles external to the circular. Outside the muscular coat is a layer of connective tissue in -which the blood-vessels and nerves ramify before entering the muscular layer. The mucous membrane is composed of areolar tissue, and is lined by transitional epithelium, like that of the bladder. The urinary bladder has a muscular wall lined by a strong mucous mernbrane and covered in part by a serous coat. The muscular coat consists of three layers, but the innermost is incom- plete. The principal fibres run longitudinally and circularly ; the circular fibres are collected into a layer of some thjckness which immediately surrounds the commencement of the urethra.- The mucous membrane is 386 THE ESSENTIALS OF HISTOLOGY lined by a transitional stratified epithelium (fig. 531). The shape and structure of the cells have already 'been studied (p. 66). Many of the «>. 1 W-" -t ' ''' -1 t-> J^ / . .. "!SA • , ' ( Fig. 530. — Section across ureter: hug. Magnified 90 diameters. superficial cells have two nuclei. Gland-like invaginations of the epithelium are occasionally found near the base of the bladder in man (fig. 531) ; in the bladder of some animals well-marked glands constantly occur. r Fir; fiSl. — Section or Vakt ot wall of B.isli mf uladder: human. (Lendorf.) Magnified 230 diameters. The section passes through a glandular invacrination of the epithelium, ep^ epithelivuii ; c, corium. The nerves to the bladder form gangliated .plexuses, and are distributed to the muscular tissue and blood-vessels : some are said to enter the epithelium. THE MALE GENERATIVE ORGANS 387 LESSON xxxvir. THE MALE GENERATIVE ORGANS. 1. Sections across the penis (child or monkey). The blood-vessels of the organ should be injected with the hardening fluid so as the better to exhibit the arrange- ment of the venous spaces which constitute the erectile tissue. Notice the large venous sinuses of the corpora cavernosa and the smaller spaces of the corpus spongiosum ; in the middle of the latter is seen the (flattened) tube of the urethra, 2. Section of prostate gland (child or monkey). Notice the glandular tubes and the plain muscular tissue of the prostate. Th,e character of the urethral epithelium may also be observed. 3. Section of testicle and epididymis. The sections may be made from testicles (rat, cat) hardened in formol ; they can be stained with hsematoiylin and eosin or with iron-hsematoxylin. In these sections notice the strong capsule surrounding the gland, the substance of which consists of tubules which are variously cut ; and the epithelium of the tubules, which is in different phases of development in differeiit tubules. Observe the strands of polyhedral interstitial cells, much niore abundant in the cat than in the rat, lying in the loose tissue between the tubules ; also the lymphatic clefts in that tissue. Notice in sections through the epididymis the lining epithelium and spermatozoa within the lumen of the tube. Sketch carefully under a high power the contents of some of the seminiferous tubules to illustrate the mode of formation of spermatozoa. 4. Section of vesicula seminalis, fixed and hardened in formol and stained with hsematoxylin and eosin or with iron-hsematoxylin. Notice the two-layerod epithelium, the more superficial cells long an^ columnar but not ciliated ; the deeper cells short and swollen out by clear fluid. 5. Examination of spermatozoa. Spermatozoa may be obtained fresh from the testicle or epididymis of a recently killed mammal and examined in saline solution. Their movements may be studied on the warm stage- ," to display their structure a very high power of the microscope is necessary. They may be preserved and stained as " film " preparations, as with mariow (p. 32). THE PENIS, URETHBA AND PEOSXATE. • The penis is for the most part composed of cavernous tissue which is collected into three principal masses— the two corpora cavernosa, one on each side but conjoined in the middle line, and the corpus spongiosum inferiorly. The corpus spongiosum i^ expanded at the extremity of the penis to form the glans. It is traversed throughout by the tirethra, which extends from the bladder to the apex of the glans. Each of these masses is bounded by a strong capsule of fibrous and plain muscular tissue, containing many elastic fibres and sending in strong septa or trabeculse* of the same tissues, which 388 THE ESSENTIALS OF HISTOLOGY form the boundaries of the cavernous spaces of fhe erectile tissue (fig. 533). The arteries of the tissue run in the trabeculae, and their capillaries open into the cavernous spaces. On the other hand, the spaces are connected with efferent veins. The arteries of the cavernous tissue can sometimes in injected specimens be observed to form looped or twisted projections into the cavernous spaces (helicine arteries), into which they may open directly. The arteries of the cavernous tissue often show localised thicknesses of the ■*», ^■^ Fig. 532.— Tkansvekse section of glans rBnis of child. (Rothfeld.) C.C., corpora cavernosa ; 6'p, corpus sponfjiosum ; f;p\ corpus spongiosum urethric, with the lumen of the urethra in the centre appearing as an irret^lar slit with folded walls. inner coat, and many of the veins have longitudinal muscle-fibres in the inner coat which form pad-like projections into the lumen. The integument, especially tha,t of the glans, contains numerous special nerve-end organs of the nature of end-bulbs. Pacinian bodies are found upon the deeper nerves of the penis. Lymph vessels are numerous in the integument of the organ and in the submucous tissue of the urethra. Urethra. — The lumen of the urethra appear^ in sections across the penis in the form of an irregular cleft in the middle of the corpus spongio- sum (fig. 532). It is lined in the prostatic part by transitional, but elsewhere by columnar epithelium, except near its orifice, where the epithelium is stratified. The urethral epithelium rests upon a very THE MALE GENERATIVE ORGANS 389 vascular mucous membrane. Outside this is a coat of submucous tissue, with two layers of plain muscular fibre— an inner longitudinal and an outer circular. Some of the fibres are cross-striated. Outside the muscular coat is a close plexus of small veins which is connected with, and forms part of, the corpus spongiosum. The mucous membrane of the urethra is beset with small mucous glands, simple and compound {glands of Littre). There are also a number of oblique recesses termed lacunae. Besides these small glands and glandular recesses, two Compound racemose glands open into the bulboiis portion of Fig. 533. — Section of erectile tissue. (Oadiat.) a, trabecule of connective tissue, with elastic fibres, and bundles of plain muscular tissue, some cut across (c) ; &, blood-stnuses. the urethra in the male (Gowper's glands). Their acini are lined by clear columnar cells like those of the . glands of Littre (fig. 534), yielding a mucns-like secretion. The prostate, which surrounds the commencement of the urethra in the male, is a muscular and glandular mass, the glands of which are composed of tubular alveoli, lined by columnar epithelium, with smaller cells lying between them and the basement-membrane (fig. 535). Their ducts open upon the floor of the urethra. In older subjects the tubules often contain colloid or calcareous concretions. The muscular tissue is of the plain variety. The prostate is pierced by the two common ejaculatory ducts which open one on each side of a median elevation of the mucous membrane of the floor of the urethra. Between these orifices is an aperture leading into the prostatic utricle (uterus masGulinus)i The blood-vessels and 390 THE ESSENTIALS OF HISTOLOGY nerves of the prostate are numerous. The nerves are provided with small ganglia and are distributed partly to the muscular tissue, partly to the ^m Fig. 534. — Section thhough the opening of tiie duct of a gland into THE MALE URKTURA. (Llchtenberg. ) g, gland ; m, its mouth ; n, epithelium of urethra. The ^,'1.111(1 is similar in structure to Cowper's glands, but simpler in uunformation. Its i-ells are niucus-secretiiig. glands ; others which are sensory pass to the capsule, and to the wall of the urethra. The sensory nerves end in plexuses and in peculiar terminal corpuscles like simple Pacinian bodies. f *-. ','1 •'-5 . .-. ■ " /i' 'j 0' "•?.''%; ^ hV f>\ 4* , ^•; "" H'*;!' '<■■. '"-* 'i 'iV > '^.Ir. A 1 \ |3;; y vk„„ %r l.v';/'::'-: .-r3^--'"^-V-'^ a-^|^^%fr^^?ri'^^ ■ ^ — '""'ll' ^- ■' \. ■•':/ Fio. 535.— Section of pkostatis of monkey. (Marshall.) u., alveolus ; 6, a concretton within an alveolus ; c, stroma ; d, a blood-vessel. a b Fig. .536.— Section of human testis and epididymis. (Eohm .and v. Davidoff.) a dandular substance divided into lobules by septo of connective tissue ; 6, tunica albuginea ; «, ' head of epididymis ; d, rete testis ; e, middle part or body of epididymis ; /, mediastmum givmg — =— -■ '■- ^h- zzr^t:. : ;. i^.zJul.un^i ^t i.r«c ui»io,uic,'iiiuig vas deferens. 392 THE ESSENTIALS OF HISTOLOGY Ki.:. .".:i7. Fi(.. 5:is. Fic TiilT. — Plan of arrancf.ment hf TrrruN amp nrcTS of tfsttii.k. ,., tlllilili r,, III,, I'll ; /,, hiliiili iTi-li; c. rc-U- li-Slis; rf, i;i^,a .-fftliiit ia ; >'.f,:i. innvolutt-il tlllif of tlir ijiiiliilv iiii^ ; /,, \ a^ deferens ; /, tunica allniiriijea with traiieruia-. Fic, 538. — Transvfkse sf.otion of tf:stii']j; ami Ai'IDIDYMik: jiax. (Eberth.) «, tunica allni^finea; .v./,. st'iniiiiferous tnliulf^^: ,*-■. tralieculte ili\it]inix tlie Lrlaiid into icliule-j; c. tunica Mii^Miialis; r', ca\it\ of tunica \'acaiialis ; m, uieili^t^tinum teyti,^; c, epidii1\ iiii^ ; c. ca|,ut. c]ii'li'iviu^ : '/, \ as (ietereris {rut I cur limes) ; /-.c, \ai^a etTerentia. Fig. 539. — I'ahsauk of convoldted skminiferous ti'iuujES imto straight TUHUl.KH AND OF TIIKSK INTO TIIK UKTE TKSTIS. (MilialkowicZ.) u, u, HQUjiiiiferous tubules ; b, flbroua stroma I'oiitinued from the mediastinum testis ; c, I'ete testis, THE MALE GENERATIVE ORGANS 393 THE TESTICLE AND ITS DUCTS.- The testicle is enclosed by a strong fibrous capsule, the tunica albuginea (figs. 536, 537, 538). This is covered externally with a layer of serous epithelium reflected from the tunica vaginalis/ From its inner surface there proceed fibrous processes or trabeculce, which imperfectly subdivide the organ into lobules. Posteriorly the capsule is prolonged into the interior of the gland in the form of a mass of fibrous tissue, which is known as the mediastinum testis. Attached to the posterior margin of the body of the gland is a mass (epididymis) which when investigated is found to consist of a single convoluted tube, receiving at its upper end the efferent ducts of the testicle and prolonged at its lower end into a thick-walled muscular tube, the vas deferens, which conducts the secretion to the urethra. The glandular substance of the testicle is wholly made up of convoluted tubules (tubuli contorti), which when unravelled are of very considerable length. Each ' commences near the tunica albuginea, and after many windings terminates, usually after joining one or two others, in a straight tubule. The straight tubules (tubuli recti) pass into the mediastinum, and there form by their union a network of intercommunicating vessels of varying size, which is known as the rete testis (fig. 539). From the rete a limited number of efferent ducts or tubules (vasa efferentia) arise, and after a few convolutions pass into the tube of the epididymis. The straight tubules which lead from the convoluted seminiferous tubes into the rete testis are lined by only a single layer of clear flattened or cubical epithelium cells. The tubules of the rete also have a simple epithelial lining ; both in these and in the straight tubules a basement-membrane is absent, the epithelium being supported directly by the connective tissue of the fiaediastinum. The efferent tubides which pass from the rete to the epididymis are lined by columnar ciliated epithelium. In man their lumen js irregular in section, and the inner surface is pitted with glandular depressions lined by short clear non-ciliated cells. Epididymis. — This is composed of a single convoluted tube 6 to 8 metres long which receives the vasa efferentia above, and below is continued into the yas deferens. The tube is lined by long columnar cells with oval nuclei, having at their bases smaller polyhedral cells with spherical nuclei (figs. 540, 541). The columnar cells are provided with bunches of cilia projecting into the lumen of the tube, but it is alleged that these cilia are not always vibratile. The cells exhibit canaliculi in their cytoplasm, which, according to Holmgren, communicate with the exterior a£ the attached border of the -cell (fig. 542). The vas deferens (fig, 543) is a thick-walled tube, having an outer layer formed of longitudinal bundles of plain muscular tissue, and an inner equally thick layer of circular bundles, of the same tissue ; within this again 394 THE ESSENTIALS OF HISTOLOGY is a thinner layer of longitudinal muscle. There'is a good deal of connective and elastic tissue between the muscular bundles. The tube is lined by a Fig. 540. — From a section of the epididymis : human. Magnified 60 diameters. Photograph. From a preparation by Prof. M. Heidonhain. ■■"'- VjBJ- Fin. 541. — Part of the same section. Magnified 200 diameters. The tubules rontain spermatozoa. mucous membrane, the inner surface of wliich is covered by columnar non- ciliated epithelium. THE MALE GENERATIVE ORGANS 395 The vesiculse seminales are glandular structures, consisting on each side of a main part, with several accessory parts, each part being composed of a Fig. 542. — Cells of kpididymis, showing canalisation of the cytoplasm. (E. Holmgren.) n, nucleus. In two cells the canals extend to the basement-membrane. convoluted tubule of considerable length when unravelled, corresponding vas deferens. The tubules are lined by long columnar epithelium. Their convplutions are held together by connective tissue containing many blood- vessels and cleft-like lymphatics (fig. 544). Between the bases of the epithelium-cells is a row of bladder-like cells occupied by clear fluid and having a very char- acteristic appearance in stained sections. The columnar cells yield a secretion which is poured out from them in the form of droplets which accumulate to form a clear or opalescent fluid filling the tubes. This fluid, in some animals {e.g. guinea-pig), has the property of coagulating when it is ejected into the vagina. The duct joins the MICEOSCOPIC STEUCTUEE OF THE TESTICLE. Fic. 543. — Section across the commence- ment OF 'BHE VAS deferens. (Kleiii.) (t, Gpithelium ; h, mucous membrane ; c, d, &, inner, middle, and outer layers of the nmscular coat ; /, bundles of the internal cremaster muscle ; //, section of a blood-vessel. The intertubular tissue. — The connective tissue between the tubules of the testicle is generally of very loose texture, and contains numerous lymphatic clefts, which form an intercommunicating aystein of commencing lymphatic vessels. Lying in this intertubular tissue are strands of poly- 396 THE ESSENTIALS OF HISTOLOGY Fig. 544,— Vesioula seminalis of ox. Photograph. Magnified 200 diameters. Drops of secretion are seen at the free ends of some of the cells. Fio. 545. — Hdman testicle. Magnified 50 dimeters. Photograph. From an iron-ha>matoxylin preparation by Prof. M. Heidenhain. The masses of interstitial cells are stained dark in this section. hedral epithelium-like cells (^interstitial cells, figs. 545, 546, 547) of a yellowish colour ; they are more abundant in some species of animals (cat, boar) than in others. They accompany the blood-vessels before these break THE MALE GENERATIVE ORGANS 397 up to form the capillary networks which cover the walls of the seminiferous tubules. The interstitial cells contain in many animals yellowish-brown lipoid -■■- N -■^■-■rn-.-Z' ' ** .;'i'« * r '^'' ;-» -«*^ ■.;^»; r^j^a ■* .4 f : Fig. 546. —From a section of testicle of cat. Photograph. Magnified 200 diameters. t, section of a tubule ; i, interstitial cells, lying between three tubules. Fig. 547.— Section of testicle of a boy of nine years old. Highly magnified. (Spangaro.) a, enlarged cells (spermatogonia), some of them dividing ; several^ con tain crystals (Lubar's crystals) J- b, cells lininj2f the tubule ; c, coagulated contents of tubule ; d, interstitial tissue j e, mast-oells. 398 THE ESSENTIALS OF HISTOLOGY or fatty globules (staining with osmic acid), and sometimes needle-shaped crystals (protein). Similar fatty globules may occur in the Sertoli cells of the seminiferous tubules ; they are believed to pass into those cells from the interstitial tissue. The seminiferous tubules. — The setniniferous tubules are formed of a connective tissue membrane, which has a lamellar structure. The lamellse are covered by flattened cells ; fibres, chiefly elastic, occupy the substance of Fio. 548.- -Section from the testicle of a man 42 yeaks old. about 350 diameters. (Spangaro. ) Magnified a, interstitial cells ; 6, some containing pigment ;' c, nuclei of ordinary connective-tissue cells \ d, mast-cell. In the section of the tubule may be seen in succession from without in, spermato- gonia, spermatocytes, spermatids, and spermatozoa. A few spermatids and spermatozoa are detached and occupy the middle of the tubule. each lamella. In the adult the tubules contain several layers of epithelium- cells, but in the child there is no clear distinction into layers, the cells being all more or less similar (fig. 547). Of the layers seen in the tubules of the adult testicle, the one next to the basement-membrane is a stratum of clear cubical cells {spermatogonia or spermatogons, fig. 548), the nuclei of which for the most part exhibit the irregular network which is characteristic of the resting condition, but in some tubules show indications of division. Here and there between the spermatogonia some of the lining epithelium- cells are enlarged, and project between the more internal layers, bein$; THE MALE GENERATIVE ORGANS 399 connected with groups of developing spermatozoa. These enlarged cells are the aelh of Sertoli (fig. 552, a, a ; fig. 555). Next to this lining epithelium is a zone of largpr cells (spermatocytes, fig. 552, 6), the nuclei of which are usually in some stage of hetero- or homo-typical mitotic division (see p. 1,6); these cells may be two or three deep (as in fig. 548, and in o, fig. 549). Next to them, and most internal, are to be seen in some tubules (fig. 548, 'and fig, 549, h and c) a large number of small protoplasmic cells with simple spherical nuclei [spermatids, fig. 552, c). In other tubules the spermatids are elongated, and the nucleus is at one end, and in others again these elongated cells are .^ / d- '\ Fig. 649. Fig. 550. Fig. 549. ^Section of paets of tiibbe seminiferous tubules of the eat, as seen under a low power. ft, with the spermatozoa least advanced. in development; b, more advanced; c, containing fully developed spermatozoa. Between the tubules arc seen stra^ids of interstitial cells with blood- vessels and lymph-spaces. Fig. 550. — Human speematozoa. Magnified 1000 diameters. (G. Retzius.) 1, in profile ; 2, viewed on the flat ; h, head ; c, middle-piece ; d, tail ; c, end-piece of the tail, which is described as a distinct part by Retzius. completely converted into spermatozoa, which lie in groups : their heads projecting between the deeper cells and connected with one of the Sertoli cells of the lining epithelium, and their tails emerging into the lumen of the tubule (fig. 549, h). As the spermatozoa become matured they gradually shift altogether towards the lumen, where they eventually become free (c) ^ from the Sertoli cells. During the time that one set of spermatozoa has been forming, another set of spermatocytes is produced by the division of the spermatogonia, and after the discharge of the first set of spermatozoa the process of division of spermatocytes to form spermatids and development of spermatozoa from these is repeated as before (see diagram, fig. 552). The spermatids were termed young spermatozoa by S. H. Brown, from whose investigation of the subject the above account is mainly derived. 400 THE ESSENTIALS OF HISTOLOGY The spermatozoa. — Each spermatozoon (sperm cell) consists of three parts, a head, a middle part or body, and a long tapering tail (fig. 550). In man the head is of a pointed oval shape, somewhat flattened especially towards its apex ; in some animals it bears a small barb-like projection at this extremity. The apical part is coveced by a c fii^ r«';^ ''■■.'- ^.^'■'' -,r'' ■ , ■' ■■'■-^*'f d'y-:i'^--W. ■■..;""-■-■■-;■■-::.: ■;:--■; ''i y^'--':.^ WMSMuMii L^i^ii^{<,4i^i^ Fig. 557.— Section of ovary of rabbit. Photograph. Magnified 60 diameters. One large Graafian follicle and a number of smaller follicles are seen, the smallest forming a layer near the surface. Notice the tunica albuginea covering the surface; itself covered by columnar epithelium. 4o6 THE ESSENTIALS OF HJSTOLOGY ,,i>V •«'.;l ,"r.f"; ; :i^s^ Fig. 558. — Photograph of a section through a mature human ovum, surrounded BY the cells of THE DISCUS PROLiGEKUS. Magnified 600 diameters. (From A. Thomson, Journal of Anatomy, vol. liii.) t^.yuj i M'' ^wrf'^rnr i^y i 7 ■tfl.ffi^ 'fif ^ ^■^ -- K \1 *- J," V„- v^ N ^4. I'/Vi llG. 559. — blCCTION (11' TART OF HUMAN OVAR\ !' ^V "'-- ^ ,'-.•'1 J Fio. 563A. — Sjsctiok of a Gkaafian follicle of tub sabbit wmcii has KECKNTLY BimuBBD. Photograph. Magnified 50 diameters. The ovum and follicular ci)ithelium have hecome entirely extruded and the follicle is occupied by a blood-clot. verge to a bentral strand of connective tissue occupying the axis of the nodule (fig. 564B). The columns of cells are not unlike those of the cortex of the suprarenal capsule. In the human subject the cells of the corpus luteum are massed into plaits or folds, arranged, perpendicularly to the wall of the follicle, with vascular connective tissue in the interspaces. Numerous capillary blood-vessels, of a sinus-like character, ramify amongst the luteal cells ; the latter probably yield an internal secretion to the blood. Development of the corpus luteum. — There is reason to believe that corpora lutea may be developed in either of two ways, viz. : (1) from cells in the wall or theca of the folliclei which multiply and pass into the cavity of the empty follicle after all its contents have been extruded. (2) From the membrana granulosa of the follicle after the ovum and discus prolig6rus alone have GENERATIVE ORGANS IN THE FEMALE 411 been extruded. In certain species both membrana granulosa cells and theca cells may take part in the formation of thacorpus luteum. 1. In some animals — including, it is believed, man — the corpus luteum is derived from the wall or theca of the Graafian follicle. This becomes thickened by multiplication and hypertrophy of its cells (figs. 563A and 563B). These grow into the cavity of the follicle which has become emptied of its contents at the time of the rupture of its wall, and form intercom- municating trabeculae (figs. 564A and B). Between these cell-trabeculse connective tissue and blood-vessels pass in from the vascular wall of the follicle; converging along with the trabeculae towards the centre of the Fig. 563B. — Pakt of the aeovi!) SEOTioisr. Photograph. Magnified 200 diametei's. The figure shows the fibrous wall (theca) of the follicle containing enlarged cells in its thickness. The complete disappearance of the follicular epithelium is obvious. The cavity of the follicle is occupied by a coagulum of blood, the network of fibrin-filaments being well displayed.^ follicle, where the remains of a blood-clot, derived from the blood-vessels of the follicle at the point of rupture, may long continue to be visible. Ultimately the centre becomes occupied by a kind of scar tissue, which may be continued to the surface of the ovary at thq point where the rupture of the follicle originally occurred. Sometimes there is no clot in the follicle, its cavity being at first occupied by lymph, and the luteal cells .grow into this. 2. In other animals, of which the mouse (Sobotta) and the ferret (Robinson) furnish characteristic, examples, the corpus luteum is developed by proliferation and enlargement of the cells of the membrana granulosa which have remained attached to the wall of the follicle after its rupture (figs. 565, 566). Into this thickened epithelium processes of the wall or theca grow, carrying in blood-vessels and probably theca-cells, so as partially to 412 THE ESSENTIALS OF HISTOLOGY W ''■!■"■ '^^^^^V' ^10- 564A.— Com-us lu- i.i, • -I-f^Vgjj^^ TEUM OF BABBIT rOBMED OF TEABEOULa) OF LAEGE LUTEAL CELLS WHICH HAVE DEVELOPED FBOM THE CELLS OF THE THBCA. Photograph. Magnified 60 diameters. The remainder of the ori^nal blood-clot (62) is still seen n ear the middle of the corpus luteum. Just below this is a kind of cicatricial fibrous tissue fonued by organisa- tion of part of the clot. \U/ ■:' Fio. 564B. — A PARTOF the section SHOWN IN the ABO^^; figure. Photograph. Magnified 200 diameters. The columns of luteal cells and the cicatricial tissue to which they con- verge are well seen in this figure. ;^. ".^ GENERATIVE ORGANS IN THE FEMALE 413 separate the epithelium into what in sections look like trabecule converging towards a central cavity. The further development is the same as in the other case, the cells filling the follicle becoming transforrned into luteal cells. The difference between these two modes of development is striking; but from the morphological point of view need not be unexpected since it is ^ I X aiai-*"*' Fig. 565. — Three stages in the formation op the corpus luteum in the mouse. (Sobotta.) A. Follicular epithelium* hypertrophied (/e), and vascular proceasea (a) of the internal theca (i/i) growing into it. B. The vascular processes are arranged radially and subdivide the epithelium — now converted into a moss of luteal cells— into lobule-like masses (0; e, epithelium of surface of ovary. C. The lobule-like masses are more columnar, and the luteal'mass almost fills the follicle, leaving, however, a central space occupied by coagulated fluid. X t<> Va %, L probable that the epithelium of the Graafian follicle and the theca-cells are both derived from the original germinal epithelium of the foetal ovary. After persisting for a time the corpus luteum gradually disappears, its cells becoming merged into the surrounding stroma. In the human subject it usually becomes aborted and shrunk, and, losing its colour, is known as a corpus albicans. Corpora lutea grow larger and persist longer in the event . of pregnancy supervening. THE FALLOPIAN TUBES AND U.TERUS. The Fallopian tubes or oviducts are lined by a very vascular mucous membrane which is covered with ciliated epithelium, and has numerous 414 THE ESSENTIALS OF HISTOLOGY longitudinal folds or rugse with depressions between (fig. 567). Externally the tube is covered by a serous coat, within which is a thin longitudinal stratum of plain muscular fibres overlying circular fibres of the same tissue ; these layers are not distinctly marked off from one another. The Fallopian tubes commence near the ovary with an open end, the margins of which are spread out into a number of processes termed fimhricE. One or two of these fimbriae are directly attached to the surface of the ovary in the manner shown in fig. 568. Each Fallopian tube terminates distally in the uterus ; opening, in the human subject, at the upper angle of the 'T"^^ * i' s - ^;h Pig. 566. — More advanced stage in the development of the cokfus lutei-m OF THE MOUSE. (Sobotta,)' The luteal tissue is now highly vascular, and the central cavitj^ is obliterated. body of the uterus. In animals which possess a bicorned uterus, the Fallopian tube is directly continued into the corresponding cornu. The human uterus is composed of two parts, the body and cervix. The body is formed of the following layers (fig. 569) : — 1. A serous layer, derived from the peritoneum, which covers the greater part of the fundus. 2. A muscular layer, which is of great thickness and is formed of plain muscular fibres disposed in three, more or less blended, strata. Of these the outer is thin and has its fibres arranged partly longitudinally, partly circularly. The middle, on the other hand, is thick ; its fibres run in different directions, and it contains the ramifications of the larger blood-vessels. Tlie inner layer, again, is thinner and b^s both longitudinal and circular fibres, many GENERATIVE ORGANS IN THE FEMALE 415 of the latter being prolonged internally into the deeper part of the mucous membrane ; the extremities of the uterine glands extend between and amongst the muscle-fibres. 3. A mucous membrane (fig. 669, mm), composed of soft connective tissue containing a large number of spindle-shaped cells. It is lined by ciliated epithelium and contains long, simple, tubular glands, which take a curved or convoluted course in passing through the membrane (fig. 570, gl, and fig. 571). Their epithelium is continuous with that which covers the inner surface of the mucous membrane and is also ciliated for some distance within the glands. In the cervix the mucous membrane is marked by longitudinal and oblique ridges ; the glands are shorter but more complex than those of the Fio. .567. — Skction acuoss the Fallopian tube. (Somewhat diagrammatised. ) body of the uterus, and are lined by columnar mucus-secreting cells. Near the OS uteri the epithelium becomes non-ciliated columnar ; at the margin of the OS uteri this passes into a stratified epithelium which overlies vascular papillie of the corium. The mucous membrane is very vascular ; it also con- tains a large number of lymph-vessels. In those animals the uterus of which is composed of two eornua, the arrangement Of the muscular tissue is simpler than in the human uterus (which was originally double in the embryo and has been formed by the fusion of two such tubes). Fig. 571 exhibits the structure of a cornu of the uterus of the rabbit showing the convoluted glands extending through the mucous membrane ; the thick innermost muscular layer which occupies the deepest part of the mucosa ; the large blood-vessels in the submucous layer, and the two strata of the true muscular coat outside the main vessels. , • Ohanges accompanying menstruation.— At the commencement of each 4i6 THE ESSENTIALS OF HISTOLOGY menstrual period the mucous membrane of the uterus becomes thickened and extremely congested with blood. Eventually the blood-vessels near the surface become ruptured and the superficial part* of the membrane becomes S^ Fig. 568. — Section of ovakt of guinea-pig at the place of attachment of the FIMBRIATED END OF THE Fallopian TUBE. Photograph. Magnified 200 diameters. Notice the ciliated epithelium covering the fluibrise, continued into the much smaller non-ciliated oella of the ovarian surface. Observe also the numerous and large blood-vessels of the fimbria. ;,j.r(^^ ,.-5-; ,-.%/.,.:,■"■;:..••.;- ;-#'N''^, 'r ^ ^ -c K-? Fig. 569."— Section op human uterus. (Sobotta.) Twice the natural size. s, serous layer ; Im, longitudinal muscular fibres ; rw, circular jriuscle ; wm-, mucous membrane ; ;, cavity of uterus ; U, ligamentum latum ; bl, blood-vessels, GENERATIVE ORGANS IN THE FEMALE 417 Fio. 570. — Section or the uterine mucous membkane. (Sobotta.) Magnified 150 diameters. ep, epithelium of cavity ; gl, glands ; ra, part of muscular wall. Fig. 571. — Section oe a oobnu of the rabbit's uterus. <), serous layer; l.m., longitudinal musoUar fibres; cm., circular muscular fibres of the muscular coat ; a, areolar tisSIiS with large blood-, vessels ; m.m., muscularis mucosBe ; m, mucous membrane. THE ESSENTIALS OF HISTOLOGY FiQ 672 — Section of mucous membrane of human uterus during menstrua- tion, SHOWING MASSES OF BLOOD ESCAPED FROM RUPTURED CAPILLARIES INTO THE INTEKGLANDULAR TISSUE; AT ONE PLACE (♦) THE BLOOD HAS BROKEN THROUGH THE SURFACE EPITHELIUM. (Sellheim.) Fig. 573.^Diagram to illustrate the embedding of the o\tjm in the dkcidua and the first formation of the fostal villi in the form of a syncytial TROPHOBLAST (derived from the outer JjAYKR of the ovum) WHICH IS INVADINIi SINUS-LIKE BLOOD-SPACES IN THE DEOIIjUA. (T. H. Bryce.) disintegrated and thrown off (fig, 572). These changes are accompanied by a considerable escape of blood into the cavitv of the uterus and thence into GENERATIVE ORGANS IN THE FEMALE 419 the vagina. The return to the normal conditions then begins and the renewal of the disintegrated membrane proceeds rapidly. Should pregnancy supervene, the process of renewal results at certain parts in the formation of a greatly thickened mucous membrane, wifh long convoluted glands : this is known as the decidua. The muscular layer also becomes enormously hypeftrophied during pregnancy; the hypertrophy is produced by the enlargement of the individual muscle-cells. The phenomenon of heat in animals is attended by changes in the utei'us which are analogous to those occuri'ing during menstruation in the human subject. The m.iK «y Fig. 574, — Diagram of a fuktheb, stage in the formation of the placenta, showing this fcetal villi within the eloon-spaces of the placenta and PARTLY ATTACHED TO THE DECIDUAL WALL. (T.= H. Bryce. ) The villi are now occupied by a core of vascular mesoderm. They are covered by a syncytium (continued over the decidua), within which is a layer of epithelium^cells ; f.v., foetal vessels ; m.w., maternal vessels ; m, mesoderm of chorion ; a, a villus cut across ; 6, attachment of a villus ; sy, syncytial covering to villi continued at s^ on to decidua ; ep, epithelial layer under syncytium. whole series of alterations which accompany this condition — including the changes preparatory, accompanying, and succeeding the periodical blood-flow from the uterus — is known as the oestrous cycle. Structure of the placenta. — When the developijig ovum reaches the uterus it becomes embedded in the thickened mucous membrane (decidua) to which it attaches itself firmly by means of its outer layer or chorion, processes of which penetrate into the decidua. The chorion and its processes are povered by a thick syncytium termed the trophoblast ; this burrows its way into the uterine mucous membrane and gives off villus-like branching processes — chorionic villi — which enter large vascular sinuses in the decidua, where they become bathed with arterial maternal blood (fig. 573). In the meantime tissue conveying blood-vessels has grown into the chorionic villi from the mesoderm of the foetus bringing to them foetal blood by way of the umbilical arteries. Later the original epithelial covering of the villi becomes attenuated and only a thin syncytial layer of cells separates the tissue of the villus containing ftetal capillaries from the maternal blood in the sinuses. Some of the villi remain hanging freely into the sinuses, others are attached to 420 THE ESSENTIALS OF HISTOLOGY their wall or to fibroua septa and trabeculae which expend across the sinuses or serve partially to separate these into loculi .(fig. 574). The maternal blood is conveyed to the sinuses of the decidua by small spiral arteries and is taken away by corresponding veins. A section across the discharged placenta or afterbirth shows it to be bounded on the fuetal side by the chorion, covered by the smooth amnion, and on the maternal side by the thin and somewhat uneven detached part of the decidua — a separation '^""■^S ■> o o .offbft, oo oo cp::, ' °e CiJ! f-'-ofJ^"" "•""*■ o. -r.. 'Aoo fS°^ f O ^ Fig. 575. — Section of a placenta at full time. (T. H. Bryoo.) From ii, preparation by J. H. Teacher. ( )ne or two of the villi show a fibrinous change. For the sake of distinction the tcetal blood-corpuscles arc represented as solid dots, the maternal as circles. having occurred in the substance of the decidua when the placenta becomes detached from the uterus. Between these two boundaries is a spongy mass which in sections e.\amined under the microscope (fig. 575) appears to be formed of a continuous blood-space in which an enormous number of fiietal villi and fibrous trabeculne of varying thickness are seen, cut in various directions. Each villus (fig. 576) is composed of jelly-like connective tissue covered by a syncytial layer of epithelium. Within the larger villi arterioles and venules are seen and in some, capillaries as well ; within the smaller only capillaries. Some villi are observed which appear to be undergoing a fibrinous change '" ' GENERATIVE ORGANS IN THE FEMALE Fig. 576.— Section as A VILLUS FEOM A PLACI5MTA AT THE SEVENTH MONTH. Highly magnified. (T. H Bryce. 421 v Fig. 585. — Diagram showing the site of dbgbnbbation in the dorsal column which results from unilateral ' section oe the dorsal roots oe the SECOND SACRAL TO THE SIXTH LUMBAR NERVES OE THE DOG. (Singer.) a, sixth lumbar segment ; 6, fourth lumbar ; c, from the mid-thoracic region. Fig. 586. — Degenerations following unilateral section of the dobsal roots OF THE eleventh AND TWELFTH THORACIC NERVES OF THE DOG. (Singer.) a, at level of twelfth thoracic ; 6, of third thoracic ; c, from mid-cervical region. Fitf. 587.— Degenerations following bilateral sections of the dorsal roots OF THE SECOND THORACIC TO FIFTH OE&VIOAL NERVES OF THE DOG. (Kahler.) a, at level of first thoracic ; b, at sixth cervical ; c, at first cervical. (fig. 579). This tract ends amongst the cells of the nucleus gracilis of the medulla oblongata. 2, Tract of Burdaeh. — The dorso-lateral colurrtn is also mainly composed of fibres of the dorsal nerve-roots, which run for a certain distance in it before entering the grey matter of the cord or. of the medulla oblongata. As each mass of dorsal root-bundles enters the column close to the apex of the horn it, so to speak, pushes the root-fibres which have already entered nearer to the median fissure ; hence those derived from the lowest nerve roots are nearest that fissure (tract of Goll), while those derived from the highest remain near the horn (tract of Burdaeh) (figs. 585 to 587). Many of the fibres of both tracts pass into the grey matter either im- mediately on entering the cord or in their course upwards; the rest are 432 THE ESSENTIALS OF HISTOLOGY continued into the medulla oblongata, and those of the tract of Burdach end by arborising amongst the cells of the nucleus cuneatus. 3. Comma tract. — Besides the tracts of Burdach and Goll, which are wholly composed of long "ascending" fibres having their cells of origin in the ganglia on the dorsal roots, there are a few fibres which have a shorter "descending'' course in the dorsal columns. These are thought by some authors to arise from descending branches of the dorsal root-fibres, by others from cells in the grey matter of the cord. They form the so-called eomm/i tract (fig. 588, 5). Proprio-spinal or endogenous fibres of the dorsal column. — These com- prise a few fibres {septomarginal), chiefly accumulated near the median fissure {oval bundle) and near the dorsal surface {median triangle bundle), as well as others scattered in the column; they are derived from cells in the grey matter Fig. ."588. — Diagram showing the ascending (right side) and descending (left side) tracts in the spinal cord. 1, Crossed pyramid tra). Another group {middle cell-column) lies in the middle of the crescent (fig. 584, e). Cellfi are very numerous in the dorsal horn but are not collected into definite groups. Those of the sub- Fio. 593.— From LoiN'filTuniNAii section or CORD OF CHICK EMBRYO, SHOWING ENTKRING DORSAL KOOT-l'lBRES AND THE PASSAGE or COLLATERALS FROM THEM INTO THE GREY MATTER. AmO THREE CELLS OF THE DORSAL HORN SENDING THEIR AXONS INTO THE WHITE MATTER, (Cajal.) A, entering root-fibres ; S, dorsal white column ; O, strey matter ; 0, D, E, cells of dorsal horn ; B, F, G, I, arborisation of collaterals in );rev matter. Fig. 59|. — Arborisation of col- laterals FROM THE dorsal ROOT- FIliRES around CELLS OK THE DORSAL HORN OF GREY MATTER. (Cajal.) A, fibres of dorsal column derived from dorsal root -, B, collaterals ; O, D, nerve-cells in grej- matter surrounded by the arborisations of the collaterals ; E, an arborisation shown separately. stantia gelatinosa of Rolando send their nerve-fibre processes partly into the lateral, partly into the dorsal columns. The cells which send their axons into the adjacent parts of the white columns but not into any special tract are sometimes termed tlie " cells of the white columns." CENTRAL NERVOUS SYSTEM 441 CONNEXION OF THE NERVE-EOOTS WITH THE SPINAL CORD. The ventral {anterior) roots leave the ventral horn in a number of bundles. Most of their fibres are directly continued from the nerve-cells in the ventral and lateral horns j according to Golgi in part also from cells in the dorsal Fig. 595. — Collaterals from the dorsal column fibres passing into THE GREY MATTER : NEW-BORN MOUSE. (Cajal. ) Golgl method. . A, a bunch of collaterals ending amongst the cells of the iniddle cell-column ; B, ending of collaterals, a, in the ventral horn : a few side branches of these collaterals, &, are passing to the middle cell-column ; C, collaterals to dorsal horn ; c, others to substance of Rolando. horn. The cells, from which the ventral root-fibres arise, are surrounded by an interlacement of ramified nerve- endings, derived from various sources, especially from axons of cells of the dorsal horn, from collaterals of the dorsal root-fibres (see below), and from those of the fi'bres of the adjacent white columns. Whether the pyramid fibres send any branches to end amongst the ventral horn-cells is not certainly known ; but Sherrington found a secondary degenera- 442 THE ESSENTIALS OF HISTOLOGY tion of these cells in a cliimpaniiee from whicli he had removed the motor cortex cerebri of the opposite side ; an observation which suggests a more direct con- nexion than the intermediation of cells of the dorsal horn, to which most of the branches of the pyramid tract fibres are directed (see also p. 446). The fibres of the dorsal {posterior) roots originate in the cells of the root ganglia and enter the dorso-lateral column (see diagram, fig. 589), but the smallest fibres pass to the marginal bundle of Lissauer, and some go directly into the dorsal horn. On entering the spinal cord the fibres bifurcate (fig. 593), one branch passing upwards, the other downwards. Both from the main fibre and from its branches collateral fibres pass at frequent intervals into the grey matter, and end in arborisations of fibrils which envelop the nerve-cells both of the dorsal (fig. 594) and of the ventral horn (fig. 595), and, in the thoracic region, the cells of Clarke's column and those of the intermedio-lateral column. Many of the main fibres also ultimately end in a similar manner in the grey matter, some after a short course only, others after a long course. But a considera,ble number of fibres pass upwards in the dorso-lateral and dorso-medial columns (in the latter especially those of the lower spinal nerves), until they arrive at the medulla oblongata, where they end in terminal arborisations around the cells of the nucleus gracilis and nucleus cuneatus (fig. 589, 6, 7). CENTRAL NERVOUS SYSTEM 443 LESSON XLI. CENTRAL NERVOUS SYSTEM. The Medulla Oblongata. Sections of the medulla oblongata (made in the same way as with the spinal cord) : (a) at the level of the decussation of the pyramids, (f>) just above the decussation, fnninnliis griinilis dorsal median fisiSiu funiculus ruT eatus nurrlpu ^r\( desc. root of Vth — t-4 bundle from fun. cuii. ■~- subst. ffelfit, Rol tract of Fleoh.sig pyramid bundles I*"' "Z-*:'?^ decussation of pyramids ' An ,j,l 3 ventral medim h "^ure- \ 1 \ 1 inud 'A J..V \ Fig. 596. — Section across the lower part of the medulla oblongata in the REGION OF THE DECUSSATION OF THE PTEAMIDS. Magnified 6J diameters. (o) opposite the middle of the olivary body, and {d) through the uppermost part of the olivary body, or just above it. Divisions of the brain. — The brain consists of three great morphological divisions associated with the three primary cerebral vesicles of the embryo ; they are termed respectively the hind-brain, mid-brain, ^n^ fore-brain. The hind-brain includes the parts around tjie fourth ventricle, viz. the medulla oblongata (m'yelenoephalon) and the pons,- consisting of a stem, and of peduncles uniting it with the cerebellum (metencephalon) : the medulla 444 THE ESSENTIALS OF HISTOLOGY oblongata and pons-stem form a continuation of the spinal cord termed the " spinal bulb.'' The mid-hrain includes the region of the corpora quadri- gemina (mesencephalon). The fore-hraht comprises the parts immediately above that region and centering around the third ventricle ; its lower portion includes the thalami (thalamencephalon), its upper portion the corpora striata and cerebral hemispheres (telencephalon). ilorpal Tnedian fi-ssiire nucleuH grarilis funiculus ouneatu« nucleus cunf-atu; desc. root of r>Ll f-entral raiia >iuIiHtantia RoIainJi— p rentral filjres of \t\-\ int. arcuate tlbres tract of Flet-hsiy— ;^ traft of Gowc-TS raphe accessory oli^■. unci. silit|ua olivip. olivai-,\ nui'leuH- pyramid arcuate nucleus. Fig. 597. — Section taken immediately above the decdssation of the PYRAMIDS. Magnified 64 diameters. GENERAL STRUCTURE OF MEDULLA OBLONGATA. The structure of the medulla oblongata can best be made out by the study of a series of sections taken from below upwards, and by tracing in these the changes which occur in the constituent parts of the spinal cord, taking note at the same time of any parts which may be superadded. A section through the region of the decussation of the pyramids (fig. 596) has much the same form as a section through the upper part of the spinal cord ; most of the structures of the cord can be recognised in it. A considerable alteration of the grey matter is, however, produced by the passage of the large bundles of the crossed pyramid tract from the lateral column of the spinal cord on each side through the base of the ventral horn and across the venti'al median fissare to the opDOsite ventrsj column of the CENTRAL NERVOUS SYSTEM 445 Medulla oblongata. medulla oblongata, where, together with the fibres of the direct pyramid tract, which already lies in the ventral column of the cord, they constitute the prominent mass of white fibres which is seen on the ventral aspect of the medulla oblongata, on each aide of the middle line, known as the pyramid, from which the name of the tract is derived. By this passage of fibres through the grey matter the tip of the vei;itral horn is cut ofi' from the rest and is pushed to the side ; part of it appears as an isolated, mass of grey matter, known as the lateral nucleus. In sections a little higher, viz. just above the decussation of the pyramids, a wavy band of grey matter makes its appearance on the lateral aspect of each pyramid, corresponding with a promin- ence on the surface which is known as the olive. The wavy or plicated grey matter is termed the olivary nucleus (figs. 597, .599, 600). , The pyramids of the medulla oblon- gata are formed of fibres which originate in the frontal region of ~ the cerebral cortex, and can be traced from the axons of the large cells in the grey matter of that cortex. The fibres course through the white matter of the hemisphere, through the middle third or more of the internal capsule and crusta, and through the pyramid bundles of the pons into these structures (pyramids) of the medulla oblongata. As we have just seen, they pass at the lower limit of the bulb chiefly to the opposite or crossed lateral column of the cord, but partly to the lateral column of the same side, and, in man and anthropoid apes, partly to the mesial part of the ventral white column. They collectively constitute the tract of the pyramid, which is smaller in the medulla oblongata than in the pons, since many of its fibres leave the main tract whilst within the pons and pass across the middle line towards Fig. 598. — Diagram to show the COUKSB or THE DORSAL ROOT- HBRES AFTER ENTERING THE CORD. li, afferent fibres before entering ganglion ; g.s., sglnal gantrlion-cells ; g.V., ganglion of , fifth nerve ; c, descending branches (forming comma traofc) giving off collaterals to grey matter. The ascending branches are shown partly ending in grey matter of dorsal horn, partly in the nucleus gracilis in.ff.) and nucleus cuneatus (71. c.) of the medulla oblongata; s.Ro.^ substantia Rolandi ; /, fibres of fillet arising in nuclei of medulla oblongata and crossing the raphe to the opposite side ; e, efferent nerve-fibres from motor nerve-cells. 446 THE ESSENTIALS OF HISTOLOGY the grey matter which lies in the dorso-lateral part of the pons and medulla oblongata, especially in that portion of the grey matter with which the sensory fibres of the cranial nerves are connected. Sometimes such a bundle of fibres,' after passing towards the sensory nuclei in the lateral part of the medulla oblongata, does not end in them, but again comes ventralwards and joins the main or central part of the pyramid tract near its decussation {bundle of Pick). funiculus ciiiif-atus nucleus i.-iiiteatns fasciculus solitarius dorsal nucleus of Xth (lesc. rout of \th nucleus nf Xllth sulist. ^^eliil. Uolarirl; tract of I'^ld'hsi^' int. arcuate tiWres ruljro-spinal tract iHsuing tibres of Xllth tract of (Jowera biliijua nli\ Lc oli\ar\ miuleus ext. arcuate fibres », \ pyrauiitl m^^±ti'i * lor^al lony bundle entral lony. bundle ai'uuale iiuuleua Fig. 599. — Section across ttie medulla oblongata at the point of the OALAMDS scriptorius oe THE FOURTH VENTRICLE. Magnified CJ diameters. It is not a little remarkable that altliougli the fibres of the tract of the pyramid give off numerous collaterals to the grey matter of the cerebral cortes, the basal ganglia of the cerebrum, the substantia nigra of the mid-brain, the nuclei of the pons and the base of the dorsal horn of the spinal ^ord, no collaterals are seen to leave them in their course through the pyramids of the medulla oblongata, except it very few to the olivary nuclei. Various observers have professed to describe collaterals and terminations of the pyramid fibres as passing to the motor nuclei of the cranial nerves as well as to the motor cells ii\ the ventral horn of the spinal coidj but statements to this effect must be received with caution, for although current in most text-books, they have not been substantiated by accui-ate observa- tions. It is certain that most if not all of the fibres of the pyramid tract end not in the ventral but in the dorsal part of the spinal grey matter. Sherrington has, however, found degenerative changes in the cejls of the oontralateiul ventral horn to follow, eventually, a lesion of the jnecentral con\olution on one side of the brain in a chimpanzee. This observation suggests a more direct connexion in this CENTRAL NERVOUS SYSTEM 447 animal between the pyramid fibres and tlie motoi' c^Ils in the cord than is usually found. In any case the occurience of degeneration in the cells is difficult of explanation. In consequence of the increased development of the dorsal columns of white matter, a change also occurs in the grey matter of the dorsal horns, which in the medulla oblongata are pushed towards the side, the V which they form with one another being thus opened out ; at the same time the tip \"cytiliu!ni' luiclen desc. \L'stitmlar IiItl's dorsal mul. of Xt, / faficiculus snjit. =— restifonn horly nucl. of Xllth SUbst. f^flat. desc. root of Vth subst^. g;elat int. arc. fibres and nucl. amb. issuing fibres of Xth issuint,' fibres of Xllth olivary nucleus, ext. arcuate fibres^ jiU'^luid \i urte lull leu Fig. 600.— Section across the medulla oblongata, at about the middle OF THE olivaky BOUT. Magnified 64 diameters. of each horn becomes enlarged and causes a prominence upon the surface of the medulla oblongata, which is known as the tubercle of Rolando. Below, this is continuous with the substantia Rolandi of the apex of the dorsal horn of the cord. Above, its grey matter is prolonged into the sensory nucleus of the fifth nerve. On its outer side and partly embracing it is a bundle of fibres seen in every section of the medulla oblongata, and traceable up to the pons Varolii. This is the inferior or descending root of the fifth nerve — formerly known as the "_ascending '' root. Its fibres' extend down as far as the upper cervical region of the spinal cord. Grey matter also soon becomes formed within the upward prolongations of the gracile funiculus (dorso- 448 THE ESSENTIALS OF HISTOLOGY mesial column), and of the cuneate funiculus (dorso-lateral column), appear- ing at first as thin strands in the middle of the columns (fig. 596), but rapidly increasing in thickness (fig, 597) so as eventually tp occupy almost the whole of them, forming the nucleus gracilis and th^ nucleus cuneatus respectively. It is in these nuclei that the fibres of GpU's and Burdach's tracts, which are continued up from the dorsal columns of the spinal cord, find their ultimate ending in complicated arborisations amongst the cells of the nuclei. These nuclei do not, however, receive all the ascending branches of the dorsal root-fibres, for a considerable nunsiber of these have already disappeared by entering the grey matter of the cord, in which they also end by arborisation amongst the cells. The cgUs of the nucleus gracilis and nucleus Cuneatus are of small or moderate size with long dendrons. Their axons pass as internal arcuate fibres through the reticular formation into the inter-olivary layer, cross the median raphe dorsal to the pyramids (fig. 598, y^, and then turn upwards, constituting the tract of the fillet. This tract, which in its lowest part is thus formed by the nerve-fibres which belong to the second relay (second neurones) of one of the sensory spinal paths, is reinforced in 'the higher regions of the medulla oblongata and in the pons by fibres derived from cells of the sensory nuclei of the cranial nerves. The majority of its fibres end in the lateral nucleus of the thalamus, but some pass to both the anterior and posterior corpora quadrigemina. According to Van Gehuchten the fibres of the fillgt which ai'e derived from the nucleus cuneatus lie dorsally to those which are derived from the nucleus giacilis. The continuation of the central canal of the spinal cord is still seen in the lower medulla oblongata (figs. 596, 597), but it comes nearer to the posterior surface and eventually opens out at the point of the calamus scriptorius of the fourth ventricle (fig. 599). The grey matter which surrounds it contains two well-marked groups of nerve-cells ; the ventral of these is the lower part of the mt<:leus of the hypoglossal or twelfth nerve, the dorsal, with smaller cells, that of the vago-accessory or tenth and eleventh. But most of the grey matter of the crescent becomes broken up, by the passage of bundles of nerve-fibres through it, into a well-marked reticular formation. And instead of the comparatively narrow isthmus which joins the two halves of the spinal cord, a broad raphe now makes its appearance ; this is formed of fibres coursing obliquely and ventro-dorsalJy,- together with some grey matter containing nerve-cells. In the section at about the middle of the olive (fig. 600), it will be seen that a marked change has been produced in the form of the medulla oblongata and the arrangement of its grey msttter, by the opening out of the central canal into the fourth ventricle. This causes the grey matter, which lower down surrounded the central canal, to be spread out at the floor of the fourth ventricle, and the collections c(f nerve-cells from which the hypoglossal and vagus nerves respectively arise, now, therefore, lie in a CENTRAL NERVOUS SYSTEM 449 corresponding situation near the ventricular floor. At this level the outer small-celled group which corresponds with the nucleus of the spinal accessory in the lower part of the bulb has become the dorsal nucleus of the vagus or tenth nerve, and yet higher up the dorsal nucleus of. the glosso-pharyngeal or ninth nerve. The nerve-bundles of the roots of these nerves can be seen in some of the sections (fig. 600) coursing through the thickness of the bulb and emerging, those of the hypoglossal just outside the pyramids, those of the vagus at the side of, the medulla oblongata. The dorsal part of the section is chiefly occupied by the grey matter of the floor of the fourth ventricle, and by fibres which are passing obliquely upwards and outwards towards the cerebellum, forming its inferior peduncle (restiform body). The grey matter forming the nucleus of the funiculus gracilis and of the funiculus cuneatus has now almost disappeared, but in place of these nuclei and near the outer part of the floor of the fourth ventricle are seen some masses of grey matter with a number of bundles of nerve-fibres amongst them. The grey matter is the lower part of the principal nucleus of the vestibular nerve (see p. 457), and the white bundles are formed of descending branches of the fibres of that nerve. Below these structures is the descending r.oot of the fifth, with its nucleus mesial to it. The ventral part of the section is occupied by the pyramid, and dorsal to this by a reticular formation (reticularis alhd), composed of longitudinally coursing bundles of fibres belonging to the tract of the fillet and to the dorsal and ventral longitudinal bundles, interlaced with internal arcuate fibres that are passing across the raphe from the nuclei of the contralateral dorsal columns into the fillet, and from the opposite olive into the restiform body. The middle portion of the section consists for the most part of a similar reticular formation, but with more grey matter and nerve-cells (reticularis grisea). This is a development of the formatio reticularis of the cervical cord, and the longitudinally coursing white bundles in it are probably formed of fibres derived from cells in the upper part of the cord. The nerve-cells of the grey reticular formation in the medulla oblongata give origin to fibres which bifurcate and pass both upwards to the same formation in the pons, and downwards towards the upper part of the cord, probably serving to associate these parts. Some also are said to give origin to arcuate fibres, which either traverse the raphe, or remain on the same side and e^entu- ally enter the cerebellum through the inferior peduncle (Van Gehuchten). Ventro-laterally is the olive, within which is. developed a peculiar wavy lamina of grey matter containing a large number of nerve-cells ; this is the dentate nucleus of the olive. The lamina is incomplete at its mesial aspeqt (hilus olivce), and here a large number of fibres issue, and, passing through the raphe, course as internal arcuate fibres to the opposite restiform body, and thus to the cerebellum. Some, however, turn sharply round and course below the dentate nucleus, forming an investment and capsule to it (siliqua 2Q 4So THE ESSENTIALS OF HISTOLOGY olivm), passing towards the restiform body of the same side : the main con- nexion of the olivary nucleus is, however, with the cerebellar hemisphere of the opposite side. The olives receive numerous collaterals'from the neighbouring white columns, including a few from the pyramids. Dorsal, or dorsolateral to the olive, is the continuation upwards of the ventral spino-cerebellar bundle (tract of Gowers) of the spinal cord ; the continuation of the dorsal spino- cerebellar bundle (tract of Flechsig), just above it, is now passing into the Fig. hoi. — DiAcjRAMS illustrating the origin and relations of the ROOT-FIBRES OF THE CRANIAL NERVES. Aj- efferent fibres only : profile view. B, shows on the left the motor nuclei and efferent fibres {except those of the fourth nerve), and on the right side the afferent fibres : view from the dorsal aspect. The_p.irts are supposed to be transparent. restiform body. Lastly a tract of fibres which ouiginate within the thalamus passes over the lateral surface of the nucleus oliyas and ends within its grey matter {thalamo-olivary tract, central tegmental tract of Bechterew), The cells of the dentate nucleus have numerous dendrons'; their axons all pass towards the hilus, whence they emerge, and, for the most part, cross the raphe, pierce the opposite olivary nucleus, and pass, aa already mentioned, into the restiform body {olivo-cerehellar tract). Nerves arising from the medulla oblongata. — The twelfth, eleventh, tenth, ninth, and eighth nerves all take origin in the medulla oblongata, and CENTRAL NERVOUS SYSTEM 451 their fibres may be seen emerging on each side, those of the twelfth ventrally between the pyramid and olive, and those of the other three nerves in succession from beltfw up at the side (A the medtllla oblongata between the olive and restiform body. The twelfth or hypoglossal nerve arises from a nucleus of large cells, similar to those of the ventral horn of the cord. This nucleus is situated in the lower part of the bulb ventro-lateral bo the central canal (fig. 597) ; in the upper part near the floor of the fourth ventricle close to the middle, line (figs. 599, 600). None of the fibres cross to the opposite side ; accord- ing to Van Gehuchten, this is true of all the cranial nerves, except a few fibres of the third nerve and the whole of the fourth nerve. The hypoglossal nucleus extends throughout the lower two-thirds of the bulb (fig. 601, nXII). It receives many collaterals from adjacent sensory tracts in the reticular formation and from the descending sensory fibres of the fifth, ninth, and tenth nerves, as well as from the dorsal longitudinal bundle. These form within the nucleus a plexus of fine fibrils which is highly characteristic. A similar plexus is seen in the oculomotor nucleus. Mesial to the hypoglossal nucleus, in the open part of the medulla oblongata, is the nucleus of the fasciculus teres, a column of moderate-sized cells which extends towards the lower margin of the pons and appears to receive fibres from the cerebellum (Edinger). The eleventh or spinal accessory nerve begins to take origin from cells in the lateral part of the grey matter of the spinal cord as low down as •the fifth cervical nerve. Its fibres from the cord (spinal fibres) are those to the (voluntary) sternomastoid and trapezius muscles. They pass from the cells of origin in the lateral part of the ventral horn {motor nucleus) at first dorsalwards ; they then take a sharp bend outwards through the lateral column to emerge at the side of- the cord and medulla oblongata. The fibres which join the vagus (bulbar fibres) take origin in a nucleus of rela- tively small cells lying dorso-laterally to the central canal of the medulla oblongata and behind the hypoglossal nucleus. This nucleus is continuous above with the corresponding nucleus of the vagus, and with it forms the dorsal vago-accessory nucleus (figs. 597, 599 to 601). Below, it extends nearly as far as the first cervical nerve ; its upper part (vagal part) is in the floor of the fourth ventricle lateral to the hypoglossal nucleus, and reaches nearly as far as the lower border of the pons. Of the whole nucleus about the lower two thirds, i.e. as far as the lower end of the calamus scriptorius give origin to fibres of the accessory. These fibres, as already stated, join the vagus, to which they supply certain motor fibres, including those of the thyro-arytenoid muscle (Van Gehuchten). The twelfth and eleventh nerves are entirely efierent. The tenth or vagus nerve (pneumogastric) contains both motor (efferent) and sensory (afferent) fibres. The efferent fibres arise (1) from the upper part of the dorsal vago-accessory nucleus just djescribed, (2) from a nucleus 452 THR ESSENTIALS OF HISTOLOGY c/.n.X X/. of grey matter containing large cells situated in the reticular formation (figs. 600, 602, n.amh.). This nucleus begins near the lower limit of the bulb and extends nearly to the facial nucleus, which it resembles in general position ; it is known as the nucleus ambiyuus or ventral nucleus of the tenth nerve. The axons of its cells are directed at first dorsalwards and inwards and then turn sharply round in the lateral direction to join the rest of the issuing fibres of the nerve, coursing in the same manner as the spinal fibres of the accessory ; indeed, this nucleus is continuous below with the column of cells from which those fibres take origin. 'The sensory fibres of the vagus take origin in" the ganglion of the root and the ganglion of the trunk (jugular and plexiform ganglia), from unipolar cells like those of the spinal ganglia (fig. 602, g). They enter the medulla oblongata, and then bifur- cate, one branch, a short (ascending) one, passing at once into an upper sensory nucleus, the other, a long one, descending. The upper sensory nucleus {principal nucleus), in which the short branches from the sensory root end, lies in grey matter near the floor of the ventricle, and is continuous with the grey matter which accompanies the fasci- culus solitarius (figs. 599, 600, 602). This is formed by the descending fibres, with similar fibres of the ninth and those of the pars intermedia of the seventh, and is to be regarded as the descending root of facial, vagus, and glossopharyn- geal. It is traceable to the lower limit of the medulla oblongata; the fibres end in a nucleus of grey matter lying along the mesial border of the root [descending nucleus of facial, vagus, and glossopharyngeal). Thi.s nucleus approaches the middle line as it descends, and in some animals terminates by joining its fellow of the opposite sicie over the central canal to form the commissural nucleus of Cajal. The ninth or glossopharyngeal nerve also contains both efferent and aiFerent fibres. The former have their cells of origin in a special nucleus (motor nucleus oj glossopharyngeal) which occupies a position similar to Fig. 602. — Plan or the origin of the twelfth and TENTH NERVES. PV*', pyramid ; n. X 11.^ nuciens of Hypoglossal ; XII. , fibre of hypo, glossal; d.ii.X.Xi., dorsal nuek-us of vapus and accessory; n.amb., nucleus ambiffuus ; /.«., fasciculus solitarius (descend- ing root of vagus ana glossopharyngeal); f.s.n.y ita nucleus; X"., emerging motor fibres 6t vagus ; 17, cell in ganglion of vagus giving origin to a sensory fibre ; d,V,, descending root of fifth ; ■/', corpus restiforme. CENTRAL NERVOUS SYSTEM 453 that of the nucleus ambiguus, and lying near the anterior end of that nucleus, just below the nucleus of the facial, The aiferent fibres of the n.IX n.IX. * ^^^" ' -J , „. ^ ■' ■' ;.« r ■ ^ -■ i -• r f , -i-^ , rn-r ~ ' X VI I I.e. Fig. 603.- -Section of medulla oblongata at the level ob the eighth NERVE. Magnified about 6 diameters. 7i.v,, part of vestibular nucleus ; n.IX., parts of nucleus of ninth nerve ; D, nucleus of Deiters ; u, descending fibres of vestibular nerve; f.s., fasciculus solitarius; n.r., small nucleus in restiform ; »*, restiforni body; IX,, fibres of ninth nerve; n.a., nucleus ambiguus; n. F., sensory nucleus of fifth nerve; V.d., descending root of fifth; n.c, part of dorsal cochlear nucleus; - YIIl.c., cochlear division of eighth nerve; v.n.c, ventral cochlear nucleus; n.L, lateral nucleus ; o, olivary nucleus ; n.ar., nucleus of arciform fibres ; jpy, pyramid ; n.g., grey matter in floor of fourth ventricle ; n.XlI.^ nucleus of twelfth ; VII L', fibres of cochlear nerve entering raphe ; p.l., dorsal longitudinal bundle ; ra., raphe^ a.Z., ventral longitudinal bundle ; rt.o., accessory olivary nucleus ; h.o., fibres issuing from the nilus of the olive ; f, fibres of fillet. nerve arise in the jugular or upper and in the petrosal ganglia^ from unipolar cells like those of the spinal ganglia. Their central axons enter the medulla oblongata, and, like other sensory fibres, divide into two branches, ascending 454 THE ESSENTIALS OF HISTOLOGY and descending. The course of these is like those of the vagus, the descending passing down in the fasciculus solitarius (extending to about one-third of its length, according to A. Bruce), and ending by aVborising in the grey matter accompanying it {descending root and its nucleus), while the ascending branches pass nearly horizontally backwards and inwards to a nucleus {principal nucleus) beneath the inferior fovea of the fourth ventricle ; this is continuous with the upper end of the nucleus of the descending root. The arrangement of the roots is almost exactly a counterpart of that of the vagus shown in the dia- n.TTZZp. gram 602. given fig- According to Edinger the sensory nuclei of these nerves receive fibres from the cerebellum ; con- stituting it cerehello- biilhar tract, which is much better marked in lower vertebrates than in man and mammals. A section taken through the wpper- viost part of the olivary prominence will still show very much the same form and structural arrangements as that just described (fig. 603). The nucleus of the hypo- glossal (figs. 603, 604, n.XII) is still visible in the grey matter of the floor of the' ventricle near the middle line, but the nerve which is now seen connected with the lateral part is the eighth or auditory {VIIT), the, bundles of which, as they enter the bulb, embrace the inferior peduncle of the cerebellum {corpus resti/orme, c.r.), which is now passing into that organ. The origin of the eighth nerve is thus subdivided into two principal parts, known respectively as the dorsal or cochlear and the ventral or vestibular divisions (fig. 604). The eighth nerve. — The fibres of the cochlear division take origin in the ganglion of the cochlea ; those of the vestibular division in the ganglion of Scarpa. These ganglia, which are situated at* the periphery, the former within, the latter near the internal ear, are composed of bipolar cells, of Fic, 604. — Transverse section of the upper part of the MEDULLA OBLONOATA. Four times the natural size. (Sohwalbe.) ^, pyramid ; o, olivary nucleus ; V, descendinff root of the fifth nerve ; VIIT, root of the auditory nerve, formed of two parts, n, cochlear, and b, vestibular, which enclose the restiform body, c.r. \ n.VIIIp, principal nucleus of the vestibular division ; n. Vlllae, ventral or accessory nucleus of the cochlear division ; g, dorso-lateral nupleus of the cochlear division; n.f.t., nucleus of the funiculus teres; *n.XIT, nucleus of the hypoglossal ; r, raphe ; /.r., reticular formation. CENTRAL NERVOUS SYSTEM 455 which the peripheral axons end by ramifying amongst the cells of the sensory epithelium, and the central axons form the cochlear and the vesti- bular divisions of the auditory nervo, and pass into the medulla oblongata in the manner here described. The fibres of the dorsal or cochlear division (coclilear nerve) bifurcate as they enter the medulla oblongata. Each fibre divides into a thick and a thin branch. The thicker branches pass . partly to a mass of ganglion-cells which is wedged in between the two roots and the restiform body, and is known as the ventral or accessory auditory nucleus (figs. 604, 605, n.acc), applying themselves with a peculiar form of terminal arborisation to the tu6.ac. FIBRES TO NUCL.LEMNISCI &CORPORA QUADRIGEMINA NERVE-ENDINGS IN ORGAN OF CORTI Fio. 605. — Flan or the coukse and connexions of the fibres formino the COCHLEAE. KOOT OF THE AUDITORY NERVE. r, restiform body ; V, descending root of the fifth nerve ; tub.ao., tuberculum acusticum ; n.acc.^ accessory nucleus; s.o,, supeirior olive ; nM\, nucleus of trapezium ; n.VI., nucleus of sixth nerve ; F/., issuing root-fibre of sixth nerve. The " acoustic strisB " are seen at the dorsal part of the section. /' " cells of this nucleus ; partly over the restiform body to terminate in a prominent mass of grey matter which overlies thSit body, and also extends to the lateral part of the floor of the fourth ventricle at its widest part (dorso- lateral nucleus, tuberculum acusticum). The cells of the tubercle have a peculiar spindle shape and are set vertically to the surface. They begin to appear in the root itself, lying amongst the fibres of the nerve. Here they are sometimes spoken of as forming the "ganglion of the root.'' The thinner branches of the bifurcated cochlear fibres pass downwards for a certain distance and break up into a plexus of fine fibrils. These two nuclei, viz., the accessory nucleus and the acoustic tubercle, are the nuclei of ending of the cochlear fibres. E'rom their nerve- cells new fibres arise which continue the auditory path centrally (see fig. 605). Those from the accessory nucleus enter the trapezium — which consists of transverse fibres running behind the pyramid bundles of thp pons Varolii — and pass in 456 THE ESSENTIALS OF HISTOLOGY it partly to the superior olive and trapezoid nucleus o£ the same side of the pons, but mostly to the corresponding structures of the opposite side. Some end in those nuclei, but others merely traverse them, giving off numerous collaterals to them and to the superior olives and other nuclei near by (see pons), and then turn upwards in the lateral part of the tract of the fillet to pass ultimately towards the posterior corpora quadrigeraina ; in tending towards these structures they form at the side of the mid-brain the laUral fillet, or fillet of Reil, which is there conspicuous. Some of the fibres from the cells of the accessory nucleus do not pass directly to the trapezium, but TO VERMIS FIBRES OP VESTIBULAR ROOT NERVE ENDINGS IN MACUL>E 8.AMPULL/E Fio. 606. — Plan of the course and connexions of the fibres forminq THE vestibular ROOT OF THE AUDITORY NERVE. r, restiform body ; l^ descending root of fifth nerve ; p., cells sof principal nucleus of vestibular root ; d, fibres of descending vestibular root ; n.rf , a cell of the descending vestibular nucleus ; D, celly of nucleus of Deiters; B, cells of nucleus of Bechterew; /i.(., cells of nucleus tecti (fagtigii)of the cerebellum; pXb,, fibres of the dorsal longitudinal bundle. No attempt has been made in this diagram to represent the actual positions of the several nuclei. Thus a large part of Deiters' nucleus lies dorsal to and in the immecfiate vicinity of the restiform body. first curve round the restiform body (Held) ; these form the most dorsally situated fibres of the trapezium. The fibres which arise in the acoustic tubercle pass for the most part over the floor of the fourth ventricle, where they are seen superficially as the medullary or acoustic strice (fig. 605), and entering the raphe, traverse it in a dorso-ventral direction ; they then join the others from the accessory nucleus in their course to the superior olive and lateral fillet of which they constitute the deeper layer. A few fibres are directed into the fillet of the same side as their cells of origin. Edinger states that, at least in the dog, all the fibres of the trapezium end in its nucleus or in the superior olivary nucleus, the central ' acoustic path being wholly continued, so far as the trapezium fibres are concerned, by fresh neurones, the cell-bodies of which lie in those nuclei, and the axons CENTRAL NERVOUS SYSTEM 457 of which pass into the lateral fillet. On the other hand, from the cells in the tuberculum acusticum, the axons are said to be continued upwards in the opposite lateral fillet without the intervention of any corresponding nuclei. The lateral fillets paes above' into the posterior corpora quadrigemina. The accessory nucleus also receivos fibres through the trapezium, which end by ramifying amongst its cells. These are perhaps derived from the accessory nucleus of the opposite side. Both sets of fibres (from the accessory nucleus and tuberculum) give ofi^ collaterals near their origin, which terminate within these nuclei. The ventral or vestibular division (vestibular nerve), which enters a little in front of (above) the cochlear division, passes between the restiform body and the descending root of the fifth (fig. 6D6), to enter a mass of grey matter containing for the moat part cells of small size, which is termed the principal or dorsal nucleus of the vestibular division. Here each of its fibres bifurcates with ^ Y-shaped division into an ascending and descending branch (fig. 606). The descending branches are collected into small bundles (descending vestibular root) which run downwards towards the lower part of the medulla oblongata, and gradually end by arborising around cells in the adjacent grey matter (descending vestibular nucleus), which is continued down from the principal nucleus. The ascending branches pass upwards on the inner side of the restiform body towards the nucleus tecti of the cerebellum. In their course they give off numerous collaterals which arborise round the large cells of two nuclei which occur in this part of the medulla oblongata and pons near the outer part of the floor of the fourth ventricle. These two nuclei are termed respectively the nucleus of Deiters and the nucleus of Bechterew (fig. 606). Van Gehuchten states that the nucleus of Bechterew alone receives fibres from the ascending branches and that all the other nuclei (dorsal, descending, and nucleus of Deiters) are furnished with fibres from the descending branches. The nucleus oj Deiters is especially characterised by the large size of its cells and by the manner in which they are enveloped as by a basket work by the ramifications of the collaterals in question. From these cells fibres arise which pass to the dorsal (posterior) longitudinal bundles of both sides : in these the fibres bifurcate (Oajal), one branch passing upwards to the oculo- motor nucleus and giving off collaterals to the nucleus of the sixth nerve, and the other downwards, eventually reaching the ventral column of the spinal cord (ventro-lateral descending tract), and terminating by arborisations amongst the cells of the ventral horn (see p. 434), By means of the collateral fibres which supply the sixth and oculomotor nuclei it is probable that the conjugate movements of the two eyes are brought about, and by the fibres to the spinal cord the associated movements of the head and trunk. Fibres have also been described as passing from Deiters' nucleus to the nucleus tecti of the cerebellum. Owing to its connexion with the semicircular canals, the cerebellum, the oculomotor nuclei, and the nuclei in the ventral horn of the 458 THE ESSENTIALS OF HISTOLOGY spinal cord, this nucleus must exercise important functions in connexion with co-ordination of head and eye movements and equilibration in general. The fibres which originate in the nucleus of Bechterev- pass into the reticular formation and become lon'gitudinal, but their destination is not certainly known. Some are said to pass into the ventral column of the cord. The reticular formation still occupies the greater part of each lateral half of the bulb between the grey matter at the flooi; of the fourth ventricle and ' the pyramids, and a small portion of the olivary nucleus may still be seen. The descending root of the fifth nefve with ijts adjacent grey matter' is conspicuous. The restiform body is formed (1) of the fibres of the dorsal spino-cerebellar tract of the same side, which are derived below from cells, of Clarke's column, and pass above into the middle lobe of the cerebellum, (2) of fibres from the opposite olivary nucleus, and (3) of fibres from the olivary nucleus of the same side. The olivary fibres pass mainly to the cerebellar hemisphere, According to some authorities the restiform body, also contains fibres derived from the nucleus gracilis and nucleus cuneatus of the opposite side, as well as some from a nucleus which lies just outside the main mass of grey matter of the funiculus cuneatus, and is known as the outer cuneate nucleus. Fourth ventricle. — The Jloor is covered by a layer of ciliated epithelium- cells, continuous below with those lining the central canal, and above, through the aqueduct, with the epithelium of the. third and lateral ventricles. The epithelium rests upon, and its cells assist in forming, a layer of neuroglial tissue known as the ependyma of the ventricle. The fourth ventricle is roofed over by a layer of pia mater, with projecting choroid plexuses ; the under surface of these is covered by a thin epithelial layer continuous at each side with the ciliated epithelium of the floor. The roof becomes somewhat thickened as it is continued into the ependymal layer of the floor of the ventricle ;_this thickened part (twnia or ligula, figs. 599, 600) is often left attached when the thin epithelial roof is removed along with the pia mater which covers it. CENTRAL NERVOUS SYSTEM 459 LESSONS XLII. AND XLIII. CENTRAL NERVOUS SYSTEM. The Pons Varolii, Mesencephalon, and Thalamencephalon. 1. Sections through the lower, middle, and upper parts of the pons. 2. Sections across the region of the corpora quadrigemina, one at the level of the inferior, the other at the level of the superior, pair. 3. A section across the posterior part of the third ventricle passing through the thalami. In all the above sections sketch under a low prtwer the general outlines of the grey and whjte matter, inserting the positions of the chief groups of nerve-cells. ' . [The tissue is hardened and the sections are prepared, stained, and mounted in the same way as those of the spinal cord and medulla oblongata.] GENEEAL STRUCTURE OF THE PONS VAROLII. Sections through the lower part of the pons (fig. 607) show much the same arrangement of grey and white matter as that met with at the upper part of the medulla oblongata, but the general appearance of the sections is much modified by the presence of a large number of transversely coursing bundles of nerve-flbres, most if not all of which are passing to the hemispheres of the cerebellum (fibres of middle peduncle of cerebellum). Some of the most anterior- of these peduncular fibres often form a detached bundle which is known as the tmnia pontis. In the interstices of the transverse bundles is a considerable amount of grey matter (^nuclei pontis) from the cells of which the fibres of the middle peduncle of the opposite side are derived. Amongst the cells of the nuclei pontis many collaterals of the pyramid tracts end, and the cortico-pontine fibres (see below) also terminate here; in this way is formed a connexion between the* cerebral hemisphere of the one side and the cerebellar hemisphere of the opposite side. The con- tinuation of the pyramids of the medulla oblongata in the pons takes the form of a number of separate bundles (fig. 607, py.) which run between the transverse bundles. These bundles are collectively much more bulky than the pyramids of the medulla oblongata, for, in addition to fibres of the pyramid tract proper (^corticospinal), derived from the motor area of the cortex, they are largely composed (especially the dorso-lateral bundles) of other fibres (cortico-pontine) connecting the cortex with this part of the hind-brain. The pyramid bundles are separated from the reticular formation by deeper transverse fibres, which belong to a difierent system from those of the middle peduncle. They form what has already been rbferred to as the trapezium 460 THE ESSENTIALS OF HISTOLOGY (figs. 605, 607) ; a collection of fibres which forms* part of the central auditory path; some appear to be commissural between the auditory nuclei of the two sides. The fibres of the trapezium traverse a collection of nerve-cells lying ventral to the superior olivary nucleus, aad known as the nucleus of the trapezium (fig. 605, n.tr.). This nucleus is characterised by the peculiar chalice-like synapses which the Fig. 607. — Transverse section through the lowermost part of the i>ONS. From a photograph. Magnified 4 diameters. v.lV.f fourth ventricle; c, white matter of cerebellar hemisphere: c.(f., corpus dentatum; Jl.j iloeoulus ; c.n, corpus restiforme ; R, Viundle of Roller, composed of the descending branches of the vestibular nerve ; D, nucleus of Deiters ; VII^., issuing root of auditory nerve ; Vlll.d.f principal or dorsal nucleus of the vestibular nerve ; VIll.v., nucleus of cochlear nerve; (c, trapezium; n.tr., its nucleus; /, fillet; jt.hh., dorsal longitudinal bundle; f.i:, formatio reticularis; n, n', n", various nuclei within it; F.a., descending root of fifth nerve; s.r;., substantia gelatinosa ; s.o., superior olive; VII. ^ issuing root of facial nerve; ~n.YIl., its nucleus; VI., root-biuidles of sixth nerve; py., pyramid bundles; H.p., nuclei pontis. entering axons of the larger acoustic fibres form with the cell-bodies (Held). According to Cajal these large fibres are continued directly from the root-fibres of the cochlear nerve, and are not derived from the cells of its accessoiv nucleus. The olivary nucleus is no longer seen, but there are one or two small collections of grey matter, more conspicuous in some animals than in man, which lie in the ventral part of the reticular formation, known as the superior olivary nucleus {o..t.), the pre-oUrary imoleu^, and the semilunar nucleus (Cajal). All these, as well as the nucleus of the trapezium itself, are connected with the fibres of the trapezium which form the central CENTRAL NERVOUS SYSTEM 461 ye/rir //r auditory path ; these fibres either ending in the nuclei in question or giving off to them numerous collaterals ; whilst from the cells of the nuclei axons pass into the trapezium or into the adjacent lateral part of the fillet. On the other hand, the superior olive is said to receive some fibres from the posterior colliculi of the corpora quadrigemina. The nucleus of Deiters, which begins to appear in the upper part of the medulla oblongata, where it has been already studied (p. 45'7), extends into the pons Varolii ; where it lies near the floor of the fourth ventricle, a little mesial to the restiform body (D, fig. 607). The nerve-fibres connected with its cells pass towards the middle line and enter the dorsal longitudinal bundle. Here, as already stated, they divide, one branch passing upwards in the bundle and terminating by arborescence chiefly in the opposite oculo- motor nucleus ; the other branch extending downwards in the medulla oblongata and cord. In the spinal cord they are found in the ventre - lateral descending tract : fibres from each nucleus of Deiters occur in both of these -tracts (E. H. Fraser). They terminate by arborescences in the ventral horn of the spinal cord. Nerves of the pons Varolii. — The nerves which enter or emerge from the grey matter of this region of the brain are part of the eighth, the seventh, the sixth, and somewhat higher Up the Jifth cranial nerve. Of these the eighth (already considered) and fifth are connected with groups of nerve-cells which occupy the grey matter opposite the external border of the floor of the ventricle ; the sixth with a nucleus which is placed in the grey matter of the floor of the ventricle but nearer the middle line, and the seventh with a special nucleus which lies in the formatio reticularis. The seventh or facial nerve and the nerve of Wrisberg (pars intermedia). — The motor fibres of the seventh nerve arise from the facial nucleus in the formatio reticularis. This nucleus is homologous with the nucleus ambiguus seen in sections of the medulla oblongata. It has been shown that the motor fibres to the stapedius arise from the mesial part of the nucleus, and then in succession those to the external ear muscles, those to the mouth and face muscles, and, finally, from a group of cells situated dorsally to the ITio. 608. — Plan of the origin of the and seventh nekves. SI}fTH VT., sixth nerve; VII., seventh nerve; a.VII., ascending part of root of seventh shown eut across near the floor of the fourth ventricle ; (/, genu of seventh ; n. VI., chief nucleus of the sixth nerve; n'.VI,, accessory nucleus of sixtlf; n.VII., nucleus of seventh; d.V., descendinjr root of fifth ; pyr., pyramid bundles ; VIII.v., vestibular root of eighth nerve. 462 THB. ESSENTIALS OF HISTOLOGY rest, the motor fibres supplied to the superior branch of the facial (Marinesco, Van Gehuchten), From the nucleus of origin th'e fibres first pass obliquely backwards to the floor of the ventricle, then longitudinally upwards for a short distance (fig. 601, A; fig. 608), and finaHy bend obliquely forwards and downwards to emerge between the transvesse fibres at the side of the pons. None of the fibres of the seventh are derived from the nucleus of the sixth, as has sometimes been thought to bo the case. As they curve over that nucleus the fibres of the seventh give off fine branches which cross the ac'c, niotor root of \\ h motor- niiol. ot \'lli -/■ scilHOi-y imoi. of \ I h sen. root tiljro^ of \"tli nucl. in tL-f,Miientiiin gre3' mattt-r latcnil / .siil>. cerebellar ■-■[- perttmole jiTx'"™' '■"■'■■"It'"* nucl. fun. tcr. to fillet, white matter of cere- „ bellar heniisi^here fentral liundle of Vtll dorKil long. bund. ventral long;, bund. -I X *? '' ■ ^ ^^''^' — f'^'-si'in- tract central nucleus fillet o raniid bundles libres of pons nuclei pontic Fig. 609.- -Section across the middle of the pons varolii. about 4 diameters. ^— fibres of pons Photograph. Magnified raphe; their destination is unknown. The nucleus of the facial receives collaterals from the adjacent sensory tracts in the formatio reticularis. The facial is not a purely motor nerve, but has a ganglion upon it of the spinal type (geniculate tjanglion) from which fibres arise (fig. 601, B) which pass centrally into the pars intermedia of Wrisberg. This last enters the pons between the seventh and eighth nerves, and its fibres bifurcate into ascending and descending branches like other sensory nerves ; the descend- ing branches pass into the solitary bundle and end like those of the glosso- pharyngeal in the upper part of its accompanying grey matter. The peripheral axons of the cells of the geniculate ganglion pass into the large CENTRAL NERVOUS SYSTEM 463 superficial petrosal and chorda tympani — to wliicli they furnish afferent, probably gustatory, fibres. Other (efferent) fibres pass into the pars inter- media and ultimately into the chorda tympani from certain moderately large cells in the dorsal part of the facial nucleus. These are probably the secretory fibres of the chorda to the submaxillary and sublingual salivary glands. The sixth nerve (ahducens). — The fibres of the sixth nerve (figs. 601, 608), which are purely motor, leave the nucleus at its mesial aspect and turn forwards ; passing between the pyramid bundles they emerge at the lower margin of the pons. A few fibres are derived from a small ventral nucleus lying near the nucleus of the facial ; these run ajt first backwards and then turn forwards to join the others (Van Gehuchten) (fig. 608, re'.F/.). The fifth or trigeminal nerve emerges at the side of the pons in two roots, a smaller motor and a larger sensory (fig. 610). The motor root is derived partly from fibres which arise in the upper part of the pons and lower part of the mesencephalon from large spherical unipolar nerve- cells lying at the side of the grey matter bounding the Sylvian aque- duct (accessory or superior motor nucleus of fifth, fig. 601, nVms ; fig, 611, m!.n.V.), partly from the motor nucleus proper (figs. 601, nVm ; 611, m.n.V.) which lies in the grey matter at the lateral edge of the fourth ventricle (figs. 609, 610). As they pass the motor nucleus proper the fibres from the superior or accessory nucleus give off into it a large number of collaterals which ramify between ^nd around its cells. The fibres of the sensory root are derived from the cells of the Gasserian ganglion which are homologous with the cells of the spinal ganglia. These fibres of the sensory root when traced into the pons are found to bifurcate, the ascending branches ending in a mass of grey matter (principal sensory nucleus of the fifth, fig. 611, p.s.n.V.) lying just lateral to the motor nucleus, while the descending branches trend downwards into the medulla oblongata where they form the descending or spinal root of the fifth (fig. 611, d.s.V.); some even reach the upper part of the spinal cord. They lie immediately Fig. 610.— Section taken somewhat ok- liqumly thkonoh the pons following the cotjksfi 01" the, issuing boots oe the fifth nerve. 'in.s., median sulcus; Z, dorsal long^itudinal bundle; s.f., substantfa ferrueinea ; n.v, sensory, and n.v', motor nucleus of fifth ; V, sensory, and V, motor roots of fifth ; r, raphe ; ^y, pyramid bundles ; p, transverse fib»es of middle peduncle of cerebellum. 464 THE ESSENTIALS OF HISTOLOGY lateral to and in close connexion with the substantia gelatinosa Rolandi which forms the inferior sensory nucleus (d.s.n. V.) ; it is continued above into the principal nucleus. The substantia gelatinosa which forms the sensory nucleus of the fifth contains numerous nerye-cells, both small and large ; many of the small cells are grouped into nestUke clusters (islands of Calleja). The axons of the larger cells pass for the most part across the raphe to the formatio reticularis of the opposite side, where they reinforce the ascending fibres of the intermediate fillet, but some ascend CK r cK in the fillet m;ny. ! of the same side ; others pass to a special ascending bundle of fibres on the opposite side of the raphe lying nearer the floor of the fourth ventricle, and in the tegmen- tum of the mid-brain lies lateral to the dorsal longitudinal bundle ; hence it is continued upwards into the thalamus. Collaterals are given off from these ascending fibres to the adjoining grey matter, and especi- ally to the nucleus of the facial nerve. Branches also pass Fig. 611. -Plan (LONGiTumMAL) of the origin of this FIliRES or THE FIFTH KEBYE. G, Gosserian jranglion ; «, &, c, three divisions of the nerve ; it^S. V., superior motor nucleus; m.?i. r., principal motor nucleus; j?.*«.7i.F., , r^ * f fV» principal sensory nucleus; d.8.n.V., descending sensory nucleus; aownwaras inCO tne rf.s.r., descending root ; c. F., c'.r., central sensory tracts composed « ,. f 1 " of fibres emanating from the sensory nuclei ; r, plane of the raphe. lormatlO reilCUJariS. DESCENDING TEACTS IN THE PONS AND MEDULLA OBLONGATA. Tract of the pyramid. — The fibres of this tract are much more numerous in the pons than in the medulla oblongata. They send numerous collaterals into the grey matter of the nuclei pontis (fig. 612, A). The cortiao-bulbar tract lies mesial to the fillet (see p. 468), It consists of fibres passing from the motor cortex towards the nuclei of the facial and hypoglossal. In the crusta of the mid-brain these fibres lie mesial to the CENTRAL NERVOUS SYSTEM 465 ordinary pyramid fibres, but they then leave the latter and pass into the ventral part of the tegmentum and are continued downwards in the formatio reticularis into the medulla oblongata. The dorsal (^posterior) longitudinal bundle forms another very distinct tract. It contains both ascending and descending fibres and runs just ventral to the grey matter of the floor of the fourth ventricle, near the middle line. FiCf. 612. — Section of pons (A), medulla obloijgata (B), of cervical (C), THORACIC (D), LUMBAR (E), AND SACRAL (F) REGIONS OF SPINAL CORD OF MONKEY WHICH HAD SUFFERED REMOVAL OF THE PRECENTEAL GYRUS OF THE RIGHT CEREBRAL HEMISPHERE. The sections are stained by the Marchi method. As already noticed it connects Deiters' nucleus with the oculomotor nucleus, the nucleus of the sixth, and the ventral horn cells of the spinal cord ; it probably receives some of its fibres from the axons of certain large cells of the formatio reticularis. Other descending tracts in the pons which are not so distinctly marked in the normal condition, but which can be traced by special methods, are: 1. The rubrospinal tract; 2. The ventral longitudinal bundle; 3. The ponto spinal lateral tract ; 4. The vestibulospinal, tract ; 5. The central tract of the tegmentum. 466 THE ESSENTIALS OF HISTOLOGY Th/ilamus FibrefroTn. sensory nueleut of cereiral — ierve(Vth)tx) thahar/ius Upper or main_ Fibre of lows? or lateralfiUst — Co Corp. gwukpoat. Fibre of nutin .fUiet to thabamus fUrefrom corjd to thalcvmua CtangUon-cell of cerebral n ' "^ \~ Sensory nucleus of \ 1 1 cereirral nerve fVth.) nerve (Tth) Ganglvon-ceU. of cochbear nerve JJedian jjla/ne Fig, 613. — Diagram of sensory path to mid"- brain and thalamus Qrey matcer qf cU}T^(tb horn Monahow's bundle or tlte ruhro-spinal trad has already been seen as the prepyramidal tract of the spinal cord (p. 434). Its fibres arise from the cells of the red nucleus of the mid-brain of the opposite side, crossing the raphe CENTRAL NERVOUS SYSTEM 467 in Forel's decussation (p. 474, footnote). In the upper part of the pons it is dorsal to the mesial fillet, but lower down runs in the lateral part of the tegmentum, dorsal to the lateral fillet. The ventral longitudinal bundle {tectospinal tract) consists of fibres which arise in the opposite superior quadrigeminal body. These cross the raphe in Meynert's decussatioii (p. 474), and run down ventral to the dorsal longitudinal bundle, giving off collaterals to the oculomotor nuclei and the nuclei of the fourth and sixth nerves as they descend. Its fibres eventually mix with those of the dorsal longitudinal bundle, and pass into the ventral column of the cord, joining the ventro-lateral descending tract (p. 434). The panto-spinal lateral tract is formed of fibres which arise from large cells of the reticular formation, and run down within the lateral area of this formation in the pons and medulla oblongata to reach the part of the lateral column of the cord which lies between the grey matter and the tracts of Monakow and Gowers. It iS, however, mixed here with many fibres of different origin. The destination of its fibres is similar to those of the dorsal and ventral longitudinal bundles, viz. : the adjacent grey matter of the ventral horn. The vestibulospinal tract is composed of fibres derived from the cells of the nuclei of Deiters and Bechterew, and is therefore similar in its origin to the fibres of the dorsal longitudinal bundle. The destination is in part also similar, for the fibres pass below into the ventral root zone of the cord and end in the grey matter of the ventral horn; but in their course downwards they lie in the lateral part of the medulla oblongata mixed up with those of Monakow's tract and the ponto-spinal tract, as well as with the ascending fibres of Gowers'. tract. The central tract of the tegmentum (Bechterew) runs in the pons exactly in the middle of the reticular formation of the tegmentum, but in the medulla oblongata it lies more ventrally near the olivary nucleus, beyond which it has not been traced. The origin of its fibres is not certainly known, but appears to be the thalamus ; their destination is the olivary body of the same side (see p. 450, thalamo-olivary tract). Ascending tracts in the pons and medulla oblongata — Tract of the fillet. — In the ventral part of the reticular formation is a very well-marked tract of fibres somewhat flattened dorso-ventrally in the pons ; this is the tract of the fillet. Its fibres are partly derived from cells in the nuclei of the opposite funiculus gracilis and funiculus cuneatus of the medulla oblongata which have crossed the raphe as internal arcuate fibres ; partly from cells in the nuclei which are connected with the terminations of the sensory cranial nerves. In the mid-brain the fillet splits up into two distinct bundles of fibres termed respectively the lateral or lower and the intermediate or v/pper fillet. The fibres of the lower fillet are seen at the side of the mesencephalon (fillet 468 THE ESSENTIALS OF HISTOLOGY o/Reil), and are traceable partly to the grey matter of the inferior corpora quadrigemina (fig. 620), partly to the mesial geniculate bodj', in both of which they terminate ; they are derived from the sensory nuclei of the medulla oblongata and pons (mainly from the acoustic nuclei). Those of the •dipper fillet go to the thalamus (fig. 625) ; they are chiefly the fibres from the cells of the opposite dorsal columns of the medulla oblongata (fig. 613). TitorcroHsiiifr '"if I'ourth iier\L'S i-rf I m-ll ff n'Mi y, .Ti> 111"! r I t r Ml part rjt Intel ;il I II t dorsal Inmj. 1 II ventral lopiu^. 1 interraediati-' nili-l. substantia v\'i'rx central nucl crusta or pe^i \ ' f uli \ pedunc >-<.^ breaking up of orn^ta iiiti pyramid liuinllo FlQ. 614. TkANSVKKSF. SECTKIN TIIROUIIII the ITI'HR TART OF THE RONS. Photograph. Magnified about SJ diameters. Besides the ascending fibres of the tract of the fillet, this bundle includes a certain numb3r of fibres which degenerate below a section of the tract and are therefore descending (centrifugal) ; their cells of origin appear to lie in the thalamus ; these iibres are situated mesial to the t^ue fillet of which they were formerly considered to be a part (being termed " mesial " fillet) : they form a t'haliiiiw-hiilbar tnict. Mesial to the tract just mentioned is a bundle, also con- sisting of descending fibres, belonging to the system of the pyramid tract, and containing fibres which eventually come into relation with certain of the cranial motor nuclei (Hoche). This constitutes the rorticit-hilhar truct (see p, 464). In the crusta it lies dorso-lateral to the other pyramid tract fibres. CENTRAL NERVOUS SYSTEM 469 Many of the fibres ■which continue the sensory path of the cranial nerves upwards lie in the formatio reticularis (tegmentum), somewhat dorsal to the tract of the fillet, forming a homologous but not clearly defined tract, which runs up through the pons and mid-brain to terminate in the subthalamic region and, in the optic thalamus (central tract of the sensory cranial nerves). Fig. 615. — Diaceam showing the oriqin, ogukse, and destination of the spino - ceebebllab mbkbs constituting the tkacts OB Flechsig and OB GOWBES. li, cells of Clarke's column in the dorsal horn of the spinal cord, giving origin to fibres which pass into both spino-cerebellar tracts ; 6, tract of Flechsig, passing above hy way of the restiform body to the cerebellar vermis ; c, tract- of Gowers ; d, passage of most of its fibres along the superior peduncle to the vermis of the cerebellum : they are seen turning sharply backwards immedi- ately after passing the level of the place of exit of the 5th nerve (V). Some of the fibres of this tract leave it in the medulla oblongata and join the fibres of the tract of Flechsig which are passing to the cerebellum by its inferior peduncle. One such fibre is shown in the diagram. 470 THE ESSENTIALS OF HISTOLOGY Another ascending tract is the special bundle of fibres from the sensory nucleus of the fifth to the thalamus previously referred to (p. 464). At the wpper part of ihe fotvs (fig. 614) tWe fourth ventricle narrows gradually towards the Sylvian aqueduct, and above on each side of it two considerable masses of longitudinal white fibrlss make their appearance. These are the superior peduncles of the cerebellum. They tend,. as they pass forwards, gradually to approach the middle line ; immediately below and in the region of the posterior colliculi of the corpora quadrigemina, they pass across this, decussating with one another, to enter the formatio reticu- laris of the opposite side. The fibres of the superior cerebellar peduncles take origin in the cerebellum, emerging from its dentate nucleus, from the cells of which they are derived. They cross the raphe in the mid-brain and terminate in the red nucleus of the (opposite) tegmentum; but some of them give off a descending branch within the peduncle after crossing : its destination is not known. The ventro-lateral ascending tract of the spinal cord (p. 436) is continued up in the lateral column of the medulla oblongata dorsolateral to the olive and thrqugh the ventral part of the pons Varolii lateral to the pyramid bundles, but at about the level of the exit of the fifth nerve many of its fibres begin to pass obliquely towards the dorsolateral part of the pons (fig. 615), where the superior cerebellar peduncle is emerging from the cerebellar hemisphere. The tract in question (ventral spina-cerebellar tract) now curves over the lateral aspect of this peduncle (fig. 616, Tr. apino-cereb. ventr.), and then takes a sharp backward turn, passing over the dorsal aspect of the peduncle to enter the middle lobe of the cerebellum in the superior medullary velum. Fig. 616. — The corpora quadrigemina and NBIGHliOtlRING PARTS OF THE BRAIN. (Edinger from G. Retzius.) Brach. ant. cerebeUi, the superior cerebellar peduncles, between them the anterior medullary velum partly covered by the lingula ; Tr.spmo-cei-eb, mntr., tract of Gowers curving round the peduncle ; lemnii>cus, the lateral fillet; JS.troehl,, fourth nerve; N.V,, fifth nerve. THE MID-BRAIN OR MESENCEPHALON. In sections across the mesencephalon (figs. 618, 619, 621) the upward CENTRAL NERVOUS SYSTEM 471 continuity of the parts which have ah-eady been described in the lower nerve- centres can still in great measure be traced. The Sylvian aqueduct (fig. 619, Sy), with its lining of ciliated epithelium, represents the central canal of the cord and the fourth ventricle of the medulla oblongata. In the grey matter which surrounds it (central grey matter) there is seen in all sections of the region a group (column) of large nerve-cells (oculomotor nucleus) lying ventrally on each side of the middle line, close to the reticular formation. From the lowest cells of this column the root-bundles of the fourth nerve arise at the lower part of the mesencephalon and pass obliquely backwards and d(jwnwards around the central grey matter, decussating with those of the opposite side to emerge Just above the pons Varolii (figs. G14, 617). Hijj;her up, in the region of tlie s.m r /' -Section throucii the okigin of the foukth keuve. (Sehwalbe , transverse section at the place of emerjjence of the ner\"e-nijres. It, oblique section carried alon^ the course of the bundles from the nucleus of oi'ifrin to the place of emerjrence. A.(., stria medullaris; nr.., nc'., nucleus caudatus, and nl., nucleus lenticularis of the corpus striatum ; i.e., internal capsule ; 7, its angle or genu ; nc'., tail of the nucleus caudatus appearing in the descending cornu of the lateral ventricle ; cL, claustrum ; 7, insula. CENTRAL NERVOUS SYSTEM 481 into the white matter of the hemisphere, and eventually to the cortex. From the outer part they tend especially towards the occipital region, assisting to form the central visual tract which passes to the visual cortex. From the inner and deeper 'part they converge towards the subthalamic region. Here many are collected into the ansa lenticularis (see p. 484), by which they pass into the nucleus lenticularis, while others, as already stated, enter the corona radiata and thus reach the cortex of the hemisphere. Fig. 625.r^DiAGRAM or the connexions of the thalamus with thb asoendikh FIBRES or THE rifTH NERVE, AND OF THE UPPER FILLET ON THE ONE HAND, AND "^ITH THE CORTEX CEREBRI ON THE OTHER. (Oajal.) A,'B, 0, D, is, various nuclei in thalamus ; I, afferent fibres passing to mammillarj' body, P ; G, tract of upper, fillet ending in A (at c),' and giving collaterals to D (posterior nucleus) ; H, central tract from sensorj' nucleus o( fifth ; T, cortex cerebri ; V, visual cortex ; R, anterior colli- culus; J, optic chiasma ; S, optic fibres; K, hippocampus. (0, fibres from cortex to thalamus, ending at e ; h, fibres from cells in thalamus (d) to cortex ; f, fibres from lateral geniculate body and thalamus to visual coytex, ending at ^ in stria of Gennari. These fibres from the thalamus to the cortex probably form the third and the last link in the chain'of sensory neurones, tjie second being formed by the neurones of the fillet and the first by the neurones of the sensory roots. On the other hand, the thalamus receives fibres both from the cortex and from the corpus striatum, to end amongst its cells. Corpora geniculata. — Attached to the thalamus below and behind are the geniculate bodies (fig. 626). These at first sight appear to be both connected with the optic tract, but only the lateral one actually receives optic fibres, the mesial body receiving fibres from the central auditory tract through the lateral fillet. Of the geniculate bodies the outer or lateral has a lamellated structure consisting of alternating layers of grey 482 THE ESSENTIALS OF HISTOLOGY and white matter, the white layers being composed partly of the entering optic fibres and partly of fibres emerging from the grey matter and passing to the central optic path, while the grey substance contains very numerous nerve-cells amongst which the fibres of the optic tract end in complex arborisations. From these cells axons arise and join a bundle of fibres Fig. 626. — Figure showing the olfactorv tracts and thkir roots, the optic chiasma and optic tracts, the (ieniculate rodies ami the rulyinar THALAMI. (Edinger.) The pons is exit through at the anterior part, and the section shows the Sylvian aqueduct, the fillet (lamina lafjuuari^), superior cerebellar peduncles, etfl| The corpora mammillaria arc partly concealed by the pons ; Ijetween and in front of thcnvis seen the infundibulum. which enters the white matter of the hemisphere above and along with the internal capsule, and passes to the visual area of the cortex (central visual tract). Some of the fibres from the corpus geniculatum laterale, as they enter the visual tract, send branches downwards towards the tegmentum. The cells of the mesial geniculate body are collected into two main nuclei, dorsal and ventral. Most of the cells are small, but at one part there is a group of large cells. The axons appear to pass throiish the CENTRAL NERVOUS SYSTEM 483 brachium and eventually to the cortex : probably to that of the temporal lobe. The ganglion of the habenula (fig, 628, g') is a collection of nerve-cells which lies at the posterior part of the thalamus on each side, near the roof of the third ventricle. This ganglion receives on the one hand the fibres of the habenula or stria medullaris, and on the other Iiand gives off from its cells the fibres which form iht fasciculus relrqflexus or Meynert's bundle (fig. 654), Fig. 627. — Diagram to .show the vrobablb course and relations of the optic fibres. Only single fibres are shown emerging from the anterior quadrigreminal -and external gfeniculate 'bodies, continuing the course of the two fibres from corresponding points in the retinic. This is merely to simplify the diagram, and is not intended to assmne that the retinal impressions are fused in those situations. passing downwards to the interpeduncular ganglion (p. 476). The two ganglia of the habenulse are joined by a white commissure. The corpora mammillaria (fig. 626) are seen at the base of the brain immediately below the posterior part of the, third ventricle Bach is com- posed of white matter externally and grey matter internally. Each receives fibres from the anterior pillar of the fornix of the same side ; these fibres arise from cells in the hippocampus and end in the mammillary body. Accord- ing to Edinger some fibres from the olfactory tract pass directly to it. The axons of its cells bifurcate ; one branch, the coarser, passing into the anterior and upper part of the thalamus in the bundle of Vicq d'Azyr, and the other into the tegmentum of the mid-brain in v. Gudden's bundle. The corpora mammillaria form part of the central olfactory apparatus (fig. 654). 484 THE ESSENTIALS OF HISTOLOGY Subthalamic region. — The tegmentum of the crus cerebri is prolonged below the thalamus, and between it and the internal capsule is represented by a mass of grey substance, with longitudinally and obliquely crossing white bundles, which is known under the name of subthalamus or hypothalamus (fig. /"* *^ Fig. 628. — Section takek oblujuelv thkuugh Tiifi TiiALA:sius ami internal CAPSULE SHOWING SOME OP THE STRANDS OF FIBRES OF THE SUBTHALASIUS. Magnified 2i dinraeters. From a photograph. Th., thalamus; f.u'i., third ventricle; t.. taenia, or attachment of epithelial roof of ventricle; str., stria meduUaris or habenula; (f, ganglion of the habenula; n.t., mesial nucleus of thalamus; opl.^ optic fibres passing into pulvinar of tbalamus<; £./., zona incerta, from which fibres are seen emerging and sweepmg as the aittia lentiaularis, a.L, rountl the internal capsule, c.i., to pass toward the lenticular nucleus ; c,s., corpus subthalamicum ; /, anterior pillar of fornix passing backwards to corpus mammillare ; V.A., bundle'of Vicq d'Azyr, passing up\\'ards and forwards from corpus nLimraillare into thalamus ; g, group of nerve-cells, probably belonging to the nucleus of the corpus mammillare ; x, fasciculus retroflexus. 628). Its deepest part contains a lens-shaped mass of grey matter prolonged forwards from the substantia nigra known as the corpus subthalamicum of Luys. A mass of fibres sweeps round this and round the internal capsule, passing bet^flfeen the thalamus and the nucleus lenticularis ; the terms zona incerta and ansa lenticularis are employed to denote some of these strands, but their origin and destination have not been definitely ascertained. CENTRAL NERVOUS SYSTEM 485 LESSONS XLIV. AND XLV. CENTRAL NERVOUS SYSTEM- The Cerebellum and Cepebrum. 1. Sections of the cerebellum- vertical to the surface, (a) across the direction of the laminae, (6) parallel with the laminse. 2. Sections across the whole of one hemisphere of the cerebrum of a monkey or cat passing through the third ventricle. 3.' Vertical sections of the cerebral cortex : — one across the central gyri, another from the occipital lobe (calcarine region), another across the superior temporal gyrus and island of Reil, and one across the hippocampal gyrus and hippocampus. 4. Transverse sections of the olfactory tract and bulb. In all these preparations make outline sketches under a low power of the arrangement of the grey and white matter, and the disposition of nerve-cells in the grey matter. Sketch some of the details under a high power. The preparations are made in the same way as those of the spinal cord. Other preparations may be made by the Golgi method to exhibit the relation of the cells to one another. Such preparations may have been already partly studied (Lessons XVII. and XVIII.). . • THE CEIIEBELLUM. The cerebellum is composed of a white centre and a grey cortex (fig. 629). Both extend into all the folds or laminse, so that when the laminse are cut across, an appearance is presented of a white arborescence covered super- FiG. 629. — Section THEOtroH one of the hemispheres or the cerebellum, SHOWING the laminated AKBOKBSCBNT APPEARANCE OF THE GREY MATTER AT THE SURFACE AND THE ' NUCLEUS DENTATUS (n.d.) IN THE MIDDLE OF THE WHITE CENTRE. The pons is indicated by a dotted outline. 486 THE ESSENTIALS OF HISTOLOGY ficially by grey matter. The whit« matter is* in largest amount in the middle of each corebellar hemisphere. There is here present a pecuHar wa\y lamina of grey matter, similar to that in the olivary body, and known as the nucleus dentatus (fig. 629, n.d.). This receives numerous nerve-fibres from the cells of Purkinje of the cortex, which end by arborising around its cells. The latter give off axons which become the fibres of the superior cerebellar peduncles, and for the most part end in the opposite red nucleus (p. 471), 7}l>oi i -faf-vn- is S£ ■^?-"— — Fig. 630. — Section across the oebebellum and medi-lla oblongata showtn(! THE position OF THE NUCLEI IN THE WHITE CENTRE OF THE CEaEBELLUM. (Stilling.) n.d., nucleus dentatus cerebelli ; ^■.c.J7., fibres of superiorjpeduncle ; com, com', com". commissural fibres ; X, root-fibres of va^s ; XII, root-fibres of hypoglossal nerve. but some pass beyond this into the subthalamic region. The dentate nucleus also receives collaterals from fibres of the inferior peduncle (Cajal). Other isolated grey nuclei lie in the white matter of the middle lobe over the roof of the fourth ventricle and constitute collectively the nuclei of Stilling. The most important of these appears to be the nucleus tecti sen fastigii (fig. 630). This receives many of the ascending fibres of the vestibular nerve (p. 457) and collaterals from the spino-cerebellar tracts, and gives origin to a bundle of fibres which crosses to the opposite side and descends in the mesial part of the restiform body to the reticular formation of the medulla oblongata (Risien Russell). The grey matter of the cerebellum appears of essentially similar structure throughout the whole extent of the cortex. It consists of two layers. The CENTRAL NERVOUS SVSTEJl/ 487 inner or granule layer (fig. 631, d, and fig. 633, B) lies next to the white centre, and is composed of a large number of very small nerve-cells intermingled with a few larger ones and some neuroglia-cells. The outer or molecular layer (fig. 631, b, and fig. 633, A) is thicker, and is formed chiefly of fine nerve-fibres with small nerve-cells scattered through it. Into its outer part processes of the pia mater conveying blood- vessels pass vertically. Lying between the two layers of the grey matter is an incomplete stratum of large flask-shaped cells, termed the cells of FurMnje (fig. 631, c ; fig. 632, fig. 633, a). Each of these cells gives off from its base a fine process (axon), which becomes the axis-cylinder of one of the my- elinated fibres of the white centre, while from the opposite pole of the cell large ramified processes (den- drons) extend into the superficial layer of the grey matter. The detidrons of the cells of Purkinje spread out in planes trans- verse to the direction of the lamellte of the organ, so that they present a different appearance according to whether the section is taken along a lamella or across it (compare fig. 633, I and II). These den- drons are invested at their attach- ment to the cell and, for some extent along their branchings, by a basket-work formed by the terminal arborisations of certain fibres (^climbing or tendril fibres) of the medullary centre (fig. 635 ; fig. 636, cl.f.). The body of the cell of Purkinje is further invested by a felt- work of Ifirbrils formed by the arborisation of axis-cylinder processes of nerve-cells (basket-cells) in the outer layer of the grey matter (figs. 634; 636, b). ' Each cell has therefore a double investment of this nature, one coveringthe dendr%s, the.other investing the body of the cell and extend- ing a,long the commencemejit of, the axon, Fig. 631. — Section of cortex or cerb- BBiiLUM. (Sankey. ) ti, pia mafcer ; b, outer or molecular layer ; c, cor- . puscles of Purkinje ; rf, inner or granule layer ; e, medullary centre. 488 THE ESSENTIALS OF HISTOLOGY The granules of the inner layer of grey mat.ter are mostly small nerve cells, each with a few dendrons penetrating aipongst the other granules, and an axon directed between the cells of Purlcinje into the outer layer. After penetrating a variable distance into this layer the axon bifurcates, and its two branches pass in opposite directions at right angles to the main stem, and parallel to the direction of the lamella (fig. 633, I). What ultimately becomes of the branches is. not known. In sections cut across the lamella the cut ends of these fibres give a finely punctated appearance to the outer layer (fig. 633, 11). Some of the cells of the granule layer are far larger than the others, and send their much-branching axons amongst the smaller granules. They are known as cells of Golgi, fig. 636, G. Certain other large "granules" have been noticed by Cajal, occurring both in the granule layer and in the white centre, with long axons passing into the white matter of the cerebellum. These are comparatively .few in number. Ramifying amongst the cells of the granule layer are peculiar fibres derived from the white centre, and characterised by having pencils of fine short branches at intervals, like tufts of moss (fig. 636, m.f.). These have been termed by Cajal the moss-fibres ; they end partly in the granule layer, partly in the molecular layer. The neuroglia of the cerebellum is peculiar in containing, besides the ordinary "spider" and "branched" neuroglia-cells (fig#636, gl^, gl^), othe^r large cells with long parallel processes which extend through the molecular Fig. 632. — A cell of Purkinje op the cierebellum, SHOWN BY (JOLOl'S METHOD. (Cajal.) It, axon ; b, collateral (rom axon ; c, d, arborisation of dendrons. CENTRAL NERVOUS SYSTEM 489 Fig. 633. — Sections of coetex 'cbrbbelli stained by Golgi's method. (Caj'al.) I.— Section made in the direction of a lamina. II. — Section taken across a lamina. A, outer or molecular layer ; B, inner or granule layer ; C, medullary centre. (f, corpuscles of Purkinje ; 6, small granules of inner layer ; c, a protoplasmic process (dendron) of a granule ; d, nerve-fibre process of a gi-anule passing into the molecular layer, where it bifurcates and becomes a longitudinal fibre (in II these longitudinal fibres are cut across and appear as dots); e, bifurcation of another fibre ; g, a granule^lying^in the white centre. Fig. 634. — Basket-cell op cerebellum showing the arborisations of its AXON over the cells OF PuRKiNJE. (Cajal.) A, row of Purkinje cells ; B, basket-cell of molecular layer ; d, its dendrons ; c, its axon ; a and h, endings of axon. 490 THE ESSENTIALS OF HISTOLOGY layer to bo attachod to the surfaco of the lamella' (,'//''). The f-ell-bodies lie at about the same level as those of Pui'kiiije's cells. Fibres of the cerebellar peduncles. -The peduncles of the cerebellum have been already studied in connexion with the medulla oblongata, pons, and mid- brain, but it may be convenient briefly to summarise what has there been stated. The inferior peduncle (reatiform body) is composed mainly (1) of ascending fibres derived from the dorsal spino-cerebellar tract running in its outer part ; and (2) of fibres from both olivary nuclei, but chiefly from that of the opposite side. This peduncle is also said to receive fibres from the nuclei of the gracile and cuneate funiculi, from cells and nuclei of the reticular formation of the medulla oblongata, and from the sensory nuclei of the cranial nerves, especially of the vpstibular nerve. Most of the fibres of the peduncle pass to the lower part of the vermis, crossing to the opposite side over the fourth ventricle, but before doing so they give ofl' strong collaterals to the hemisphere of the same side. Besides its ascending fibres the peduncle also con- tains a small bundle of fibres descending to the medulla oblon- gata from the nucleus tecti of the opposite side: this bundle bends round the superior peduncle to join the inferior ped- uncle, its fibres lying between those of the superior peduncle and tTowere' ti-act (Eisien Russell). In the middle of the inferior peduncle is a very small nucleus of grey matter (Dejerine^ which is almost com- pletelv concealed amongst the mass of white fibres (^fig. 603, n .r.). The middle ped- uncle is formed of fibres from the cells of the nuclei pontis which are passing to the opposite hemisphere of the ce.rebellum. The superior peduncle is formed of fibres which mostly take origin in the corpus dentatum oerebelli, but some are said to arise in the hemisphere and pass through this nucleus. The superior peduncles decussate in the mid-brain across the raphe, and their fibres then bifurcate into ascending and descending branches. The ascending branches pass forwards and end in the red nucleus, but some fibres go past this into the ventral part of the thalamus. The descending branches are traceable into the dorsal part of the reticular formation of the pons. The superior peduncle, as it issues from the hemisjihere, is joined by the bundle of Gowers, which runs over it, and passes backwards along its mesial border to the vermis. Fig. 035. — Ending of a "tendril" fibrf. over the den- DRONS OF A PtlRKIN.IE CELL: HUMAN. (Cajal.) CENTRAL NERVOUS SYSTEM 491 TlfE CEREBRUM. The grey matter of the cerebral cortex is always described as if composed of a number of layers, but the strata are not sharply differentiated and they vary in number and in relative development in different regions of the cortex. Fio. 636. — Diagrammatic sbctiost of cbrebellum to show the chabaotbks ahd BBLATIONS OF THE CELLS AND EIEKES MET 'WITH IN THE SEVERAL LAYERS ■AS EXHIBITED BY THE CHROMATE OF SILVER METHOD. (After KoUiker.) P, a cell of Purkinje ; G, a cell of Golgi ; 6, a basket-cell ; m, m, other cells of the molecular layer ; ffr, granules; p, a nerve-fibre of the white substance derived from a Purkinje cell; i«.../".^ " moss "-fibres ; cl.f., a climbing fibre ; ffl\ gl^, gV-\ types of neuroglia-cells. Most of the cells are of a long, irregularly conical sbape : these are known as the pyramidal cells of the cortex, a name which ig somewhat inappropriate as a term intended to describe their form (fig. 637). They vary considerably in size in different levels. The following eight strata are generally distinguish- able, but in some parts of the cortex a larger number can be made out, whilst in other parts there are fewer. 492 THE ESSENTIALS OF HISTOLOGY 1 . A peripheral stratum {moleculcur or plexiform layer) containing scattered nerve-cells and many neuroglia-cells (figs. 637, 638, 1). In the most superficial part of this layer, im- mediately under the pia mater, is a thin stratum of nerve-fibres running parallel with the surface ; the layer also contains a large number of ramified fibres. Most of the fibres of this plexiform layer are derived from nerve-cells of the deeper parts of the cortex. Intermingled with the fibres a few ramified cells, each with numerous dendrons and a long axon, are disposed parallel with the surface ; the axons terminate by arborisations within thp layer itself {horizontal cells of Cajal) (fig. 638). Other cells with shorter sd^is-cylinder processes also occur in this layer. 2. A layer of closely set small pyramidal nerve-cells, several deep (layer of small pyramids, fig. 637, 2). This layer also contains other cells with short axons. 3. A layer of medium-sized pyra- * midal cells less closely set, with small granule-lite cells amongst them (layer o* mediurr^-sized pyramids, fig. 637, 3). 4. A layer of larger pyramidal cells (superficial large pyramids, fig. 637,4). 5. A layer of small irregular cells (small stellate cells, fig. 637, 5). The large pyramids may extend down into this layer. 6. A layer of still larger pyramids (deep largp pyramids, fig.' 637, 6). In themotor region of the cortex, which in man appears to be confined to the pre- central gyrus and paracentral lobule, pyramidal cells of very large size (giant- cells) occur within this layer, disposed in small clusters or "nests" (Betz, Bevan Lewis). The fibres of the pyra- FiG. 637. — Ascending parietal or post- central CONVOLUTION : GOLOl METHOD, (Cajal.) 1, plexiform layer; 2, small pyramids; 3, medium pyramidB ; 4, superficial large pyramids ; 5, granules; (smalt stellate cells); (i, deep large pyramids ; 7, deep mediiim pyramids. CENTRAL NERVOUS SYSTEM 493 Fig. 638. — Diagram showing the relations of some of the cells of the ■ OEBEBEAL CORTEX. (Barker, after Starr, Strong, and Learning. ) 1, plexiform layer with horizontal cells of Oajal; 2, small (do c) and middle size (/) pyramids ; 3, large pyramids ig, g, ft) ; also m, cell with -axon passings towards the surface, but soon ramifying ; n, h, cell of Golgi's second type, with axon ramifying in the adjacent grey matter ; one of these helonge to the kind termed by Oajal ' ' double-hrush " cells ; i, polymorphous cells, of which p sends its axon towards the surface and q its axon into the medullary centre ; '^ -'" ." " cells in the grey matter, and including also 494 THE ESSENTIALS OF HISTOLOGY mid tract arise from these giant-cells. In some parts of the cortex the layer of large pyramids is either absent or is blended with the next layer. 7. A layer of medium-sized pyramidal cells {deep medium pyramids, fig. 637, 7). 8. A layer of small scattered cells (fig. 638, 4), many of a fusiform shape {polymorphous layer). This layer lies next to the white centre. In the island of Reil it is considerably developed, and is separated from the rest of the grey matter by a layer of white substance. It is here known as the claustrum, and on that account the layer is termed the claustral layer. iSuiue authorities describe the coitex as consisting only of three layers, viz. : the moleculai- layer, the layer of pyramids, and the layer of polymorphous cells ; others of four, five, etc., up to nine. As a matter of fact, the complexity and the number of distinct layers largely vary in diflerent regions. Each pyramidal cell has several basal and one large apical dendron. This process extends to the plexiform layer, on approacting which it breaks up into iiumei'ous lamifications which have a general vertic|,l direction and extend almost to the outer surface. The apical dendron is beset, both in its undivided part and in its branches, by minute spinous projections : similar "spines" may also .Fi<;. 639. — Sei'tiiinb of ciskebkai. coKvoiii Tio.N's. (After Baillarger. ) Natural size. a, from the neighbourhood of the calear'me fissure with only one white line clearly visible (the line of «'',•-• I; lilt [• i',. j\, 41 ^li' Fm. e*;"). Fill. 643. Fig. Ii44. Fig. (i43.— Section ok post-central oysuS: of man, stained by Nissl's method. (Cajal.) 1, plexiform layer ; 3, small pymmids ; S, medium pyramids ; 4, superficial lar^ pyramids 5, small stellate cells (granules) ; (J, deep large and medium pyramids ; 7, fusiform cells. Fig. i;44. — Section of precentkal gyrcs (^t.0T0R cortex), stained BY Nissl's method. (Cajal.) 1 to 08 before ; a, c, small cells amongst the pyramids ; i, a large pyramid ; (f, a giant- cell of Eetz. Fig. 64.">. —Section of one of the motor convolutions (man), STAINED BY WeIGERT-PaL METHOD. (Cajal.) Only the nerve-flb"°° """ ""o" '" ^'^ie nroruimtinn K^ .■.•■■»' #4?*' "mm Silt? Mm ',4. .'\h[ U Fig. 646. I'. 1' > ^'l •.'•'I ! I ' Fig. 647. ;=-^'<; V' ;i- Fig. 646.— Caluakinb (visual) oobtex or man. (Cajal.; Fir. 648. Nissl's method. 1, plexiform layer ; 2, small pyramids ; 3, medium pyramids ; 4? large stellate cells (characteristic of this part of the cortex) ; 5, small stellate cells ; 6, a deep jalexiform layer, containing some small pyramids ; '7, large pyramids ; 8, layer of small and mediiun pyramids with bent ascend- ing axons ; 9, fusiform cells. Pig, 647. — Section" of fiest temporal gyeus (acoustic cortex) of man, stained by Nissl's method. (Cajal.) 1, plexiform layer ; 2, layer of small pyramids ; 3, superficial medium pyramids ; 4, large pyramids ; 5, small stellate cells (granules) ; 6, deep medium pyramids.; 7, fusiform cells. Fig, 648. — Section of the first temporal gyrus (man) stained by Weigbrt-Pal method. (Cajal.) Only the nerve-flbres are seen in this preparation. 500 THE ESSENTIALS OF HISTOLOGY in different regions.' In some they arc large arid numerous (motor part of frontal lobe, calcarine area, hippocampal area), in others fine and much less conspicuous (gyrus fornicatus, temporal area,, parietal area, prefrontal area, insula and lobus pyriformis), whilst an intermediate condition presents itself in the occipital area (except the calcarine legion), the transverse temporal gyri and superior temporal gyrus, and the part of the frontal immediately in front of the motor region. These differences have been employed by Campbell Fli;. 469.— SdpEEFICIAL LAYEKS OF MOTOR CORTEX OF qftlLD ; GoLGl METHOD. (Cajal.) A, B, C, cells of Cajal in plexiform layer ; D to K, cells cf^type ii. of Golgri (\\ith axons ramifying near cell-body) ; H, J, "double-brush ' types of cell. in an attempt to differentiate the functions of the various cerebral regions by a corriparison of their structure.^ THE RHINENCEPHALON. The rhinencephalon (olfactory region of the tielencephalon), on account of the peculiarities of its structure, its importance in most animals, and the ' Except, perhaps, in the bundle of Lissauer in the cord there are no nonmyelinated fibres in the central nervous system, exclusive of a few which pass to the membranes and blood-vessels from the sympathetic chain of ganglia. ^ For further detaila regarding the cells and fibres of different regions of the cortex and the special characters of the several region.s see flie volume of Qihxiti.* Anatomy dealing with Neurology. CENTRAL NERVOUS SYSTEM 501 fact that it has been the part of the telenceph'alon to appear first iu phylo- genetic development, merits a special description, although in man and 3 48 2 Fig. 650. Fie. 651. Fig. 650. — Sbction across the hifpooami-us majob, dentate rissunE, DEHTATE FASCIA AUD IIMBRIA. (W. KraUSB. ) D, fascia dentata, or dentate convolution ; F, fimbria, composed of longitudinal fibres here cut across ; H, medullary centre of the hippoeampal gyrus prolonged around the hippocampus, as the so-called alveus, into the fimbria ; 1, layer of large pyramidal cells ; 2, their processes (stratum radiatum) ; 3, stratum granulosum ; i, plexiform layer (stratum laciniosum) ; 5, super- ficial white layer ; 6, nerve-cells of fascia dentata' 7, stratum ^anulosum of fascia dentata ; 8, termination of superficial white layer, its fibres becoming longitudinal. Fig. 651. — Hippocampal region ; Goloi method. (Oajal.) A, B, hippoeampal gyrus ; C, hippocampus major ; D, dentate gyrus ; E, fimbria ; F, white matter of hippoeampal gyrus ; G, in lateral ventricle ; the line points to the crossed spheno-hippo- campal bundle ; H, fibres of corpus callosum. a, efferent fibres of hippoeampal gyrus ; h, afferent fibres of hippoeampal gyrus ; c, afferent fibres of hippocampus and dentate gyrus ; d, others perforating grey matter of hippo- eampal gyrus ; e, others cut obliquely ; /, fibres of alveus ; g, h, cells of hippocampus major sending their a.\ons into the alveus and towards the fimbria ; i, k, collaterals from these axons passing to the molecular layer ; i\ collateral fibres of alveus. The arrows indicate the probable course of the nerve impulses; Primates generally, and in some other (microsmatio) mammals, it is reduced to a comparatively rudimentary condition. In the so-called osmatic (macrosmatic) mammals the rhinencephalon oonsists of a large hollow olfactory bulb, the cavity of which communicates with the lateral ventricle. S02 THE ESSENTIALS OF HISTOLOGY It forms the anterior termination of a thick olj'actory lobe which broadens out "behind and becomes continuous with the hippocampal gyrus and hippocampus. The whole forms a pyriform mass, separated from the rest of the cortex by a well-marked fissure — the limbic fissure — and has special connexions through the anterior commissure and fornix with other parts of the brain on the same and on the opposite side. In man the rhinencephalon consists anteriorly of the small, olfactory bulb from which the thin olfactory tract extends backwards to the grey matter at the base of the brain and to the hippocampal region. Posteriorly the cortex of the rhinencephalon is doubled in so as to foriii a projection {hippocampus m.ajor) in the descending cornu of the lateral ventricle : its edge here thins oiF and is continued merely as a- thin layer of epithelium covering the choroid plexus of the pia mater, which is invaginated into the ventricle. At this thin -edge the white matter comes to the surface as the fimbria which is continued on each side into the commissural band known as the fornix. Lying along the fimbria is the small and half-concealed dentate gyrus, which is formed by the sharp bending of the grey matter, and is traceable round into the hippocampus major, the hippocampal fissure being between them : the hippocampus major is continuous externally with the gyrus hippocampi. The olfactory tract is connected directly with the hippocampal region by a lateral root, whilst a mesial root passes into the anterior commissure and forms a connexion with the rhinencephalon of the opposite side. The structure and connexions of all these parts as they occur in man may be briefly given. In the region of the hippocampus major (figs. "650, 651) the cortex is simpler in structure than elsewhere, and in the hippocampus major itself, which is an infolded part of the cortex, the pyramids are reduced to a single layer of large cells lying in the deeper portioii and sending their apical dendrons as long fibres into the plexiform layer. The plexiform layer and the superficial white stratum overlying it are both very strongly marked, the plexiform layer having a distinctly reticular aspect, due partly to neurbglia-cells, partly to the arborescence of the dendrons of the pyramids. The plexiform layer is here termed stratum laciniosum ; internal to it near the dentate gyrus is a layer of closely packed small cells termed stratum granulosum. The pyramidal cells lie close to a white layer known as the alveus. This is the part of the hippocampus sften within the ventricle, and represents the white matter of the hemisphere, here greatly attenuated. The alveus is prolonged externally into the fimbria, in which its fibres become longitudinal in direction and are continued into part of the fornix. In the dentate gyrus (fascia dentata, figs. 650, 651) the pyramidal cells (6) arc arranged in an irregularly radiating manner. They occupy the centre of the convolution, and are surrounded by a ring of closely packed small cells (stratum granulosum of fascia dentata, fig. 650, 7). External to these small cells is a thick plexiform layer (stratui)i laciniosum). CENTRAL NERVOUS SYSTEM S03 In some animals the The anterior part of the hippocampal gyrus, known as the lobus pyri- formis, receives the lateral root of the olfactory tract. It is characterised by the presence in the plexiform layer of peculiar nests of nerve-cells. The cells in these nests are of two types, viz., large polymorphous cells and small pyramidal cells, each being confined to its own nest. This part of the cortex is regarded by Cajal as the true olfactory region, anterior perforated space forms a distinct promin- enca of the cortex (tuber- culum olfactorium) and this is also characterised by cell-nests {islets of Calleja). They also occur in the cortei of the hippocampal fissure. The olfactory" tract is an outgrowth of the brain which ivas originally hollow, and remains so in many animals ; but in man the cavity has become obliterated, and the centre is occupied by neuroglia, containing no nerve-cells. Outside the central neuroglia lies the white or medullary substance, con- sisting of bundles of longi- tudinal white fibres. Most externally is a thin super- ficial layer of neuroglia. The olfactory bulb (fig. 652) has a more com- plicated structure thart the tract. Dorsally there is a flattened ring of longitudinal white bundles enclosing neuroglia (1, 2, 3), as in the olfactory tract, but below this ring several layers are recognised as follows : — 1. A white or medullary [layer (fig. 652, 4, 5), characterised by the presence of a large number of small cells (" granules ") with reticulating bundles of myelinated nerve-fibres running longitudinally between them. 2. A layer of large nerve-cells (6), with Smaller ones ("granules") inter- mingled, the whole embedded in an interlacement of fibrils derived from the cell-dendrons. From the shape of most' of the large cells of this layer (fig. 653, m.c.) it has been termed the "mitral" layer. These cells send their I I , v. f (jfn.'-i^ Fig. 652.— Section across a i-art of the olfactory BULB. (Henle. ) 1, 3, bundles of very fine transversely cut nerve-fibres, forming' the flattened medullary ring, enclosing the central neuroglia, 2 : this ring is the anterior continuation of the olfactory tract ; 4, 5, white layef with nnnlerous small cells (granules) ; 0, mitral-cell layer ; 7, layer of olfactory glomeruli ; 8, layer of olfactory nerve-fibres, bundles of which are seen at # passing through the cribriform plate of the ethmoid bone. S04 THE ESSENTIALS OF HISTOLOGY axons upwards into the next layer; they eventually become fibres of the olfactory tract and pass along this to the bas6 of the brain, giving off' numerous collaterals into the bulb as they run backwards. 3. The layer of olfactory glomeruli (fig. 652, 7; fig. 653, gl.). This consists of rounded nest-like interlacements of fibrils which are derived on the one hand from the terminal arborisations of the non-myelinated olfactory fibres which form the subjacent layer, and on the other hand from arborisa- tions of dendrons of the large " mitral " cells of the layer above. There are Fig. 653. — Diagram to show the relations of cells and fibres in the olfactory bulb. olf.c, olfactory cells in the olfactorj' mucous membrane, sending their hasal processes as (non- myelinated) nerve-fibres into the deepest layer of the olfactory bulb (ulf.n.) ; lyi., olfactory glomeruli containing the terminal arborisations of the olfa tory fll>re8 and of processes frorii the mitral cells ; mc, mitral cells, sending processes down to the olfactory glomeruli, others laterally to end in free ramiBcations in the nerve-cell layer, apd their axis-cylinder processes, a, a, upwards, to turn sharply backwards and become fibres ot the olfactory tract (ii tr ) Numerous collaterals are seen coming oS from these fibres ; n' , a nerve-flbre of the olfactory tract ending in a free ramification in the olfactory bulb. also a few small nerve-cells immediately external to and extending within the glomeruli (periglomerular cells). These are short-axoned cells and appear to connect neighbouring glomeruli. The layer of olfactory nerve-fibres (fig. 652, 8 ; fig. 653, olf.n.). These are all non-myelinated, and are continued from the olfactory fibres of the olfactory mucous membrane of the nasal foss«. In this mucous membrane they take origin from the bipolar olfactory cells, which are characteristic of the rnembrane (see Lesson XLIX., fig, 696), and they end in arborisations within the olfactory glomeruli, where they come in contact with the arbor- isations of the mitral cells. The relations of the olfactory cells and fibres to the mitral cells, and the continuation of the axis-cylinders of the latter CENTRAL NERVOUS SYSTEM- SOS upwards and backwards in the olfactory tract, ate shown in the accompany- ing diagrams (figs. 653, 654). Besides the centripetal nerve-fibres there is a certain number of centrifugal fibres which end by ramifying in the olfactory bulb amongst the mitral cells (fig. 653, n'). As shown in fig. 654, many of the fibres of the olfactory tract pass to the Fig. 654. — Diagram oi the olfactory path in the bbain. To simplify the diagram the various divarications of the olfactory path have been represented by branchings of individual fibres, although in some oases the, divergence is brought about by the turning aside of bundles of entire fibres. hippocampal region~of the brain, terminating by arborescence in the grey matter (molecular layer) of the base of the olfactory lobe in the region of the anterior Fig. 655. — Frontal section through the cerebrum in the region oj? the middle COMMISSURE. Natural size. cc, corpus callosum ; /, fornix ; n.c, nucleus caudafcus ; (A, thalamus ; s.t.r.f subthalamic region; CJ'., crusta passing into internal cap- sule ; s.Ti., substantia nigra ; a, e, i, various nuclei of thalamus ; a, its latticed layer ; 1, H, -i, parts of subthalamus ; n.l., nucleus lenfii- Gularis ; R.c, external capsule; ol., claustrum ; i, insula ; m-c, middle commissure ; above and below it is tiie third ventricle, communicatinpf - above on each side through the foramen of Monro with the lateral ventricle. Below the fornix are seen the choroid plexuses; t.s,, stria terminalis. perforated space, as well as in that of the uncus and the hippocampal gyrus. Fibres are also given off from the olfactory tract to the anterior commissure which proceed to the opposite tract and bulb. Besides these the anterior commissure contains many fibres which are passing from the hippocampal region on one side to the corresponding region on the opposite side of the brain. From the pyramid-cells of the base of the olfactory lobe and hippo- campal gyrus fibres pass to the grey matter of the hippocampus, and from the pyramid-cells of the hippocampus others proceed by way of the fimbria 5o6 THE ESSENTIALS OF HISTOLOGY and fornix to the hippocampus of the other side, to the subcallosal gyrus and septum lucidum, to the ganglion of the habenula, and finally by the anterior pillar of the fornix to the corpora mam miliaria. LOR?US STRIATUM. Besides the grey matter of the cerebral cortex the cerebral hemispheres conceal, in their deeper parts certain other masses of grey substance (figs. 6^5, 656). The principal of these are the corputi striatum (con- sisting of nucleus caudatus, u.c, and iii(c/piiK hnticularis, n.l.) and thalamus (th.). Between them run the bundles of white fibres which are passing downwards to the crus cerebri, forming a white lamina termed the internal capsule. Above the level of these nuclei the internal capsule expands into the medullar^' centre of the hemisphere. Below the thalami are the prominent gang- lia known as corpora albicantia or mammillaria. Of these the optic thalami and corpora mam- millaria have already been noticed. The nucleus caudatus of the corpus striatum is composed of a reddish-grey substance containing nerve ceils some with long, others with shorj axon-processes ; some of the cells with long processes being very large. It receives fibres from the part of the internal capsule which sepai'ates it from the nucleus leuticularis. Ne.xt to the lateral ventriole it is covered by a thin layer of neuroglia, and over this by the epithelium of the cavity (ependyma). The nucleus lenticularis, which corresponds in position internally with the island of Reil externall}'', is divided by two white laniintv into three /.ones. It is separated from the nucleus caudatus and optic thalamus by the internal capsule (i.<\), which consists of the bundles of fibres which are passing between the white centre of the hemisphere and the crus cerebri. It receives on its inner side many fibres from the capsule ; these impart Fig. 656.— Hoeizontal section throuuh the thalamus and corpus striatrji. Natural size. r.l., lateral ventricle, its anterior cornii ; cc, corpus callosum ; K.i., septum lucidum ; a./., anterior pillars of the fornix ; I'J, third ventricle ; th, thala- mus ; ^t., stria medullaris; n.c,, nucleus caudatus, and n.l,, nucleus lenticularis of the corpus striatum ; i.e., internal capsule ; g, its angfle or genu ; n.c'., tail nf the nucleus caudatus appearing in the descending: cornu of the lateral ventricle; cl., elaustrum ; 1. insula. CENTRAL NERVOUS SYSTEM 507 to it a radially striated aspect. Many of the nerve-cells of the nucleus lenticularis contain yellow pigment. The fibres of the ansa lenticularis (p. 484) appear to arise from some of them, but .the exact course and destination of these fibres is not known. The internal capsule (i.e.) is continued below into the crusta. It con- sists mainly of fibres connected with the cortex cerebri, and passing to (or from) the corpus striatum, thalamus, mid-brajn, pons, medulla oblongata, and spinal cord. A horizontal section across the internal capsule (fig. 656) shows it to be bounded laterally by the lenticular nucleus, mesially by the caudate nucleus, the stria medullaris, and the thalamus. Such a section shows a sharp bend in the plane of the capsule — the genu. Fibres J'iG. 657. — Section through the upper part of the ekain, to show the BELATiONS OE ITS MEMBRANES. (Axel Key and Gxistaf Retzius. ) c.c, corpus oallosum; /, gi'eat longitudinal Assure between the hemispheres conta.ining the projection of dura mater known as the falx cerebri; s.rt., aubarachnoid space between pia mater which closely covers the surface of the brain and dura mater which lines the skull. The arachnoid is in this part close to the dura mater into which and into the great longitudinal veiious sinus in the middle it sends villous projections (Pacchionian glands). from the motor region of the cortex (pyramid-tract) pass down in the part of the capsule extending from the genu ^s far as the posterior limit of the lenticular nucleus. IJn this area the fibres for the head and eyes are massed chiefly in the anterior part : those for the lower limb in the posterior part, while those for the face, arm, and trunk occupy intermediate positions from before backward, in the order named (Beevor and Horsley), but without being strictly confined to definite zones. The fibres from the cortex to the thalamus lie mainly in the anterior limb of the internal capsule, while afferent fibres from the thalamus to the cortex occur in the posterior part of the posterior limb ; but they extend forwards so as to mingle with the descending fibres of the pyramid-tract. So8 THE ESSENTIALS OF HISTOLOGY MEMBEANES OF THE BRAIN. The membranes of the brain (fig. 657) are similar in general structure and arrangement to those of the spinal cord with which they are continuous through the occipital foramen. The dura mater is, however, more closely adherent to the inner surface of the bony enclosure than is the case in the vertebral canal, wliile the arachnoid is in most places close to the dura mater, and separated from the pia mater by a wide subarachnoid space, which is bridged across by finely reticulating bands of areolar tissue. In the vicinity of the longitudinal sinus, small rounded elevations (arachnoidal villi. Pacchionian bodies) project into the dura mater, and even become embedded in the skull itself. The pia mater is closely adherent to the surface of the brain, and dips into all the sulci, but without forifling actual folds (Tuke). In it the blood-vessels ramify before passing into the substance of the brain, and they are accompanied, as they thus enter the cerebral substance, by prolonga- tions of the pia mater, which do not, however, closely invest them, but leave a clear space around each vessel, presumably for the passage of lymph (peri- vascular space). The capillary network i« much closer in the grey than in the white matter. The larger veins are enclosed^ by two layers of the dura mater, within which they run in certain parts in the -form of sinuses ; the chief of these are found at the lines of junction of the principal folds (falx, tentorium) with the main portion of the membrane. The pia mater sends highly vascular infoldings of the pia mater into the ventricles known as the choroid plexuses ; they are believed to play the part of glands for the secretion of the cerebro-spinal fluid. They are covered with ependymal epithelium. THE EYE 509 LESSONS XLVI., XL7II., AND XLVIII. THE EYE. 1. Sections of the eyelid vertical to its surfaces and across its long axis. Notice the long sacculated Meibomian glands lying in dense connective tissue close to the conjunctival surface, their ducts opening at the margin of the lid. External to these the small fibres of the orbicularis palpebrarum are cut across ; a few of the fibres of the mussle lie on the- conjunctival side of the dYict. A short distance from the Meibomian gland' may be observed a tolerably large sebaceous gland : outside this again are the eyelashes. In the skin , covering the outer surface of the eyelid a few small hairs may be seen. At the attached part of the eyelid are some bundles of involuntary muscular fibres cut longitudinally in the section, and in the upper eyelid the fibrous insertion of the elevator muscle may be observed attached to the dense connective tissue. Make a general sketch under a low power. 2. Sections through the posterior part of an eyeball (man or pig). These sections will show the relative thickness of the several coats and the layers of which each coat is formed. Sections which pass through the point of entrance of the optic nerve will also exhibit the manner in which the nerve pierces the several coats to reach the inner surface of the retina. The modifications which are found in the neighbourhood of the yellow spot may be made out in sections through that region ; but they must be taken from the human eye. 3. Sections of the anterior half of an eyeball. These sections should pass through the middle of the cornea. The lens may be left in situ, but this renders the preparation of the sections and the mounting of them difficult on account of the extreme hardness which is imparted to the lens-tissue by alcohol.^ In these sections make a general sketch under a low .power, showing the relations of the several parts one with another ; and study carefully, and sketch in detail, the layers of the cornea, the junction of the cornea and sclerotic, the ciliary muscle, the muscular tissue of the iris, the mode of suspension of the lens, and the pars ciliaris retinee. 4. Mount in glycerine thin tangential sections of a corijea stained with chloride of gold by Oohnheim's method ; if from the frog, the cornea can be torn with fine forceps into thin lamellae, which are mounted whole. Sketch three or four of the connective-tissue cells (corneal corpuscles). The arrangement and distribution of the nerve-fibres and their termination amongst the epithelium-cells as shown in chloride of gold preparations have been already studied (Lesson XIX.). 5. Mount in glycerine or dammar sections of a cornea which has been stained with nitrate of silver. Notice the branched cell-spaces corresponding with the connective-tissue cells of the last preparation. This preparation is best made by rubbing the surface of the cornea of a recently killed animal with lunar caustic, first scraping ofi' the epithelium with a scalpel. After ten minutes (by which time the nitrate of silver will have pene- trated the thiol5;ness' of the cornea) the eye is washed with distilled water, and exposed to the light. When brown, tangential sections may be made, for which purpose the stained cornea may be hardened in alcohol or soaked with gum and frozen. 6. Remove the sclerotic from the anterior part of an eye which has been preserved in MUUer's fluid, and tear off thin shreds from the surface of the choroid, including amongst them portions of the ciliary muscle. Stain the shreds with hsematoxylin and mount them in glycerine. Sketch the branched pigment-cells, the elastic network, the mode of attachment of the fitires of the ciliary muscle, etc. 1 The oelloidin method of embedding is best for preparations of this kind. 5IO THE ESSENTIALS OF HISTOLOGY 7. Injpcted preparation of elioroid and iris. Mount portions of the choroid coat and iris from an eye (preferably of an albino rabbit or rat), the blood-vessels of which have been filled with coloured injection. Make sketches showing the arrangement of the capillaries and veins. 8. Teased preparation of human retina. Break up with needles in a drop of glycerine a minute fragment of retina which h'aa been placed in 1 per cent. A osmic acid solution for some hours, and has subsequently been kept in dilute glycerine. Complete the separation of the retinal elements by tapping the cover-glass. Draw care- fully under a high power some of the isolated elements — e.g. the rods and cones with their attached fibres and nuclei, the inner granules, the gang- lion-cells, the fibres of Mtiller, hexa- gonal pigment-cells, etc. In some of the fragments the arrangement of the elements in- the retinal layers may be made out even better than in actual sections.' Measure the length and diameter of some of the cones, the length of the cone-fibres, and the diameter of some of the outer and inner nuclei. 9. Teased preparation of frog's retina. To be prepared in the same way as 8. Notice the very large rods, their outer segments breaking up into disks, and the relatively small cones. Also the pigment extending between the rods, the distance vary- ing according as the eye has been kept in the dark or in the light before treatment with osmic acid. A fresh frog-retina may also be teased in vitreous humour. 10. Sections of retina of ox or dog, which have been prepared by Golgi's method. A curled-up piece of fresh retina is placed in osmium- bichromate mixture and is subse- quently treated with nitrate of silver solution.^ 11. Teased preparation of lens. Separate in water the fibres of a crystalline lens which has been mace- rated for some days in bichromate of potassium. Sketch some of the fibres, together and separate. I'lG. 6.58. — Veetical section TimonGH the UPPER EYELID. (Waldeyer.) a, skin ; 6, orbicularis ; 6', ciliary bundle ; c, involuntary muscle of eyelid ; d, conjunctiva ; e, tarsus wtii Meibomian gland ; /, duct of l^he gland ; 9, sebaceous ^land near eyelashes; //, eyelashes; i, small hairs in outer skin ; j, sweat g:lands ; fr, posterior tarsal glands. The eyelids (fig. 658) are covered externally by the skin, and internally or posteriorly by a mucous membrane, the conjunctiva, which is reflected from ' For the distribution of the nerve-fibres and cellprocesseB within the retina Golgi's silver ohromate method is employed (see § 10). - See Appendix. Cajal's reduced silver method may also be used. THE EYE Sii over the globe of the eye. They are composed in the main of connective tissue, which is dense and fibrous under the nonjunotiva, where it forms what is known as the taraus. Embedded in the tarsus is a row of long sebaceous glands (the Meibomian glands,/), the ducts of which open at the edge of the eyelid. The rest of the thickness of the eyelid is composed of a somewhat loose connective tissue, which contains the bundles of the orbicularis muscle (6). In the upper eyelid the levator palpebrce is inserted into the tarsus by a fibrous expansion ; some bundles of involuntary muscle are also present near the attachment of the eyelid. The skin has the usual structure ; it* includes small sweat glands and the follicles of small hairs, and, in addition, at the edge of the eyelid, the large hair-follicles from which the eyelashes grow. The epithelium of the conjunctiva palpebree is columnar, passing at the edge of the lid into the stratified epithelium of the skin ; it also becomes strati- fied in the part which is reflected over the globe of the eye. The nerves of the conjunctiva terminate for the most part in end-bulbs, which in man are spheroidal, and formed chiefly of a small mass of polyhedral cells ; but in the calf and most animals they are elliptical (see Lesson XIX.). The lacrimal glands may be mentioned in connexion with the eyelid. They are compound racemose glands yielding a watery secretion. Their alveoli are lined by columnar or polyhedral cells (fig. 659), which are normally filled with granules, but, after profuse secre- tion, "these disappear, and the cells become shorter and smaller. The ducts, of which there are several, open at the upper fold of the conjunctiva near its outer extremity. THE SCLEROTIC AND CORNEA. The globe of the eye (fig. 660) is enclosed by three coats, the cornea- sclera, choroid-iris, and retina. It is filled by the vitreous and aqueous humours and the crystalline lens which lies between them. The sclerotic coat (sclera) is composed, of dense fibrous tissue, the bundles of which are intimately interlaced. It is thickest at the back of the eyeball. It is covered externally with a lymphatic endothelium, while internally it ia Fig. 659. — Alveoli op lacrimal oland op man. Photographed from a preparation by Prof. Martin HeidenWn. Magnified 200 diameters. Some of the cells show secretion granules. In one or two situations th(i intercellular canaliculi which open into the lumen of the alveolus can be made out. 512 THE ESSENTIALS OF HISTOLOGY lined by a layer of connective tissue containing pigment-cells, which give it a brown appearance (lamina Jusca). At the entrance of the optic nerve the sclerotic is prolonged into the sheath of that nerve, the bundles of which, piercing the coat, give a sieve-like aspect to the part (lamina cribrosa). The cornea (figs. 661, 662) consists of the following layers (enumerated from before back) : — CANAL OF 6CHLEMV SCLEROTIC CENTRAL ARTERY OF RETIN OPTIC NERVe Fig. 660.— Diagram of a section theough the (right) human evi; passi>-g HORIZONTALLY NEARLY THROUGH THE MIDDLE. Magnified about 4 diameters. u, i, equator ; sc. y, optic a\is. 1. A stratified epithelium continuous with the epithelium of the conjunctiva. ii. A thin lamina of homogeneous connective tissue (membrane of Bow- man), upon which the deepest cells of the epithelium rest. 3, A thick layer of fibrous connective tissue which forms the proper substance of the cornea. This is continuous laterally with the tissue of the THE EYE S13 sclerotic. It is composed of bundles of white fibres arranged in regular laminae, the direction of the fibres crossing one another at right angles in the alternate laminse. Between the laminas lie flsittened connective-tissue cor- axaiinj y-^s> Fia. 661.— Vertical section or human coknea from near the margin. (Waldeyer. ) Magnified. I suithelium • « anterior homogeneous lamina; 3, substantia propria cornes ; i, posterior homo. ■ ^peneous felasti ")lamina : 5, endothelium of the anterior chamber ; a oblique fibres in the antemor f^verSf the Sst^ntia propria; h, lamella with their-fibves cut across, producing a dotted imearance° coorneal corpuscles appearing fusiform in section ; rf, Jamelta with their fibres cut rSSnaily ■ Ttrtn^tion to the sclerotic, with more distinct fibrillation and surmounted by fthicto Epithelium ; /, small blood-vessels cut across near the margm of the cornea. puscles (fig. 663). These are branched" and united by their processes into a continuous network ; there is, of course, a corresponding network of cell- spaces (fig. 664). In vertical sections the cells appear narrow and spindle- 5'4 THE ESSENTIALS OF HISTOLOGY shaped (fig. 661). In the superficial lamihoa near the margin there are few bundles of fibres wliich run obliquely towards the surface (fig. 661, a). Fig. 662.— Section of human cornea, showing the stratified epithelium, the membrane of bowman, and the supf.rficiai. layers of the propria. Photograph. Highly magnified. 4. A homogeneous elastic layer (membrane of Deficemet). This completely covers the back of the cornea, but near the angle which the cornea forms Fifj. 003. — Cells of rabbit's cornea stained with gold chloride. Magnified 300 diapieters. with the iris it breaks up into separate fibres (ligainentnm pectinatum) which are partly continued into the iris as the pillars oj the iris. 5. A layer of pavement-epithelium {endatheliuni of Descemet's membrane) covering the posterior surface of the elastic lamina, and lining the front THE EYE 51S of the anterior chamber of the eye (fig. 661^ .'7). At the sides it is continued over the ligamentum pectinatum into a similar endothelium coverin" the anterior surface of tlie iris. The cells of the (jndotlielium of r ^^j^ .m^. a- i-, from i>ia THE EYE 525 ganglionic or optic nerve-cell layer (fig. 681) and are passing centripetally to enter the brain, but some are centrifugal and are derived from cells in the brain : these traverse the ganglionic and molecular layers to form a Fig. 681. — Section or dog's bbtina, Gol(1i method. (Cajal.) It, cone-fibre ; 6, rod-fibre and nucleus ; c, d, bipolar cells (inner g;ranules^ with vertical ramifica- tions of their outer proceases or dendrons : in the centre of the ramification lie the enlarged ends of rod-fibres ; e, other bipolars with flattened raraificationa abuttinj^ against ramified ends of cone-fibres ; /, large bipolar with fiattened ramifications ; .(7, inner granule-cell sending an axon towards the rod- and cone-fibres ; \ amacrine cell with diffuse arborisation of its processes in inner molecular layer ; i, j, m, centrifugally conducting nerve-fibrils passing respectively to outer molecular, inner nuclear, and inner molecular layers ; n, ganglionic cells, with axons passing into nerve-fibre layer ; A, outer molecular layer ; B, inner molecular layer. Fig. 682. -Section theouoh the inner layers op the retina of a bird, PREPARED BY GOLGl'S METHOD. (Gajal.) A, nerve-fibres of optic nerve layer ; B, some of these fibres passing through the inner molecular layer to end in an arborisation at the junction of the inner molecular and inner nuclear layers. The layers in this and in the two succeeding cuts are numbered in correspondence with the layers in 'fig. 678. terminal arborisation in the inner nuclear layer (fig. 681, i, j, m, and fig. 682). The layer of nerve-fibres becomes gr.adually thinner towards the anterior part of the retina. 2. The layer of optic nerve-cells, or ganglionio layer, is composed of nerve- cells somewhat like the cells of Purkinje of the. cerebellum. They vary in 526 THE ESSENTIALS OF HISTOLOGY size, although those of large size are prevalent in most parts of the retina. In the yellow spot, on the other hand, smaller nerve-cells are met with; they may here lie several deep. The cells have a* fine axis-cylinder process prolonged into a fibre of the layer of optic nerve-fibres and a thick branch- ^"Jcu ■■-■11 ''.A CXWi r V T /(TiT FiQ. 683.— Section across the MOLBCtJLAK ANiy ganglionic layers of A bird's retina, prepared ey Golgi's method. (Cajal.) Three or four ganglionic cells, A, B, C, and the terminal arborisations ot their dendrons, J a, h, c, in the molecular layer, are shown. Fio. 681. — Section of a bird's retina, prepared by Golgi's method. (Cajal.) A, large (amacrine) cell of inner nuclear layer ; B, C, smaller amacrine cells ; D, small bipolar nerve- ctUs with the one process ramifying in the inner molecular layer, and the other one ramifyinjr in the outer molecular layer and extending: (E) as far as the rods and cones .ts a fibre ot Landolt ; P, G, rod- and cone, nuclei respectively ; H, I, cells with dendrons ramifying in outer molecular layer ; J, fibre of ifiillf r. ing process, the ramifications of which terminate in the inner synapse layer in flattened arborisations at different levels (fig. 683, a, b, c). 3. The inner synapse layer (inner molecular layer) is comparatively thick. It has an appearance very like parts of the grey* matter of the nerve-centres. A few small cells are scattered through it, but it is mainly occupied by the processes of the optic nerve-cells and of the, inner granules which form THE EYE 527 synapses within it ; it is also traversed by centrifugal fibres from the optic nerve layer, as well as by the fibres of Muller. 4. The layer of inner granules (also termed inner nuclear layer) is mainly composed of bipolar nerve-cells containing large nuclei. One process (the axon) of each of these cells (fig. 681) extends inwards into the inner mole- cular layer where it spreads out into a terminal arborisation. These arborisations occur at diiferent levels in the layer, forming synapses with the optic nerve-cells. Another process (dendron) is directed outwards, and arborises in the outer molecular layer, where it forms synapses with the terminations of the rod- and cone-fibres. Tt has been shown by Ram6n y Cajal that there are two kinds of bipolars, one kind (rod-bipolars, fig. 681, cd) being connected externally with the rods of the retina, and passing inwards to ramify over the bodies of the nerve-cells ; whilst the others (cone- hipolars, e) are connected with the cone- fibres, and ramify in the middle of the inner molecular layer. The outwardly directed processes of the cone-bipolars are, in some animals, but not in mammals, con- tinued as far as the external limiting mem- brane, where each ends in a free extremity {^fihre of Landolt, fig. 684, e). Besides these bipolar nerve-cells, there are other larger inner granules (spongioblasts of some authors) which are different in character, having ramified processes which extend into the inner molecular layer (figs. 681, h; 684, A, B, o), in which also their bodies are often partly embedded. The cells in ques- tion have been regarded as of the nature of neuroglia-eells, but according to Cajal they are probably nerve-cells. He termed them amaarine-cells, since he believed them to be destitute of a long process ; but some of the amacrine-cells have since been noticed to give off, besides the branching processes or dendrons, which ramify in the molecular layer, an axis cylinder process extending into the nerve-fibre layer. There are also certain cells in the outer part of the granule layer which send, their processes entirely into the outer molecular layer (fig. 684, h). .These are the horiaontal cells of Cajal (spongioblasts of outer molecular layer of some authors). The fibres of Muller have nucleated enlargements (fig. 684, j) amongst the bipolars of this layer. 5, The outer molecular layer is thin, and is composed mainly of the arborisations of the inner granules and of the rod- and cone-fibres, as Fig. 685. — Diagrammatic repris- sWlATION OF THE BOD- AND CONE-ELEMENTS OE THE RETINA. (After Sohwalbe.) The designation of tlie numbers is the same as in fig. 678. 528 THE ESSENTIALS OF HISTOLOGY well as of the horizontal cells (figs. 681, 684), which all form synapses in this layer. 6 and 7. The outer nuclear layer and the layer of rods and cones are composed of elements which are continuous through the two layers, and they should properly, therefore, be described as one. It has been termed the sensory epithelium of the retina (fig. 685, 6 and 7). The elements of which this nerve-epithelium consists are elongated cells of two kinds. The most numerous, which may be termed the rod-elements, consist of peculiar rod-like structures {retinal rods) set closely side by side, each of which is prolonged internally into a fine varicose fibre {rod fibre) which swells out at one part of its course into a nucleated enlargement, and ultimately ends (in mammals) in a minute knob within the outer molecular layer, where it is Fig. 686. — Diagram or the connexions of the retinal elements with one ANOTHER AND WITH THE CENTRAL NERVOUS SYSTEM, (Cajal.) a to g, laj'ers of retina ; a, rods and cones ; 6, outer nuclear layer ; c, outer molecular layer ; d, inner nuclear layer ; e, inner molecular layer ; /, nerve-cells giving origin to fibres of optic nerve ; g, h, i, a centrifugally conducting fibre, arising from a cell in the brain, and with its terminal arborescence in the retina ; j, grey matter of corpus nuadri. geminum. embedded in the ramifications of the dendrons of the rod-bipolars. The rod consists of two segments, an outer cylindrical and transversely striated segment which during life has a purplish-red colour if the eye has not been recently exposed to light, and an inner, slightly bulged segment which in part of its length is longitudinally striated. The nucleus of the rod-element in some animals, but according to Flemming not in man, has a transversely shaded aspect in the fresh condition (fig. 685). The cone-elements are formed of a conical tapering external part, the retinal cone, which is directly pro- longed into a nucleated enlargement, from the further side of which the cone- fibre, considerably thicker (in mammals) than the rod-fibre, passes inwards, to terminate by an expanded arborisation in the outer molecular layer ; here it comes into relation with a similar arborisation of the dendrons of a cone- bipolar. The cone, like the rod, is formed of two segments, the outer of which, much the smaller, is transversely striated'; the inner, bulged segment THE EYE 529 being longitudinally marked. The inner ends of the rod- and cone-fibres, as already stated, form synapses with the peripheral arborisations of the bipolars, Fig. fiS7. — Pigmknted epithelium of t?ie human retina. {M. Schultze. ) Highl}^ magnified. li, cells seen from the oviter surface with clear" lines of intercellular substance between ; '*, two cells seen in profile with fine offsets extending" inwards; c, a cell still in cunne,\ion \\'ii.h tVie outer ends of the rods. A B Ji.J,lu WJ Fig. 688. — A. Part of a section of the retina from the eye of a froi: WHICH had been kept IN THE DARK FOR SOME HOURS BEFORE DEATH. (v. Genderen-Stort. ) The i)i;,nnent is collected towards the outer ends of the rods,* which were red, except the outer detached rod, which was green. The cones, wliicli in tiie fro^^ are much smaller than the rods, are mostl.v elongated. B. A SIMILAR SECTION FROM A FROG WHICH HAD BEEN EXPOSED TO LIIIHT. The pi^auent is extended hetwcen the rods, and is acoiuiiulated near their bases. The rods were colourless. All the cones are contracted. and through the latter elements and their synapses in the inner molecular layer a connexion is brought about with the n^rve-cejls and nerve-fibres of the innermost layers. The connexion of the retimi elements with one another and through the optic fibres with the central nervous system (anteiioi' corpoiu quadrigemina and lateral geniculate bodies) is shown diagrammatically in fig. 686. S30 THE ESSENTIALS OF HISTOLOGY In birds, reptiles, and amphibia a small oil-globule, often brightly coloured red, yellow, or green, is found in the inner segment of each cone. Many other varia- tions of structure are met with in different animals. The cones are moat numerous at the back of the retina ; they are fewer in number, and the rods are proportionally more numerous towards the anterior part. — — m.l.e tn.l.i. Fig. 689.— a fibre op MOlleb from the dog's retina : golgi method. (Cajal.) 1, nerve-fibre layer ; 2, nerve-cell layer ; 3, inner molecular layer ; 4, inner granule layer ; 5, outer molecular layer; 6, outer g-ranule layer ; b, nucleus of the fibre ; a, a process extending- into inner molecular layer ; 'Wul.i., membrana limitanB in- terna; m.l.e.t membrana limi- tans externa. Fig. 690. — Internal limitix; mkbiukajni; or RETINA TREATED "WITH SILVER JSITRATE, SHOW- ING THE OUTLINES OF THE BASES UF THK FIBRKS OF MOller. (G, Retzius.) 8. The pigmenta/ry layer forms the most external part of the retina. It consists of hexagonal epithelium-cells (fig. 687), which are smooth externally where they rest against the choroid, but are prolonged internally into thin lamellae which extend between the rods. The pigment-granules, many of which are in the form of minute crystals, lie in the inner part of the cell, but after prolonged exposure to light they arc found extending along the THE EYE 531 cell processes between the rods (Kiihne), their function being probably connected with the restoration of the purple colouring matter, which Fig. 691. — Section throuch the central tart of the fovea centralis. '200 diameters. (Photographed from a preparation by C. H. Golding-Bird.) uuwwWWWi Fx(.i. (j'J2. ^LlIAGilAM UE THE AlirLiNGEMKNI OE* THE KETIKAL ELEMENTS AT THE CENTRAL EDVEA. M, bases ol Miillerian fibres ; f]^ ganglion-cells _; &, nuclei of innel- granules (bipolars) ; 71, cone-fibre nuclei ; c, cones. has been bleached by the light. This extension of the pigment is accom- panied by a shortening of the cones (Bngelmann) (fig. 688). Fihres of Miiller.— The fibres of Mtiller (fig. 684, J, and fig. 689) are long cells which pass through several of the retinal layers. Commencing 532 THE ESSENTIALS OF HISTOLOGY at the inner surface of the retina by expanded bases which unite with one another to form the so-called internal limiting membrane (fig. 690), they pass through all the layers in succession, until they reach the outer "granule layer. Here they branch and expand, into a sort of honeycomb tissue which serves to support the fibres and nuclei of the rod- and cone- elements. At the bases of the rods and cones this sustentacular tissue ceases, being here bounded by a distinct margin which has been called the external limiting membrane (fig. 689, m.l.e.), but delicate sheaths pass from it around the bases of the rods and cones. Each Mtillerian fibre, as it passes through the inner granule layer, has a nucleated enlargement (6), indicating the cell-nature of the fibre. The fibres of Miiller represent Fig. t)93. — Section of human retina at oba SEfeKATA, showing the abrupt TERMINATION OF THK USUAL RETINAL LAYERS ANII THE CONTINUATION OF THE RETINAL SHEET AS TWO LAYERS OF CELLS, WHICH FORM THE I'ARS (JILIARIS RETINA. (Pier^'ol.) (t, n, pigment layer ; h, fod- and cone-layer ; c, outer nuclear layer ; d, outer molecular layer ; c, inner nuclear layer ; /, inner molecular layer ; r;, ganglion-cell and nerve.fibre layers ; b, section at transition line ; t, columnar cells of pars ciliaris ; t, a cyst (sucli cysts occur occasion- ally here). ependyma-cells or long neuroglia-cells such as are found in some parts of the nerve-centres. There are two parts of the retina which call for special description. The macula lutea (yellow spot), with its central fovea, is the part of the retina which is immediately concerned with direct vision. It is characterised, firstly, by its greater thickness (except at the middle of the fovea) ; secondly, by the large number of its ganglion-cells, which are relatively small ; and thirdly, by the number of cones it contains as com- pared with the rods. In the central fovea itself (figs. 691, 692) there are no rods, and the cones are very long and slender, measuring not more than 2/i in diameter ; all the other layers become gradually thinned down almost to complete disappearance, so that the middle of the central fovea is the thinnest part of the retina. Since there are few rods, the outer granule layer loses in great measure its appeamnce of being composed of closely packed nuclei, and the cone-fibres are very distinct, forming the so-called fibrous layer. Except at the very centre the direction of these fibres is oblique in this part of the retina. THE EYE 533 Fk;. (195. — Fibres of the crystalline LENS. 350 diameters. K, loiigitudinal'view of the fibres of the lens of the ox, showing- the serrated edges. E, trans- verse section of the fibres of the lens of the human eye. C, long;itudinal view of a few of the fibres fror^i the etinatorial reg^ion of the human lens. Most of the fibres in C are seen edpewise, and,^ towards 1, present the swell- inyfs and nuclei of the "nuclear zone " ; at 2, the flattened Kides.of two fibres are seen. (A and E from Knlliker; C from Henle,) r Fig. 694. — Section through the MARGIN OF THE RABBIt'S LENS, SHOWING THE TRANSITION OP THE EPITHELIUM OF THE CAPSULE INTO 534 THE ESSENTIALS OF HISTOLOGY The pigmentary layer is thickened over the fovea, and there is also a thickening in the choroid coat here, due to a large accumulation of capillary vessels. The pars ciliaris retinae, which commences at the ora serrata, where the retina proper abruptly ends (fig. 693), is composed of two epithelial layers without nervous structures. Of the two layers, the external is a thick stratum of pigmented epithelium formed of rounded cells and con- tinuous with the pigmentary layer of the retina on the one hand, and with the uvea of the iris on the other ; the inner is a layer of columnar cells (fig. 671 ; fig. 693, a, k). Vessels of the retina. — The retina contains relatively few blood-vessels. The central artery enters and the vein leaves it in t)ie middle of the expansion of the optic nerve. The larger vessels ramify in the nerve-fibre layer. There are capillary networks in this layer and in the inner nuclear layer. Perivascular lymph-spaces surround the veins and capillaries. The sensory epithelium receives no blood-vessels, it is nourished from the vessels of the choroid. THE LENS AND VITREOUS HUMOUB. The lens. — The lens is a laminated fibrous body enclosed by a trans- parent elastic capsule to which, around the Circumference, the fibres of the suspensory ligament are attached (fig. 673). Immediately within the capsule, in front and at the sides, there is a layer of cubical epithelium termed the epithelium of the capsule, but at the margin of the lens the cells become longer and pass by a gradual transition into the lens-fibres (fig, 694). The fibres which compose the lens a^e long and riband-shaped, with finely serrated edges (fig. 695, A) ; their transverse sections are prismatic (B). Many of the superficial fibres are nucleated (C), the lens- fibres having originally been developed by the elongation of epithelium- cells. The vitreous humour. — This is composed of soft gelatinous tissue, apparently structureless when examined in thg fresh condition, but con- taining fibres and a few scattered cells, the pfocesses of which are often long and varicose, and the cell-bodies distended by large vacuoles. The hyaloid membrane, which invests the vitreous humour, is homogeneous and structureless except in the region of the ciliary processes, where it is fibrous in structure, forming the zonule of Zinn and spreading out into the suspensory ligament of the lens (fig. 673). This part of the hyaloid membrane is connected with an annular fibrous portion of the \itreous humour which serves to give additional firmness to the attachment of the fibres of the suspensory ligament of the lens (Anderson Stuart). THE NOSE AND EAR 535 LESSONS XLIX. .AND L. THE NOSE AND EAR. 1. Vertical sections of the nasal mucous membrane' The sections may be carried either across the upper turbinate bone, after decaloification, or across the upper part of the nasal septum. Make a sketch under the low power. Notice the difference in the character of the epithelium in the olfactory and respiratory parts of the membrane. 1 2. Teased preparation of the epithelium of the olfactory mucous membrane. A piece of the membrane is placed quite fresh in osmic acid (1 per cent.) for a few hours, and is then macerated for two days or more in water. The epithelium is broken up in dilute glycerine ; the cells easily separate from one another on tapping the cover-glass. Notice the two kinds of cells. Sketch some of the cells under a high power.' 3. Sections of the external ear (these have been already studied for the cartilage. Lesson XII.). 4. Sections across the cartilaginous part of the Eustachian tube. These may be included in the same preparation that furnishes sections of cochlea. Sketch under the low power. 5. Preparation of the membrana tympani. A piece of the membrane, stained with magenta and gentian violet (see Lessoji IX., § 2), is mounted flat in dammar. Determine the composition of the membrane — i.e. the several layers composing it — by focussing carefully with the high power. 6. Sections across one of the membranous semicircular canals of a fish (skate). 7. Longitudinal sections through the ampulla of a semicircular canal (skate). 6 and 7 may be hardened in chromic and osmic acid (see below under 10) and embedded in oelloidin. 8. Golgi preparations of the macula of the utricle from the skate. 9. Teased osmic preparations of the auditory epithelium of an ampulla or of the macula of the utricle, from the skate. 10. Vertical sections through the middle of the cochlea of a mammal (guinea-pig). The part of the petrosal containing the cochlea is put quite fresh into 02 per cent, chromic acid containing one-fifth its volume of 1 per cent, osmic acid, or into undiluted Flemming's solution, or into 10 per cent, neutral forniol. The decalcification can be effected by the use of the phloroglucin-nitric acid fluid, or by sulphurous acid. (See Appendix.) When decalcified, the preparation is well washed, and then transferred to alcohols of gradually increasing strength. The semicircular canals and their ampullae may also be seen cut across in these sections of the petrosal. In preparing sections of the membranous labyrinth it is advisable, in order that the epithelium should be kept in position, to embed in celloidin. If the paraffin method of embedding is used, the sections are fixed to the slide by the albumen process. The organ should preferably be stained in bulk. ' The connexion of the olfactory cells with the olfactory nerve-fibres is displayed in embryos, the method of Golgi being employed. ^ 536 THE ESSENTIALS OF HISTOLOGY 11. Teased osraic preparations of the epithelium of the organ of Corti from tho guinea-pig. Make sketches from all the.se preparations under the high powei-.' THE OLFACTORY MUCOUS MEMBRANE. The olfactory region of the nasal fossfe includes in man the upper and / H Fig. 696. — Cells and terminal nebve-fibres op the oleactobt eegiox. Highly magnified. J, from the frog : ;? and 3, from man. In 1 and 3 : — a, sustentacular cell, extending^ deeply into a ramified process ; /^, olfactory cells ; c, their peripheral processes ; e, the extremities of these, seen in 1 to be prolonged into fine hairs ; d, their central filaments. In 3 : — A, hairlets ; c, free border of cell ; p, peripheral process ; 6, body ot cell ; », nerve-flbre. 1 and % from M. Schultze ; .5 from V. Brunn. middle turbinate processes and the upper third of the septum. It is covered by a soft vascular mucous membrane of a yellow colour. The epithelium of the olfactory mucous membrane (fig. 697, a) is very thick and is composed of long cells, set closely side by side and bounded superficially by a cutioular lamina, through which the free ends of the cells project. The cells are of two kinds : 1. Long, narrow, spindle-shaped, or bipolar nerve-cells consisting of a larger part or body (fig. 696, h) containing the nucleus, and of two processes or poles, one (c) straight and cylindrical and ^ For details of the somewhat complicated methods §f obtaining the various parts of the labyrinth for mioroaoopical examination, the student is referred to the author's Cov/rse of Practical Histology. THE OLFACTORY MUCOUS MEMBRANE 537 extending to the free surface, the other {d) very delicate and varicose, looking not unlike a nerve-fibril and extending down towards the corium. The position of the nuclear enlargement varies, and with it the relative length of the two processes. The distal or free process terminates in a small clear projection, which passes beyond the cuticular membrane ; in amphibia, reptiles, and birds, and perhaps also in mammal^, it bears fine stiiF hair-like filaments (fig. 696, i, S). The proximal or va,ricose process becomes lost amongst the plexus of olfactory nerve-fibres, at the base of the epithelium. It is continuous with one of these fibres, and ultimately passes through the cribriform plate of the ethmoid to end in an arborisation within an olfactory glomerulus (see diagram, fig. 653, p. 504). These cells have been termed the Fig. fi97. — Section of obpactory mucous membrane. (Cadiat. ) (i, epithelium ; &, glands of Bowman ; c, nerve-bundles; olfactory cells. 2. Long columnar epithelium-cells (fig. 696, a), with compara- tively broad cylindrical nucleated cell-bodies pladed next to the free surface, and forked, branching, tail-like processes extending down to the corium. These are regarded not as sensory epithelium-cells, but merely as serving to support the proper olfactory cells. They are termed sustentacular cells. 3. Tapering cells are present, at least in some animals, in the deeper part of the epithelium. They rest by their bases upon the corium, and project between the other cells, which they assist to support. The corium of the olfactory mucous membrane is also thick (fig. 697). It contains, besides numerous blood-vessels, bundles of the olfactory nerve- fibres (which are non-myelinated), and a large number of granular-looking serous glands known as Boieman's glands (b), which open upon the surface by ducts passing between the epithelium-cells. 538 THE ESSENTIALS OF HISTOLOGY THE EXTERNAL AND MIDDLE EAR. The external ear proper (pinna) is composed of elastic fibro-cartilage, invested by a thin closely adherent skin. The skin is covered by small hairs, and connected with these are the usual sebaceous follicles. In the lobule there is a considerable amount of adipose tissue ; voluntary muscular fibres are in places attached to the cartilage of the pinna, and are seen in sections. The external auditory meatus is a canal formed partly of cartilage- Fifi. 698. — Section of ceruminous gland op the external ear. Photograph. d, duct of gland, having: a spiral course and therefore cut several times ; it is partly lilled with cerumen ; gl, secreting tuhules of gland ; g, extremity of aotuhule of a sebaceous gland which extended as far as the base of the ceruminous gland. continuous with that of the pinna, partly of bone. It is lined by a pro- longation of the skin and is closed by the membrana tympani, over which the skin is prolonged as a very thin layer. Near the orifice the skin has hairs and sebaceous glands ; the meatus is also provided throughout the cartilaginous part with convoluted tubular glands of a brownish-yellow colour, which yield a waxy secretion {ceruminous glands). They represent modified sweat glands. A section of one is represented in fig. 698. The tympanum is lined by a mucous membrane which is continuous through the Eustachian tube with the mucous membrane of the pharynx ; it is also prolonged into the mastoid cells. The epithelium is columnar and ciliated in some parts, but in others — e.g. roof, promontory, ossicles, and membrana tympani — there is a pavement-epithelium. THE EAR 539 The membrana tympani is a thin membrane, formed of fibrous bundles which radiate from a central depression (umbo). Within the radial fibres are a few annular bundles. Covering the fibrous membrane externally is a thin layer continuous with the skin of the meatus ; covering it internally is another thin layer, derived from the mucous membrane of the tympanic cavity. A few blood-vessels and lymphatics are distributed to the membrane, chiefly in the cutaneous and mucous layers. The Eustachian tube is the canal leading from the tympanum to the r-TO 1^ ^ \ k'l^^M ' wm y'h ' I fi Fig. 699. — Section across teie cAiiTiLAr,iNous part of the Eustachian TUBE. (Riidinger. ) 1,-2, bent cartilaginous plate ; 3, muse, dilatator tubse ; to the left of 4, part of the attachment of the levator palati muscle ; 5, fibrous tissue uniting the tube to the base of the skull ; G and 7, mucous glands ; S, 10, fat ; 9 to 11, lumen of the tube ; 12, connective tissue on the lateral aspect of the tube. pharynx. It is formed of i bone near the tympanum, but below, near the pharynx, it is bounded partly by a bent piece of cartilage (fig. 699, 1, 2), partly by fibrous tissue. The latter contains numerous mucous glands (6, 7), which open into the tube, and on the other side §, band of muscular tissue (3) which joins the tensor palati. The epithelium is ciliated. THE INTERNAL EAR. The labyrinth, which is the essential part of the auditory organ, consists of a complex membranous tube lined by epithelium and filled with endolymph, contained within a bony tube — the osseous labyrinth— of corresponding complexity of shape (figs. 700, 701). The membranous labyrinth does not wholly fill the bony cavity ; the rest of the space is occupied by perilymph. 54° THE ESSENTIALS OF HISTOLOGY The membranous labyrinth (fig. 700) is composed of the utricle {u), the three nemicireular canals (each with an enlargement or ampulla at one end), the saccule (s), and the canal of the cochlea ix.c). The branches of the auditory nerve pass to certain parts only of the membranous labyrinth, viz., the maculae of the utricle and saccule, the cristae of the ampullsB, and along the whole length of the canal of the cochlea (the shaded parts in fig. 700). At these places the lining epithelium is specially modified to form a sensory or nerve-epitheliums; elsewhere it is a simple pavement-epithelium. The membranous semicircular canals and the utricle and saccule are composed of fibrous tissue, which is adherent along one side to the endosteum (jSmS*. Fig. 700. Fig. 701. Fig. 700.^Plan or the bight membkanous labyhinth viewed from THE MEDIAL ASI'ECT. Magnified*'2^ times. It, utricle, with its macula; s.s,c., p.s.c, and e.s.c, the three semicircular canals with their ampulla? ; s, saccule ; aq.v., aquseductus vestibuli ; s.e., saccus endolymphaticus ; c.r., canalis reuniens : e.c, canal of the cochlea. Fig. 701. — View of the interior of the left osseous labyrinth. The bony wall of the labyrinth is removed superiorly and external|3 . 1, fovea heniielliptica ; 2, fovea hemisphajrica ; 3, common opening of the superior and posterior semicircular canals ; 4, openini: of the aqueduct of the vestibule ; 5, the superior ; 6, the posterior, and 7, the external semi- circular canals ; 8, spiral tube of the cochlea ; 9, scala tympani ; 10. st-iila vestibuli. of the bony canal ; from the opposite side bands of fibrous tissue pass across the perilymph (fig. 702). Within the fibrous membrane is a thick clear tunica propria, which, in the semicircular canals, may form papilliform elevations in the interior of the tube. The places of entrance of the nerve-fibres are marked in each ampulla by a transverse, inwardly projecting ridge (crista), in the saccule, and utricle by a broader thickening of the tunica propria (macula). The epithelium at these places is formed of columnar cells (fig. 703), which are surmounted by long, stifi) tapering hairs (fig. 703, h ; fig. 704). Around these liair-cells the axis-cylinders of the nerve-fibres ramify (fig. 705) ; they are therefore — like the gustatory cells of the taste-buds — sensory epithelium-cells. Between them are a number of thin and somewhat rigid nucleated cells (fibre-cells of Eetzius), which rest upon the basement-membrane, and are connected at THE EAR S4I their free extremity with a cuticular membrane, through which the above- mentioned hairs project. The hairs do not jut freely into the endolymph, but into a soft mucus- like substance, of a dome-like form in the ampullae {cupula terminalis, fig. ^6 Fig. 702. — Section of sbmtcirculak canal, xew-born child. (Sobotta.) Magnified 55 diameters. c.t,, connective-tissue strands, between membranous canal and endosteum of bony canal; m, membranous canal ; 6, waU of bony canal ; c, remains of fcetal cartilage ; eTid, endosteum ; v, blood-vessels. 703) ; in the saccule and utricle this substance has a quantity of calcareous particles (otoliths) embedded in it. The cocMea consists of a bony tube coiled spirally around an axis which is known as the columella (figs. 706, 707). The tube is divided along its length by a partition — formed partly by a projecting lamina of bone (spiral lamina), partly by a flat membrane (basilar membrane) — into two parts 542 THE ESSENTIALS OF HISTOLOGY {sGolce); the upper (supposing the cochlea resting base downwards) being termed the scala vesiibuli, the lower scala tympani ; the latter is closed near its larger end by the membrane of the fenestra rotunda through which, in the macerated bone, the cavity of the tympanum communicatee with the scala tympani. The scalae are lined by endosteum, and are filled with perilymph, continuous with that of the rest of the labyrinth at the com- Fl<:. 703. — L(i ilTlTjINAl, SKCTIIIN IIF CRISTA ACUSTICA AN AMLTLl.AOP' (diagrammatic). A FISU THKim.H Till. rt*yf7'., Cavity of the ampulla; «c.c, semicircular canal opening out of it; c, connective tissue attached to the wall of the membranous ampulla and traversincr the perilymph ; c, e, flattened epithelium of ampulla ; A, hairs projecting from the columnar cells of the epithelium into the cupula, cup.term ; u, blood-vessels ; n, nerve-fibres entering the base of the crista and passing into the columnar epithelium. mencement of the scala vestibuli ; they communicate with one another at the apex of the cochlea by an opening, the helicotrema. The scala vestibuli does not occupy the whole of that part of the bony tube of the cochlea which is above the partition just mentioned. Its outer and lower third is cut off by a delicate <;onnective-tissue membrane (ineni- hrane of Beissner, fig. 708, H), wMch springs from near the end of the spiral lamina, and passes upwards and outwards to the outer wall, thus separating a canal (d.c.) triangular in section, which is lined 6y epithelium, and represents the membranous labyrinth of the cochlea (diict or canal of the cochlea). The floor of the canal of the cochlea is formed (1) of the extremity THE EAR S43 of the spiral lamina, which is thickened above by a peculiar ' kind of con- nective tissue, forming an overhanging projec6ion known as the limbus r 1 -.'•rx^t'i-^^.. ^::*i*S*. Fig. 701.— Section of' ampulla of guinea-pig. Photographed from a preparation- by H. Pringle. li, epithelium becomin{r columnar over the crista, where the cells are furnished with haitiets ; c, corium of delicate connective tissue, with the nerve-fibres passing to the epithelium ; b, bone with canals containing bundles of nerve-fibres. Fig. 705. Nerve tjlkmiin'ation's in macula; Goloi method, (v. Lenhossik.) . (fig. 708, I) ; and (2) of the basilar membrane (h.m.), which stretches across from the end of the bony lamina to the outer wall, and is attached to this 544 THE ESSENTIALS OF HISTOLOGY by a projection of reticular connective tissue tprmed the spiral ligament {l.sp.). The basilar membrane is composed of stiff straight fibres, which extend from within out, and are embedded in a homogeneous substance. The membrane is covered below by a layer of connective tissue continuous with the endosteum of the soala tympani ; the modified epithelium which forms g^p Fig. 700.— Section throui.;h the cochlea of the f.\T. (Sobott-a.) Magnified 25 diameters. duot of cochlea ; mv, soala vestibuli ; sol, scala tympani ; w, bonv wall of cochlea ; C, org.-ui of Oorti on membrana basilaris ; in R, membrane of Reiasner ; h, nerve-fibres of cochlear nerve ■ (JSP, ganglion spirale ; str.v., stria vascularis. the organ of Corti rests upon its upper surface. It becomes gradually broader in the upper turns of the cochlea (rather more than twice as broad in the uppermost as compared with the lowermost turn), and its constituent fibres become therefore gradually longer. The organ of Corti consists of the following structures ;— 1. The rods «/ Corti, two series (inner and outer) of stiff, striated structures, of a peculiar shape, the inner somewhat like a human ulna tlie THE EAR- 545 cmxoX of scala membrane of the cochlea vestibuli Reissner scalct basilar tympani membrane Fig. 707. — Vertical section through the middle of the human cochlea. { Diagrammatic. ) Fig, 708. — Vertical section of the first turn of the human cochlea, (G. Retzius.) s.-y, scala vestibuli; s.t, scala tympani; d.c, canal or duct of the cochlea; sp.l, spiral lamina; n, n ewe -fibres ; l.sp, spiral lig-ament ; str.v, stria vascularis; s.s'p, spiral sulcus; R, section of Reissner's membrane ; Z, limbus laminae spiralis ; m.t, membrana teotoria ; tC, tunnel of Corti ; b.m, basilar membrane ; hA^ h.e^ interniil aud external hair-cells. 546 THE ESSENTIALS OF HISTOLOGY outer like a swan's head and neck (fig. 709), They rest by one extremity (the foot) on the basilar membrane a short distance apart, and are inclined towards one another, their larger ends (heads) being fixed together ; the series of rods thus encloses a sort of tunnel, the floor of which is formed by Fio. 709. — A PAIR or rods of Corti, from the rabbit's cochlea, in side VIEW. Highly magnified. fi, &, basilar membrane ; t.y., inner rod ; e.j'., outer rod. The nucleated protoplasmic masses at the feet, which represent the cells from which the rods have been formed, are also shown. a part of the basilar membrane (fig. 711). Close to their feet may usually be seen the remains of the cells from which they have been formed. The inner rods are narrower and rather more numerous than the outer. The head of each outer rod has a process which e?.tends outwards and is known as the phalangeal process. This forms part of — 2. A reticular lamina (fig. 711, l.r.), which is a cuticular structure extending like u, wire-net over the outer epithelium-cells of the organ of Limbus. Meinbranft tectoria. Outer hair -cells. Cells iif Diilci-s. Fio. 710. —Section through the oroak oi' (^obti of the human cochlea. {i ai.,.ii<„i n,;fi,„..(. APPENDIX . ' 553 deteriorating. Organs which contain much librous tissue, such as the skin and tendons, should not go into stronger alcohol than about 80 per cent. ; otherwise they become too hard to cut. Alcohol (80 to 90 per cent.) is generally used after other fixing reagents to complete the hardening, and as a preservative ; but previous to passing into xylol for embedding in paraffin all trace of water must be removed from the tissue by absolute alcohol. If mercuric chloride is an ingredient of any fixing fluid, iodine must be added t6 the alcohols subsequently used (eicept the final alcohol), to get rid of a mercurial precipitate which otherwise forms in the tissue. This object can also be effected by washing the sections with a solution of iodine in alcohol. A mixture of mercuric chloride (saturated solution) (2 parts) and alcohol (1 part) is sometimes used ; this requires about two days to harden a tissue. Mercuric chloride is one of the best fixatives for obtaining the full value of dyes, but is slow in penetration and it is difficult to wash out the excess of the salt. The pieces taken must always be very small, and must be washed at least twenty-four hours in running water and then kept in a large quantity of 80 per cent, alcohol containing iodine. Many tissues are instantly fixed by being plunged for a minute into boiling water and then placed in alcohol ; this is not, however, a good method for glands. For tissues that are to be hardened in chromic acid an immersion of from seven to ten days is generally necessary ; they riiay then, after washing for some hours or days in running water, be placed in alcohol for preservation and to complete the process of hardening. The alcohol should be changed once or twice. Organs placed in bichromate of potassium or Miiller's fluid are ready for section in a fortnight or three weeks ; they may, however, be left a somewhat longer time in those fluids without deterioration. With picric acid the hardening process is generally complete in two days ; the organs may then be transferred to alcohol, which must be frequently changed. The hardening of the brain and spinal cord in Miiller's fluid takes from three weeks to as many months. It is hastened by warmth, and by the addition of acetic acid to the fluid. Tissues containing calcareous matter, e.g. bone and tooth, may be rapidly decalcified in a solution made by dissolving, with the aid of heat, 1 gm. phloro- glucin in 10 c.c. nitric acid, and filling up to 100 c.o. with water, to which more nitric acid may be added if desired. Another rapid decalcifying fluidi is com- mercial sulphurous acid solution. If it is desired to preserve the soft parts within fresh bone, it should first be placed for a few hours in 10 per cent, formol. The following fluids decalcify more slowly, (1) 1 per cent, solution of nitric acid in water or alcohol, (2) saturated solution of picric acid containing a superabundance of crystals, (3) 1 per cent, solution of chromic acid. After decalcification the tissue must always be washed in running water for at least twenty-four hours. Embedding of hardened tissues, and preparation of sections. — Sections\are most advantageously made with some form of micro,tome. It is generally needful to support the hardened tissue whilst it is being cut ; with this object it is embedded in some substance which is applied to it in the fluid condition and becomes solid' on standing. The embedding substance can either simply enclose the tissue, or the tissue may be soaked in it ; the latter method is the one commonly employed. The embedding substance chiefly used is paraffin of about 50° 0. melting point. The precise temperature depends upon that of the atmosphere. In summer and in hot climates a paraffin of higher melting point may be required. Embedding in paraffin. — Before being soaTsed in melted paraffin, the piece of tissue may be stained in bulk (see p. 559) ; it is then dehydrated by a series of S54 THE' ESSENTIALS OF HISTOLOGY alcohols (50 per cent., 75 per cent., 95 per cent.); finishing up with absolute alcohol ; after which it is soaked in cedar-wood oil, xylol, or chloroform. If chloroform is employed the piece of tissue can be left overnight in a saturated solution of paraffin in chloroform. This is especially advantageous for delicate objects. The prepared piece is now transferred to molten paraffin, which should not be too hot but kept only ju.st molten : it is soaked iu this for from one to several hour.s, according to thickness. For this purpose an incubator is employed. When thoroughly impregnated with the paraffin the object is placed in a paper mould or in a metal capsule : this is first partly filled with the molten paraffin : the piece is placed on this ; more paraffin is then pouifed in, and the whole allowed to cool quickly. A square block of the paraffin containing the tissue is then cut (jut and fixed in the desired position on the microtome ; thin sections are made and fixed to a slide (see below) ; the paraffin is dissolved out by xylol, and the sections mounted in dammar. If it be desired to cut a riband of successive sections, and the paraffin used prove too hard for them to stick to one another at the edges, a paraffin of lower melting point (40° C.) is smeared over the opposite sides of the block ; the sections then adhere together as they are cut. Preparation of frozen sections. — The bichromate solutions and forniol are the best fluids to use for preserving tissues which are ta be frozeji in place of being embedded. If alcohol is employed for fixation it sholild be thoroughly washed out with water. The tissue is soaked in gum-water before being placed upon the freezing microtome. A thin syrup of either gum ai;abic or dextrin may be used. The preliminary soaking in gum is not necessary after formol. Emhedding in oelloidin. — The piece to be embedded, which should not be thicker than 2 or 3 mm., is dehydrated by absolute alcohol, transfeiied for a few hours to a mixture of absolute alcohol (1 part) and ether (3 parts) and then placed anothei' twenty -four hours or more in a solution of celloidin in alcohol and ether similar in strength to ordinary collodion ; finally it goes into oelloidin solution of double strength. After twenty-four hours in this it is removed and placed iipon a wood or metal holder. When the celloidin is set by evaporation of its ether the holder is phmged in alcohol (80 to 85 per cent.) ; after a few hours, sections may be cut with a knife wetted with spirit of the same strength. Thu sections aie placed in 95 per cent, alcohol ; then passed through cedar-wood oil or bergamot oil into dammar. They must not go into clove oil, nor into absolute alcohol. The advantage of the method is that the celloidin, which is quite trans- parent, need not be got lid of in mounting the sections, and serves to keep the parts of a section together ; it is thus useful foi' fiiable tissues or for largo sections. The tissue may either be stained in bulk before embedding, or the sectiouH may be stained. They can be attached to the slide, by transferring them to, it from 95 per cent, alcohol, and allowing ether vapour to pour out of a half full bottle on to their surface. They may then be pressed down by Centring with filtei' or tissue paper, the thumb being passed firmly Qvcr the paper ; this fixes them securely enough to allow of their being treated by seining and clearing solutions. Microtomes. — A section-cutting apparatus or microtome is essential for histological woik. Useful instruments for studc^nts, are the tripod microtome for objects which have been embedded in paraffin and the Cathcart microtome for freezing. The tripocl microtome is a simple and efficient little instinniLot, and has the advantage of being inexpensive. It consists of a metal frame (fig. 71(i) in which a razor is securely clamped. It is provided with a uiiciometcr screw liy which the height of the razor-edge is adjusted. T'^o «ni.r,H;,, ki.,..i- „„„f„:„;.,.. *i,., i.; „ ;- Appendix S55 ^'^ '^^.'^ Fig. 716. — Tmpod miokotomis. (Birch's pattern.) The paraffln-block should be cut with square edges. , Fig. 717. — Oathoakt rREEziNc microtome. fixed by the aid of heat on a flat piece of glass or on a glazed tile over which the tripod slides. The block should be cut with square, parallel edges after being fixed on the glasfe. The razor-edge is lowered after each successive section by turning the micrometer screw at the back of the frame. Tn thfi riathcarfc frp.p.zino- microtome (flg. 717) the tissue, after being soaked in THE ESSENTIALS OF HISTOLOGY Fig. 718.-ROCKIKO MICROTOME WITH SIMPLE OBJECT-HOLDBB. FlO. 719.-MiNOt'8 AUTOMATIC BOTAKy MIOKOTOME. g„.te. is placed on a n.etal ^^f^f^^'^Z^'^'^i^'::^^^^^^ Refrigerating spray on the "'^der Burfaoe f th p a^- 2 ^L ^ ^,^^ J^_ ,„ by a finely-cut micrometer screw, and tb" '^'X'*'" APPENDIX 557 guided over the plate by passing over plate-glass sli]5s. Instead of the ether-spray, plate, a solid brass block may be fitted to the microtome. This block is plunged in an ice-and-salt freezing mixture for half an hour : it is then taken out, wiped dry, put in the microtome, and the gum-soaked tissue is placed on its upper surface, where it freezes into a solid miiss. The block is moved "upwards by the micrometer screw below, and sections are successively cut as with the ether method. When using any freezing microtome, especially for the nervous system, it is important that the tissue should not be frozen too hard, otherwise the sections will roll up and crack. If necessary the surface can be temporarily thawed just before cutting by breathing upon it. More expensive and complicated, but also more efficient, instruments are the rocking microtome of the Cambridge Scientific Instrument Company (fig. 718) and the microtomes designed by C. S. Minot and by DeWpine : the last is arranged for freezing with liquid COg. The action of all of these is automatic, i.e. every movement of the handle not only cuts a section of the tissue of definite thickness, but also either moves the knife or the tissue in such a manner that another Fig. 720. — Inclined plank microtome. section of , exactly the same thickness is cut by the next movement, and so on indefinitely. By employing a rectangular block of paraffin of the proper consistency, a long series of sections of the same object, of equal thicltness, can be obtained and made to adhere together in a riband (as shown in fig. 718). Such sections can be mounted in series upon a slide in any° desired number. For celloidin-embedded preparations it is necessary to cut the sections with a knife kept wetted with spirit. For this purpose a sliding microtome (fig. 720), in which the knife or razor is moved horizontally over the tissue, with the edge obliquely inclined to the direction of movement, is the most useful. The best arrangement for this purpose, especially for large sections, such as those of brain, is .one in which the celloidin-soaked object is immersed in spirit during the process of cutting. For every kind of microtome it is all-important that the edge of the knife or razor should be in perfect order : to secure this frequent stropping is necessary. If the razor edge has irregularities every section will be scored by them. Methods of mounting in xylol balsam or dammar. — Fixation with albumen. — Paraffin-cut sections, such as are cut with the rocking and other microtomes, are fixed to a glass slide or cover-glass- -as a preliminary to being treated with stains and other fluids^n the following way : The slide (or cover-glass), after having been carefully cleaned, is smeared very thiijly with fresh white of egg: 558 THE ESSENTIALS OF HISTOLOGY this can be done with the finger or with a clean rag \ the albuminized slide is then put aside to dry, protected from dust. A dilute solution of agar jellj (1 gm. per 1000 G.e. distilled water) may be used in place of white of egg. It is convenient to prepare a large number of slides at a time in this way, and to keep them at hand in a suitable receptacle. When required for use a little water is poured on to the slide and the riband of sections is placed on the water, which is then warmed on a hot plate or over a small flame until the paraffin becomes flattened out, without actually melting. But it is not always necessary to use albuminized slides for fixing the sections. For most objects, especially those mixed with formol and alcohol, an ordinary well-cleaned slide answers every purpose, the section or sections being flattened out in a drop of warmed water (see also below). In either ca.sc the water is then drained off', the slide put in a warm place for the remainder of the water to evaporate (this will take from half an hour to an ho\ir according to the size of the section and the temperature a£ which it is kept), and then heated just sufficiently to melt the paraffin. It is next immersed in xylol to remove the paraffin, after which the sections may, if already stained, be mounted at once in dammar. If not stained, they are treated,, after xylol, first with absolute and then with gradually lower grades of alcohol, then with water and stain, and finally are passed through water, alcohol (in grades, ending with absolute alcohol), and xylol, into dammar. For many sections some of the grades of alcohol can be omitted, but it is always well to employ 50 per cent, alcohol between water and absolute alcohol, and to wipe oiT excess of moisture before the absolute alcohol. Wdter-fi.ration. — A simple method of fixation, but one which, in most cases, answers the purpose well, is to place the riband or the individual sections cut from paraffin on the surface of water in a basin, just sufficiently warm to flatten out the paraffin, but not to molt it, then pass a perfectly clean slide under the surface of the water and float the sections on to it ; remove, drain off the water, and put the slide and sections aside for an hour or more until all the water has evaporated. The sections are found to have adhered firmly to the slide. They may, if desired, be yet more firmly fixed by drawing a brush moistened with solution of celloidin in oil of cloves over them. The paraffin can now be removed by washing the slide with xylol or immersing it in xylol. If not previously stained they can then be passed through alcohols and stained and mounted as just described. After certain hardening solutions have been used (bichromates or osmic acid) the sections cannot be fixed by the water method alone : an albumenized slide or celloidin solution' is necessary. It is convenient to keep the several solutions which are required for removing the paraffin and for staining, dehydrating, and clearing the sections after they are fixed to the slide, in cylindrical tubes or in grooved glass receptacles in a regular row upon the working table, the slide being ti'ansferred from one to the other in succession. Such a series would be (1) xylol ; (2) absolute alcohol ; (3) It) per cent, alcohol ; (4) .'iO per cent, alcohol ; (5) distilled water ; (6) staining solution ; (7) tap water ; (8) distilled water ; (9) .'iO per cent, alcohol ; (10) ".") per cent, alcohol ; (11) absolute alcohol ; (12) -xylol. The changes are sometimes effected by pouring the solutions over the sections and draining otT. After the paraffin has been removed by xylol the sections must never, on any account, be allowed to dry, or they will inevitably be spoiled. The following table shows the methods to be adopted foi- the treatment of paraffin-cut sections or ribands of sections ;—, APPENDIX 559 1. Float on to a alido or coverglaaa in warm water : the glass may previously have been smeared with egg-white. 2. Drain off water and allow to dry compUtdy. 3. Warm until paraffin ia just melted. I 4. Dissolve paraffin away with xylol. If tissue is already stained in bnllf . If tissue is not already stained. 5. Mount in dammar. 5. Absolute alcohol. • I 6. Descending grades of alcohol. 7. Stain. For sections cut by the freer-inrj \ method, if the tis.gue has 8. Water, already been stained in bulk, | the sections must be put 9. Ascending grades of alcohol, through Nos. 8, 9, and 10, | previously to being mounted 10. Xylol (this may be preceded by barga- in dammar. If the tissue has mot oil), not already been stained, begin | at No. 7. 11. Mount in dammar. Methods of staining. — Staining by dyes is dependent partly upon the physical processes of osmosis and adsorption, partly upon chemical affinities. The theory of stains has been treated of at great length by various authors : it would occupy far too much space to deal with the matter in this work. The methods of staining employed for teased preparations have been dealt with under the several tissues. We may here, therefore, confine our attention to the staining of sections. The fluids most commonly employed for the staining of sections are : (1) Solutions of hsematoxylin. and alum ; (2) solutions of carmine with or without alum ; (3) certain aniline dyes. The time of immersion in the staining fluid varies according to the strength of the iiuid and the mode by which the tissue has been hardened. The necessity of staining sections may in some cases be avoided hy staining the tissue in bulk before embedding. For this purpose a small piece of hardened tissue well washed with distilled water is placed for twenty -four hours or more in dilute solution of htemalum or of Ehrlich's hsematoxylin or borax-carmine. The tissue is then passed through ascending grades of alcohol into absolute and then through xylol satui'ated with alcohol-soluble eosin into parE^ffin ; the sections being mounted in dammar. But if to he cut by the freezing method the tissue goes into gum after being stained and the sections are placed in tap-water to remove gum, floated on to a slide, and the excess of water allowed to drain off. Alcohol is then dropped on from a drop bottle and the sections pressed fiat with blotting or tissue paper.- This fixes them to the slide. They are then dehydrated by absolute alcohol and passed through xylol into dammar. If the tissue has not been stained in bulk the sections are usually stained on the slide in the manner described on p. r)58. The most useful general method for class purposes is to immerse the slide on which the sections from paraffin are fixed, and which has been carried through xylol and alcohol into water, in hiematoxylin solution for fifteen minutes ; after rinsing with water they are counter-stained with water-solution of eosin for five minutes, and then carried through alcohol and xylol into dammar. Sections , may be stained whilst still infiltrated with paraffin by floating them, 3,s they are cut, on to the surface of a staining solution, which is gentlj' -warined 56o THE ESSENTIALS OF HISTOLOGY (but not enough to melt the paraffin) ; under these circumstances they require far longer exposure to the stain. The subsequent treatment is simple, for they need only be transferred to warm water, floated on to a slide and allowed to dry. The paraffin is then melted and allowed to set ; the solidified paraffin is dissolved away with xylol, and the sections are mounted in daniniar. The following are some of the principal staining solutions : — 1. Delafield's hmmatoxijlin. — To 150 c.c. of a satarated solution of potash alum in water add 4 c.c. of a saturated solution of heematoxylin in alcohol. Let the mixture stand eight days, then decant, and add 25 c.c. of glycerine and 25 c.c. of methyl alcohol. The 'solution must stand a few days before it is ready for use. To stain free sections add a few drops of this solution to a watch-glassful of distilled water. If overstained the excess of colour can be removed by alcohol containing 1 per cent, nitric or hydrochloric acid. With long keeping this haema- toxylin solution becomes reddened ; a trace of ammonia will restore the blue colour. 2. Ehrlich's hanniitn.ryUn. — Dissolve 2 gm. hsematoxylin (or hfematein) in 100 c.c. alcohol ; add 100 c.c. water, 100 c.c. glycerine, and 10 c.c. glacial acetic acid ; also potash alum to saturation. This solution will keep almost in- definitely : it is valuable for staining in bulk, since it does not easily overstain. For sections the solution may be diluted either with distilled water or with a solution containing one part alcohol to two parts distilled water. After the sections have been stained they must be thoroughly wa-shed with tap-water. This develops the blue colour of the hnematoxylin. 3. Kidtxvhit-l-jfshcematoxjiUn. — Dissolve 1 gm. hsematoxylin in a little alcohol, and add to it loo c.c. of a 2 per cent, solution of acetic acid. This solution is valuable for staining sections of the nervous system by the Weigert-Pal process (p. .'iru). 4. Hceinahim. — H;«matoxylin-alura solutions acquire theii- colouring properties only as the hsematoxylin on keeping becomes converted into hasmatein. The latter substance may, therefore, as recommended by Mayer, be used advantageously in place of hsematoxylin if the stain is required immediately. The following is the mode of preparing the solution : Dissolve 50 gm. of ammonia alum in 1 litre of distilled water, and 1 gm. of hsematein in 100 c.c. of rectified spirit. Add the haematein solution gradually to the alum. The mixture is ready for staining at once, either as it is or diluted with distilled water. A small piece of thymol or a little carbolic acid should be added to prevent the growth of moulds. 5. R. Heidenhairi's method. — After hardening in alcohol, or in satui"ated solution of picric acid and then in alcohol, place the tissue from twelve to fourteen hours in 0'3 per cent, aqueous solution of ha^matoxylin, and then from twelve to twenty-four hours more in a 0'5 per cent, solution of yellow chromate of potash, which may be changed more than once. Then wa^h in water, place in alcohol, pass through xylol, and embed in paraffin. 6. M. He.idcnhain!s iron-hcemato.vylin method.—'Hs.vAe.n in formol, followed by alcohol ; fix sections to slide by water method ; transfer ttr iT) per cent, iron alum (sulphate, or tartrate, of iron and ammonia) and leave a quarter of an hour or longer ; rinse with distilled water ; place in 05 to 1 per cent, pure luvniatoxylin in water containing 10 per cent, alcohol, for a few minutes ; wash with water : differentiate in the iron and ammonia solution until nearly decolorised : the sections must be examined from time to time with a low power after wa^hinsj away the iron alum with water. When differentiated wash for fifteen minutes in tap-water ; dehydrate and mount in the usual way. This method is especially adapted for exhibiting the centrosomes of cells and the alterations of the nucleus in cell-diviaion. It is also a good general method for many tissues, APfendix 561 Both the process of mordanting with iron alum and the subsequent staining with hematoxylin may often with advantage be considerably prolonged (up to twel\ e hours or more). 7_ Caniudum. — This is useful either for sections or bulk staining. If the sections are subsequently passed through alcohol containing picric acid in solution a double stain is produced. Carminio acid 1 gni. Ammonia alum 10 gm. Distilled water 200 c. c. Boil together, allow to cool, and filter. Add 1 c.c. formol or carbolic acid to prevent the growth of moulds. 8. Carminate of ammonia. — Prepared by dissolving carmine in ammonia, and allowing the excess of ammonia to escape by slow evaporation. The solution may be diluted with water as required. 9. Bnra.v-carniiiie. — Dissolve 4 gm. borax and 3 gm. carmine in 100 c.c. of water with the aid of heat. Add 100 c.c. of 70 per cent, alcohol, let stand two days or more and filter. This solution improves on keeping. It is used for staining in bulk. The piece of tissue can be left in it for several days or weeks. It is transferred, without washing, to 70 per cent, alcohol containing 5 drops of hydrochloric acid to 100 c.c. in order to fix the colour. It should remain in this for two or three days. Then proceed with dehydration. 10. Picro-carminate of ammonia. — This is a double stain unsuitable for sections, but useful for some tissues. The staining occurs very slowly, a. lianvier's picro- carmine. — To a saturated solution of picric acid add a sti'ong solution of carmine in ammonia, until a precipitate begins to form. Evaporate on the water bath (or, better, allow it to evaporate spontaneously) to one half its bulk, adding a little carbolic acid to prevent the growth of moulds ; filter from the sediment. (3. Bourne's piaro-carmine. — "Add 5 c.c. of ammonia to 2 gm. carmine in a bottle capable of containing about 250 c.c. Stopper, shake, and put aside till next day. Add slowly, shaking the while, 200 c.c. of a saturated solution of picric acid in distilled water. Put aside till next day. Add slowly, constantly stirring, 11 c.c. of 5 per cent, acetic acid. Put aside till next day. Filter ; to the filtrate add four drops of ammonia, put back in the stoppered bottle " (Langley). 11. Van GivsmCs stain. — This is also a double stain. It consists of a saturated solution of picric acid in water, with 5 c.c. of a 1 per cent, aqueous solution of acid fuchsin added to each 100 c.c. It stains the white fibres of connective-tissue bright red ; elastic fibres, muscle-fibres and epithelium yellow. Sections may first be stained deeply with haemalum or hematoxylin, then placed in Van Gieson's stain for five minutes, then passed through 75 per cent, alcohol, absolute alcohol and clove oil or xylol, and mounted in dammar. The method is suitable for frozen and celloidin sections. It is valuable for the nervous system, especially as a counterstain in the Weigert-Pal method ; for this it is recommended- to -fticrease the propoiiion of the acid-fuehsin solution to fifteen parts per cent. AnUine dyes. — These are used either in simple aqueous solution, or in O'Ol per cent, solution of caustic potash, or in water shaken up with aniline oil ; it is usual to overstain a tissue with them, and subsequently to decolorise with absolute alcohol containing one -fifth its bulk of aniline oil (from this the sections pass through absolute alcohol into xylol) or with alcohol containing O'l to 1 per cent, hydrochloric acid : this is also followed by absolute alcohol and this by xylol. The aniline colours most employed are the " basic " dyes — methylene-blue, gentian violet, toluidin-blue, thionin, saffranin, and vesuvin ; and the "acid" dyes — eosin, 562 THE ESSENTIALS OF mSTOLOGY erytluii.sin, magenta nr acid fuchsin, orange G. and mutliyl-blue ; so-called " neutral " dyes aie also used. 12. Eusin. — A 1 per cent, solution in water. The soctionK are fiist stained deeply with hiematoxylin anil i-insed with distilled water. They are then stained with the eosin solution, passed through 75 per ceijt. alcohol, and then through absolute alcohol — whicli is allowed to dissolve out some but not all of the eosin stain — into xylol : they are finally mounted in dammai-. Erythrosin may be used in place of eosin. An alcohol-soluble eosin is also employed (see below). Eosin colouiii hiemoglobin of an orange-red colour, so that the blood-corpuscles are well shown when a fixing fluid has been employed which does not remove the haemoglobin fiom them (such as mercuric chloiide,! bichromate of potassium, or formbl). 13. AlcohoUr eosin and mHhi/lime-hlue. — The sections are first stained for one minute in 1 per cent, alcohol-soluble eosin, and after rinsing with water for another minute in 1 per cent, methylene-blue in water, after which they are again rinsed, and the slide wiped dry of moisture ; they are then decolorised rapidly by absolute alcohol. The decolorisation is aorested by xylol. 14. Jennei'$ stain. — This is made by dissolving , iu pure methyl alcohol the precipitate which is produced when eosin solution^ is added to methylene-blue solution. It is valuable for blood films, which may be stained for foui- or five minutes. Then wash, dry, and mount in dammar. 15. Leishman's staiii, is largely used for the same purpose. It is made by dissolving 1 part pui'c methylene-blue in 100 parts of O'O per cent, sodium bicarbonate solution with the aid of heat and precipitating by five times its bulk of a O'l per cent, aijueous solution of yellow water-soluble eosin. The precipitate is collected on a filter, and when dry ij dissolved in methyl alcohol in the proportion of O'l gm. to 60 c.c. (Wright). The stain is applied for one minute, when an equal amount of distilled water should be added ; the diluted Leisliman is left to stain for about five minutes. The film may then be washed, dried and mounted. 16. Mann's double stain. — A good double stain for sections is the methyl-blue- eosin of < >. Mann. To prepare this take 35 c.c. of a 1 per cent, solution of methyl- blue in distilled water, and 4r) c.c. of a 1 per cent, solution of eosin in distilled water : mix and add 100 c.c. of distilled water. In sections it stains connective- tissue fibres and mucus-containing cells deep blue. 17. Mail's double ainia. — .Sections of formol-hardened tissue are fixed on a Mide, a saturated solution of alcohol-soluble eosin in lectififid spirit poni-ed on and heated over a lamp, When nearly dry rinse with water, place for three minutes in saturated solution of potash alum, and again rinse. Decolorise with alcohol con- tiiining a trace of ammonia. Wash again and stain with saturated methvlene-blue solution for- a few minutes ; then rinse once more, pass through grades of alcohol and xylol ; mount in dammar. IH. Fu'-h.'tiii or moi/eiita. — -V 1 per cent, solution in 50 ]ier cent, alcohol (to which 1 drop of 1 per cent, alcohol-solution of gentian or methjl-\iolet may be added per cubic ccntinieter just before use) is an excellent stiiin for fresh connective tissue. For this purpose the mixture should be diluted tweiity times with distilled water. It colours all the elements of the tissue but most intensely the elastic fibres. ]1». MaUiinfs mcl/iod. — Sections are treated for three minutes «ith acid fuchsin (1 per cent.) ; then washed in water and immersed for several minutes in phospho- raolybdic acid. They are then again thoroughly washed in water, and placed for two minutes or moi'O in the following solution : — APPENDIX 563 Aniline blue Oo g. Orange G. '2'0 g. Oxalic acid 2'0 g. Water - 100 c.c. After being stained with this they are passed through water, alcohol, and xylol into dammar. This is a good method for demonstrating connective tissue ; it also shows the zymogen granules in gland-cells, and serves to display the various types of cell met with in the gastric glands. 20. ■ Orw'm is a dye obtained from lichens. It is chiefly useful for staining elastic fibres in sections of organs. For this purpose 1 gni. orcein is dissolved in 100 c.c. absolute alcohol, containing 1 c.c. hydrochloric acid. The sections are placed in some of this solution in a watch-glass f&r about an hour. ■ They are dehydrated in alcohol, .which removes the excess of stain ; then passed through xylol into dammar. Either saffraiiin or neutral red may be employed as a counter- stain. 21. Plemming's •mnthod for staining dividing nuclei. — The tissue is fixed in Flemming's solution (see p. 552), and small shreds or thin sections are placed for two days in saturated alcoholic solution of saffranin, mixed with an equal amount of aniline water. They are then washed with distilled water and decolorised in aniline alcohol or in alcohol containing 1 per 1000 hydrochloric acid until the colour is washed out from everything except the nuclei. They are then again rinsed in water, and placed in saturated aqueous solution of gentian violet for two hours, washed again in distilled water, decolorised with aniline alcohol until only the nuclei are left stained, then transferred to bergamot oil or xylol, and from this are mounted in dammar. Gentian violet and several other basic aniline colours may be employed in place of saflranin from the first. Delafield's hocmatoxylin, followed by acid, and Ehrlich's hsematoxylin also stain mitotic figures well. Heidenhain's iron-hsematoxylin method is also used for this purpose, as well as for exhibiting centrioles and the achromatic spindle of the dividing cell. 22. Staining with nitrate of silver (v. Recklinghausen). — Wash the fresh tissue with distilled water ; immerse in 1 per cent, nitrate of silver solution for from one to five minutes ; rinse with distilled water and expose until just Brown to bright sunlight. The tissue, if it is a thin membrane, may be mounted in glycerine. But a better plan is to spread it out flat in water on a slide, drain ofl' the water, allow the tissue to dry completely, ancl then mount it in dammar. This method is used to exhibit endothelium, and generally to stain intercellular substance. It depends upon the fact that the chlorides of the tissues are almost exclusively confined to the intercellular substance. The following methods are especially useful in investigations relating to the nervous system : — 23. ilarchi's method. — This is of value for staining nerve-fibres in the earlier stages of degeneration, before sclerosis sets in (especially a few days after the establishment of a lesion). The degenerated myelinated fibres are stained black, whilst the rest of the section remains almost uhstained. In employing the method for the brain or cord the organ is first fixed and partially hardened by immersion for ten days in MuUer's fluid (p. 552). Thin pieces of the tissue are then cut and are placed singly, resting on a little cotton wool, in a fairly large quantity of a mixture of two parts Muller's fluid and one part 1 per cent, osmic acid. They are left in this for at least a week; the fluid should be changed once or twice. The pieces are then washed in water, and passed through grades of alcohol and S64 THE ESSENTIALS OF HISTOLOGY through xylol into paraffin ; the sections are mpunted— after removing the paraffin with xylol — iu daiuraar without further staining. 24. Weiy(jrt-Fal metliod.-~Th.is is chiefly used for the central nervous system. By it normal myelinated nerve-fibres are stained dark, while grey matter and sclerosed tracts of white matter are left uncolouredt The following modification of the original method is recommended : Pieces which have been hardened in Miiller's fluid and afterwards transferred to and kept a short time in alcohol (without previous washing in water) are embedded in celloidin, and sections are cut as thin as possible. Or sections may be made by the freezing method direct from Miiller's fluid, the pieces to be cut being first soaked in gum-water for a few hours. In either case the sections are placed in water, and from this are transferred to Marchi's fluid (see above, ^ 22) in which they are left for six to twelve hours. They are then again washed in water and transferred to Kultschitzky's hftimatoxylin (see p. 560, S 3). In this they are left overnight, by which time they will bt completely black. After again washing in water they are ready to be bleached. This is accomplished by Pal's method as follows : Place the overstained sections, first in O'S.'J per cent, solution of pota.ssium permanganate for five minutes (or for a longer time in a weaker solution) ; rinse with water ; transfer to the following bleaching solution, viz., sulphite of soda 1 gni., oxalic acid 1 gm., distilled water 200 C.C.' The stain is usually sufficiently diflFerentiated in a few minutes ; but the sections can be left longer in the bleaching solution without detriment. If after half an hour they are not difi'erentiated enough, they must be put again (after washing) into the permanganate for some minutes, and then again into the bleaching solution. After dilfereutiation they may_ be counterstained with Van Gieson and subsequently passed through water, grades of alcohol (with or without eosin), and oil of bergamot (or xylol), to be mounted in dammar. The advantages which this modification has over the original metjiod are : (1) even the finest myelinated fibres are brought to view with great surety ; (2) the staining of the fibres is jet black, and ofl'ers a strong conti'ast to the coloui'less grey matter ; (3) the sections are easily seen and lifted out of the acid hiematoxylin, which has very little colour ; (4) it is difficult to overbleach the sections ; (5) the stain is remarkably permanent. As a further improvement, J. >S. Bolton recommends to harden with formol, place the sections for a few minutes in 1 per cent, osmic acid, stain for two hours in Kultschitzky's htematoxyliu at 40° C, and then proceed with the bleaching process. 25. Stainlnji with chloride of gold. — a. Cohnhcitn's melhod. — Place the fresh tissue for from thirty to sixty minutes (according to thickness) in ii 0'5 per cent, solution of chloride of gold ; then wash and transfer to a large quantity of water faintly acidulated with acetic acid. Keep for t^\•o or thiee days in the light in a warm place. This answers very well for the cornea. If it is principally desired to stain the nerve-fibrils within the epithelium, the cornea may be transferred after twenty-four hours (the outlines of the larger nerves should be just apparent to the naked eye) to a mixture of glycerine (1 ])art) and water (2 jiarts), and left in this for twenty-four hours longer (Klein). fi. /jdicit'n method. — Place small pieces of the fresh tissue in a mixture of 1 part of formic acid to 3 parts of water for one minute ; then in 1 per cent, chloride of gold solution for fifteen minutes ; then back again into the formic acid mixture for twenty-four hours, and into pure formic acid for twenty-four ' Diluted sulphurous acid solution may be employed to bleach ihe sections instead of this solution. APPENDIX 56s hours more. After removal from the gold, and whilst in the acid, the tissue must be kept in the dark. This method is especially good for motor nerve- endings in cross -striated muscle. 7. liaiivier's method. — Immerse in lemon-juice for ten minutes, then wash with water and place in 1 per cent, gold-ohloride solution for twenty minutes. Then treat either as in Oohnheim's or as in Ltiwit's method. 26. Golgi's c/iromate of silver inethods. — These arc chiefly employed for in- vestigating the relation.s of cells and fibres in the central nervous system. Two methods are mostly used, as follows :-^ a. Very small pieces of the tissue, which has been hardened for some weeks in 3 per cent, bichromate of potassium or Miiller's fluid, are placed (without previous washing) for half an hour in the dark in U'75 per cent, nitrate of silver solution, and are then transferred for twenty-four hours to a fresh quantity of the same solution (to which a trace of formic acid may be added). They may then be placed in 96 per cent, alcohol (half an hour), and sections, which need not be thin, are cut from celloidin with a microtome or with the free hand after embedding (but not soaking) with paraffin. The sections should be placed in dammar on a cover-glass and the dammar allowed to dry in a uniform layer. The glass is inverted over a thin glass ring and fiyed to a slide with the surface of the dammar dependent and exposed to air. Golgi-stained preparations must not be mounted and covered in the usual way. ;8. Instead of being slowly hardened in bichromate, the tissue is placed at once in "very small pieces in a mixture' of bichromate and osmie acid (.3 parts of 3 per cent, bichromate of potassium or of Miiller's fluid to 1 of osmic acid). In this it remains from one to eight days, a piece being transferred each day to O'TS per cent, silver nitrate. The subsequent procedure is the same as described under a. ITor some organs it is found advantageous to repeat the process, replacing the pieces for a day or two in the osmic-bichromate mixture after silver nitrate and then putting them back into silver nitrate (Oajal's double method). This method is not only more rapid than that in which bichromate of potassium alone is used, but is more sure in its results. A combination of the methods under a and ^ is often found advantageous. To employ this a number of very small pieces of the tissue are placed in 3 per cent, bichromate of potassium as in the slow method. Of these one is every day transferred to osmium-bichromate solution and alWwed to remain in this for a few days, after which the silver treatment follows as before. 27. CoK^s chromate of mercwry method. — This serves the same purpose as the Golgi methods but is not as good for fine details, Mix 20 c.c. of 5 per cent, corrosive sublimate solution with 30-40 c.c. distilled water, and add slowly 16 c.c. of 5 per cent, chromate of potassium solution, then add 20 c.c. of 5 per cent, bichromate of potassium solution to the mixture. Larger pieces of tissue may be taken than for the Golgi methods ; they are left for two months or more. Sections are cut by the freezing method and passed through water and successive grades of alcohol, and then through clove oil into dammar. They may be mounted with a, cover-glass in the usual way, and as the cells remain white they show up well by reflected light and quite thick opaque sections can be examined. If it' is desired to convert the white impregnation into a black one, this can be done by passing the sections through dilute ammonia, but after this they must be mounted - like the Golgi preparations without being sealed up. 28. Nissl's method of staining the chromatic granules of nerve-cells. — This is a method of overstaining with methylene-blue and subsequent differentiation with 566 THE ESSENTIALS OF HISTOLOGY alcohol (see § 14). Nissl recommended 90 per cent, alcohol as the hardening agent, but both formol and corrosive sublimate followed by alcohol may be equally well employed. Toluidin-blue (Mann) may be used in place of methylene-blue. The sections are stained with 1 per cent, methylene-blue or toluidin-blue, and differentiated in absolute alcohol ; they may be counterstained by being passed through xylol-oosin. The effect of heating the solutions to about 70° C. is to accelerate and accentuate the staining. A Nissl stain may also be obtained by staining in bulk thin pieces of the fixed and hardened nervous tissue in 1 per cent, solution of thionin for several days ; the tissue is then dehydrated and embedded in paraffin. 29. CajuVs methods for exhibiting neyroJUiri/x. — a. A small piece of the tissue (brain, spinal cord, ganglion, etc.), not more than 4 mm. thick, and preferably from a young or fri'tal animal, is placed in 50 c.c. of rectified spirit. After four or five hours in this, followed by twenty-four hours in absolute alcohol, rinse with distilled water and place in a large quantity of l-§ per cent, solution of silver nitrate, which is maintained at a temperature of about 35 C. After being five or six days in this, the piece is removed, rinsed for a few seconds in di.itilled watei-, and transferred for twenty -four hours to the following developing solution : — Hydrokinone 1 to To gm. Distilled water 100 c.c. Formol 5 „ Rectified spirit 10 „ The addition of rectified spirit to the above is not indispensable, but favours penetration. The piece is then washed in water for some minutes, transferred to alcohol, embedded in celloidin or paraffin, and sections are prepared and mounted in dammar. /3. Place several small pieces of the fresh tissue direct in 2 per cent, silver nitrate solution at 35° C. in the dark : a piece is taken out on the third and on each subsequent day until the eighth. The piece is rinsed in distilled water for a minute or two and then immersed in the above developing solution for twenty-four hours : after which proceed as before. The tissue should be placed on cotton wool in the silver solution. The central parts of the tissue are usually best, the superficial parts being often too dark. 30. Bi/'h'hoirnh/'s metliod for nenrn/ihrih. — Place small pieces of tissue in 12 per cent, formol for twenty-four hours ; wash for several hours in distilled water which should have been redistilled from potassium permanganate (da Fano) ; cut sections by freezing method. Proceed as follows : Place the sections in H per cent, nitrate of silver for twenty-four hours ; wash in redistilled water for a few minutes. Then transfer them to the following solution, viz. : -2 per cent, nitrate of silver 20 c.c, to which three drops of a 40 per cent, solution of caustic potash are added, and enough ammonia to cause the disappearance of the brown precipitate produced. The sections may be left in this solution for some time. They are then passed through redistilled water and transferred to 20 per cent, fonni.il solution made with tap water. After twenty-four houis in the formol the sections can be washed witli water, dehydrated and mounted in dammar, but it is preferable first to tone them with chloride of gold. This is done by placing the washed sections in very dilute (002 per cent.) gold chloride solution acidified with acetic acid. They must then be lixed with 5 per cent, acid sodium hyposulphite solution, washed with water, and passed through alcohol and xylol into dammar. APPENDIX 567 IXTUA VITAM STAININ(i MRTIIOUS 31. Methylene-hbie method. — Tins method is of great \aliio for exhibiting nerve- terminations, and in some cases tlie relation of nerve-cells to nerve-fibres in the central nervous system. For its application the tissue must be living ; it is there- fore best applied (Ehrlich) by injecting a solution qf niethylene-blue (1 part to 100 of warm Ringer) into a vein in an annasthetised mammal, until the whole blood is of a bluish colour ; or the injection may be made through the vessels of the part to be investigated, immediately after killiing an animal. Good results can sometimes be obtained by immersing small pieces of fi'eshly excised living tissue in a less concentrated solution (O'l per cent.), oi-, in the case of the central nervous system, bydusting the methylene-blue powder over a freshly cut surface, allowing some time for it to penetrate and then treating it with picrate of ammonia and Bethe's solution (see below). In either case the tissue should be freely exposed to air ; only then does the blue colour appear in the nerve-cells and axis-cylinders, to their finest ramifications. It does not, however, remain, but after a time fades from them, and other tissues then become coloured. To fix the stain the tissue is taken at the moment that the nerve-fibres are most distinctly seen and is placed for an hour or two in saturated solution of picrate of ammonia, after which the preparation can be mounted in glycerine containing picrate of ammonia. But to allow of sections being made for mounting in balsam or dammar, the pieces of tissue must, subsequently to the treatment with picrate of ammonia, be placed for some hours in Bethe's fluid, viz. : — Molybdate of ammonia 1 gm. Chromic acid 2 per cent, solution 10 o.c. Distilled water 10 o.c. Hydrochloric acid 1 drop. This I'enders the colour insoluble in alcohol. 32. Dogiel's modifioation of the methylene-hlue method. — The fresh tissue is placed in a capsule containing 1 per 1000 methylene-blue and kept at 36° C for two hours. It is then placed in 6 per cent, molybdate of ammonia for twenty- four hours ; washed during four hours in distillpd water ; dehydrated with alcohol, and passed thi'ough xylol into dammar. 33. Neutral red. — This is really a basic dye of a neutral tint, readily converted by alkalies to yellow and by acids to red. It is a relatively non-poisonous sub- stance and can be used . for iritra vitam injection as a concentrated solution in normal saline. It- has no specific affinity for neurofibrils but it colours certain cell-granules intensely. It has been used by Bensley for exhibiting by its selective stain the islets of Langerhans of the pancreas. 34. Janug^reen. — This is a basic aniline dye, re^Jiily soluble in water. It can be employed in very dilute solution (1 to 300,000 normal saline) for injection into the blood-vessels. It has been used by Ehrlich fbj- staining nerves intravitally, and by Michaelis for the granules of gland-cells. Bensley has employed it also for showing the islets of Langerhans. 35. Bismarck -hmoii or reniBin has also been recommended for^ intra ritam injection. It is used in a 0'3 per cent, solution ; the tissues are subsequently fixed with 0'2 per cent, chromic acid or 1 per cent, osmic acid. ADDITIONAL NOTES TO APPENDIX OF ESSENTIALS OF HISTOLOGY.i DISSOCIATION METHOfiS. Special methods of dissociation are given under the notes of preparation at the beginning of each chapter, but there are certain general principles which must be remembered in order to make successful preparations. The dis- sociation may be of fresh tissue in Ringer's solirtion, but is most frequentl}' of a tissue which has been macerated for some days in dilute chromic acid (1 in 2000), bichromate of potassium (1 in 800), or one-third alcohol (1 part rectified spirit to 2 parts water). Osmic acid preparations are first fixed in 1 per cent, osmio for an hour and then macerated in water for several days : they can be kept permanently in a mixture of equal parts of water and glycerine and are available for use at any time. A piece of thymol should be added to the macerating fluids. In all cases a small fragment of the macerated tissue is rinsed in distilled water. Tt is then placed on a slide in a drop of distilled water, and broken up into as minute pieces as possible with needle? and covered with a cover-glass. This is then repeatedly and firmly tapped with the handle of a mounted .needle held balanced lightly between the first and second fingers, care being taken not to break the cover-glass. To prevent crushing of the cells a small hair from the back of the hand is cut off and placed in the drop prior to covering it. The stains to be used are introduced at one edge ; or the dissociation can be made in the diluted stain instead of distilled water. When the cells are stained a small drop of glycerine and water is brought in contact with one edge of the cover-glass and is allowed gradually to diffuse under this. It must not be sucked under with filter paper. The cover is fixed next day ^'ith gold size. In some cases it is of advantage to add a little glycerine to the diluted stain in which the tissue is dissociated, and to cover the specjmen in this fluid, allowing the water to dry off at the edges before fixing the cover -glass with gold size. METHODS OF FIXATION. Formal. — When formol is used as a fixative its solutions should be made up with isotonic saline (0'6 per cent, for frog tissues, 0'9 per cent, for mammahan), not with water (Carleton). Sometimes black granules (of tri-oxymethylene) make their appearance in formol fixed specimens. They can be got rid of by treatment with 1 to 5 per cent, ammonia in 70 per cent, alcohol. BouirCs solution : — Picric acid, saturated solution 75 c.c. Formol 25 c.c. Glacial acetic acid (or saturated solution of citric acid) 5 c.c. Place the tissue in this for twelve to eighteen hours, wash out the picric acid with 50 per cent, alcohol (to which has been added a few drops of a saturated solution ^ I have to thank Dr May L. Walker and Dr C. Da Fauo for assistance in preparing these notes. ■565] [57o] THE ESSENTIALS OF HISTOLOGY of lithium carbonate) for twelve hours. Then transfer through 70 per cent, alcohol to 80 per cent. The fixative penetrates well and equally. Finer details of cell structure are much better preserved than after formol alone, and tissue."^ so fixed stain well if the picric acid has been thoroughly removed, which can be done if a small amount of Hthium iodide (Landau) is added to the alcohols through which the tissue is passed. They can then be dehydrated and embedded in the usual way, or may first be stained in bulk with hsematoxylin and eosin (see p. [573], Staining in bulk). "Bouin" is unsuitable for saUvary glands or for any cells containing mucigen, which becomes greatly swollen by I he acetic acid. Osmk acid (see Appendix, p. 551). — In 0-5 to 2 per cent, solution, or as osmic vapour, it fixes protoplasm well, but tends to swell the tissues slightly. Fix half to two hours, wash thoroughly and transfer to dilute alcohol. Or suspend thin pieces of the fresh tissue in gauze over 2 per cent, osmic acid in a stoppered bottle for one and a half hours at 37° C. ; then transfer to 50 per pent, alcohol. For cj-tological purposes the pieces may be put from the osmic acid into Altmann's fiuid (equal parts of 5 per cent, potassium bichromate and 2 per cent, osmic acid). Osmic acid does not penetrate readily and is only suitable for the fixation of small objects. Its vapour is irritating to the eyes : it must therefore be used with care and kept covered. The action of hght tends to reduce it, so that it must be kept in the dark and in bottles covered with black paper. Staining after osmio acid fixation is difBcult, but if the sections are treated with a soluti6n of hydrogen peroxide, they stain well, even with Delafield's hsematoxyhn. Pal's method (Appendix, p. 564) can be used with advantage instead of hydrogen peroxide. Cham.py's method. — Small pieces of tissue are placed for twenty-four hours in the following fluid : — 3 per cent, potassium bichromate 1 per cent, chromic acid 1 per cent, osmic acid and then washed for six hours in runnuig water. Heidenhain's " sima " solution. — This is made as follows : — SubUmate salt solution (saturated) Trichloracetic acid Formalin Glacial acetic acid Distilled water " Susa " is a very good general fixative. The acetic acid and trichloracetic acid counteract the tendency to shrinkage caused by the subUmate. Tissues cut more easily after " susa " fixation than after alcohol, formol, or Zenker (Appendix, p. 552). and their staining qualities are uniformly good. As with Zenker and other fluids containing merourjo chloride, it is necessary after fixation to get rid of the excess of mercury salt by iodised alcohol (see p. [571] \d) i. Szent-Oyurgi's fluid for fixing the whole eyeball. — This is made up as follows : — Concentrated sublimate salt solution 50 e.c. Glacial acetic acid ,-; p.p Formalin 40 c.c. Acetone 125 c.c. Distilled water 50 c.c. Add the other reagents to the sublimate solution immediately before using. Fix two to three days for small eyes, six to seven days for large. Then add to the fluid 7 c.c. 7 c.c. 4 c.c. 50 c.c. 2 gm. 20 c.c. 4 c.c. 30 c.c. ADDITIONAL NOTES TO APPENDIX [571] half its total volume of acetone, and leave two to four days longer. Dehydrate in pure acetone ; change to fresh acetone after two days ; in two days more transfer to ether-alcohol, equal parts, and leave for twenty-four Hours. Cut with a sharp knife into suitable pieces and embed in celloidin. Ftxatires which also ilecakify (Appendix, p. .553).— Trichloracetic acid, a 5 per cent, solution in water, fixes and decalcifies at the same time. Larger pieces will take from eight to ten days, although forty-eight hours may be sufficient for small objeota ; test with a needle. Wash out the acid with 96 per cent, alcohol, changing three times at intervals of three hours. Water must not be used for this as, after trichloracetic acid, it causes sweUing of the tissues. The fixed tissue is dehydrated with absolute alcohol and embedded in celloidin ; the sections (40 fi) are stained and passed through alcohol and xylol-creosote (xylol 2 parts, creosote 1 part) to dammar. White's method of decakification. — The novelty of this method lies in the use of a neutral instead of an acid fluid. It works very well after formalin or Bouin fixation and does not affect any subsequent staining. The fluid is a solution of ammonium citrate which has the property of dissolving the insoluble salts of calcium (phosphate, carbonate, sulphate) even when neutral or alkahne from an excess of ammonia. It is made up as follows : A saturated water-solution of citric acid is diluted 1 : 10 with H^O. A little methyl red and a little a-naphthol-phthalein are added and then strong ammonia until the fluid is of a clear yellow colour. Too much ammonia wiU turn the fluid green. Add a little chloroform to prevent the growth of moulds. After decalcification is complete, tlje tissues must be well washed in running water before being placed in alcohol. Embed either in paraffin or celloidin. Treatment after fixation. — The fluid employed for fixation must be washed out as indicated under each fixative, or according to the following rules : — - (a) After osmic acid, chromic acid, or mixtures containing these acids, prolonged washing in running water is necessary. (&) After, fixatives containing formol or bichromates, rinse or wash for a short time in water and transfer to the ascending series of alcohols, beginning with 60 per cent. and ending with 96 per cent, alcohol. Tissues fixed in fluids containing chromic acid or its salts must be kept in the dark while being washed out by alcohol, since alcohol causes a precipitate in these fluids under the influence of light. (c) After fixatives containing mercuric chloride or picric acid wash at once with 80 per cent, alcohol, changing several times, unless otherwise indicated. (d) Further, after aU fixatives containing subUmate it is necessary to get rid of the mercury ; otherwise, small needle-shaped or amorphous crystals of mercury chloride remain in the sections. To effect this the first alcohol is iodised, i.e. coloured tawny brown with a solution of 2 per cent, iodine in 3 per cent, alcoholic solution of potassium iodide ; but since iodine is harmful to stains, espeoiaUy anilin stains, it must be removed by subsequent alcohol baths. Or, instead of treating the tissue in bulk with iodine, sections may be placed in iodised alcohol for fifteen minutes and then treated with 0-25 per cent, sodium thiosulphate for fifteen minutes. Rmse m water before staining. METHODS OF EMBEDDING. Embedding tissues in paraffin (p. 553).— The tissue is passed from absolute alcohol, in which it has been dehydrated, either through xylol, or spirit of turpentine, or carbon tetrachloride followed by carbon disulphide. Xvlol although freely miscible with alcohol, ether, resins, paraffin, takes up no [572] THE ESSENTIALS OF HISTOLOGY water, therefore very perfect dehydration is neoesBary, and it is advisable to proceed through absolute alcohol and xylol equal parts, before transferring the tissues to pure xylol. This step or the use of xylol-creosote is generally useful in transferring tissues from alcohol to xylol, since it combats the tendency of xylol to produce shrinkage. Xylol is chemically inert, and is therefore suitable for the embedding of material impregnated with silver, gold, or osmium, as it does not affect these. Other ethereal oils, such as tuipentine and cedar-wood oil, oxidise and are therefore unsuitable for metal-impregnated tissue. Tissues must not be left too long in xylol, especially if much connective tissue or plain muscle is present, since the hardening they undergo may make cutting difficult. Spirit of turpentine is freely miscible with alcohol, xj'lol, etc., and, urdike xylol, can take up a moderate amount of water. It interferes with the action of some stains and may be deleterious to metal impregnations. It is not, therefore, suitable for tissues stained in bulk with ha;matoxylin, or by Qajal's reduced silver methods. It penetrates well and makes connective tissue and smooth muscle easy to cut, and is useful for large topographical sections, and for dense tissues such as the uterus, prostate, scalp, etc. It is not very easily extracted in the paraffin bath, but even if » trace remains it does no harm, and has the advantage of keeping the tissue softer and more easy to cut. For tissues containing much smooth muscle or connective tissue it is well to use Mliller's fluid as a fixative, and after dehydration to pass the material through turpentine into parafBn. Carbon disulpkide and tetrachloride. — Even if the purest carbon disulphide obtain- able is used, brown granules will be found in the periphery of the tissue. But if carbon tetrachloride is used first, the tissue remains free from granules, and carbon disulphide is then used to ensure that the tissue will cut easily. Complete dehydration is essential. Since carbon disulphide has an objectionable smell it should be kept in tightly stoppered bottles. (The process of transference is best carried through in one special shelf of a dark cupboard, so that the solutions are disturbed as little as possible and are protected from light.) It penetrates readOy and is easily replaced by paraffin. It is possible to c«t a cry thin sections (2 to 3 /i) by this method. In embedding through carbon tetrachloride and carbon disulpliide, tissues are passed from absolute alcohol into a mixture of absolute alcohol and carbon tetra- chloride, equal parts, then into pure carbon tetrachloride for twenty -four hours. They are given two baths of carbon disulphide, twenty-four hours in each, and embedded, through paraffin saturated with carbon disulphide, in pure paraffin. Embedding in celloidin (Appendix, p. 554) — Da Fano's method for serial sections. — Pieces of any desirable size are embedded in celloidin by means of paper boxes or a similar device which may allow one to arrange them according to the way in which the series will have to progress. At the same time care should be taken that the pieces are surrounded by an amount of celloidin sufficient for subsequently writiaig a progressive number on the sections. The celloidin blocks are stuck to appropriate supports and these are fixpd on the microtome as usual. A rather large, flat glass plate is placed near the 'microtome and covered with a sheet of thick blotting paper of the same size. Tnis is thoroughly wetted with 70 per cent, alcohol. Numbered strips of thin smooth paper are then placed in a given order on the wet blotting paper and cutting is started. The sections are collected from the knife by means of a soft brush and placec^ in series on the paper strips. When a sufficient number of sections has been cut the ftrst paper strip with its sections is lifted from the wet blotting paper and placed on a dry strip. The sections are then gently pressed and dried a httle with a piece of repeatedly folded filter paper. Without any loss of time a number ia written on a corner of the celloidin surrounding the ADDITIONAL NOTES TO APPENDIX [573] sections by means of a small brush with a mixture of 10 o.c. of Indian ink and 3 CO. of equal parts of anhydrous ether and acetonej. The figures dry instantane- ously. If the paper strip with the sections is moved about in a dish of 60 or 70 per cent, alcohol, the sections float in it. One then proceeds to number the sections placed on the second paper strip and so on until all sections are used. The numbers thus written on the ceUoidin are not obliterated by water and common reagents such as alcohol, xylol, the Weigert mordant, the bath used for toning and fixing Golgi-Cox specimens, and so on. Many sections can, therefore, be stained and treated as desired at the same time and finally mounted according to the progression of their numbers ; provided, of course, that media which dissolve ceUoidin are not used. If it is imperative to dissolve the ceUoidin before mounting, the sections should be first arranged in definite serial order on slides previously numbered by means of a diamond point. METHODS OF STAINING AND COUNTERSTAINING. Staining in hulk. — Tissues fixed in various ways, but especially in Bouin's solution, may be stained in bulk with heematoxyUn and eosin as follows : Transfer the tissue to Bhrhch's haematoxylin diluted with 3 parts of distilled water in the case of inverte- brate and embryonic material or with 2 parts of 2 per cent, acetic acid if the tissues are from adult vertebrates. The pieces remain in the dilute hsematoxylin from two to four weeks or longer — according to their thickness, more or less compact structure and state of development — while the hsematoxylin is changed once at the end of the first week. After a quick wash the materipJ is kept for two or three hours in 0-5 to 1 percent. HCl in 70 per cent.- alcohol, washed in tap water overnight, and then passed through the ascending series of alcohols up to 95 per cent, alcohol. This is replaced vvith a 1 per cent, solution of eosin in alcohol of the same strength, and the pieces are left therein for about a week. They are now washed for some hours in 95 per cent, alcohol, dehydrated in absolute alcohol, cleared in xylol and embedded in paraffin. An alternative method of obtaining the eosin counterstain is to add a little eosin to all the alcohols used. DelafieWs hcematoxylin (Appendix, p. 560). — The stock solution must be diluted with distilled water 1 in 5, and should be filtered each day before using. The activity of the stain increases for a few months as it ripens, but after that it decreases. The time necessary for staining sections varies with the sample of stain and the fixative which has been employed. Tissues fixed with Zenker or Flemming are very resistant to Delafield. The best fixative for good nuclear staining with Delafield is alcohol, but " susa," sublimate, formol, or trichloracetic are also good. Sections are stained until the nuclei stand out clearly and the protoplasm and connective tissues are stiU almost colourless when viewed with a low magnifying power. With those fixatives which are more resistant, e.g. those containing chromic acid, it is best to leave the sections in the fluid until they are overstained, and then to differentiate by removing the excess of colour (see below). After staining with Delafield's hsematoxylin the sections are washed for at least ten minutes in tap water, either running or frequently renewed. The slight alkalinity of the water neutralises any acid present ; the sections become blue, losing their reddish tinge. The neutraKsation may be effected most quickly by inverting the sUde over dilute ammonia and exposing to the vapdur for a second, then washing thoroughly in water. Or the neutralisation with ammonia may be done when the sections are in xylol immediately before mounting them. Decolorisation of overstained sections. — If the excess of colour is alight, decolorise [574] THE ESSENTIALS OF HISTOLOGY in distilled water weakly acidulated with acetic acid. The result is a clearing of the sections without harming the nuclear stain. The acid must be thoroughly removed by washing in tap water. If more heavily overstained, use 10 per cent, of concentrated picric acid solution in distilled water. The yellow of the picric acid tones down the bluish shade of the protoplasm and a very pure nuclear stain is obtained. Chromolrop 2M. — This is the best protoplasm stain to use after Delafield's hsema- toxyliii. The sections are rinsed in water, alkaUnised over ammonia vapour, and passed through dilute alcohols to absolute alcohol. They are placed for two minutes in a saturated solution of chromotrop 2R in absolute alcohol, rinsed in alcohol, transferred to xylol and mounted in dammar. Chromotrop gives a beautiful red colour and a very sharp contrast ; it is permanent. Eosin (see Appendix, p. .562, 12). — Delafield stained sections to be treated with eosin must be neutralised only with tap water ; eosin Will not stain well if a trace of alkaU:is present, and will fade in a comparatively short time if alkali remains in the preparation. Chromic-fixed tissues are best for staining with eosin. Thiazin red. — This is a water-soluble, permanent anilin dye to be used after Delafield's hsematoxylin, or Heidenhain's iron-haematoxyUn. Sections stained in hsematoxylin are placed for from two to five minutes in a solution of — Thiazin red, 0-5 per cent, in water 45 c.c. Concentrated picric acid 5 c.c. Alcohol, 96 per cent. 15 c.c. Distilled water 100 c.c. They are then passed through water and alcohol into xylol, alkalinised b,\ inverting over ammonia vapom', and mounted in dammar. Befor'e counterstaining with thiazin red, Delafield hjematoxylin sections require only to be rinsed. Heidenhain iron- hsematoxyUn sections must be washed for fifteen minutes in running or frequently changed tap water. For muscle, cardiac or voluntary, Heidenhain uses thiazin red aft^er iron- hsematoxylin. Or thin sections of tissues fixed in 5 per cent, trichloracetic acid are stained in 1 per cent, thiazin red solution for thirty 7rimutes, then rinsed in distilled water and placed in 1 per cent, water -solution of methylene-blue for from one to two hours ; the excess of blue is in turn removed by 96 per cent, alcohol, and the dehydrated sections are cleared and mounted. Eosindulin. — A saturated solution in absolute alcohol is used after Delafield's haematoxyUn as a contrast stain for developing bone, and is differentiated, if over- stained, in alcohol. Heidenhain's " azan " method. — This is a modification of Jlallory's method (p. 562 of Appendix). It is a very good stain for connective tissue, and is also useful for general purposes. Zenker's fluid, " susa," or other subhmate mixtiu-es are the best fixatives to employ for it, but good results are also obtained after Bouin, formol, etc. Place sections for one hour at .5.5° C. in 0-2 per cSnt. solution of azocarmine Gx acidified with 1 per cent, acetic acid. Rinse in distilled water. Differentiate in 01 per cent, anilin oil in 96 per cent, alcohol until the protoplasm and connective tissue are pale pink and the nuclei stand out sharply. The differentiation proceeds suffici- ently gradually to allow of perfect control, but if too slow a few drops of distilled wator may be added to the alcohol. Control the differentiation by rinsinir in acid alcohol — 96 per cent, alcohol with 1 per cent, glacial acetic acid. This interrupts the process momentarily and gives time for ani examination imder the low power. When the differentiation is complete rinse in this acid alcohol. Transfer to 5 per cent, phoaphotungstic acid for two hours. In this the connective tissue and ADDITIONAL NOTES TO APPENDIX [575] protoplasm become quite colourless. A pure nuclear stain is thus ensured, while the connective tissue is mordanted for the anilin bliie. Rinse in distilled water. Counterstain with orange G and anihn blue. For this purpose a stock solution is prepared as follows : — Orange G 2 gm. Anilin blue, water-soluble (Griibler) 0-5 gm. Acetic acid 8 c.c. Distilled water 100 c.c. Dilute for use with twice its volume of water. Stain until the very finest fibres of connective tissue are sharply stained ; rinse with distilled water. Dehydrate quickly through 96 per cent, absolute alcohol, and clear in xylol, mount in dammar. Azocarmine Gx (Badische Anilin- u. Soda-Pabrik) is an acid anihn dye, obtained as a dark red powder, very insoluble in water. A 0-2 per cent, solution is made with boiling distilled water and is filtered on cooling, and acidified with 1 per cent, acetic acid. This contains very fine needle crystals, but at the staining tem- perature these are in solution. Note that in the counterstain Heidenhain has replaced the oxalic acid of ordinary Mallory with acetic acid, since oxahc acid is harmfxil to azocarmine. The " azan " method coloiu'S all the nuclear chromatin red, protoplasm pink, connective tissue, including basement membranes and the fine reticular fibres of lymph glands, blue ; muscle yellow to red, according to the fixative ; coUoid materia] blue ; bone-corpuscles red ; cell-granules red, yellow, or blue, according to their nature ; neurogha red. The method brings out very clearly the presence of small bundles of plain muscle- cells lying in much connective tissue. It is useful for embryological tissues, for lymphatic structures, and for all glandular organs, especially the thyroid and ovary. It is very permanent. Aix)carmine B. — This is an acid, water-soluble anilin dye. Sections are first stained in Delafield's hsematoxylin for ten miautes, rinsed in distilled water, and then placed for ten minutes in the following solution : — Azocarmin B, 1 per cent. 3000 c.c. Distilled water 6000 c.c. Glacial acetic acid 2 to 3 drops Differentiate in 1 per cent, picric acid solutionj rinse in distilled water, bring through alcohols to xylol, alkahse over ammonia, and mount. This is a good and permanent stain after Delafield. Heidenhain uses it as a selective stain for oornified substance, differentiation being continued until the red coloration has faded from the other tissues. It is recommended for striated muscle (Walker). Azocarmine with indigo carmine and picric acid (Walker). — Sections fixed with " susa " are stained fifteen to thirty minutes in a solution of azocarmine Gx at 55°, and differentiated in anUin alcohol. They are rinsed in acid alcohol and placed for fifteen minutes in a solution of 0-2 per cent, of indigo carmine in a saturated aqueous solution of picric acid. They are dehydrated in absolute alcohol, cleared in xylol, and mounted in dammar. Counterstain for Nissl's method (Appendix, p. 5|)5, 28). — Sections after being stained in a solution of I per cent, toluidin blue containing a trace of sodium bicar- bonate, for tliirty minutes, at a temperature of 37° C, are counterstained by alcohol to which has been added 1 per cent, of a saturated solution of chromotrop 2R in absolute alcohol. The chromotrop hastens the differentiation, faintly tinges the ground tissue of the section and increases the permanence of the blue stain. After the desired [576] THE ESSENTIALS OF HISTOLOGY point of difierentiation is reached the sections may be placed for ten minutes in a 5 per cent, solution of phosphotungstic acid in water ; this ensures permanence. Milochondria and Centridles. Eegaud's iron-hcematoxylin method. — Small pieces df fresh tissue are fixed in a mixture of 4 parts of 3 per cent, potassium bichromate and 1 part of commercial formalin (neutralised over calcium carbonate) for fouj days, changing the mixture every day. Mordant in 3 per cent, potassium bichromate for eight days, changing every second day. Wash in running water, twenty-four hours. Dehydrate in alcohols of increasing strengths, commencing with 30 per cent., pass through equal parts of absolute alcohol and xylol, clear with xylol, embed in paraffin melting at 56' to 58" C. The sections must be as thin as possible and mounted by the albumen method. Pass them quickly through xylol and absolute alcohol down to water, and mordant them in 5 per cent, iron-alum at 36° C. for twenty-four hours. Rinse in distilled water and stain for twenty-four hours in hscmatoxyhn made up by dissolving 1 gm. of haematoxylin (cryat.) in 10 c.c. of absolute alcohol and adding 10 c.c. of gljcerine and 80 c.c. of distilled water. Differentiate in 5 per cent, iron-alum under micro- scopic control. Wash in tap water, dehydrate, clear and mount in the usual way. In successful specimens, besides mitochondria, nuclei and centrioles aie stained. Cowdry's method. — Treat the tissue as by Regaud'S method until the sUdes with the sections on them are in distilled water. Pass them for about thirty seconds into 1 per cent, potassium permanganate, rinse in distilled water and bleach in 5 per cent, oxalic acid for about thirty seconds ; wash in several changes of distilled water ; stain with Altmann's anilin fuchsin prepared as follows : Add some anihn oU to 100 c.c. of distilled water, shake and filter ; add 10 gm. of acid fuchsin ; shake vigorously and let stand for twenty-four hours : it must be used within a month. To stain, dry the slide with a cloth, except the small area on which the section is placed ; cover the section with the stain and heat over a flame" until fumes come off ; allow to cool for about six minutes ; return the excess of stain to the bottle, and rinse the slide quickly in distilled water. AUow a little 1 per cent, methyl green in water to flow from a pipette over the section, holding the slide over a piece of white paper so that the colour may be seen. Apply the methyl green for five seconds at first and modify as required. Drain ofi excess of stain ; plunge into 96 per cent, alcohol ; rinse in absolute alcohol, clear in xylol or toluol ; mount in balsam or dammar. In successful specimens the nuclei are green, while mitoehondria and certain secretion granules (pancreas) are red. Modification of the Champy-Kull method. — Very sma,ll pieces are fixed in the slightly modified Champy fluid suggested by Kolatschev ; this consists of 4 parts of 1 per cent, chromic acid, 4 parts of 3 per cent, potassium bichromate, and 2 parts of 2 per cent, osmic acid ; to each 10 c.c. of this mixture 2 to 3 drops of a 01 per cent, solution of pyrogaUic acid may be added. After twenty-four hours the pieces are washed for some hours in running water and placed (Nassonov) for three to seven days m 1 per cent, osmic acid at room temperature in summer, in an incubator at about 30° C. in winter. After washing, dehydrating, and embedding in hard paraffin, sections are made and fixed to sUdes by the albumen method. The sections, which need not be bleached, are stained with Altmann's anilin fuchsin a* by Cowdry's method. Rinse in water and counterstain for one to two minutes with either 0-5 per cent, toluidin blue or 1 per cent, thionin ; wash in distilled water ; differentiate for twenty to thirty seconds in 0-5 per cent, solution of aurantia in 70 per cent, alcohol ; pass through 96 per cent, alcohol, absolute alcohol and xylol into balsam or dammar. This method is difficult, but it is important for the study of the relationship between ADDITIONAL NOTES TO APPENDIX [577] mitochondria, Golgi's apparatus, and secretory activity in certain glandular organs. In successful specimens the nuclear chromatin is bluish ; mitochondria, purple-blue to purple-violet ; secretion granules, golden-red ; ground cytoplasm, golden-yellowish ; Golgi's apparatus, black. Oolgi's Internal Apparatus. The fixation is important. In general a fixation with osmic-ohromio mixtures is good. The methods of Cajal (uranium nitrate). Da Fano (cobalt nitrate), and Golgi (arsenious acid) are also useful. CajaFs method. — Pieces of fresh tissue, 4 mm. thick, are placed in Uranium nitrate - 1 gni. Neutral forniol 15 o.o. Distilled water 85 o.c. Tor the Golgi apparatus it is best to use tissue from young mammals, and fixation must only be for from ten to twelve hours ; for neuroglia twenty-four to forty-eight hours. Rinse in distilled water and place in 1-5 per cent, silver nitrate solution for two or more days at room temperature. Wash quickly in distilled water and reduce for twenty-four hours in Hydroquinone 1 gni. Formol 5 o.o. Distilled water 50 c. c. Sodium sulphite, just sufficient to give a yellow tinge to the solution. Rinse with water, dehydrate, and embed either in paraffin or celloidin. Da Fane's method. — ^This is a modification of CajaFs uranium nitrate method, and is recommended for routine work, as it seldom fails. Pieces of quite fresh tissue no more than 4 mm. thick are fixed for six to eight hours in a solution of cobalt nitrate 1 gm., distilled water fOO c.c, formahn 15 c.c. The solution can be prepared beforehand and keeps unaltered indefinitely. The formalin need not be neutrahsed unless strongly acid. ¥ox embryonic organs and in all cases in which a shrinkage of delicate tissues is to be feared the quantity of formahn may be reduced to 10, 8, or even 6 o.c. for every 100 c.c. of distilled water, particularly during the first one to two hours of fixation, after which the fixing fluid is changed for one containing the usual amount of formalin. In the case of tissues from invertebrates this can usefully be raised to 20 c.c. for every 100 of distUled water. The time of fixation should be reduced to two to four hours for very small organs such as spinal gangha, pituitary body and suprarenals of mice and rats, as well as small pieces of pancreas, etc. Pieces of spinal cord, cerebrum, and cerebellum from adult mammals give the best results if fixed for ten to eighteen hours. If fixation is carried out in an incubator at 25^ to 36^ C, mitochondria stain frequently at the same time as the Golgi apparatus. After fixation the pieces are quickly washed in distilled water and transferred to 1 -5 per cent. AgNOg for about two days at room temperature. Each piece is then spUt into two halves, and after a quick wash passed into Cajal's reducing fluid (see above). Dehydrate through the ascending series of alcohols, clear with cedar-wood oil, embed in paraffin. The sections can be stuck to shdes in series, toned, fixed, counterstained, and finally mounted in balsam or dammar in the usual way. Golgi's method. — The tissues are fixed for twenty-four hours in equal parts of 20 per cent, formalin, saturated solution of arsenious acid, and 95 per cent. alcohol. [578] THE ESSENTIALS OF HISTOLOGY They are then transferred to 1 per cent, silver nitrate solution, in which they are left for some hours (up to forty-eight) ; rinsed in distilled water and transferred to Cajal's reducing fluid. Alter reduction, wash in water, quickly dehydrate with alcohol, and embed in paraffin. The sections can be afterwards toned (see p. [582]). N euro- Fibrils, Nerve- Endings, Nerve-CeMs, Neuroglia, etc. KultscMizky' s method for motor and sensory endings in muscle. — Small shreds of perfectly fresh muscle, preferably snake or lizard, are. placed in 20 per cent, formic acid or in lemon juice. Use as Uttle fluid as possible in proportion to the amount of tissue. Keep the tissue well under the surface, by touching with a glass rod, and leave until transparent (five to fifteen minutes, depending on size). Throughout, no metal instrument must touch the tissues, and only needles of glass or of unoxidisable metal and bone or paraffin-coated forceps should be used. Transfer to a glass plate and remove the excess of acid with filter paper. Place in 1 per cent, gold chloride 1 part 20 per cent, formic acid 3 parts for half an hour, or until the tissue takes on a distinct yellow tone. Remove the excess of fluid again with filter paper, and keep in 20 per cent, formic acid in the dark, or in water acidulated with a few drops of acetic acid in the hght. Leave at least twenty-four hours, preferably two to three days. Transfer to glycerine and water equal parts, or glycerine, water, and alcohol, equal parts, and keep in this. Examine small pieces from time to time. It may be good immediately, but may improve up to one or two years. When good preparations are obtstined they may be mounted in glycerine and ringed with gold size, or in Apathy's fluid, which is made as foUows : — Pure gum arabio 50 gm. Crystalline cane sugar 50 gm. Distilled water 50 c.c. Dissolve over a water bath and add thymol '05 gm. Kultschitzky's method for nerve-endings in tendons. — Small shreds of tendon are fixed and stained overnight in 3 per cent, uranium nitrate 100 c.c. 1 per cent, osmic acid 1 c.c. They are then mounted in glycerine, in Apathy's fluid or, after dehydi-ating and clear- ing, in dammar. Ruffiiifs method for nerve-end ings in muscle and tendon. — Pieces of fresh tissues are immersed in a 25 per cent, solution of pure formic acid for ten to fifteen minutes, using the minimum quantity of fluid for complete immersion. They are then trans- ferred from the acid and pressed gently between the folds of a clean towel or filter paper to absorb as much acid as possible. They are now placed in a 1 per cent, gold chloride solution — sufficient only to cover them thoroughly — ^for fifteen minutes, using no metal instrument, but agitating until they become an even golden brown. After the excess of fluid is removed by a cloth or filter paper, they are again placed in a minimum quantity of 25 per cent, formic acid and left in absolute darkness for twenty-four hours. The colour becomes reddish-purjle ; if stiU light red or yellow ADDITIONAL NOTES TO APPENDIX [579] leave for a longer period ; if very dark purple the tissue has been over-reduced and must be retoned in the gold solution. Remove the excess of fluid again as above, transfer to pure glycerine, and leave in ordinary light in a closed vessel. The longer the tissue is left in glycerine the clearer it becomes ; the best results are got in tissue examined after several years. Golgi's rapid silver method for nerve-cells (Appendix, p. 565, 26, /3). — Recom- mended for young or foetal vertebrate tissues and adult invertebrate. The tissues must be absolutely fresh and not larger than 4 mm. cub. They are fixed for two to five or six days, or, in the case of young embryos, for two to three or four days, in the bichromate-osmium mixture. The container is sealed with paraffin and kept in the dark in an incubator at 22° to 24° C. The pieces of tissue are rinsed in a small quantity of 0-75 per cent, silver nitrate before being placed in a larger amount of the same fluid for thirty hours or more. In addition to the double method referred to in the Appendix, p. 365, as used by Cajal, the same authority recommends a third impregnation if necessary, the tissue being returned for a third time to bichromate- osmium mixture and retransf erred to silver nitrate solution. Exact times must be found out by trial for each tissue, the times varying with the species and age of the animal and the particular tissue to be studied. Thus, neuroglia-oells usually require from two to three days in the osmic- bichromate mixture, ganglion-cells three to five days, and nerve-flbres five to six days. CajaVs rapid silver method. — ^Tissues fixed in 14 per cent, formol for fourteen days or longer are cut with the freezing microtome and received again into the formol solution. They are rinsed in two baths of distilled water and rapidly immersed in 2 per cent, silver nitrate - 10 c. c. Pyridin 5 drops In this they are heated to below 50° C. until they become dark brown, or if con- venient they may remain in the dark, at room temperature, for twelve to forty-eight hours. Sections are rinsed for half a minute in 96 per cent, alcohol to which 2 drops of a 2 per cent, silver nitrate solution may be added and are then reduced in Hydroquinone 0'2gra. Formol 30 c.c. Distilled water 70 c.c. The reduction is rapid, a few seconds being sufficient. The sections are rinsed in water, transferred to absolute alcohol, cleared in origanum oil or in carbol-xylol, and mounted in dammar. Chromate of mercury method for nerve-cells (Appendix, p. 565, 27). — This method can be used for the impregnation of relatively large pieces of nervous tissue from young and even adult vertebrates as well as for whole brains of small animals. The impregnating fluid should be renewed once after twenty-four hours and agaia on the third or fourth day. The container should be kept in an incubator at 22^ to 24° C. for about a month and at room temperature for another six months or longer. The material is then washed for some hours in running water, passed through many changes of alcohols of ascending strength, starting from 60 per cent., and embedded in ceUoidin. The blocks can be preserved indefinitely in 70 per cent, alcohol. If a sufficient amount of oelloidia is left round the pieces a progressive number can be written on the sections by Da Fano's method (see p. [572]). The sections, which should be 20 to 40 /j. thick or more, are floated in 70 per cent, alcohol, passed through a weaker alcahol and washed in running tap water for half an hour. They are then collected in distilled water and transferred for about ten minutes to 5 or [58o] THE ESSENTIALS OF HISTOLOGY 10 per cent, ammonia. After another prolonged wash in repeatedly changed dis- tilled water they are toned by means of the following solutions : — (a) Distilled water 1000 c.c. Sodium hyposulphite 155 g™- Potassium alum 20 gm. Ammonium thiocyanate 10 gm. Sodium chloride 40 gm. Allow to stand for eight days and then filter. This solution keeps for months, and can be used even if it becomes turbid, (6) Gold chloride 1 gm- Distilled water 100 c.c. At the moment of use, filter into a glass dish 50 c.c. of solution a, 40 c.c. of old (used) combined bath, and 7 c.c. of solution 6. The sections are transferred from the distilled water into this bath and kept therein for half an hour, or longer if they are rather thick. They are then washed for a;nother half hour in repeatedly changed distilled water, while the toning and fixing mixture is poured into a bottle and kept for further use as " old combined bath." It is not necessary to bleach the sections, which can be faintly counter- stained with a dilute solution of alum-carmine. This may be preserved in a separate bottle for further use. The sections are finally passed through alcohols of ascending strength up to 95 per cent., cleared with carbol-xfylol and mounted in balsam or dammar under thin coverslips. The specimens keep unaltered for j'ears. Modifications of Cajal's methods for exhibiting neuro-fihriU (see Appendix, p. 566, 29). — In addition to a and (i several different fixation fluids are recommended by Cajal. Of these the most useful are the following : — (a) Instead of rectified spirit, as in 29, a, 95 per cent, alcohol to which has been added three to five drops of ammonia to each 50 c.c. may be used. Fix for twenty-four hours and then proceed as in a. (h) Tissues are fixed for twenty-four hours in 70 per cent, pj-ridin, washed for at least twelve hours in running water to remove all traces of pyridin, then placed in ^ absolute alcohol for twenty-four hours. They are dried superficially with filter paper and transferred to the silver bath. Useful for peripheral nerve-endings. (c) For endocrine organs and peripheral nerve-endings in general, the tissue may be placed in the following fluid : — Chloral hydrate 5 gm. Absolute alcohol 50 c.c. Distilled water 50 c,c, for two days, then transferred to ammoniacal alcohol as in (a). (i) For tissues which require at the same time to be decalcified the best method (De Castro) is to fix for twenty-four hours in the following : — Urethane 2 gm, (or ohloralhydvate 5 gni,) Alcohol 40 c,c. Distilled water 40 e,c. Concentrated nitric acid ,"? c,c. The tissues are then washed for twenty-four houjs in running water and trans- ferred to ammoniacal alcohol, as in (a), for twenty-fbpr hours, before placing in the silver bath. ADDITIONAL NOTES TO APPENDIX [581] Eor adult mammals in all cases the silver bath should contain 3 to 5 per cent. AgNOg in preference to weaker solutions, but for young mammals 1 -5 per cent, is a useful routine strength, while for embryos and very young mammals and for invertebrates 0-75 is sufficiently strong. Oajal's gold-sublimate method for neuroglia. — Absolutely fresh material is placed for two to fifteen days in 15 c.c. of neutral formol, 2 gm. of ammonium bromide, and 85 c.c. of distilled water. This fixation is for the neuroglia of both grey and white matter ; with longer fixations only the astrocytes of the white matter will be stained. Sections are out frozen, 25 to 30 /* in thickness, rinsed rapidly in distilled water and placed in the following solution : — Gold chloride (brown variety), 1 per cent, solution 6 c.o. Mercuric chloride crystallised in needles 0'5 to 0'8 gm. Distilled water 38 c. e. Dissolve the mercuric chloride in the gold chloride solution at the moment of use. The above amount is sufficient for about six large sections. They are flattened out carefully, by means of a glass rod, on the bottom of a glass crystallising dish sufficiently small to give a depth of about 1 cm. of fluid. After four to six hours at 18° to 22° C. the sections take on an intense purple- red tone, and are then transferred to a bath of distilled water and left for several minutes. They are fixed in Sodium hyposulphite, 5 per cent. 40 c.c. Alcohol, 96 per cent. - 10 c.c. for from six to ten minutes. After washing for several minutes in one-third alcohol they are arranged on slides, dried by firm pressure with fine filter paper, then treated with absolute alcohol, origanum oil, and xylol, and mounted in dammar. The method gives good results with human, mammahan, and all vertebrate tissues. Del Bio-Hortega's rapid silver method ftyr normal and pathological tissues. — Tissues are fixed in formol for five days at room temperature, ten to fifteen hours at 37°, or ten minutes at 60°. They are cut frozen, 20 jj. thick, and washed in several baths of distilled water, then placed in a solution of silver carbonate prepared as follows : — Silver nitrate solution, 10 per cent. 50 c.c. Sodium carbonate solution, 5 per cent. - 150 c.o. Add pure ammonia very carefully until the precipitate is dissolved, then 500 c.o. distilled water. Keep in the dark in brown glass bottles. The solution containing the sections is warmed over a spirit lamp to 45° to 50°, and kept gently agitated at this temperature for one to two minutes until the sections become pale yellow, when they are transferred to 2 to 10 per cent, formol, where they become dark yellow. They are toned in 0-2 per cent, gold chloride solution at room temperature until they become dark grey, then warmed until they become purple. They are fixed in 5 per cent, sodium thiosulphate s'olution, and may be counter- stained. Dehydration is through alcohol, carbol-xylol, to dammar or balsam. For connective tissue, especially when it is difficult to colour, e.g. that of striated muscle, give a preliminary bath in 2 per cent, silver nitrate at 40° C. until sections are yellow, then transfer, after rinsing in distilled water, to the silver carbonate bath with 2 drops of pyridin added to each 40 c.c. until they become dark brown. The sections are again rinsed in distilled water and transferred singly to the 10 per cent, formol (where they become very dark) and toned as above. If the tissue is fixed by formol-bromide as in C^ajal's gold-sublimate method, [582] THE ESSENTIALS OF HISTOLOGY and if the sodium carbonate (see above) is replaced by lithium carbonate (saturated solution), the method is suitable for neuroglia. Toning of Sections Stained by Silver Methods. The very dilute solution of gold chloride suggested in the Appendix, p. 566, 30, is too weak ; a solution not weaker than 0-2 per ceiit. is as a rule needed. It is, however, not usually necessary to have recourse to an exact dilution. It is more convenient to have some 1 per cent, solution of gold chloride ready in a drop- bottle, by means of which it is added to a dish containing 30 to 50 c.c. of distiUed water. Add as many drops of the 1 per cent, solution as wiU give the water a bright yellow colour, and then three to four drops of acetic acid. The sections, no matter whether from ceUoidin or parafiin blocks or made by freezing, are transferred to the gold bath from distiUed water and kept therein until the peculiar yellowish -brown colour of the untoned sections has disappeared. Microscopical control may occasionally be necessary. The -operation should be carried out by daylight. A\'ash the sections in distilled water, pass them for a few minutes through 5 per cent, sodium hyposulphite, wash again, counterstain if desirable, dehydrate, clear, and mount in balsam or dammar. Por toning sections exhibiting either neuro-fibrils or the Golgi internal apparatus of cells, the following solutions may be used : — (a) Sodium hyposulphite 3 gm. Ammonium sulphocyanate 3 gm. Distilled water 100 e.e. (h) Gold chloride 1 gm. Distilled water 100 cc. Equal parts of (a) and (6) are taken and mixed just before use. This mixture strengthens the impregnation ; it should only be used when it seems necessary to do this. However, if after toning the background is too dark, the sections can be carefully bleached by Pal's method. AftOr toning (and bleaching) thev are washed in distiUed water, dehydrated with alcohols, cleared, and mounted iu the usual way in balsam or dammar. INDEX. ACH Achromatic apindle, 8, 18, 19 Adenoid tissue, 91 Adipose tissue, 81, 8S Adrenals. See suprarenal capsules Agglutination of blood corpuscles, 51 — of blood-platelets, 38, 57 Air-bubbles, '28 Ameloblasts, 316 Amitosis, 11 Amoeba, 3 Aniceboid movements, 3, 6, 7, 8, 35, 36, 37, 46, 55 Aniline dyes, 561 Ansa lentioularis, 481, 484, 507 Aorta, 212 Appendix, vermiform, 359 Aqueduct, 471 Arachnoid, 423, 508 Archoplasm,'8, 403 Arcuate iibres, 448, 449, 478 Areolar tissue, 81, 82 cells of, 84 fibres of, 82 Arrector pili, 282 Arteries, vessels and nerves of, 221 — structure of, 209 — variation in structure of, 212 — and veins, smaller, structure of, 217 Articular corpuscles, 193 Association fibres, 496 Attraction particle, 8, 18, 19 — sphere, 8 Auditory hairs, 540, 547 — meatus, 538 Auerbaoh, plexus of, 344, 348 Auriculo-ventricular bundle, 290 Autonomic nerves, 153 Axis-cylinder, 149, 163, 183 Axon, 158, 183 Bacteria, 29 Baillarger, lines of, 495 Basement membranes, 96 Basilar membrane, 541, 544 Basket-cells, 487 Bechterew, nucleus of. See nucleus Bellini, ducts of, 378, 380 Bethe's fluid, 567 Bielchowsky's method for neurofibrils, 566 Bile-channels, 367 Bile-duets. 388 Bladder, 374 CAP Blastoderm, 23 Blood, 30 Blood-oells, 38 Blood - corpuscles, action of reagents upon, 49, 52 — of amphibia, 53 — coloufed, 33, 48, 53 — colourless, 33, 35, 52, 55 amoeboid phenomena of, 58 granules of,- 35 migration of, 59, 62, 220 varieties of, 35, 36 — development of, 41, 43, 47 — enumeration of, 32 — human, 30 — structure of, 33, 49 Blood-crystals, 49, 62 Blood-film, 31 Blood-islands of Pander, 42 Blood-platelets, 30, 33, 38, 57, 221 Blood-vessels, development of, 41, 222 — structure of, 207, 216 Bone, 81. 112 — development of, 118, 127 — lacunae and canaliculi of, 114, 117 — lamellffiof, 114, 117 — marrow of, 45, 113 Bowman, glands of, 5.37 — membrane of, 512 Brain, 443. Sf. cerebrum, cerebellum, medulla oblongata, mesencephalon, pons — divisions of 443 — membranes of, 508 Brain-sand, 263 Bridging fibrils, 66, 146, 267 Bronchi, 299 Bronchial tubes, 299 Bronchioles, respiratory, 300 Brownian< movements, 29 Brueh, membrane of, 518 Briinner, glands of, 341, 353 Bundle. See tract Burdach, tract of, 430, 448 Cajal's methods for neurofibrils, 566 Calleja, islands of, 464, 503 Canaliculi, bile, 368 — of bon^, 114 — of nerve-cells, 162 Capillaries, 218, 220 — circulation in, 220 — lymphatic, 227 569 S70 INDEX CAB Garnoy's fluid, S.'il Carotid gland, 254 Cartilage, 81, 100 — articular, 104 — calcified, 104 — costal, 106, 107 — development of, 110 — embryonic. 111 — fibro-, 100, 100, 109 — hyaline, 101, 106 — ossification of, 119 — parenchymatous, 110 — transitional, 104 — varieties of, 100 Cartilage-bone, 119 Cartilage-cells, 101 — capsules of, 101 Cell,"division of, 11 amitotic, 11 reduction, 16 — embryonic, 1, 23 — membrane of, 2, 9, 7 — nucleus of, 2, 10, 12 — structure of, 2 Celloidin, embedding in, 534 Cell-plate, 19 Cell-spaces, 2, 80, 82 Cement of tooth, 309, 315 — substance, 2, 63 . Central canal of cord, 424, 426, 448 — fovea of retina, 532 — tendon of diaphragm, 216 Centriole, 8 Centrosome, 8, 13 Cerebellum, 485 — grey matter of, 486 — peduncles of, 490 inferior, 490 middle, 459, 490 superior, 470, 472, 480, 490 Cerebrum, 485 ^ basal ganglia of, 506 — cortex of, 491 . structure of different parts, 497 — peduncle of, 476 Chemotaxis, 8 Ctiondrin-balls, 101 Choroid coat of eye, 510, 518 — plexuses, 508 Chromatic substance, 10 Chromatolysis, 177 Chromaffin or chromaphil cells, 253, 254 Chromomeres, 11 Chromosomes, 11, 13, 10, 17, IS Cilia, 72, 78 — action of, 72, 78 theories regarding, 79 Ciliary muscle, 520 Circulation, 216, 220 Clarke, column of, 438 ClasmatocytijH, 86 Claustrum, 494 Clitoris, 422 Oocoygoal gland, 254 DIV Cochlea, 535, 54 1 — canal of, 540, 542 Cu'lom, 231 Cohnheiip, areas of, 131 — method of staining nerve-endings, 564 Collagen, ^3 Collaterals, 106 Colliculi, 476 CoUiculus riervi nptiei, 523 Colloid substance, 255, 2lj0 Colostrum-corpuscles, 287 Columella, 541 Commissiiral fibres, 47s, 495 Commissures of cereV)rum, anterior, 505 — • — posterior, 478 — of spinal cord, 424 Conjunctiva, 510 Connective tissue, cells of, SO, X4 development of, 97 fibres of, 82, 83, 93, 94 — — jelly-like, 96 — tissues, 1, 80 Corium, 269 Cornea, yll, 512 — nerve-endings in, 200, 515 Corpora albicantia s. mamniillaria, 483, 506 — geniculata, 481 — quadrigemina, 47(i Corpus cavernosum, 387 — luteum, 410 — spongiosum, 387 — striatum, 506 — subthMamicum, 4S4 Corti, organ of, 536, 544 — rods of, 544 Cotton fibres, 29 Cowper, glands of, 3S!I Cox, chcomate of mercury, method of. 5B5 Crista acustica, 540 Crus cerebri, 476 Crusta, 475, 507 — petrosa, 309,315 Cupula tcrminalis, 541 Cutis vera, 266, 269 Cytomitome, 8 Cyton, 158 Cytoplasm, 2, S Dkcalcifyini; fluids, Xi'?, Deoidua, 419 Decussation of pyi''""ids, 443 DeitoTH, cells ^)t', 547 nucleus of, 457, 4()1 Delafield's ha!niat Tetrads, 16 Thalamencephalon, 444, 459, 480 Thalamus, 480, 506 Thermotaxis, 8 Thigmocytes, 40 Thrombocytes, 38, 57 Thymus gland, 232, 246 Thyroid body, 25(1, 2.")4 Tissues, enumeration of, 1 — formation from blastodermic lajers, 23 Tongue, 320 Tonsils, 2.32, 243 — pharyngeal, 244 Tooth. Sff teeth Trachea, 295 Tract or tracts, methods of stud5'ing, 4.30 • Tract or tracts or bundle — anterior (ventral) longitudinal. Si.t tectospinal tract — anterolateral (ventro-lateral) ascend- ing. iSee tract of (Jowers — descending. 6Ve tractof Loewenthal — ascending, 430, 431, 432, 430, 467 — bulbo-thalamio. iSee tract of fillet — of Burdach, 4S0, 448 — central of acoustic, 474 of cranial nerves, 469, 480, 482 of tegmentum, 4."i(l, 465 — cerebello-bulbar, 4.54 — comma, 432 — of cord, 430 — cortico-bulliar, 464. 468 — corticopontine, 4,V.l, 47(i — corticospinal, ^'(l pyramid tract — crossed pyramidal. iS'i ' pyramid tract — descending, 430, 432, 434, 43.i, 4li4 465, 478 — descending cerebellar, 434 — direct pyramid. Ste. pyramid tract — dorsal or posterior longitudinal, 434, 449, 4.57, 461. 4H,5, 472 — myelination of, 430 — of fiUgt, 44H, 449, 4.'ili, 474, 480 — of Flenhsig, 436, 450 ~ of (loll, 430, 448 — of (iowers, 436, 4.iO, 4T0 — of (iuddcn, 474, 483 — of Holweg, 436 — of Lissauer, 43(i — of Loewenthal, 434, 4r>7 — of Marie, 438 — of Meyncrt, 473, 476, 478, 4S3 — of Mon'akow, 434, 46(i, 472 — of Miinzer, 473 — of Pick, 446 — of Risien Russell, 490 INDEX 577 TRA Tract or tracts or bundle — of Vioq d'Azyr, 483 — olfactory, 502, 503 — olivo-cerebellar, 450 — olivo-splnal. .SVe tract of Helweg — optic, 469, 477, 478, 480, 481 , — ponto-spinal, 434, 467 — prepyramidal. See, tract of Monakow — pyramid, 432, 444, 445, 459, 464, 476 — rubro-spinal. fee tract of Monakow — spinocerebellar, 436, 450, 470, 490 — spino-tectal, 436 — spinothalamic, 436, 480 — sulco-marginal, 438 ' — 'tecto-spinal, 434, 449, 467, 473, 478 — thalamo-bulbar, 468 — thalamo-olivary, 450, 467 — transverse peduncular, 479 — ventral or anterior longitudinal. See, tecto-spinal tract — vestibulo - motor. See dorsal or posterior longitudinal tract — vestibulo-spinal, 465, 467 Trapezium, 455, 460 TrophospongiiTm, 5, 162 Tubercle of Eolando, 447 Tuberculum acusticum, 455 — olfaotorium, 503 Tympanum, 538 Ueetee, 385 Urethra, 388, 389 Urinary bladder, 385 Uriniferous tubules, 375, 380, 382 Uterus, 404, 413 Utricle, 540 ZYM Vagina,. 422 Vas deferens, 393 Vasa vasorum, 221 Vasoformative cells, 43, 223 Veins, structure of, 207, 213 — valves of, 214, 215 — variations in, 214, 217 Ventricle, fourth, 448, 457, 470 — lateral. 483 — third, 444, 480, 483 Vermiform appendix, 359 VesicuUe seminales, 395 Villi, arachnoidal, 508 — chorionic, 419 — of intestine, 353 — of synovial membrane, 104 Vitellus, 408 Vitreous humour, 534 Volkmann, canals of, 115 Wallekian degeneration, 175, 430 Wander-cells, 87 Warming apparatus, 58 Weigert-Pal method for staining sections of the nervous system, 664 Wharton, jelly of, 98 Woollen fibres, 29 Wrisberg, nerve of, 461 Yeast, 28 Yolk, 408 Zenker, fluid of, 552 Zinn, zonule of, 534 Zymogeri, 331 PRINTED IN GREAT BRITAIN AT THE DARIEN PRESS, EDINBURGH