THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA PRESENTED BY PROF. CHARLES A. KOFOID AND MRS. PRUDENCE W. KOFOID NORTHWESTERN U#TVERS!TY MEDICAL SCHOOL LIBRARY. A MANUAL HISTOLOGY EDITED AND PREPARED BY THOMAS E. SATTERTHWAITE, M.D., OF NEW YOKK President of the New York Pathological Society, Pathologist to the St. Luke's and Presbyterian Hospitals, etc. IN ASSOCIATION WITH DRS. THOMAS D WIGHT, J. COLLINS WARREN, WILLIAM F. WHITNEY, CLARENCE J. BLAKE, and C. H. WILLIAMS, of Boston; DR. J. HENRY C. SIMES, of Philadel- phia ; Dit. BENJAMIN F. WESTBROOK, of Brooklyn ; and DHS. EDMUND C. WENDT, ABRAHAM MAYER, R. W. AMIDON, A. R. ROBINSON, W. R. BIRDSALL, D. BRYSON DELAY AN, C. L. DANA, and W. H. PORTER, of New York City WITH ONE HUNDRED AND NINETY-EIGHT ILLUSTRATIONS NEW YOKK WILLIAM WOOD & COMPANY 1881 COPYRIGHT BY WILLIAM WOOD & COMPANY 1881 TROW'S PRINTING AND BOOKBINDING COMPANY 201-213 East iztk Street NEW YORK PREFACE. FOR some years past there has been a general demand among the members of our profession for a manual of Histol- ogy, summarizing, in concise and plain language, our present knowledge in this fundamental branch of medicine. It is true many books have been written on the subject, but their great brevity, on the one hand, or an unnecessary diffuseness on the other, have prevented them from meeting with acceptance at the hands of physicians and students. In the one class belong the little handbooks of Rutherford and Schaefer, which have done much to simplify and therefore popularize histology, but they were intended for beginners, and especially students doing class-work under the laboratory system now so much in vogue. But both physician and student need something of wider scope, and they have been compelled to turn to Klein & Smith, Strieker, or Frey 1 , though no one of these excellent works is thoroughly adapted to their wants. Apart from the expense of the two former, they all are deficient in matters relating to human histology. The practical experience of a teacher made it evident also that the volume to fill such an obvious gap should take the form of a text-book. And the present time seemed opportune for its appearance, since we have latterly made much positive IV PREFACE. advance in liistological studies, while liistologists themselves are now more of one mind in microscopical matters. That such . a book should appear under American auspices seemed further to be eminently proper, as we have in various parts of the coun- try a goodly number of medical men who are either engaged in teaching histology or in studying some special branch of it. The advantages of utilizing their accumulated experiences was therefore apparent by the editor, and he gladly applied to them for assistance when it was found that one individual could not prepare the volume within a reasonable time or in a manner that would be satisfactory. It is hoped that the names of the collaborators furnish a sufficient guarantee that proper representatives of American histology have been selected. In some respects the object sought for has not been wholly attained, as, for example, in the effort to separate purely human histology from the comparative. But this is impossible at the present time, mainly because our knowl- edge is still too limited. It is a matter of regret, also, that the original illustrations have been so few in comparison with the total number, but the great expense attending their production would not warrant any one in attempting much in this direc- tion. Through the kind co-operation, however, of Messrs. Wil- liam Wood & Co., the editor has been able to utilize many excellent cuts that were in their possession. As a further means of relieving the tedium associated with a work that is so largely descriptive, the various authors havo aimed to intersperse here and there throughout the text mat- ters of physiological or pathological import. Still, intelligent practitioners do not have to be reminded that rational thera- peutics has found a substantial support in the revelations of pathological anatomy, which, in turn, rests upon histology, PREFACE. y so that the relation between microscopic anatomy and the sci- entific practice of medicine is readily appreciated. Emanating as the v.olume does from American sources, the editor finds it a fitting place to give proper space to American contributions, and the reader may therefore find due notice of the physiological desquamation of blood-vessels, considerations on the nature of nerve-termini, matters relating to the intimate structure of the striped muscular fibre and nerves, with the results of studies on the structure and development of certain connective substances, and novelties in microscopic apparatus and methods. A special chapter is also given to the thick cutis vera, now for the first time described as a distinctive portion of the skin. In it will be found detailed the discovery of the fat-columns, which are calculated to explain certain pathological changes that have been imperfectly understood. The first chapters of the book are devoted to the mechanism of the microscope, and to certain formal methods of work with which the beginner should be familiar. Of the illustrations, sixty-five were prepared for the volume, while forty have never, it is believed, appeared in book-form. The remainder are mostly from the manuals of Strieker and Frey. A limited number of bibliographical references have been in- serted where it was thought they were desirable in guiding the reader to the literature of the subject. For the prepara- tion of these tables and much valuable assistance, the editor here desires to express his thanks to Dr. E. C. Wendt, of this city. It was thought best to omit the subject of optical principles which figure so conspicuously in some of our histological manuals. Those who wish information on these matters are referred to any of the standard text-books on physics, where VI PEEFACE. tlie subject is treated at greater length than was permissible in the present instance. For a similar reason, and also because it would prove a needless expense, the price-lists of instrument-makers have been omitted. Full particulars relating to the various sorts of microscopes and their accessories can be obtained from any of the leading opticians, who from time to time issue lists con- taining ample illustrations of the most recent improvements in all that pertains to practical working of the instrument. In conclusion, the editor finds himself compelled to reiter- ate the well-worn statement, that circumstances over which he has had no control have united to delay the press- work of the volume, and at the end have made its final revision rather hasty. A kind indulgence is therefore asked for any error that may, through oversight, have escaped his notice. T. E. S. TABLE OF CONTENTS. PART I. CHAPTER I. BY THOMAS E. SATTERTHWAITE, M.D. MATERIALS REQUISITE FOR HISTOLOGICAL WORK. How TO USB THE MICRO- SCOPE. TESTING THE MICROSCOPE. ITS USES Page 1 Appliances for microscopic work, 1. Chemical reagents, 3. Illumina- tion, 4. Stage diaphragms, 5. The mirrors, 5. Direct and oblique light, 5. Arrangement of the object, 6. Kind of lens to use, 6. How to keep the instrument clean, 7. Magnifying power of a lens, 7. How to estimate the size of an object, 8. Testing a lens, 8. How to illuminate the object, 9. Testing the eye-piece, 10. Testing high lenses, 10. Measuring the angle of a lens, 10. CHAPTER II. BY THOMAS E. SATTERTHWAITE, M.D. METHODS FOR PREPARING MICROSCOPIC OBJECTS Page 12 General directions, 12. To prepare fresh objects for rapid examination, 13. Ordinary methods of preparing tissues, 13. Mailer's fluid, 14. Potas- sium bichromate solution, 14. Ammonia bichromate solution, 14. Alcohol and acetic acid mixtures, 14, 15. Molybdate of ammonia, 15. Solution of osmic and chromic acids, 15. Alcohol and acetic acid, and muriatic acid solution, 15. Method of hardening the brain, 15. How to embed speci- mens, 15. Embedding in glycerine and tragacanth, 16. The hand section- cutter, 16. Freezing section-cutters, 17. Hailes' microtome, 19. The Vincent microtome, 21. Staining fluids, ammonia carmine, 21. Borax car- mine, 22. Double staining, 22. HEematoxylon solutions, 23, 24. Solutions for multiple staining, 24, 25. Preparation of the cornea, 25. Triple stain- Vlll TABLE OF CONTENTS. ing, 26. Double, triple and quadruple staining-, 26. Bismark brown, 26. Solution of alum carmine, 27. Naphthaline yellow for bone, 27. Methyl green and induline, 27. Purpurine, 28. French archil, 28. Alizarine, 28. Metallic solutions, staining with osmic and oxalic acids, 28. Chloride of gold and lemon juice, 28. Nitrate of silver, 29. Chloride of gold, 29. Osmic acid, 29. Methyl green for waxy change, 29. Wickersheimer's liquid, 29. Methods of injecting the blood-vessels, 30. CHAPTER III. BY THOMAS E. SATTERTHWAITE, M.D. THE BLOOD Page 34 Red corpuscles, 34. Comparative measurements in men and animals, 36. Number of, 37. Corpuscles in an indifferent fluid, 38. Brownian and amoeboid movements, 39. Heating slide, 40. Action of dilute salt solution, 40. Action of distilled water irrigation, 41. Action of carbonic acid gas, 42. Action of acids, 43. Action of alkalies, 44. Action of electricity, 44. Exhibition of the circulation, 45. Internal structure of red corpuscles, 46. Development, 47. White corpuscles, 48. Counting corpuscles, 48. Blood crystals, 53. Haemoglobin, 53. Hsemochromometer, 54. Bibliography, 54. CHAPTER IY. BY THOMAS E. SATTERTHWAITE, M.D. EPITHELIUM Page 56 Ordinary flattened or squamous epithelium, 57. Ciliated epithelium, 58. Effect of reagents, 59. Columnar or cylindrical epithelium, 60. Other va- rieties, 61. Structure of epithelial corpuscles, 61. Bibliography, 61. CHAPTER Y. BY THOMAS E. SATTERTHWAITE, M.D. THE CONNECTIVE SUBSTANCE GROUP. Mucous OR GELATINOUS TISSUE. ADENOID TISSUE. NEUROGLIA. FAT TISSUE. FIBROUS TISSUE PROP- ER. CORNEAL TISSUE. INTERMUSCULAR TISSUE. TENDON TISSUE. ELASTIC TISSUE , Page 62 Connective substances in general, 62. Mucous or gelatinous tissue, 63. Development of fibrous tissue, 64, 65. Fibrous tissue, 6(5. Adenoid tissue, 69. Neuroglia, 70. Tendon tissue, 72. Fat tissue, 73. Intermuscular tissue, 74. Corneal tissue, 75. Elastic tissue, 77. Pavement endothe- lium, 80. Bibliography, 81. TABLE OF CONTENTS. IX CHAPTER YL BY THOMAS E. SATTERTHWAITE, M.D. THE CONNECTIVE-SUBSTANCE GROUP (Continued). CAKTILAGE Page 82 Hyaline cartilage, 82. Parenchymatous cartilage, 83. Division of the corpuscle, 84. Calcifications, 84. Methods of studying hyaline cartilage, 84. Yellow elastic cartilage, 85. Fibrous cartilage, 86, Structure of cor- puscle, 87. Bibliography, 88, CHAPTER YIL BY THOMAS E. SATTERTHWAITE, M.D. TnE CONNECTIVE-SUBSTANCE GROUP ( Continued). BONE Page 89 Compact tissue, 89. Ossein, 89. Bone-corpuscles, 90. Haversian sys- tem, 90. Preparation of dry bone, 92. Preparations of decalcified bone, 92. Sharpey's fibres, 94. Cancellous tissue, 94. Marrow, 95. Periosteum, 95. Development of bone, 96 ; through cartilage, 97 ; from membrane, de- velopment and absorption, 99. Howship's lacunae, 100. Formation of cal- lus, 100. Bibliography, 101. CHAPTER YIII. BY THOMAS E. SATTERTHWAITE, M.D. THE TEETH Page 102 The enamel, 102. Dentine or ivory, 103. Dentinal globules, 104. Cement, 105. Pulp, 105. Development of teeth, 105. Primary enamel organ, 107. Development of enamel, 108. Bibliography, 108. CHAPTER IX. BY THOMAS E. SATTERTHWAITE, M.D. GENERAL HISTOLOGY OP THE NERVOUS SYSTEM Page 109 Nerve-fibres, 109. Myelinic fibres, 109. Staining in picro-carmine, 111. Staining with silver, 112. Staining with osmic acid, 113. Semi-desicca- tion, 113. Transverse sections of myelinic nerves, 114. Preparation by ammonia bichromate, 115. Modern conceptions of myeliuic nerves, 116. Fibres of Remak, preparations in osmic acid and picro-carmine, 118. Prep- arations of Remak's fibres in hsematoxylon, 118. Ganglionic bodies, 119. Ganglia of the cranial and spinal nerves, 120. Gasserian ganglion, 120. Ganglionio bodies of the spinal cord, 120. Brain, 121. Sympathetic, 121. Meissner's plexus, 122. Auerbach's plexus, 123. Termination of nerves, 123. Tactile corpuscles, 124. Pacinian bodies, 124. Nerve-terminations in muscle, 125 ; in epithelium, 126. Connective tissue of nerves, 126. Bibliography, 127 TABLE OF CONTENTS. PART II. CHAPTER X. BY THOMAS D WIGHT, M.D. MUSCULAR FIBRE. Page 128 Involuntary muscular fibre, 128. Voluntary muscular fibre, 130. Physi- ological attributes, 134. Nuclei and muscle corpuscles, 136. Conclusions, 137. Peculiarities of voluntary muscles, 138. Termination of muscle in tendon, 139. Muscular fibre of the heart, 140. Bibliography, 140. CHAPTER XL BY EDMUND C. WENDT, M.D. THE BLOOD-VESSELS Page 14lood-globules in an indifferent fluid. In order to get a proper conception of the various influences that act upon the red corpuscles, so as to alter their form, size, and internal appearance, it is essential to subject them to some of the more common, such as water, acids, alkalies, electricity, etc. In no other way can the student appreciate the extraordinary changes' which these bodies suffer, and indeed a knowledge of such matters is quite necessary in studying the histology of either normal or diseased tissues. Unfortunately we are not always able to use human blood for these demonstrations because the corpuscles are too small, and consequently the alterations do not admit of easy observa- tion. We naturally turn to an object that has larger corpuscles and may be procured with little trouble or expense. The frog is therefore selected, or, even better still, the newt, which is especially well suited for this purpose. At first the blood may be examined in a menstruum similar to the liquor sanguinis or plasma, and the frog's aqueous humor is usually found satisfactory. To a drop of this latter add an equal quantity of the blood, mix them well with a glass rod, and adjust an ordinary | inch circle. The aqueous humor exerts no special influ- ence over the corpuscles, and is therefore called an indif- ferent fluid. If it be impossible to obtain aqueous humor, an excellent substitute may be found in the fresh fluid from a hydrocele or ovarian cyst, or we may use serum to which iodine has been added, which is then called iodized serum. To six ounces of the fluid twenty grains of finely powdered iodine are added. After prolonged agitation the iodine will be dissolved, and the mixture thus prepared may be kept for a number of months. Suspended in this liquid the blood is studied to advantage with a lens of moderate power, such as an ordinary THE BLOOD. 39 i inch. The contents of the disk will appear homogeneous, which is a term that merely indicates an apparent absence of structure. The nucleus and nucleolus should also be invisible. The shape of the corpuscles is oval, and they are flattened and have rounded edges, with hollowed centres, in which a promi- nence is usually seen (Fig. 13). The protoplasm is the sub- stance of which the disk is made ; it has a light yellow color, and is dull or pellucid in appearance, much like semi-solid jelly. Brownian and amoeboid movements. Using the same method of preparation the white corpuscles or leucocytes are seen to good advantage. They are much smaller than the red disks (in the frog the reverse of human blood), and there is wide range in size, one histologist (Klein) having described as many as thirty varieties. In the interior, little dark spots are sometimes seen in constant vibration. By a skilled observer they are readily detected, even with a good \ inch glass. When such specks are numerous the bodies are said to be granular. In the newt's blood this phenomenon is usually best seen. The word granule has been , applied in these cases from the notion once prevalent that the little dots were molecules sus- pended in a menstruum of some sort that filled the corpuscle. This subject is now eliciting much study, but the movement, whatever its significance may be, is called the Brownian move- ment. Klein, who states that the newt's leucocyte is traversed by an intracellular network, believes that the movement just described is due to the motion of the "disintegrated network" under the stimulus of imbibed water. Under this explanation the oscillatory movement in the corpuscles of the human saliva would indicate death rather than life. When fluid has been withdrawn by evaporation the phenomenon ceases. According to other histologists this vibratile motion is an indication of vital action. The remarkable change in form which these corpuscles un- dergo is a more positive indication of vital power in the leuco- cyte. When the little body is placed under conditions which imitate those of its natural state it commences to put forth processes and then withdraw them, carrying on these move- ments slowly, but with a certain degree of regularity. While this is being accomplished the corpuscle is observed to move about from place to place. 40 MANUAL OF HISTOLOGY. FIG. 15. Leucocytes: a, putting out pro- >, having withdrawn them. (Rollett.) In Fig. 15 the leucocytes are seen. Those marked with the letter a are engaged in amoeboid motion. The one marked b i? in a state of contraction. This phenomenon is called amoe- boid movement, because it resem- bles that of the amoeba the lit- tle microscopic organism found in stagnant water. In order to permit these changes to continue for some length of time, it is well to paint a little oil or glycerine around the edge of the circle. Evaporation is thus prevented. If the warm slide be used the changes will follow with greater rapidity. Both Brownian and amoeboid movements are usually confined to a limited number of the corpuscles, and the former often to only a small portion of the interior. The slide * for heating consists of an ordinary glass slide (Fig. 16) upon which is riveted a thin copper plate (b) perfor- ated in the centre, so as to allow space for the drop of blood which is to be examined. From the copper plate extends an arm (c) over which is slipped a spiral copper wire (e), which is heated by the flame of an alcohol lamp. By this means the glass plate is kept warm and with it the drop of blood. In order to secure a proper amount of heat and no more, it is customary to put a little bit of cocoa butter upon the corner of the slide. The butter melts at the tem- perature of the body, and after this point has been reached the lamp should be carried along the wire away from the slide until the precise distance is found at which this particular degree of heat will be maintained. Action of a dilute salt solution. It is often difficult, and, FIG. 16. Slide for heating : o, slide; &, copper plate ; c, arm over which the spiral wire (d) is slipped 1 Made by T. H. McAllister, 49 Nassau Street, New York City. THE BLOOD. 41 indeed, impossible, to obtain aqueous humor or even an animal Huid such as has been described, and microscopists have accord- ingly made use of a substitute that can be prepared at any time and kept indefinitely. This is a solution of common salt in distilled water (1 400). Add a drop of fresh frog's blood to a drop of the salt solution, mix them well, and it will be seen that the delicate protoplasm of the red blood-corpuscle, most susceptible of change, is not altered in appearance, though the body itself will change in form from the elliptical to the spher- ical. This salt solution has been found, in practice, an excellent substitute for blood-serum, and is very generally used in ex- amining fresh specimens, where it is important to avoid any material change in the corpuscle. Action of distilled water Irrigation. The effect of water is also noteworthy, as it is a very important consideration in both histological and pathological work, especially the latter. Take a drop of frog's blood, add to it an equal quantity of distilled water and apply a cover. The nucleus or central body will now be readily seen, surrounded by a yellow border ; the body of the corpuscle or peripheral part will at the same time gradually become paler and larger. Now add distilled water slowly, drop by drop, in the following way : Take a long strip of tissue or filter paper about half the length of the slide and in breadth equal to one-half the diameter of the cover. Apply the water with an ordinary minim dropper, close to the edge of the cover, on the side opposite to the paper strip. This latter will now take up the excess of water and cause a stream to pass through the specimen. This process is called irrigation. Push the paper a short distance under the edge of the cover, and the solid particles in the fluid will be carried to the edge of the paper, where they will remain at rest and may be ob- served at one' s leisure. This plan is often useful in other sorts of microscopic work, as in looking for renal casts, urinary crystals, etc. It may save much valuable time. I first learned it from my friend, Dr. Edward Curtis, of this city. Continued addition of water will cause the corpuscles to swell and after a time burst, or, at any rate, become so expand- ed that they can scarcely be seen. When water is applied slowly to human blood, the corpuscles soon begin to lose their MANUAL OF HISTOLOGY. disk-like form and assume a spheroidal, perhaps spherical con- tour. The coloring matter then escapes, in most instances, and they become quite transparent (see Fig. 17). Such corpuscles are often seen in human urine where they appear as colorless rings. In frog's or newt's blood the body of the disk first imbibes the FIG. 17. Human red blood-globules : a, with haemoglobin ; 6, without it. (Rol- l3tt.) FIG. 18. Red corpuscles of the frog that have imbibed water. (Rollett.) water ; later, the nucleus, which then has a sharply defined outline. Sometimes the material of which the body is largely composed (haemoglobin) is gathered about the nucleus, sending off radiating prolongations to the periphery, while the imbibed fluid is stored in the intervening spaces (see Fig. 18). Action of carbonic acid gas. This experiment requires a special apparatus. First of all it is essential to have a moist chamber (Fig. 19). Take a small, flat bit of wood about 1J inch wide, 3 inches long, and f inch thick ; make a square opening in the centre, sufficiently large to admit an ordinary f inch cover-glass ; this is to be pressed to the bottom and firmly fixed, thus making a shallow well with a glass bottom. Into this cham- ber are admitted, through side holes, glass tubes (one on each side), so that air or gases can be carried into the chamber. When in use, the chamber is kept moist by a drop of water, which is put in one corner of the well, while the specimen of blood to be ex- amined is dropped upon a large glass cover, and the latter in- verted over the mouth of the well. In determining the effect of carbonic acid gas upon animal life, we have merely to con- nect the gas-chamber just described with a jar in which carbonic FIG. 19. Moist chamber. THE BLOOD. 43 acid gas is generated. Fig. 19 illustrates a gas or moist cham- ber of the same general character, and devised by Dr. J. H. Hunt, of Brooklyn. Take a large gallon flask, fill it partly full of pulverized marble-dust, attach it by means of a rubber tube through a perforated stopper to a Wolff's bottle, which latter must be connected with the moist chamber. Now gener- ate the carbonic acid gas in the flask by pouring muriatic acid upon the marble-dust. When the gas is being evolved it will be known by the ebullition of the water in the Wolff's bottle. Now place the moist chamber upon the stage of the micro- scope. Take a drop of newt's blood, dilute it with serum or an indifferent fluid, and mount it upon a glass cover, which invert over the well, first seeing that the edge of the cover is oiled, so that it will remain in place. Now connect the tube of the moist chamber with the tube of the gas-generator, and the carbonic acid gas will enter and pass through the chamber. The rapidity with which the current moves may be regulated by a spring clip. As soon as the gas enters, the central body or nucleus becomes distinctly visible, and is surrounded by a yellow halo ; when, however, the gas is withdrawn and atmospheric air is admitted, the nucleus and colored zone disappear. This double experiment may be repeated a number of times. Finally a point will be reached where all action will cease. This cen- tral body, under such circumstances, has been called the zooid, and the corpuscles proper the oikoid (Bruecke). Action of acids upon the blood. Acetic acid is commonly used in observing the changes that are produced by an acid solution. Take the ordinary dilute watery solution of acetic acid (1 per cent.) so much used in laboratories, add a drop of it to an equal amount of frog's blood. The red globules instantly exhibit nuclei. The colorless globules also cease their motion, if any has existed, and they become granular and shrivelled. The term granular is used merely in a relative sense and has no special reference to granules whether present or not, but merely to an appearance that has already been explained. These phenomena are more marked if the solution is con- centrated. The red bodies, also, in such case, are apt to crack and split up. A good way of determining the proper strength for the ordinary acetic acid solution is to pour a little into an ordinary watch-glass, and then add chemically pure acetic 44 MANUAL OF HISTOLOGY. acid drop by drop until the solution is faintly acid to the taste. Action of alkalies upon the Hood. Take a drop of the newt's blood and mount it in a drop of serum or of salt solu- tion. Then, affixing a strip of bibulous paper in the way that has been described, add drop by drop a weak solution of aqua ammonite. A similar strip of paper, somewhat larger in size, upon the other side, will cause a current and carry the corpus- cles to the side of the field where the paper strip is largest, and there the corpuscles may be observed at rest, and the altera- tions effected by the alkali duly noted. It will be seen that after a little time the corpuscles, both red and colorless, will swell up and finally, after a time, provided the alkali be in sufficient amount, disappear or become so expanded as to be invisible. Sometimes they will burst, leaving the field evenly stained with a homogeneous glutinous-looking substance. Action of electricity. It seems to make little difference, so far as the microscope is concerned, whether the continuous or interrupted current is employed, as in either case the phe- nomena observed are the same in quality. Take bits of tin- foil and attach them to an ordinary glass slide, in such a way that they are just -- inch distant from one another. The pieces of foil should be triangular in shape and have their pointed extremities turned to one another. The specimen should be a drop of newt's blood diluted with an equal amount of serum, both perfectly fresh. They should be intimately mixed with a glass rod. Depositing a drop of this solution upon a cover-glass, it should be inverted and placed upon the slide in such a wa}^ that it occupies an intermediate position between the bits of tin-foil. The ordinary stage clips of the microscope are then to be used in holding the slide firmly ih position and to press upon the tin-foil. The only remaining task is the attaching of conducting wires from the electrical instrument, one to each clip. The bits of tin-foil are easily fastened to the slide ; they have merely to be hammered out flat, when they will adhere by simple pressure. Sometimes it may be desirable to approxi- mate the poles. In such cases it is necessary to use two fine bits of platinum wire. They should be flattened, and shaped like the letter S. Rest them upon the bits of tin-foil, opposite to one another and at the required distance apart. The cover- THE BLOOD. 45 glass should press on them. Some little mechanical dexterity is required to get them in position, and they are apt, after using, to become so charged that their action upon the corpuscles commences before they are connected with the battery. The phenomena at the negative pole are those of an acid ; at the positive, those of an alkali. At a distance from the line of the current, secondary changes occur of a less regular character. Harting has devised an apparatus which is somewhat more elaborate, but in principle the same. Other changes in the red corpuscles. If a drop of blood be taken from the finger, by pricking with a needle (the triangu- lar or glover's is the best), it will be seen after a time that the exterior of the corpus- cle is indented or crenated, as this change is called. It is well shown in Fig. 20. Examination of the circulation in the web of a frog's foot. Take a medium-sized frog and curarize him by injecting beneath Plo 2 o -Human the skin, with an ordinary hypodermic syr- d t v*** crenated - < R inge, two drops of a weak solution of curara (12,000 in water) or a few minims of a 50 per cent, solution of chloral hydrate (Schaefer). After a variable time the ani- mal will be completely paralyzed, but the circulation will go on as before. There are many difficulties in the use of curara, depending on the variable strength of the drug, the idiosyncrasies of the animal, and other causes that we do not appear to understand. A solution which will produce a proper amount of paralysis in a frog on one day will rapidly kill another frog the next day. To ensure any reliability of action, it is well to have a specimen of which the strength has been properly tested. Then, if time enough is at one's disposal, a weak solution, such as the above, may be injected every hour until the symptoms of the drug are apparent. If the subsequent recovery of the animal is not of vital importance, the amount may be increased, for the circu- lation will often be well shown, even if the animal does not eventually survive. My friend, Dr. W. H. Welch, who is in charge of the Histological Labora- tory at the Bellevue Medical College, employs a watery solution of curara. He keeps on hand a | per cent, solution of the drug ( 1 gramme to 200 c.c. of distilled water), and then dilutes it as occasion may warrant to i per cent., or even -^ per cent. (1500 or 11,000). Of this diluted solution he injects four or five drops into the dorsal lymph- sac of the frog. A still more dilute solu- tion he is often in the habit of using, so that the frog does not come under the influence of the drug for an hour or an hour and a half. After twenty-four to 46 MANUAL OF HISTOLOGY. forty-eight hours the animals entirely recover, but if a stronger solution is used, he finds the results are frequently fatal, though the animals may survive long enough to permit a ready demonstration of the circulation, emigration of leucocytes, etc. Now envelop Ms body in a damp cloth and extend him upon a cork plate about a quarter inch thick and large enough to support the entire body. Make a small opening in the cork, and over it place the web of the frog's foot, fastening the latter by ordinary pins. The circulation may in this way be studied at one' s leisure. The red and white blood-corpuscles are seen in the arteries, veins, and capillaries. While the red bodies pass rapidly through the central portions of the vessels, the white creep slowly along the walls, altering their shape as they meet with any obstruction. Where, however, a small artery divides, it will sometimes be seen that the corpuscles, especially the red, are caught at the bifurcation ; parb bending to go down one branch, and part down the other ; taking, in fact, the shape of a saddle-bag. Such a phenomenon exhibits the elastic and distensile properties of the corpuscle. Apply an irritant, such as a weak solution of nitrate of silver, and after prolonged and careful watching, the gradual exit of both white and red cor- puscles may be seen. This procedure requires extreme pa- tience and a co-operation of peculiarly fortunate conditions, which are not likely to favor the beginner in microscopy. Internal structure of the red corpuscles. As yet the inti- mate structure of blood-corpuscles is a matter little understood, though an abundance of theories are rife about it. Klein main- tains that these corpuscles, in common with others in the body, are traversed by an intracellular network. In the red cor- puscles of the newt, especially, he says there is a network of fibrils, with an interfibrillar hyaline ground substance, both together forming the so-called stroma. The nucleus contains a network of fibrils in connection with the network of the cor- puscle proper ; the haemoglobin, a colored fluid, is contained in the substance of the meshes of the network of the corpuscle proper. Drs. Cutter, of Boston, and Heitzmann, of this city, also state that there is an intracellular network. The former regards it as due to the mycelium of a parasitic growth. Dr. Elsberg, of this city, also states that he finds a reticu- lar appearance after using a solution of the bichromate of THE BLOOD. 47 potash (30 per cent, to 50 per cent, of a saturated solution in water). Real granules are often present in the corpuscles, as may be proved by adding water in large quantity. They will then become greatly distended, and bursting, the granules will be scattered throughout the field. If finely ground vermilion is sprinkled in the liquid, some of the white corpuscles will take up the granules, perhaps with- out losing their amoeboid character ; finally, they may eject them after a longer or shorter sojourn. According to Boettcher, the human red blood-corpuscle has a nucleus. He exhibits it in the following way : Taking a saturated solution of corrosive subli- mate in alcohol (96), he diffuses about fifty volumes with one of blood. The corpuscles are deprived of their hsematin, but at the same time are preserved. The mixture is frequently agitated, but in about twenty-four hours it is allowed to subside, when the superincumbent fluid is poured off and alcohol added. By further agitation for another twenty-four hours the corpuscles are thoroughly washed, and then settle at the bottom of the vessel. Prof. Boettcher claims in this way to have found three classes of red globules. The first are homo- geneous and shiny throughout ; the second are clear externally, but granular within ; the third variety exhibit a nucleus and nucleolus. Development of ike Hood-corpuscles. In early foetal life all the corpuscles are colorless (Klein). According to Balfour and Foster, both colored and colorless corpuscles, at least in the chick, are developed from solid sprouts of protoplasm, de- rived from the middle germinal layer. There seems good rea- son, however, to believe that the leucocytes are formed in part, at least, from the lymphatic glands, and Klein thinks that they are thrown off from the "germinating buds" of serous membranes. Later, the red ones make their appearance, and for a time are nucleated. The investigations of Neumann and Bizzozero, showing that the red corpuscles in the medulla of bones are also nucleated, favors the theory that bone-marrow is one of the theatres for such corpuscular metamorphosis. According to Hayem the production of red corpuscles in the blood is accomplished through the agency of hcematoblasts, i.e., minute red corpuscles. In convalescence from acute fe- vers, or after a considerable loss of blood, these smaller bodies may be observed in the blood for a variable time, even some weeks. 48 MANUAL OF HISTOLOGY. According to Recklinghausen, the colorless corpuscles may be generated from the red corpuscles, but it is probable that they may be formed in the tis- sues at many points, and the connective substances through their intimate asso- ciation with the lymphatics are capable of manufacturing them in almost any quantity. Neither of the two varieties of corpuscles, the red or the white, have a cell-wall or outer investing membrane that can be demonstrated, though it is not unlikely that the outer layer of protoplasm has greater density than the more internal portions. Wliite or colorless blood- corpuscles. The white blood-cor- puscle is much larger, on an average, in the human species, than the red. It is rounded in form, and is estimated as varying between .0077 and .0120 mm. The average is .0091 mm. (Frey). In contour they are apt to be more or less rough, and exhibit processes. In some of these corpuscles the nucleus is distinct, though when quite fresh a nucleus is rarely seen. If the eye of the observer can watch the corpuscle when it is upon a heated stage and under suitable conditions, its division may be seen. The number contained in the system is variable, as we shall see, depending upon a great number of conditions. The personal observations of the author do not incline him to regard the network which has attracted so much attention of late years as satisfactorily shown to exist in living corpus- cles, although there is no question but that it has been seen in corpuscles after exposure to chemical reagents. According to Dr. Richard Norris, there is, in mammals, a third corpuscular element which is usually invisible and of the same size as the red ones. Some doubt is thrown upon his alleged discovery, by the fact that the method he employs is likely to produce artificial appearances, and therefore leads to the supposition that the alleged bodies were merely red corpuscles decolorized. Mode of counting the blood-corpuscles. Thanks to the instruments of Malassez, Hayem and Nachet, and Gowers, we are in a position to count the red blood-corpuscles with a fair degree of accuracy. The methods are somewhat different, but are not difficult to understand. Schaefer describes his plans as follows : In order to separate the corpuscles and prevent coagulation, the blood used is first diluted to a definite extent say a hundred times with a 10 per cent, solution of sulphate of soda. The mixing can be per- formed in a measuring-glass if the blood is in sufficient quan- THE BLOOD. 49 tity, but if only a small drop is obtainable, such, for example, as is got by pricking the linger, a mixer is better. This con- sists of a capillary tube terminating in a bulb, the capacity of the bulb between the marks 1 and 101 being exactly 100 times that of the tube from its point to the mark 1. A small glass ball is inclosed in the bulb, and serves, by its movements, to facilitate the mixing. The capillary tube is allowed to fill with blood as far as the mark 1 ; sulphate of soda solution is then sucked up as far as the mark 101. As it passes in, it of course pushes the blood before it into the bulb, and the two are there thoroughly mixed by gentle agitation. The next thing is to count the corpuscles in a known quan- tity of the mixture. The most convenient plan is that of Hayem and Nachet. A slide is used, having a glass ring -J- mm. in depth, cemented on to its upper surface. A drop of the mixture, but not enough to fill the cell so formed, is placed in the middle of the ring, and a perfectly flat cover-glass is so laid on that the drop touches and adheres to it without reaching the sides of the cell. The slide is placed on the microscope, and as soon as the corpuscles have settled down to the bottom of the drop, the number in a definite area is counted. If the area chosen is -J- mm. square, this will give the number which were contained in | mm. cube of the mixture,, and multiplying this by the number of times the blood was diluted, the result will be the number of corpuscles in -- mm. cube of blood. Schaefer thinks that it is more convenient to have the quad- ratic markings upon the micrometer glass of the eye-piece than upon the slide, which is a practical point. The quadratic markings are shown in Fig. 22. To measure any square, it is only necessary to take the stage micrometer, ruled in milli- metres and decimals, and adjusting the draw tube, make the side of one square correspond exactly to an interval of | mm. on the stage micrometer. It will then be convenient to mark the tube at this point, and then, in all subsequent work, if the tube be kept at this line and a slide is used of the thickness of the micrometer and the same lens and eye -piece, the side of a square will always be | mm. This method is the one in general use. Another less frequently employed is that of Malassez, which is also described by Schaefer as follows : A little of the mixture of blood and sulphate of soda is transferred to a very fine flat- 50 MANUAL OF HISTOLOGY. tened capillary tube, the capacity of a given length of which has been ascertained previously and marked on the slide to which the tube is fixed. Thus, in his capillary tube a length of 400 mi- cromillimetres represents the T ^V.^ P art f a cubic millimetre of the mixture. The counting is performed with the aid of a squared ocular micrometer, the microscope tube having been previously so adjusted by the aid of a stage micrometer that the side of the square shall have the value of one of the lengths (400 n l for example) marked on the slide. The result of the FIG. 21. Hayem and Nachet's apparatus for blood-counting. counting gives the number of corpuscles in a known quantity (TBT.-S c.mm.) of the mixture, and the number in a whole cubic millimetre can therefore be readily determined. Dr. Keyes uses a modification of the method of Hayem and Nachet, making a dilution of 1 to 250, in order to render the counting more easy. In Fig. 21 the pipette, A, is filled up to the mark, 5 D ; it is then emptied into the glass vessel, F. The pulp of the finger of the patient whose blood is to be tested should be pierced with a triangular needle (glover's). Quick A micromillimetre (O = THE BLOOD. 51 but firm pressure down the finger will at once force out a drop from the punctured spot. The blood must be drawn imme- diately into the capillary pipette lest it coagulate. When the pipette is full to the mark 2, its point should be rapidly wiped clean of any blood adhering to the outside, and the contents at once blown into the artificial serum in the cup, F. A little suction back and forth clears the tube of any blood-corpuscles which may have adhered to the glass within. Both tubes should be carefully washed before being put away. The mixture is now to be thoroughly agitated with the glass rod, and before it has time to settle, a drop is placed in the middle of the cell on the slide, D, care being taken that the drop is not large enough to touch any part of the circumference of the cell. The covering glass, E, should at once be placed upon the cell. Should the drop be too large, so that when the thin cover is adjusted it spreads out too much, the glass should be cleansed and the attempt made anew. Finally, a small drop of water or saliva is applied to the edge of the covering glass, under which it circulates around the top of the cell, serving to hold the cover in place and pre- vent evaporation. The slide is then put in position and when the corpuscles have all settled to the bottom of the fluid, the counting should begin. The following detailed plan is then given by Dr. Keyes : "It is better to count each of the sixteen squares and write down its number separately, so that in counting the square beneath it, should there be any doubt about counting a given corpuscle lying upon the line, a glance at the number recorded for the square above may remove all doubt. Many corpuscles will be found lying upon the outside lines bounding the large square. I have adopted the rule of rejecting all those lying upon the upper and right-hand outside lines (of the large square) and counting all those lying on the lower and left- hand outside lines. After having thus obtained the number of red corpuscles FIG. 22. Blood corpuscles as seen with the squared ocular micrometer. (Keyes.) 02 MANUAL OF HISTOLOGY. situated within the large square, it becomes easy, by a simple equation, to find the number in a cubic millimetre. A single count, however, exposes to sources of error, and in order to approach more nearly to exactness, I have uniformly counted the number contained in the large square in five different por- tions of the field (sometimes ten), and have taken a mean of the whole number of counts as the standard. The computation is as follows : The glass cell on the slide is % mm. deep. The eye-piece micrometer marks off -- mm. square, therefore the count of red corpuscles (or white, as the case may be) must indicate the number contained (in the dilu- tion used) in -J- mm. cube. But J mm. cube is -^ of a c.mrn., therefore the number counted must be multiplied by 125 ; and the blood was diluted by adding 250 parts of fluid to 1 of blood (2 c.mm. to 500 c.mrn.), therefore the product above obtained must be again multiplied by 251 to get the number of corpus- cles in a c.mm. of pure blood. Instead of multiplying twice, a single multiplication by the product of 125 x 251, 31,375, will give the same result." This method should, theoretically, be absolutely accurate, but there are vari- ous errors which will unavoidably creep in. First of all, the tubes should be verified as to accuracy. This has been done for me at the Winchester Observa- tory, of Yale College, by Leonard Waldo, Esq., the astronomer in charge. My larger glass tube is slightly different in shape from the one here represented, and is marked so that the line at ^ indicates a capacity of 500 cubic millimetres (0.5005 grammes of distilled water at 26.4 C.). The cubical contents of the reservoir from the point to the line i- = 0.2425 + 0.008 = 2505 grammes = 250 c.mm., approximately. Accordingly, the marks and indicate i and -J- a cubic centimetre, within a limit of error so small as to be practically insensi- ble. The smaller glass tube, which is capillary, is marked 2, 2, 4, and 5. The level 5 indicates a capacity of 5 c.mm. The capacity between the pointed extremity and 2 is 2 c.mm., less Vfn c.mm. ; the space between 2 and 2| con- tains .55 c.mm. ; the space between 2 and 4 contains 1.45 c.mm. ; the space between 4 and 5 contains exactly 1 c.mm. (Waldo). The determination of these capacities was made by using distilled water, and comparing the weight, when filled to the various levels, with the same tube after careful drying. These estimates are given to show one of the errors which may be met with, and that an instrument, before using, should be verified by some one who has special means for determining capacities of this kind. My eye-piece mi- crometer was made for me by Rogers, of Cambridge, and the entire field was subdivided into squares, so that every portion of it may be counted without moving the slide. My method has been practically the same as that of Dr. K3jes, except that I prefer diluting with one thousand parts of the diluent, THE H^EMOCHROMOMETER. 53 and use iodized serum in place of urine. The ordinary per cent, solution of common salt in water will also answer sufficiently well. Kecent investigations, such as those conducted by Drs. Cut- ter and Bradford, of Boston, have established that there is great variation in the number of globules of an individual, de- pending on various causes, such as the locality from which the blood is drawn, the loss of fluids, as by diarrhoea, sweating, increased urinary secretion, etc., and even the period of the day, week, or year. These general conclusions have also been sustained by Hayem, of Paris, in researches which are still being prosecuted. When one further considers that we have no definite stand- ard of comparison ; that the instrument is apt to be imperfect ; that there is a liability of errors to the amount of 10 per cent.; that skill and practice are required in manipulation, it is by no means difficult to see that the haematometer is not calculated at present to introduce much scientific precision into medicine, unless the most extraordinary precautions are taken in every case, and these all duly noted. Blood crystals. The pigment of the blood occurs usually in an amorphous form, and is called haematine. The brownish red needles found in extravasated blood are known as haema- toidine. Haemoglobin also occurs in most mammalian blood, and is deposited under the form of rhombic plates. It is estimated that about 125 grammes are present in the blood of a healthy adult. THE HJEMOCHROMOMETER. According to Mantegazza and others, richness in haemoglo- bin indicates a corresponding richness in red corpuscles, and any special depth of color in the blood may be regarded as im- plying a certain given number of red corpuscles to the cubic millimetre. While this ratio appears to hold true in health, it fails in disease. Thus, a condition which we recognize as anae- mia may be almost wholly due to a loss of haemoglobin in the corpuscle, or an actual loss of red corpuscles, together with a diminished amount of haemoglobin in those that remain. In the cachexia of cancer the number of the corpuscles may be sustained, but their haemoglobin diminished. In diabetes mel- 54: MANUAL OF HISTOLOGY. litus, on the other hand, there may be an excess of red cor- puscles, while there is a diminution of their haemoglobin. In anaemia, from hemorrhage, there is an actual loss both of cor- puscles and of haemoglobin in those that remain. To facilitate the estimation of haemoglobin, an instrument has been devised by Malassez and Verick (Paris), called the TicemocTiroinometer, 1 which is easily manipulated, and bids fail- to establish some facts of practical utility (see Archives de Phys., 1877, p. 1). It consists of a hand-screen, to which a movable prismatic trough, containing a colored fluid, is attached, and a modified Potain pipette. By means of this apparatus the richness of the blood in haemoglobin, and the maximum quantity of oxy- gen which it can absorb, may be determined. To use the ap- paratus the pipette is first filled up to a certain point with the blood to be examined, and then diluted with 100 parts of water. The reservoir of the pipette is then filled with the diluted blood. The screen has two holes; behind one of these the prismatic trough is made to slide up and down, the color of the fluid contained in it of course varying in intensity, according to the extent of the upward and downward motion. Behind the other opening the reservoir of the pipette is secured by means of a little elastic ring. The screen is now held against the light (preferably white light ; sunlight is to be especially avoided), and the trough moved until the color of the blood mixture is matched by its own color. Then the figure on the scale attached to one side of the trough is read off, arid this indicates, by reference to the table annexed to the apparatus, the points to be determined. If the blood to be examined be deeply colored, the aqueous blood-mixture is made in the pro- portion of to 100 ; if it be but slightly colored, in the propor- tion of 2 to 100. BIBLIOGRAPHY. WELCKER. Pragervierteljahreschr. XLIV., p. 60. 1854. Zeitschr. f. rat. Med. 3, XX., p. 280. SCIIULTZE, MAX. Archiv f. mikrosk. Anat. I., p. 35. 1865. KOI.LETT. Strieker's Manual of Histology. New York, 1872. WOODWARD. Ara. Jour, of the Med. Sci., Jan., 1875. N. Y. Med. Rec., Jan. 31, 1880. 1 To be obtained of J. F. Reynders & Co., New York city. BIBLIOGKAPHY. 55 KELSCH. Arch, de Phys. Vol. II. 1875. KEYES. Am. Jour, of the Med. Sci., Jan., 1876. HEITZMANN. New York Med. Jour.. April, 1877. MANTEGAZZA. Berl. Klin. Woch., April 1, 1878. RANVIER. Traite technique d'histologie. Paris, 1877 et seq. HAYEM. Archives de Phys. 2 Ser., T. VI., p. 201 et seq. 1879. BIZZOZERO, G., and SALVIOLI, G. Centralb. f. d. Med. Wiss. 16, p. 273. 1879. POUCHET. Gaz. Med. de Paris. 14, 16. 1879. CUTLER, E. G., and BRADFORD, E. H. Journal of Phys. Vol. I. 18781879. BOETTCHER. Archiv f. raikrosk. Anat. Bd. XIV. p. 73. 1877. KL'EIN and E. NOBLE SMITH. Atlas of Histology. 1879. ELSBERG. Annals of the N. Y. Academy of Sciences. Vol. I. , Nos. 9 and 10. 1879. (A very extensive bibliography.) SATTERTHWAITE, T. E. Arch, of Comp. Med. N. Y. II. 1880. BAXTER and WILLCOCK. Lancet, March 6, 13, 20, 1880. CHAPTER IV. EPITHELIUM. THE skin, mucous surfaces of the body and various pas- sages in connection with them, are evenly coated with bodies of peculiar shape, which are united together to form a cover- ing of one or more layers. In some places, as upon the external portions of the epider- mis, the corpuscles are more or less flattened. Elsewhere, as in the ducts of secreting glands and in the trachea and fallopian tubes, they are cylindrical, and the free extremities are often surmounted by cilia fine, hair-like processes, which have a vibratile movement that propels solid matters, such as sputa and ova, in some special direction. In other parts, again, as in the collecting tubes of the kidney, near the apices of the pyra- mids, a cuboidal variety is found. Intermediate or transitional forms are also frequently met with in all parts of the body. A characteristic of epithelium which is especially note- worthy is that the same species is not found uniformly in the same position. Sometimes this mutation of type is governed by the physical laws that regulate the growth and development of the subject, or it may be a consequence of disease. An ex- ample of the former peculiarity is to be noted in the larynx, where the ciliated corpuscles of infancy part with their cilia from advancing age, or indeed may become flattened. As an example of pathological change it is not uncommon to find villosities covered with the most beautifully marked cylindrical epithelium, springing from the ordinary mucous membrane, just where the superficial corpuscles happen to be somewhat flattened in their normal state. The use to which the part is put has also an important influ- ence in governing the shape and other attributes of the corpus- cles. Where they are exposed to the drying action of the air, to harsh usage, and continued friction, as upon the hands and EPITHELIUM. 57 feet, they become flattened, dry, and horny ; in the interior of the body, on the other hand, where such conditions do not exist, they are succulent and pliable. Ordinary flattened or squamous epithelium. This is best obtained by scraping the back of one's tongue with a blunt instrument. The scrapings should then be mounted in equal parts of the common salt solution (J per cent.) and glycerine. The epithelial bodies may in this way be readily studied. They are separate or grouped together in collections of two or more. In diameter they vary between ^TT an & TTT incn - Tne sur ~ faces are all bevelled, and at the same time are uneven or ridged ; consequently they overlap one another to a certain degree, and the inequalities of one corpuscle fit into those of another. The most superficial epithelium is the thinnest, and, conversely, the deepest is apt to be the most nearly spheroidal. Intermixed in the mucus will be seen the so-called mucous or salivary corpuscles. They are not very numerous, but are de- tected by the "molecular" or Brownian movement of their in- terior. In size they closely resemble the white corpuscles of the blood, but, as a rule, exhibit no amoaboid motion ; the white glob- ules, on the other hand, rarely have any Brownian movement. The surfaces of the epithelia are often so covered with bac- teria that they are only recognized with some difficulty. These little bodies are wonderfully uniform in size, and are disposed in the most regular manner. Looking straight down upon them they appear to be minute spheres with a diameter aver- aging between ^QT and ^TUTTF incn - Closer inspection and examination of the corpuscles at their free edges shows that the bacteria are in reality rod-shaped, and that they adhere to the corpuscles by their extremities, standing in such cases vertical to the surface. A high power, such as the immersion T V, develops this point quite clearly. Incidentally the mucin of the mucus may be seen to advan- tage in the scrapings of the mouth or tongue. To a drop or two add another drop of commercial alcohol and a drop of the or- dinary hsematoxylin solution. The alcohol will coagulate the mucin, which then takes the form of filaments and branching networks ; the logwood will make them distinctly visible. Epithelium from the skin may be studied in one of two methods. Take a fresh specimen from the palmar surface of the hand or plantar of the foot, freeze it in a section cutter, 58 MANUAL OF HISTOLOGY. take off a thin slice with a knife, immerse for a few seconds in a dilute solution of acetic acid (J per cent.), and then mount in glycerine and water ; or a similar portion of the skin may be steeped in a weak, sherry-colored, watery solution of the bichro- mate of potassium (gr. ij. iij. f. j.) for several days and then hardened in alcohol, first of 80 per cent., then of 90 per cent., finally of 95 per cent, strength ; this latter process taking several days, and ending when the specimen is thoroughly hard. Sec- tions may then be made in the usual way. By the use of acetic acid the nuclei will readily be seen in the lower strata of the epi- dermis, while the outermost layers have none, or, at least, none that can be demonstrated by the usual histological methods. Three different strata can now be recognized : 1, the stra- tum corneum, or corneous layer, in which the corpuscles are flattened, and appear to have no nuclei ; 2, the rete mucosum, or malpighian layer, immediately underlying the former, and composed of cuboidal elements, armed with spines or prickles, as they are often called ; lastly, 3, there is the pigmented layer, which overlies the papillae. The bodies of the latter corpuscles are infiltrated with particles of melanine, which is the cause of the dark color in the skin of the negro and swarthy races. Maceration of the epidermis in liquor potassse is an excellent method for exhibiting the individual elements ; after a few min- utes they will swell up and detach themselves from one another. It was thought, until quite recently, that these prickle cells interdigitate with one another, but Ranvier has claimed that they are continuous with those of adjacent corpuscles (see chapter on the Skin). This point is difficult to set- tle, as it requires a special method and lenses of high power. Ranvier injected a one-fourth per cent, solution of osmic acid into the lower layers of the epider- mis, using a hypodermic syringe, and driving the fluid right and left. There is a form of flattened and pigmented epithelium that may be seen by examining the external surface of the choroid, the ciliary processes, and the posterior surface of the iris. In the choroid these bodies look like a mosaic of polyhedral cells. Such specimens may be permanently preserved by simply dry- ing them, and then mounting in dammar or Canada balsam. Ciliated epithelium. The movement of living cilia is readily seen. All that is necessary is to take the common frog (Rana temporaria), draw out his tongue, and then observing the teat- like projections at the posterior part, snip one off. NC MEDICAL SCHOUL LiumA EPITHELIUM. 59 This little piece is then to be mounted in a one-fourth per cent, salt solution, or serum, and examined. Along the free edge of the mucous membrane the cilia will be seen engaged in active vibratile motion. The appearance presented by a broad expanse of moving cilia has been aptly described as resembling a field of grain which is being swept by the wind, though the motion is often much more rapid than this comparison would imply. It will be seen that various substances, such as blood globules, are propelled in a definite direction. When the frog's mouth is open, all solid particles that are lodged upon the mucous membrane are carried quietly but inevitably toward the gullet, and down toward the stomach. The power of the ciliary movement may be estimated, in a measure, by placing some light but adhering body upon the anterior portion of the roof of the mouth, and then inverting the animal. The sub- stance immediately begins to ascend against gravity, and soon is wedged in the gullet. The same force, though acting in an opposite direction, expels mucus, pus, and indeed all solid matters, from the cavities of the human lungs ; it also propels the ova through the Fallopian tubes into the uterus. In ex- cessive catarrh from mucous membranes the epithelial bodies may themselves be expelled, so that they are not infrequently found with their cilia attached, as in the nasal discharges. After death cilia are hard to recognize ; they contract down to little knobs on the surface of the cells, and can only be demonstrated when the eye looks directly down upon them. Osmic acid is useful to preserve them in their natural condition. Take a fresh specimen and immerse it for twenty-four hours in a one-fourth percent, osmic acid solution, and for another twenty -four hours in dilute alcohol ; then tease and mount in glycerine and water. It will be observed that each cilium is a slim, straight rod, which is apparently structureless ; they rest upon a band, which, with a high power, may be seen to have vertical striations. Effect of reagents. By making use of the moist chamber (Fig. 19, p. 42), and placing a drop of chloroform in the cor- ner of the cell, it will be seen that the action of the cilia rap- idly stops, while, if the chloroform be removed, it will again resume its activity. If carbonic acid gas is admitted, the action of the cilia will at first be accelerated, but subsequently retarded, and eventu- ally stopped (Kuehne). 60 MANUAL OF HISTOLOGY. After shutting off the carbonic acid gas and admitting oxy- gen, the action will again commence. When the ordinary motion has ceased, the gradual application of heat will cause it to return ; but if the temperature be raised continuously, a point will soon be reached where the excessive heat will cause the motion again to stop. Columnar or cylindrical epithelium. This is the epithe- lium^ar excellence of the digestive tract, clothing the mucous membrane from the cardiac orifice of the stomach to the anus. It is also found at the orifices of the ducts of the large excretory glands, such as the liver and pancreas, in the milk-passages of the nipple, and in some parts of the generative system. These cells are tall and narrow, standing vertical to the surface of the mucous membrane. Sometimes they are broadest at their free extremity, at other times about the middle, so that when viewed from above they appear to be separated from one another. The nuclei are rounded, and are either placed about the middle of the cell or near the attached border. They admit of consider- able variation, however, as to size and shape, some of those in immediate contact being broad at one extremity, and some broad at the others ; the free edge also may be uneven. Scrape the surface of a frog's tongue or a rabbit's intestine after washing ; the cells will be seen to advantage. Place some of the scrapings in a drop of glycerine and water to which another drop of dilute acetic acid (J per cent.) has been added, and mount. In this way the nuclei will be brought clearly into view. The cells closely resemble in their shape the columnar variety, except that they have no cilia. Among them will almost always be found chalice or goblet cells. They lie among the columnar corpuscles, and are usually shorter, but broader, expanding in the centre, and terminating at their attached extremities in a single or double process. The sur- face is cupped. They contain one or more nuclei ; whether they are a distinctive cell or not is as yet uncertain. Some suppose them to be the ordinary columnar cell undergoing mucoid degeneration ; others that they are not epithelial at all. Frey regards them as artificial productions. 1 1 The most rational explanation is that furnished by F. E. Schultze. The intra- fibrillar substance is, according to this observer, converted into hygroscopic mucin, which swells up. This constitutes a change in the cell which, from being columnar, becomes goblet-shaped. The wall finally ruptures, and the mucin is poured out. EPITHELIUM. 61 Other varieties of epithelium will be taken up in connection with the different organs. As already stated, many transi- tional varieties occur, even in direct association with the typi- cal forms we have described. Structure of epithelial corpuscles. According to the views of Heitzmann, Klein, and others, the substance of the cor- puscle is pervaded by a network, the minute fibres of which may be seen under a lens of high power. The nucleus or cen- tral body is also similarly provided. Within the meshes of this network there is a hyaline substance, the abundance or paucity of which determines the size of the meshes. The "granules," which have often been described, are, ac- cording to this view, the nodal points of the mesh work. It is also stated that the epithelial cells sometimes have a fine limiting membrane (Klein) ; but even in such instances it IB merely a condensation of the outer part of the corpuscle. Within the nucleus there are also, according to the same ob- servers, fibres, within the meshes of which are not infrequently real granules (nucleoli). The epithelial corpuscles are at- tached together, either by an interlacement of their processes, as in the liver, or by a peculiar cement substance, as in pave- ment epithelium, or by a continuity of their processes, as in the rete mucosum. Recent histological studies have narrowed the field formerly occupied by the epithelial bodies, and, in accordance with these views, the flattened corpuscles which cover serous mem- branes, such as the pleura and peritoneum, will be arranged under the connective-tissue series, rather than under the epi- thelial. The reasons for this change will be given in a subse- quent chapter. BIBLIOGRAPHY. SCHULTZE, M. Die Stachel- und Riffzellen. Virchow's Arch., Vol. XXX., 1864, p. 260. SCHULTZE, F. E. Epithel. u. Driisenzellen. Arch. f. mikrosk. Anat. 1867. RANVIER. Traite technique d'histologie. Paris, 1875. DEL AFIELD. Studies in Pathological Anat. New York, 1878 et seq. KLEIN and E. NOBLE SMITH. Atlas of Histology. 1879-80. HEITZMANN. New York Medical Record, July 31, 1880, p. 133. FREY. The Microscope and Microscopical Technology. New York, 1880. CHAPTER V. THE CONNECTIVE SUBSTANCE GKOUP. MUCOUS OR GELATINOUS TISSUE ; ADENOID TISSUE ; NEUROG- LIA ; FAT TISSUE ; FIBROUS TISSUE PROPER ; CORNEAL TIS- SUE ; INTERMUSCULAR TISSUE ; TENDON TISSUE ; ELASTIC TISSUE. THE term connective substance was first proposed by Reich- ert in 1845, and is now applied to a class of animal tissues whose offices are very important in the economy. Prominent among them is bone, which forms the solid framework of the body, gives it strength, and supplies points of attachment for muscles and tendons ; another group comprises the ligaments, which assist in holding the bony parts, and also some organs, in their proper relations ; others again, of a more delicate nature, fur- nish support or protection for epithelial bodies, blood-vessels, and nerves. Just at the present time the histology of connec- tive substances has an important bearing on many points that relate to inflammation, degeneration, and the development of certain new growths, and it is therefore desirable to have a clear conception of them. This object is best effected by studying each variety separately, not only in its normal condition, but under the changes it exhibits when acted on by the factors that are concerned in the processes of disease. It is a property of these substances that they supplant one another at different times or under peculiar circumstances. As an example, the hyaline cartilage of young life may change into true bone in old age, while, on the other hand, there is always a tendency for fully formed tissue, if inflamed, to re- vert toward the embryonic type. The connective substances may be subdivided as follows : 1, mucous or gelatinous tissue ; 2, adenoid tissue ; 3, neurog- THE CONNECTIVE SUBSTANCE GEOUP. 63 lia ; 4, fat tissue ; 5, fibrous tissue proper ; 6, corneal tissue ; 7, intermuscular tissue ; 8, tendon tissue ; 9, elastic tissue ; 10, bone; 11, cartilage; 12, enamel; and 13, dentine. The word connective tissue was first proposed by Johannes Mueller, and is sometimes used as synonymous with connective sub- stance, but erroneously. The former is merely a variety of the latter, and is usually intended to indicate one or other of the flexible connective substances that form the interstitial material of the body, and in that sense we shall use it for convenience sake, but without implying any special histological character. In precise histological descriptions it is always best to use the special name of the variety intended, such as mucous tis- sue, adenoid tissue, and the like, where the structure happens to be known. It is also well to state here that the term "cellular" tissue, found in many of our anatomies, is apt to mislead the student. The word "cellular" has no reference to cells, i.e., corpuscles, but to the large cavities or spaces that exist in all loose connec- Fio 23. Gelatinous or mncous tissue. Human umbilical cord. tive tissues, of which the subcutaneous is an example. These spaces are easily seen by the naked eye, when inflated with air. Mucous or gelatinous tissue. This is the most simple form that is met with. It is seen to great advantage in the embryonic umbilical cord, which also contains several other varieties of connective tissue. The following method has been found best suited to demon- strate it. Take a small piece of cord at about the third month and immerse it a few weeks in Mueller' s fluid ; make a thin sec- tion through the very soft gelatinous part, then soak it a few minutes in distilled water, to which subsequently a few drops 64 MANUAL OF HISTOLOGY. of acetic acid are to be added so that the solution shall not con- tain more than 1 per cent, of acid, and then mount in glyce- rine. It will then be seen that the softest portion contains numbers of irregularly-shaped, thin plates, some provided with an oval, flattened nucleus, others having none that are appa- rent (Fig. 23). Some of these flattened bodies anastomose by these processes with those of other plates, others are quite free. The substance tying between the cells, the intercellular sub- stance, is quite homogeneous, or slightly granular, in the softest portions, and has at first no defined fibrillation. In the neigh- borhood of the former tissue, lines of fibrillation occur, while at the same time these flattened bodies become smaller, although they are still flattened (Fig. 24, b). Mucous or gelatinous tissue, FIG. 24. Connective tissue in an advancing stage of development. From the umbilical cord. as it is seen in the umbilical cord of an embryo, is properly an embryonic or developmental form of connective tissue which is never found in normal adult life. All the phases of develop- ment may here be seen, from the most primitive, comprised in Wharton' s jelly, to the firm, fibrous fascicles that encircle the vessels. Properly speaking, the true mucous tissue is, as its name implies, a viscid material, and, indeed, is much like half-set glue, in which the corpuscles are scattered with little or even no cohesion. The intercellular substance differs from albumen in not con- taining sulphur ; from chondrin and gelatin, in not being pre- cipitated by boiling, tannin, or the bichloride of mercury. THE CONNECTIVE SUBSTANCE GROUP. 65 At an early stage there are no marks of fibrillations in the intercellular substance, but later fibrils are seen in the vicinity of the corpuscles, and are some of the early signs that organi- zation of the tissue is commencing. The corpuscles at the same time become smaller, and about the central body or nucleus we see a delicate expansion (Fig. 24 a\ which is the envelope of the connective-tissue corpuscle a film of great tenuity. Klein believes that in these corpuscles there are two portions, a granular or firmer part continuous with the processes, and a delicate expansion that is hardly visible. It is certain that the connective-tissue corpuscle is frequently in connection with one or more of its fellows by a mutual anastomosis of processes. The fibrillation appears to be at first limited to certain areas about the cellular elements, so that the long, flattened and pointed lamellae of fibrous tis- sues on which the corpuscles are attached look like large cor- puscles with correspondingly large nuclei. Using a earners- hair brush and pencilling off the specimen under examination, after soaking in a 10 per cent, watery solution of common salt; the apparent nuclei with their delicate envelopes are partially (Fig. 24 1)) or wholly removed. We then see small strips of more or less fibrillated tissue, having no central body that can be recognized, even with the use of strong staining solutions. These and similar observations tend to establish a conviction that the fibrillated portion arises from the soft, gelatinous ma- terial by a process of fibrillation inaugurated by the presence and under the formative action of the connective-tissue cor- puscle. It is not impossible that the fibrin of the blood, which, though fluid in the blood-current, is often known to be de- posited in delicate filaments, may contribute largely, if not wholly, to the formation of the fibrillse. As the tissue becomes firmer, the little plates with their anastomosing branches form a loose network which separates the fibrils into distinctive bundles or fascicles, and encircles them more or less completely. There is another view which is offered as an explanation of the process by which connective tissue becomes organized. It is this. The change is derived wholly from the corpuscles. Some of them split up into fibrils, constituting the fibrous part of the tissue ; the others remain, and are developed into connective-tissue corpuscles. This view has the support of excellent histologists. 5 00 MANUAL OF HISTOLOGY. The white corpuscles of the blood are pre-eminently suited for building tissue. When blood is organized, which occurs not infrequently, the white corpuscles at once assume an im- portant role, while the red are soon melted down into a homo- geneous mass, that is usually absorbed. This change is ob- served under various pathological conditions. Fibrous tissue. This substance, which is also known as fibril] ated connective tissue, is the fully developed material that has just been described. It occurs either in parallel FIG. 25. Reticular form of connective tissue. From the human umbilical cord. bundles or fascicles, in interlacing lamellae, or as a fenestrated material containing larger or smaller openings. A special va- riety, the reticular, is seen to great advantage in the umbilical cord of an infant at birth (Fig. 25). If a cut be carried through the spongy portions of the cord, it will be seen that the tissue is composed of bright, shining, branching bundles, <#, superimposed upon which are a num- ber of oval, flattened plates, a, at intervals ; about them is THE CONNECTIVE SUBSTANCE GROUP. 67 a delicate envelope, &, which appears to be highly elastic, so that it will stretch or relax, according as the networks are compressed or dilated. By teasing with needles or immersion for a few days in a 10 per cent, watery solution of common salt, these corpuscles can often be separated from the bundles, and then they will be seen to form a connected system. When entirely isolated from one another, they often appear spindle- shaped. That this is not their character may be shown by passing a current of fluid through the specimen a method already described under the name of irrigation. It is accom- plished in this way : having affixed small strips of filter-paper to the edges of the cover on either side, and moistened one side with fluid, the excess will be absorbed by the other slip, caus- ing a current by which the corpuscles may be made to roll over. We then learn that they are disks of an irregularly flattened form, having longer or shorter processes (c, c, Fig. 25) variations in form which seem to depend, in a great measure, upon the tension to which they are exposed, and the position they occupy in the tissue. This explanation will serve to show why all measurements of such corpuscles are merely approximative, and have but little value. They are shrunken by immersion in alcohol, swollen by the imbibition of water, are drawn out into long, flattened spindles when the tissue is put on the stretch, or become rounded, per- haps nearly spherical, during relaxation. They may assume almost any form as the result of pressure. The nucleus may be regarded as more of an exception to this rule ; at any rate it seems that in fresh specimens, when the substance has been swollen by immersion in water, it is always oval and flattened. The bundles upon which these bodies lie are somewhat cylindrical in form, branched, and composed of separate fila- ments, that can be separated by Mueller's fluid, or a 10 per cent, wate^ solution of common salt. Two other forms of corpuscles may also be noticed : (1) the kind observed by Waldeyer, and called plasma cells, and thought by him to be corpuscles peculiarly prone to take up fat to make fat tissue, bodies four or five times the size of a lymphoid corpuscle, and rounded in form, containing a cen- tral body ; and (2) the ordinary lymphoid corpuscles, seen at times in all tissues. G8 MANUAL OF HISTOLOGY. The form of fibrous tissue that occurs in parallel lamellae is well shown in the mesentery of the frog, and in serous mem branes generally. No great difficulty will be met with in pre- paring this tissue, for it is only necessary to remove it from the frog in the fresh state, acidulate it in a weak (1 per cent.) watery solution of acetic acid, and mount it in glycerine. It will be seen that these so-called spindle-cells are really flattened plates, when viewed flat-wise, and generally irregu- larly quadrilateral, though the form varies somewhat in each instance. It is not improbable that some which appear spindle-shaped, and lie in the interfascicular spaces, have a double office, one of which is to guard the nutrition of the tissue, and the other to form a partial lining of a lymphatic channel. The researches FIG. 26. Connective tissue in the mesentery of the frog. of Klein tend to establish this double relation, for they show that these corpuscles lie in the walls of the tymphatic radicles, which are themselves in direct communication with the perito- neal cavity by breaks in the endothelial connective-tissue cor- puscle coating and in actual apposition with the endothelial elements of the serous membranes. During the last few years there has been a tendency to regard the serous membranes, especially such as have large openings and slight reticula, as having no connective-tissue corpuscles, other than the endothelial, which form, THE CONNECTIVE SUBSTANCE GliOUP. GO a covering over them. In the larger trabecles, however, there are connec- tive-tissue corpuscles, in addition to those just mentioned; they are well seen in profile, interposed between the bundles (Fig. 26). Adenoid tissue (Fig. 27). Adenoid tissue is the name given to the delicate substance that forms the framework of the lym phatic glands. It consists of fibres in networks which form an FIG. 27. Adenoid tissue from a human lymphatic gland. intricate texture, that is filled with the rounded bodies com- monly known as lymphoid cells. It is exceedingly difficult to analyze these tissues, because it is not easy to demonstrate any- thing that conveys to the eye our idea of a cell, i. e., excepting, of course, the lymphoid corpuscle. The best mode of proced- ure is the following : Take a lymphatic gland such as the in- guinal in the early stage of inflammation : harden at first, in Mueller's fluid, and then in alcohol, and make sections through it. On viewing such a specimen under the microscope it will exhibit a delicate meshwork, packed with lymphoid corpuscles (Fig. 27, a). Now, if we take such a section and agitate it in a test-tube with water for a considerable length of time, and then place it upon a glass slide, pencilling it with a camel' s-hair 70 MANUAL OF HISTOLOGY. brush, most of the lymphoid cells will be removed, and the delicate network, c, will be very thoroughly exposed. It will be seen that, at certain parts of this mesh work, there are flattened bodies, b, of small size, lying upon the larger cords of the meshes. It has been held by Klein and other his- tologists that the reticulum is made of branching corpuscles ; but this statement must be modified. In some instances the appearance of netted corpuscles is well seen in those portions of the glands that are regarded as the lymph passages, where the adenoid tissue forms the framework of the part. The net- work seems to be comprised of delicate, silk-like cords, enclos- ing vast numbers of lymphoid corpuscles, and exhibiting, at the nodal points of the meshes, flattened corpuscles. These delicate fibres, however, are often replaced by heavy trabecles, , has processes which corne clearly in- to view where the corpuscles are iso- lated. Pavement endotJielium (epitheli- um). From the views that have been advanced it is plain that we are pre- pared to abandon the old idea that the mesentery, peritoneum, the pleura, endocardium, serous cavities, and ten- Fl( ^ 32 Development of fibrous tis- dinous sheaths are lined with epithe- sue. Fibroma of the scalp. r lium. It is becoming more and more evident from studies in the lymphatics that they are lined with connective-tissue corpuscles, which, on the one hand, are in actual continuity with the interfascicular connective-tissue cor- puscles, and, on the other, with the pavement corpuscles of the serous cavities. It is but a step farther and in the same direction to trace the endothelium of the endocardium out through the arteries and veins into the capillaries and recog- nize the connective-tissue corpuscle as the one cellular element of all these tissues. The special methods by which these parts are studied may be found described in the chapters more es- pecially devoted to these topics. Nitrate of silver and chloride of gold are still prominent among the reagents that demon- strate them most distinctly. Ehrlich has recently described peculiar connective-tissue BIBLIOGRAPHY. 81 corpuscles, which he previously supposed to be identical with Waldeyer' s plasma cells, but which he is now inclined to re- gard as a distinctive group of bodies. They are characterized by a special power of intense coloration in specimens treated with certain of the aniline dyes. Red and violet colors appear to be best suited to reveal the presence of these bodies, called by Ehrlich granular cells. Acetic acid produces a diffuse staining of the nucleus in these aniline stained cells. At the same time the conspicuous granules lose their color. The same author also states that the granular cells commonly found in such great abundance in inflammatory processes are not modi- fied leucocytes, but are derived from the fixed connective- tissue corpuscles. According to Ravogli, the connective-tissue corpuscles of the corium and subcutaneous tissue are branching cells, whose processes unite to form anastomoses. With advancing age these cells undergo structural alterations, and their processes begin to form reticula of elastic tissue. Simultaneously with this metamorphosis the cell-bodies are said to become flattened, elongated, and united in longitudinal rows. At length the cells as well as their processes are transformed into ordinary elastic tissue. BIBLIOGRAPHY. SATTERTHWAITE, T. E. On the Structure and Development of Connective Sub- stances (Prize Essay). New York Med. Jour. , July, 1876, and Monthly Micro- scop. Jour., October and November, 1876. FLEMMING. Arch. f. Anat., etc. 1879. 401454. STRICKER. Allg. Wien. med. Ztg. 1879. XXIV., 547. KOLLMANN. Centralbl. f. d. med. Wiss. 1878. XVI., 881. EHKLICH. Verhandl. d. Berliner phys GeselL Jan. 17, 1879; Arch. f. Anat. u. Phys. Phys. Abtheil. pp. 166169. 1879. RAVOGLI. Wien. med. Jahrb. Heft 1, p. 49. 1879. Also the more recent text-books of Klein and Eanvier. 6 CHAPTER VI. THE CONNECTIVE SUBSTANCE GKOUP Continued. CARTILAGE. CARTILAGE is divided into three prominent varieties : 1, hyaline ; 2, fibrous ; and 3, elastic or yellow. There is, in addition, a form called ossifying, which will be described in connection with the development of bone. Hyaline cartilage is the tissue from which the bones of the skeleton are first made ; it is also found in the articular and costal cartilages, and in the cartilages of the larynx, trachea, and bronchi ; possibly also in some of the nasal cartilages, and in portions of the sternum. All of these tissues consist of a solid material or matrix, in which are capsules which contain the true cartilage corpuscles. The character of the intercellular substance determines the particular variety. Thus, hyaline cartilage appears, under the microscope, to be structureless and homogeneous. Fibrous cartilage, on the other hand, has distinct lines of fibrillation extending through it. Elastic cartilage is permeated by net- works of elastic fibrils. Hyaline cartilage, though so-called because of its apparent absence of structure, is now known to be less often structure- less than has been supposed, for the researches of Tillmanns have revealed distinct marks of fibrillation in some adult artic- ular and costal cartilages. Soaking the tissue in a 10 per cent, solution of common salt will dissolve out the cement sub- stance and isolate fibrils, though the tissue has previously ap- peared homogeneous. Staining with the picro-carminate of ammonia (Ranvier's formula) will also demonstrate the fibrils. Each capsule is probably invested by a delicate membrane, which is thicker in some instances than in others. Extending THE CONNECTIVE SUBSTANCE GROUP. 83 from tliis cavity are minute canals, which communicate with those of other capsules in many instances, and thus, in all probability, establish a system of serous channels which convey the plasmatic fluid, i.e., the lymph. Many years ago H. Mueller gave a description of minute passages radiating out from the cartilage capsules. Since this time the matter has been studied by numbers of observers, but opinions have been divided as to their existence. More recently A. Budge has detailed a method by which he claims that a complete lymphatic system can be demonstrated in hyaline cartilage. Em- ploying a solution of Berlin blue, he injected the cartilage of an epiphysis from which the articular lamella had been cut off. Having thus opened and exposed the substance of the cartilage, he found it permeated with minute blue net- works that were in communication with the cartilage capsules. A connection with the lymphatics of the bone was also shown. Nykamp, who prosecuted his investigations about the same time (1876-77), verified the work of Budge, though his methods were different. He experi- mented on rabbits, injecting one gramme of indigo carmine (in substance) into the abdominal cavity. Blue granules appeared in certain spaces, which had shown themselves to be hollow passages by a previous soaking in the neu- tral chromate of ammonia. The cartilage commonly known as hyaline was also, by this means, shown to be fibrillated. Round about every cartilage capsule there is usually an area' of hyaline material. When very thin sections of cartilage are made, these areas sometimes become visible ; soaking in acids is said also to bring them into prominence (Klein). The amount of intercellular substance in comparison with the capsules varies ; as a rule, there is less of this substance near the periphery of the cartilage. When the amount is so very small that the tissue is almost cellular, it is called par- encJiymatous cartilage ; this condition is observed in all carti- lages, at an early stage of development, and in some portions of the adult forms. The cartilage corpuscles are rounded bodies, sometimes oval and sometimes pyriform. In the nor- mal condition they fill up the capsule, but after the application of reagents that shrivel, such as alcohol, they are withdrawn from the walls of the capsules, being only attached at a few points (perhaps where their processes extend out through the canaliculi). The cell-corpuscles and nuclei are said, by some recent ob- servers, to exhibit networks in their interior (Schleicher and Flemmirig). They frequently contain, in addition, moving bodies, which are often oil-globules of minute size. 84 MANUAL OF HISTOLOGY. The cartilage capsules do not usually appear to have any connection with one another when examined in an indifferent fluid, though in the episternal cartilage of the frog, immedi- ately beneath the perichondrium, a connection may occasion- ally be seen. Division of tlie cartilage corpuscle. One of the prominent features seen in cartilage is the division of the cartilage cor- puscle. First we notice the splitting of the nucleus ; then of the corpuscle itself. When such a division has taken place the corpuscies are called daughter-cells (Fig. 33). As a next step each daughter-cell may divide and again subdivide, and PIG. 33. Fresh cartilage from the triton. (Rollett.) thus we have developed in one capsule four or eight cor- puscles. Sometimes it will be observed in the same specimen that with each division of a corpuscle, hyaline matter from without the capsule pushes in, and so from the original capsule two are now formed. Calcification of hyaline cartilage. Hyaline cartilage in old age is infiltrated by a deposit of the salts of lime, which, when seen under the microscope, have a granular appearance. The deposit occurs first round about the cartilage capsule (Ranvier). Nerves and blood-vessels are not supplied to hyaline car- tilage proper, though blood-vessels which belong to adjacent tissues sometimes dip into it or pass through it. Methods of studying hyaline cartilage. An excellent and simple plan is to snip off the tip of the episternal cartilage THE CONNECTIVE SUBSTANCE GROUP. 85 from the frog ; strip it of pericliondrium and mount in serum. The shoulder-girdle of the triton (newt) may also be employed. It will then be seen that there are numbers of granular cor- puscles, with nuclei scattered irregularly throughout an ap- parently homogeneous, i.e., structureless matrix. If now a little water be added to the preparation, it will be seen that the corpuscles are made to shrivel, and in so doing they expose the wall of the cavity or capsule in which they lie. The cor- puscles do not appear to have any uniform size or shape : some- times they are single ; again they are double (daughter-cells) ; occasionally they are united with the corpuscles in adjacent capsules. The nucleus is apt to be round and full ; the corpus- cles are apt to be filled with dark spherical bodies which are usually fatty molecules, as may be shown by employing a di- lute solution of osmic acid (1 per cent.). Using the silver method it will be seen that there exists, in the apparently homogeneous matrix, numbers of corpuscles whose nature is not fully under- stood. Incidentally it may be mentioned that the silver method often exhibits curious markings in all tissues. / Sometimes these appearances are due to the silver itself, and some caution is therefore necessary in deducing conclusions from the method. The gold method J shows that there are concentric rings about the capsules, but it is highly probable that this phenomenon is artificial. Eanvier recommends, as a staining fluid, purpurine, the formula of which is as follows : Take one gramme of powdered alum and add to it two hundred grammes of distilled water, which boil in a porcelain dish. To this solution add some pow- dered purpurine diluted with water. If the boiling be now con- tinued, a portion of the purpurine will dissolve. Filter while warm, and receive the colored fluid in a flask which contains 60 c.c. of alcohol. This liquid has a rose-orange color. The nuclei of the corpuscles will be colored red and have a double contour ; the cell-body will be bright red. Hyaline cartilage may be well exhibited in the respiratory tract of young children, as in the cricoid cartilage of an infant two or three years old. Yellow elastic or reticular cartilage is a very distinctive form. It consists of the hyaline variety permeated with elas- tic networks. Examples of it may be obtained from the human 1 See chapter on General Methods. 86 MANUAL OF HISTOLOGY. epiglottis, laryngeal cartilages, and the pinna of the ear (Fig. 34). The presence of elastic fibres is proved by their resistance to boiling in acids and alkalies, and their failure to color with carmine. Sections may be made with the knife and prepared in almost any of the ways already mentioned. The appearances already described are not seen in the early development of elastic tissue, but are easily identified in adult FIG. 34. Section of the boiled and dried auricle of the human ear : a, retiform cartilage ; 6, connec- tive tissue. (Rollett.) life. Even then the elastic fibrils may only be found in the in- terior of the cartilage, while at the periphery the matrix is hyaline. Elastic cartilage is coated over with a delicate mem- brane the pericJwndrium. Fibrous cartilage. This variety is also known as fibril - lated or fibro-cartilage. The matrix has probably no elastic fibrils, but is interspersed with connective- tissue bundles. It is found in the cartilages which make the lips of the joints, the inter-articular cartilages, the cartilaginous deposits in tendons, the cartilage of the symphysis pubis and of glenoid fossae, and possibly in the intervertebral ligaments and sesamoid carti- lages. There is often more or less hyaline material about them. In many instances the line of distinction between cartilage and fibrous tissue is difficult to make out. ' Where, however, dis- tinct corpuscles can be demonstrated, the tissue may properly be regarded as cartilage. These bodies are similar to those seen in hyaline and reticular cartilage. Division of the cartilage-corpuscle. A problem that has THE CONNECTIVE SUBSTANCE GEOUP. 87 attracted the study of various histologists for a number of years, since Leidy, in 1849, first directed attention to it, is the mode in which cartilage-corpuscles divide. Various theories have been afloat, each with its special supporters. Dr. W. S. Bigelow, of this country, in 1878 reviewed the subject carefully, pursuing his investigations on the hyaline cartilage of the triton, tree-toad, frog, various fishes, the guinea- pig, total pig, and the human embryo in health and disease. His inquiries were especially concerned with reference to the statement of Buetschli, that in the divisions of the corpuscles, the splitting of the nucleus and cell-body are simultaneous. As the result of Dr. Bigelow' s work, he concludes that the old theory is still tenable, viz., that at first there is a division of the nucleus, and that subsequently a septum is found in the cell-body. After division takes place the matrix of the carti- lage penetrates between the corpuscles, and thus two cavities are formed. This view has received confirmation from very extended and elaborate researches by Schleicher, to which Flemming has also expressed a provisional assent. Structure of the cartilage-corpuscle. According to Schlei- cher the nuclei are provided with peculiar filaments and gran- ules which undergo amoeboid movements when they are in the act of dividing. In the cell-body of young cartilage-corpuscles he has seen no network, such as has been described by some later writers (Heitzmann, Klein, etc.), though in the adult tissue peculiar linear markings are evident. He thinks that the nu- cleus is not permeated by a network, but is homogeneous. Reticulated appearances are apt, he thinks, to be the result of using reagents that alter the natural quality of the tissues. According to Flemming, the nucleus of the cartilage-corpus- cles contains a network which gives the appearances described as " coarsely granular." In the drawings of this author the cell-bodies nowhere exhibit a network, but, on the contrary, linear markings, which have often a concentric direction. In many, the internal structure is represented as homogeneous. The conflict of opinion now apparent in this matter, and the marked differences in the micro- scopic drawings of the same object, make it apparent that these topics are still to be regarded as subjudice. Structure of the intercellular substance. According to Spina there is an intra- cellular substance in cartilage which is directly continuous with the intercel- lular substance, which itself exhibits an extremely delicate network. This 88 MANUAL OF HISTOLOGY. condition, which he regards as an early form of cartilage, undergoes changes, in so far that the intercellular network is enlarged and narrowed so as to give the appearance of fascicles or bundles of parallel fibres. The meshes are filled with a finely granular substance which is thought to be partly formed at the expense of the network. The method employed in demonstrating these ap- pearances consisted in taking the articular extremities of frog's bones, im- mersing them three to four days in alcohol, then cutting thin sections, and finally, examining them in alcohol. BIBLIOGRAPHY. TILLMANNS. Archiv f. mikrosk. Anat. X. Bd. X. p. 401. 1874. BUDGE, A. Archiv f. mikrosk. Anat;. Bd. XIV., S. 65. 1877. NYKAMP. Archiv f. mikrosk. Anat. Bd. XIV., S. 492. 1877. HEITZMANN. Studien am Knochen u. Knorpel. Wien. med. Jahrb. 1872. V. and H.'s Bericht. BIGELOW, W. S. Arch. f. mikrosk. Anat. XVI., 2. 1878. SCHLEICHEB. Ibid. FLEMMING. Ibid. KLEIN and E. NOBLE SMITH'S Atlas of Histology. 18791880. RANVIER. Traite technique d'histologie. 1877. BUETSCHLI. Zeitschr. f. wies. Zool. 29, p. 206. SPINA, A. Sitzb. de k. Akad. der Wiss. Bd. LXXX., LXXXI. 1879, 1880. CHAPTEE VII THE CONNECTIVE SUBSTANCE GROUP. Continued. BONE. THEEE are two principal varieties of bone known to anato- mists, the compact and the cancellous or spongy. The former is found in the shafts of all the long bones of the body and along the outer surface of all the short and flat bones. The latter occurs in the articular extremities of all long bones and in the interior of all short and flat bones. Compact tissue consists of an unyielding, almost inelastic, massive framework, which is traversed by networks of blood- vessels and lymphatics, and perhaps by nerves. The dense organic substance forming the groundwork of all bone ossein is in reality nothing but a form of connective substance almost precisely resembling ordinary fibrous tissue, but which is evenly infiltrated with minute molecules of the carbonates and phosphates of lime and some other inorganic salts. These insoluble matters are so thoroughly intermixed with the fibrous tissue that they give it great solidity, though at the same time they restrict its flexibility, and therefore increase its suscepti- bility to fracture. Like other forms of the connective-tissue series, it contains corpuscles that are disposed in a regular way between lamel- lae, which here correspond to the fascicles of fibrous tissue. The province of these corpuscles is doubtless the same as that of other connective-tissue corpuscles, viz., to preside over the nu- trition of the tissue in which they are found. After decalcification by strong acids, such as the nitric or muriatic, if the residue be boiled it will yield gelatin or chon- drin. These corpuscles that have just been described are not al- 90 MANUAL OF HISTOLOGY. ways easily recognized, and, in fact, have often been ignored by writers of anatomical text-books. They were not detected for a long time, because the capsules in which they are em- bedded received all the attention, and were even called 'bone- corpuscles. But when it was discovered by Yirchovv that these bodies had nuclei, and that they could be separated, to- gether with their processes, from the bone, it was supposed that the nutrition of the tissue was maintained through them, acting in the capacity of hollow tubes. This view Virchow at one time supported. Subsequently it was discovered that in- jection fluids could be forced into the canaliculi and round about the corpuscles, so that three facts became assured : (1) the existence of capsules in the bony substance with radiating and anastomosing passages, the lacunae and canaliculi ; (2) the presence of nucleated and branched corpuscles in the lacunae ; and of spaces (3) about the nucleated corpuscles and their processes, suitable for the movement of fluids designed for the nutrition of the part. The structure of bone then became clear, and its similarity with other connective substances well established. These bony canaliculi extend to the wall of the Haversian canal, the great channel conveying the blood-vessels and larger lymphatics. Thus a lymph-canalicular system permeates the bone in close connection with the blood-vessels, bathing every bone-cor- puscle. When a cross-section is made of any long bone, it will be observed that most of the lamellae have a concentric arrange- ment about each Haversian canal (Fig. 35, b). But it will also be seen that there are other groups of lamellae whose arrange- ment is slightly different. For example, at the periphery of the bone their direction is parallel with the surface. Such lamellae may be represented at a. They are known as the intermediate or circumferential (Tomes and De Morgan). Another group, only partly encircling each canal, is known as the peripJieric or interstitial, c. The first mentioned, imme- diately about the canal, are the concentric, b. Schaefer believes with Sharpey that each lamella consists of fibres crossing each other diagonally, and separated on either side by a homogeneons layer. According to Von Ebner, the peculiar cross striations belong only to Canada balsam preparations that are old. These markings are due to the peculiar refractive power of the balsam which fills the canaliculi. THE CONNECTIVE SUBSTANCE GKOUP. 91 The arrangement just described is found in all compact bone where there is any considerable thickness, but when, as in flat bones, the cortex is very thin, the lamellae often pursue a straight arid parallel course. Some of these lamellae or plates exhibit transverse striations ; others are homogeneous. In Fig. 35 may be seen the lacunae lying between the lamellae. They appear as dark spaces disposed at quite regular intervals and, having their long axes parallel with the course of the lamellae. Laterally each corpuscle gives off numbers of pro- cesses, many of which branch, while all, or near- ly all, anastomose with corresponding branch- lets of other corpuscles- A branchlet is also given off from the end of each corpuscle, and forms a connection with the adjacent bodies lying in the same inter- lamellar space and in the same plane. The Haversian canals form a broad-meshed network through- out the bone, establishing a communication between the central marrow cavity and the external surface of the bone (Fig. 36). The arrangement of parts comprised by each Haversian canal, with its investing lamellae, and interposed lacunae and their anastomosing carialiculi constitutes an Haver sian system. Though found mainly in the compact tissue, they may also be seen in the large trabeculae of the spongy substance. As seen in Fig. 36, the Haversian canals form a network of which the longitudinal tubes are the larger and longer. Besides convey- ing blood-vessels and lymphatics they have a certain amount of connective tissue which varies according to the locality, and establishes a more or less complete connection between the con- nective tissue of the marrow cavity and of the periosteum. In young bone this is well seen ; in adult bone the direct continuity can with difficulty be traced, as the vessels are apt to till the tubes pretty completely. PIG. 35. Transverse section of human femur, deprived of inorganic material by hydrochloric acid. (Rollett.) 92 MANUAL OF HISTOLOGY. Preparation of dry bone. In order to study the char- acteristics which have just been described, any human long bone may be taken. It should be stripped of its soft parts, bleached, and well dried. Thin sections are then to be made both in a longitudinal and transverse direction, with a watch- spring saw. Next, cleanse them well in water to which a little bicar- bonate of soda has been added ; then place on a whetstone and grind down by rubbing backward and forward with the finger until they are suffi- ciently thin ; or the sections may be placed between two plates of ground glass and rubbed down. Finally, when so thin that type may be read through them, mount either dry or in Canada balsam or dam- mar varnish. All the char- acteristics already described may then be seen. Preparation of decalci- fied bone. Another method consists in first removing the earthy salts. If it is desira- ble to accomplish the work rapidly, cut the bone to be prepared into the smallest available pieces and immerse from four to five days in a 10 per cent, watery solution of Fio. 36. -Longitudinal section of human nlna, show- hydrochloric acid, ing the Ha versian canals forming meshes. (Rollett.) m , , ,. ,, . The completion of this process may be determined by testing the bone with a fine cam- bric needle. So long as it meets with resistance, the presence of the bone-earths is certain ; on the other hand, if it enter easily, the process of decalcification is over, and the piece ready for cutting. Now wash thoroughly in water, so as to remove the acid, place in 80 per cent, alcohol, gradually increasing the strength to 95 per cent. The specimen is then ready for use and may THE CONNECTIVE SUBSTANCE GROUP. 93 be treated precisely as any other tissue of the body. If more time is at the disposal of the student, chromic acid may be used in a J per cent, solution. This process is rather slow, re- quiring several months. It may be materially hastened by the use of nitric acid (2 per cent.). It has been found that after immersion in chromic acid for a few days, the soft parts are rendered insensible to the action of other strong acids, such as nitric and hydrochloric, when used in the dilute form. These chromic acid preparations are exceedingly beautiful objects FIG. 37. Bone lacunaa with their processes. (Rollett. ) when seen with low powers. The matrix is of a deep grass green. If a thin section is stained with borax-carmine (Arnold's formula) the bone-corpuscles and connective tissue are stained red, and the contrast of color brings out the finer elements very distinctly. Picro-carmine may also be used, and then the muscular tis- sue, if any chance to adhere to the bone, is stained yellow ; or eosine and hsematoxylin may be used instead of borax car- mine, and thus very excellent examples of triple staining pro- cured. Sometimes a saturated solution of picric acid is em- ployed to decalcify, but the excess of acid, after taking out the bone-earths should be thoroughly removed by soaking in 94 MANUAL OF HISTOLOGY. water before immersion in any staining fluid. In preparing a specimen for cutting with the knife it may conveniently be held in the hand, or, if the microtome is used, the bone may be embedded in the ordinary mixture of wax and oil, pith, or liver, according to methods already described. Rutherford re- commends glycerine jelly for this purpose. Any of these plans of preparing decalcified bone will reveal the presence of the bone-corpuscles within the lacunae. These will be found to correspond quite closely in size and shape with the cavities. They may also be shown to have a direct continuity with the connective- tissue corpuscles of the perios- teum. In growing bone this is more evident. A nucleus can also sometimes be seen in the bone-corpuscle. In Fig. 36 the lacunae, with their canaliculi, are well shown. Sharpens perforating fibres. Attached to the outer sur- face of compact tissue, and penetrating the bone at right an- gles, are certain fibres which have been named after Sharpey, their discoverer. Take a flat bone of the skull that has been decalcified, seize pieces with the forceps, tear them out from the surface, and examine in water. In some of the fragments the bundles of fibres will be seen ; in others the lamellae, perforated for the fibres. If a portion of tendon adhere to the bone, and a sec- tion be made through the two at their line of apparent junc- tion, it will be seen that the tendon-fibres are continuous in the bone with Sharpey' s fibres. A very prevalent view is that they constitute the remains of the periosteal processes, which we shall see are largely con- cerned with the ultimate development of bone. Cancellous tissue. All of the elements of bone, that go to make up a Haversian system, are found in the cancellous tissue, so that, in this respect, it does not differ from the com- pact. The chief peculiarity lies in the marrow cavities, or channels, as they might appropriately be called, and they indi- cate either, on the one hand, that the bone is passing through a developmental stage ; or that it is being rarefied by a process of retrograde metamorphosis ; or, finally, that it has reached a stadium of repose in either of the first-named changes. These points will be further particularized when the growth and de- velopment of bone is explained, but the reader is now prepared THE CONNECTIVE SUBSTANCE GEOUP. 95 for the rather remarkable proposition that compact bone is formed out of spongy, and spongy out of compact. These marrow channels are a series of branching and anasto- mosing tubes, rich in corpuscular elements and vessels. In young bone the latter are known as red marrow. When a longitudinal section has been made through a tubular bone, it will be seen that the channels are enclosed in an osseous net- work, whose meshes differ much in shape. In the articular extremities they are long and narrow ; at other points, more nearly quadrilateral. There is a second variety of marrow, known as yellow, which is found in the central cavity of the long bones. The yellow color is due to the presence of fat, though it also contains peculiar, small, colorless corpuscles, not unlike the leucocytes of the blood, and known as marrow-cells, together with the ordinary branched and nucleated connective-tissue corpuscles, also large multi-nucleated bodies that are usually granular and sometimes striated, and blood-vessels. The large corpuscles are the myeloplaxes of Robin (giant-cells). The red marrow also contains marrow-cells, though but few fat-cells. It is remarkable for being the seat of the peculiar nucleated blood-corpuscles that have been described by Neu- mann and Bizzozero. They are transitional between the white and the red in size, and have a uniform yellowish green color (Klein). The authors above referred to found the nucleated corpuscles in the red marrow of the ribs and bodies of the vertebra ; they resembled blood-corpus- cles that are found in the human embryo, and were regarded as evidence that the bones have bloodmaking properties. Later researches (Orth and Litten) have seemed to corroborate these views, and to have shown that in certain morbid states of the blood, as in carcinoma, phthisis, and syphilis, an effort of this kind is made for the relief of the constitutional infection. Experiments upon dogs have also added further testimony and have shown that after extreme artificial anaemia there is a new formation of blood-globules, in which the nucleated bodies play an active part, together with other elements, such as the giant-corpuscles of Hayem, etc. These views, however, have met with opposi- tion, and Eutherford (" Pract. Histology," p. 88) maintains that the nucleated corpuscle is an indication of corpuscular disintegration rather than of new- formation. The periosteum is a layer of dense fibrous tissue closely covering the bone, and connected with it by a thinner layer of 96 MANUAL OF HISTOLOGY. looser texture. The external portion may be composed of sin- gle, double, or treble laminae of varying thickness. The inner or osteogenetic portion is of great interest and importance, as it contains the osteoblasts, which are active agents in the formation of a great part of all bones, as we shall presently see. Development of bone. Views as to the method by which bone is formed have undergone great changes within the past few years, and it may be stated that most modern observers have given in their adhesion to the theory that bone is not developed by a calcification of cartilage, but by a long and complicated series of changes inaugurated by the corpuscles of the marrow cavities, on the one hand, and those of the periosteum, on the other. These conclusions have been the result of very extended researches conducted by a variety of methods and upon many kinds of animals. As the mode of growth in man and horned cattle is identical, a good method of procedure is as follows. Take the hoof of a yearling bullock, and, removing the bones, macerate them a few days in a 10 per cent, watery solution of h3 7 drochloric acid and then in chromic acid (gr. ij. lj.). In a few days they will be decalcified sufficiently to allow of a thin section being shaved off from the surface so as to include parts where ossifi- cation has already commenced. The sections may then be stained in a neutral solution of carmine and mounted. The gradual stages between the advancing bone and the liquefying cartilage can now be studied. Following the changes from the surface of the articulation toward the centre of the bone, there is seen at first, beneath the fibrous layer, a stratum of hyaline cartilage. The corpuscles are long, flattened, and lie parallel with the surface. Passing to a greater depth they become larger, and increase in number by gradual progression. As these capsules enlarge and their contents multiply, they begin to be arranged about the wall of the cavity, while the matrix gradually wastes away. A little farther and there is a deposit of calcific material in the intercapsular sub- stance. Another step internally and the cartilage capsules have in part coalesced, and now they are beginning to be filled by the marrow tissue pushing up from the central parts of the bone. When the connective tissues and vessels that constitute this arborescent growth have entered the capsules, the corpus- THE CONNECTIVE SUBSTANCE GROUP. 97 cles that line them are called osteoblasts. Whether or not they are identical with the cartilage-corpuscles, or belong to the budding marrow-processes, seems to be a matter of doubt. Klein intimates that the cartilage-corpuscles disintegrate. Ran- vier has seen no proof of it. It is probable that some of the cartilage-corpuscles persist, certainly to a limited extent, and preside over the remains of the calcified cartilage. The bulk of the new bone is made up, however, of new material which is deposited under the form of concentric lamellae about the marrow cavities, most likely by a proliferation of the osteoblasts. These changes may all be observed to advantage in the specimen just mentioned, and the successive gradations of the process can be conveniently magnified, so as to be easily seen, by making sections obliquely to the surface of the bone. With a low power the specimens will have uncommon beauty, as the corpuscles take the carmine well, while the interstitial tissue is of a bright, transparent grass-green. In a vertical section of a long bone, while the process is essentially the same, there are some modifications in the suc- cessive steps. Thus the spongy bone of the epiphysis en- croaches on the cartilage, causing it to be absorbed in the man- ner already described, but the intermediary cartilage, lying between the epiphysis and diaphysis, is seen to have its cor- puscles arranged in long lines parallel with the axis of the bone ("step-ladders"). The bone meshes of the encroaching bone are also shaped in correspondence with the cartilage cap- sules, that is, they are long and narrow. Formation of bone through the medium of cartilage. The successive changes in this species of bone development have been best described by Klein. According to him the hyaline cartilage that is destined to prepare the way for bone is covered with perichondrium, consisting like the periosteum of two layers. This membrane does not at first contain mature fibrous tissue, but merely the rudiments of it, under the form of spin- dle-shaped corpuscles ; its internal layer, however, is early pro- vided with spherical corpuscles, the future osteoblasts, and is rich in vessels. Subsequently this osteogenetic envelope puts out processes (periosteal processes, Virchow) that penetrate into the carti- lage-capsules, which, melting as the external growth makes its 7 98 MANUAL OF HISTOLOGY. way inward, develop communications between the capsules, so that in this way a cartilaginous network is formed that is filled with the arborescent tissue. This change in the cartilage, which is characterized by absorption and rarefaction, is called chondro-porosis. At a more advanced stage the cartilage around the oldest channels has become transparent in places, while the walls are irregular, because portions of calcified trabeculse project into them. These irregular spaces are called primary marrow cavities. Now upon the walls may be seen, not the cartilage- corpuscles, but the osteoblasts, which are proceeding to develop concentric layers of osseous tissue. When this process has been completed, the osseous tissue will be found to have replaced the calcified. cartilage, and true bone has been formed. But this action may be no sooner completed than absorption will again commence, and at first in the last or most internal layer of the Haversian system. This process is essential for the development of the central marrow cavity. After an Haversian system has been removed, the matrix will also disappear. Now, while this cavity is filling up with marrow a gradual development of bone is taking place from the periosteum, which slowly encroaches upon the bone whose formation we have just described. This last stage results in the formation of adult bone. When it has been completed all the first formed bone has been absorbed before it. This periostea! or metaplastic bone is at first spongy, as is all new bone ; in the fulfilment of its task it next appears to form compact bone, and then part of this latter is rarefied, as, for example, along the wall of the central cavity. Thus, as we have already seen, compact bone is formed from spongy, and spongy from compact. The peri- pheric or interstitial lamellae are either the remains of calcified and unabsorbed trabeculse, or perhaps the walls of other Haver- sian systems forming sides of the bony network. Formation of bone from membrane. This second method of bone-formation is seen in the bones of the skull and face. The steps are precisely similar to those already described. The inner layer of the periosteum, which is lined with osteoblasts, produces both matrix and bone corpuscles by a process of bud- ding. The change first begins at the points of ossification. THE CONNECTIVE SUBSTANCE GKOUP. 99 At first the bone is spongy, but later absorption takes place osteoporosis. Around some of the marrow- tubes concentric lamellae are formed, and in this way a Haversian system de- velops. The unabsorbed portions of the trabeculae are thought to constitute the lamellae known as the intermediary. Com- pact tissue is thus formed from spongy. This theory, which has been placed in its present acceptable light by Klein, is very simple and appears to accord with observation, and explains all the phenomena. Yet those' who have believed in the direct transmutation of cartilage into bone are still in the field. Kolliker maintains that both views are correct. According to this last named author the differences between primary or primordial and the tegumentary or secondary bones are, from a morphological point of view, sharp and complete. The former are ossifications of the carti- laginous skeleton. The tegumentary are never cartilaginous at first ; the primordial bones, on the other hand are, without exception, formed from cartilage. The method and manner in which bony tissue is formed is the same in both bones. The pri- mordial skeleton in the lower vertebrates ossifies only in part from the peri- chondrium, in part perichondrally, and, in part, endochondrally. According to Kassowitz, in the tuberosities and spines of the bones the periosteal processes of the periosteum, which develop the bone, are primarily cartilaginous, the fibrillated tissue being converted into hyaline cartilage, which is at first calcified and then undergoes direct conversion into bone. According to the experiments of Strawinsky a transplanted periosteum will develop either bone or cartilage, when the conditions are favorable. The con- ditions of nutrition determine which it shall be. When the supply is best, cartilage is formed ; when poorest, bone. The earliest evidences of ossification were seen by this observer between the fourth and fifth days. The formation of vessels preceded that of bone. Absorption commenced between the second week and the second month. The new formation of periosteum is partly derived from the border of the wound and partly from the Haversian canals, which contain a small amount of connec- tive tissue. Development of bone and absorption. It has been seen that these two processes go on hand in hand. As soon as the periosteum has commenced to deposit new layers of bone on the surface of the primary spongy bone, absorption takes place along the marrow canal. First of all, as we have already said, the innermost of the concentric lamellae yield. In this way the Haversian canals are widened and become Haversian spaces, as they were at first ; then the interstitial lamellae, and finally 100 MANUAL OF HISTOLOGY. the spaces disappear, and in place of them there is a single dilated central cavity. Howship's lacunce are the pits or lacunae seen in bone beneath the periosteum. They usually contain a multinuclear corpuscle (giant-cell), which is in some way related to absorp- tion, and, therefore, has received the name osteoclast (Kolli- ker). It has been surmised (Klein) that they are the agents by which an acid is formed that dissolves the lime-salts. Whether they are developed out of the osteoblasts or not is a matter of uncertainty. All the steps, both in development and absorption of bone, have been carefully studied and placed upon a most satisfac- tory foundation (Lieberkuhn and Bermann). The absorption of bone has also been actually proved by measurements of the bones in children (Schwalbe). By comparing the bones of the third and fourth years of life, it was found that the marrow cavity had enlarged in the latter, while the compact bone had diminished in thickness. The change commenced at the sixth month. This physiological process is closely allied to the pathological one exhibited in rachitis ; in the latter the de- velopment of bone from the periosteum has the character of foetal bone, but the formation of the lamellsD is slow and incomplete. It has been claimed that the growth of bone takes place by an expansion of the intercellular substance (Strelzoff), but this is denied (Kolliker, Wegener, Schwalbe, and others). The ossein appears to increase somewhat, but it is at the ex- pense of the bone- corpuscles, which are thereby diminished in size. Formation of callus. The method is the same as in the de- velopment from periosteum. A corpuscular blastema is devel- oped from the periosteum and intermuscular tissue. This presses in between the fibres and bundles of the loose con- nective tissue, pressing them asunder, assuming considerable volume. This new tissue is hyaline cartilage. In from three to six weeks it ossifies, being in part directly transformed into bone, in part mediately, i.e., through the agency of medullary spaces and osteoblasts. Where the extremities of the bone are widely separated there is a formation of bone in the medullary spaces of the broken ends of the bones. The pre-existing bone- corpuscles have no part in the new-formation. This compact THE CONNECTIVE SUBSTANCE GROUP. 101 bone thus formed will be absorbed in a few months, in its internal portions, by rarefying ostitis, so that the marrow cavi- ties of the broken diaphysis will be in communication. BIBLIOGRAPHY. The student is referred, for further particulars, to Klein's Atlas of Histology, Ban- vier's Traite technique d'histologie, Strieker's Manual of Histology, and also to the following recent writers : SCHAEFER. Pract. Histology. 1872. LIEBERKUHN and BERMANN. Ueber Kesorption der Knochensubstanz. 1877. AUFRECHT. Ueber Riesenzellen in Elfenbeinstiften. Med. Centralblatt, No. 26. Jahresb. d. Fortschritte der Anat. und Phys. 1878. ARNOLD, J. Virchow's Archiv. Bd. 71, p. 17. 1877. VON EBNER. Sitzungsbericht der Wiener Akad. III. Abtheil. Bd. 75. Hofmann und Schwalbe's Jahresb. 1878. KASSOWITZ. Med. Centralblatt, No. 5. Hofmann und Schwalbe's Jahresb. 1878. SCHWALBE. Sitzungsb. dermed. naturwiss. Gesellschaf t zu Jena. 1877. H. und S.'s Jahresb. 1878. STRAWINSKY. Ueber Knochenresorption. H. und S.'s Jahresbericht, p. 109, 1878. LITTEN, M., and ORTH, J. Berliner klin. Woch. No. 51, p. 743. 1877. KOLLIKEB. Entwickelungsgeschichte. V. und S.'s Jahresb. 1878. CHAPTER VIII. THE TEETH. FROM the standpoint of descriptive anatomy, every tootli is composed of three parts : (1) the crown, that portion which stands above the level of the mucous membrane of the gum ; (2) the neck, a constricted part at the level of the gum ; and (3) the root, which terminates in one or more fangs, and is firmly embedded in the alveolar process of the jaw. Each fang also is pierced from below by a canal, which extends up into the crown, and is filled by a soft material rich in nerves and ves- sels, called the pulp, which has the special province of sup- plying nutriment to the dense tissue about it. From a histological point of view, every tooth may be di- vided into : 1, enamel ; 2, dentine, or ivory ; 3, cement, or true bone. The enamel forms the covering for the crown, the cement for the root ; but they meet at the neck, and there the cement slightly overlaps. The ivory or dentine lies intermediate be- tween the outer coatings and the pulp. The enamel. This substance, which is the hardest met with in the body, consists of a series of long polyhedral columns grouped in bundles and disposed mostly at right angles to the surface of the dentine which lies beneath it. Each column or pillar is a hexagonal prism, having a diameter varying between nrJiro and -^5^ inch. When viewed in cross-section these col- umns look like a tesselated pavement. They are not, however, closely applied to one another, but have interspaces which are said to be filled with a homogeneous substance or fluid. All of the groups of columns do not stand vertical to the dentine ; some are parallel to it, and thus are interwoven with the vertical ones. This crossing of the fibres produces an alternation of light and dark bands (Fig. 38, 1). But there are other systems of markings. In the same figure are wavy THE TEETH. 103 lines running parallel to the surface. These are the " brown, parallel stripes of Retzius" They pursue a somewhat curved course. No unity of opinion exists about their significance, one (Hertz) attributing them to deposits of pigment, another (Von Bibra) to the pres- ence of the oxide of iron. Still other striae are ob- served, and are thought to represent the zigzag or spiral course of the enamel prisms. It is observed that when the prisms are isolated, which can be accomplished by immersion in a dilute hy- drochloric acid solution, they have a somewhat spiral form, and have bulging sides and cross markings, the signifi- cance of which will be alluded to at another place. Near the line of the dentine there are spaces between the prisms which are continuous with the cavities in the dentine. These are called the in- terglobular spaces of Czermak. They also oc- cur at irregular intervals in the dentine. % T n Trrmno* cnVnrtc section, magnified 15 diameters. 1, enamel with decussating 111 7 IDjeC . and parallel string ; 2, dentine with Schreger's lines ; 3, eel there is a delicate mem- brane covering the sur- face of the enamel. It is composed of laminated epithelial scales, and corresponds to the corneous layer of the skin, of which, indeed, it represents the vestiges. The dentine or ivory (Fig. 38, 2) consists of a dense and hard matrix impregnated with the salts of lime. It contains FIG. 38. Premolar tooth of the cat, in situ. Vertical and parallel striae ; 2, dentine with Schreger's lines ; 3, ce- ment ; 4, periosteum of the alveolus ; 5, inferior maxillary bone. (Waldeyer.) 104 MANUAL OF HISTOLOGY. numerous passages having, like the enamel prisms, a direction at right angles to the surface of the bone. These passages, the dentinal canals, are united with one another laterally by minute oblique branches, and form undoubtedly open channels of communication between the pulp cavity and the spaces be- tween the enamel prisms in the crown and the bone lacunae of the cement in the fang. Each canal -^=^^^E^^^ is lined with a particularly delicate and resistant membrane, the den- tinal sheath of Neumann. Upon the internal surface of the dentine, or the external surface of the pulp- tissue, is the layer of odontoblasts (Schwann). These cor- puscles, according to Waldeyer, have long branching processes ex- tending in three directions, inward into the pulp-cavity, outward through the dentinal channels, forming the dentinal fibres of Tomes, and laterally so as to form connection with adjacent corpus- cles. On the outer surface of the dentine the canals connect with the interglobular spaces of Czer- mak, and they in turn are con- tinuous with interstices between the enamel prisms. The dentinal tubules never appear to be in di- rect communication with the enam- el spaces, but only mediately, as has been described. These cavi- ties are filled with protoplasmic material. Those immediately adjoining the cement are small in size, and form what is known as the granular layer of Tomes or PurJcinje. Dentinal globules (Fig. 39, 2) is the name given to certain spheroidal masses that are regarded (Waldeyer) as calcified remains of the corpuscles in the spaces. The contours of these masses correspond in outline with those of the interglobular spaces. FIG. 39. Canine tooth of man, present- ing a portion of the transverse section of the root : 1. cement with larsre lacunae and parallel striae ; 2, interglobular substance ; 8, dentinal tubulea. Magnified 300 diame- ters. (Waldeyer.) THE TEETH. 105 Beneath the cement the intercommunication of interglobu- lar spaces and bone-lacunae is well shown. The interglobular substance is apt to be present in layers ; the lines which are then called the incremental lines of Salter, are supposed to show that there has been growth by successive stages. The lines of Schreger (Fig. 38, 2) are also waving parallel lines ; they are thought to be due to the curvature of a series of adjacent fibres. In some instances vascular channels have been found in the dentine, which has acquired the name osteo or vaso- dentine. In pathological conditions masses have also been found containing bone-lacurise. They have been called odonto- mata by Yirchow. The cement is true bone-tissue, containing lacunae and canaliculi, and in them the bone-corpuscles with their pro- cesses. The matrix is also subdivided into lamellae. The peri- osteum of the gum dipping down into the bony socket from the surface of the gum forms a coating over the cement. Oc- casionally Haversian canals and blood-vessels are seen where the cement is thick (Salter). Sharpey' s fibres may also be seen, according to Waldeyer. The pulp is a substance that belongs to the connective- tissue series. Adjoining the dentine are two layers of corpus- cles. The nearest are long cylindrical bodies whose oval nuclei are distant from the dentine. Wedged in between them, and forming a layer intermediate between them and the pulp, are peculiar branched corpuscles of a spindle or pyramidal shape. According to Klein, these latter send processes into the den- tinal tubules, while, according to Waldeyer and Boll the odon- toblasts send the fibres, and are also connected to one another by lateral processes. The pulp tissue is very rich in non- medullated nerves ; their prolongations penetrate between the odontoblasts, but it is a matter of question whether they enter the dentinal canals. Capillaries are abundant and form close networks in the pulp. The lymphatics are said to accompany the blood-vessels and to be surrounded by endothelial sheaths. Development of t?ie teeth. Waldeyer, whose views on the teeth are the most complete and satisfactory extant, makes the following succinct statement : "The anatomical model of a tooth of a vertebrate animal is a large papilla of the mouth or of the pharyngeal mucous 106 MANUAL OF HISTOLOGY. membrane, which in consequence of chemical and histological conversion of its constituents has acquired a remarkable degree of hardness, and according to whether the connective- tissue substance of the papilla participates in the hardening or not, two large groups of teeth are distinguished dentinal teeth and horny teeth. The horny teeth are by far the most simple in FIG. 40. Vertical section of the inferior maxilla of a hu- man foetus, measuring 11 ctms. from the vertex to the. coccyx. Magnified 25 diameter?. 1, dental groove ; 2, remains of the enamel germ ; 3, enamel organ presenting externally epitheli- um, as also where it forms the enamel germ of the papillae of the dental sacculus ; 4, secondary enamel germ : rudiment of the permanent tooth ; 5, dental germ : 6. lower jaw ; 7, Meckers cartilage. (Waldeyer.) FIG. 41. 1, various forms of odontoblasts, with the three kinds of processes ; 2. three enamel cells, with a few cells of the stra- tum intermedium attached ; 3, an enamel cell, with a hmall portion of enamel ; 4, fragments of ena- mel fibres from young and soft enamel ; 5, old '.-namel fibres with transverse Ptrias and rounded ex- tremities. (Waldeyer.) their structure. They appear as more or less developed papil- lae covered with a thick horny investment. They are never continuous with portions of the skeleton, but constitute the transition to other horny formations, as hairs, stings, etc." "In the dentinal teeth the connective-tissue matrix of the papillae plays a most important part in the hardening process, which here proceeds in a manner precisely similar to the ossi- fying process, except that no true bone is formed, but only an allied substance, of much harder consistence, and differing more or less in histological structure, termed dentine. The epi- thelium of the tooth papillae either atrophies to a rudimentary THE TEETH. 107 horny investment the cuticula (membrane of the enamel) or it becomes elongated in a remarkable manner into long, petri- fied prisms, which collectively invest the dentine and are known as the enamel." Preparations for the development of the teeth take place at a time when the epithelium of the mucous membrane of the mouth is found growing downward, like a solid peg, with a rounded extremity. This has been called the primary enamel organ. As a next step, the material which is to give form to the tooth pushes upward as a papillary growth, and meeting the epithelial peg, pushes in or invaginates its rounded extremity. This is the tooth papilla, and as it pushes upward ihspri- mary enamel organ becomes the secondary enamel organ, or the enamel cap. We have now two tissues which are embedded in the soft embryonic substance, that happens at this early period to be gelatinous. That portion of it immediately surrounding the papilla and cap is called the tootJi-sac. The papilla, which becomes highly vas- cular, is covered, on its outer surface, by the odontoblasts, a layer of columnar epi- thelial corpuscles, which elongating, are transformed directly into the dentinal sub- stance at their outer extremity. According to Kolliker and others, they excrete the dentine. The former view seems to have the most weight of argument in its favor, but it seems less likely that the odon- toblasts both make the matrix and send fibres into the tubulse. The view of Klein already given seems to be preferable, and in conformity with what we know of other connective substances. The separation of the tooth-sac from the mucous membrane is effected by the gelatinous tissue, which, gradually closing in the neck of the sac, finally cuts it off. The epithelium of the enamel cap is abundant and of various kinds ; into it push a number of papillary processes downward from the gelatinous tissue. Later the enamel cap is changed into three membranes. FIG. 42. Longitudinal sec- tion of a milk tooth from the foetal sheep, carried through the margin of the dentine pulp and adjoining portion of the enamel organ. Magni- fied 200 diameters. 1, dental sacculus; 2, external epithe- lium and stratum interme- dium here united to the in- ternal epithelium or enamel cells ; 3, after the disappear- ance of the enamel pulp ; 4, young layer of enamel de- tached from the enamel cells ; 6, dentine ; 6, odontoblasts : 7, part of the dentine pulp. (Waldeyer.) 108 MANUAL OF HISTOLOGY. The middle membrane is a peculiar cellular network, formed by the transformation of the middle epithelium layer into a network of cells, below which there is a deposit of a hyaline material. The inner membrane is formed of cylindrical epithe- lial bodies, which are called enamel-cells ; outside of them are one or more layers of polygonal cells ; they form the stratum intermedium of Hannover. The outer membrane is composed of several layers. Finally, the middle membrane disappearing, the outer and inner membranes are brought into close apposition. Development of the enamel. This is formed by the enamel- cells (inner epithelium, Kolliker), presumably in the same way as the dentine by the odontoblasts. There is a direct con- version of the outer extremities of the enamel-bodies into en- amel. Kolliker, Hertz, and Kollmann, however, regard the enamel as an excretion from the enamel-cells. The former view appears the more natural, especially as the enamel-prisms are continuous with the enamel-cells, having the same form and shape. The successive stages of growth, it is believed, give rise to the transverse markings. Whether or not, in the interstitial substance of the enamel, there are corpuscular elements (Boedecker), is a matter that will require further investigation. The outer membrane even- tually gives rise to the cuticle covering the enamel. The development of the cement takes place precisely as bone is produced, viz., from the periosteum, or, which is the same in this instance, from the fibrous tissue of the tooth-sac, the periodontium. BIBLIOGRAPHY. The following systematic works and journal articles may be consulted : RETZIUS. Miiller's Archives. 1837. NASMYTH. Med.-Chir. Trans. Vol. 22. 1839. KftLLiKER. Man. of Human Histology. 1853. WBNZEL. Arch. d. Heilkunde. 1868. HENLE. Anatomic. 1871. STRICKER. Manual of Histology. Am. Ed. 1872. TOMES. Manual of Dental Anatomy, Human and Comparative. Lond., 1876. OWEN. Comparative Anat. and Phys. of Vertebrates. 1866. BOEDECKER. Dental Cosmos. XXL, 409 416. Phil., 1879. HEITZMANN. Microscopic Anat. of Human Teeth. Med. Rec., N. Y., 1879. XV., 187. KLEIN. Atlas of Histology. 187980. CHAPTER IX. GENEKAL HISTOLOGY OF THE NERVOUS SYSTEM. WE may gain a clear conception of the nervous system in its general outlines by remembering that it consists essentially of a series of delicate cords which, on the one hand, proceed from the nucleated bodies of the gray matter, conveying voli- tional impulses to the periphery of the organism ; or, on the other hand, of sensitive peripheral extremities that take up the impression of external objects and carry them back to the cen- tral gray substance. In either case both the conducting cords and the central corpuscles of the gray matter possess no distinctive differences, such as may be appreciated by the microscope, while, on the other hand, the peripheral termini appear under many different forms, the peculiarity of ending being dependent in part upon the type of tissue in which they are found, partly upon the office they have to perform, and partly upon other causes that are unknown to us. The nerve-centres are located in the brain, spinal cord, and in the ganglia of the cerebro-spinal and sym- pathetic system. The methods of nerve- terminations that have been described may be briefly enumerated here. They are by (1) peculiar terminal bodies, (2) loops, (3) networks, (4) end bulbs, (5) proto- plasmic bodies (cells), (6) free or pointed extremities. Nerve-fibres. Of these there are three kinds that have distinctive differences : 1. The myelinic or medullated fibres. 2. Fibres of RemaJc. 3. Ultimate fibrils. Intermediate forms, such as have been described by various writers, under the names of protoplasmic processes, primitive fasciculi or naked axis- cylinders, varicose cylinders, etc., will be noticed in other con- nections. Myelinic fibres. These are also known as the medullated. 110 MANUAL OF HISTOLOGY. To the naked eye they appear white and glistening, and are the main constituents of the peripheric nerves, though they occur in less number in the sympathetic and also in the brain and cord. Each fibre is made up of three distinct parts : (a) a central cylindrical cord, the axis-cylinder, about which is a (b) coating of soft homogeneous fatty material, called myeline (medulla, white substance of Schwann), forming for the axis- cylinder a sort of tubular sheath, while exterior to both is a delicate membrane or envelope (c\ the sJieath of ScTiwann or primitive sheath. 1 These fibres run a parallel unbranching course, except near their termini or origin, and are surrounded by a connective-tissue coating of varying thickness. Their diameter varies also according to their situation and the degree of their tension or relaxation. In the nerve-trunks the average diameter lies between -fa an ^ iio- millimetre. In the brain they are described as having sometimes a diameter of -g-J-g- jnilli metre, but it is difficult to determine the presence of a medulla in such small fibres. To study the properties of a myelinic nerve, we may take a portion of the sciatic from a frog that has just been killed. Having removed it with care and placed it in a drop of water on a slide, we should separate the fibres carefully with needles, taking care not to tear them. Then adjusting a covering glass, it will be seen that from the broken end of the nerve a soft substance is exuding (Fig. 43, 5) ; in a few minutes it is pushed off in the form of drops of irregular shapes (Fig. 43, c). This material is the myeline or medulla. It will be seen to re- fract the light strongly, and show concentric markings. It will also be seen that each fibre has a double contour and is divided at tolerably regular intervals by transverse divisions, which are now known as Ranmer* s nodes. (See Fig. 47.) Midway be- tween each node we may perhaps see an oval body surrounded by a broad expansion of protoplasm. In a few fibres we may even see that a fine thread-like process is projecting from the broken ends of the nerve-fibre the axis-cylinder (Fig. 43, d) while the whole fibre is enclosed by a delicate tightly investing membrane, the sheath of Schwann. Possibly we may also see the 1 A most unfortunate source of confusion among histologists has arisen from the use of the word neurilemma, which by some is spoken of as synonymous with Schwann 1 s sheath (Frey), and by others as the connective tissue which binds the nerve-fibres together (Klein, Rutherford). We shall avoid the term altogether. GENERAL HISTOLOGY OF THE NERVOUS SYSTEM. Ill oblique or arrow markings (incisures of Schmidt) (Fig. 43, /), which seem first to have been accurately described by Schmidt, of New Orleans, later by Lantermann, of Cleveland, Shaw, and others. The same appearances can be also obtained by the use of iodized serum. The double contour is not visible in all the myelinic nerves, but is most marked where they show varicose swellings, a con- dition that is due to a preponder- ance of myeline at the enlarged point. From this fact and anoth- er, that the drops of myeline when separated from the fibre show the same double contour, it is argued that the double marking in the fibre is due to a refracting (double) of the myeline, and has nothing to do with the membranous sheath. These varicosities just mentioned are not to be confounded with the bulgings of the ultimate fibrils, or with the " necklace " appearances seen in the course of the fibres of Remak, both of which latter may probably be regarded as artificial productions, either from stretching in the act of teasing or from the imbibition of water. In the brain of the calf they are frequently seen, and they are said to be found in the intracranial part of the olfactory, optic, and acoustic nerves. The fibres in which this change occurs are usually quite small. Staining in picro-carmine. This reagent has been recommended by Ranvier. It is satis- factorily prepared by Rutherford's process. 1 Taking precau- tions not to injure the nerve in removing it, mount in the solu- 1 He takes 100 c.c. of a saturated solution of picric acid. Next he prepares an ammoniacal solution of carmine by dissolving one gramme in a few c, c. of water, with the aid of an excess of ammonia and heat. He then boils the picric acid solu- tion on a sand-bath, and when boiling adds the carmine solution. The mixture is Fio. 43. a, Myelinic fibre in a state of " coagulation ; " &, myeline exuding from the broken end of the fibre ; c, drops of mye- line separated from the nerve-fibre ; rf, axis cylinder ; gr. xv. j. distilled water. 116 MANUAL OF HISTOLOGY. it is to be immersed in water for a few hours ; then in 90 per cent, alcohol, and then in a weak solution of gum-arabic, which fills the interstices between the bundles, and finally in strong alcohol (95 per cent.), which hardens the gum sufficiently. The sections, cut as thin as possible, should be placed on a slide to remove the excess of alcohol, which may be done with filter-paper. A drop of water is then to be added ; about the cover put a few drops of carbolized water ; remove to a damp place. At the end of twenty -four hours the gum will have dissolved, and then the glycerine may be allowed to enter slowly without displacing the elements (Ranvier). In examining such cross-sections, the medullated nerves will present various diameters, and the contour of the myelinic sheath will vary in width and outline according as the cut comes through the broadest part of the arrow-marking, or through the thin overlapping parts. (See Fig. 43.) If the cut chances to pass close to the annular constriction, no myeline will of course be seen. For these reasons, the cross-sections of such nerves, when stained with osmic acid, are very different. Modern conceptions of myelinic nerves. The specimens that have been studied according to the methods given will not have shown any termination of the nerves, or any division, either into trunks of any considerable size or into the fibrils of which they are said to be composed. They do, however, as we have already said, divide both near their origin and near their termination. It is presumed that each fibril of which the axis- cylinder is composed passes directly through from its point of origin of the nerve-centres, to its final point of distribution, without branching. It is difficult, however, with the instru- ments in ordinary use, to see any distinct marks of fibrillation in cross-sections of the axis- cylinder, and it is in them that we should expect to see them best. The ideas pf Ranvier are well worthy of consideration, as he has given more form and solid- ity to our conception of the intimate structure of a myelinic nerve-fibre than any previous writer. According to him, each section of nerve between the annular constrictions represents an ultimate morphological element. It is, in fact, a tubular cell, whose proper external portion (the membrane of the cell, according to common phraseology) is the sheath of Schwann, while the myeline or medulla fills the interior, just as in adi- pose tissue a globule of oil fills out and distends an ordinary GENERAL HISTOLOGY OF THE NERVOUS SYSTEM. 117 connective- tissue corpuscle. Each of these bodies, which he calls an interannular segment, begins and ends at the constric- tion. It contains a single ovoid flattened nucleus, which fills a niche in the myeline, and is surrounded by a broad, thin ex- pansion of protoplasm (the body of the corpuscle). The axis- cylinder has nothing to do with this body that we have de- scribed, except that it pierces it. Instead of stopping short at each constriction, it goes on indefinitely. As we have already seen, the annular constriction and the biconical disk are not always at the same point, which argues strongly for Ranvier's views. The myelinic sheath probably protects the delicate fibre from external injury, but whether it also insulates it, is problematical. In the foetus all nerves are devoid of myeline. Fibres of Remak. These are called by some the amyelinic or non-medullated fibres, by others the pale, gray, or gelati- nous fibres. The term Remak' s fibres has come into use re- cently as the distinctive name for certain nerve-fibres abound- ing in the sympathetic, as distinguished from others which also contain no myeline, and are found in the cranial portions of the optic, auditory, and olfactory nerves. Each fibre is marked with oval nuclei at pretty short intervals, and has an indistinct longitudinal striation, probably the evidence of fibrils such as are believed to exist in the axis-cylinder. The nuclei are imbedded in a homogeneous sheath. There being no breaks in the continuity of the fibre, there can be no sheath of Schwann in the sense that has been described. In diameter each fibre va- ries between -fa and T i 7 millimetre. In 1838 Remak first called attention to them, but his views were received with disfavor. More recently, Max Schultze, Frey, Leydig, and Henle have joined in representing them as long, cylindrical, continuous, slightly striated, and dotted with nuclei. The fibres of Remak are found in great abundance in all the nerves of the organic system, but they also exist in all the mixed nerves, varying with the kind of nerve and the animal. They are not found in special nerves. The pneumogastric of the cat is well adapted for the study of them, as the myelinic fibres are present in considerable quantity, and make the mechanical separation of the bundle easy. Associated with them, fibres are often seen, that are shown in Fig. 48, c. They are delicate, run a wavy course, and sometimes exhibit curious varicosities (a), (necklace appearance). The nuclei are placed at about the 118 MANUAL OF HISTOLOGY. same distances apart as in the other form of fibre already men- tioned. Preparation in osmic acid and pier o-car mine. Remove the pneumogastric in the following way, from a cat that has just been killed : Having exposed the nerve, slip under it in situ a long narrow strip of cork, to which, pin down the nerve with some adjacent tissue, all of which may be removed at once and placed in a solution of osmic acid (11,000) for twenty -four hours ; the nerve may then be separated from its attachments and placed in the picro-carmine solution for still another twenty -four hours. The excess of the col- oring agent may be removed by dipping for a few seconds in acetic-acid solution (J- per cent.), and then the nerve may be placed in alcohol, afterwards in water, and fin- ally mounted in glycerine. It will be seen that the nerve- fibres are stained a reddish yellow, while the nuclei are brick-red. The picric-acid yellow is apt, however, to diffuse. Careful separation of the fibres may show that they branch, as shown in Fig. 48, A, B ; and yet this char- acteristic, which Eanvier in- sists upon, is by no means easy to see in most of the fibres, in fact it requires much care- ful work before it is apparent. The myelinic nerves will be dis- tinguished by their greater average size, their dusky, granular medulla, broken at points, and by the axis-cylinder, which, if it does not project, may be seen winding spirally along be- neath its medullary coat. In them, too, as a rule, each in- terannular segment contains but one nucleus. Preparation of Remak" 1 s fibres in hcematoxylin. One of FIG. 48. Fibres of Remak. A, Pneumogastric of the cat haeiuatoxylin specimen : a, nerve nu- clei ; &, appearances of branching ; c, connective- tissue sheath. B, Same. Picro-carmine specimen. The branching in this case is more evident. C, Same haematoxylin specimen. The necklace ap- pearance is >shown at a. GENERAL HISTOLOGY^ OF THE NERVOUS SYSTEM. 119 the most rapid and successful methods is by the use of hsema- toxylin. The pneumogastric nerve of a cat is removed and immediately placed in the hsematoxylin solution ; then, after thorough staining, which may only take a few minutes, in dilute acetic acid (^ per cent.), and finally mounted in gly- cerine. In this way the nuclei will be stained a beautiful pur- ple, while the fibres will be unaffected. The number of nuclei and absence of medulla will serve to distinguish the fibres of Eemak from the medullated. It is difficult by any method of preparation to see that there are any precise limits to the lon- gitudinal lines in the fibres, i.e., that the striation is due to little, short, narrow rods, lying side by side (Ranvier). The nitrate of silver demonstrates no transverse markings and no constrictions or crosses. There is but little likelihood in these specimens to mistake the fibres for connective- tissue bundles. In the first place, the nuclei, and what cell-bodies happen to be about them, of the one, are small, flattened, ovoid bodies occurring at pretty regular intervals, while the connective-tis- sue corpuscles are usually larger, longer, and, though they may appear oat- shaped, when the side is turned to the observer, are broad plates with irregular edges when seen flatwise. In the second place, the fibres run their course in long, narrow bundles, as no connective tissue does. Ganglionio bodies. Of these there are three kinds : 1. Those that are connected with the spinal and some cerebral nerves. 2. Those found in the gray substance of the brain and spinal cord. 3. Those in the ganglia of the sympathetic sys- tem. These bodies are of such large size that they may often be seen with the naked eye. In the human species they are usually in close connection with the origin of the nerves, though they also may be interspersed at points through the course of the fibres or may be present near their points of distribution (ganglia of AuerbacTi). Their immediate connection with the nerve-fibre is made in the following ways : 1. A large process, which does not at first appear to branch, passes off, and is continuous with the axis- cylinder. 2. Fine branches are given off from one or more corpuscles, and, uniting, contrive to form a nerve-fibre (either a fibre of Eemak or a myelinic fibre). 3. These branches after combination may pass through a gangli- onic corpuscle, which then is called bipolar (Gerlach, Wal- deyer). In the sympathetic system we have the unbranched 120 MANUAL OF HISTOLOGY. process and the superficial or spiral fibre, which corresponds to the branched fibre of the ganglionic bodies of the brain and spinal nerves. Ganglia of the cranial and spinal nerves. These organs, which appear to the naked eye as nodular enlargements of the nerves with which they are connected, consist of groups of peculiar large corpuscles which are interspersed among the nerve-fibres. In shape they are usually large and ovoid, or pear-shaped. About and between them are bands of connective tissue studded with nuclei, forming for each separate body a kind of capsule ; the vascular supply to them is liberal. The contents of these bodies are soft, elastic, and beset with gran- ules. They have a large, globular, or ovoid nucleus or nucleo- las, and may appear to have no process, or to be unipolar or bipolar, as in the lower animals. 1 Examination of the Gasserian ganglion in ihe frog. Take a frog that has just been killed, or, better still, one that has been some time in Mueller' s fluid ; trace the fifth nerve into the skull. On it will be seen, just within the bone, a yel- low enlargement. This is to be removed with forceps and teased with needles. The ganglionic bodies usually appear to have no processes (apolar), but they probably have one or more, and the apparent absence of them is because they have been torn off in teasing. Examination of the ganglia of the spinal cord. Take the cord of a bullock, and prepare it while fresh, or after it has been a greater or less time in Mueller' s fluid, or a weak so- lution of the bichromate of potash (gr. xv. % j.). Having cut it into transverse segments, the gray substance may be easily seen. Snip out with fine curved scissors small pieces from the anterior horns in the lumbar regions where the corpuscles are very numerous ; if the specimen be fresh, immerse in osmic acid (1 1,000) for twenty-four hours. Then, by careful brush- ing in water with the camel' s-hair brush, or by teasing, or agi- tation in a test-tube with a little distilled water, some of the ganglionic corpuscles will be successfully removed. They will be seen to vary much in size, and be multipolar, i.e., they will exhibit a very large number of branches (Deiter' s protoplasmic 1 According to Key and Retzius, they are probably all unipolar. Stud, in der Anat. d. Nerven-Syst., 2 Hiilfte, V. and H.'s Jahresb., 1878. GENEKAL HISTOLOGY OF THE NERVOUS SYSTEM. 121 processes) which divide and subdivide, and, it is said, form a network which unites with a similar one proceeding from the ganglionic bodies of the posterior roots. There is, in addition, a single straight process (naked axis- cylinder), which, proceeding outward, soon receives a medul- lary sheath. The nucleus is very large and circular, and usu- ally displays a nucleolus. The contents of the body of the corpuscles are more or less granular, and a mass of pigment in granules is usually seen piled up in some one portion. The corpuscles thus separated may be preserved in glycerine and water, or, after staining in borax-carmine, in dammar varnish or Canada balsam. In the posterior horns the corpuscles are similar in character, but smaller. Gerlach claims that the ganglionic bodies of the anterior horns are connected together through networks formed of the branching processes given off from each. Carriere, working under Prof. Kollman, of Mu- nich, has examined the spinal cord of the calf in the fresh con- dition, and has satisfied himself that the ganglionic corpuscles are connected together by their fine processes, being thus in agreement with Stilling, Wagner, Remak, and many others. ArcTi.f. mikroskop. Anat.^ xiv., 2, 1877. Ganglionic bodies in the human 'brain. Thin sections made through the cortex of the human brain show that there are conical ganglionic corpuscles of medium size, whose base is directed toward the white substance, and apex toward the superficies. From either end processes are given off, from the broad end several, and from the apex a single one ; both subse- quently branch. In the upper strata the corpuscles are small- est. Disseminated throughout this substance are two other forms of corpuscles, one star-shaped (spider-cells), 1 and the other the lymphoid corpuscles that belong to all tissues of the body. Possibly the spider-cells, which have a variable number of processes, are the cells of the neuroglia. Brush-cells 2 have also been described. Perhaps they should also be regarded as a variety of the spider-cells. Ganglionic bodies of the sympathetic system. They occur either singly or in groups, interspersed among the nerve-fibres, or in lines, or form enlargements in the nerve-plexuses, as 1 Described by Jastrowitz. 3 Arch. f. mikrosk. Anat, 1874, LXI., p. 93. 122 MANUAL OF HISTOLOGY. in the digestive tract. Preparations of the cceliac ganglion of the frog may be made according to the methods that have al- ready been described. The aorta and bulbus arteriosus of the frog are recommended by Klein, and the gold method is the best to show them. It was in these corpuscles of the green tree-frog that Beale noticed a spiral fibre. It was a delicate one, wind- ing round the axis-cylinder, finally going off in an opposite direction. He also thought, from an examination of the gan- glia in the mammalia, that the same fibre existed in them. Sub- sequently Julius Arnold corroborated his views, and even de- scribed a network of fibres which was connected with the nucleolus, and extended through the corpuscle, at its final exit forming the spinal fibre. Recent observers, however, have failed to confirm Arnold's opinion, and even the existence of a spiral fibre is held to be in doubt. 1 These corpuscles, which are either globular or oblong, may appear to be apolar, unipolar, bipolar (when two processes are given off in the opposite direc- tions), or multipolar (when two are given off in the same direc- tion, or several are given off in various directions). Meissnef s plexus. This network, named after its dis- coverer, is situated in the submucous tissue, and consists of nerve-bundles of medium size, which have nodular enlarge- ments studded with nuclei at certain points. An excellent way of securing them is the following : Take a piece of cat's intestine, three or four inches in length ; cleanse thoroughly by passing through it a stream of water ; then ligate one ex- tremity. Fill an ordinary two-ounce syringe with a solution of the chloride of gold (). Slip the nozzle into the other end of the intestine, and, tying it in, inject with such force as to dis- tend the gut to its utmost extent without bursting. Then pass another ligature round the gut beyond the nozzle, and draw it tight. Remove the syringe, and place the specimen in an open vessel containing the same solution, but allowing fully one- half of it to be uncovered by the liquid. After twenty -four hours the part thus exposed will have taken a mauve or violet color. Then remove from the liquid, and open with scissors, let it partly dry, and, seizing the mucous membrane with the forceps, tear it off in pieces. The submucous tissue will then 1 Key and Retzius did not find the spiral fibre in the human species, but in the frog occasionally. Op. cit. Many other excellent observers agree with them. GENERAL HISTOLOGY OF THE NERVOUS SYSTEM. 123 be exposed, and small bits are to be torn out in a similar way. They may be mounted in glycerine or dammar varnish. The nerve-trunks can be readily seen ; they will contain, on an average, from two to three fibres perhaps, and form a large- meshed plexus. The ganglionic enlargement may be found where three or four bundles meet, or in the course of a single bundle. The diameter of the enlargement is three to five times the size of the bundle. AuerbacJi's plexus, called after its discoverer, is seen by taking the same specimen, and tearing out thin laminse from the muscle, at the junction of their longitudinal and trans- verse coats. The ganglionic bodies are nodular, and contain numerous nuclei. It is said that they may be isolated by immersion of the muscular tissue eight to ten days in a 10 per cent, solution of common salt. Guinea-pigs furnish the best specimens. 1 There are both coarse and fine networks. Termination of nerves. There are various methods which have been described, and these are : 1, by undivided or free endings (tendons, conjunctiva) ; 2, by end bulbs (cornea) ; 3, by terminal loops ; 4, in corpuscles (seminal canals Letzerich) ; 5, by networks (peritoneum) ; or, finally, 6, in a special appa- ratus (Pacinian or Meissner's corpuscles). When nerves termi- nate by networks, the meshes may be formed from the medul- lated fibres, or those of Remak, and may consist of one or more fine fibrils. They have been found in the skin, and are to be seen in the submucous tissue of the intestines, in the cornea, and elsewhere. Termination by bulbs has been closely investi- gated by Krause. The bulbs are described as having a diam- eter of V millimetre, and ovoid-shaped in man, with a thin capsule of connective tissue. One or more fibres appear to enter the bulb, and, penetrating some distance, end in a knob. They have been found in the conjunctiva, in the mucous mem- brane of the floor of the mouth, lips, soft palate, and tongue, and in the glans penis and clitoris. In the cavity of the mouth they are placed in the papillae. The bodies Krause has ob- served in the clitoris are somewhat peculiar ; they are variously shaped, and have a mulberry-like surface. These corpuscles, about which there has been so much dis- cussion, and which some excellent observers (Waldeyer, Arnold) 1 Frey : Das Mikroskop., Leipzig, 1877. 124 MANUAL OF HISTOLOGY. had failed to see, were investigated a few years ago by Long- worth, of Cincinnati, and their existence established as a matter of no doubt. He took the human eye, freshly removed with the conjunctiva, and made the examination immediately. At- taching the conjunctiva with threads, so that it preserved its natural tension, he immersed it in a -J- per cent, solution of os- mic acid, or exposed it to the vapor of the same solution. After twelve to twenty-four hours the membrane was deeply stained, and the epithelium could usually be removed with a brush or the finger-nail. Next, a thin piece of cornea was removed and examined in water, or in 1 to 2 per cent, acetic- acid solution. It was then mounted in glycerine. This method was preferred to the gold chloride. In some conjunctive they were found almost entirely absent ; in others, or in certain por- tions, quite numerous. The entire interior was seen to be filled with nucleated corpuscles. Waldeyer, in commenting on the work of Dr. Longworth, agreed to it fully, and retracted his former opinions. He places these bodies intermediate between the tactile and Pacinian bodies. The tactile corpuscles of the skin (called also Meissner's or Wagner's corpuscles) are to be seen in the papillae, and especially well in the tips of the fingers, and in the internal genitals. They have a length of about T \ millimetre. Speci- mens hardened and preserved in the ordinary way show them well. They are oblong, rounded, and marked by transverse wavy lines. A nerve-fibre may be seen running into their centre. The Pacinian bodies, discovered by Yater, in 1741, but first carefully described by Pacini, of Pisa, are oval or pear-shaped bodies, attached to the nerves like berries to a stem. They are found in the subcutaneous tissues of the finger (Kolliker), in the labia majora, prostate, corpora cavernosa, and in many other places. They are seen to the best advantage, however, in the mesentery of the cat, where they are so large as to be easily visible to the naked eye. Cut out a small piece of the mesentery, place it in a weak solution of osmic acid (1 100), and after a few minutes, when it has become brown, detach the capsule carefully with needles. Mounting at once in glycerine, the whole interior of the Paci- nian will be superbty shown, constituting one of the most beau- tiful specimens in histology. The medullated nerve may be GENERAL HISTOLOGY OF THE NERVOUS SYSTEM. 125 seen winding in at one end (Fig. 49), covered with a dense coat- ing of connective tissue, and accompanied by a small artery. After penetrating a variable distance, it leaves its medulla and is continuous with a straight fibrillated band that is called the core. It terminates in one or more granular expansions, appar- ently. In two cases, how- ever, I saw the nerve passing through the body, giving off its medulla on entering it, and assuming it again on leaving. This has been observed by Klein, Pappenheim, and oth- ers. Round about the core, forming a series of pretty reg- ularly oval markings, are con- centric tunics. Toward the periphery they are at a pret- ty even distance apart. Be- tween them, applied closely to the tunics, 1 are small ovoid nuclei. The spaces between the lamellae are probably tilled with a clear fluid. In my experience these bodies are not successfully pre- served in glycerine, even after hardening in osmic acid. The chloride of gold may answer better. Nerve - terminations in muscle are quite easily seen. It is only necessary to take a bit of muscle from the thigh of a frog just dead, and immerse it in dilute acetic acid, and then in glycerine. When the tissue is thoroughly transpa- rent, as it will be in a few minutes (ten or fifteen), there will be little difficulty in finding a medullated nerve, and then in tracing it into a muscle-fibre. Reaching the sarcolemma, it 1 According to Schaef er, the nuclei belong to epithelioid corpuscles which cover the tunic on both sides. Practical Histology, p. 134 j Quarterly Microscop. Journ., 1875. FIG. 49. Pacinian body from the cat's mesentery. 126 MANUAL OF HISTOLOGY. penetrates it at a prominence (Doyere* s eminence). From tliis point it divides into fibrils, which form delicate networks, and one, or possibly two filaments will be seen to enter an irregular body placed in the centre of the fibre. This body is highly nucleated, and may without much difficulty be distinguished from the muscle nucleus, which lies either on the bundle or in it. This body is called the motor ial plate. It is not certain, however, that the ultimate fibrils actually end there, for in some instances one is in connection with one side, and one with the other. Yaricosities are described in the primitive fibrils when osmic acid or chloride of gold is used. Gschleiden, of Breslau, one of the most recent writers on this subject, has traced (in the leech) the ultimate fibrils to the cement substance between the contractile muscle-corpuscles (unstriped muscular tissue). He never saw them end in plates or in networks. Ganglion-cells are closely attached to the fibres near their termination, and they may be unipolar, bi- polar, or even multipolar, the former being the most numer- ous. Termination of nerves in epithelial bodies has been de- scribed by a good many observers. The demonstration of such endings, however, is extremely difficult. The ultimate fibrils are liable to be confounded with elastic tissue, possibly with connective-tissue fibres. To be quite sure of their character they should be traced into connection with nerve- trunks, on the one hand, or ganglionic bodies on the other. Connective tissue of nerves. In our description we have adhered to the idea that the sheath of Schwann is the one that immediately incloses the medulla, without any intervening substance. Ranvier has called the first sheath, exterior to Schwann' s, " the sheath of Henle. " (Fig. 43,. e.) The term perineurium is often applied to the sheaths of the funiculus or bundle. The connective tissue separating the funiculi in a large trunk has been called the endoneurium, while epineurium is the great sheath 'of the whole trunk. Each bundle or funiculus, the smallest element that we see in making a gross dissection of a nerve, is covered with one or more layers of endothelium, forming a special sheath. These funiculi do not run parallel without anastomosing, but two, joining, form a third, which again divides. There is much practical difficulty in the way of giving pre- BIBLIOGEAPHY. 127 else limits to these sheaths, from the fact that they are apt to be continuous with one another, while one or more may be absent, according to the size or quality of the nerve. BIBLIOGRAPHY. COHNHEIM. Virchow's Archiv. Vol. XXXVIII. , p. 343. 1867. CLEVELAND. Ueber d. feineren Ban d. Markhalt. Nervenfasern. Arch. f. inikrosk. Anat., 1870. Vol. XIII., p. 1. SCHULTZE, MAX. Strieker's Histology, p. 117. 1872. SCHMIDT. On the Construction of the Dark or Double-bordered Nerve-fibre. Month. Micros. Journ., May 1, 1874. LONGWORTH. Arch. f. inikrosk. Anat. Vol. II. 1875. SCIIAEFER. Practical Histology. Quart. Micr. Journ., p. 134. 1875. KRAUSE. Arch. f. mikrosk. Anat. Vol. XII. 1876. SHAW. Some Peculiarities in the Myelinic Peripheral Nerves, etc. Jour, of Nerv. and Ment. Dis., Jan., 1876. GsCHLEiDEN. Arch. f. mikrosk. Anat. Vol. XIV. 1877. - RANVIER. Logons sur 1'histoire du systeme nerveux. 1878. KEY and RETZIUS. Stud, in d. Anat. d. Nerv. -Syst. V. & H.'s Jahresb. 1878. His, W. Arch. f. Anat. u. Phys., p. 455. 1879. RAWITZ, B. Arch. f. Anat. u. Phys. 1879. RUMPF. Zur Histol. d. Nervenf aser, etc. tint. d. Phys. Inst. d. Univ. Heidelberg. Vol. II. SCHULTZE, H. Axencylinder u. Ganglienzelle. Arch. f. Anat. u. Phys. 1879. KUHNE, W. Zur Histol. d. motor. Nervenendig. Tint. d. phys. Inst. d. Univ. Heidel- berg. Vol. IT. HESSE, FR. Zur Kennt. d. peripher. Markhalt. Nervenf aser. Arch. f. Anat. u. Phys. 1879. KUHNE, W., and STEINER, J. Beobacht. ueber Markhaltige u. Marklose Nerven- fasern. Unt. d. Phys. Inst. d. Univ. Heidelberg. Vol. III. His, W. Ueber d. Anfange d. peripher. Nerven-System. Arch. f. Anat. u. Phys., p. 455. 1879. WALDEYER. Ueber die Endig. d. sensiblen Nerven. Arch. f. mikros. Anat. Vol. XVII., pp. 367-382. 1880. RANVIER. Le9ons d'anat. gen. App. nerveux term. , etc. Paris, 1880. PART II. CHAPTER X. MUSCULAR FIBRE. BY THOMAS DWIGHT, M.D., Instructor in Topographical Anatomy and in Histology at Harvard University. THE physiological attribute of muscular tissue is contrac- tility. This may or may not be under the control of the will. The structure of voluntary muscular fibre is very different from that of the involuntary. This distinction, however, is not absolute. The muscular fibre of the heart presents a structure intermediate between the two typical forms. Striped fibres are found in some places, as, for instance, in the upper part of the oesophagus, over which most people have little or no control. There is also an un- doubted difference in the manner of contraction among volun- tary muscles. Whether this is associated with a difference of structure is an interesting but very uncertain question that will be alluded to later. INVOLUNTARY MUSCULAR FIBRE. Unstriped muscular fibre is shown with great advantage in the bladder of the frog. It should be stained with gold chlo- ride, logwood, or carmine. 1 After the specimen has lain two 1 If one's object is to study the muscular tissue only, gold has no advantages over the other agents, and should not be used, because it is less certain. The writer has obtained remarkably beautiful stainings of the bladder by using carmine, following Beale'o method. INVOLUNTARY MUSCULAR FIBRE. 129 or three days in glycerine, the lining epithelium is easily brushed off. The bladder of the frog is peculiarly favorable, because it affords an opportunity of studying the fibres, both Fio. 50. Fia. 51. Fio. 62. Fio. 50. Muscular fibres treated with serum. FIG. 51. Muscular fibres from the muscular tissue of the intestine, isolated by means of nitric acid. FIG. 52. Muscular fibres from a pleuritic membrane. J. Arnold. separately and in bundles, in its walls and in the coats of the minute arterioles which nourish it. The plain fibre is composed simply of one or more elongated 130 MANUAL OF HISTOLOGY. cells. (Fig. 50.) The nucleus is at about the middle. The cell swells out around the nucleus, and quickly contracts again be- yond it. A small cell, such as is found in the wall of a small blood-vessel, is consequently spindle-shaped, but we find many in the frog's bladder that run out into fine threads of indefinite length. Sometimes one end of a cell divides into two fibres. (See Figs. 51 and 52.) The nucleus sometimes appears to be homogeneous, though it usually contains one or more granules, sometimes considered to be nucleoli. When using a high power the writer has some- times found that the nucleus contained many granules, so ar- ranged as to suggest very strongly a transverse stria tion. A row of granules at each end of the nucleus is sometimes found. Muscular fibres in the walls of small, transparent blood-vessels are very instructive objects, because by changing the focus we can observe them as they curve round the vessel, both in longi- tudinal and in transverse section. At those places where a transverse section of one end of the cell is in focus we see what appears to be a granule merely. If another part near the nu- cleus is brought into focus, it shows as a small circle, while if the nucleus happens to be cut transversely, it gives the effect of a dark spot inside a circle. VOLUNTARY MUSCULAR FIBRE. No tissue is more easily recognized than striped muscular fibre, yet none is more difficult to understand. 1 The fibres are cylinders or irregular prisms of varying length. 'Their diameter in the human body varies, according to Frey, from .0113 to .0563 mm. Each fibre is tightly inclosed in a struc- tureless elastic membrane, called the sarcolemma. This sheath is not very easily demonstrated ; but if fresh muscle be roughly picked to pieces in water, shreds of it may be seen at the torn ends of fibres, and sometimes it can be made out where the muscular substance has been injured in the course of a fibre. 1 Any attempt at an account of the many views that have been and are held, Would make this article far too long. A few only will be mentioned, and these inci- dentally. It is hoped that this defect, if it be one, will be compensated for by the lulness of the bibliography. VOLUNTARY MUSCULAR FIBRE. 131 The existence of a sarcolemma being admitted, it is clear that it must be highly elastic so as to accommodate itself to the changes both of length and breadth which the fibre undergoes. The phenomena of contraction show, moreover, that it must be attached at definite points to the muscular substance. Fresh muscular fibre of a vertebrate animal, when teased out and examined under a moderately high power, presents a series of alternate black and white cross stripes, which are held to be characteristic of voluntary muscle. (Fig. 53.) This appearance is beautifully distinct in some fibres, and very vague in others. It may vary greatly in different parts of the same fibre ; the stripes may run perfectly straight across the fibre ; they may present a uni- form curve, or they may be interrupted at intervals, some parts of the line being in advance of others. (See Fig. 53.) As a fibre taken from an animal im- mediately after death naturally draws it- self together (without, however, necessarily J FIG. 53. Striped muscular presenting the phenomena of physiologi- *>>: > black 8trf p e ; &. fc- r *-.-'* *'* termediate stripe; c, white cal contraction), it is desirable to ascertain * nucleus - whether this modifies the appearances. To do this, fibres from a recently killed animal should be ex- amined in a state of extension. A cut should be made in the body of a muscle, a few fibres teased out and stretched on the slide under the covering glass before their attached ends are divided. It will be seen that the light stripe is more affected by the stretching than the dark one, though both are broader than in the non-extended fibre ; but the most important effect is the appearance, often seen with high powers, of a very narrow, in- terrupted black line in the middle of the light band. Beside this cross striation, the fibres of vertebrates show more or less plainly minute longitudinal lines. It is to be no- ticed that when the cross stripes are very distinct the longitu- dinal ones are very faint, or even invisible, and that when the latter are well marked the former are the reverse of it. Some reagents tend to divide a fibre into disks, others into fibrillae. Among the former are solutions of acetic acid in water (1 in 132 MANUAL OF HISTOLOGY. 100200), hydrochloric acid (1 in 50200), and among the latter a solution of chromic acid (1 in 200). It is very probable that the amount of longitudinal striation varies in different muscles, being related, perhaps, to physiological properties, or possibly the result of mechanical causes. It is certain that both kinds of striation may be found in great perfection in fibres treated with almost any reagent that does not destroy them. Some- times muscle is seen to be split into fibrillse, each of which shows the transverse stripe, though the shreds are so fine that each disk is represented by a dot merely. 1 This may be de- tected very well in the muscle of the lobster after it has been picked to pieces in glycerine. Returning to the transverse stripes in vertebrates, the striae are very near together in the frog, and thus this useful animal is not specially desirable. The muscle of the rabbit is much better, and human muscle is, perhaps, better still. The muscle of the human embryo in the last months of pregnancy is par- ticularly good. A very high power will often show the narrow black line in the midst of the white band. Sometimes one edge of each black stripe will be very sharply marked against the glaring white, while the other side will present a less marked contrast. If the stage of the microscope admits of rotation,' in- structive effects can also be obtained. As the field turns round, the brightness at the sharp border of the black stripe gradually decreases, to return on the other side. Again, this change may not occur. Sometimes, when the upper edge of the fibre is pre- cisely in focus, the black and white stripes may be made to ap- parently exchange places, if the lens is slightly depressed. This is probably to be accounted for as follows : First, we may for the present assume that the black and white bands are caused by disks of different nature. Take a series ,of such disks and imagine them somewhat inclined to one side, like a roll of coins on their edges leaning against a support. A vertical line, representing the line of vision, that passes through a black disk at the upper border of the roll will strike a light one at a deeper level. A peculiar effect may be obtained by removing the diaphragm and employing very oblique light. The black 1 The fact that muscle removed from the body can be reduced to fibrillae does not prove that these are pre-existing elements. 2 It is to be regretted that this movement is not more common. VOLUNTARY MUSCULAR FIBRE. 133 band then is often replaced by two narrow black lines with a light space between them. This is more frequently observed when the rays strike the fibre longitudinally. The fibres of invertebrates, though on the same plan as those of higher animals, are better fitted for study, because the elements are farther apart, and because the phenomena of con- traction may, in some cases, at least, be observed under the microscope. The muscles from the thorax and legs of large flies are very good. Merkel recommends that they be examined in fresh al- bumen from the egg, in which they will continue to contract. The fibre is crossed by narrow black stripes which, be it re- membered once for all, correspond to the black stripes of ver- tebrate muscle. On each side of these stripes there is a bright, glittering border, which gradually shades off into a dull band, midway between the two stripes. The substance between the black stripes is all of one nature, the difference between its middle and end portions being an optical effect. The dull band corre- sponds to the fine line which high powers reveal in vertebrate muscle. Its greater breadth is due to the greater distance of the black stripes. Fibres from the legs and wings of the large water-beetles (Hydro- philus and Dytiscus) are admirable objects. Schafers valuable obser- vations were made on those of the legs. He found the black stripe to consist of a double row of highly refracting granules, which were the ends of dumb-bells embedded in the contractile substance. These struc- tures are arranged side by side, the adjacent ends of the dumb-bells forming the stripe, while the handles constitute the slight longitudinal striations. (See Fig. 54.) The bright borders are due to the refraction of light from the spherical heads of the dumb-bells. It is clear that they must cause a greater amount of rays to pass through the sub- stance directly beside them than go through the substance midway between them, which latter appears dark in conse- FIG. 54. Muscle of large water-beetle (Dytiscus) : a, dull hand ; 6, bright space around ; c, the highly refractive ends of the dumb-bells ; d, the handles of the dumb- bells ; 6, sarcolemma. After Schafer. 134 MANUAL OF HISTOLOGY. quence. Some years before Schafer's theory was advanced Heppner had shown that the bright borders of the black stripe must be due to the reflection of rays through them from the surface of the stripe. The phenomena observed on rotating the stage of the microscope are in accordance with this theory. There are, no doubt, some apparent exceptions, but these lose their weight when we consider how many .elements there are that complicate the problem. If, for instance, as is often the case, the disks do not present their edges quite evenly to the eye of the observer, but are somewhat inclined, like the roll of coins above mentioned, the conditions are at once changed. Again, light thrown up vertically through a small diaphragm must produce different effects on the object from light striking it very obliquely. Some years ago the writer was fortunate enough to discover an excellent object for the study of living muscular fibre in the detached legs of the Gyrinus. This is a small beetle, known in the country as the " lucky bug," which describes most ec- centric figures on the surface of ponds. A leg should be cut off close to the body, and examined in a drop of water under a very thin covering glass. The shell is transparent, and as the muscles are undisturbed, except in the segment cut in remov- ing the leg, they are in a perfectly normal condition, lacking only their vascular and nervous supply. They will frequently contract for more than an hour, if the covering glass be lightly tapped occasionally. The part of the leg known as the tibia, which is easily recognized by a large Y-shaped air-tube, has the thinnest shell, and is usually the best place for study, though occasionally better views are obtained in the two parts next above it, in which it is easier to find a single layer of fibres. The leg is very apt to flex itself between the femur and tibia, thus obscuring one of the best places. If necessary, this can be prevented by putting a thin piece of paper against the inner side of the leg. The anterior pair of legs, which project for- ward, are made on another plan, and are less desirable. A very high power is necessary, as, for instance, Hartnack's 10 immersion lens. Much practice also is needed to follow the steps of contraction, and indeed this can be done only when it has become very slow. The fibre, when at rest and moderately stretched, appears to be a cylinder with straight edges, and composed of a semi- VOLUNTARY MUSCULAR FIBRE. 135 fluid, transparent ground-substance. This is crossed by the black stripes with shining borders, such as have been described. The black stripe usually appears granular, and may be divided into two parallel rows of granules. Some- times the two borders are equally bright ; sometimes one much out- shines the other. Some fibres are found which, not being subjected to any tension, are much more drawn together. The black bands are, perhaps, only half so far apart as in the case just described. They are never divided into two, and though some appear granular, others are homogeneous. The edges of the fibre are no longer straight, but slightly scalloped, the centre of each projection being midway between the black stripes. (See Fig. 55.) When active contraction takes place, the whole fibre is involved, and presents nothing but a series of transverse black and white bands with scalloped edges. To study the successive stages of contraction we must wait until it is feeble and in- volves but a small part of the fibre. It runs like a wave from one end of the fibre to the other, pauses a mo- ment, and then runs back again, and sometimes starts anew, but with diminished force. It is hard to fol- low the steps, for the elements are changing their shape and position at the same time ; the black stripes become broader, less granular, and each runs toward its neighbor in the direction of the wave ; the gray band disappears, and the edge of the fibre bulges. As the elements in front of the FiQ. 55. Semi-diagrammatic repre- sentations of muscular fibres of Gyrinus. Fibre supposed to be in situ and showing the different appearances which the black stripe may present. The wave of contrac- tion is travelling toward A. At C we notice that a part of the fibre, after con- traction, has been subjected to stretching after the passage of the wave; at B the elements are in a state of active contrac- tion. The longitudinal striation made unavoidable in the woodcut, does not, as a rule, exist in the living fibre. 136 MANUAL OF HISTOLOGY. wave enter into the contracted condition, those behind as- sume their normal state at first, but do not retain it, for they are immediately subject to a severe stretching by the course of the wave, and present new and very instructive appear- ances. The fibre becomes much narrower, the black stripes are resolved into two rows of granules some distance apart. The whole substance of the fibre is lighter than in the other conditions, and though the bright borders of the stripes are still there, they are much less glaring, and present less contrast with the intermediate por- tion. In some of these fibres an indistinct longi- tudinal striation is seen, but the writer is not satisfied that it is in the substance of the fibre. Transverse sections of muscle have been ap- pealed to for elucidation of the structure of the Fr g ey. bnheim1sareas ' fibl>e - Cohnheim showed a network of whitish lines surrounding small, dull-colored polygons on cross-cuts of frozen muscle (Pig. 56). The muscles of the crab are said to show this particularly well. Schafer found in the muscles of the water-beetle the appearance of granules on a clear ground. A similar appearance is seen in the fibres of vertebrates. The writer has observed in the cross-section of fibres from the tongue of the mocassin snake, granules which presented, at least, the suggestion of bright points in their cen- tre. In some fibres these were collected into groups, separated by clear spaces. Cohnheim's areas cannot be considered equivalent to fibril- ISD, but rather, as Kolliker claims, to bundles of them, sup- posing always, we would add, that fibrilke exist at all. It is pointed out in the account of the transverse striae that these are often interrupted, and there is no doubt that this may be due to the limits of the muscle-columns. Of course, we must assume that there are many more columns than would be in- ferred from these interruptions ; for if the transverse stripes of two neighboring columns exactly correspond, no break will appear. , Nuclei and muscle-corpuscles. In mammalian m uscle acetic acid demonstrates a number of oval nuclei which may contain one or more nucleoli. Their long axis runs in the same direc- VOLUNTARY MUSCULAR FIBRE. 137 tion as that of the fibre. A small amount of granular matter may be seen at their extremities. Cross cuts of fibres show that, with possibly some exceptions, they lie directly beneath the sarcolemma. In the frog, and in many invertebrates, as the beetles, they lie in the substance of the fibre, and, especially in the latter class of animals, are surrounded by a mass of granular protoplasm. Weber denies that in the adult frog they are surrounded by this mass. Conclusions. From what precedes, it seems demonstrated that striped muscular fibre consists of a transparent, semifluid ground-substance, which is the contractile element. At certain intervals a double layer of minute granules or spherules is placed, which practically forms a transverse disk. The refrac- tion of the light causes the substance bordering this disk to appear brighter than the intermediate portion, which is only occasionally seen in mammalian muscle as an indistinct and usually a broken line, because the black stripes are so near to- gether that the bright borders of two neighboring ones coalesce. In invertebrates, as beetles, for instance, they are so far apart that the dim stripe is proportionally broad, but it necessarily disappears when by contraction the black stripes are brought nearer together. Variations in the direction of the light, or any obliquity of the disks, will cause peculiar effects, well- nigh defying analysis. The writer' s views coincide, in the main, with Schafer's, except that he cannot accept the "handles " of the latter's dumb-bell-shaped structures. As the writer has stated in another paper, muscles in the leg of the Gyrinus which have been exhausted by electricity show the stripes very indistinctly, and contain a number of stray granules. Klein has pointed out that if fresh muscular fibre of the frog is teased out in salt solution, when a break of the substance ocr curs inside the sarcolemma, " inside this tube a greater or less number of granules are observed in active molecular move- ment." These observations appear to confirm the views given above. A good deal has been written about the effect of polarized light on muscular fibre, and very different results have been reached. Ranvier thinks it of no value in the discussion, be- * cause the same substance may be either doubly or singly re- fracting, according to the pressure to which it is subjected. This is certainly a strong argument against its value, espe- 138 MANUAL OF HISTOLOGY. cially in view of the discrepancy of the observations made with it. Each fibre is, moreover, divided longitudinally into a vary- ing number of what are called muscle-columns, held together probably by a delicate cement. Between these are lodged the muscle-corpuscles in the lower forms of animals. In opposition to most authorities, the writer is inclined to question the exist- ence of fibrillse in the living muscle, at all events, as essential parts of its structure. The granular appearance of cross sec- tions is in accord with the views given above, and does not necessarily imply the presence of fibrillse. Peculiarities of voluntary muscles of different functions. Ranvier was the first to discover a physiological and struc- tural difference in the red and white muscles of the rabbit' s leg and in some other animals where both kinds exi^t. He found that the semitendinosus of the rabbit, a red muscle, if acted on by an induction current, gradually contracted till it became tetanized, and remained so until the current was stopped, when it gradually relaxed. White muscles, on the other hand, when treated in the same way, contracted sud- denly, and continued to give jerks corresponding to the inter- ruptions of the current as long as it was continued. With its cessation the muscle instantly returned to its original length. From this he concludes that the white muscles are those of sudden action, while the red ones serve to regulate power and to maintain equilibrium. As to structure, he found out that the white muscles had a very distinct transverse striation, and a very faint longitudinal one, while in the red the longitudinal lines were very marked, interrupting the cross ones at many points, and giving the fibre a granular appearance. The nu- clei were much more numerous in the red. fibres, and, instead of being flattened and situated just beneath the sarcolemma, as in the white, were oval and projected into the fibre, some even lying in its interior. Eanvier showed later that the vascular supply of the red muscles differed from the usual arrangement, which consists simply in elongated meshes of capillaries in the main parallel with the fibres. In red muscle, not only were the minute ves- sels more numerous, but the longitudinal capillaries were more varicose, the meshes nearly as broad as long, and the transverse vessels, both of the capillaries and small veins, presented fusi- VOLUNTARY MUSCULAR FIBRE. 139 form dilatations, the object being, as he points out, to keep the muscle supplied with oxygen during its long-continued con- traction, which must interrupt the circulation. E. Meyer has since shown that Kanvier was over-hasty in his generalization. What is true of the semitendinosus of the rabbit is not necessarily true of other red muscles. The writer is able to confirm this statement. As to the dif- ference between the semitendinosus and white muscle, he is in- clined to admit the greater number of nuclei of the former, but the difference in the stripes did not seem to him conclusive. The peculiarity, however, of the minute blood-vessels of the semitendinosus is very striking ; but in another red muscle of the rabbit' s thigh he did not find the same arrangement. The richness of the capillary network varies greatly in different muscles of the same animal. Future investigations will, per- haps, show that modifications in the arrangement of the minute blood-vessels correspond with the function of the muscle. The termination of muscle in ten- don. This occurs in several ways. Sometimes the fibre divides again and again, ending in small bundles of fibrillse which have lost all muscular characteristics. Again, instead of spreading out, a fibre may become pointed, and the enveloping sarco- lemma, reinforced with more or less fibrous tissue, runs on as a delicate tendon. Both these modes of end- ing can be seen in the tongue. 1 The cases in which a fibre loses its stria- tion, and is apparently continued as a tendon of about the same size, present greater difficulties. By sep- arating the fibres of a frog killed by immersion in hot water, Ranvier has succeeded in demon- strating that the sarcolemma incloses the tendinous end of the fibre. The whole subject, however, of the ending of the fibres is not exhausted. 1 Thin sections of the hardened tongue of a small animal are to be recommended, not only for the study of this point, but for that of striped muscle in general. FIG. 57. Anastomosing muscular fibre of the heart, seen in a longitudinal section. On the right, the limits of the separate cells with their nuclei are ex- hibited somewhat diagrammatically. After Schweigger-Seidel. J. Arnold. 140 MANUAL OF HISTOLOGY. The muscular fibre of the heart. This is transitional in structure between the voluntary and the involuntary. The fibres of the heart of the frog resemble chiefly the latter, being made of elongated, narrow, nucleated cells, which differ from it only in being transversely striped. In the mammalia the fibres are broader and composed of nucleated cells placed end to end. These cells frequently give off lateral processes which support others, thus forming a network of fibres. The cells have both a longitudinal and a transverse series of stripes, but the latter are not so clear as in well-marked voluntary muscle. BIBLIOGRAPHY. BOWMAN. On the Structure and Movements of Voluntary Muscle. Philosoph. Transactions. 1840-41. AMICI. Ueber die Muskelfaser. Virchow's Archiv. Bd. XVI. 1859. WEISMANN. Ueber die Muskulatur des Herzens beim Menschen und in der Thier- reihe. Reichert & Du Bois-Reymond's Archiv. 1861. IBID. Ueber die Verbindung der Muskelfasern mit ihren Ansatzpunkten. Zeit- schrift fiir ration. Medicin. 3te Reihe. Bd. XII. 1861. COHNHEIM. Ueber den feineren Bau der quergestreiften Muskelfaser. Virchow's Archiv. Bd. XXXIV. 1865. DWIGHT. The Structure and Action of Striated Muscular Fibre. Proceedings Bos- ton Soc. Nat. Hist. Vol. XVI. 1873. SCHAEFEB. On the Minute Structure of the Leg Muscles of the Water-Beetle. Philos. Transact. 1873. ENGELMANN. Mikroskopische Untersuchungen iiber die quergestreifte Muskelsub- stanz. Pfluger's Archiv. Bd. VII. 1873. KSLLIKEB. Handbuch der Gewebelehre. Leipzig, 1867. HENSEN. Arbeiten aus dem Kieler physiologischen Institut. 1868. HEPPNEB. Ueber ein Eigenthumliches Verhalten der quergestreiften Muskelfaser. Archiv fiir mikroscop. Anat. Bd. V. 1869. DOENITZ. Beibrage ziir Kenntniss der quergestreiften Muskelfaser. Reichert & Du Bois-Reymond's Archiv. 1871. SCHWEIGEB-SEIDEL. The Heart. Strieker's Histology. 1872. MEBKEL. Der quergestreifte Muskel. Archiv fiir mikro. Anatomic. Bd. VIII. 1872. BRUECKE, E. The Behavior of Muscular Fibres when examined by Polarized Light. Strieker's Histology. 1872. SACHS. Die quergestreifte Muskelfaser. Reichert & Du Bois-Reymond's Archiv. 1872. WAGENEB. Ueber die quergestreifte Muskelfibrille. Archiv fiir mikro. Anat. Bd. IX. 1873. BIBLIOGRAPHY. 141 IBID. TJeber einige Erscheinungen an den Muskeln lebendiger Corethra plumicornis- larven. Archiv. ftir mikro. Anat. Bd. X. 1874. KAUFMANN. Ueber Contraction der Muskelfaser. Reichert & Du Bois-Reymond's Archiv. 1874. THIN. On the Minute Anatomy of Muscle and Tendon. Edinburgh Medical Jour- nal. Sept., 1874. WEBER. Note sur les noyaux des muscles stries chez la grenouille adulte. Archives de physiologic. 1874. RANVIER. De quelques fait relatifs a 1'histologie et a la physiologic des muscles stries. Archives de phys. 1874. IBID. Note sur les vaisseaux sanguins et la circulation dans les muscles rouges. Archives de phys. 1874. IBID. Traite technique d'histologie. Paris, 1875. FREDERICQ. Generation et structure du tissu musculaire. Bruxelles, 1875. MEYER. Ueber rothe und blase quergestreifte Muskeln. Reichert & Du Bois- Reymond's Archiv. 1875. FREDERICQ. Note sur la contraction des muscles stries ohez 1'hydrophile. Bulletin Acad. Roy. de Belgique. Tome XL. 1877. RENAUT. Note sur les disques accessoires des disques minces dans les muscles strips. Compt. rend. Tome LXXXV. No. 21. 1877. BIEDERMANN. Zur Lehre vom Ban der quergestreif ten Muskelfaser. Wiener Acad. Sitzungsbericht. Bd. LXXXV. No. 21. 1877. SCHAEPER. Quain's Anatomy. Eighth edition. New York: Wm. Wood & Co. 1878. NASSE. Zur microscopischen Untersuchung. des quergestreiften Muskels. Pfliiger's Archiv. Bd. XVII. 1878. FRORIEP. Ueber das Sarcolemm und die Muskelkerne. Archiv f iir Anatomic und Entwickelungsgeschichte. 1878. ENGELMANN. Nouvelles recherches sur les phenoinenes microscopique de la con- traction musculaire. Archives Neanderlaises des Sciences exactes et natu- relles. 1878. FLEMMING. Ueber Formen und Bedeutung der organischen Muskelzellen. Zeit- schrift fiir wissenschaftliche Zoologie. XXX. Supplement. 1878. UNGER. Untersuchungen iiber die quergestreiften Muskelf asern des lebenden Thiers. Wiener medinische Jahrbiicher. 1879. (Largely pathological.) NEWMAN. New Theory of Contraction of Striated Muscle, and Demonstration of the Composition of the Broad Dark Bands. Journal of Anatomy and Physi- ology. Vol. XIII. 1879. CHITTENDEN. Histochemische Untersuchungen iiber das Sarcolemm und einige verwandten Membranen. Untersuchungen aus der Physiol. Institut der Uni- versitat Heidelberg. Bd. III. 1879. KLETN and SMITH. Atlas of Histology. Part V. 1879-80. RANVIER. Leqons d'anatoraie generate sur le systeme musculaire. Paris, 1880. CHAPTER XL THE BLOOD-VESSELS. BY EDMUND C. WENDT, M.D., Curator of St. Francis' Hospital, New York City, etc. IN man, a closed circuit of branching tubes, which proceed from a central organ, the heart, and, ramifying throughout the body, return the blood to this central organ, constitutes the blood-vascular system, as it has been named. Of these vessels we recognize three different kinds : arteries, capillaries, and veins. The arteries convey the blood to the various capillary districts, whence it is again collected and car- ried back to the heart by the veins. The arteries, highly elastic throughout, are composed of three superimposed layers or tunics. The veins, less elastic, and consequently more flaccid and compressible, likewise con- sist of three coats or tunics. In both sets of vessels these coats have 'received the names of intima for the inner, media for the middle, and adventitia for the external layer. The capillaries, intervening between the two, form minute branch- ing tubules, which generally have but a single exceedingly thin and permeable membrane as the sole constituent of their walls. Of course, all these vessels merge into one another, so that a sharp line of demarcation can nowhere be drawn ; but in their typical forms they present clearly defined structural dif- ferences, necessitating a separate description of them. We begin with the simplest and yet most important class : The capillary blood-vessels. They are composed, as we have already said, of a single layer of cells, arranged in tubu- lar form, and containing nuclei. These corpuscles are di- rectly continuous, on the one hand, with the inner coat of THE BLOOD-VESSELS. 143 the terminal arteries, and, on the other, with the intima of the veins, hence also with the lining membrane of the heart. They are called endothelia, and since they constitute the only struc- tural elements which enter into the composition of all blood- vessels, we will first consider them and their relations to these vessels. The vascular endothelium. Histologists understand by the term endothelium a thin layer of flattened cells lining the free surface of various membranes, canals, sheaths, and cavi- ties, all belonging to the serous type. Epithelium, on the other hand, is found covering the skin and mucous surfaces. All endothelia, in common with the blood, the blood-vessels, and connective tissues, are derived from the mesoblast, or mid- dle of the three fundamental layers of the embryo. The epi- thelia, it will be remembered, originate in the two other layers, called epiblast and hypoblast, respectively the former being the superior and the latter the inferior layer of the embryo. In adult human subjects the vascular endothelia are made up of thin, polygonal, sometimes irregularly pentagonal, flat- tened cell-plates. Most of the elements are furnished with a rounded or ovoid nucleus, of central or more or less peripheral location (Fig. 58). Some have two nuclei. In general, the cells are somewhat elongated in the longitudinal direction of the ves- sel to which they belong. They also grow slightly narrower as the calibre of the vessel decreases. Their borders are serrated or scalloped, and dove-tailed into one another. An albuminoid substance, ordinarily invisible, cements their adjoining edges. This substance has the peculiar property of effecting an ener- getic reduction of silver nitrate. Hence, by proper manage- ment, the outlines of each individual cell may be made visible as a black zigzag surrounding a nucleus. Every cell represents a plate-like expanse of modified protoplasm. Remnants of this original substance may be seen to surround the nuclei of young vessels, where they appear in the shape of varying quantities of distinctly granular matter. Klein has described an intra- cellular network, formed by plexuses of minute fibrils, and associated with a second denser reticulum within the nucleus, called the intranuclear network. Whatever interpretation we choose to give these minute structures, the fact of their exist- ence is indisputable. In man, however, their presence is not as readily demonstrable as in animals. 144 MANUAL OP HISTOLOGY. An isolated endotlielial cell, when tilted up on its edge, pre- sents the appearance of a straight or curved double contour, with a central thickening corresponding to its nucleus. Viewed en face, we observe the sinuous outline and the central or ec- centric nucleus, with its surrounding granules of protoplasm. The shape and contour of endothelial cells are subject to con- Fio. 58. Endothelium of the carotid artery of man, after treatment with nitrate of silver: a, cells; 6, clearer, c, darker intermediate spaces ; d, intra-cellular circular and spotted markings. Eberth. siderable variations in the different vascular districts. Such differences also occur in the same district, with the varying de- gree of expansion or contraction of the particular vessel under observation. The capillaries proper. In point of wideness of distribu- tion, this variety of blood-vessels greatly exceeds all others. Indeed, the capillaries occupy a rank, in this respect, second only to the connective- tissue group of histological struc- tures. As regards importance to the economy, it will only be necessary to advert to the vital processes of nutrition, secre- tion, respiration, and excretion, to recall the quality and extent of their physiological usefulness. Throughout the THE BLOOD-VESSELS. 145 body l capillary plexuses are interposed between arteries and veins, which constitute a series of conveying and returning tubes. Thereby the direct continuity of these blood-channels is established. It is in these intermediate territories, and in them only, that the blood serves its true function of giving and taking. True markets of exchange, then, these capillary districts, where the system is supplied with new material, and in return gets rid of useless or even deleterious by-products of tissue-life. Hence, the para- mount importance of these vessels in the maintenance of life and health. Hence, also, the direct practical utility of knowing their minute anatomy' and physiological dignity. Every practitioner of medicine will see the important relation this branch of histology holds to pathology, and therefore to thera- peutics. At the same time we should not forget that the role played by the capillaries in the system is normally due to the inherent mechanical and physical properties of a fine- ly elastic animal membrane, rather than to any specific action of their cellular constitu- ents. Robin, following Henle's example, dis- tinguishes several varieties of these vessels. It seems to me proper to limit the term capil- laries to those minute tubules which are entirely devoid of muscular elements. This corresponds to the classification adopted by Yirchow, Kolliker, Eberth, Ranvier, Frey, and others. It is the one therefore that has Plo 59 ._ Arather lanre generally been accepted, and is both simple JP^fcSjJ'JJS^g^ and locriral membranous and nucleated iu logical. tunica adventitia Eberth> The diameter of these tubules varies from 0.0045 to 0.0115 mm. Their structure is readily understood. Examined in the living animal with a high power, we see mere- ly a delicate, hyaline, double-contoured membrane, having an 1 Hoyer has shown that a direct communication of arterioles with venules occurs normally in the tips of the fingers, the matrix of the nails, the tip of the nose, and various other parts. 10 146 MANUAL OF HISTOLOGY. average thickness of 1 to 2 micro-millimetres (0.001 0.002 mm.). This membrane forms a tubule, the parietes of which are studded at intervals with rounded or oval nuclei, often containing one or more bright nucleoli. When oval, these nu- clei have their long axis parallel with the direction of the ves- sel. Their average size is 0.0056 to 0.0074 mm. They possess the property of eagerly imbibing most of the staining fluids employed in histology, and of resisting the action of dilute acids, alkalies, and other reagents. (See Fig. 59.) Besides nuclei, the capillary wall contains at various points peculiar granules, which indicate its protoplasmic nature. In addition, Strieker and Eberth have described lateral processes and pointed prolongations jutting out from the parietes of the FIG. 60. Capillaries of the lungs of the frog, with irregularly dentated cells : a, vascular meshes. Eberth. capillary tubes. In growing tissue these-are readily demonstra- ble, often forming thread-like connecting bridges between neigh- boring vessels ; at a later period they are hollowed out into true capillaries. The shorter sprouts are also protoplasmic buds, capable of further development into similar vessels. (See Fig. 61.) By employing weak solutions of silver nitrate, the capillary- wall may be shown to consist of variously shaped areas, each one corresponding to a nucleated cell. They are the endothelia, and represent, as already stated, the sole essen- tial constituents of all capillaries. Their form varies with the calibre of the vessel, the smaller capillaries being composed of THE BLOOD-VESSELS. 147 corpuscles which are comparatively narrow, the larger vessels having broader cells. In man they have an average length of 0.07560.0977 mm., and an average breadth of 0.010.05 mm. The intercellular boundaries, brought out as dark lines by means of the silver salt, frequently exhibit little nodular swell- ings. (See Fig. 58.) In addition to the ordinary endothelia, we find smaller areas, generally without nuclei ; they have rounded or some- what dentate contours, and are interposed be- tween the other cells. Eberth believes that some of these intercal- ated areas, as Auerbach has called them, proba- bly correspond to por- tions of strangulated vas- cular cells. It is more logical to regard them as the remnants of an in- complete endothelial des- quamation, a process which is of physiologi- cal occurrence through- out the blood-vessels. These remaining bits are finally destined to be- come quite detached from the vascular wall, and are then swept away by the rush and flow of the blood-current. The detached portions of such endothelia and their nuclei appear as free granules in the blood, where they have puzzled many observers, and have been vari- ously called microcytes, hcematoblasts, etc. From this descrip- tion it is plain that Cohnheim's view, that these spaces are openings or stomata, is not sustained. True, we find in serous membranes of certain animals real openings, but these always appear of rounded shape, and are, to say the least, not com- monly observed in human blood-vessels. This statement of the case does not militate against Cohnheim's well-known views that the corpuscles emigrate through the vessels, for, remembering the protoplasmic nature of the endothelial tubes, FIG. 61. A, A, stellate connective-tissue cells connected by B,B, delicate protoplasmic threads to C,C, sprouts of endothe- lial tubes ; D, protoplasm connecting two capillaries ; B, nu- cleus imbedded in a primitive sprout of protoplasm, budding from wall of capillary. Specimen prepared by silver nitrate. 148 MANUAL OF HISTOLOGY. we can readily account for the phenomena in question. The capillary-wall is elastic, extremely thin, and permeable. By virtue of these qualities, it may allow the passage of a leu- cocyte or colored globule through its substance without suf- fering a permanent breach of continuity. The writer's views on endothelial desquamation as a normal process of physi- ological import may strike the reader as insufficiently substantiated by known facts. But when we remember that similar processes have been actually ob- served taking place under the microscope, all doubts as to the probability of this endothelial desquamation should vanish. The author refers to the recent observations of Altmann (Arch.f. mikros. Anat., Vol. XVI., p. 111). This his- tologist investigated the changes which take place in the serous epithelium (i.e., endothelium) of the exposed frog's mesentery. Multiple swellings of the endothelia were seen to occur ; then portions of these cells would become de- tached. Such detached bits were found to resemble in their appearance ordi- nary leucocytes. But, in spite of this apparent breaking up of the endo- thelia into these nucleated corpuscles, they often retained their individuality unaltered. The production of bodies resembling leucocytes from endothelia has, therefore, been actually observed in connection with serous membranes, and vascular desquamation is essentially the same process. The capillary blood-vessels occupy the interstitial connec- tive tissue of organs, without entering their parenchyma proper. Cartilage, the teeth, the hairs and nails, the cornea, and cer- tain structures of the nervous system and organs of special sense are devoid of capillary supply. Most of the larger tubes are invested by a delicate, exter- nal, sheath-like structure, called the capillary adventUia or vascular peritTielium. It is composed of a rather close net- work of delicate connective- tissue fibrils. Prolongations of pe- culiar stellate cells, which clasp the capillary- tube, may some- times be seen to join these fibrils. (Fig. 62.) Such branching cells are also encountered at some distance from the capillaries. They show delicate processes, which may anastomose with the offshoots of the adventitial corpuscles. In other places we only find external plates of connective-tissue cells (Krause's ino- blasts), which have become more or less fused with the capil- lary-wall. In many instances the perithelium is inseparable from the connective-tissue stroma surrounding the vessel. In reference to the manner of anastomosis, the forms and modes of ramification of different networks vary with the dif- ferent tissues and organs of the body. Hence, a simple in- THE BLOOD-VESSELS. 149 spection of capillary reticula will generally enable us to decide the nature of the tissue or organ in question. From a physio- logical point of view, we recognize a causal relation between high capillary development and great functional activity. Therefore, the abundance of capillaries will determine the physiological importance of an organ. The chief forms of ramification may be grouped as follows : 1. Loops (a), simple or compound; e.g., the skin and the hard FIG. 62. Capillaries from the hyaloid membrane of the frog: er,o, capillary-wall; 6,6, nuclei of the same; c,c, cells of the tunica ad ventitia ; rf,rf, processes of these cells clasping the capillary-wall; e, stel- late cell anastomosing with the cells of the tunica adventitia. Eberth. palate ; (b) reticulated (the intestinal villi). 2. Tufts (the kid- ney). 3. Irregularly polygonal networks (the glands and the mucous membranes). 4. Rounded reticula, with round or polygonal meshes (adipose tissue). 5. Reticula with elongated meshes (the muscles, bones, and tendons). There would be a certain satisfaction in knowing that this or that vessel had a precise breadth, and its coat a certain thickness. The precision would be apparent, however, rather than real, because such 150 MANUAL OF HISTOLOGY. measurements vary greatly at different times in the same ani- mal, and even more so in different animals. It may be stated, in general, that the calibre corresponds to the size of the largest blood-globules. In man, therefore, we have an average diam- eter of about 0.007 mm. The largest capillaries exist in the mucous membrane of the stomach and colon, the periosteum and bones, and the pituitary body. The smallest are found in the skin, the small intestine, the lungs, the muscles, the gray substance of the brain, and the retina (Valentin, Weber, and Henle). The genesis, reproduction, and regeneration of capillaries. There is still much uncertainty about the mode in which blood-vessels are first formed in the embryo. My personal FIG. 63. Growth and development of capillaries by nucleated sprouts of protoplasm : A, poly-nucle- ated large sprout with filiform process ; B, B, blood-globules ; C, branched cell ; D, delicate protoplasmic tendril linking C with E, a smaller mono-nucleated sprout of endothelial wall. observations on this subject, while working recently under the supervision of Kolliker, appear to confirm the view held by Foster and Balfour. These authors' account of the interesting process may be summed up as follows : About the second day of incubation in the chick, certain mesoblastic cells send out solid processes, which, uniting, form a protoplasmic network containing nuclei. A majority of the latter acquire a reddish tint, and are ultimately transformed into colored blood-glob- ules. Other nuclei, however, remain unaltered, and, receiving an investment of protoplasm, form walls inclosing the reddened THE BLOOD-VESSELS. 151 nuclei. The protoplasm of these central nuclei rapidly becomes liquefied, thus forming the blood-plasma. And now we have a, system of communicating tubules, containing corpuscles float- ing in a plasma, their walls consisting of nucleated cells. Hence, the blood-vessels do not arise as intercellular spaces, but are hollowed out to form channels in an originally solid reticulum of protoplasm derived from mesoblastic cells. This explanation of the way in which vessels are formed aids us in understanding both how capillaries are reproduced in the adult, and their regeneration under pathological condi- tions. The capillary -wall itself, under the influence of favor- ing circumstances, begins to bud, as it were ; the delicate proto- plasmic sprouts send out more delicate filaments, which, uniting with similar offshoots from neighboring vessels, establish a connection between two capillaries. In due time these solid structures undergo the familiar process of hollowing out, and the newly formed vessel is complete. Frequently the proto- plasmic threads communicate, forming a reticulum which Ran- vier has called vasoformative network. This author also ob- served that capillaries develop from special cells, termed vasoformative cells. They resemble leucocytes, and form by their prolongations a. network of solid protoplasm. This is originally quite independent of already existing capillaries. Subsequently, however, a consolidation is effected, and the blood then flows through these new channels in the usual manner. The author has been able to trace collections of emigrated leucocytes through various stages of progressive development, culminating in the formation of true capillaries. The experi- mental investigations on this subject were carried out in Pro- fessor v. Hi ndfleisch's laboratory, and have been fully described by his former assistant, Dr. Ziegler, of Wiirzburg. The arteries. If we follow the capillaries in a direction toward the heart, we soon find the endothelial tube receiving an investment of unstriped muscle-cells. These are wound transversely or obliquely around the capillary, thus forming a second tube, as it were, surrounding the first. Externalto the muscular layer there appears some connective tissue, mingling with which elastic elements may be observed. The direction of these additional fibres is mainly longitudinal. They form the third or external coat, called the adventitia, the second or 152 MANUAL OF HISTOLOGY. middle being represented by the muscle- cells, and the first or internal by the endothelial tube. The latter now receives the name of intima. When the layers of its walls are arranged in this simple manner the vessel is called an arteriole, and this constitutes the type of all arteries. Arterioles, however, commonly contain a few additional fibres between the intima and the media, as the first indication of what afterward becomes a special layer. This structure, known as the internal elastic coat, attains considerable devel- opment in the larger vessels. With the growth of an artery in calibre its individual coats are reinforced by additional layers. Hence the thickness of the entire wall increases at the same l&Sssm FIG. 64. FIG. 65. FIG. 66. FIG. 64. Minute artery showing optical section of alternate groups of muscle-cells, and an external nu- cleated membrane, representing the tunica ailventitia. FIG. 65. A, intima ; B, delicate internal elastic coat ; E, media (as in Fig. 64) ; D, adventitia. Arteriole, from a child's mesentery. FIG. 66. Elastic internal tunic of the basilar arteries. time that its structure is rendered more complex. But new tissues never appear. Moreover, the increased thickness is not uniformly proportionate to the enlarged 'calibre ; neither does it take place by equal participation of the different tissues men- tioned. In vessels of small and medium size there is a prepon- derance of muscular over elastic elements. In the larger trunks the reverse condition obtains. It is, therefore, proper to dis- tinguish arteries of the muscular from those of an elastic type. The latter class is represented by the principal distributing trunks, all the remaining arteries belonging to the muscular type. There exist, however, no abrupt lines of- demarcation between these main forms the one merging gradually into the other. The interposition of the internal elastic coat between the THE BLOOD-VESSELS. 153 intima and the media marks the transition of a minute into a small artery. This new layer consists at first of delicate fibrils of elastic tissue, or an apparently homogeneous membrane. Vascular contraction throws it into folds, which appear as longitudinal striae or a transverse series of continuous festoons. As the vessel grows larger this coat gets thicker, becomes dis tinctly fenestrated, and presents a reticulat- ed appearance. It is now made up of inter- lacing bundles of connective tissue and elas- tic fibres, with spaces left between them. The latter constitute the fenestrse of this layer, which in the large vessels becomes a double or triple lamellated membrane. Be- tween it and the lining endothelium there appears still another structure, which has re- ceived various names from different authors. Thus, Kolliker has called it the striated in- ternal coat; Remak, the innermost longi- tudinal fibrous coat ; and Eberth, the in- ternal fibrous coat. We shall employ the last term. The internal fibrous coat consists at birth of a granular substance, which be- comes distinctly fibrillated in the adult. Embedded in this membrane lie numerous branching corpuscles, containing large, con- spicuous nuclei. Besides these cells, smaller, so-called granulation-bodies are frequently seen. So far from regarding them as of path- ological origin (Eberth, in ''Strieker's His- tology"), I prefer to consider them as ma- trix-cells for the regeneration of desquamated endothelia. My reasons for so doing are Fio. 67. Small artery clei of the tunica adventitia; 6, muscle nucleus ; c, elastic TI T . i 11 -i i internal tunic : d. membrane as follows : In the blood-vessels of young formed of fusiform Eberth. animals and newly born infants I have fre- quently noticed thick, dark, and granular bodies immediately below the endothelial lining. These subendothelial cell-plates were smaller and more polyhedral than ordinary endothelia, and invariably contained one or even two nuclei. They ap- peared to resemble germinating endothelial cells, such as Klein has described as occurring in serous membranes. They did not, however, occur in single layers, as Klein has seen them, 154 MANUAL OF HISTOLOGY. but in strata. They were observed in particular vessels of young animals. It seems likely that these cells disappear or shrivel with the growth of the individual, but their sudden reap- pearance in pathological processes leads the author to believe that at least some of them persist through life. Talma ( Vir- cTiow's Arch., Vol. LXXVIL, pp. 242-269) observed similar elements, but thinks they are derived from the ordinary en- dothelia, instead of vice versa. He is also convinced that the latter are merely modified leucocytes ; but this view has been shown to be erroneous by Virchow (ArcTiiv f. path. Anat., Vol. LXXVIL, pp. 380-383). Endothelial desquamation is probably, as already stated, a physiological process of constant ' -.^-, ^,^:^,;,, - ^ w. The lower surface of the rete adapts itself to the upper mrface of the corium, and between the papillae projects down- 274 MANUAL OF HISTOLOGY. PIG. 118. Horizontal section of skin through a papilla. The migrating cells are observed as dark bands between the epithelial cells and amongst the connective tissue of the papilla. Pagenstecher. ward and forms the interpapillary rete Malpigliii. Wandering lymphoid cells are frequently present in the rete. They are especially numerous in some pathological conditions. They (Fig. 118) are elongated spindle-shaped bodies lying between the rete cells, and sending out minute processes. They color deeply in carmine, have a small nucleus, and are most numerous in the lower part of the rete mucosum. The granular layer (Fig. 115, b) consists of one or two strata of flattened, granular- looking bodies, which, in perpendicular section appear spindle - shaped, with their long diameter parallel to the free surface of the epidermis. In this stratum the cells are no longer connected with each other by bands, as in the pre- ceding layer. The nuclei of these corpuscles are very distinct, and flattened in the same direction as the cell-body. The latter has a very coarsely gran- ular appearance, which is most marked near the nucleus, and gradually diminishes in degree as the periphery of the cell is approached. The structure of these bodies is best shown with hsematoxylon. The stratum lucidum, also called the stratum of Oehl, is composed of at least three layers (Fig. 115, c). It presents a clear, homogeneous, or striated appearance. Within the flat- tened cells composing it, a staff-shaped nucleus is found. The cells of this layer are formed from those of the granular stra- tum. In their movement to the free surface the latter become less granular and the inter-granular substance grows more trans- parent and shining (Unna). This change from a granular to a homogeneous translucent appearance commences around the nucleus, whence it gradually extends to the periphery of the cell. The nucleus, also, usually becomes invisible. In vertical section the corneous layer appears (Fig. 115, d) to be composed of wavy fibres and horny, transparent cells of various sizes and shapes. This variation in bulk and form THE SKIN. 275 depends in great measure upon the thickness of the layer. The nearer we approach to the stratum lucidum, the more dis- tinct are the cells. If the layer is very thin the cells appear as elongated, flat, or curved bodies, giving to this part of the epidermis a fibrous appearance. When the corneous stratum is thick these cells present various forms and sizes. The cor- puscles of the lower layers color slightly in carmine, are poly- gonal or spindle-shaped, and frequently contain a shrivelled nucleus. As the surface is approached they grow flatter and drier, are more bent upon themselves, and color less and less in carmine. The nucleus also becomes invisible. The most su- perficial layers are composed of elongated, flat, dried-up cells, the so-called epidermic scales. These bodies are best studied after they have been subjected to the action of liquor potassse, which ca-uses them to swell up. The corpuscles of the stratum corneum are arranged in lay- ers as in the other parts of the epidermis, but the elements forming a layer are more closely united with each other than with those of the adjoining layers. Hence this stratum can be separated into lamellae, as occurs in some pathological states of the skin. It accompanies, for example, the formation of some vesicles, where the exuded liquid, prevented from pass- ing toward the surface, accumulates between the layers, and thus separates them from each other. The corneous layer participates in the elevations and de- pressions of the underlying layers. This causes the undulat- ing or wavy appearance of the lamellae, as observed in sections where the papillae are well developed. It varies greatly in thickness in different parts of the body, and reaches its great- est development on the palms of the hands and soles of the feet. Its thickness does not depend upon the rete Malpighii, as it sometimes forms a thin layer where the rete is thick, and vice versa. The subcutaneous connective-tissue layer of the skin con- sists principally of connective-tissue bundles, which, coming from the underlying fasciae of the muscles or from the peri- osteum, pass in an oblique direction to the corium. These fasciculi are generally cylindrical in form, and variable in size ; by their anastomoses or divisions they form larger or smaller networks, with correspondingly large or small interfascicular spaces. Generally large bundles anastomose with each other 276 MANUAL OF HISTOLOGY. in this layer, and hence a loose connective tissue is formed. Within this layer adipose tissue is found in greater or less quantity. The 'fat-cells are collected into masses or lobules, the number of cells which form a lobule varying greatly in num- ber. Each of these latter may be regarded as a fat-gland, as it is provided with an afferent artery, a capillary plexus between the corpuscles, and one or more efferent veins. Several lobules are sometimes united together in the form of an acinous-like gland, and are likewise seen to be surrounded by a general sheath of connective tissue. The individual fat-cells are round, flattened, polyhedral, or oval-shaped, the form depending upon the degree and direction of the pressure exerted upon them. Owing to the amount of fat-tissue so often found in this layer, it has been called the panniculus adiposus. Such fat-lobules are absent in the penis, scrotum, labise minorse, eyelids, and pinna. The corresponding spaces in these regions are tra- versed by fine connective- tissue bands or single fibrils. From this adipose tissue fat-columns pass upward in a somewhat oblique direction to the bases of the hair-follicles, especially to those of the fine hairs. Their long axes form a slight angle with the axes of the follicles, and they are nearly parallel to the erector pili muscles (Warren). In cases of starvation, in the so-called wasting diseases, and in all acute diseases at- tended with excessive loss of tissue, the fat-cells disappear to a greater or less extent. The skin, in such instances, becomes correspondingly flaccid and wrinkled. Adipose tissue gives to the skin its tension and fulness, and to the body its appear- ance of roundness or plumpness. Obesity consists in an exces- sive production of fat-cells. The interfascicular spaces differ in size in proportion to the amount of lymph present, and to the closeness of the anasto- moses between the bundles. In oedema the lymph-spaces are increased in size proportionately to the increased amount of liquid present. The interfascicular spaces all communicate with each other, as is shown by the rapidity with which a hypodermically injected liquid can be dispersed by manipu- lation. The connective-tissue cells of this layer and of the corium consist of branched cells (Ravogli) which surround the white fibrous bundles and send in processes between the fibres. Ac- cording to some observers, these cells are epithelioid in charac- THE SKIN. 277 ter. The elastic-tissue fibres are developed from the processes of the branched cells. Besides connective-tissue fibres and cells, lympJioid corpus- cles are present in this layer. They exist in greatest number near the blood-vessels and glands. In this situation they are of a roundish form, but in the parts distant from the blood- vessels they are more or less spindle-shaped, and are to be regarded as wandering cells. The convoluted part of the sweat-glands and the lower part of the hair-follicles of deep-seated hairs lie in this layer. Blood-vessels, lymphatics, and nerves are present. The blood-vessels are large, and after giving off small branches to the hair- follicles, sweat-glands, and fat-lobules, pass upward to the corium. Pacinian corpuscles are found in connection with some of the nerves. For a description of these bodies the reader is re- ferred to the article on the nerves. The principal part of the corium consists of white fibrous and elastic tissue, the latter increasing in amount with advancing age. Here the white fibrous tissue forms a much denser, firmer structure than in the previous layer. It consists of deep oblique, and superficial horizontal bundles. The latter com- prise fine bundles of connective tissue which run parallel with the surface of the skin, and by their division and anastomoses form a very fine network with small interfascicular spaces. From this layer bundles pass upward into the papillae, and these form a second denser network. The deeper layer is formed by a continuation upward of the subcutaneous con- nective-tissue bundles. These pass upward in an oblique direc- tion, and as they reach the corium divide into fasciculi. Here they continue to divide and anastomose with each other and with fibres from the horizontally running bundles. The anas- tomoses are very close ; hence, the corium is formed of a dense network of connective tissue, except in those parts which are traversed by blood-vessels, lymphatic vessels, nerves, hair-folli- cles, and sebaceous and sweat glands. Immediately around the hair-follicles, sweat-ducts, and sebaceous glands the con- nective tissue is dense, and the fibres run parallel with the di; rection of the organs. Owing to the greater size of the connec- tive-tissue bundles in the lower part of the corium, and the consequent looseness of the network formed by their anasto- 278 MANUAL OF HISTOLOGY. moses, this part of the corium lias been called the pars reticu- laris corn, in contradistinction from the finer network formed in the upper part, to which the name pars papillarls has been applied. But neither between these two parts nor between the subcutaneous layer and the corium is there any sharp dividing line, the transition being a gradual one. As already mentioned, the size of the interfascicular spaces depends upon the closeness of the anastomosis between the bundles and fibres. The direction of the bundles corresponds with that taken by the blood-vessels. The connective-tissue corpuscles of the corium resemble those found in the subcutaneous layer, and also bear the same relation to its connective-tissue bundles. From the upper portion of the corium fibres pass upward to make the papillae. The form of the papillae is very variable in different parts of the body. Where they are most developed, as on the inner surface of the terminal phalanges of the fingers and toes, they are conical in shape. In some other regions they form only slight elevations on the corium, giving a wave-like appearance to its upper surface. They consist of a close network of white, fibrous connective tissue combined, especially in the central part of the papilla, with a large number of elastic fibres. Those papillae which contain tactile corpuscles are called nerve-pa- pillae. The corium is separated from the stratum mucosum by a thin, transparent basement-membrane, containing oval nuclei. Its under surface is not sharply defined, and from it prolonga- tions pass upward between the cylindrical cells of the rete, giving this surface a notched appearance similar to that ob- served on the inner margin of the internal sheath of the hair- follicle. Elastic fibres are present in large numbers in the corium, especially in its upper part, where they form a network around and between the white fibrous tissue-bundles. In the lower part of the corium they form a large network, which becomes finer as the surface is approached. The number of elastic fibres increases with advancing years. With this increase of elastic fibres there is a corresponding decrease of the white fibrous connective-tissue cells (Ravogli). Numerous wander- ing cells are met with in the corium, especially in the vicinity of the blood-vessels and glands. Hair-follicles, sebaceous THE SKIN. 279 glands, sweat-ducts, nerves, lymphatic vessels, and non-striated muscles are also present in this layer. For a fuller descrip- tion of the intimate structure of the connective-tissue bundles and cells, see the subject of connective tissues. Blood-vessels. Only the corium and subcutaneous tissue are provided with blood-vessels. The arterial blood-vessels supplying the skin form two parallel horizontal layers, a su- perficial and a deep one. The deep layer lies in the subcuta- neous tissue, and consists of large vessels running parallel to the general surface. From this horizontally lying deep layer, branches are distributed to the sweat-glands and fat-follicles of this region. The principal branches, however, pass perpendicu- larly or obliquely upward through the corium to its upper part, and form immediately beneath the papillae (after free branch- ing and anastomosis) a superficial horizontal layer, the stratum subpapillare. From the vessels ascending through the corium branches are given off to the hair-follicles, sebaceous glands, and gen- eral tissue of the corium. From the stratum subpapillare small branches pass upward into the papillse, where they become capillary ves- sels, which proceed to the summit of the papilla. (See Fig. 119.) Before reaching this point, however, they frequently divide into two or more branches. Frequently, those papillse in which tactile corpuscles are seated have no blood-vessels. The veins are arranged on the same plan as the arteries : they form a superficial and a deep layer, and have their origin in the papillae. From the superficial layer larger vessels pass downward, receiving blood from the veins of the hair-follicles, sebaceous glands, and the general tissue of the corium, thus forming a deep subcutaneous layer or venous network. Nerves. Medullated and non-medullated nerve-fibres are present in the skin. They are found in combination in the nerve- trunks of the subcutaneous tissue, the medullated fibres being most numerous in those regions of the skin where the Pacinian and tactile corpuscles are most abundant. In the subcuta- neous connective-tissue region, and in the lower part of the corium, some nerve-fibres leave the nerve-trunks and pass to the glands, blood-vessels, and Pacinian corpuscles found in this region. In the corium some of the fibres lose their medullary 280 MANUAL OF HISTOLOGY. sheath, and afterward continue their course as non-medullated fibres. The nerve-bundles pass upward in a more or less oblique direction from the subcutaneous connective tissue through the corium to the subpapillary network of blood-vessels, around which they form a plexus. From this subpapillary plexus medullated fibres run upward and pass into the tactile cor- puscles. The non-medullated nerve-fibres form a reticulum around the blood-vessels of the pars reticularis corii and the capilla- ries of the papillae. They consist of thick or fine, smooth, varicose fibres with numerous nuclei. These fibres proceed from the network around the subpapillary blood-vessels up- ward toward the rete Malpighii, and either pass directly into the rete or run for a short distance parallel to its under sur- i'ace, and then finally enter that layer. Within the epider- mis the fibres run between the cells and terminate in a manner not yet definitely known. Their mode of division and termina- tion within the epidermis is probably similar to that occurring in the cornea. Within the papillae the nerve-fibres frequently divide before entering the rete. The manner of distribution and termination of the non- medullated nerve-fibres can only be studied successfully in tis- sue stained with gold chloride. The tissue must be fresh, and a weak solution of the gold chloride used. When sufficiently stained the tissue is placed in -distilled water slightly acidu- lated with acetic acid and exposed to the light. The Pacinian corpuscles are found in greatest abundance in the skin of the fingers, toes, palm of the hand, sole of the foot, but also occasionally in other regions of the skin. Their struc- ture is described in the article on the nervous system. Tactile corpuscles. As already mentioned, some of the medullated nerve-fibres forming the plexus surrounding the subpapillary blood-vessels, pass upward and enter the so-called tactile corpuscles. These corpuscles are generally seated in the papillae, but occasionally they are found in the subpapillary region, i.e., the upper part of the corium. The majority of the papillae containing such corpuscles have no blood-vessels. They are more or less oval in form, and can be easily recog- nized under the microscope by their dark contours and by the oblique lines produced by the transversely running connective- tissue fibres of the outer surface of the corpuscle. There may THE SKIN. 281 be two or more corpuscles within a single papilla (Thin), but each corpuscle invariably has a special nerve passing into it. Frequently, however, an appearance as if two corpuscles were present is produced by a single corpuscle having the shape of a figure 8. The medullated nerve-fibre, in passing to the corpuscle, pursues a more or less curved course, and usually enters it at or near its lower extremity. It may, however, en- ter at any part of the corpuscle, and sometimes winds around it for a considerable distance before entering. After entering the corpuscle the medullary sheath is lost, and its course now becomes difficult to pursue, except in the case of very small or young corpuscles. The intimate structure of these bodies and the arrangement of their formative elements are still mat- ters of discussion and uncertainty. The external portion of a corpuscle appears to be composed, in great part, of larger or smaller bundles of white, fibrous connective tissue anastomos- ing with each other and running transversely, or in a spiral direction, to the long diameter of the corpuscle. This part of the corpuscle differs, as regards irregularity of surface, with the size and the manner in which the fibrous fascicles divide and anastomose. The coarser the bundles and the anastomo- ses the more irregular will be its sur- face. Between the fibres are found oval or round bodies which color deep- ly in gold, and have been regarded as elastic elements (Thin). Other obser- vers consider them as connective tis- sue, or nerve-fibres. Some of these bodies undoubtedly represent the nerve-fibre in transverse or oblique section ; for the nerve pursues a more or less zigzag course within the corpuscle, and, consequently, a section of the body will probably show the nerve cut across in one or more places (Pig. 120, b). The arrangement of the elements forming the central part of the corpuscle is not yet thoroughly understood. These bodies have hitherto been usually regarded as end-organs that is, it has been believed that the medullated nerve-fibre terminates within the corpuscle, hence the name, tactile corpuscle. Observers, however, have Fio. 120. Tactile corpuscle, show- ing termination of nerve : a, corpuscle; 6, nerve, cut obliquely; c, apparent division of nerve-fibre ; e, similar ap- pearance as at c ; /, blood-vessel ; g, rete cells; A, nerve-fibre cut trans- versely. 282 MANUAL OF HISTOLOGY. not agreed as to the mode of termination of the nerve, and some have maintained that it has not been clearly proven that they really do terminate in the corpuscle. From specimens which I have recently obtained I am led to believe that the nerve does not terminate within the corpuscle, but passes on into the rete Malpighii. The best corpuscles for studying this point are small ones, as in these a section is more likely to include the entire upper extremity of the corpuscle at the same time that it is not too thick for examination with the microscope. Even in a small corpuscle, however, unless the nerve passes onward in a direct level with the corpuscle after leaving it, the nerve, in a vertical section, will be cut across, and it will, therefore, be impossible to follow it from the corpuscle into the rete. I believe the nerve frequently, perhaps generally, changes the direction of its course after leaving the corpuscle, and hence we often see a transverse section of the nerve at the upper extremity of the corpuscle. In Fig. 120 is seen the location of the termination of the nerve-fibre as observed in one of my specimens. In one place its course between the rete cells was very indistinct, though recognizable. The nerve passed obliquely upward be- tween the cells of the rete to the space between the second and third rows of cells, where it assumed a longitudinal di- rection. At the commencement of the curve the nerve ap- peared to have undergone division (c). After passing a short distance horizontally it ran almost perpendicularly downward, and near g was lost to view. At e it appeared to have again undergone division. According to the appearances here fig- ured the corpuscles are not the structures in which the nerve terminates, the latter passing from the corpuscle (as -a non- medullated fibre) into the epidermis, where it divides and probably terminates in the same manner as the other nerves. This mode of termination cannot be regarded as strange, as we have already seen that some medullated nerve-fibres lose their medulla deeper in the corium, and afterward continue their course as non-medullated fibres. The tactile corpuscles are found in greatest number in the ends of the fingers. They are also present on other parts of the hand and on the foot, and sometimes in the lips and nipple. The sweat-glands. The sweat-glands glandulce sudorif- THE 283 erce are found in the skin of all parts of the body except that of the glans penis and margin of the lips. They are most nu- merous in the palms of the hands and the soles of the feet, where they number, according to Krause, 2,685 to 2,736 to the square inch. A sweat-gland is composed of two parts, viz.: the gland proper, or secreting part, and an excretory duct. The gland proper lies in the subcutaneous tissue, and consists of the lower part of the sweat- gland rolled and coiled upon itself into a more or less globular form, the tube ter- minating in a cul-de-sac, the blind extrem- ity generally lying in the centre of the coil. The diameter of the secreting tube is greater than that of the excretory duct. The former is composed of secreting cells, unstriped muscular fibres, and a basement- membrane. The cells (glandular or secret- ing epithelial cells) are polygonal in shape and form only a single layer. They are strongly granular in appearance and have a very distinct nucleus. Their basal end is sometimes notched where they are in- serted into the basement-membrane. In normal conditions these bodies are never found in the sweat-fluid, but in inflamma- tion of the surrounding connective tissue they frequently become separated from the basement-membrane. Oil-globules are frequently seen in the cell- body, and are to be regarded as a normal constituent of the corpuscles. The basement-membrane is a thin, transparent structure, lying beneath the epithelial cells and composed of flat endo- thelial elements, as shown by the action of silver nitrate on the fresh tissue. In certain glands, especially those of the axilla, a layer of unstriped muscular fibres is found external to the basement- membrane. These fibres are present in only a small number of sweat-glands ; by their contraction they assist in the expul- sion of the secreted sweat. They are the smallest unstriped muscular fibres met with in the human body. FIG. 121. Lower part of a sweat-gland : a, excretory duct ; 6, coil of secreting-tube ; c, sc- creting-tube cut transversely; d blood-vessels cut across. 284 MANUAL OF HISTOLOGY. The sweat-glands are surrounded by a somewhat loose fibrous connective tissue, from, which fibres pass inward and form a closer network between the coils of the gland. Some of the fibres run parallel, and others transversely or obliquely, to the long diameter of the convoluted tube. A large number of lymphoid cells are always present in this interglandular connective tissue. The sweat-glands are richly supplied with blood-vessels. The excretory duct passes upward from the gland proper in a more or less vertical direction through the different layers of the skin to its free surface, where it opens with a funnel- shaped orifice. In passing through the corium it pursues a straight or slightly wavy course, and enters the lowest part of the inter-papillary rete. The structure of this part of the excretory duct differs from that of the gland proper, in the shape of the cells, the absence of muscle-fibres, and the presence of a cuticula. This cuticula lines the inner surface of the epithelial coating and limits the lumen of the duct. As the rete Malpighii is entered there are generally two or more layers of cells lining the duct, the number increasing as the rete is approached. The transition from secreting cells to lining cells is gradual, so that the presence of a cuticula decides the nature of the tube. The basement -membrane corresponds in structure with that of the gland proper. The fibres of surrounding connective tissue run parallel with the duct. As the duct approaches the rete Malpighii its epithelial cells increase in number and form two or more layers, which are really only a continuation downward of the cells of the rete. When the duct enters the rete it loses its basement- membrane and is formed only of the cells of the mucous layer, which have become more or less flattened and spindle-shaped. The direction of the duct through the rete is sometimes straight and sometimes spiral. In passing through the stratum corneum the duct pursues a spiral direction on account of the horizontally flattened cells of this layer (see Fig. 114, /), and the number of spirals pres- ent depends upon its thickness. The largest number is found in the palms of the hands and soles of the feet, where it may amount to twenty or more, whilst on some parts of the body there is not even a single complete spiral. The wall of the THE SKIN. 285 duct is formed of the cells of tlie corneous layer, and the duct opens on the free surface at the summit of the ridges. The formation of the sweat-glands commences in the fifth month of foetal life by the pushing of epithelial cells from the rete mucosum into the cutis. In the seventh month the epi- thelial cells form a canal, and the lower end of the tube be- comes dilated and somewhat twisted. In the ninth month the tube is coiled upon itself to form the gland proper. According to Ranvier, who believes that the muscular fibres lie between the epithelial cells and the basement-membrane, the muscle- cells arise from the external cells of the gland proper by a process of simple differentiation. The lumen of the tube is formed not by a softening down of the central cells, but by the formation of the cuticula, which occurs first at the lowest part of the excretory duct (Ranvier). The sebaceous glands. The sebaceous glands are seated in the corium and are in close connection with the hair-follicles. When the hairs are large the sebaceous glands appear as ap- pendages to the hair-follicles into which their ducts enter, and by which their contents are carried to the free surface. As regards the small downy, or lanugo hairs, they may be said to open into the ducts of the sebaceous glands, the ducts of the latter having in this case a much greater diameter than in the previous instance. They also open directly on the free surface. The sebaceous glands are almost without exception acinous glands, the number of lobules forming a single gland, ranging from two to twenty, or more. The largest glands are seated in the nose, cheeks, scrotum, about the anus, and in the labia. Occasionally the secreting portion of a sebaceous gland con- sists of a single tubule, or sac, whose duct opens into a hair- follicle. Every sebaceous gland is composed of two parts, viz.: the secreting portion, or gland proper, and the duct. The gland proper is formed of a basement-membrane, or sac, externally, and secreting cells, or their products, internally. The basement- membrane is continuous with the transparent membrane de- scribed as lying directly beneath the rete Malpighii and above the corium, and has a similar structure. This basement-mem- brane passes from the sebaceous gland to the hair-follicle, where it forms the inner layer of the hair-sac. The membrane of the sebaceous gland is surrounded externally by bands of dense 286 MANUAL OF HISTOLOGY. connective tissue containing blood-vessels, nerves, and lym- phatics. The secreting part of the gland (Fig. 122, t) is composed of layers of cells very similar to the cells present in the epidermis, those of the outer part corresponding to the cells of the rete Malpighii. The first layer of cells, viz., those seated upon the basement-membrane, is composed of cylindrical, or cubical, cells, like those of the rete. They have a very distinct nucleus. Further inward the cells become larger, more or less polyhe- dral in form, and contain fat, which obscures or conceals the nucleus. If the fat is extracted the nucleus can be seen lying in the centre of the space previously occupied by the fat. The nearer the centre of the gland the greater the quantity of fat in the cells. The most external layer of cells contains but a small quantity. In the centre of the gland, free fat, fat-crys- tals, and remnants of epithelial cells are found. The duct of the sebaceous gland is similar in structure to that of the gland proper. Externally is the basement-mem- brane, lined inside by epidermis-like cells, containing more or less fat, and enclosing a central cavity through which the seba- ceous matter passes to reach the hair-follicle or the free surface. The contents of this canal are fat, fat-crystals, and remnants of epithelial cells. Internal to the polyhedral cells of the duct are the cells of the corneous layer of the epidermis, which di- minish in number in proportion to the distance from the free surface. In large hairs the duct of the sebaceous gland opens at an acute angle into the hair-follicle near its upper third, and the gland proper lies about on a level with the middle third of the hair-follicle. At the place of union of the hair-follicle with the sebaceous gland the cells of the latter become continuous with the cells of the external root-sheath of the hair. This latter root-sheath becomes continuous above with the cells of the rete Malpighii. The development of the sebaceous glands commences at the third month of foetal life, as a projection downward and out- ward of a part of the external root-sheath of the hair, at the place where the future opening of the duct will be situated. It consists, at first, entirely of epithelial cells, which by sub- sequent multiplication and further projection downward, form the sebaceous gland. THE SKIN. 287 Muscles. Striated and non-striated muscles are present in the skin. The former are found both in the smooth and in the bearded parts of the face, and also in the nose. They arise from the deeply seated muscles, and passing vertically, or more or less obliquely, upward between the hair-follicles and the glands of the skin, terminate in the corium. The non-striated muscles are very numerous, and run either in a parallel or in an oblique direction to the general surface of the skin. Those lying parallel with the general surface run either in a straight or circular direction. When they run in a straight direction and anastomose with each other they form a network, as in the scrotum, prepuce, and perineum. The straight running muscles are found, especially in the scalp and in the axilla, both above and below the sweat-glands. Where the muscles have a circular course, as in the areola of the nip- ple, a continuous ring muscle is formed. The majority of the muscles running in an oblique direc- tion have a special relation to the hair-follicles. The muscle arises from the internal sheath of the hair-follicle and passing obliquely upward, skirting the lower surface of the sebaceous gland, terminates in the upper part of the corium (Fig. 122, ri). Occasionally two muscles, situated on opposite sides, arise from a single hair-follicle sheath. A muscle in its course up- ward frequently divides into two or more bundles, these sec- ondary bundles afterward pursuing different directions from each other, and sometimes uniting with fibres from other mus- cles, form a network in the corium. Sometimes an entire muscle, or a secondary bundle, passes upward into a papilla of the cutis and is inserted into the dense fibrous connective tis- sue directly beneath the rete Malpighii. Occasionally several secondary bundles run nearly parallel with each other and ter- minate either separately in the corium, or conjointly, after uniting. The skin is provided with other muscles which have no spe- cial relation to the hair- follicles, but pass more or less verti- cally upward from the subcutaneous tissue to be inserted in the corium. The number of muscles present in the skin varies in differ- ent regions of the body. They are most numerous in the scro- tum. The order of frequency in the different parts of the body is as follows : Scrotum, penis, anterior part of perinseum, scalp, 288 MANUAL OF HISTOLOGY. forearm, thigh, arm, shoulder, forehead, abdominal wall, ax- illa, fore-leg, face, volar and dorsal surfaces of the hands and feet (Neumann). They are less developed on the flexor than on the extensor surfaces. The size of the individual mus- cles varies according to the person and the region of the body. It is impossible, therefore, to recognize with certainty a slight hypertro- phy or atrophy of these structures. For information as to their blood, lymph, and nerve supply see the article on unstriped muscle. TJie Jiair. The parts to be studied in connection with the hair proper are the hair-follicle and the hair-papilla. Tb e hair proper is a cylindrical structure seated within the hair-follicle and upon the hair-papilla. Its base lies embedded either in the subcuta- neous connective tissue or in the corium. The portion of the hair proper within the follicle is called the root of the hair, and the re- mainder the shaft of the hair. The true hair-follicle includes all that part of the hair-sac below the place where the sebaceous duct enters the hair- follicle. It is of very variable size and con- sists of a blind extremity and a funnel - shaped orifice (a). The follicle is narrowed just below this funnel-shaped orifice and forms the so-called neck of the hair-follicle (5). This is the nar- rowest part of the follicle, and is the place where the duct of the sebaceous gland enters. From the neck downward the hair-follicle increases in size, be- Fio. 122. Hair from beard : a, canal of exit ; ft, neck of hair-follicle ; c, lower part of hair-follicle : d, external sheath of hair-folli- cle ; e, internal sheath of hair-follicle : /, ex- ternal root-sheath of hair; gr, internal root- Bheath of hair ; h, cortical substance ; k, me- dulla of hair; /, root of hair ; m, fat-cells ; n, arector pili ; o, papillae of skin ; p, papilla of hair ; , rete mucosum ; t, sebaceous gland ; ep, stratum corneum, which is continued into the follicle. Biesiadecki. THE SKIN. 289 ing largest at its lower end, where it rests upon the papilla. Below the neck we have the follicle and the root of the hair. The follicle consists, anatomically, of three layers : the ex- ternal, middle, and internal hair-follicle sheaths. The external sheath of the follicle (d) consists of connective- tissue fibres, which extend from the upper corium and running parallel to the long axis of the hair-follicle surround the base of the latter and send some fibres into the papilla. The fibres forming the inner portion of this sheath are arranged much more closely than the fibres forming the external part. In this latter situation there is no sharp dividing line between the sheath and the surrounding loose connective tissue, the one merging gradually into the other. Within this sheath run the special blood-vessels and nerves of the hair-follicle. The middle sheath of the follicle consists of a few transverse- ly running connective-tissue fibres, between which lie oval nuclei imbedded in a granular substance. Tliese latter, probably, represent organic muscle-cells. This sheath begins at the neck of the follicle and, surrounding its lower part, passes also within the papilla. In this tissue is a close network of blood-capil- laries. Nerves have not as yet been observed, though they probably exist. The internal sheath of the follicle is composed of a trans- parent, homogeneous-looking structure the basement-mem- brane, which is riot altered by the action of acids or alkalies. It is merely a continuation of the transparent membrane found between the rete mucosurn and the corium, which it resembles in its structure. It contains neither blood-vessels nor nerves. The external surface is smooth, but the internal surface has a notched appearance, caused by prolongations inward between the cells of the external root-sheath of the hair. The hair -papilla is formed from the stroma of the hair-fol- licle sheaths, especially from that of the middle sheath. It consists of connective-tissue fibres, between which are found numerous round cells. The internal follicle sheath separates it from the root of the hair. Within the papilla are found one or more arteries and veins besides non-medullated nerve- fibres. The papilla has a narrow neck, a thicker body, and a conical apex. It is, on an average, twice as long as it is broad. The breadth is in direct proportion to the length of the hair. 290 MANUAL OF HISTOLOGY. The hair-follicles and hairs stand obliquely to the surface of the skin. Their direction varies in different regions of the body, and depends upon the structure of the connective tissue of the corium and the degree of its tension. The contents of the hair-follicles are the external and internal root-sheaths and the hair proper. The external root-sheath (/) adjoins the inner follicle sheath and consists of rete cells continued into the hair-follicle from the general rete mucosum layer of the skin. This sheath does not extend as far as the lowest part of the follicle, generally ending about on a level with the apex of the hair-papilla, though it is sometimes continued as far as the base of the latter. All the different kinds of cells present in the epi- dermis are also found in this sheath as far down as the neck of the follicle. Beyond this point the cells of the rete Mal- pighii only enter into its formation. The number of rows of cells forming it is subject to great variation. It diminishes as the base of the follicle is approached, so that finally the sheath is formed of a single row of cells. At the neck of the follicle the sheath is usually narrower than directly above or below this point, owing to the pressure to which the cells are here subjected. Their form is very similar to that of the corresponding cells of the rete mucosum. Those of the deepest row are cylindrical, and those of the second row polyhedral. In the other rows the cells are flatter, with the exception of the most internal row, where all these bodies are large and round. This last row is not subject to the same changes as the others, and has been considered to be a distinct, independent row of cells (Unna). The nuclei of all the cells color strongly in carmine, haematoxylon, etc. Nerve-fibres have been described as running between the cells of this sheath (Langerhans). The internal root-sheath (g) lies in direct contact with the external root-sheath. It is usually described as consisting of two layers, an external one, also called the sheatli of Henle, and an internal one, or slieath of Huxley. Strictly speak- ing, this division into two sheaths is incorrect, as it has been shown (Unna) that the two sheaths supposed to be distinct have a common origin from the cylindrical epithelial cells sur- 'rounding the neck of the hair-papilla at its lowest part. These cells color very deeply in carmine. They surround the root of THE SKIN. 291 the hair like a sheath. In the thick hairs of the beard the sheath consists of three rows of cells the external row, after- ward forming Henle's sheath, and the two inner rows of cells, the sheath of Huxley. In finer hairs there are only two layers of such cells. These corpuscles are originally similar in structure, having a very granular appearance and an indistinct nucleus. The sheath is thinnest where the hair-papilla is broadest. The cells of the external layer (Henle's) become paler and lose their nuclei earlier than those of the inner layer, so that on a level with the upper part of the papilla there is a marked dif- ference in the appearance of the two layers of cells. Formerly it was supposed (Biesiadecki) that Henle's sheath commenced at this point and was a product of the external root-sheath, corresponding in this respect with the corneous layer of the epidermis. The cells of Huxley's layer afterward become transparent also and lose their nuclei, and can then no longer be distinguished from the cells of Henle's layer. The internal root-sheath is now formed of transparent, non-nucleated, spin- dle-shaped, or flattened bodies which surround the hair-cutl- cula as far as the neck of the hair- follicle. Within the internal root-sheath lies the liair proper, which consists of a knobbed extremity, the root of the hair, and a cylindrical portion, the shaft. Between the hair proper and Huxley's layer lies the hair-cuticula. This latter consists of two rows of cells an external one, closely united with Hux- ley's layer, and an internal one, united to the hair-shaft. They both arise from the cylindrical cells seated directly upon the upper part of the neck of the papilla to the inside of the cells producing the internal root-sheath. The cells of the inner cuticula (the hair-cuticula) are at first round, then cuboid in form, and finally, long and prismatic. Above the papilla they are more elongated, and commence to overlap the cells above them, With the flattening out of the cells they assume the form of rhomboid or ovoid plates, so that above the free sur- face of the skin one cell partly covers the bodies of four or five others. At first they lie perpendicularly to the long axis of the hair, but afterward they are parallel with it. Above the papilla they form spiral rows around the hair shaft, so that in any sec- tion of this part the cells appear of a long cylindrical or spin- dle-shape. The external or root-sheath cuticula consists at first of round cells which afterward flatten and lie in the same 292 MANUAL OF HISTOLOGY. direction as the flat cells of the previous cuticula. Before the internal root-sheath is pierced by the growing hair both cuti- culse are composed of similar cells. The root of the hair consists of cells closely resembling those of the rete mucosum. The corpuscles seated directly upon the basement-membrane of the papilla are cylindrical in form, and the more superficial ones polyhedral. Near the hair- shaft they are spindle-shaped and firmer. The lower cells of the central part of the root of the hair are round, have a large nucleus, and a small amount of cell-body. Afterward the cell- body increases in size. They bear a close resemblance to em- bryonic corpuscles and color deeply in carmine. In the upper part of the root of the hair the cells of the external part of the bulb become oblong, spindle-formed, and, finally, are lengthened out like fibres, in which condition they form the fibrous part of the hair-shaft. The pigment in the root of the hair is sharply limited externally by the cells of the hair-cuticula. The shaft of the hair consists of a central part or medulla, and a fibrous portion covered by the hair-cuticula. The medulla consists of polyhedral cells containing fat and pigment gran- ules. Toward the free end of the hair it becomes smaller, and finally ends near the point. The fibrous portion forms the principal part of the hair- shaft, and consists of flattened, fusi- form cells, containing numerous spin- dle-shaped granules. From the foregoing description of the hair and its follicle it is clear that in transverse sections it will present different appearances, according to the situation in which the section is made. A description of trans- verse sections in different regions of the hair is here unneces- sary. We reproduce, however, above, a figure from Biesiadecki, which will sufficiently explain this matter (Fig. 123). A hair increases in length by the formation of new elements in its root, and they, by their subsequent elongation and move- Pio. 123. Transverse section of the hair beneath the neck of the hair- follicle : a. external sheath of the hair- follicle ; fe, transversely cut blood-ves- sels ; c, inner sheath of hair-follicle ; d, basement-membrane of hair-follicle; , extern^ root-sheath ;/, cells of Hen- le's layer; g, cells of Huxley's layer; A, cuticula ; J, hair-shaft. THE SKIN. 2S3 ment upward, push the shaft of the hair and its cuticula before them. The structure of an adult hair can be best studied iu the stiff, gray hairs of the beard. For the study of the origin of the root-sheaths young hairs should be chosen. There are still many points in regard to the structure of the skin and its appendages which appear to be rather doubtful, owing to our insufficient knowledge. The first development of the hair-fol- licle takes place at the end of the third or beginning of the fourth month, and it originates as a projection downward of the cells of the rete mucosum. It is seen as a finger-shaped collection of rete cells surrounded by the connective tissue of the corium. The papilla is formed later, By the numerical increase of round cells the follicle is enlarged, and the external cells are pushed sideward, thus forming the external root- sheath. The origin of the other parts of the hair has been already described. The first hairs are always of the lanugo kind that is, they are fine hairs, with a very short hair-folli- cle. In certain regions the hairs always remain fine ; in other parts they give place to thicker ones. In the latter case a pro- longation downward of the external root-sheath takes place. This forms the hair-papilla. The papilla of the first hair atro- phies, the hair falls out, and its place is occupied by a thick hair. The permanent hair grows to a certain length, which varies in different persons and in different parts of the body. If a hair has reached its proper term of existence it falls out and is replaced by a new hair, which grows from the old papilla. A hair ceases to be produced when no new cells are formed in the hair-root. The last-formed cells become con- verted into the hair proper, and form a conical or knobbed ex- tremity to the lower end of the hair-shaft. The nails. The nail is merely a modification of the epi- dermis, and differs from the stratum corneum only in being harder and firmer. It is a longish, four-sided, hard, elastic, transparent, dense, flat body, situated in a fold of the skin on the dorsal surface of the terminal phalanges of the fingers and toes. It is slightly curved in its long diameter, the convex sup face being above and the concave below. Its posterior and two lateral sides are connected with the other structures of the skin ; the anterior side is free. The fold of skin in which the pos- terior and two lateral surfaces are imbedded increases in depth from before backward, and at the posterior margin is continued 294 MANUAL OF HISTOLOGY. forward for a short distance on the surface of the nail. This fold of skin is called the nail fold, and the tissue upon which the nail is seated is termed the bed of the nail. That part of the nail imbedded in the flesh posteriorly is the root of the nail, and the remainder its body. The flesh underlying the root the corium is called the matrix, and that underlying the body of the nail the bed of the nail proper. The matrix and bed of the nail proper are separated by a more or less convex line, gen- erally easily seen through the nail and known as the lunula. The bed of the nail is composed of corium and rete Malpighii tissue. There is no fat in its subcutaneous tissue. The rete here dips down between the papillae of the corium as in other parts of the skin. The papillae in the matrix project forward, and are shorter and closer together than in the bed of the nail FIG. 124. Transverse section of the nail through the bed of the nail proper: o, nail ; 6, loose cor- neous layer beneath it : c, mucous layer : rf, transversely divided nail ridces : e. nail-fold without papillae ; /, the horny layer of the nail-fold which has pushed forward on the nail ; 0, papillae of the skin of the finger. proper. In this latter structure the papillae also project for- ward (Fig. 124, d) and increase in length as the free margin of the nail is approached. The rete Malpighii covers the papillae of the nail, forming cones, which fill the space between the papillae. In the bed of the nail proper the transition from rete cells to horny cells is very rapid, whilst in the matrix it is gradual. Consequently, this portion of the nail is softer than the other. It is from the matrix that the nail is formed, and from the corneous cells of the body of the nail that the nail is made thicker. The soft cells are directed forward and become more horny as they advance. The under surface of the nail- fold covering the posterior part of the nail is provided with epidermis, which is continued forward a short distance on the upper surface of the nail. THE SKIN. 295 The tissue of the nail is nourished by blood from the bed of the nail and from the nail-fold. Nails grow more rapidly in children than in adults, and more rapidly in summer than in winter. The rapidity of growth varies according to the person and the particular nail. The rate of growth in individual nails can be learned by observing the rate of progress toward the free margin of the white spots seen on nails. The nail begins to form in the third month of intra-uterine life as a fold covered with a layer of embryonic epidermic cells. In the fourth month a layer of new cells, which afterward be- come the horny cells of the nail, appear between the rete Mal- pighii and the embryonic epidermic corpuscles. At the fifth month the epidermic covering disappears and the nail lies ex- posed. Between the sixth and eighth months the nails are somewhat firm, but do not quite extend to the ends of the fingers. At the eighth month the nails are well developed and extend to the extremities of the fingers. For the .microscopical study of the horny part of the nail, sulphuric acid, or caustic soda, or potash must be employed to soften the corpuscles. For the other structures of the nail no special procedure is necessary. BIBLIOGRAPHY. WAGNER. Miiller's Archiv. 1852. MEISSNER. Beitrage z. Anat. u. Phys. d. Haut. Leipzig, 1853. OEHL, E. Annali univ. di med. 1857. KRAUSE. Die term. Korp. d. einf. Sens. Nerven. Hannover, 1860. SCHROEN. Contrib. alia anat. fisiolog. e patholog. della cute umana. Torino, 1865. AUPPHAMEU. Wurzburger Verhandlungen. Band I. 1809. TUOMSA. Arch. f. Derrnat. 1873. LOTT. Ueber den feineren bau u. die phys. Regeneration des Epithels. Leipzig, 1874. THIN. Journal of Anat. and Phys. Vol. VIII. 1874. HEYNOLD. Ueber die Knaueldriisen des Menschen. Virchow's Archiv. Bd. LXI. 1874. UNNA, P. Archiv f. mikrosk. Anat. XII. 1876. FISCHER, E. Ibid. RAVOGLI. Med. Jahr. Wien. H. I. 1879. RANVIER. La France medicale. January, 1880. CHAPTER XIX. THE CENTRAL, NERVOUS SYSTEM. BY R. W. AMIDON, M.D., NEW YORK CITY. THE spinal dura mater is a serous membrane. Its structure from without inward is : first, loose connective tissue ; then dense fibrous tissue ; lastly, a layer of lymph-vessels and endothe- lium. If one tears, with forceps, a shred from the outer surface of the dura mater, fresh or hardened, stains with hsematoxylon, teases, and examines in glycerine, there is seen a loose network of connective- tissue bundles containing free and fixed connec- tive-tissue cells, blood-vessels, minute nerves, and some fat- cells. This layer is continuous with the loose adipose tissue which normally surrounds the dura mater. The denser tissue next in order may be treated in the same way, and perhaps a few spindle-shaped connective-tissue cells and elastic fibres may be isolated. On transverse section, however (a very difficult thing to make, by the way), the bulk of the membrane is seen to be a dense mass, 0.5 1.0 mm. thick, composed of longitudinal and horizontal connective-tissue bundles, interspersed here and there with elastic fibres. In this layer blood-vessels and nerves are very scanty and small. Next, immerse a piece of dura mater, as fresh as possible, in a one per cent, solution of nitrate of silver. Leave it for sev- eral hours, and then expose it for a few minutes to the sunlight. When a brown tint is developed on the inner surface, remove it, wash it in distilled water, and strip off the internal surface with forceps. The shreds of tissue thus obtained show beautifully the structure common to all serous membranes : first, a delicate en- dothelial layer (see Fig. 125), consisting of fiat, unequal, irreg- ularly shaped cells, most of which are furnished with large, THE CENTRAL NEKVOUS SYSTEM. 297 round nuclei ; here and. there are seen stomata marked by an ag- gregation of nuclei, which are all located at the edge of the cells surrounding a stoma ; secondly, irregularly disposed lymph- spaces and vessels. The lymph-spaces appear as irregular, transparent patches lying just under the endothelium, and the lymph-vessels are seen as varicose chan- nels, which begin by a blind extremity, an- , astomose freely, re- ceive tributaries, and, iinally, empty by a constricted orifice called a stoma. Their ' " ^- *"" " e, WallS are in places FIG. ISS. Diagram representing the internal surface of the i-i 1-4. fi- dura, mater treated with nitrate of silver. Shows endothelium Him, DUG more Olien with nuclei and intercellular masses of protoplasm and a lymph- , -i . -i -, , channel, L.c., lined by delicate endothelial cells, which termi- IlllCK anOL 11'regUlar nates at S, an opening called a stoma about which is an aggre- , -, . gation of nuclei, x 300. from the aggregation of masses of protoplasm along the sides. The capillary lymph- atic radicles are lined by a very delicate endothelial layer, which can only be demonstrated in completely successful sil- ver preparations. Some are seen to contain lymph-corpuscles, others are found empty. The spinal arachnoid is also a serous membrane, much more delicate, however, than the dura mater. Its extreme thinness allows it to be examined in the fresh state or stained by car- mine or hsematoxylon. It is seen to be essentially a large- meshed connective-tissue network, containing many elastic fibres. Good silver preparations demonstrate an endothelial coat and a lymph system similar to, but more delicate than that of the dura mater. It is doubtful whether blood-vessels exist in the arachnoid in its normal state. The spinal pia mater consists of a small amount of connec- tive tissue, holding together a vascular plexus. It is firmly adherent to the cord, dips into all its fissures, and is intimately connected and continuous with the connective-tissue frame- work of the cord. The pia mater is best studied by means of fresh specimens stained in hsematoxylon, as this demonstrates beautifully the different coats of the small vessels. The spinal fluid should be clear, and contain only a few lymph-corpuscles ; but it usually, when examined post-rnor- 298 MANUAL OF HISTOLOGY. tern, contains some blood-corpuscles and swollen epithelial cells. General histology of tlie spinal cord. The spinal cord is composed of connective tissue, blood-vessels, nerve-structures, and epithelium. The connective-tissue framework or neuroglia of the cord is constructed as follows : At tolerably regular intervals the pia mater at the periphery of the cord sends off prolonga- tions which form septa, dividing the white substance into a large number of prisms (base outward). From each of these septa smaller branches spring, forming a delicate network, or stroma, which encloses the nerve-fibres. Generally one, but sometimes two or more fibres are contained in the same mesh. At the points of junction of these ultimate fibres are seen, here and there, small branching cells> the so-called spider- or neuroglia- cells. This fibrous structure reaches to the central gray matter and penetrates it by very delicate processes, which chiefly accompany the nerve-fibres. Three large prolongations of pia mater are of constant oc- currence, viz., the posterior median septum and a less complete septum on either side, dividing the posterior column into two ; the larger, anterior, or column of Burdacli / and the smaller, posterior, or column of Goll. The connective-tissue elements are best brought out by hsematoxylon. The blood-vessels of the cord are derived from its pia mater, follow its prolongations, and are most numerous in the gray matter, especially that of the anterior horns. In transverse sections there will be seen a clear space about all the blood- vessels. This is the perivascular space or lymph-channel, in which all the blood-vessels are contained. During life these sheaths probably serve a double purpose: an auxiliary nutri- ent function by lymph-circulation ; and a means of accommo- dating the ever-varying degrees of vascular distention. In some diseases they become enormously dilated. They are all connected with the space between the pia mater and the cord, and an injection forced into this space will follow the blood- vessels for long distances. These perivascular spaces are also said to be lined with endothelium. The vessels of the cord present no other peculiarities. Their structure is best brought out by the use of a dilute hjematox- ylon solution, or by the slow carmine staining. The perivas- THE CENTRAL NERVOUS SYSTEM. 299 cular canals may be more clearly demonstrated by forcing a colored gelatine injection at any point under the spinal pia mater care being taken, if the cord is cut, to secure the ends of the sections by ligatures. Nerve elements of the cord. The consideration of the ner- vous elements of the cord will now be taken up in a general way, and the peculiarities of different regions explained later. The white substance of the cord contains, besides the blood- vessels and neuroglia already mentioned, myelinic nerve-fibres of different sizes. These fibres pursue a vertical course, with the exception of those forming the root-radicles and commis- sures. On examination with a low power, the white substance, in a transverse section stained with carmine, seems to be a collec- tion of minute rings, each with a red dot in the centre. More highly magnified, the transverse section of a nerve-fibre appears as a delicate, rather irregular circle, on the circumference of which, in some cases, are seen nuclei resembling those of the sheath of Schwann, but which are really nuclei of the neurog- lia. Next comes a broad ring of colorless, transparent mate- rial, the medullary or myelinic- sheath, which very often ex- hibits concentric lamination. Lastly, usually in the centre, is seen the solid axis-cylinder. When these fibres pursue a more or less horizontal direc- tion they give the appearance of broad, clear bands traversed by longitudinal red fibres (axis- cylinders). The myelinic fibres average about 5 yu- 1 in diameter. Fibres, when isolated by teasing, present the varicose aspect of myelinic nerve-fibres, which lack the sheath of Schwann. To demonstrate this they are best treated when in the fresh state by osmic acid (see p. 114), the result being a black myelinic sheath and brownish axis-cylinder. The gray matter is composed of nerve-cells, medullated and non-medullated nerve-fibres, and an amorphous matrix. The most striking elements are the cells of the anterior horns. These, whether teased from specimens fresh or hardened in chromic acid, or whether examined in sections, always present the same general appearance. They are large, multipolar cells, having a slightly granular, protoplasmic body, a large, oval 1 /* micromillimetre = roVo millimetre. 300 MANUAL OF HISTOLOGY. nucleus, and a round nucleolus. These cells are polyhedral in form, as is shown by the fact that sections made in all direc- tions give them the same pyramidal or polygonal outline. In nearly all the large cells there is in some part of the body an aggregation of granules, which are often distinctly pigmented, giving the appearance of a heap. Striations of the body have been frequently described and depicted (Schultze, Schmidt, etc.), and this appearance has been attributed by some to plications of a very delicate invest- ing membrane, by others to ex- pansions of the ultimate nervous fibrillse, of which the axis-cyl- inder was thought to be com- posed. The motor cells average about 40 fji. in diameter. The cell -processes vary in number. Most of them are bifurcating. One, however, connected with nearly every cell, can be fol- lowed for a long distance with- out dividing, and when the cell is situated near the anterior FIG. 126. Diagram of a motor-cell from the anterior horn of a human cord in the cervical rOOtletS this prOCeSS lomS them enlargement, x 800. J and acquires a myelinic sheath. This is called the axis-cylinder process. The branching pro- cesses are called the protoplasmic processes, and are supposed by some to freely anastomose with those of other cells. This anastomosis, if it exist at all, is very delicate, and difficult of demonstration. A certain number of the cells of the anterior horns, espe- cially those located in the lateral region of the cornua, present an elongated, fusiform aspect, and appear to have but two processes. The nerve-cells in the posterior horns are of an elongated oval or fusiform shape, their long diameter corre- sponding in direction with that of the posterior horn. They are very much smaller than the anterior cells, and less numerous. Their average diameter is about 15 p,. They are seldom seen to have processes. The myelinic nerve-fibres of the gray matter are seen prin- cipally in the anterior horns, and converging from the cell- groups to form the anterior root-radicles. Here and there fibres THE CENTRAL NERVOUS SYSTEM. 301 appear in transverse section, which, singly or in bundles, pur- sue a longitudinal direction. Amyelinic fibres are found everywhere in the gray matter pursuing various courses. The gray commissure is composed almost completely of amyelinic fibres connecting the lateral gray masses. Besides the above-described elements the gray substance seems to have a structureless or slightly granular matrix, in which the other elements are embedded. In the study of the spinal gray matter osmic acid and carmine preparations are by far the most useful, although much is to be learned by the ex- amination of fresh specimens teased in serum. To study the cells, cut out a piece from the anterior horn of a fresh cord and tease in serum. A preliminary treatment with osmic acid or ammoniacal carmine is sometimes advantageous. The epithelium of the spinal cord lines the central canal. The most internal layer is of the cylindrical, ciliated variety. On account of the difficulty in obtaining fresh specimens the cilia are never seen in the human cord, though they undoubt- edly exist. The epithelial cells, as they do exist in the human cord, have a square base, taper to a slender thread toward the apex, which penetrates the layer of young, round epithe- lial cells, and is lost in the granular central gray matter. The cells of the second layer are round, granular, and thickly crowded. The sub epithelial tissue, for some distance around the cen- tral canal, consists of embryonal cells in a granular matrix. The central canal * has no constant shape, varies greatly in size, and is often choked with desquamated epithelium. Its position, as its name indicates, is in the middle of the gray commissure, on a line passing between the anterior fissure and posterior septum. The general features of the spinal cord hav- ing been pointed out, the peculiarities of different regions will now be shown. Special study of the different portions of the cord. The cord will be studied from below upward. The mode of study will mainly be by sections made after Clarke's method. The cord, after slitting the dura mater with the scissors up the front and back, is cut in segments 3 ctm. long, which adhere 1 Sometimes double. See Seguin: Am. Jour. Med. Sci., p. 427. 1872. 302 MANUAL OF HISTOLOGY. to the undivided dura mater. Thus prepared it is suspended in Muller's fluid (see p. 15), or dilute chromic acid (see p. 14), until hardened. The segments are then embedded in a microtome (see p. 16), and horizontal, transverse sections made. These are washed in distilled water and stained with carmine or hsBmatoxylon (see p. 23). A few minutes' immer- sion in alcohol previous to this manipulation makes the tissues take the coloring more quickly. After staining and washing, dehydrate the sections with alcohol and absolute alcohol, make transparent with oil of cloves, and mount in Canada balsam or dammar varnish (see p. 23). Hidden in the cauda equina is found the filum terminate, which is the end of the cord. Sections near its end exhibit lit- tle of the structure of the cord. At a point where it is 1.5 mm. in diameter it presents the appearance of a peripheral nerve, except that it has an opening the central canal in its centre. Its transverse section shows a collection of large and small myelinic nerve-fibres pursuing a vertical direction. A little higher up, where the filum measures 2 mm. in diam- eter, there is little difference, except that the central canal is nearer the surface (anterior) and surrounded by a small amount of gray matter. Now and then there are seen small, oval nerve- cells in the region posterior and external to the central canal. A little higher still, where the filum is 3 mm. in transverse and 2 mm. in antero-posterior diameter, back of the central canal on each side, where the future posterior horn is to be, there is a small collection of spindle-shaped cells. Sections from a region a little above this present an entirety different picture. The gray substance is here much more devel- oped and occupies the larger part of the section. It is divided into a club-shaped anterior horn, containing a few large poly- hedral cells, and a posterior horn which is rounded and formed of peripherally directed nerve-fibres and oblong nerve-cells. From this point up sections gradually become more circular arid develop more and more a resemblance to the structure of the cord, until, at a point where the sections are about 3.5 mm. in diameter, the anterior fissure and posterior septum become well marked. The anterior horns contain few cells, and the fibres emanating from them pursue a very oblique course down- ward through the anterior columns. From the lateral gray matter arise bundles of nerve-fibres THE CENTRAL NERVOUS SYSTEM. FIG. 127. Three sections of the filum terminate: , its transformation into the coccy- geal nerve ; 6, section higher up before the giving off of the last sacral filaments; c, its commencement. which curve around the posterior horn, and, meeting similar h'bres from the posterior columns, together form the posterior nerve-root. These two bundles form an arciform structure sur- rounding the round extremity of the posterior horn. (See Fig. 127.) The gray commissure occupies one-third the diameter of the cord. The central canal is large, slit- like, and antero-posterior in direction. To summarize then, there seems to be in the filum terminale, especially its lower por- tion, a preponderance of the posterior or sensory part of the cord. About two centimetres from the end of the cord nearly the same picture is pre- sented. The transverse section is circular and about 6 mm. in diameter. Many large nerve-cells appear at the outer side of the anterior cornua, mostly at their junc- tion with the posterior horns. Fibres from this cell-group, instead of running a direct course, curve backward and inward (see Fig. 127), then run forward and emerge from the anterior horns. Many oval cells appear in the posterior horns, which now reach the surface of the sec- tion, and the posterior roots begin to show their origin from the posterior columns and horns. In the lumbar enlargement trans- verse sections have a circular shape. (See Fig. 128.) The white substance here predominates, and has but one peculiarity, which will be noticed in greater or less prominence through- out the remainder of the cord. At the bottom of the anterior fissure is a broad band of white substance called the white commissure. This is formed of myelinic nerve-fibres, which pursue a course from the base of the anterior horn of one side, forward, across the median line and downward to join the anterior column of the opposite side at a lower level. (See Fig. 129.) The anterior horns in the lumbar region are large and square, as are also the cells contained in it. TJie gray FIG. 128. Three diagrams show- ing the relations of gray and white matter in different regions of the cord: . lumbar enlargement ; 6, mid-dorsal region ; c, cervical enlargement. 304 MANUAL OP HISTOLOGY. commissure is narrow, and the central canal has its long diam- eter placed transversely to the cord. Transverse sections in the dorsal region are circular and 8 mm. in diameter. The white commissure is thin, otherwise the same structure as in the lumbar region is observed. The anterior horns are narrow and sparsely filled with rather small multipolar cells. JN~o continuous tracts of nerve-fibres can be traced through the anterior columns, as their course is so oblique (downward) as to give almost a transverse section of the bun- dles. The posterior horns, just behind the gray commissure, are swollen out, and contain a number of large nerve-cells some multipolar, some oval. They approach the type of the cells in the posterior horns. This collection of cells is called the column of Clarke. Transverse sections in the cervical enlargement measure about 14 mm. The antero-posterior diameter is about 11 mm. The white commissure in this region presents about the same characteristics as in the lumbar region. The anterior horns are fan- shaped ; the anterior roots curve forward, outward, and downward. The central canal is triangular. The posterior horns are slender, and contain a few small nerve-cells. The posterior roots are also more intimately connected with the posterior horns than lower down. In the upper cervical region the gray matter assumes more the shape of the dorsal gray matter. In the lateral region, at the junction of the anterior and posterior horns, longitudinal bun- dles of myelinic nerve-fibres begin to appear. These bundles curve over (see Fig. 129), and pass rather obliquely upward and outward through the lateral columns, emerging nearer the posterior than the anterior horns. They are joined by fibres curving back from the cells of the anterior horns, and also emanating from the central gray matter. In this structure is seen the first appearance of the spinal portion of the spinal accessory root-fibres. The longitudinal bundles mentioned FIG. 129. Diagram of transverse section of the cord in the upper cervical region, showing coarse connective-tissue reticulum in left half of diagram, commencing decnssation of the lateral columns across the base of the anterior horn into the opposite anterior column, taking the place of the anterior commissure lower down, and the root of the spinal accessory, 11 : A.R. = anterior root ; P.R. = posterior root. In this figure and in others small crosses must be understood as nerve-cells. THE CENTRAL NERVOUS SYSTEM. 305 evidently come from cells of the anterior horns lower down. Some of the fibres, passing back from the anterior horns to join the root, are seen to arise directly from the motor cells. In taking leave of the cord, the introduction of a diagram 1 showing its regional anatomy, looked at from a physiological standpoint, is deemed ad- vantageous. It will enable p the microscopist to properly record localized lesions. In studying the spinal cord by means of horizon- tal transverse sections, it is of the utmost importance, particularly in pathological cases, to know which is the right or left side, and whe- ther one is looking at the upper or under surface of a section. Of so much impor- tance is this knowledge, that some means must be employed to acquire it. One of the best means is a method devised by Dr. E. C. Seguin, and published in the translator's note appended to Schultze' s article on the spinal cord, in the American translation of Strieker's " Histology," p. 647. He there recommends, be- fore placing the segment of the cord in the microtome, that a slight longitudinal incision be made in the right lateral column. By this means all the sections have a nick in the right lateral column, and can easily be placed. This method, however, has many drawbacks. One is that it is a process easily forgotten during the manipulations. Another more serious drawback is the fact that, make the incision slight as you can, the resulting nick often causes extensive fissures and crumbling of the lateral column or whole section, especially in pathological or over- hardened specimens. The requirements by the new method are two : 1st, the sections must be nearly horizontal ; and 2d, they must be suf- FIG. 130. Diagram of transverse section of the spinal cord : A, anterior median fissure ; P, posterior median septum ; 1, columns of Goll ; 2, columns of Burdach ; 8, direct cerebellar column ; 4, crossed pyra- midal column ; 5. lateral column ; 6, anterior funda- mental column ; 7, direct pyramidal column ; 8, pos- terior gray horns ; 9, anterior gray horns ; stippled part, gray matter ; shaded part, sesthesodio system ; unshaded part, kinesodic system. 1 Dr. E. C. Seguin : Lectures on Localization, in N. Y. Medical Record, April 27, 1878, p. 323. 306 MANUAL OF HISTOLOGY. ficiently well stained and transparent to demonstrate the con- stituent parts of myelinic nerve-fibres. The mode of determi- nation depends entirely on the fact that the anterior roots pursue an obliquely descending course .through the anterior columns, and for this reason horizontal sections cut the ante- rior rootlets obliquely. (See Fig. 131.) What is the natural inference to draw from this fact \ It is this : let the reader look at the upper surface of a transverse section of the spinal cord and bring the anterior roots into the field ; that is, let him look down the anterior column. He readily perceives that the central ends of the anterior root- fibres are nearer his eye than the peripheral ends. He sees that while the central ends are at the focus, the peripheral ends are beyond the focus, and he needs to bring the eye nearer to define them. This nearing the focus also gives the fibre- bundle an apparent peripheral motion, while increasing the focal distance causes an apparent central motion. The application of this method to a chance section is easy. Suppose we examine the anterior columns of a section and find by focussing that the central ends of the anterior root-fibres are farther from the eye than the peripheral ends. We will immediately know we are looking up the cord or at the under surface of the section. Now, all it is necessary to do is to turn over the section, either in your mind or on the slide, and put the anterior horns forward. The section is then in position. In* sections of the cord where the anterior roots do not show, the posterior roots may be used in a similar way, as they, too, pur- sue a slightly descending course. Their use is not so easy, as the fibres are short and pursue a slightly wavy course. In sections or fragments of sections, where neither of these struc- tures avail, a study of the course of the fibres in the anterior white commissure will lead to detection. These fibres pursue a course downward and across the median line, from the base of one anterior horn into the anterior column of the opposite side. FIG. 131. Diagram of vertical section of human cord through the anterior arid iposterior columns and the anterior horns. It is intended to demonstrate how a trans- verse, horizontal section, S, cuts the an- terior nerve-roots obliquely. (From Ar- chives of Medicine, August 1, 1879, p. 70.) THE MEDULLA OBLONGATA. 307 In sections of the upper cervical region the spinal accessory roots may be made use of, remembering, however, that they pursue a course obliquely upward through the lateral columns. The application of these rules to the medulla will be pointed out later on. NOTE. To demonstrate the obliquity of the anterior rootlets, find, by a trans- verse section, the exact direction of the anterior rootlets, and then make longi- tudinal sections through the anterior column and horn on this line. THE MEDULLA OBLONGATA. In the upper part of the cervical region changes take place in the arrangement of the elements of the cord transforming it into the medulla oblongata. The changes are as follows : be- fore the external signs of decussation ap- pear, it is seen that the fibres of the later- al columns change their vertical course and bend forward and inward. This fact is demonstrated by the oblique sections of bundles and fibres. A little higher these bundles and fibres can be traced across the gray matter be- hind the anterior horn into the opposite an- terior column, which is to become by this addition the anterior pyramid. The decussating fibres take the place of the ante- rior commissure lower down, and the fibres pass upward and forward across the median line. The fibres of the anterior columns do not decussate at all, but give way to and mingle with the fibres from the lateral columns. The shape and structure of the anterior horns are about the same as lower down. The posterior horn expands suddenly at FIG. 132. Diagram of the medulla, pons, etc., natural size, to show the direction of sections for displaying the different nuclei and roota : ll/, line of section to show the early decnssation of the lateral columns and spinal accessory tract; 11, line of section to show the spinal accessory tract and decussation of the pyramids ; 11 & 12, region of the spinal accessory and hypoglossal ; 10, pneu- mogastric; 9, glosso-pharyngeal ; 8, acoustic; 6 & 7. abducens and facial ; 5. trigeminus ; 4, patheticus ; 3, motor oculi ; c. g., corpora quadrigemina ; c. c., crua cerebri. 308 MANUAL OF HISTOLOGY. its peripheral extremity into a bulbous termination (see Fig. 133), from which the posterior root emerges. The central gray matter between the two horns is traversed and intersected by the decussating fibres from the lateral columns. Numerous pro- longations from this gray matter spread out into the lateral columns, presenting a coarse reticulum, called iheformatio FIG. 133. Diagram of transverse section of human medulla below external decussation of pyramids, showing bulbous posterior horns: F R, formatio reticularis; 11, spinal accessory root and decussation of the lateral columns. FIG. 134. Diagram. Decussation of the pyra- mids, shows decussation of the lateral columns, the swelling of the posterior horns, the shrink- age of the anterior horns, the spinal accessory root 11, and a partial decussation of the posterior columns behind the central canal. reticularis. The gray commissure is very broad, the central canal having its long diameter directed antero-posteriorly. In sections at the decussation of the pyramids proper, i.e., where they are seen to decussate externally, a slightly different picture is presented. The lateral columns have nearly disap- peared, having now almost all entered into the decussation, which is here very broad (see Fig. 134), and presents a peculiar zigzag appearance from the interweaving of bundles of fibres from the opposite lateral columns. These fibres, after curving around the anterior columns for a short distance, seem to dis- appear by assuming a vertical direction. The club-shaped ex- tremities of the posterior horns remain, while the rest is pushed back into the posterior columns, and contains many large cells. The anterior horns are also displaced backward, pushed back by the anterior columns increased in size by the addition of the lateral columns. Hence, the anterior roots have a longer path through the anterior columns and approach the type of the hypoglossal nerve-roots seen a little higher up. (See Fig. 135.) The spinal accessory nerve curves out and back from the lateral gray matter where a group of cells is situated. THE MEDULLA OBLONGATA. 309 Let us next take up a section involving the lower end of the olivary body. We have the following view presented. The section is slightly cordiform. (See Fig. 135.) The decussa- ting fibres at the base of what remains of the anterior fissure, which has all along become shallower, now forms the com- mencement of the rapke, a structure which extends all through the rest of the medulla and pons, separating the two motor tracts. The union of the lateral and anterior columns now nearly complete, forms the anterior pyramids. The fibres here have a general vertical direction, except that a broad band which emerges from the decussation at the bottom of the anterior fissure, curves around the margin of the anterior pyramid, and then, sometimes in the sub- stance, sometimes at the surface of the medulla, almost completely sur- rounds it, the bundle becoming lon- gitudinal on the posterior surface. These bear the name of the arciform fibres. The rest of the white matter is so cut up as to render it hardly divisible into regions. The central canal, which is very long antero-posteriorly, has almost coalesced with the gradually deepening posterior furrow soon to become the fourth ventricle. The gray matter originally in the cord is now collected about the central canal. Anterior and external to the central canal there is a small group of multipolar cells. This is the remnant of the anterior horns, which have been continually crowded back by the accumulation of fibres in the anterior pyramids. These cells in every respect are similar to those in the anterior horns. Their processes give origin to fibres which course forward in two or three bundles through the white matter of the anterior pyramids, and emerge at about the junction of the anterior pyramids and the lateral white mass. A little farther back in the gray matter, behind the central canal, is a small group of nerve-cells the remains of the spinal accessory nucleus, from which a few fibres run in a straight course outward and slightly backward, through the lateral white matter. Additional collections of gray matter now begin FIG. 135. One half of section at lower end of the olives : 11, upper spinal acces- sory root ; 12, lower hypoglossal roots. 310 MANUAL OF HISTOLOGY. to appear. In the posterior region is a large tract (see Fig. 135) containing scattered groups of many small cells evidently con- nected with the arcit'orm fibres. This is probably a part of the lower origin of the pneumogastric. A little in front and external to this is a small group of larger nerve-cells which help to form the lower sensory origin of the fifth nerve. Still farther forward in the lateral region is a large collection of multipolar nerve-cells. Although this group is traversed in many directions by fibres, single and in bundles, still it seems to give rise to fibres which run back and upward, evidently to curve upon themselves and join the peripheral fibres of the spinal accessory root. (See Figs. 135 and 137.) Farther forward still there is a collection of small cells arranged in a wavy line (see Fig. 135), the commencement of the olivary nucleus. Through this the roots of the hypoglossus all pass. Some seem to be lost in it, others appear to arise from it, but this is probably due to the arrangement of roots often seen to curve into the nucleus and then out again. As this is the first appearance of the olivary body, it will be well here to describe it. THE OLIVARY BODY. The olivary nuclei are situated in the medulla, under the oval projections on its anterior surface called the olivary bodies. The nucleus consists of a strip of gray matter arranged in gen- eral like. a piece of fluting folded on itself, so as to form almost an ellipse. From the concavities of the fold on either side pro- ceed bundles of fibres, the external ones joining the formatio reticularis, the internal ones passing into the raphe. Their connection with the hypoglossal roots is probably not im- portant. The intimate structure of the olivary fold is that of a dense gray matrix holding numerous small polyhedral cells having delicate protoplasmic processes. Let us now go a trifle higher (see Fig. 137), and observe that in sections the central canal, which has all along been elongat- ing and receding backward, now opens into the apex of the fourth ventricle. There is now, therefore, quite a deep notch in the posterior part of the section, covered with the same cylin- drical epithelium which lined the central canal. On each side, THE OLIVARY BODY. 311 and in front of the bottom of the fourth ventricle, lies a large group of multipolar cells, the Jiypoglossal nucleus, from which bundles of fibres course forward through the olivary body, which is here much enlarged and more complex than in the last section. On the inner side of the hypoglossal roots in the olivary region is an elongated mass of gray matter con- taining small cells, called the parolmary nucleus. There is an oval group of fusiform cells at, behind, and external to the hypoglossal nucleus, from which indistinct and broken bands of fibres pass outward to emerge from the lateral re- gion of the medulla. This constitutes the upper spinal acces- sory nucleus and root. Behind this nucleus, forming the FIG. 136. Diagram showing structure of one fold of the olivary nucleus : C, centripe- tal fibres ; P, peripheral fibres, x 64. FIG. 137. One-half transverse section of the human medulla at the point of fusion of the central canal and the posterior fissure to form the-fourth ventricle : 11, spinal acces- sory root ; 12, hypoglossal root ; B, raphe. eminence on each side of the fourth ventricle, is a large mass of gray matter containing a great number of small nerve-cells, which also seems to be rather indistinctly connected with the spinal accessory root. External to this nucleus is a con- tinuation of the collection of large cells seen in the section lower down, the lower sensory nucleus of the fifth. In front of the spinal accessory root is seen a group of multipolar cells not so large as in preceding sections. The peripheral circular fibres in this region are confined to the anterior and external aspect of the medulla, and are still seen to be in connection with the raphe by the arcuate fibres which traverse obliquely the intervening nervous tissue. From this point to the middle of the olives, sections differ 312 MANUAL OF HISTOLOGY. FlG. 138. One-half transverse section of the human medulla through the middle of the olives : 4, fourth ventricle ; 10, pueumogastric root ; 12, hypoglossal root. little, except that in this space the root-fibres of the spinal accessory seldom appear, although figured by most writers. The region formerly occupied by the spinal accessory nucleus contains a group of small cells which form part of the pneu- mogastric nucleus. The fibres between this nucleus and the point of exit of the pneumo- gastric root run so obliquely upward, that no direct connec- tion between them can be traced. It is in sections at the mid- dle of the olives that the pneu- mogastric begins to appear dis- tinctly. Most of its fibres seem to be connected with a small group of cells situated in the PTaV matter, at the lUnction of O y s%C5x rior motor tracts or pyramids, before mentioned, begin to separate into the crura cerebri, the fourth nerves are seen. They are supposed to arise from a nucleus at the floor of the fourth ven- tricle lower down, curve around the outer wall of the ventricle, decussate in the median line in the valve of Yieussens, and pass from the pons behind the tubercula quadrigemina. From this point they curve forward around the crura, on the outer side of which they appear at the base of the brain. At about this point and a little higher are seen bundles of fibres emerging from the gray matter containing small cells, in front of the fourth ventricle, diverging and pursuing an arcuate course through the crura, to converge again and emerge from the inner side of each crus. (See Fig. 144.) This consti- tutes the nucleus of origin, the course and point of emergence of the third nerve a view hard to get unless just the right obliquity is given to the section. Imbedded in the crus, in the region through which the third nerve passes, is a collection of pigmented cells forming the locus niger. Higher the crura separate and enter their respective hemispheres. Their further course is better shown by a trans- verse vertical section of the hemispheres at the large part of the thalamus opticus. (See Fig. 145.) Here we see a great part of the substance of the crus flat- tened in form passing upward, between the optic thalamus and a gray mass called the nucleus lenticularis, forming what is THE CEREBELLUM. 317 denominated the internal capsule. The posterior third of the internal capsule is distributed to the posterior part of the hemisphere, and when destroyed produces loss of sensibility on the opposite side of the body. The anterior two-thirds of the internal capsule is distributed to the middle or motor re- gion of the hemisphere, and its destruction causes a paralysis N C M R o EC ML FIG. 145. Modified from Charcot's diagram to show position, relation, and distribution of the inter- nal capsule as seen in a vertical transverse section of the brain on a level with the greatest development of TO, thalamus opticus ; 1C, location of the internal capsule : NL, nucleus lenticularis ; EC, external capsule ; D, claustrum ; NC ; nucleus caudatus ; MRC, motor regions of cortex cerebri ; 1, fibres repre- senting the radiation of the internal capsule vertically to the motor region of the cortex. From "Lec- tures on Localization," by Dr. E. C. Seguin : New York Medical Hecord, p. 142, August 24, 1878. of the opposite side of the body. The fibres expanding from the internal capsule, joined by those emanating from the gan- glia at the base and the corpus callosum, form a fan-shaped expansion of white fibres called the corona radiata. THE CEREBELLUM. The white centre of the cerebellum, formed from the ex- pansion of the peduncular tracts, incloses a collection of gray substance, the corpus dentatum. This body, visible in all sections, bears some resemblance to the olivary body in the medulla, on account of its irregular, dentated outline. Its greater consistence causes it to stand out in a section from the surrounding tissue. In intimate structure this body consists 318 MANUAL OF HISTOLOGY. of a collection of small fusiform and polyhedral cells with minute processes, imbedded in a basis-substance much more dense than the surrounding white matter. The body is made to appear striated in a peripheral direction by bundles of fibres and blood-vessels pursuing a parallel course. The surface of the cerebellum, deeply gashed by sulci and their subdivisions, presents, on section, its well-known com- pound, arborescent appearance. This arrangement of the gray matter causes the greatest possible surface to come in con- tact with the blood-current furnished by the pia mater, and hence secures the greatest nutrition of the elements of the cortex. The gray matter of the cortex is easily divisible into an external or granular layer, a middle or cellular layer, and an internal or nuclear layer. The latter consists of a vast number of small granular cells about the size of white blood- corpuscles, which take staining fluids with great avidity. The middle stratum is a clear space in which there is a single layer of large corpuscles, called the cells of Purkinje, 10 to 40 p. in diameter. They are scattered at some distance from each other, and present pe- culiarities pos- sessed by no other cells in the body. The cells are of large size, vary- ing in form from fusiform to flask- ' 146 '~ Diagram o the cerebeUar ""^ showin s the krge ceUs of shaped, accord- ing to the plane of the section. Their central side is round, and in most cases has no processes. Often the usual rounded contour of the cell- body is broken by an angle, seemingly the remains of a broken process. Here and there a large non-branching axis-cylinder process is seen emerging from the base of a cell and pursuing a course parallel to the cortex. That these basal processes exist in all cases, and ultimately acquire a myelinic sheath, there is no doubt. (See Fig. 146.) From the peripheral side large arborescent processes spring, pun'e THE CEREBRAL GANGLIA. 319 which pursue quite a direct course through the external or granular layer and disappear when near the periphery. The primary processes, one or two in number, have a tendency to spring from the cell-body at an obtuse angle, and give off at almost right angles to themselves the straight peripheral pro- cesses already mentioned. The nuclei of these cells are oval and coarsely granular ; the nucleolus is round and small. TJie cortex proper consists of a granular matrix vertically striated by the cell-processes and parallel blood-vessels. There is also a moderate sprinkling of small round cells and nuclei similar to those in the third layer. The cortex is very vascular. THE CEREBRAL GANGLIA. As examples of these structures the optic thalami and cor- pora striata may be taken. . They are collections of gray matter through which part of the fibres, emanating from the crura to help form the corona radiata, pass. In the corpus striatum these fibres pass through in bundles visible to the naked eye, which gives to this body its striated appearance. These bundles radiate toward the periphery of the body, thus leaving ever increasing spaces between them. These spaces at the base of the body, at the point of entrance of the bundles from the crura, are narrow, filled with nerve- fibres running in horizontal, vertical, and diagonal directions, seemingly commissUral in nature, and multipolar cells few in number, large, and resembling somewhat cells of the anterior horns of the spinal cord, whose processes mingle with the fibres mentioned. Nearer the periphery of the organ, where the bun- dles of fibres are more widely separated, the intervening mass of fibres and cells abruptly changes to a finely granular gray ma- trix, holding in its substance numerous small blood-vessels and small nerve-cells, mostly round some, however, triangular in shape, similar to those of the second layer of the cere- bral cortex. They have large nuclei and many delicate pro- cesses. The optic thalami consist of a mixture of gray matter and fibres, not, however, so regularly arranged as in the corpus striatum. The gray matter contains a few oval cells having many delicate processes. The cerebral ventricles. Continuous with the central canal 320 MANUAL OF HISTOLOGY. FIG. 147. Diagram illustrating the structure of the ependyma of the cere- bral ventricles. of the cord, and doubtless like it in function, the cerebral ven- tricles resemble it in their structure. They are lined through- out with a structure called the ependyma. This consists first of a finely granular layer covering all the nervous matter bounding the ventricles. Besides the minute granules, this layer contains a few small nuclei here and there, but no fibres. On its free surface rests a single layer of cylin- drical epithelium. The cells of this layer have square free ends, while they are anchored by one or more delicate processes which emerge from the attached end and pierce the sub- jacent granular-matrix. These epi- thelia in the fresh state undoubtedly have cilia. This layer of epithelium is apt to be arranged in folds, giving a section of the ependyma a wavy appearance. The choroid plexus of the lateral ventricles has for its basis an artery which enters the descending horn of the lateral ven- tricle from the base of the brain. This artery gives off along its course short arterial trunks which repeatedly subdivide, and each ultimate arteriole terminates in a convoluted capillary loop, resembling the Malpighian tuft of the kidney. Some of the twigs seem to end in a cse- cal extremity ; but it is doubtful wheth&r they do, the preparations giving this appearance being prob- ably artificial. The peculiarity of the choroid plexus is that all the vessels composing it, large and small, are covered by a layer of polyhedral epithelial cells, each having one, sometimes two large nuclei. This presents a beautiful example of the so-called tesselated epithelium, each cell being sepa- rated from its neighbor by a transparent intercellular sub- stance. This epithelial covering causes the tufts of the choroid plexus to resemble, in a degree, the villi of the chorion. The best plan in studying the choroid plexus is to use hsema- toxylon, or alcoholic specimens slightly teased. FIG. 148. Diagram showing structure of the choroid plexus of the lateral ven- tricles. THE CEREBRAL GANGLIA. 321 The cerebral dura mater differs from the spinal in the fact that, its outer surface serving as periosteum, it lacks the layer of loose connective tissue present in the spinal dura mater. Its bulk consists of two layers of dense fibrous tissue running in opposite directions. The inner serous surface is coated with endothelium and lymphatics. The outer or periosteal surface is the most vascular. The cerebral differs from the spinal arach- noid only in being perhaps a little more closely attached to the pia mater. The pia mater of the brain is extremely vascu- lar, and shows more beautifully than the spinal membrane the system of perivascular spaces. The cerebral cortex. The cerebral cortex is a thin sheet of gray matter spread on the outer surface of the hemispheres. The outer surface of the hemispheres is grooved by furrows (sulci) less deep in proportion to their size, and less regular than those of the cerebellum. The convolutions produced by these sulci, although seemingly very irregular, still have a cer- tain symmetry in different brains by which they can be classi- fied and named. A definite knowledge of these facts is neces- sary for an understanding of the current literature on the subject and of properly recording cases. The fetal hemisphere at an early date is smooth. Furrows soon begin to appear, the first and most important of which is the fissure of Sylvius, extending upward and backward, from about the anterior third of the base of the brain, and the fis- sure of Rolando, running from near the posterior extremity of the fissure of Sylvius upward to the superior longitudinal fis- sure. One after another the other fissures appear, till in the adult brain they seem innumerable. Even here, however, there is a certain constant arrangement of fissures and convolutions on which a nomenclature may be based. The original fissures of Sylvius and Rolan do remain. From the anterior inferior part of the frontal lobe three furrows run obliquely upward and backward toward the two fissures just named, dividing the frontal region into the three frontal con- volutions, while a convolution in front of the fissure of Rolando receives the name of the ascending frontal or anterior central convolution. A similar convolution behind the fissure is called the ascending parietal or posterior central convolution. The parietal region is irregularly divided from above downward, as is also the temporo-sphenoidal and occipital region. The 21 322 MANUAL OF HISTOLOGY. base of the brain is also divided into a series of basal frontal, temporal and occipital convolutions. By far the most impor- tant region of the cortex, according to our present knowledge, is that along the fissures of Sylvius and Rolando, the so-called motor tract of the TiemispJieres. The exact physiological func- tions of the anterior frontal, the occipital, temporal, and basal FIG. 149. Modified from Ferrier ; letters and figures the same : 8, fissure of Sylvius ; c, fissure of "Ronaldo : po, parieto-occipital fissure ; A, ascending frontal gyrus ; B, ascending parietal gyrus ; F 2 , .third frontal gyrus ; P a ', gyrna angularis ; circle I., seat of lesions which (on the left) cause aphasia; 'circle II., seat of lesions which convulse or paralyze the upper extremity of the opposite side; dotted circle III., seat of lesions which probably convulse or paralyze the face on the opposite side ; dotted oval IV., seat of lesions which probably convulse or paralyze the lower extremity of the opposite side. These districts receive their blood-supply chiefly from the middle cerebral artery. From Lectures on Localiza- tion by Dr. B. C. Seguin : N. Y. Medical Record, October 19, 1878, p. 301. regions of the hemispheres, is not known, inference, however, making them the seat of general and special sense, vaso-motor, psychic centres, etc., etc. The middle or f ronto-parietal region, however, is the proven seat of motor centres for the face, limbs, and body, and the faculty of articulate language. The centre for speech occu- pies the region at the base of the third frontal convolution and the island of Reil on the left side, a similar location on the right side being occupied by a centre for articulatory movements. A little higher on the ascending frontal and parietal convolutions is an area having control over the move- ments of the tongue and face. Still higher is found a larger space, the centre for the arm of the opposite side. A larger space at the junction of the fissure of Rolando and the su- THE CEREBRAL GANGLIA. 323 perior longitudinal fissure, including a tract on the inner aspect of the hemisphere, called the paracentral lobule, is the centre for movements of both extremities, especially the lower. On account of the anatomical variability of the convolutions in different brains, these centres must be allowed some lati- tude, and should not be made so small and exactly located as they are by some authors. Their location has been pretty definitely determined, however, by experimentation on animals, and lesions in man, such as trauma- tisms, neoplasms, abscesses, hemor- rhages, atrophy following amputa- tions, retarded development, etc. Possessing such important proper- ties we should naturally expect the cerebral cortex to be a very complex structure, and so it is. Minute structure of the cortex. In order to get a satisfactory view of the elements of the cortex, great care has to be exercised in making sections. It is not enough to make a section exactly perpendicular to the cortex. The plane of the section must exactly coincide with the direction of the fibres of the corona radiata as they enter the convolution. This can be rather easily accomplished by paying close atten- tion to the arrangement of the white and gray matter in the piece from which the sections are to be made. Cuts with any obliquity will give erroneous impres- sions as to the exact shape and structure, especially of the cellular elements of the cortex. The cortex cerebri is generally divided into five layers, but it is easily divisible into three only. The outer layer, lying immediately under the pia mater, is more transparent than the rest, and is composed of a fine net- work of neuroglia containing many quite large openings, giving it a spongy appea,rance. It also contains a few large, round nuclei, and a small number of triangular nerve-cells. The second layer, thicker than the first, consists of a gray basis-substance, dense and granular, holding an immense num- ber of small, triangular and conical cells, their apex being di- FIG. 150. Diagram showing the elements and relation of parts in the cerebral cortex. (See text.) 324 MANUAL OF HISTOLOGY. rected toward the periphery and often drawn out into a slen- der axis-cylinder process, while from their base several delicate processes are given off. These cells all have large nuclei and nucleoli. Here and there are seen larger conical cells, which will be described with the next layer. The characteristic fea- ture of the second layer, however, is the presence of a great number of small, round cells and free nuclei similar to those in the third layer of the cerebellar cortex. In the third layer the matrix is still more dense, and con- tains, besides a few small triangular cells, round cells, and free nuclei, a large number of large conical corpuscles, the so-called u giant cells" of the cortex, the distinguishing feature of this layer. When isolated from their surroundings these cells ap- pear like cones which taper gradually from a broad base to a very slender apex, which, when it attains the size of an axis- cylinder, can be traced for a long distance without showing a division. This undoubtedly terminates in a myelinic nerve- fibre. The base of the cell is not square, but crenated and notched by the giving off of numerous delicate basal processes which are lost in the granular matrix. The cells all have nuclei and nucleoli, most of which are round, but some of which seem also to have a triangular shape corresponding to the cell-body. The cells average 25 /*. in diameter. A great difference is made in the apparent shape of the cell by obliquity of the section. If the line of section is moderately oblique, it shortens the cells ; if still more oblique, it makes them very short and blunt ; while if the section is at right angles to their axis, all the cells appear round and of various sizes. In the deepest parts of this layer the giant-cells gradually disappear, and the gray matter of the cortex merges into the white matter. In the two inner layers of the cortex there are seen many fibres and bundles of fibres having a ver- tical direction, which, with the blood-vessels (the largest of which being perpendicular to the surface), give the cortex a somewhat striated appearance. We see, then, that the only difference between the second and third layers of the cortex is the greater number of small cells in the second and the greater number of large cells in the third, while the division of the third layer into three, as is accepted by most authors, seems purely arbitrary, there being a gradual gradation into the white substance. BIBLIOGRAPHY. 325 Some writers l lay much, stress on the difference of structure of the cortex in different regions of the hemisphere. It is true that, in the non-excitable or sensory regions, the cortex is thin- ner and perhaps less highly organized ; but here are met the same elements as form the cortex in the motor region (centre, for the arm, for instance). (See Fig. 150.) Even the giant-cells are found less numerously than in the motor regions. Another fact demands attention, that is, that the structure of the cortex is the same at the bottom of a fissure as on the surface of a convolution, and for this reason lesions of the sides and bottom of fissures should receive as much attention as those of the surface of the convolutions, implicating, as they do, equally im- portant structures. BIBLIOGRAPHY. SPINAL CORD. CLARKE, J. L. Researches into the Structure of the Spinal Cord. Philosoph. Transactions. 1850. BONDERS, F. C. Dissertatio anatomica inauguralis de cerebri et medullae spinalis systeraata vasorum capillari in statu sano et morboso. 1853. JACUBOWITSCH, N. Mittheilungen iiber die f einere Structur des Gehirns und Riicken- marks. Breslau, 1857. JACUBOWITSCH, N. Further Researches into, etc. Breslau, 1858. BIDDER, F., und KUPFFER, C. Untersuchungen iiber die Textur des Riickenmarks, etc. Leipzig, 1859. VAN DER KOLK, SCHROEDER. Minute Structure and Functions of the Spinal Cord and Medulla Oblongata, and on the Proximate Cause and Rational Treatment of Epilepsy. New Sydenham Society. London, 1859. STILLING, B. Neue Untersuchungen iieber den Bau des Ruckenmarks. Cassel, 1859. LUYS, J. Recherches sur le systeme nerveux cerebro-spinal ; sa structure, sea fonc- tions et ses maladies. Paris, 1865. His, W. Zum Lymphsystem. Leipzig, 1865. HIRSCHFELD, LuDOVic. Traite et iconographie du systeme nerveux et des organes des sens de 1'homme. Paris, 1866. JOLLY, F. Ueber die Ganglienzellen des Ruckenmarks. Miinchen, 1866. KOLLIKER, A. i&lements d'histologie humaine. Traduit par Marc See. Paris, 1868. 1 See Betz : Anatomischer Nachweis zweier Gehirncentra. Centralblatt f iir die Medicinischen Wissenschaften, August 1 and 8, 1874, pp. 578 and 595. He finds " nests " of enormous cells in the motor area, especially of the paracentral lobule. 326 MANUAL OF HISTOLOGY. HENLE, J. Handbuch der Nervenlehre des menschen. Braunschweig, 1871. GEULACII, J. The Spinal Cord. Translated by Dr. E. C. Seguin, in Strieker's His- tology. 1872. ScnULTZE, MAX. The General Character of the Structures Composing the Nervous Substance. Translated by Henry Power. Strieker's Histology. 1872. RETZIUS, GUST, och KEY, AXEL. Studier i nervsystemets anatomi. Stockholm, 1872. ERB, W. H. Diseases of the Spinal Cord and Medulla Oblongata (Anatomical Intro- duction). Ziemssen's Cyclopaedia of Medicine. Vol. XIII. American Edi- tion. 1878. SEGUIN, E. C. Lectures on the Localization of Spinal and Cerebral Diseases. N. Y. Medical Record. 1878. FORT, J. A. Lemons sur les centres nerveux. Paris, 1878. HUGUENIN, G. Anatomie des centres nerveux. Traduit par Dr. Th. Keller. Paris, 1879. BRAIN. BERLIN, RUDOLF. Beitrag zur Structurlehre des Grosshirnwindungen. Erlangen, 1858. KUPFFER, GUST. De cornus ammonis textura. Dorpat, 1859. CLARKE, J. L. Researches on the Intimate Structure of the Brain, Human and Comparative. 1857 and 1867. ARNDT, RUDOLF. Studien iiber die Architektonik der Grosshirnrinde des Men- schen. Bonn, 1867-68. JENSEN, JULIUS. Die Furchen und Windungen der menschlichen Grosshirn Hemis- pharen. Berlin, 1870. MEYNERT, T. The Brain of Mammals. Strieker's Histology. Am. edition. New York, 1872. HITZIG, EDWARD. Untersuchungen iiber das Gehirn. Berlin, 1874. CHARCOT, J. M. Lejons sur les localisations dans les maladies du cerveau. Paris, 1876. BENEDIKT, MORIZ. Anatomische Studien an Verbrecher-Gehirnen. Wien, 1879. BOYER, H. DE. Etudes topographiques sur les lesions corticales des hemispheres cerebraux. Paris, 1879. FERRIER, DAVID. The Localization of Cerebral Disease. New York, 1879. STRICKER und UNGER. Untersuchungeu iiber den Bau der Grosshirnrinde. Wiener Anzeiger, 1879. BEVAN LEWIS and CLARKE, H. The Cortical Lamination of the Motor Area of the Brain. Proceedings of the Royal Society, Vol. XXVII. 1879. CEREBELLUM. HESS, N. De cerebelli glorum textura. Dorpat, 1858. SCHULTZE, F. E. Ueber den feineren Bau der Rinde des kleinen Gehirnes. Ros- tock, 1863. CENTRAL NERVOUS SYSTEM. DEITERS, OTTO. Untersuchungen iiber Gehirn und Riickenmark des Menschen und der Saugethiere. Braunschweig, 1865. BIBLIOGRAPHY. 327 DEECKE, THEODOKE. Perivascular Spaces in the Nervous System. American Jour- nal of Insanity. January, 1874. WALDEYER. Beitrage zur Kenntniss der Lymphbahnen des Centralnervensyst. Arch. f. mikr. Anat. 1879. KESTEVEN, W. H. The Structure and Functions of the Olivary Bodies. St. Bar- tholomew's Hospital Reports. 1879. SEE, MARC. Sur la communication des cavi'tes ventriculaires de 1'encephale avec lea espaces sous-arachno'idiens. Revue mensuelle. 1879. BROCA, P. Localisations cerebrales. Revue d'anthropol. 1879. CHAPTER XX. THE EYE. BY C. H. WILLIAMS, M.D., BOSTON, MASS. THE eyelids are very complicated structures. Their exter- nal coating is formed of skin, which is modified for the special purpose it has to serve in this situation. Beneath the skin is a loose sheet of connective tissue ; still more internally is the lit- tle orbicular is palpebrarum muscle ; behind this again is loose connective tissue, which shades off gradually into the tarsus. This latter is not formed of cartilage, as was formerly sup- posed, but of dense fibrous tissue. The conjunctiva tarsi lines the inner surface of the tarsus. The skin of the lids exhibits the usual layers of horny, serrated, and cylindrical epithelium. At the upper portions the papillae are sparsely developed and short, but they gradually increase in size and number as they approach the free edges. A peculiarity of this skin are the pigment-cells, which are scattered throughout the cutis. They are more abundant in brunettes than in blondes. At the confronting margins of the lids are found the cilia or eyelashes, which resemble the ordinary larger hairs in their formation and mode of growth ; they are placed in two or three rows, are well supplied with pigment, and have a definite direction given to them by the deep follicles from which they grow. Ordinary sweat-glands are quite numerous, especially in the upper portions of the lid ; at the lower border we occasionally find them in a modified form, opening into sebaceous follicles near or just behind the cilia ; they have a long and wide ori- fice, and the tubules are filled with fine granular matter, con- taining occasional roundish masses resembling particles of albumen. Beneath the cutis is a loose connective-tissue layer through THE EYE. 329 which numerous blood-vessels and nerves pass ; behind this, and covering the whole extent of the lid, are bundles of the orbicularis palpebrarum ; some small fasciculi of this muscle are also found at the lower and inner angle of the lid, enclosing the openings of the Meibomian glands. These bundles, known as the musculus ciliaris Riolani, have fibres which are among the smallest of the striped variety of muscular tissue. Behind this layer is a thin sheet of loose connective tissue, which merges without any sharp boundary line into the tar- sus ; this latter body forms a leaf-shaped plate about twenty millimetres in length by one millimetre in thickness, and is composed of very dense connective-tissue fibres separated only by minute lymph-spaces ; it has few blood-vessels or nerves, and serves to give the requisite stiffness to the looser tissues of the Ud. The Meibomian glands are imbedded in the tarsus. Their excretory ducts, which are directed at right angles to the pal- pebral margin, have their openings on the surface of the lid near its posterior angle. They are lined with epithelium, which at the external orifice is similar to that in the superficial parts of the skin ; more internally it is serrated, while in the acini of the gland it has a cuboidal shape. These glands have a straight central tube, around which the acini are clustered, and into which they discharge the sebum, a material composed of epi- thelial cells that have undergone fatty degeneration. This oleaginous substance serves to moisten the edges of the lid and to prevent the overflow of tears. Above the Meibomian glands, and in part imbedded in the tarsus, are the acinous glands, which have their openings on the surface of the conjunctiva fornicis. Above these glands the smooth muscular fibres of the little palpebralis muscle of Muller are inserted, through a tendon, into the upper part of the tarsus ; the fibres of this muscle are quite large and have peculiar irregular cells with pigmented nuclei scattered throughout them. To prepare sections from the lids they should be pinned fiat on a piece of cork and then immersed in Muller' s fluid' for eight days. After being washed in water they are placed in absolute alcohol until sufficiently hard ; or they may be hard- 1 See chapter on General Methods. 330 MANUAL OF HISTOLOGY. ened by placing in the ordinary per cent, solution of chloride of gold. This last method shows very clearly 'the nerves of the lid and conjunctiva, which take a deep violet or mauve color. For rapid work the lids may be hardened in a saturated solution of picric acid. They may then be stained with picro- carmine or hsematoxylon, and mounted in glycerine or balsam. (See chapter on General Methods.) The caruncula lachrymalis is a small, rounded mass of skin ; it is placed between the lids at their inner angle, and contains hairs, vessels, and glands, such as are found else- where in the cutis. Its office is to prevent the overflow of tears. The conjunctiva. Just behind the tarsus, and separated from it by a thin layer of fibrillated connective tissue, is the conjunctiva, which, after lining the inner surface of the lid, passes backward as a loose connecting fold (fornix) to the sclera, over which it is reflected forward as far as the margin of the cornea. The conjunctiva consists of an external or epithelial layer and a tunica propria or proper investing mem- brane. There is also a subconjunctival layer. The lower portion of the conjunctiva, where it takes its origin from the margin of the lid, is quite smooth ; but near the upper edge of the tarsus it becomes more or less infiltrated with lymph- cells, and is thrown into numerous folds, which have sometimes been mistaken for glands. The epithelial ele- ments of this part vary much in shape ; in general there are two layers : a superficial one, composed of cylindrical bodies which are a continuation of the superficial strata of the skin, and a deeper one of small, round cells, representing the changed cylindrical elements of the Malpighian layer or rete mucosum. The tunica propria consists of fine connective- tissue fibres, in which a few elastic fibrillse are interspersed. The subcon- junctival layer resting immediately upon the tarsus is very thin. That part of the conjunctiva forming the fornix has an abundant subconjunctival tissue, which is composed of loose elastic fibres and vessels ; the epithelial layers are also thicker here, and small racemose glands, supposed to secrete mucus, are also found there. On the conjunctiva covering the bulb the epithelium con- tains here and there the large mucus-cells corresponding to the goblet- cells of the intestines. It gradually begins to change its character and passes over into the variety which is seen in THE EYE. 331 the cornea, and, in fact, is continuous with it. The tunica propria has an abundant supply of blood-vessels, and is loosely connected with the sclera by fibres, which become more numer- ous and firm in the vicinity of the corneal margin. The nerves of the conjunctiva may be seen by cutting small pieces of fresh conjunctiva from a pig or calf and examining them in aqueous humor, or in a 1 per cent, aqueous solution of common salt care being taken to support the cover-glass at the sides, in order to avoid pressure. The nerve-fibres can then be seen passing under the epithelium ; they can be distin- guished with certainty by their annular constrictions (anneaux constricteurs) ; after penetrating a short distance, however, they lose their medullary sheath and form open networks under the epithelium ; a few fibres find their way toward the surface between the epithelial cells. The gold method is of special use in exposing the finer nerve-branches. The question of the manner in which the nerves ultimately end is still a point in dispute. The lymph-spaces of the conjunctiva are quite numerous, especially near the corneal border ; here they are narrow, and finally pass forward to unite with the lymph-spaces of the cor- nea, from which they can be injected by means of a solution of alkanet-root in turpentine. 1 The normal conjunctiva does not have any true papillae, but on the tarsal portion the surface often has small papilliform projections covered with epithelium. The cornea. This tunic is covered with stratified epithe- lium (a), comprising layers of flat, serrated, and cylindrical cells. Directly beneath these is the anterior limiting or Bow- man's membrane (b) ; this is a clear, homogeneous stratum, which differs from the substantia propria of the cornea only in containing no lymph-spaces or cells. It can be divided up into the same line fibres as the cornea itself, and its inner bor- der has no distinct limit, the fibres passing directly into the corneal tissue ; when this layer has been destroyed, as by a perforating ulcer or wound, it is not regenerated. The substantia propria of the cornea (&, c) is made up of lamellae, like the leaves of a book ; these lamellae, which at first appear homogeneous, can be separated into fine fibres, just See chapter on General Methods. 332 MANUAL OF HISTOLOGY. like other connective-tissue membranes, by dissolving out the cementing substance in a 10 per cent, solution of common salt. With the exception of tlivfibrcearcuatce, which curve for- ward through several strata in the anterior portions of the cornea, the fibres pursue the same direction as the layers ; but, although most of the fibres run parallel to the surface of the cornea, yet they may have a different direction in each layer, FIG. 151. Meridional section through the cornea of the human adult, from an eye hardened in Mill- er's fluid. The section was colored with carmine, and made transparent by the oil of cloves. so that when viewed from above the fibres will appear to cross one another. This explains the formation of the stellate fig- ures which are sometimes observed after the injection of fatty substances into the cornea, or by the infiltration of bacteria between the fibrils. In the interfibrillar material are found the lymph- canals and spaces, which contain the fixed corneal corpuscles (Fig. 152). These spaces are stellate and broad when seen from above, but thin and spindle-shaped on side view ; they have numer- ous branches and branchlets given off from them at right angles (lymphatic channels) (Fig. 152, A). The spaces and branches usually lie in the plane of the lamellae, anastomose freely with one another, and are filled with the corneal corpus- cles and lymph (Fig. 152, B). THE EYE. 333 In life these fixed bodies nearly fill the lymph-spaces and conform to their size and shape ; they are flat corpuscles, usu- ally nucleated, and have short, sharp-pointed processes, which pass out into the minute lymph-canals. In the lymph-spaces of the cornea are also found, even in normal conditions, a few migratory cells, resembling white blood-corpuscles ; they are very numerous when the cornea has been irritated, and can be seen in a frog's cornea, which has been kept five to fifteen minutes in serum or aqueous humor in a moist chamber, and examined without pressure on a warm slide. Beneath the subs tan tia pro- pria of the cornea we find the posterior limiting layer, or Descemef s membrane (d) (Fig. 151). This is transparent, ap- parently homogeneous, rolls up when cut, is intimately connect- ed with the posterior fibres of the cornea proper, and is lined on its inner surface with endo- thelium (e). It contains no cel- lular bodies, but, like the anterior limiting layer, can be sepa- rated into fibrillse, and appears to represent a concentration of the corneal fibres rather than a separate structure. The endothelium is a single layer of flat cells lining the anterior chamber. Blood-vessels are found only in the normal cornea at the periphery, where they form a fine network con- necting with the conjunctival and scleral vessels. The nerves enter the cornea at the posterior part of the periphery ; they soon lose their neurilemma and medullary sheath, and pass forward obliquely, as small axis-cylinders, toward the epithelial layer ; here they divide up into branch- lets, often having a ganglionic enlargement at the point of divi- sion. Under the epithelium these delicate fibres form a net- work which sends some very minute filaments upward between the epithelial cells. Their further course is unknown. To separate the cornea into its constituent fibres, small pieces should be soaked for twenty-four hours in a concentrated pi- Fio. 152. -Lymph spaces and canals, A ; fixed corneal cell, partly filling these spaces, B. After Waldeyer. 334 MANUAL OF HISTOLOGY. eric acid solution ; they can then be washed in water and easily picked to pieces. In order to see the arrangement of the fibrillse in the different layers, the cornea of a rabbit should be pricked with a needle in several places ; then some highly infectious fluid, as the exudation in puerperal peritonitis, is to be brushed over the surface, and in a few days an infiltration will have taken place throughout the interfibrillar substance. We shall then see the lines of pus-cells crossing one another in different directions, and sometimes collections of micrococci forming stellate figures. A very delicate preparation of the fixed corneal cells may be made by removing a fresh cornea, and then immersing it from three to six hours in aqueous humor, in a moist chamber. In examining it take care, as before mentioned, to avoid any pressure upon the cover-glass. It is easier, however, to demonstrate the cells and lymph- spaces by staining with silver or gold. To do this the nictitat- ing membrane of a live frog should be cut off or held to one side by an elevator ; the exposed cornea is then placed near the mouth of a test-tube, in which some water has been raised to the boiling point ; when the epithelium begins to appear opaque it should be carefully wiped off with a fine cloth ; a per cent, aqueous solution of nitrate of silver is then applied ; when the cornea has become thoroughly white by this method, it is to be removed, washed in a weak solution of common salt, placed in distilled water, and exposed to the light until it be- comes brown. It should then be cut at the edges and mounted in glycerine. In ten or fifteen minutes it will be transparent and ready for examination. Instead of removing the epithe- lium by steam, a solution of silver nitrate (-J- per cent.) may be used, the lids being held out of the way until the epithelium appears whitish; this outer layer is then removed, and the same process repeated as before. The substantia propria as- sumes a brown color, and the corpuscles appear as lighter spaces in it. The nuclei may be exposed by hsematoxylon. The best preparations, both for the lymph-spaces and the nerves, are made with chloride of gold. A fresh cornea, pref- erably one from a live pigeon, is removed immediately after decapitation and immersed for five minutes in lemon- juice, then washed in distilled water, placed for fifteen minutes in a 1 per cent, solution of chloride of gold, again washed, and this THE EYE. 335 time soaked for twenty-four hours (well protected from the light) in a 2 per cent, solution of formic acid. After another washing in distilled water the cornea should be cut in two and placed in glycerine ; one portion can then be separated into thin layers, by tearing with tine forceps or needles. Examine in glycerine for the corneal corpuscles, nerves, and lymph-spaces, which latter appear dark on a light blue or red background ; or the piece may be imbedded in wax or some such material, and sections made parallel to the surface of the cornea. The remaining half of the specimen is to be imbedded or held in liver or pith. Transverse sections may then be made. These will exhibit on lucky sections the fine plexuses of nerve-filaments under the epithelium, with occa- sional fibres passing up between the individual corpuscles. The different layers of the cornea will be well shown, also the narrow corneal cells (as seen on side view), together with the remains of the endothelial layer on the inner surface. The peripheral portions of the cornea are particularly inter- esting. We have here the transitions from cornea to conjunc- tiva and sclera, the origin of the ciliary muscle, the ligament of the iris, and the numerous vessels of the part. The epithelium of the cornea (a) forms a gradual transition into the epithelium of the conjunctiva, but the anterior limit- ing membrane (Bowman's) becomes thinner as it approaches the edge of the cornea, until finally it merges with the fibres of the anterior corneal layers into the tunica propria of the conjunctiva. No sharp boundary line has been demonstrated between the cornea and the sclera. Under the microscope the fibres appear to have no distinct limit ; the lymph-spaces also of the cornea are continued directly into the sclera, and the scleral and corneal fixed corpuscles are much the same. The posterior limiting membrane (DescemeV s] (c), like the anterior, becomes gradually thinner and loses itself in a small bundle of scleral fibres which surround the edge of the mem- brane and form the anterior support to the ligamentum pec- tinatum iridis. The endothelium (Fig. 153 6, ) passes uninterruptedly over this ligament (e f ) and is reflected forward over the anterior sur- face of the iris (e") to the edge of the pupil. In the ^ngle between the iris and cornea, forming buttresses, 336 MANUAL OF HISTOLOGY. as it were, to hold the iris in position, is the ligament of the iris (d), composed of loose connective tissue with an abundant open mesh work, enclosing spaces (Fontantfs spaces), (f), which, on the one hand, connect with the anterior chamber by small openings lined with endothelium, and on the other with the lymph-spaces of the cornea and sclera, as may be shown by injecting a solution of aniline blue into the anterior chamber. FIG. 153. Corneal margin from a meridional section of the human eye : a. a', external epithelium of the cornea ; a', a", epithelium of the conjunctiva bulbi ; 6, &'. &', corneal tissue ; ft 7 , &', &", &", sclerotica ; fc, *, conjunctiva; v, v', canal of Schlomm; c, c', membrane of Descemet; d, process of the iris: /", iris; e, endothelium of the membrane of Descemet; e'. e\ e', of the ligamentum pectinatum iridis ; e'\ e'\ e", of the iris ; /, mesh work of the space of Fontana ; m, musculus oiliaris. At the inner part of the sclera, close to its junction with the cornea and the ligament, is the canal of Schlemm (v, a'), a ring- shaped passage, oval on section. It is lined with a single ]ayer of endothelium, varies in size in different specimens, often ap- pearing as if divided into two parts, and, according to Wal- deyer, probably connects with the anterior chamber and also with the scleral veins. Through this passage and Fontana? s spaces the fluid of the anterior chamber is supposed to escape from the globe, and it is worthy of note that in glaucoma, with increased intra-ocular tension, we find the iris attached to the periphery of the cor- THE EYE. 337 nea over a circular space which would entirely cover these probable channels of exit. Preparations of these parts can be made from eyes which have been placed in Miiller's fluid while quite fresh and al- lowed to remain in it three to four weeks, the fluid being re- newed from time to time. Hsematoxylon is well adapted for coloring them, and they may be preserved in glycerine. The solera. In the sclera we find the same minute struc- tures as in the cornea, i.e., bundles of fibres, cementing sub- stance, lymph-spaces, and fixed corpuscles. The fibres, how- ever, are not laminated, as in the cornea, but run in various directions, weaving a very dense tissue, so that the lymph- canals have a correspondingly tortuous course. Chemically there is a difference between the two, as the sclera is found to yield on boiling a true connective-tissue gelatine ; the cornea, on the other hand, a substance resem- bling chondrine. We find also in the sclera, near the foramen for the optic nerve, a few pigment-cells. The sclera is covered by the conjunctiva from the corneal border to the insertion of the recti muscles, and the fibres of the subconjunctival tissue pass directly into it. From the en- trance of the optic nerve to these muscular insertions, and even passing up between them, the scleral portions of Tenon's cap- sule form the covering, which consists of delicate filaments of connective tissue passing directly into the sclera itself. On the inner surface the sclera is covered with a large-celled endothe- lium lining the perichoroidal space. At the round opening for the entrance of the optic nerve, the outer fibres of the optic nerve sheath pass directly into the outer scleral layers ; the inner portions of the sheath partly mingle with the inner layers of the sclera, and partly, after the addition of some true scleral fibres, form the lamina cribrosa, a fine, sieve-like net- work of fibrous tissue, which stretches across the opening in the sclera on a level with its inner surface. This lamina can be easily shown in specimens where the delicate nerve-fibres .which pass through its openings have been macerated out. The sclera is perforated in the equatorial region by the trunks of the vena vorticosce ; they are accompanied by the lymph-vessels which form the connection between the pericho- roidal and Tenon's lymph-spaces. The direction of the canal through which they pass is so oblique that it is supposed to be 338 MANUAL OF HISTOLOGY. easily contracted in diameter by any increase in intra-ocular pressure. The arteries of the sclera, with their thick adventitial coats, the peculiar sheaths of the veins and capillaries, as also the nerves, are best studied in hematoxylon preparations. A solu- tion of silver nitrate (a quarter to one per cent.) will expose the endothelial cells, while sections of the tissue may be made from specimens preserved in alcohol or Miiller's fluid. The tunica vasculosa, consisting of the choroid, ciliary body, and iris, forms one continuous mem- brane through which the principal blood-supply of the eye is carried. The choroid. This tunic lines the sclera from the entrance of the optic nerve to the junction of sclera and cornea, and is united to it at those points ; over the remaining portion there is a loose connection formed by scattered fibres and the numerous vessels and nerves which pass through the sclera to the clio- roid. The meshes of the open network between the layers of the choroid and the sclera form lymph-sacs the perichoroidal spaces which connect with the sac enclosed in Tenon's capsule, and this in turn unites with the su- pra-vaginal space surrounding the , , , . an Slieatll OI the ODtlC nerV6. 1116 ret- FIG. 154. -sciera,*; choroid :ma, ?; perichoroidal space, pdi; lamina Buprachoroidea, sc; lamina chorio-capilla- iris, cc \ lamina vitrea, ; layer of pigment- cells between choroid and retina,!?. After cllOrOld COnSlStS Of Several layers, .Merkel. v 7 with limits not distinctly marked. The lamina suprachoroidea (Fig. 154, sc) lies next the .sclera, and consists of fine elastic and connective-tissue fibres, holding in their meshes pigmented and transparent cells: the first are stellate, often with projecting arms by which several are joined together ; the latter resemble lymph-cor- puscles. The layer of large vessels is traversed by branching arteries and veins ; between them are numerous pigmented corpuscles, THE EYE. 339 while the whole is held together by the firm connective-tissue network which extends throughout the entire choroid. The lamina chorio-capillaris (cc) consists of a network of fine vessels interspersed with pigment, and extends over the whole inner portion of the choroid. The vitreous layer (v) is very closely connected with the lamina chorio-capillaris ; though it appears homogeneous, fibres may be detected in it after long maceration in a ten per cent, solution of common salt. Where this layer covers the cil- iary processes the surface is no longer smooth, but has fine, elevated ridges upon it ; here the membrane also is thicker, and is more easily affected by reagents. The dense lamina of hexagonal pigment-cells between the choroid and retina has sometimes been classed with the former, although* it belongs more properly to the retina. The long and short posterior, and the anterior ciliary arte- ries, furnish the numerous blood-vessels which constitute the great mass of the choroid. The short posterior ciliary arteries, four to six in number, give off some twenty branches which penetrate the solera, pursuing a. straight course near where the optic nerve enters ; then, continuing their course in a tortuous manner, they divide into fine networks which supply the greater part of the lamina chorio-capillaris. About the entrance of the optic nerve they also form a network of fine vessels, and even send occasional branches. to anastomose with vessels from the sheath and cen- tre of the optic nerve. The two long ciliary arteries penetrate the sclera in a very oblique course, a little anteriorly to those last mentioned, and in the horizontal meridian ; they pass forward in the outer lamina of the choroid without branching until they reach the ciliary muscle ; here they divide, and penetrating the muscle, form near the periphery of the iris a circle (circulus arteriosus iridis major) by uniting with the artery of the opposite side. The anterior ciliary arteries, eight to ten in number, arising from muscular branches of the ophthalmic artery, penetrate the sclera near the insertion of the recti tendons ; they also unite with the circle just described, which forms the principal distributing point for the vessels of the iris and ciliary body. From this circle also are sent back a few small branches to unite with the choroidal capillaries, and there is formed the sole con- 340 MANUAL OF HISTOLOGY. nection between the short posterior or choroidal arteries pro- per and those which supply the circulus arteriosus. A small amount of the blood which returns from the capillaries of the choroid, ciliary body and iris finds its exit from the eyeball through the veins accompanying the anterior and posterior ciliary arteries, but by far the larger part is collected by the large veins in the outer layers of the choroid (venae vorticosse), converging so as to form four or six great trunks, which perfo- rate the sclera obliquely in the equatorial region, and empty into the ophthalmic vein. The long and short ciliary nerves supply the tunica vascu- losa with fibres from the third and fifth pair and the sympa- thetic. The long nerves, two or three in number, are branches of the nasal division of the ophthalmic nerve ; the short, ten to fifteen in number, arise from the ciliary ganglion. These nerves penetrate the sclera near the optic nerve, and then, passing for- ward on the outer portion of the choroid, form, in the ciliary muscle, a fine plexus with ganglionic corpuscles at the nodal points of the meshes ; from this plexus fibres are distributed to the cornea and iris. At the junction of the anterior and middle thirds of the eyeball the choroid undergoes a change, the membrane be- comes thinner, the capillaries turn back toward the veins, only a few vessels continuing forward in a straight course. In this region the retina also undergoes a change and loses all its nervous elements, the connective tissue supporting fibres alone being continued forward under the name of the pars cili- aris retinae. The very narrow zone between the points where these changes occur and the irregular line formed by the begin- ning of the ciliary processes is called the orbiculus ciliaris^ and the line of origin of these processes the ora serrata. The ciliary body. Crossing the orbiculus, the choroid is seen raised in radial folds, some seventy in number, which in- crease in size until they reach the thickness of a millimetre. This increase is caused by the development of smooth muscular fibres in addition to the usual constituents of the choroid. These fibres arise just behind the canal of Schlemm, from the sclera and cornea ; passing backward, they together form a ring, which on section appears as a right-angled triangle, with the base turned toward the anterior chamber, and the hy- pothenuse toward the vitreous (Fig. 155). THE EYE. 341 This triangle consists largely of the fibres of the ciliary mus- cle, which are divided into meridional fibres, or those which occupy the side next the sclera, and radial fibres, which pass FIG. 155. Section through the ciliary region of a hypermetropic eye. Ivanof. from the point of origin to the hypothenuse ; the circular fibres of Miiller's muscle lie next to the base of the triangle, and are concentrically arranged. In highly myopic eyes the meridional and radial fibres PIG. 156. Section through the ciliary region of a myopic eye. Ivanof. are strongly developed (Fig. 156), while the circular fibres are Scarcely seen, and the angle of the ciliary body at the point of origin is changed from a right to an acute angle. 342 MANUAL OF HISTOLOGY. In very hypermetropic eyes, on the contrary, tlie circular fibres are abundantly developed (Fig. 155), the meridional fibres are shorter, while the angle at the point of origin of the mus- cle becomes somewhat obtuse, so that by these changes one can determine, even in a microscopic section, what considerable refractive error the eyes have had. The meridional fibres are either prolonged some distance into the stroma of the choroid and end in a delicate fringe, or they terminate at the anterior and outer layers of this mem- brane in stellate knots with fine anastomosing branches. The radial fibres form a looser network than the last, but also have the same terminal interlacement of their fibres ; the circular fibres form fewer anastomoses, and only those bundles which lie next to the radial fibres are extensively connected with them. The nerves of the ciliary body are derived from the plexus formed in its stroma by the ciliary nerves ; the vessels are largely supplied from the circulus iridis major, lying in the an- terior part of the body. The iris arises from the anterior side of the ciliary body, and from the connective tissue surrounding the fibres of the ciliary muscle ; it is also attached to the cornea and sclera by the ligamentum pectinatum. (See Fig. 153). It consists of a loose connective-tissue stroma, which sup- ports a rich vascular network, a complete muscular structure, and the nerves. It is covered anteriorly by a continuation of the endothelium of the cornea, and posteriorly by a thick layer of pigment-cells continuous with those which line the ciliary body. The vessels arise from the circulus, have adventitial coats which are thick in proportion to their calibre, and pass radially to the margin of the pupil, where they form a network of fine capillaries, the circulus arteriosus iridis minor, ending final- ly in veins which return in the same general direction as the arteries, but lie beneath them, emptying finally into the venae vorticosse. Near the margin of the pupil, and forming a ring about it 1 mm. in breadth by T V mm. in thickness, is the sphincter muscle of the iris. It is composed of unstriped muscular tissue, and is situated in the posterior portion of the iris. The dilator muscle, at its inner border, is in close connection with the sphincter, and its fibres run radially to the periphery THE EYE. 343 of the iris, where they are woven into a thick anastomosing circle. The nerves of the iris are derived from the ciliary plexus ; at the periphery they divide and scatter in various directions : the pale fibres to the posterior layers, forming a fine network about the dilator muscle; the fibres with a medullary sheath to the anterior portion ; another set supplies the sphincter muscle these being, in the order of description, the branches possibly of the sympathetic, sensory, and of the third pair. The posterior surface of the iris, which, near the pupil, rests upon the anterior capsule of the lens, is covered with a thick layer of densely pigmented cells, the uvea, which can rarely be so separated as to determine their shape, and which appear to have no distinct limiting membrane behind them. This layer extends from the pupil, where it meets the endo- thelium of the anterior surface, back to the pigment of the ciliary body, with which it is continuous and from which it can be distinguished by having no connective tissue covering it. The pigmented cells, which are more or less thickly scat- tered through the stroma of the iris, determine the color of the anterior surface. Transverse sections through the sclera and choroid are best made from eyes hardened in Muller's fluid. An eye which has been injected with colored gelatine, introduced through the aorta after that vessel has been tied beyond the carotids, will show the fine meshes of the chorio-capillaris, when the pigment- layer covering the choroid has been brushed away under gly- cerine. Such injections are best made on albinotic rabbits. Good sections of the ciliary body can be made from eyes hardened in alcohol or Muller's fluid, and the blood-vessels can be easily seen in injected specimens. The muscular tissue of this body and the iris may be examined in specimens treated with a 30 to 40 per cent, solution of potash. Carmine may then be used to color. The vessels of the iris are best seen in the eyes of a young albino rabbit, injected with colored glycerine or Berlin blue. The retina lines the whole inner surface of the choroid as far as the ora serrata ; it is composed of nervous elements, connective tissue, and blood-vessels. The following division into well-marked layers from within outward has been generally adopted. (See Fig. 157). 344 MANUAL OF HISTOLOGY. a, membrana limitans interna. Z>, optic nerve fibre-layer. c, ganglion-cell layer. d, inner granular layer. e, inner nuclear layer. ^ outer granular layer. <7, outer nuclear layer. 7i, membrana limitans externa. i, layer of rods and cones. Pigment layer. The fibres of the optic nerve generally lose their medullary sheath at the lamina cribrosa, and proceed thence as naked axis- cylinders through the opening in the choroid to the level of the retina, where they spread over its entire in- ner surface to form the nerve-fibre layer, which is thick in the vicinity of the nerve, but gradually decreases as it approaches the ora serrata, where it ends. At the macula lutea the fibres do not form a distinct layer, but, curving toward this spot from above and below, are lost in the layer of ganglion-cells, either entering them or passing on to the inner granular layer. The ganglion-cell layer consists of large branching cells in most places but one row deep, though near the macula there may be two or more layers. They are very transparent, have no visible cell-wall, and are provided with a varying number of pro- jecting arms ; when fresh they contain fine granular matter with a clear, large nuclei and nucleoli, and appear finely fibrillated. They receive an axis-cylinder on their inner side, and on the outer send out branches which ultimately divide into fine fibrillae, and are lost at the inner granular layer in a tangled network. It is probable, however, that some of these fibres are connected with the cells of the inner nuclear layer. The inner granular layer partly surrounds the ganglion- FIG. 157. Transverpe sec- tion of the retina. After Ze- hender. THE EYE. 345 cells and forms a sort of spongy network between these and the inner nuclear layer ; its composition is still a matter of doubt, but it appears to be made up of a more or less homo- geneous substance, in which are numerous fine openings filled with some material of a peculiar refractive power. It does not belong to the nervous substance of the retina, and when placed in a 10 per cent, solution of common salt, dissolves, leaving the supporting connective-tissue fibres unaffected. The inner nuclear layer is made up of numerous oval cells with large nuclei ; they belong mostly to the nervous tissue, but scattered among them are also cells of the supporting con- nective-tissue framework. The nerve-cells resemble small bipolar ganglion-cells, hav- ing two fine processes, the inner of which probably connects with the ganglion-cell layer, or directly with the optic nerve fibres. Near the macula these cells are more numerous ; to- ward the ora serrata they gradually decrease in number. Next comes the outer granular layer, a thin stratum re- sembling the inner in appearance and composition ; here the fine fibres from the outer and inner nuclear layers become lost in a tangled mass. Between this layer and the membrana limitans externa is the outer layer of nuclei, made up of a number of oval cells, connected more or less closely with the inner ends of the rods and cones. The larger nerve-fibres, which pass through the outer gran- ular layer, are joined to the nuclei of the cones, which lie di- rectly within the membrana limitans and are connected to a prolongation of the base of the cones themselves. The smaller fibres pass to the nuclei of the rods, which form an irregular layer at varying distances from the limiting membrane, and from which fine tangled fibres pass to the base of the rods. These nuclei resemble those of the inner layer ; they con- tain a small amount of granular matter with a nucleus and nu- cleolus, and sometimes exhibit, as the result of post-mortem changes, peculiar transverse stripes. Directly beyond the membrana limitans externa, and rest- ing upon it, are tlie rods and cones, each composed of an outer ' and inner member. The rods are small, cylindrical bodies of high refractive power ; when fresh they appear homogeneous, but with the 346 MANUAL OF HISTOLOGY. beginning of decomposition, which occurs very quickly, the inner half appears as if filled with a finely granular substance, while the outer exhibits transverse striations, and finally breaks up into small disks, which can only be distinguished from those of the outer segment of the cones by their red color (visual purple of Kuhne), which soon fades on exposure to light. The inner segment of the cones is larger than that of the rods ; it tapers rapidly toward the outer part, where it is filled with a peculiar oval-shaped body ; the outer segment does not equal that of the rods in height, but divides into similar disks. The pigment-layer, in which the ends of the rods and cones are imbedded, consists of a single layer of hexagonal cells, more densely pigmented in the part next the retina, and by some observers said to be provided with fine processes, which are lodged between the rods and cones. This pigment is more dense at the macula and varies with the color of the person, being most abundant in negroes, whereas it is absent in albi- nos ; from this layer, according to Kuhne, the visual purple of the rods is reproduced. At the macula lutea, which is situated a little to the outer side of the entrance of the optic nerve, the ganglion-cell and inner nuclear layers have their greatest thickness. The fibres which pass from the outer granular to the outer nuclear layer are lengthened and run in a more horizontal direction toward ihefovea, which forms a slight depression in the centre of the macula. Over this fovea the layers of nerve-fibres and ganglion-cells are absent, and the other laminae become so much thinned that the membrana limitans interna approaches nearly to the nuclear layer; the rods are also absent, and the cones be- come lengthened and slightly convergent. The meiribrana limitans interna lies between the retina and vitreous body ; it is a transparent homogeneous structure, and from its outer surface spring the connective-tissue fibres which form the supporting framework for the nervous part of the retina. These fibres arise in the form of thin fenestrated plates, connected together by numerous arms ; they soon contract, however, to smaller radiating bands, which surround the gan- glion-cells and pass on to the inner nuclear layer, where they THE EYE. 347 contain occasional nuclei. From this point they again ex- pand into broader sheets, which, after surrounding the outer nuclei, are united to form the membrana limitans externa. This membrane lies just at the base of the rods and cones, and it is provided with numerous holes, through which those struc- tures pass ; from its outer surface fibres extend up between the rods and cones to form supporting sheaths. The blood-vessels of the retina come from the arteria cen- tralis retince, which usually divides into two or more branches at the entrance of the optic nerve ; these vessels lie in the layer of nerve-fibres, and, arching above and below the macula, give off numerous fine branches, from which capillaries penetrate as far as the inner nuclear layer. The larger retinal vessels are surrounded by lymph- spaces, which probably unite with those of the optic nerve. At the periphery the retina becomes much thinned, and at the ora serrata the nervous elements are discontinued, the con- nective tissue alone being prolonged over the ciliary body to its anterior angle, thus forming the pars ciliaris retinae. This membrane consists of long cylindrical cells of varying shapes ; they rest on the pigment and are covered by a thin stratum, which sends processes between them and seems to be a prolongation of the membrana limitans interna of the retina. It is very difficult to prepare good sections of the retina, but the following plan is recommended : enucleate with care the eye of a frog or some small animal, and immediately sus- pend it in a well-stoppered bottle containing a small bit of solid osmic acid ; when sufficiently hard the posterior portion of the eye can be cut in pieces and sections made by imbed- ding or holding between pieces of liver. Another method is to place the eye unopened in Muller' s fluid for some two weeks, frequently changing the fluid ; af- terward harden in alcohol. Sections may then be made in the same manner as before. To obtain the separate constituents, place a fresh retina in a T V per cent, aqueous solution of osmic acid for fourteen days, then in glycerine for seventeen days ; after this, place a small piece on a slide in glycerine, with the cover-glass so arranged that no pressure is made upon the specimen ; now tap gently on the centre of the glass until the motion of the fluid causes the retina to fall apart. 348 MANUAL OF HISTOLOGY. The optic nerve, after leaving the optic canal, passes through the orbit surrounded by three coverings, continuations of the cerebral membranes. The dural coat, composed of dense connective tissue with a few elastic fibres, forms the outer covering ; the fibres are at- tached to the periosteum, where the nerve leaves the bony canal, and where it enters the eyeball they are continued directly into the outer layers of the sclera. Within this covering, and separated from it by a very nar- row space, are the delicate fibres of the arachnoidal coat, and the lymph-space between the two is called the subdural space. Within the arachnoidal coat, and separated from it by a wide lymph-space, is the pial coat closely surrounding the nerve-fibres, and sending processes of connective-tissue be- tween their bundles. This membrane passes into the inner layers of the sclera, and also sends numerous fibres to the la- mina cribrosa. Its outer surface is covered with endothelium, and between it and the arachnoid coat is the subaraclinold space, which reaches to the inner layers of the sclera, and is continuous with the same space in the brain. The optic nerve itself, closely surrounded by its vagina fibrosa, passes forward through the orbit, receiving the central artery and vein at about 15 to 20 mm. from the sclera. These vessels pass to the centre of the nerve and lie in a connective- tissue sheath until they emerge on the inner surface of the eye- ball to branch over the retina. On cross-sections of the nerve, bundles of connective tissue are seen to pass inward from the pial sheath and form a cross- network, through the openings of which the nerve-fibres pass. On longitudinal sections the connective tissue appears in irregular fenestrated sheaths ; this tissue can also be demon- strated by macerating thick sections in a J per cent, solution of chromic acid and then brushing out the nerve-elements. These nerve-filaments themselves are extremely small, but vary somewhat in size. They consist of an axis-cylinder sur- rounded by its medullary sheath; they are grouped in large bundles which pass through the meshes of the connective tis- sue. The fibres appear to be held fogether by a kind of homo- geneous albuminous substance neuroglia, and have on their surface occasional nucleated corpuscles, distinguished from THE EYE. 349 those of the connective tissue by being larger and more irregu- lar in shape. Blood-vessels are found not only in the centre of the nerve, but also scattered through various parts of the connective tis- sues. At the lamina cribrosa there is an anastomosis with the ves- sels of the circle of Holler, which, coming from the short poste- rior ciliary arteries, forms a vascular circle in the sclera, about the entrance of the optic nerve. Where the nerve-fibres pass through the sieve-like openings of the lamina cribrosa they lose their medullary sheath, and from that point pass on to the nerve-fibre layer of the retina as transparent axis- cylinders ; but in rare cases the sheaths are continued from the optic disk some little distance over the retina, and are seen with the ophthalmoscope as very white patches radiating out from the disk, or following the vessels and gradually fading into the general color of the f undus by a fine, fringe-like border. The vitreous body is a transparent, jelly-like mass, of spher- ical shape, with a depression at the anterior part, in which the lens rests. It is bounded behind and on the side by the retina, in front by the lens with its attachments, and appears to have no true hyaloid limiting-membrane of its own. It is very diffi- cult to demonstrate any definite structure in this substance ; toward the periphery it appears to be arranged somewhat in concentric layers, but in the centre is more homogeneous. From the optic disk to the lens there is a small canal about 1 mm. wide in front and spreading out behind ; it is lined with very transparent cells, and filled with a substance more fluid than the rest of the vitreous ; it marks the position of the arteria hyaloidea^ which is usually obliterated at about the seventh foetal month. The vitreous body also contains numerous corpuscles, espe- cially near the periphery ; these consist of round lymph- cells, stellate cells, with one or more nuclei, and irregular arms, and of branching cells which seem to have a transparent vesicle filling up a part of their interior. The vitreous contains no nerves, and after birth no blood-vessels ; it may be examined fresh or hardened in a \ per cent, solution of chromic acid. Sections may be colored blue with aniline, and preserved in glycerine. 350 MANUAL OF HISTOLOGY. The lens (Fig. 158) is a transparent, biconvex body, sur- rounded by a structureless, elastic capsule, which is thicker in front where it touches the iris, and thinner behind where it rests in the fossa patellaris of the vitreous. The inner surface of the anterior capsule is covered with a single layer of hexagonal epithelial cells, which become longer near the equator of the lens, and gradually pass over into the lens-fibre. After birth these fibres consist of long, transparent tubes, on section resembling flattened hexagons closely joined together by their serrated edges; they are arranged in concentric meridional layers with their broad side out- ward. They do not pass around the entire circumference of the lens, but arise on the anterior surface from three lines, which, uniting at the axis, make a figure like an in- verted Y, with the arms set at an angle of about 20 to each other ; on the posterior surface this star is reversed, the Y standing upright. In adult life the rays are more numerous, and the fluid contents of the tubes become more solid and of greater refractive power, espe- cially toward the centre of the lens. On a meridional section of the lens one sees the concentric ar- rangement of the lens-fibres, and near the equator a collection of nuclei (the nuclear zone). These nuclei belong to the lens- fibres, each one of which originally had one, although in adult life they are found more abundantly in the peripheral region. The fibres of the supporting ligament of the lens (the zonula ciliaris) are attached to the anterior and posterior capsule near the equator ; from here they converge to the apex of the ciliary body, to which they are fastened. The fibres form for the most part an anterior and posterior layer, and have occasional nuclei, especially toward the ora serrata ; between these layers is the canal of Petit, the result Fio. 158. Meridional section through axis of the human lens. THE EYE. 351 of post-mortem changes, which quickly destroy the delicate fibres that ordinarily lill this space. Specimens for study may be made in the following way : harden an eye for fourteen days in Muller's fluid ; then open, remove the lens, and preserve in alcohol. Sections may be made in any direction ; they should be colored with hema- toxylon and mounted in glycerine. To examine the epithelium under the anterior capsule, a piece of capsule should be peeled oif from a fresh lens and ex- amined with or without previous staining. Single lens-fibres or groups of fibres may be obtained by macerating a portion of lens in dilute sulphuric acid ( per cent.), or in a -J per cent, solution of chromic acid, after which it can be easily separated into its elementary parts. The lachrymal gland is situated under the upper and outer edge of the orbital wall, resting partly in a shallow fossa of the frontal bone, to which it is attached by r firm bands of connec- tive tissue. It is an acinous gland, divided into a larger upper portion (glandula Galeni), some 20 mm. long, 10 wide, and 5 thick, and a lower part of about half the size (glandula Monroi) ; they are supplied with blood by a branch of the ophthalmic artery, and with nerves from the fifth pair. The connective tissue which envelops the gland also ramifies through its substance, dividing it into numerous small alveoli, in which are the true secreting cells of the gland, and from which fine ducts pass out to coalesce, and finally discharge on the free surface of the conjunctiva fornicis at its upper and outer part. The upper part of the gland is quite dense, but in the lower portion the alveoli are less closely packed, and often near- ly surrounded by the orbital fat. The alveoli are covered by a fine membrane composed of flat cells with numerous branches or processes, which spread in various directions and serve to unite the cells of the investing membrane, and also the different alveoli ; they form a shell which is surrounded on its outer side by a distinct lymph-space, and on its inner surface is Jined by the secreting cells of the gland. If these lymph-spaces have been injected with Berlin blue, and especially if the blood-vessels are injected with some other color, the arrangement of the lymph-spaces can be very well 352 MANUAL OF HISTOLOGY. seen. The openings from the alveoli are at first lined with fine, fiat cells ; then, as the tube grows larger, they assume the character of cylindrical epithelium. BIBLIOGRAPHY. GRAEFE u. SAEMISCH. Handbuch der gesammten Augenheilktmde. Vol. I, Leipzig, 1874. J. ORTH. Cursus der normalen Histologie. Berlin, 1878. A. ALT. Lectures on the Human Eye. New York, 1880. CHAPTER XXL THE EAR BY DRS. WILLIAM F. WHITNEY AND CLARENCE J. BLAKE, OF BOSTON. FOLLOWING the natural order are to be considered, first, the external ear with the meatus externus ; secondly, the middle ear with the Eustachian tube; and thirdly, the internal ear (membranous labyrinth and cochlea). External ear. This includes the auricle, the meatus exter- nus, and the membrana tympani. The auricle is formed by a cartilaginous plate, 1-2 mm. in thickness. The fine elastic fibres of this plate, which is of the reticular variety of cartilage, can be traced into the perichon- drium, and even into the subcutaneous tissue. Both perichon- drium and subcutaneous tissue are rich in elastic fibres, the latter varying greatly in amount in different parts of the ear, being very sparingly developed on the concave surfaces, where the skin is closely adherent to the perichondrium, and immov- able in consequence, but more abundant on the convex sur- faces, where the skin is movable ; it forms, together with the fat enclosed in its meshes, the bulk of the lobule. The cutis covering the auricle is a direct continuation of that covering the face, and is well provided with downy hairs and sebaceous glands. These latter reach their greatest devel- opment in the depressions of the auricle, especially the concha. The external meatus consists of a cartilaginous and an os- seous portion. The former only differs in structure from the auricle into which it passes, in the presence of the ceruminous glands. These are tubular glands, having a coil at the bottom. They consist of a membrana propria, on which is a layer of cubical epithelium, and are the analogues of the sweat-glands. In the osseous portion of the meatus the glands are sparingly found, and the hairs are fewer and finer. Otherwise there is 354 MANUAL OF HISTOLOGY. no difference between the two portions, except that the carti- lage is replaced by bone. The ear of a new-born child can be easily removed with the cartilaginous part of the meatus, and when hardened in Miil- ler's fluid and afterward in alcohol, and imbedded in parafnne or hardened liver, furnishes sections which, when colored with hsematoxylon, show the different relations very clearly. The osseous portion must first be decalcified by allowing the bone to hang freely in a weak (-J- per cent.) solution of chromic acid, often renewed, during several months. The specimens are then to be well washed, hardened in alcohol, and prepared as above. At the inner end of the external meatus, and separating it from the middle ear, is stretched the membrana tympani. The tympanic ring, with the membrane attached to it, is to be care- fully separated from the surrounding parts by means of bone- scissors, and placed for five to fifteen minutes in a weak solu- tion (two to five per cent.) of formic or acetic acid. It shoiild then be well washed in distilled water, and the external layer of epithelium removed by a camel' s-hair brush, arid finally stained with hsemotoxylon and mounted in glycerine. In spe- cimens thus prepared there are to be distinguished three lay- ers, viz.: an external or cuticular layer, a middle or fibrous layer (membrana propria), and an internal or mucous layer. The cuticular layer is composed of simple pavement-epithe- lium, without glands or hairs. It is thickest at the periphery, and over the handle of the hammer, and along its edge. The fibrous layer (membrana propria) consists of two sets of flattened, spindle-shaped fibres, with long, thin connective- tissue corpuscles imbedded in them, and which have a close analogy with the fibres of tendons. The outer series, lying directly beneath the cutis, radiates from the handle of the hammer toward the periphery, while the inner series circles about the handle. At the periphery the two series interlace with each other and with a few fibres coming from the cuticu- lar and mucous layers to form the so-called tendinous ring, in which are also to be found a few scattered cartilage-cells. This ring is joined to the annulus tympanicus by a thin periosteum. (The handle of the hammer is joined to the membrana tympani by a cartilaginous formation which stands in close relation to the membrana propria. This is a shallow groove of hyaline THE EAR. 355 cartilage, in which the handle of the hammer lies, kept in place by the mucous layer which passes over and is firmly adherent to it ; the upper part of this furrow ends in a sort of cartilagi- nous cap, into which the processus brevis fits.) Transverse sections made after hardening the membrane in Muller' s fluid and alcohol, and then imbedding, give the best idea of these relations. The inner or mucous layer is formed of flat epithelium, sup- ported on a reticulated layer of connective tissue, and directly continuous with the epithelial lining of the middle ear. The arterial supply is furnished by a small arteriole, which follows the handle of the malleolus, and gives off lateral capillaries anastomosing with others coming from small branches which enter at the periphery. The blood is collected into venous trunks which pass out in a similar manner. Fine nerves are said to be found in close connection with the vessels. They apparently come from the sympathetic system. The middle ear. In order to obtain a clear idea of the rela- tions and structure of the middle ear a fresh temporal bone, with the soft parts still adherent, must be decalcified by soak- ing for a long time in a i per cent, solution of chromic acid, which should be frequently changed; it is then to be washed in distilled water for twenty-four hours, and hardened in alco- hol, when it will be ready for cutting. A section from a specimen thus prepared shows that the whole middle ear is lined by a layer of pavement-epithelium, supported upon two layers of connective tissue, one serving as a submucous layer and the other as a periosteum. This tis- sue is thrown into ridges corresponding to the bony promi- nences, in the hollows of which the vessels and nerves lie. Ac- cording to Kessel the submucous layer is provided with oval expansions, recalling the Pacinian bodies found in the mesen- tery of the cat. The existence of muciparous glands in the human tympanum has yet to be confirmed. A plex"us of nerves is described as distributed in the subepithelial tissue, in the nodal points of which are found scattered ganglion-cells. The lining of the tympanum passes directly into that of the mastoid cells, and has there the same general arrangement. Tlie Eustachian tube. In direct communication with the tympanum stands the Eustachian tube, composed like the ex- ternal ear of a cartilaginous and an osseous portion. The car- MANUAL OF HISTOLOGY. til age, which gives the name to the anterior part of the tube that stands in connection with the pharynx, is in the form of a hook (Fig. 159, 2), with its short end directed downward and inward. At the bend of the hook the opposing surfaces of car- tilage cannot quite apply themselves to each other, and there is thus left a little air-space between them, which Ruedinger has termed the safety- tube (Fig. 159, 9). The cartilage is of the hyaline variety, with small cells, which are much smaller and more numerous at the periphery, thus forming a sort of peri- Fio. 159. Transverse section of Eustachian tube and surrounding parts : 1, median cartilaginous plate ; 2, lateral cartilaginous hook : 3, muscnlus dilator tubae ; 4, musculus levator veli palatini ; 5. fibro-carti- lago basilaris : 6 and 7, acinous glands ; 8, deposit of fat in the lateral wall : 9, safety-tube ; 10, accessory fissure ; 11, fold of the mucous membrane ; 12, adjacent tissues. Ruedinger. chondrium. The cartilage is joined to the osseous portion by a narrow band of fibro-cartilage. The musculus dilator tubse (Fig. 159, 3), which goes to form the membranous (muscular) portion of the tube, is joined to the short end of the hook along the whole length of the carti- laginous portion. The muscle is of the striped variety, and is inserted into the perichondrium by means of a very short, flat tendon. The entire tube is lined with a mucous membrane (Fig. 159, 11), continuous at one end with that of the pharynx, and at the THE EAR. 357 other with, that of the tympanum. This membrane consists of several layers of cylindrical epithelial cells, the upper or inner of which have their broad surfaces directed inward and carry cilia. In the other layers the epithelia are wedge-shaped. The epithelium rests upon a basement-membrane, beneath which is a layer of connective tissue (Fig. 159, 5), in which lie the muci- parous glands (Fig. 159, 6, 7), which are similar to those of the pharynx and oesophagus, and lined with wedge-shaped epithelium. These glands are absent in the safety-tube. A plexus of nerves arising from the pharyngeal and tympanic plexuses has been demonstrated, the final distribution of which to the glands is probable. Before leaving the middle ear a short mention of the os sicula and their mode of articulation is in place. The bones are composed of an internal spongy and an external compact portion. The former is very rich in blood-vessels. These bones are covered in early life by the mucous membrane only, but in later life there is also a thin periosteum to be seen. Their articulation with each other is constructed similarly to that of the larger joints; i.e., their articular ends are sur- rounded by a capsule in which is a synovial fluid. The method of union of the foot- plate of the stapes with the fenestra ovale is a little more complicated. The bottom and edges of the plate are covered with a thin film of hyaline cartilage. The edges of the window are also covered with cartilage, which is united to that of the plate by means of a fine network of elastic tissue. The base of the plate rests upon a firm connective-tissue layer, a continuation of the periosteum lining the inside of the scala tympani, and called the ligamentum baseos-stapedis. The muscles connected with the ossicula belong to the striped variety, and are connected to the bones by tendons, which are covered by the mucous membrane wherever they pass through the tympanum. The internal ear. The internal ear consists of two portions, to which the auditory nerve is finally distributed, and which are the essential parts concerned in the perception of sound. These are the membranous labyrinth and the cochlea. In man and the higher vertebrates both of these parts are enclosed within bony walls, a circumstance which makes their histological study a matter of considerable difficulty. In fishes, however, although the cochlea is represented merely by a small 358 MANUAL OF HISTOLOGY. diverticulum (the lagena), the membranous labyrinth is fully developed, and, as it is large and easy of access, has always been a favorite object for demonstration. Its method of prep- aration will be given here, while that for the cochlea will be described farther on. The membranous labyrinth. Our knowledge of this part has been chiefly derived from studies upon the pike (esox lu- cius), perch (perca fluviatilis), or cod (gadus morrhua). The head is divided longitudinally in the median line, and the brain carefully removed by means of the handle of a scalpel, when there is seen directly behind the eye a second cavity filled with a grayish translucent mass, composed principally of fat and a sort of mucous tissue. This can be removed with the aid of fine forceps, and there is usually drawn out at the same time more or less of the semicircular canals with their ampullse and the remains of the utricle and saccule. With a little practice, and by carefully freeing the canals from the short, bony chan- nels by which they are held in place, the membranous laby- rinth, with a portion of the acoustic nerve, can be removed entire. Within the utricle and saccule are found the otoliths, con- cretions of lime. After the lime has been removed by means of a weak acid, they show a coarse, fibrillated structure on section. These serve as a ready means of distinguishing be- tween the saccule and utricle, as the largest otolith (called sagitta) and the smallest (asterix) occupy the saccule, the former lying on the expansion of the acoustic nerve in the sac- cule proper, while the latter lies on the expansion of the nerve in that part of the saccule called the lagena, and which corre- sponds to the cochlea of the higher animals. The medium-sized stone (lapillus) lies upon the expansion of the nerve in the utri- cle. The otoliths are embedded in a mucilaginous mass lying directly upon the termination of the nerve. In the higher ani- mals they are represented by cretaceous particles in the macula acustica. The labyrinth thus removed is to be placed, during twenty- four hours, in a 1 per cent, solution of osmic acid, and then carefully washed in distilled water. In order to obtain the separate cells, the point where the nerve enters (known by its darker color) is to be carefully teased with fine needles and examined in glycerine. To obtain good sections, the por- THE EAR. 359 tions of the canal where the nerve terminates, and the simi- lar portion of the saccule and utricle, are to be placed for twenty-four hours in a saturated solution of gum arabic in water, and then directly into strong alcohol for twenty-four hours longer, when they will be ready for embedding. The sections, made with a sharp razor, kept well wet with alcohol, are to be deprived of their gum by passing a stream of distilled water beneath the cover-glass, the water being replaced by a solution composed of one part of a saturated solution of ace- tate of potash and four parts each of glycerine and water. The structure and arrangement of the semicircular canals, except at the points of expansion of the nerve, is as follows : In the osseous fishes the canals lie embedded in a mass of adi- pose tissue, and are held in place by very short bony tubes ; in the cartilaginous fishes (shark, skate) they lie in canals hol- lowed out in the cartilage, while in man and the higher verte- brates they are surrounded by bony walls. In man the membranous part does not entirely fill up the bony canals, but is adherent to the lining periosteum at one point, and to the rest of the wall by bands of connective tissue (called ligamentum labyrinth! canaliculorum et sacculorum), in the interstices of which the perilymph circulates. In the fishes the walls of the tubes and ampullae, as well as of the utricle and saccule, are composed of what has been termed spindle- cartilage. This consists of a homogeneous ground-substance, like that of ordinary cartilage, in which lie embedded long, spindle-shaped connective-tissue corpuscles, anastomosing with each other in all directions, like the corpuscles of the cornea. The whole is lined with a pavement-epithelium. In man the structure is different. Here there are to be distinguished three layers, viz., externally, a layer of connective tissue, composed of fibrous tissue with numerous nuclei. This is connected at one point with the periosteum, and passes into the ligamenta labyrinth! canaliculorum at the other points of the circumfer- ence ; secondly, of a hyaline layer, the tunica propria ; this is raised into papilliform projections in certain parts of the tube. The internal layer is composed of simple pavement-epithelium. The distribution and termination of the nerve is as follows in the fishes: The acoustic nerve divides into two branches, the cochlear and vestibular, each of which gives off three fila- ments. Those from the cochlear portion supply the saccule, 360 MANUAL OF HISTOLOGY. lagena, and ampulla frontalis ; those from the vestibular branch go to the utricle and the ampullae of the horizontal and sagittal semicircular canals. The termination of the nerves in the saccule and utricle is called macula acustica, and in the ampullae, crista acustica. The macula is a small, roundish spot, slightly projecting above the surface. Thin sections through it show the presence of three layers of cells. Directly upon the wall proper of the canal lies a single row of small, round epithelial cells with large nucleoli (Fig. 160, 1). Next come several rows of cells hav- scp. nerx f cartilage. Pro. 160. Section through the ampulla frontalis of esox lucius: 1, basal cella ; 2, cells with thread- like prolongations : 3, cylindrical cells, with cilia. After Kuhn. ing a round or oblong (spindle-shaped) central portion, from which are given off two filiform prolongations, the one passing inward and standing in close connection with a fine plexus of nerves lying in the layer of round cells mentioned above ; the other also passing inward, but ending either as a free cilium between the layer of cells next to be described, or being joined to their inner extremity (Fig. 160, 2, and Fig. 161). The inner layer consists of several rows of cylindrical epi- thelial cells, having the end, which is directed inward, tapering into a fine filament connected with those of the middle layer, as THE EAR. 361 already described. The free surface of these cells is provided with numerous hairs (Fig. 160, 3). The arrangement of the cells in the crista acustica is essen- tially the same as that of the ma- cula, with the exception that the crista rests upon an infolding of the wall called the septum nerveum (Fig. 160, sep. nerv.), and has on each side two half - moon - shaped prominences of cylindrical epithe- lium called the plana semilunata (Fig. 160, pi. sem.), into which no nerves have been traced. At the point where the macula and plana semilunata pass into the epithe- lium lining the rest of the canal, there is found an intermediate form of cell, larger than the ordinary epithelium, and separated one from another by a fine web of connective tissue. These have received the name of protoplasmic cells, but as yet their function has not been discovered. Covering the crista in the place of an otolith is a gelatinous mass in the form of a cup, having a stri- ated appearance, and into which the fine hairs of the internal sur- face project. This is considered as a cuticular formation, and is sup- posed to act as a damper (Fig. 160, cupula). The nerve, after passing through the wall at the point opposite the crista or macula, loses all its sheaths, and forms a fine plexus in the outermost layer of cells, and this plexus has been found to communicate with the inner filaments of the middle layer of cells, the internal filaments of which ended as free cilia or were joined to cells of the inner FIG. 161. Separate cells from the ma- cula, showing the connection of the cylin- drical cells with the cells having thread- like processes, and also the passage of these processea to the surface between the cells. Kuhn. 362 MANUAL OF HISTOLOGY. layer which were provided with cilia upon tlieir free surface. This can be best understood by a study of Figs. 160 and 161. In man the arrangement, as well as can be followed, is almost identical with that of fishes. TJie cochlea. There is no easy method of obtaining good preparations of the cochlea, but that by which the best results have been obtained is as follows : The portion of the temporal bone containing the internal ear from a recently killed animal (young cat, dog, or bat) is hardened for twenty-four hours in % to 1 per cent, solution of osmic acid in distilled water, then placed in Muller's fluid for a week, and decalcified by a 0.01 per cent, solution of chloride of palladium. After decal- cification it is to be washed in distilled water for a few minutes, then soaked for twenty-four hours in a concentrated aqueous solution of pure gum arable, and finally placed directly in strong alcohol for twenty -four hours. After this hardening the preparations are ready to be embedded in soap or hardened liver, and cut. The razor is to be kept well wet with alcohol while cutting. The sections are to be placed directly upon a slide, and the gum removed by passing a stream of distilled water under the covering-glass. Small portions of the lamina spiralis can also be taken from the fresh cochlea, after opening it carefully with the bone-for- ceps, and placed in the vapor of osmic acid or in a i to 1 per cent, solution of the same for a few (twelve to twenty-four) hours. The preparations thus treated may be teased in gly- cerine, and the separate cells obtained. The sections are to be made in a direction parallel with the long axis of the cochlea, and if the central shaft (modiolus) is cut through, the following picture will be presented : On each side of the modiolus are seen sections of the canal of the coch- lea, divided by a thin partition (the lamina spiralis, Fig. 162, L sp) into an upper portion (the scala vestibuli, Fig. 162, SV) and a lower (the scala tympani, Fig. 162, ST). The scala ves- tibuli is further subdivided by means of a delicate membrane, named after its discoverer the membrane of Eeissner (Fig. 162, /, /i), which passes off at an angle from the middle of the lamina spiralis and is inserted into the wall of the cochlea. The portion of the canal thus cut off forms the ductus cochle- aris (Fig. 162, e, e t ), and in it lies the peculiar body in which the nerve terminates, and which is called the organ of Corti. THE EAR. 363 The scala tympani is a blind canal, having at one extremity the membrane which covers the fenestra rotunda, and at the upper part terminating in the cupula of the cochlea, where it s Lsp FIG. 162. Section of the cochlea of a human embryo at the fourth month, a, a, a, cartilaginous incasement of the cochlea ; ft. 6, perichondrium ; c, mucoid tissue matrix of the modiolus ; d, d, cartila- ginous septa of the individual turns of the cochlea ; e c 4 , sections of the ductus cochlearis ; /, f^ Reise- ner's membrane ; #, membrana tectoria. somewhat lifted up from the subjacent parts ; h. rudiment of the stria vascularis ; t, rudiment of the subsequent organ of Corti ; L *p, lamina spiralis ; Gl, Gl, ganglion spirale with various efferent and afferent bundles of nerves ; /ST, scala tympani ; SV, scala vesfibuli ; ST lt SV lt /Sr 2 , muccid tissue where later the scalae of the last cochleal turn will be. 10, Waldeyer. is said to enter into communication with the scala vestibuli by a minute opening, the helicotrema. The scala vestibuli stands in direct communication with the, perilymphatic space of the vestibular sacs, while the ductus cochlearis is in communication with the saccule by means of a slender canal (the canalis reuniens). The walls of the two scalse are formed of a thin periosteum, on the surface of which 364 MANUAL OF HISTOLOGY. there can be shown, by means of the silver method, a layer of endothelium. This proves that the canals are of the nature of serous cavities. The lamina spiralis is composed of an osseous and a mem- branous portion. The osseous portion reaches about one-half the distance from the modiolus to the opposite wall, and on its outer and vestibular portion is a mass of connective tissue called crista spiralis (Fig. 163, Or.), the upper lip of which is called labium vestibulare (Fig. 163, Lv.\ while the lower lip is called labium tympanicum (Fig. 163, Lt.}; the space between the two lips has received the name of recessus internus. The crista spiralis is divided by a number of parallel furrows, which gives the surface a regular toothed appearance when seen from the vestibular surface. Hence, the portions between the furrows are called "auditory teeth." The under (vestibular) of the two lips is connected with the membrana basilaris (Fig. 163, Hn, Zp'\ which is com- posed of two layers of finely fibrillated connective tissue, and is covered on its tympanic surface by a layer of endothe- lium, and on the surface turned toward the ductus cochlearis l)y the organ of Corti and its supporting cells. The inner layer of this fine connective tissue is directly continued into the bases of the pillars of the organ of Corti next to be de- scribed. The organ of Corti, so named from its discoverer, is a com- plicated arrangement of cells in which the nerve terminates, and of other cells and their modifications, which apparently act as supports to these and as modifiers of the sound. The cells proper, in which the nerve terminates, have received the name of hair-cells, from the ciliated appendages which they carry (Fig. 163, a, a" , a", a"), while the peculiar modified cells which are their chief support are called the pillars. The pillars (Fig. 163, ft, fa} are two slender, slightly shaped bodies, of a finely fibrillated structure, showing, however, in their early stages, the presence of nuclei. They stand upon the membrana basilaris, and are apparently to be directly fol- lowed into the fine layer of connective tissue beneath them. They are arranged in two rows, named inner and outer, ac- eording to their situation as regards the modiolus. The pillars are inclined toward each other, and the space between them is named the tunnel. The head of the outer is a little enlarged THE EAR. 805 and rounded, lying in a shallow depression in the head of the inner pillar, thus resembling a ball and socket-joint (Fig. 163, gia). The heads of the pillars, when seen from the surface, have Fio. 163. Section through the ductus cochlearis of a young dog : R-r f , Reissner's membrane ; Los and Los', vestibular and tympanic plates of the osseous lamina ; gap, ganglion spirals ; n, fine nerves passing through the habenula perforata at Jfn ; Cr, crista spiralis ; Lv, its vestibnla or upper lip ; rm, Mt, m', the membrana tectoria (Corti's membrane) ; S#pi, recessus iriternus clothed with epithe- lium ; fl and /a, inner and outer pillars of Corti , a and a", a", a", inner and outer hair-cells, between the latter are seen the fl^sk-shaped cells, r, r, r ; Tn. nerve passing through the tunnel to reach one of the outer hair-cells ; Hz, Henson's prop-cells : Sp, Zf/ zona pectinata ; gia, inner and outer beads of the pillars of Corti : A'p, plate called phalynx. which, when joined with its neighbors, forms the lamina reti- cularis, in which the ends of the hair-cells are supported; Lap, ligameutum spirale ; i i principal divisions, one of which ex- tends far up in the direction of the axilla. It is separated from the axillary lymphatic glands only by a small amount of adipose tissue. This would explain the ease, readiness, and frequency with which these glands become implicated in ma- lignant disease of the mamma. Since the glands at birth differ very widely from the mammae of adult women, and still more widely from those of pregnancy, it will be convenient to consider the histology of the organ under different aspects. This will be necessary, however, only with regard to the acini and the epithelia therein implanted, as these alone show such wide morphological divergencies in the dif- ferent phases of existence. The nipple (teat, mamilla, papilla mammcB) is the one struc- ture belonging to the mamma which is least liable to modifica- tions of tissue due to age and sex. It generally assumes the shape of a pigmented conical or cylindrical projection, at the apex of which the galactophorous ducts have their terminal openings. It is composed principally of a rather loosely woven connective tissue, containing abundant corpuscles, and provided THE MAMMARY GLAND. 441 with elastic fibrils. This conjunctive tissue forms a supporting framework for the milk-ducts traversing the nipple. The latter show walls of rather dense fibrous tissue, with a large pro- portion of elastic elements, and are provided with a lining of one row of short cylindrical cells. As the external orifice is approached, these cells begin to take on the character of the ordinary epidermic corpuscles of the integument. Partsch has found in many animals that the secreting paren- chyma accompanied these ducts almost to their mamillary orifices. The occurrence of unstriped muscle in the nipple, accords with the fact of its erectile properties. But the exact mode of distribution of these elements is still a matter of controversj^ among histologists. From the researches of Winkler and Kolessnikow, recently confirmed by Partsch, it would appear that they occur not in the ducts themselves, but form an in- complete ring around and external to the same. In or around the smaller galactophorous ducts, muscle-cells cannot be unmis- takably recognized, though some authors have described their occurrence there. As regards the structure of these smaller galactopliorous ducts (ductus lactiferi, milk-ducts) it is quite simple. Their membranous walls consist of a delicate and closely woven reticulum of connective tissue, with a large admixture of fine elastic fibres. Henle, Meckel, and Kolessnikow have described smooth muscle-cells in these canals, but, as already stated, Partsch and others have denied their existence. At any rate, on cross- sections the contracted condition of some of the larger ducts results in a stellate appearance of their lumina, whereas the smaller ducts always appear round or oval. The larger ducts traced into the gland tissue are found to be provided with saccular dilatations immediately beneath the nipple. These milk-reservoirs (sinus ductuum, lactiferorum, sacculi lactiferi, or ampullcE) may be 5 to 8 mm. broad, and thus become distinctly perceptible to the naked eye. Below these dilatations the ducts again grow narrower, and by numerous divisions and subdivisions form a system of ramifying tubes, which terminate in the secreting alveoli. The structure of the larger ducts does not materially differ from that of the smaller ones. Their walls are, of course, considerably thicker, and there is found in addition a greater proportion of elastic tis- 442 MANUAL OF HISTOLOGY. sue. All the different kinds of ducts show a lining composed of a single layer of short cylindrical cells, containing ellipsoid nuclei. The character of the lining cells is, however, gradually changed as the acini are approached, near which it merges into the alveolar epithelium by insensible gradations. Surrounding the nipple is a variously pigmented ring, called the areola mamma. Its surface is slightly corrugated, and this circumstance, taken in connection with its pigmentation, results in the production of the marked contrast it presents to the very white and soft integument covering the other portions of the female mamma. The areola is also provided with abun- dant unstriped muscle-fibres. Some of the latter surround the nipple in concentric rings, others pursue a radial course. The sudoriferous and sebaceous glands of the areola are conspic- uously developed, and lanugo hairs are also found. The fa- miliar changes which go on in the areola simultaneously with the development of pregnancy, are mainly due to increased blood-supply and additional pigmentation. The areola is also provided with small granules of secreting parenchyma. Some of these grains empty the products of their secretory activity by special recurrent ducts into the main excretory canals. But there are others which have special openings upon the free sur- face of the areola. Usually, little papillary eminences mark the presence of such orifices. These scattered bits of mam- mary parenchyma are known as the glandules aberrantes of Montgomery. Kolliker and others regard them as largely developed sebaceous glands. The arteries of the mamma are chiefly derived from the internal mammary artery and the long thoracic. The veins empty into the thoracic branches and cephalic vein. Both arterial and venous vessels proceed subcutaneously from the periphery to the nipple, whence branches are given off in a posterior direction. They are not guided in their course by the distribution of the milk-ducts, but are distributed to the glandular parenchyma in such a way that each lobule has its own separate supply. Finally, under the areola the veins of the nipple form a circular anastomosing chain, known as the circulus venosus of Holler. Capillary vessels surround the acini, forming networks with rather close meshes. Of course, the varying states of expansion and contraction in the ultimate alveoli, which conditions correspond to phases of activity and THE MAMMARY GLAND. 443 rest, will materially affect the size and shape of the capillary networks. They are, however, much less distinct and con- spicuous during the period of lactation than in the quiescent state of the gland. Rauber found in the glands of pregnant animals that the blood-vessels were not in immediate contact with the walls of the secreting vesicles, being separated from them by interposed lymph-channels. Coyne, Langhans, and Kolessnikow have also described these perialveolar lymph- spaces. Their presence is, indeed, readily demonstrated by injections with nitrate of silver solutions. In actively secreting glands these channels are sometimes packed with leucocytes, which also infiltrate the stroma of the organ. Lymphatics are plentiful in the mammary gland. We find them subcutaneously, as well as deep in the interior of the organ. Coyne, in 1874, described the perialveolar lymph- spaces, already mentioned, for the human mamma, and Koless- nikow, in 1870, perialveolar lymph- spaces for the mammary gland of the cow. Langhans succeeded in injecting a rich net- work of periacinal lymph-vessels, likewise lymph-channels around the excretory ducts and the lacteal sinuses. The lar- gest lymph-vessels are retro-glandular. They are without valves. The lymph-vessels of the nipple resemble those of the skin. There seems to be no free communication between the lacunal and interstitial spaces of connective tissue of the glands, and the proper lymph-channels. The principal lymph-vessels of the mamma, both deep and superficial branches, proceed to the glands of the axilla. But some of the mammary lymphatics also communicate, through intercostal branches, with the thoracic lymphatic glands. These are points worthy of remembrance in studying the mode of dissemination in mammary tumors. Nerves abound less in the secreting structure of the mam- ma than in its integumentary apparatus. The majority are of spinal origin, although the sympathetic system is by no means excluded from representation. Branches from the fourth, fifth, and sixth intercostal nerves the so-called rami glandu- lar es accompany the milk-ducts, and ramify within the organ. Satisfactory evidence concerning the manner of their ultimate termination has, however, not been hitherto obtained. Most of the nerves in the interior of the organ belong to the vascular or vaso-motor variety, and many are seen to accompany the 444 MANUAL OF HISTOLOGY. blood-vessels. Eckliard has given the most elaborate descrip- tion of the nerve-supply of the human mamma. Structure of fully expanded gland. Immediately before, during, and after lactation, the mamma appears as a distinctly lobulated organ, having a pinkish or yellowish hue, and resem- bling in consistence the human pancreas or salivary gland. The different lobuli are made up of numerous ultimate acini, having, as a rule, a rounded, pyriform, or slightly poly- hedral shape. They are of nearly uni- form size, and are closely placed, being separated from one another by only sparing amounts of connective tissue, and the capillary vascular channels therein contained. Elastic fibres and smooth muscle-cells also occur, though not constantly, between the alveoli of the lobules. Lymphoid elements, as well as branched connective-tissue cor- puscles, are always encountered there in greater or less abundance. In addi- tion to these elements, large granular corpuscles containing nuclei are found. They are most numerous along the course of the blood-vessels, and appear to be identical with the so-called plasma cells of Waldeyer. Creighton, however, also describes similar cells in the interior of the alveoli, and believes that both are identical, maintain- ing that they are derived from the acinous epithelium. According to this author's description, such cells are " not infrequently seen in the tissue outside a lobule in rows three or four deep ; again, they are found in the interfascicular spaces among thelymphoid-cells," that have been already mentioned. These large, granular, and nucleated corpuscles are said to be filled with a bright yellow or golden pigment. Now, Creighton has pointed out that the periodical subsidence of the mammary function is accompanied by the formation of much corpuscular waste material. And the production of these remarkable yel- low cells, which finally leave the gland by way of the lymph- vessels, is, according to him, but a final phase of this process. The mammary epithelium which paves the acini has been variously described as consisting of flat polyhedral (Reinhard) ; FIG. 190. Transverse section through the terminal vesicles of the gland in a nursing woman, showing mteralveolar capillaries. Langer. THE MAMMARY GLAND. 445 cubical, cylindrical (Kolessnikow) ; small polyhedral (Langer) ; and prismatic (Kehrer) cells. This discrepancy of opinion re- ceives its explanation from the fact that the epithelial cells FIG. 191. Lobule of a mamma near the resting state. Numerous large pigmented cells within the acini and in the interlobular flbrillar tissue. Creighton. have a different appearance in the various conditions interven- ing between full activity and complete rest of the gland. Creighton has given a very satisfactory description of mam- mary epithelium. He states that in the fully expanded gland " the floor of an acinus in section is covered by a mosaic of polyhedric epithelial cells, usually to the number of fifteen or twenty, while in the larger elongated acini as many as thirty may be counted. The cells are usually pentagonal or hex- agonal, and the corners are sometimes rounded. In each cell there is a central round nucleus, which colors brightly with the staining fluid, and abroad fringe of protoplasm, which stains less deeply." The nucleus varies in its relative size, generally having a diameter equal to about one-third that of the entire cell. " In a profile view of an acinus, the epithelium appears as a circlet of oblong cells, in which the nucleus at the centre occu- pies almost the entire thickness of the cell. The mammary epithelial cell may therefore be described as a flattened poly- hedric body, with a thickness about one-half of its breadth. The substance of the nucleus is apparently homogeneous, with FIG. 192. Fully expanded aci- nus, showing mosaic of polyhedral cells. Creighton. 446 MANUAL OF HISTOLOGY. a deeper line of staining round the margin ; a nucleolus is not always prominently seen." Structure of involuted mamma. Having thus briefly indi- cated the main histological features of a fully evolved gland, we are now prepared to examine the mamma in a condition of advanced involution. By involution, in this sense, is meant the periodical return to inactivity, and not to final retrograde metamorphosis, which culminates in complete senile atrophy. The glandular lobules, then, in the involuted organ are again found to be composed of closely crowded alveoli. But all the lobules appear to have become smaller, and their acinous components are likewise shrunk- en. The basement-membrane of the latter does not appear to be materially altered, but its cellular contents are considerably changed. In place of the beautiful mosaic characteristic of the active gland, there now appears only an aggregation of nucleated corpuscles to the number of five or ten. Creighton describes them as " nothing else than a somewhat ir- regular heap of naked nuclei, with no fringe of protoplasm round them, and in size little, if at all, larger than the nucleus alone of the P^fect epithelium." ' This description, how- ever > applies only to hardened specimens, for in fresh preparations the nuclei, as a rule, show a broader or narrower surrounding zone of protoplasm. As regards the diameter of the involuted acini, it is about one- fourth that of the actively secreting alveoli. Owing to the shrinkage in the glandular parenchyma, the blood-vessels and excretory ducts, as already stated, are more prominent in an involuted than in an active gland. It is not our purpose here to trace, step by step, the various processes by which a gland passes from the resting state to that condition of complete evolution which is alone compatible with active secretion. For the details of this interesting subject, the reader is referred to the work of Creighton. We may, how- ever, very briefly summarize this author's account of the trans- formations in question. The one essential circumstance char- acterizing the whole change is a process of vacuolation, which Creighton assumes to take place in the secreting cells. "The THE MAMMARY GLAND. 447 most definite and unmistakable form of vacuolation is the sig- net-ring type." This process is, according to him, a true one of endogenous cell formation, resulting in this instance in the formation of milk. Moreover, large, granular, nucleated cells, filled with a bright yellow or golden pigment, "found both within the alveoli and in the interfibrillar spaces without them" FIG. 194. Vacnolation of alveolar epithelium. From the udder of a ewe shortly after the end of lac- tation. The cells in situ are vacuolated cells, with the usual thin and, for the most part, uncolored hoop or ring of the vacuole, and the deeply stained peripheral mass. Creighton. characterize the last stage of involution, "and the pigment that belongs to them is to be found strewn over the lobules that have reached the resting state." Finally, Creighton as- serts that " the various forms of cells that characterize the various stages of involution must have resulted from a trans- formation de novo of the renewed epithelium, and not from successive changes upon the same cell." Each epithelial cell, therefore, that is used up in the formation of milk, has been at one time a perfect polyhedral corpuscle or fully equipped cell, and "has rapidly undergone the cycle of changes whereby its whole substance has been converted into milk." A distinguishing feature of one stage of evolution which 448 MANUAL OF HISTOLOGY. deserves to be mentioned, is " the presence in the cavities of the acini of a peculiar granular material, the coagulated con- dition of a fluid." Partsch has also described the occurrence of this granular mass within the alveoli, and he states that the secreting epithelia, though of normal size, were furnished with shrunken nuclei, and showed numerous light spots, as if the cells were perforated and sieve-like. It would appear that this writer has ob- served the stage of vacuolation with- out, however, interpreting the same in Creighton's sense. Creighton also describes in certain glands the connective-tissue stroma as crowded with cellular elements, which he considers equally with the pigmented corpuscles as waste-cells of the secre- tion. Others (Winkler, Brunn, and par- ticularly Rauber) have assigned a far different significance to these bodies, as will appear farther on. Finally, Creigh- ton explains that the secretion of the mammary gland " may be said to be pro- duced by a transformation of the sub- stance of successive generations of epithelial cells, and in the state of full activity that transfor- mation of the substance is so complete, that it may be called a deliquescence." Although Creighton's investigations did not extend to the human mammary gland, there is ample ground for the belief that changes of evolution and involution similar to those which he has described in animals, constantly take place in the hu- man female as well. And even if we accept only some of his views on the inter-relations of physiological action and histo- logical appearance, the discrepancy still existing in the de- scriptions given by different authors will receive a more rational explanation than has hitherto been offered by writers on this subject. Certainly some of his assertions appear rather fanci- ful in their far-reaching novelty, nevertheless they deserve the attentive consideration which we have, at least, in part bestowed on them. From the results of our own examinations, we are unable FIG. 195. Acini from a partly expanded gland, some of them filled with a granular material. From the mamma of a pregnant cat. Creighton. THE MAMMARY GLAND. 449 to concede in all respects the correctness of Creighton's inter- pretations. The evidences of epithelial destruction for purposes of milk secretion, are not positive and convincing. In the Har- derian gland, as well as in the mamma, we have observed the extrusion of fat-droplets from cells replete with them without destruction of the cell itself. Partsch agrees with us in assum- ing that the cells may burst or otherwise discharge their con- tents, and yet retain enough protoplasm to maintain their vital- ity ; and also that the vital contractions of the protoplasm may force out the oil-globules without destruction of the epi- thelium. What Creighton has called vacuolation does not mean death to the cells concerned in this action, for they retain their nuclei and sufficient protoplasm to become re-established as perfect epithelia. That this reformation of old epithelium takes place, is proven by the fact that a new formation by proliferation has never been observed, and by the additional circumstance that the mammary acini never show more than a single layer of lining-corpuscles, and, moreover, always show this layer complete. In this, as in many other respects, the mamma closely re- sembles the Harderian gland, more particularly of the roden- tia, as described by one of the writers in a monograph. The basement-membrane of the acini in every particular also corre- sponds in the two kinds of glands, being in both a homoge- neous, apparently structureless membrane, with superimposed branched adventitial cells, the so-called Stutzzellen of German writers. A basket-shaped reticulum, such as has been described by Boll, Langer, Kolessnikow, Moullin, and others, is never found to constitute this membrana propria, although artifi- cially, appearances simulating a structure of this kind are readily obtained, and have been interpreted by several histolo- gists as natural occurrences. In the cutaneous sebaceous glands the secreting vesicles are filled with several superimposed layers of epithelia, and it is this circumstance which leads to an entirely different mode of secretion. For there it would indeed appear that the cells undergoing fatty degeneration become detached from their bases and find their way into the narrow lumen of the acinus. The older or inner generation of cells thus vanishing is replaced by new corpuscles formed by gradual proliferation from the peripheral zone. 450 MANUAL OF HISTOLOGY. RaiCber* s mews on the mamma and the lacteal secretion are somewhat startling, but must occupy our attention here. From a series of very carefully conducted examinations, principally on the glands of guinea-pigs during and after pregnancy, he feels justified in concluding that milk owes its orgin to the entrance of countless leucocytes into the lumen of the gland- vesicles. The emigrated lymphoid elements, he believes, pene- trate the alveolar walls, passing through the single layer of epithelial cells which line them. Arrived in the interior of an ultimate acinus, the leucocytes undergo fatty metamorphosis, and thus at length furnish the most essential and characteristic ingredient of milk, viz., the milk-globules. Rauber, therefore, discards the notion that the formed particles of the lacteal secretion originate in the glandular epithelium, and represent the elaborated products of its functional activity. He also denies that previously formed milk globules, or colostrum cor- puscles, ever pass through the alveolar walls. Thus the prim- itive opinion advanced by Empedocles, describing milk as white pus, is in a measure revived, and milk is held to be directly -derived from the white corpuscles of the blood. Preparations of mammary glands taken from animals still suckling their young, according to him, invariably show the intraglandular lymph-vessels replete with leucocytes, the stro- ma similarly infiltrated, identical corpuscles in greater or less abundance within the vesicles, and transitional forms between lymphoid-corpuscles and milk-globules. These claims, granted to be facts, and considered in conjunction with the circum- . stance that epithelial proliferation is not seen, would certainly .go far to make Rauber's theory seem a somewhat plausible one. Nevertheless, we require corroborative evidence from Bothers, before his views can be accepted as anything more than an ingenious hypothesis. Rauber has also described the occurrence of a delicate stri- .ation within the epithelial cells of the alveoli. These striae are said to be in all respects similar to those found in the secreting elements of certain portions of the salivary glands and the iubules of the kidneys. As regards the corpuscles of Donne, or colostrum bodies, most authors regard them as the products of desquamation of the alveolar epithelium, the latter being in a condition of fatty degeneration (Winkler, De Sinety, Buchholtz, and others). THE MAMMARY GLAND. 451 Some histologists, like Strieker, hold that oil-globules may be expelled from the interior of fat-filled cells without disintegra- tion of their protoplasmic bodies. It is an undoubtable fact that colostrum corpuscles, when managed with proper precau- tions, may be seen to yield droplets of fat under the micro- scope, just as amoebae reject similar contained particles. Rau- ber, however, maintains that these bodies represent leucocytes in various stages of fatty metamorphosis, and he calls such corpuscles, when found in the gland vesicles, galactoblasts. In the gland of Harder, one of the writers has found the spacious gland vesicles lined with very large epithelia ; and these cells were in many animals entirely fat-filled. They se- creted a greasy substance not unlike thick milk. Yet destruc- tion of the cell-body did not occur, at least evidences of such a process could not be obtained. Partsch has therefore antici- pated the authors in their conclusion that the secretion of milk is accomplished in much the same way in which the creamy pro- ducts of the Harderian gland are formed, i.e., without total destruction of epithelial cells. According to our view, then, and it nearly coincides with the opinion of Strieker, Winkler, and especially Partsch, the cells containing the fat-globules may, indeed, burst and discharge their contents, but the nu- cleus and sufficient protoplasm are retained to enable the epi- thelium to recuperate, and in the course of time again and again discharge its contents. Along with this mode of milk secretion, a second process occurs. This consists of the gradual extrusion of oil-droplets, the cell body remaining entirely in- tact, since the mere vital contractions of the protoplasm suf- fice to drive out one milk-globule after another. When the activity of the gland is suddenly heightened in the period immediately before childbirth, some few epithelial cells are desquamated. These, appearing in the milk of most women, are identical with the bodies known and described as colostrum corpuscles. Of other anatomical constituents of normal milk, we only find the milk- or oil-globules. They are suspended in the fluid emulsion which milk truly represents, in countless numbers. They vary in size from 0.002 to 0.009 mm. A very delicate fringe of protoplasm adheres to their periphery, and it is for this reason that they may appear to become stained when sub- mitted to the action of proper dyes. 452 MANUAL OF HISTOLOGY. DEVELOPMENT OF THE GLAND. Like the other cutaneous glands of the body, the mamma is first formed by a proliferation inward of certain epidermal cells. In other words, the breast results from a downward extension of epiblastic corpuscles. The first unmistakable indi- cation of the future gland is seen about the third or fourth month of pregnancy. At that time it consists of a solid plug, or pro- Fio. 196. 1. Rudimentary form of gland in human fcetus: a, 6, epidermis : c, aggrega- tion of cells ; d, connective tissue layer. 2. From a seven-months' foetus : a, central substance ; &, larger, and c, smaller outgrowths. Frey. FIG. 197. Embryonal mamma : a, cen- tral mass, with 6, and c, variously shaped outgrowths. Frey. cess, extending downward from the rete-mucosum of the skin. This has been called Drusenfeld, by Huss. From the internal end of this solid process, sprouts, or offshoots, are developed, and they represent the future separate glands constituting the mature organ. These buds have a pyrif orm, or club-like shape, and are surrounded by ordinary embryonal connective tissue. The further growth of the gland takes place by a process of continuous extension and subdivision, but indications of the latter are not always found at birth. Ducts are already visible in the new-born infant, but the aggregations of cells represent- ing the future acini, remain without lumina for a much longer period. Th. Kolliker describes as a constant occurrence, especially marked in the breasts of female infants, the dilatation of a greater or smaller number of milk-ducts. Such ectatic-canals DEVELOPMENT OF THE GLAND. 453 liave their lumina filled with desquamated epithelial cells, and a whitish, granular material. Formerly, these occurrences were considered to be exceptional, and were regarded as having a pathological significance. During the first year of extra-uterine life, this characteristic process of progressive dilatation may assume such large dimensions, that the mamma may come to resemble cavernous tissue, the ectatic spaces of which are paved with flattened epithelium. Within certain limits, Kolli- ker regards this as a perfectly normal physiological event. But he adds that an exaggerated process of this kind may result in early mastitis. Such an occurrence, he thinks, may explain the rudimentary development of the breasts observed in some women of otherwise normal growth. The post-embryonal growth of the mamma has been care- fully studied by Langer, and his results and conclusions having been confirmed by the investiga- tions of Kolliker, Huss, and others, must still be received as represent- ing the true condition of things, in spite of the novel and heterodox views advanced by Creighton. Up to the time of puberty, the growth of the breast is very grad- ual and quite insignificant, even in females. Then, however, the ducts begin to rapidly ramify in all di- rections, and, by offshoots from va- rious points, true acini are at length developed. But they remain of small size until the stimulus of pregnancy causes a further evolution. In the male, the exist- ing ducts, as a rule, atrophy with advancing age. The evolu- tion changes which the mamma undergoes during pregnancy, have already been set forth, and there remain to be considered only those final phases of metamorphosis which take place in the climacteric period of life. These are readily understood, consisting essentially of a complete atrophy of all the secreting acini. Simultaneously with these atrophic changes the epithelia of the galactophorous ducts become flattened, and finally shrink, so as to form only squamous plates, which line the ramifying processes of connec- 454 MANUAL OF HISTOLOGY. tive tissue representing the former lactiferous canals. The terminal portions of these larger duct-remnants are sometimes connected with minute channels, the latter being the remnants of collapsed smaller ducts. In some measure we find a com- pensatory production of fat, which partly replaces the faded acini. The breasts of old women, therefore, consist of fibrous tissue, with a large proportion of elastic elements, fat-cells, and the remnants of the ducts. It may be remarked that the latter frequently show cystic dilatations, the cavities being filled with a dirty, slimy fluid. The blood and lymph-vessels, but especi- ally the latter, participate in the general atrophy of the tissues. This succinct account concerning the histogenesis of the mammary gland, does not, as already intimated, represent the unchallenged opinion on its first development. For Creighton, in the remarkable work already cited, radically opposes the view that the mamma takes its origin from the epiblast. He believes, on the contrary, that it starts from the mesoblast, or connective-tissue layer of the embryo, and not the upper epi- thelial layer or epiblast. According to him, moreover, and his conclusions are based on developmental studies, chiefly of the guinea-pig's gland, the process may be justly described as a centripetal one, whereas the current view represents this gland- develpoment as essentially centrifugal. We have already ex- pressed our adherence to the current view, attributing this growth to extension from a central point. Nevertheless, it seems proper to briefly give the conclusions of Creighton, es- pecially since they appear to be singularly corroborative of the account given by Goodsir of this process, as early as 1842, an account which has apparently remained almost unnoticed by workers in this branch of scientific medicine. , Creighton then concludes his inquiry as follows : " 1. The mammary acini of the guinea-pig develop at many separate points in a matrix -tissue. The embryo cells from which they develop are of the same kind that give origin to the surrounding fat-tissue. The process of development of the mammary acini is, step-for-step, the same as that of the fat- lobules." " 2. The ducts of the mamma develop from the same matrix- tissue, by direct aggregation of the embryonic-cells, along predetermined lines. The ducts develop, in the individual guinea-pig, before the acini, whereas, in the phylogenetic sue- DEVELOPMENT OF THE GLAND. 455 cession, the ducts are a later acquisition. This reversal of the order of acquisition of parts is in accordance with the prin- ciple stated by Herbert Spencer, that 'under certain circum- stances the direct mode of development tends to be substituted for the indirect.' ' Hints regarding the histological study of the mamma. The evolution of the mammary structure progresses paripassu with the development of its functional activity. It is the stim- ulus of pregnancy which determines both. Nevertheless, even during the period of its fullest physiological bloom, i.e., during lactation, variations in the degree of functional activity normally take place. Moreover, the same gland may contain lobules which are comparatively at rest, and others which are at the full height of activity. This should always be borne in mind in interpreting the results of histological inspection of this organ, lest erroneous impressions be conveyed. The alveolar epithelial cells will, therefore, not be found alike in the different acini, nor yet even in the same vesicle. We may find cuboidal cells, and cylindrical ones, and flattened corpuscles, and in addition, various transitional forms between these types. The nucleus will appear round, or oval, and about 6-7 j* in diameter. Sometimes two nuclei may be found in one cell. The radiating striation observed by Rauber in many cells, has already received mention. It is a noteworthy fact that the cells themselves contain only a very small proportion of fatty granules, whereas the intra-alveolar lumen is often replete with the same. In order, then, to study the histology of the gland at the high- water-mark of its functional activity, animals should be chosen which have either just given birth to their young, or are about to do so. For the normal conditions of the human mamma are rapidly transformed by post-mortem change, if not previously altered in consequence of the disease which caused the death of the individual. The organ may be exam- ined fresh, or else hardened and then cut in sections to be stained and mounted in the ordinary manner. 456 MANUAL OF HISTOLOGY. BIBLIOGRAPHY. RUDOLFI. Bemerkungen ueber den Bau der Briiste. Abhandl. der Berliner Akad. 1831. DONNE, AL. Du lait, etc., en particulier de celui des nourrices. Paris, 1837. COOPER. Anatomy of the Breast. 1839. GUTERBOCK. Ueber die Donneschen Corps granuleux. Miiller's Archiv. 1839. HENLE. Ueber die mikroskop. Bestandth. d. Milch. Froriep's Notizen. 1839. FETZER. Ueber die weiblichen Briiste. Wiirzburg, 1840. NASSE. Ueber die mikroskopischen Bestandtheile der Milch. Miiller's Archiv. 1840. GOODSIR. Anatom. and Pathol. Observations. 1845. REINHARDT. Ueber die Entstehung der Kornchenzellen. Virchow's Archiv. Vol. I. 1847. WILL. Ueber die Milchabsonderung. Erlangen, 1850. LANGER. Ueber den Bau und die Entwickelung der Milchdriise. Denkschr. d. Wien. Akad. 1851. Also article on the Mammary Gland, in Strieker's His- tology. LUSCHKA. Zur Anatomic der Mannl. Brustdriisen. Miiller's Archiv. 1852. ECKHARD. Beitr. zur Anat. u. Phys. 1. Band. 1. Heft. Giessen, 1855. VIRCHOW. Die Cellularpathologie, p. 305. 1859. DUVAL. Du mamelon et de son aureole. Paris, 1861. GRUBER. Ueber die Mannliche Brustdriise. Memoiren d. Petersburger Akad. 1866. STRICKER. Ueber contractile Korper, etc. Sitzber. d. Akad. Wien. Vol. LIII. 1866. ZOCHER. Beitr. zur Anat. u. Phys. d. weibl. Brust. Leipzig, 1869. HENNIG. Beitrag. zur Morphologic der weibl. Milchdriise. Arch. f. Gynakol. Vol. II., p. 331. 1871. Huss. Beitriige zur Entwickelung der Milchdriise beim Menschen, etc. Jenaische Zeitschrift, Vol. VII., 2. 1873. LANGHANS. Die Lymphgefasse der Brustdriisen in ihren Beziehungen zum Krebse. Arch, fiir Gynakologie, Bd. VIII., S. 181. 1875. Also, Zur pathologischen Histologie der weiblichen Brustdriise. Virchow's Archiv, p. 132. Bd. 58. 1873, COYNE. Sur les lacunes lymphatiques de la glande mammaire. Soc. de Biologic. 21. Nov., 1874. Also, Sur les lacunes lymphatiques de la glande mammaire. Gazette Hebdom., p. 775. 1874. DE SINETY. Eecherches sur les globules du lait. Arch, de Phys. 1874. VON BRUNN. Gottinger Nachrichten, No. 19. 1874. LABBE and COYNE. Traite des tumeurs benignes du sein. 1876. BUCHHOLTZ. Das Verhalten der Colostrumkorper, etc. Gottingen, 1877. DE SINETY. Sur le develop, et 1'histol. comp. de la mamelle. Gaz. med. de Paris, No. 6, p. 68. 1877. KOLESSNIKOW. Die Histologie der Milchdriise der Kuh. Virchow's Archiv. Bd. 70, p. 531. 1877. SCHMID, H. Zur Lehre von der Milchsecretion. Wiirzburg, 1877. WENDT. Ueber die Hardersche Driise der Saugethiere. Strassburg, 1877. WINKLER. Bau der Milchdriise. Jahresber. d. Ges. f . Natur. u. Heilkunde. Dres- BIBLIOGRAPHY. 457 den, 1874. Beitr. zur Histol u. Nervenverth. in d. Mamma. Archiv f. Gyna- kol. Vol. XI. 1877. KOLLIKER, TH. Beitrage zur Kenntniss der Brustdriise. Verh. d. phys.-med. Ges. zu Wiirzburg. 1879. RAUBER. Ueber die Absonderung der Milch. Sitzber. d. naturf . Gesel. zu Leip- zig, pp. 30-34. 1879. Also, Bemerkungen ueber den feineren Bau der Milch- druse. Schmidt's Jahrb. 1879. RAUBEII. Ueber den Ursprung der Milch. Leipzig, 1879. BILLROTH. Die Krankheiten der Brustdriisen. Deutsche Chirurgie. Lieferung 41. 1880. PARTSCH. Ueber den feineren Bau der Milchdriise. Breslau, 1880. MOULLIN. The Membrana Propria of the Mammary Gland. Journ. of Anat. and Phys. April, 1881. See also the text-books of Sharpey and Quain, Frey, Kolliker, Krause, and Sappey. INDEX. ACINI of expanded mamma, 444 of liver, 183 of lung, 260 of pancreas, 410 Adenoid tissue, 69 of lymph-glands, 178 Adventitia of capillaries, 148 of arteries, 151, 155 Afferent vessels of kidney, 206 Aglobulie intense, 38 Air-cells of lung, 260 Alcohol and acetic and muriatic acids, 15 and acetic acid mixture, 14, 15 ALIMENTARY CANAL, 386 general considerations, 386 LARGE INTESTINE, 400 blood-vessels of, 401 lymphatics of, 401 ne?ves of, 401 structure of, 400 (ESOPHAGUS, 386 blood-vessels of, 388 fibrous envelope of, 388 layers of, 386 lymphatics of, 388 mucous membrane of, 386 muscular coat of, 387 muscularis mucosse of, 387 nerves of, 388 submucous layer of, 387 RECTUM, 401 sphincter ani of, 401 structure of, 401 SMALL INTESTINE, 394 blood-vessels of, 399 Brunner's glands of, 397 corona tubulorum of, 396 follicles of Lieberkiihn of, 398 glands of, 396 lymphatics of, 399 ALIMENTARY CANAL- SMALL INTESTINE mucous membrane of, 395 muscular coat of, 394 muscularis mucosse of, 396 nerves of, 399 plexus of Auerbach, 399 plexus of Meissner, 399 Peyer's patches of, 396 serous coat of, 394 solitary follicles of, 396 submucous layer of, 396 valvulse conniventes of, 395 villi of, 395 STOMACH, 388 blood-vessels of, 392 compound peptic glands of, 390 etat mamelonne of, 389 lymphatics of, 393 mucous membrane of, 389 muscular coat of, 388 muscularis mucosss of, 389 nerves of, 393 peptic glands of, 389 pyloric glands of, 391 serous covering of, 388 submucous layer of, 389 VERMIFORM APPENDIX, 401 Alizarine, 28 Alum carmine, 27 Alveoli of lung, 260 Ammonia bichromate, 14 Amoeboid movement, 39, 40 Anastomosis of capillaries, 148 Angle of aperture, 11 of lenses, 10 Aperture, angle of, 11 Apparatus, general, for microscopical work, 1, 2, 3, 4 Appendix vermiformis, 401 460 INDEX. Arachnoid, spinal, 297 Archil, staining with French, 28 Arciform fibres of medulla oblongata 394 Areola of mamma, 442 Arnold's borax carmine staining, 22 Arrangement of object, 6 Arteria centralis retinae, 347 hyaloidea, 349 Arteries, 152 Arterioles, 152 Auerbach, intercalated areas of, 147 plexus of, 123, 399 Auricle of ear, 353 Axis-cylinder of nerve-fibres, 110 D ARTHOLINB, glands of, 241 J-* Beale, spiral fibre of, 122 Bed of nail, 294 BIBLIOGRAPHY of alimentary canal, 402 of blood, 54 of blood-vessels, 161 of bone, 101 of brain, 326 of cartilage, 88 of central nervous system, 326 of cerebellum, 326 of connective substances, 81 of ear, 367 of epithelium, 61 of eye, 352 of female organs of generation, 251 of general methods, 32 of kidney, 222 of liver, 199 of lymphatic system, 182 of male organs of generation, 238 of mammary gland, 456 of mouth and tongue, 384 of muscle, 140 of nasal fossae, pharynx, and tonsils, 375 of nervous system, 127 of pancreas, 418 of pituitary body, 419 of respiratory tract, 267 of skin, 295 of spinal cord, 325 of spleen, 418 BIBLIOGRAPHY of teeth, 108 of thymus gland, 419 of thyroid body, 419 of urinary excretory passages and su- prarenal capsules, 437 Bichromate of ammonia, 14 preparation of nerves with, 115 Bichromate of potassium, 14 Bigelow's studies on cartilage, 87 Bile-ducts, 191 Bismark brown, 26 Bladder, 430 BLOOD, 34 amoeboid movements of leucocytes of, 39 Brownian movement in leucocytes of, 39 circulation of, examined during life, 45 curara for paralysis of frogs, 45 globules of, in different fluids, 38 granules of, 39 haematoblasts of, 47 heating slide for the study of, 40 liquor sanguinis, or plasma of, 34 red corpuscles of, 34 action of acids on, 43 of alkalies on, 44 of carbonic acid dn, 42 of distilled water on, 41 of electricity on, 44 of salt solution on, 40 counting of, 48, 53 crenation of, 45 development of, 47 examination of, 47 haemochromometer for estimat- ing richness, 53 haemoglobin of, 53 internal structure of, 46 Keyes's method of counting, 50 Malassez's method of counting, 50 measurement of, 36 number of, 37 stroma of, 46 third corpuscular element of, 48 white or colorless corpuscles of, 48 31ood-corpuscles, nucleated, 95 Blood-crystals, 53 INDEX. 461 BLOOD-VESSELS, 142 methods of injecting, 30 of bladder, 431 of choroid, 337 of cornea, 333 of iris, 343 of kidney, 213 of large intestine, 401 of liver, 186 of lung, 263 of lymph-glands, 179 of mamma, 442 of mouth, 379 of oesophagus, 388 of optic nerve, 349 of ovary, 247 of pancreas, 411 of penis, 224 of retina, 347 of skin, 279 of small intestine, 399 of spinal cord, 298 of spleen, 407 of stomach, 392 of suprarenals, 436 of testis, 234 of thymus, 414 of thyroid, 416 of uterus, 245 ARTERIES, 151 advent! tia of, 151, 155 external elastic coat of, 155 internal elastic coat of, 152 internal fibrous coat of, 153 intima of, 152 media or musculosa of, 154 muscular and elastic types of, 152 ARTERIOLES, 152 CAPILLARIES, anastomosis of, 148 endothelial desquamation, 147 endothelium, 143 genesis, reproduction, and regen- eration of, 150 intercalated areas of, 147 intracellular network, 143 intranuclear network, 143 perithelium or adventitia of, 148 ramification of, 149 structure of, 146 varieties of, 145 COCCYGEAL GLAND OF LUSCHKA, 158 BLOOD-VESSELS- CORPORA CAVERNOSA, 160 general remarks on, 142 INTERCAROTID GLAND, 160 lymphatics of, 161 nerves of, 161 perivascular spaces, 161 varieties of, 142 vasa vasorum, 161 VEINS, 155 distinction between veins, arte- ries, and capillaries, 156 internal elastic coat of, 157 internal fibrous coat of, 157 points of difference from arte- ries, 156 structure of, 156 valves of, 158 venules, 156 Boehmer's hsematoxylon, 23 BONE, 89 cancellous tissue of, 94 chondro-porosis, 98 compact tissue of, 89 corpuscles of, 90 development of, 96, 99 formation of callus in, 100 formation of, from cartilage, 97 from membrane, 98 Haversian canals of, 91 Howship's lacunae of, 100 intermediary cartilage of, 97 lacunae of, 91 lamellae of, 90 marrow of, 95 cells of, 95 myeloplaxes, 95 primary cavities of, 98 red, 95 yellow, 95 metaplastic, 98 naphthaline yellow for staining, 27 osteobtasts, 96, 98 osteoclasts, 100 osteoporosis, 99 periosteal processes of, 94 periosteum of, 95 points of ossification, 98 preparation of, 92 Sharpey's fibres of, 94 varieties of, 89 462 INDEX. Borax carmine, 22 Bowman's capsules of kidney, 204 glands of nose, 372 membrane, 79, 331 Brain, method of hardening, 15 Branched corpuscles of connective tissue, 67 Bronchioles, 260 Bronchi, primary, 257 smaller. 259 Brownian movement, 39 Brunner's glands, 397 Burdach, column of, 298 CALCIFICATION of cartilage, 84 ^ of cartilages of larynx, 255 Callus, formation of, 100 Calyx of kidney, 216 Canal, central, of spinal cord, 301 of Petit, 350 of Schlemm, 336 Canals, dentinal, 104 intermediate, of liver, 184 semicircular, 359 Capillaries, 142 Capillary bile-ducts, 192 Capsule, internal, of brain, 317 of kidney, 216 of liver, 183 of spleen, 404 of suprarenal bodies, 432 of Tenon, 337 of thymus, 412 of thyroid, 415 Capsules, suprarenal, 431 Carmine, alum, 27 CARTILAGE, 82 Bigelow's studies on, 87 capsules of, 82 corpuscles of, 82, 83 division of, 86 structure of, 87 daughter-cells, 84 fibrillation of, 83 fibrous, 86 hyaline, 82 calcification of, 84 methods of studying, 84 intercellular substance of, 83, 87 intermediary, 97 parenchymatous, 83 CARTILAGE perichondrium of, 86 purpurine for staining, 85 reticular or yellow elastic, 85 varieties of, 82 Spina's views on, 87 Cartilages of bronchi, 257 of larynx, 254 Cartilago-triticea of larynx, 253 Caruncula lachrymalis, 330 Cavernous tissue, 160 Cells, giant, 95 of liver, 189 Cellular tissue, 63 Cement of teeth, 105 Central canal of spinal cord, 301 CENTRAL NERVOUS SYSTEM, 296 CEREBELLUM, 317 cells of Purkinje of, 318 corpus dentatum of, 317 cortex of, 319 cerebral ganglia, 319 cerebral ventricles, 319 CEREBRUM, 321 cortex of, 321 convolutions of, 321 fissure of Rolando, 321 of Sylvius, 321 island of Reil, 322 meninges of, 321 minute structure of, 323 cortex of, 323 motor tract of hemispheres, 322 paracentral lobule, 323 choroid plexus, 320 corona radiata, 317 corpus striatum, 319 ependyma, 320 internal capsule, 317 locus cseruleus, 315 niger, 316 medulla oblongata, 307 arciform fibres of, 309 central gray matter of, 308 decussating fibres of, 307 formatio-reticularis of, 308 raphe of, 307 nucleus lenticularis, 316 OLIVARY BODY, 310 glosso-pharyngeal, root of, 313 hypoglossal, nucleus of, 311 INDEX. 463 CENTRAL NERVOUS SYSTEM OLIVARY BODY nucleus and root of abducens nerve, 314 parolivary nucleus of, 311 roots of fifth nerve, 315 upper spinal accessory, nucleus of, 311 optic thalami, 319 pons, 315 spinal arachnoid, 297 spinal cord, 298 amyelinic fibres of, 801 blood-vessels of, 298 central canal of, 301 cervical enlargement of, 304 column of Burdach of, 298 column of Clarke of, 304 column of Goll of, 298 dorsal region of, 304 epithelium of, 301 filum terminale of, 302 general histology of, 298 gray commissure of, 304 gray matter of, 299 lumbar enlargement of, 303 methods of study of, 305 myelinic fibres of, 300 nerve-elements of, 299 neuroglia-cells of, 298 root radicles of, 299 special study of different portions of, 301 white commissure of, 303 white substance of, 299 spinal dura mater, 296 spinal fluid, 297 spinal pia mater, 297 Cerebellum, 317 Cerebral ganglia, 319 meninges, 321 ventricles, 319 Cervical enlargement of spinal cord, 304 Chalice cells, 60 Chamber, moist, 42 Chloride of gold, 28, 29 Chondro-porosis, 98 Choroid coat of eye, 338 plexus, 320 Cilia of eyelids, 328 Ciliary body, 340 Ciliated epithelium, 58 Circle of Haller, 349 Circulation of blood, 45 Circulus venosus of Haller, 442 Clarke, column of, 304 Clitoris, 240 Coats of arteries, 152 Coccygeal gland, 158 Cochlea, 362 Cohnheim's muscular areas, 136 Colostrum, 450 Columnar epithelium, 60 Column of Burdach, 298 of Clarke, 304 of Goll, 298 Columns, muscular, 138 Commissure, gray, of spinal cord, 304 white, of spinal cord, 303 Conjunctiva, 330 fornicis, 329 tarsi, 328 CONNECTIVE SUBSTANCES, 62 branched corpuscles of, 67 corpuscles of, 65 development of, 64, 65 fibrillated, 66 growth and development of, 79 intercellular substance of, 64 lymphoid corpuscles of, 67 of mesentery, 68 plasma-cells of, 67, 74 reticular form of, 66 of liver, 188 of nerves, 126 of skin, 275 Contraction, study of muscular, 135 Convoluted renal tubules, 205 Corium, 277 Cornea, 331 preparation of, 25 Corneal corpuscles, 75 tissue, 75 Corneous layer of skin, 274 Corniculum of larynx, 255 Corona radiata of brain, 317 tubulorum, 316 Corpora cavernosa, 160 Corpus albicans, 250 dentatum cerebelli, 317 luteum, 249 Corpuscles, colostrum, 450 464 INDEX. Corpuscles, corneal, 75 fixed, of cornea, 332 lymphoid, of lymph-glands, 178 of skin, 277 Malpighian, of spleen, 404 of bone, 90 of cartilage, 82, 83 of Donne, 450 of muscle, 136 tactile, 124 of skin, 280 of tendon-tissue, 73 yellow, of mamma, 444 Corpus striatum, 319 Cortex cerebri, 321 Cortex of cerebellum, 319 of kidney, 201 of suprarenal capsules, 432 Corti's membranes, 366 organ, 362, 364 Cowper's glands, 227 Creigh ton's views on the mamma, 445, 446, 454 Crista acustica, 360 spiralis, 364 Crystalline lens, 350 Curara for producing paralysis, 45 Cuticula of teeth, 107 Cylindrical epithelium, 60 Cystic duct, 198 Czermak, interglobular spaces of, 103 DARTOS, 231 Daughter-cells of cartilage, 84 Decidua, 245 Deiter's, protoplasmic processes of, 120 Dentine, 103, 106 Dentinal canals, 104 globules, 104 teeth, 106 Descemet's membrane, 79, 333 Detrusor urinae, 430 Development of blood-corpuscles, 47 of capillaries, 150 of bone, 96 of enamel, 108 of fat-tissue, 168 of hair, 293 of lymphatics. 175 of mamma, 452 of nail, 295 Development of ovary, 250 of pancreas, 412 of sebaceous glands, 286 of spleen, 409 of suprarenals, 436 of sweat-glands, 282 of teeth, 105 of thymus, 414 Diaphragms, 5 Dilator muscle of iris, 342 Direct light, 5 Division of cartilage corpuscle, 84, 186 Double staining with borax carmine and indigo carmine, 22 with cosine and aniline colors, 24 Doyere's eminence, 126 Drusenfeld of mamma, 452 Duct, cystic, 198 of pancreas, 411 thoracic, 174 Ducts, ejaculatory, 235 galactophorous, 441 Ductus communis, 198 Dura mater, spinal, 296 E AR, 353 Eustachian tube, C55 EXTERNAL ear, 353 auricle of, 353 meatus of, 353 membrana tympani of, 354 INTERNAL ear, 357 "auditory teeth" of, 364 cochlea of, 362 Corfci's membrana tectoria of, 366 crista acustica of, 360 crista spiralis of, 364 Henson's prop-cells of, 366 labium tympanicum of, 364 labium vestibulare of, 364 lamina reticularis of, 366 lamina spiralis of, 362 macula acustica of, 360 membrana basilaris of, 364 membrane of Reissner, 3G2 membranous labyrinth of, 358 modiolus of, 362 organ of Corti, 362, 364 otoliths of, 358 recessus internus of, 364 INDEX. 405 EAR- INTERNAL ear saccule of, 358 scala tympani of, 362 scala vestibuli of, 362 semicircular canals of, 359 utricle of, 358 zona pectinata of, 366 MIDDLE ear, 355 glands of, 355 structure of, 355 Ectasia of milk- ducts, 452 Efferent vessels of kidney, 206 Ejaculatory ducts, 235 Elastic fibres of skin, 277 Elastic tissue, 77 fibres of, 77 networks of, 78 of ligamentum nuchse, 79 perforated membrane of, 79 Electricity, action of, on blood, 44 Embedding specimens, 15, 16 Enamel, 102 Enamel organ, primary, 107 secondary, 107 Endoneurium, 126 Endothelium, 80 and stomata of lymphatics, 169 germinating, 1G5 vascular, 143 Eosine, 24, 25 and haematoxylon, 25 Ependyma, 320 Epidermis, 271 Epididymis, 231 Epiglottis, 255 Epineurium, 126 Epithelium, 56 bacteria of, 57 ciliated, 58 columnar or cylindrical, 60 granules of, 61 networks of, 61 pigmented, 58 squamous or flattened, 57 structure of, 61 Epithelium of bladder, 430 of collecting tubules of kidney, 211 of involuted mamma, 446 of looped renal tubules, 210 of lung, 261 30 Epithelium of mamma, 444 of mouth, 377 olfactory, 371 of renal tubules, 206 of spinal cord, 301 of thyroid, 415 Erector pili muscles, 422 Etat mamelojine of stomach, 389 Eustachian tube, 355 Expanded mamma, structure of, 444 External ear, 353 External elastic coat of arteries, 155 EYE, 328 arteria hyaloidea of, 349 caruncula lachrymalis, 330 CILIARY body of, 340 in hypermetropic eye, 342 in myopic eye, 341 CHOROID, 338 blood-vessels of, 339 lamina chorio-capillaris of, 339 lamina suprachoroidea of, 338 nerves of, 340 structure of, 338 CONJUNCTIVA, 330 lymph- spaces of, 331 CORNEA, 331 blood-vessels of, 333 Bowman's membrane of, 331 Descemet's membrane of, 333 fibrae arcuatse of, 332 fixed corpuscles of, 332 lamellse of, 331 nerves of, 333 preparation of, 334 EYELIDS, 328 conjunctiva fornicis, 329 conjunctiva tarsi, 328 cilia of, 328 Meibomian glands of, 329 muscle of Miiller, 329 orbicularis palpebrarum, 328 Eiolani's muscle of, 329 tarsus of, 328 Fontana's space of, 336 IRIS, 342 blood-vessels of, 343 dilator muscle of, 342 ligament of, 336 nerves of, 343 sphincter of, 342 466 INDEX. EYE- IRIS, uvea of, 343 LACHRYMAL gland, 351 glandula Galeni of, 351 glandula Monroi of, 351 LENS, 350 canal of Petit, 350 ligament of, 350 ligamentumpectinatum iridis, 335 OPTIC nerve, 348 blood-vessels of, 349 circle of Haller, 349 neuroglia of, 348 subdural space of, 348 vagina fibrosa of, 348 Orbicularis ciliaris, 340 Ora serrata, 340 RETINA, 343 arteria centralis of, 347 blood-vessels of, 347 ganglion-cell layer of, 344 inner granular layer of, 344 inner nuclear layer of, 345 layer of rods and cones of, 345 macula lutea of, 344, 346 membrana limitans externa of, 345 membrana limitans interna of, 346 outer granular layer of, 345 outer layer of, nuclei of, 345 pars ciliaris of, 347 pigment layer of, 346 preparation of, 347 Schlenim's canal, 336 SOLERA, 337 lamina cribrosa of, 337 perichoroidal space of, 337 structure of, 337 Tenon's capsule of, 337 tunica vasculosa of, 338 venae vorticosae of, 337 vitreous body, 349 fossa patellaris of, 350 TjULLOPIAN TUBES, 246 *- Fat-canals of cutis vera, 421 Fat-cells of skin, 276 Fat-columns of cutis vera, 421 Fat-tissue, 73 Fibrae arcuatss of cornea, 332 Fibres, muscular, 128 Fibrillation of cartilage, 83 Fibrous cartilage, 86 tissue, 66 Filum terminale of spinal cord, 302 Finibriss of tongue, 380 Fissure of Rolando, 321 of Sylvius, 321 Fluid, spinal, 297 Follicles of Lieberkiihn, 398 of lymph-glands, 176 of thymus, 412 Fontana's spaces, 336 Foramen caecum of tongue, 383 Formation of bone, 97 of callus, 100 Formatio reticularis of medulla oblongata, 308 Fossae nasales, 368 Freezing section-cutter, 17 French archil, 28 Frog's bladder, muscle of, 129 Frommann's lines, 113 ALACTOBLASTS, 451 Galactophorous ducts, 441 GaU-bladder, 197 Ganglia, cerebral, 319 Ganglia of spinal cord, 120 Ganglionic bodies, 119, 121 corpuscles of brain, 72 Gas-chamber, 43 Gelatinous tissue, 63 Genital organs, female, 240 male, 223 Germinating eudothelium, 165 Giant-cells, 95 Gibbes' double, triple, and quadruple staining, 26 Griraldes, organ of, 231 Grland, coccygeal, 158 inter-carotid, 160 lachrymal, 351 pineal, 417 thymus, 412 thyroid, 415 Grlands, Bowman's, of nose, 372 lymphatic, 176 Meibomian, 329 INDEX. 467 Glands of Bartholine, 241 of bile-ducts, 101 of bronchi, 258 of Brunner, 397 of Cowper, 227 of larynx, 256 of middle ear, 355 of small intestine, 366 of tongue, 383 peptic, 389 pyloric, 391 sebaceous, of skin, 285 sudoriparous, 282 Glans clitoridis, 241 penis, 224 Glandules aberrantes mammas, 442 Glandula Galeni, 351 Monroi, 351 Glandules of mouth, 378 Glisson's capsule, 183 Glosso-pharyngeal root, 313 Goblet cells, 60 Gold, chloride of, 28 Goll, column of, 298 Graafian follicles, 248 Granular layer of skin, 274 Gray matter of spinal cord, 299 Green coloration of nuclei, 25 Growth, post-embryonal, of mamma, 453 TT^EMACHROMOMETER, 53 H Haemoglobin, .53 Haematoblasts, 47 Haematometers, 50, 53 Hsematoxylon, preparation of nerves in, 118 solution, 23, 24 Hailes's microtome, 19, 20 Hair, 288 Haller, circle of, 349 circulus venosus of, 442 Hamilton's preservative fluid, 20 Hand section-cutter, 16 Hardening of brain, 15 Haversian canals of bone, 91 Heart, muscular fibres of, 140 Heidenhain, rods of, 207 Henson's prop-cells, 366 Hepatic artery, 186 cells, 189 Hints regarding study of mamma, 455 Horny teeth, 106 Howship's lacunae, 100 Hyaline cartilage, 82 Hydatid of Morgagni, 231 Hymen, 241 Hypermetropia, ciliary body in, 342 Hypoglossal nucleus, 311 TLLUMINATION, 4 * Induline, 27 Infundibula of lung, 260 Injecting fluids, 30, 32 Injection of blood-vessels, 30, 31, 32 of cutis vera, 424 of kidney, 214 of liver, 185 of lymph-glands. 179 of lymphatics, 169 Instrument, care of, 7 Intercarotid gland, 160 Intercalated portions of renal tubules, 211 Intercellular substance of cartilage, 83 of connective tissue, 64 Intermuscular tissue, 74 Internal capsule of brain, 317 Internal elastic coat of arteries, 152 of veins, 157 Internal ear, 357 Internal fibrous coat of arteries, 153 of veins, 157 Intima of arteries, 152 Invertebrates, muscle of, 133 Involuntary muscle-fibre, 128 Involuted mamma, histology of, 446 Iodized serum, 38 Irrigation, method of, 41, 67 Iris, 342 diaphragm, 5 Island of Reil, 322 Ivory, 103 YARYOKINESIS, 237 - Keyes's method of counting blood- globules, 51 KIDNEY, 201 afferent vessel of, capsule of, 206 blood-vessels of, 213 Bowman's capsules of, 204 calyx of, 216 468 INDEX. KIDNEY capsule of, 216 collecting tubules of, 205 convoluted tubes of, 205 efferent vessel of capsules of, 206 epithelium of collecting tubules, 211 of looped tubules of, 210 of tubules of, 206 general plan of structure of, 201 boundary layer, 201 cortex, 201 medulla, 201 medullary rays, 201 injection of, 214 intercalated portions of tubules of, 211 looped tubules of, 209 lymphatics of, 216 membrana propria of tubules of, 203 method of preparing sections of, 208 natural injection of tubules of, 216, 220 nerves of, 216 rods of Heidenhain, 207 stroma of, 215 tubules of, 203 vasa recta of, 214 Kleinenburg's hasmatoxylon, 23 Klein's hsematoxylon, 24 Klein's method of studying the omentuni, 166 Kuhnt, hohlcylinder of, 114 LABIA MAJORA, 240 minora, 240 Labium tympanicum, 364 vestibulare, 364 Labyrinth, 358 Lachrymal gland, 351 Lacunae, Howship's, 100 Lacunas of bone, 91 Lamellse of bone, 90 Lamina chorio-capillaris, 339 cribrosa of solera, 337 reticularis of ear, 366 spiral is, 362 suprachoroidea, 338 Large intestine, 400 Larynx, 253 Lens, 350 Lenses, high, testing of, 10 kinds of, 6 measuring angle of, 10 testing of, 8 Leucocytes, 39, 48 Lieberkiihn's follicles, 398 Ligament of iris, 336 of lens, 350 Ligaments of larynx, 253 Ligamentum pectinatum iridis, 335 Light, direct, 5 oblique, 5 Liquor sanguinis, 34 LIVER, 183 acini of, 183 bile-ducts, capillary, 192 Mayer's views on, 196, 197 natural injection of, 193 walls of, 196 bile -ducts, larger, 191 blood-vessels of, 186 capsule of, 183 cells of, 189 central veins of, 184 connective tissue of, 188 cystic duct, 198 ductus communis, 198 fat-droplets in cells of, 190 gall-bladder, 197 coats of, 198 glands of bile-ducts, 191 Glisson's capsule of, 183 general plan of structure of, 183 hepatic artery, 186 hepatic lobules, 183 injection of, 185 inter lobular septa of, 188 interlobular veins of, 184 intermediate canals of, 184 intralobular veins of, 184 lymph-vessels of, 198 nerves of, 199 sublobular veins of, 185 Lobule, paracentral, 323 Lobules of liver, 183 Lobulettes of lung, 260 Locus cseruleus, 315 niger, 316 Looped renal tubules, 207 Lumbar enlargement of spinal cord, 303 Lungs, 257 INDEX. 469 Lunula of nails, 294 Luschka's gland, 158 Lymphangeal nodules, 167 tracts, 167 Lymphatic glands, 176 Lymphatics of bladder, 431 of blood-vessels, 161 of kidney, 216 of large intestine, 401 of larynx, 257 of liver, 198 of lung, 264 of mamma, 443 of mouth, 379 of oesophagus, 388 of pancreas, 411 of small intestine, 399 of spleen, 409 of stomach, 393 of suprarenals, 436 of testis, 234 of thymus, 414 of thyroid, 416 LYMPHATIC SYSTEM, 163 artificial injection of lymphatics, 169 cysternse lymphaticse, 170 development of fat-tissue, 168 endolymphangeal tracts, 167 endothelium and stomata, 169 general histology of, 164 germinating endothelium of, 165 glands of, 175 adenoid or reticular tissue of, 178 afferent and efferent branches of, 176 follicles of, 176 injection of, 179 lymphoid corpuscles of, 178 medulla and cortex of, 176 methods of studying, 179 nerves of, 179 Ranvier's plan of injection of, 180 sinuses of, 177 stroma of, 176 vessels of, 179 Klein's method of studying omentum, 1G6 lymphangeal nodules or patches of, 167 lymphangeal tracts of, 167 LYMPHATIC SYSTEM lymphatic radicles, course and ter- mination of, 168 lymphatics, 175 development of, 175 of mesentery, 165 of tendons, 175 lymphatic vessels, 172 intimate structure of, 172 topographical peculiarities of, 174 variations in shape of, 173 lymph-spaces, 175 subarachnoid and subdural, 175 modern views on, 163 nerves of peritoneum, 172 perilymphangeal tracts, 167 plasma-cells, 164 plasmatic channels, 165 pseudo-stomata, 171 Ranvier's t aches laiteuses, 168 views on false stomata, 170 relations to connective tissues, 163 retrospective view of, 181 sap-canaliculi of, 165 stomata of, 165 stomata vera of, 171 thoracic duct, 174 Lymphoid cells of brain, 72 Lymphoid corpuscles of connective tissue, 67 of lymph-glands, 178 of skin, 277 Lymph-spaces, subarachnoid, 175 Lymph-vessels of penis, 224 MACULA ACUSTICA, 360 lutea, 344, 346 Malassez's method of counting blood-cor- puscles, 50 Malpighian corpuscles of spleen, 404 layer of skin, 271 Mammary epithelium, 444 MAMMARY GLAND, 439 areola of, 442 blood-vessels of, 442 circulus venosus of Haller of, 442 colostrum bodies, or corpuscles of Donne, 450 development of, 452 Driisenfeld, 452 470 INDEX. MAMMARY GLAND ectasia of miik-ducts, 452 galactoblasts of, 451 galactophorous ducts of, 441 general considerations on, 439 glandulas aberrantes of, 442 growth of, 453 Creighton's views on, 454 Harderian g-land, similarity with, 449 lymphatics of, 443 membrana propria of, 449 milk-globules, 451 milk-reservoirs of, 441 nerves of, 443 nipple or mamilla of, 440 Partsch's views on milk-secretion, 451 Rauber's views on the mamma and the lacteal secretion, 450 structure of fully expanded gland, 444 acini of, 444 Creighton's views on, 445 epithelium of, 444 plasma-cells of, 444 yellow cells of, 444 structure of involuted mamma, 446 Creighton's account of, 446 epithelium of, 446 vacuolation of epithelium of, 447 study of, 455 St&iezeUen of, 449 Wendt's views on secretion of milk, 449, 451 Mammilla, 440 Marrow of bone, 95 Measurement of red blood-corpuscles, 35 Meatus auditorius externus, 353 urinarius of female, 242 of male, 226 Media or musculosa of arteries, 154 Medulla of suprarenal capsules, 435 oblongata, 307 of kidney, 201 Medullary rays of kidney, 201 Meibomian glands, 329 Meissner's plexus, 122, 399 Mernbrana basilaris of ear, 364 limitans olfactoria, 372 propria of mamma, 449 propria of renal tubules, 203 tectoria of ear, 366 tympani, 354 Membrane of Bowman, 79 of Corti, 366 of Descemet, 79 of Reissner, 3G2 Meninges of brain, 321 of spinal cord, 296 Metallic solutions, 28, 29 Metaplastic bone, 98 Methods for preparing objects, 12 of preparing tissues, 14 of studying hyaline cartilage, 84 of studying spinal cord, 305 Methyl -green, 29 and induline, 27 Micrometer, stage, 7 Microscope, how to use, 4 testing of, 7 Microtome, Hailes', 19, 20 Vincent's, 21 Middle ear, 355 Milk-ducts, 444 Milk-globules, 451 Milk- reservoirs, 441 i Miller's picro-carmine, 23 i Mirrors, 5 | Modiolus, 362 Moist chamber, 42, 43 Molybdate of ammonia, 15 Morgagni, hydatid of, 231 Motor tract of hemispheres, 322 MOUTH AND TONGUE, 377 MOUTH, 377 blood-vessels of, 379 epithelium of, 377 glandules of, 378 lymphatics of, 379 nerves of, 379 submucous tissue of, 377 tunica propria of, 377 TONGUE, 380 circumvallate papillae of, 383 glands of, 383 filiform papillas of, 380 fimbrige of, 380 foramen coecum of, 383 fungiform papillae of, 381 papillse foliatae of, 383 taste-goblets of, 381 Mucous membrane of larynx, 255 of oesophagus, 386 of small intestine, 395 INDEX. 471 Mucous membrane of stomach, 389 Mucous tissue, 63 Muscle, 128 Cohnheim's areas of, 136 columns of, 138 conclusions regarding structure of, 137 fibres of, 128 of frog's bladder, 129 of fly, 133 of heart, 140 of human embryo, 132 of invertebrates, 133 of the ' ' lucky bug " or gyrinus, 134 of water-beetles, 133 involuntary, 128 nuclei and corpuscles of, 136 peculiarities of, associated with differ- ent functions, 138 polarized light for the study of, 137 red and white, of rabbit's leg, 138 sarcolemma, 130 striation of fresh, fibre, 131 study of contraction of, 135 termination of, in tendon, 139 transverse sections of, 136 vascular supply of, 138 voluntary fibre, 130 of Mailer, 329 of Riolani, 329 termination of nerves in, 125 Muscles of skin. 287 Muscular coat of oesophagus, 387 of small intestine, 394 of stomach, 388 fibres of heart, 140 Muscularis mucosse of oesophagus, 387 of small intestine, 396 of stomach, 389 Musculosa of arteries, 154 Mailer's fluid, 14 muscle, 329 Myelinic fibres of spinal cord, 301 nerve-fibres, 109, 116 Myeloplaxes, 95 Myopia, ciliary body in, 341 NABOTH, ovula of, 244 Nail-fold, 294 Nails, 293 Naphthaline yellow, 27 NASAL FOSSAE, PHARYNX, and TON- SILS, 368 NASAL FOSSAE, 368 Bowman's glands of, 372 indifferent cells of, 371 membrana limitans, olfactoria of, 372 mucous membrane of, 368 olfactory cells of, 371 olfactory epithelium of, 371 olfactory nerves of, 372 olfactory region of, 370 thicker membrane of, 369 thinner membrane of, 369 respiratory region of, 368 vestibulum nasi, 368 PHARYNX, 373 mucous membrane of, 373 pharyngeal tonsil of, 373 TONSILS, 373 i Natural injection of liver, 193 of kidney, 216, 220 Nerve-elements of spinal cord, 299 Nerve-fibres, varieties of, 109 Nerves of bladder, 431 of blood-vessels, 161 of choroid, 340 of cornea, 333 of iris, 343 of kidney, 216 of large intestine, 401 of larynx, 257 of liver, 199 of lung, 265 of lymph-glands, 179 of mamma, 443 of mouth, 379 of ossophagus, 388 of ovary, 248 of pancreas, 411 of penis, 225 of peritoneum, 172 of skin, 279 of small intestine, 399 of spleen, 409 of stomach, 393 of suprarenals, 436 of thyroid, 416 of uterus, 245 olfactory, 372 Nerve -terminations, 109 472 INDEX. NERVOUS SYSTEM, 109 Auerbach's plexus, 123 axis-cylinder, 110 connective tissue of nerves, 126 Deiter's protoplasmic processes, 120 Doyere's eminence, 126 endoneurium, 125 epineurium, 126 fibres of Remak, 117, 118 preparation of, in hsematoxylon, 118 Frommann's lines, 113 ganglia of cranial and spinal nerves, 120 ganglia of spinal cord, examination of, 120 gang] ionic bodies, 119 of human brain, 121 of sympathetic system, 121 Gasserian ganglion, examination of, in frog, 120 general histology of, 109 hoJdcyliuder of Kuhnt, 114 incisions of Schmidt, 111 Meissner's plexus, 122 methods of nerve-termination, 109 motorial plate, 126 myelinic fibres, 109 nerves, modern conceptions of, 116 myeline or medulla, 110 Pacinian bodies, 124 perineurium, 127 preparation by bichromate of am- monia, 115 preparation in osmic acid and picro- carmine, 118 Ranvier's nodes, 110 sheath of Schwann, 110 spiral fibre of Beale, 122 staining of, in osmic acid, 113 staining of, in picro-carmine, 111 staining of, with silver nitrate, 112 tactile corpuscles, 124 termination of nerves, 123 in muscle, 125 in epithelial bodies, 126 varieties of nerve-fibres, 109 Nervous system, central, 296 Network of epithelial cells, 61 Neumann, dentinal sheath of, 104 Neuroglia, 70, 71 fibrillse of, 72 of optic nerve, 348 of spinal cord, 298 Nipple, 440 Nitrate of silver, 29 staining of nerves with, 112 Norris and Shakespeare's method of dou- ble staining, 22 Nose, 368 Nose-piece, 5 Nuclei, green coloration of, 25 of muscle, 136 Nucleus and root of abducens, 314 lenticularis of brain, 316 of hypoglossus, 311 parolivary, 311 OBJECT, arrangement of, 6 size of. 8 Oblique light, 5 Odontoblasts, 104 Odontomata, 105 CEsophagus, 386 Olfactory epithelium, 371 nerves, 372 region, 370 Olivary body, 310 Optic nerve, 348 thalami, 319 Ora serrata, 340 Orbicularis ciliaris. 340 palpebrarum, 328 Organ of Corti, 362, 364 of Giraldes, 231 ORGANS OF GENERATION, FEMALE, 240 CLITORIS, 240 corpora cavernosa of, 241 genital nerve corpuscles of, 240 glans of. 241 GLANDS OF BARTHOLINB, 241 HYMEN, 241 FALLOPIAN TUBES, 246 ampulla of, 246 fimbriffi of, 246 isthmus of, 246 LABIA MAJORA, 240 LABIA MINORA, 240 INDEX. 473 ORGANS OF GENERATION, FEMALE OVARY, 246 blood-vessels of, 247 corpus albicans of, 250 corpus luteum of, 249 development of, 250 Graafian follicles of, 248 nerves of, 248 stroma of, 246 tubes of, 246 PAROVARIUM, 250 PLACENTA, 251 URETHRA, 242 meatus urinarius of, 242 UTERUS changes of, during menstruation and gestation, 245 decidua, 245 glands of, 244 mucous membrane of, 248 plicae palmatae of, 243 nerves of, 245 os uteri, 244 ovula Nabothi, 244 vessels of, 245 VAGINA, 241 vascular system of, 242 VESTIBULE, 241 bulbi vestibuli, 241 ORGANS OF GENERATION, MALE, 223 COWPER'S GLANDS, 227 EPIDIDYMIS, 231 blood-vessels of, 234 EJACULATORY DUCTS, 235 HYDATID OP MORGAGNI, 231 karyokiuesis, 237 ORGAN OF GIRALDES, 231 PENIS, 223 blood-vessels of, 224 genital nerve-corpuscles of, 225 glans penis, 224 lymph-vessels of, 224 nerves of, 225 tunica albuginea of, 223 Tyson's glands of, 224 PROSTATE GLAND, 227 acini of, 228 blood-vessels of, 229 epithelium of, 228 nerves of, 229 vesicula prostatica of, 229 ORGANS OF GENERATION, MALE SCROTUM, 231 dartos of, 231 semen or sperma, 235 seminal vesicles, 235 spermatoblasts, 236 SPERMATOZOA, 225 structure of, 236 development of, 236 TESTICLES, 229 blood-vessels of, 234 corpus Highmori of, 230 lymphatics of, 234 mediastinum of, 230 nerves of, 234 rete testis, 231 seminiferous tubules of, 231, 2H3 septula of, 230 tunica adnata of, 230 tunica albuginea of, 230 tunica vaginalis communis of, 230 URETHRA, 225 colliculus seminalis of, 225 lacunas Morgagnii of, 226 lymphatics of, 227 meatus urinarius of, 226 membranous portion of, 226 musculus urethralis of, 226 nerves of, 226 papillae of, 226 prostatic portion of, 225 spongy portion of, 226 structure of, 225 vas aberrans, 232 VAS DEPERENS, 232, 233 ampulla of, 232 muscular coat of, 234 nerves of, 234 Organs of respiration, 253 Osmic acid, staining of nerves with, 113 Osmic acid and picro-carmine, preparation of nerves in, 118 Osmic and chromic acids, 15 Osmic and oxalic acids, staining with, 28 Ossification, points of, 98 Osteoblasts, 96, 98 Osteoclasts, 100 Osteo- or vaso-dentine, 105 Osteoporosis. 9 Os uteri, 244 Otoliths, 358 474 INDEX. Ovary, 246 Oviducts, 246 Ovula Nabothi, 244 PACINIAN BODIES, 134 *- PANCREAS, 410 acini of, 420 blood-vessels of, 411 centro-acinal cells of, 411 development of, 412 excretory duct of, 411 lymphatics of, 411 nerves of, 411 trypsin, 410 zymogen, 410 Panniculus adiposus, 277 Papillse of cutis vera, 421 of hair, 289 of tongue, 380 Papillary sphincter, 429 Paracentral lobule, 323 Parenchymatous cartilage, 83 Parolivary nucleus, 311 Parovarium, 250 Partsch's views on secretion of milk, 451 Pavement endothelium, 80 Pelvis, renal, 428 Penis, 223 Peptic glands, 389 Perichondrium, 86 Perineurium, 126 Periodontium, 108 Periosteum, 95 Perithelium, 148 Peri vascular spaces, 161 Petit, canal of, 350 Peyer's patches, 396 Pharyngeal tonsil, 373 Pharynx, 873 Pia mater, spinal, 297 Picro-carmine. 23 staining of nerve-fibres with, 111 Picro-haematoxylon and eosine, 26 Pigmented epithelium, 58 Pigment of retina, 346 Pineal gland, 417 Pituitary body, 417 Placenta, 251 Plasma, 34 cells, 164 Plasma of connective tissue, 67 of mamma, 444 Plasmatic channels, 165 Pleura, 265 Pleural appendages, 267 Plexus, choroid, 320 of Auerbach, 399 of Meissner, 399 Polarized light in the study of muscle, 137 Pons varolii, 315 Potassium bichromate solution, 14 Preparation of bone, 92 of cornea, 334 of fresh object, 13 of tissues, 13, 14 of mamma, 455 of microscopic objects, 12 of retina, 347 spleen, 409 Preserving fluid, Wickersheimer's, 29 Preservative fluid, Hamilton's, 20 Prickle cells, 58 of skin, 272 Prop-cells, Henson's, 366 Prostate gland, 227 Pseudostomata, 171 of pulmonary lymphatics, 264 Pulp of spleen, 406 of teeth, 102, 105 Purpurine for staining cartilage, 85 Purkinje, cells of, 318 granular layer of, 104 Purpurine, 28 Pyloric glands, 391 T) ADICLES of lymphatics, 168 -t^ Ramification of capillaries, 149 Ranvier's nodes, 110 purpurine, 28 tacJies laiteuses, 168 Raphe of medulla oblongata, 309 \ Rauber's views on the mamma, 450 j Rectum, 401 i Red blood-corpuscles, 34 Reil, island of, 322 Reissner, membrane of, 362 Remak, fibres of, 117 Renal pelvis, 428 tubules, 203 INDEX. 475 RESPIRATORY TRACT, 253 LARYNX, 253 calcification of cartilages of, 255 cartilages of, 254 cartilago triticea of, 253 corniculum of, 255 epiglottis of, 255 glands of, 256 ligaments and membranes of, 253 lymphatics of, 257 mucous membrane of, 255 nerves of, 257 Santorini's cartilages of, 255 vocal cords of, 254 Wrisberg's cartilages of, 255 LUNGS, 259 acini or lobulettes of, 260 alveolar passages of, 260 alveoli or air-cells of, 260 blood-vessels of, 263 bronchioles of, 260 epithelium of alveoli of, 261 infundibula of, 260 lymphatics of, 264 nerves of, 265 pleural appendages, 267 pleura of, 265 pseudostomata of lymphatics of, 264 septa of, 262 smaller bronchi, 259 subpleural lymphatics, 237 terminal arteries of, 263 TRACHEA and PRIMARY BRONCHI, 257 cartilage rings of, 257 glands of, 258 mucous membrane of, 257 Rete Malpighii, 271 Reticular or yellow elastic cartilage, 85 Reticular form of connective-tissue, 66 Retina, 342 Retzius, stripes of, 103 Riolani's muscle, 329 Rolando, fissure of, 321 Root of hair, 283, 292 of nail, 294 a ACCITLE of labyrinth, 358 ^ Salter, incremental lines of, 105 Santorini's cartilage, 255 Sap-canaliculi, 165 Sarcolemma, 130 Sattertbwaite's section-cutter, 17 Scala tympani, 362 vestibuli, 362 Scales of epidermis, 275 Schlemm's canal, 336 Schmidt, incisures of, 111 Schreger, lines of, 105 Schwann, sheath of, 110 Sclera, 337 Scrotum, 231 Sebaceous glands, 285 Section-cutters, 16, 17 Semen, 235 Semicircular canals, 359 Seminal vesicles, 235 Seminiferous tubules, 231 Septa of lung, 262 Shaft of hair, 288, 292 Sharpey's fibres of bone, 94 Sheath of Schwann, 110 Sheaths of hair, 289 Silver, nitrate of, 29 Sinuses of lymph-glands, 177 Size of object, 8 SKIN, 269 blood-vessels of, 279 CORIUM OF, 277 pars papillaris, 278 pars reticularis of, 278 corneous layer of, 274 elastic tissue fibres of, 277 epidermic scales, 275 EPIDERMIS, 271 general plan of arrangement of, 269 general structure of, 270 granular layer of, 274 HAIR, 288 development of, 293 papillae of, 289 root of, 288, 292 shaft of, 288, 292 sheaths of, 289 lymph oid corpuscles of, 277 muscles of, 287 NAILS, 293 bed of, 294 body of, 294 development of, 294 lunula of, 294 476 INDEX. SKIN- NAILS nail and fold, 294 root of, 294: nerves of, 279 panniculus adiposus of, 276 rete Malpighii, 271 prickle cells of, 272 SEBACEOUS GLANDS OF, 285 development of, 286 stratum lucidum of, 274 stratum subpapillare of, 279 subcutaneous connective-tissue layer of, 278 fat-cells of, 276 SWEAT-GLANDS OF, 283 development of, 285 tactile corpuscles of, 280 Slide for heating, 40 Small intestine, 394 Sperma, 235 Spermatoblasts, 236 Spermatozoa, 235 Sphincter of iris, 342 ani, 401 papillary, 429 vesicge, 430 Spinal cord, 298 fluid, 397 Spina's views on cartilage, 87 SPLEEN, 403 blood-vessels of, 407 development of, 409 fibrous coat or capsule of, 404 general structure of, 403 lymphatics of, 409 Malpighian corpuscles of, 404 nerves of, 409 preparation of, 409 pnlp of, 406 serous coat of, 403 Squamous epithelium, 57 Stage diaphragms, 5 micrometer, 7 Stevenson, plan of imbedding, 1C Stomach, 388 Stomata of lymph-vessels, 165 vera, 171 Stratum intermedium of tooth, 108 lucidum of skin, 274 subpapillare of skin, 279 Striation of muscle, 331 Stroma of kidney, 215 Stutzzellen of mamma, 449 Subdural spaces of optic nerve, 348 Submucous layer of oesophagus, 387 of small intestine, 396 of stomach, 389 Subpleural lymphatics, 267 Sudoriferous glands, 282 SUPRARENAL CAPSULES, 431 blood-vessels of, 436 capsule of, 432 cortical substance of, 432 external layer of, 433 internal layer of, 435 middle layer of, 433 zona fasciculata of, 433 zona glomerulosa of, 433 zona reticularis of, 436 development of, 436 lymphatics of, 436 medullary substance of, 435 nerves of, 436 Sweat-glands, 282 Sylvian fissure, 321 Sympexions of thyroid, 415 mACTILE CORPUSCLES, 124 * Tarsus of eye, 328 Taste-globlets of tongue, 381 TEETH, 102 cement of, 105 dentinal canals of, 104 dentinal globules of, 104 dentinal fibres of tomes, 104 dentinal sheath of Neumann, 1 04 dentine or ivory, 103 development of, 105 cuticula, 107 dentinal teeth, 106 dentine, 106 horny teeth, 106 primary enamel organ, 107 secondary enamel organ. 107 stratum intermedium of, 108 tooth papilla, 107 tooth-sac, 107 development of enamel of, 108 enamel, 102 granular layer of Purkinje, 104 INDEX. 477 TEETH incremental lines of Salter, 105 interglobular spaces of Czermak, 103 interglobular substance, 105 lines of Schreger, 105 parallel stripes of Retzius, 103 parts of, 102 periodontium of, 108 pulp of, 102, 105 odontoblasts, 104 odontomata, 105 osteo- or vaso-dentine, 105 Tendons, lymphatics of, 175 Tendon-tissue, 72 Tenon's capsule, 337 Termination of muscle in tendon, 139 Testicles, 229 Testing lenses, 8, 10 microscope, 7 Thalami optici, 319 THICK CUTIS VERA, 420 blood-vessels of, 423 erector pili muscles of. 422 fat-columns or fat-canals of, 421 fibrous prolongations of, 420 injection of, 424 lymphatics of, 424 papillse of, 421 Third corpuscular element of blood, 48 Thoracic duct, 174 THYMUS GLAND, 412 blood-vessels of, 414 capsule of, 412 cells of, 413 central canal of, 414 development of, 414 follicles of, 412 lymphatics of, 414 thymic juice of, 413 THYROID BODY, 415 blood-vessels of, 416 capsule of, 415 epithelium of, 415 lymphatics of, 416 nerves of, 416 sympexions of, 416 vesicles of, 415 Tissue, adenoid, 69 cellular, 63 connective, 63 corneal, 75 Tissue, elastic, 77 fat, 73 fibrous, 66 gelatinous, 63 intermuscular, 74 mucous, 63 tendon, 72 Tissue, compact, of bone, 89 Tomes, dentinal fibres of, 104 Tongue, 380 Tooth-sac, 107 Tonsil, pharyngeal, 373 Tonsils, 373 Trachea, 257 Triple staining, 26 Trypsin, 410 Tubules of kidney, 203 Tubules, seminiferous, 231 Tunica vasculosa of solera, 338 Tympanum, 354 Types of arteries, 152 Tyson's glands, 224 TTRETERS, 429 <~> Urethra, female, 243 male, 225 URINARY EXCRETORY PASSAGES, 428 BLADDER, 430 blood-vessels of, 431 epithelium of, 430 connective tissue of, 430 detrusor urinas of, 430 lymphatics of, 431 muscular coat of, 430 nerves of, 431 sphincter vesicae, 430 RENAL PELVIS, 428 fibrous layer of, 429 mucous membrane of, 428 muscular coat of, 429 papillary sphincter of, 429 vessels and nerves of, 429 URETERS, 429 mucous membrane of, 429 muscular layers of, 429 vessels and nerves of, 429 Uterus, 243 Utricle of labyrinth, 358 Urea, 343 478 INDEX. TTACUOLATION of mammary epithe- V liurn, 447 Vagina, 241 Valves of veins, 158 Valvulae conniventes, 395 Vas aberrans, 232 Vasa recta of kidney, 214 Vas deferens, 232 Vasa vasorum, 161 Veins, 156 central, of liver, 184 interlobular, of liver, 1 84 intralobular, of liver, 184 sublobular, of liver, 185 Venge vorticosae of sclera, 337 Ventricles of brain, 319 Venules, 156 Vermiform appendix, 401 Vertebrates, muscle of, 130 Vesical epithelium, 430 Vesiculas seminales, 235 Vessels of muscle, 138 Vestibule of vagina, 241 Vestibulum nasi, 368 Villi of intestine, 395 Vincent's microtome, 21 Violet de Paris, 29 Vitreous body, 349 Vocal cords, 254 Voluntary muscle -fibre, 130 TIT ARM-SLIDE, 40 Waxy change, methyl-gieen for, 29 Wendt, method of triple staining, 26 views on endothelial desquamaticn, 147 views on secretion of milk, 449, 451 White blood-globules, 39, 48 White substance of spinal cord, 299 Wickersheimer's preserving fluid, 29 Wrisberg's cartilage, 255 W CELLS of mamma, 444-. I70NA FASCICULATA of suprarenals, ^ 433 glomerulosa, 433 reticularis, 433 pectinata of ear, 366 Zymogen, 410