Histology

HISTOLOGY. Contents: Divisions of H......................260 Historical development of H.............260 Modern H...................265 Development of Russian H................267 Histological laboratory..........269 Teaching of H..................270 Histology (from Greek histos-tissue and logos-science), literally the science of tissues (German Gewebelehre). The name H. was first proposed by C. Mayer in 1819 and introduced into use by Heusinger, a follower of Bich, who in 1822 wrote "System of Histology." Heusinger defined H. as "the doctrine of the structure (textur) of the so-called basic systems or tissues of the animal body, as well as the causes and laws of their normal and abnormal development." At this time, the study of tissues was carried out without the aid of a microscope, and the animal cell was still unknown, but one of the first guides to H. after Schwann, compiled by Kölliker in 1850, was already titled "Mikroskopische Anatomie oder Gewebelehre des Menschen" (Vol. I-III, Leipzig, 1850-54) and covered not only tissues but also the cell and organs. Kölliker remained to the end of his days a representative of the strictly morphological direction in H.; he wrote: "To describe the simplest formed parts and to find the laws of their structure and development-to this alone does H. aspire, and not to be a doctrine of elementary parts in general" ("Histologische Mitteilungen", Würzburg, 1889). Most German histologists adhered to this direction until recently; on the other hand, many French authors-Ranvier, Duval, Prenant, as well as Russians-Ognev, Maximov, and among Germans, O. Hertwig-considered it necessary to include chemistry and physiology of the cell and tissues in the scope of H., in other words, they treated H. as histophysiology or even as cell biology. In the last decade, these views have become widespread in Germany as well, and the term histophysiology has gained general acceptance. Divisions of histology. Normal histology is divided into the following parts: 1) the doctrine of the cell, otherwise cytology, 2) the doctrine of tissues, the so-called general H. (sometimes this name is applied to the first two divisions together), 3) the doctrine of organs-special H. or microscopic anatomy in the narrow sense. H. also includes the description of the development and differentiation of tissues and organs during the development of the organism-histogenesis (see), whereas the initial formation and organization of organs belong to the field of embryology (see).- Comparative H. sets as its task the comparative study of cells, tissues, and organs of all classes of invertebrates and vertebrates with the aim of deriving general laws concerning their fine structure. This science is in its infancy, although its foundations were laid in the 1850s of the 19th century, and since then a vast amount of material has been accumulated. Of the general laws, only two have been outlined so far: the principle of phylogenetic development of tissues (Haeckel) and the principle of structural parallelism (Rath and Zavarzin).- Histochemistry studies the chemical composition of cells and tissues.- Histophysics deals with the physical properties of tissues: hardness, elasticity, resistance to tearing, optical properties (double refraction), as well as the trajectory structures of certain organs: cartilage, bone, muscle. This area of histological research is also called physical anatomy (Triepel)-however, the study of trajectory structures is referred to as "mechanics of development" (see Embryology).- Histomechanics is a name proposed by Thoma to denote the purely mechanical influence of the blood flow on the formation of the vascular network during development. This name did not take hold in science, and works of a similar nature are also referred to the field of "mechanics of development". Historical development of H. As an independent science, histology began to exist only in the 19th century, but it was developed from ancient times, and the material related to it was partly included in anatomy and partly in physiology as separate chapters. The history of histological knowledge is closely connected with the main "means of production" of H.-the microscope, and can be divided into 4 periods. 1st period: H. without a microscope (from the 4th century B.C. to the 17th century). H. at this time was the doctrine of the simple, or "homogeneous" parts of the organism, which were later given the name tissues. The first scientific dissection of the organism was made by Aristotle (4th century B.C.) in his work "On the Parts of Animals." He differentiated- HISTOLOGY

Histology (from the Greek histos - tissue and logos - doctrine) is the science of the structure of tissues and organs of living beings. The term "histology" was introduced by the French scientist Bichat at the end of the 18th century. The development of histology is closely connected with the development of microscopy. The history of histology can be divided into four periods: 1) the period of macroscopic histology, without a microscope (from ancient times to the 17th century); 2) the period from the invention of the microscope to the invention of the achromatic microscope (17th century - beginning of the 19th century); 3) the period of the achromatic microscope; the development of histology on the basis of the cell theory (19th century); 4) the period of further improvement of the microscope: immersions and apochromats; development of microscopic technique; cytology (from the 1870s of the 19th century to the beginning of the 20th century). The first period - macroscopic histology without a microscope. The first attempts to study the structure of the body were made in ancient Greece. Aristotle (4th century BC) in his "History of Animals" and "On the Parts of Animals" describes the structure of organs and tissues. He assumes that they consist of elements from which homogeneous parts are formed, which in turn serve as material for heterogeneous parts or organs. Aristotle describes the following homogeneous parts in more or less detail: bone, fish bone, cartilage, skin, hair, nail, muscle, nerve, brain, cerebrum, membranes, fat, blood, semen, bile, milk. The anatomists of the Alexandrian era (Herophilus, Erasistratus) corrected some of Aristotle's mistakes, who confused nerves and tendons, the brain and spinal cord, and introduced a new term - parenchyma (blood poured out of vessels) - to denote the pulp of internal organs. In the works of Galen (2nd century AD), who gave a synthesis of ancient anatomy, one finds in general correct and rather detailed descriptions of tissues, and Galen even attempts to include tissues in the field of pathology, highlighting diseases that arise from changes in simple parts. From Galen, the doctrine of simple parts passed to the Arabs (Avicenna) and to Western European anatomy, which for a long time considered Galen an infallible authority. Faith in him was destroyed only by the works of Vesalius (16th century), who is a reformer of anatomy. Vesalius himself paid little attention to tissues, but his contemporary, also a famous anatomist, Fallopius, already read a special course - "On the homogeneous parts of the human body." These lectures (Fallopius G., Lectiones de partibus similaribus humani corporis, ex diversis exemplaribus a Volchero Coiter summa cum diligentia collectae, Noribergae, 1575), published by Fallopius' student Coiter, represent the first systematic textbook of histology without a microscope. Fallopius distinguished 16 tissues in the composition of the organism. The second period extends from the invention of the microscope to the invention of the achromatic microscope; to this period belong the discovery of the cell and the laying of the foundations of private and general histology (17th century - beginning of the 19th century). The invention of the compound microscope dates to the end of the 16th century, but its application for scientific purposes began only in the second half of the 17th century and was made by the English physicist R. Hooke (R. Hooke). In his "Micrographia" (1665) there is the first description of plant cells, the existence of which was soon confirmed by the works on plant anatomy of the English scientist Grew and the Italian Malpighi. The application of the microscope to the study of the fine structure of animal bodies was also made by Malpighi, professor of anatomy in Bologna. He was the first to describe the structure of the skin (Malpighian layer), tongue (papillae), lungs, liver, kidneys (Malpighian corpuscles), spleen (Malpighian bodies), lymphatic glands, omentum, and made observations on the circulation and the first stages of development of the chick. Malpighi's descriptions are distinguished by great accuracy, although they were made with very weak magnifications. For all this, Malpighi with full right can be called the father of private histology, i.e., microscopic anatomy. Another outstanding observer of the late 17th - early 18th century was the Dutchman Leeuwenhoek, who, not being a scientist, worked as an amateur. He himself ground lenses that gave great magnification (up to 270 times), and with his simple microscope made a series of brilliant discoveries. Leeuwenhoek discovered and studied in detail red blood cells, sperm of various animals (discovered by his student Ham), striated muscles of the skeleton and heart, nerve and tendon fibers, scales of the epidermis, infusoria, yeast fungi and even bacteria. Leeuwenhoek's drawings, in contrast to Malpighi's, are very fine and some are remarkably close to modern ones. Thus, Leeuwenhoek is the founder of general histology as the doctrine of tissues (Leeuwenhoeck A., Anatomia seu interiors rerum, cum animatarum turn inanimatarum, ope e beneficio exquisitissimorum microscopiorum detecta, Lugduni, 1687). Despite such brilliant discoveries, in the 18th century there was a complete stagnation in the field of microscopic histology, since most scientists treated the microscope with distrust, believing that it gave incorrect pictures; this opinion had a certain basis, since the lenses of that time had spherical and chromatic aberrations and gave blurry, colored images. Therefore, many anatomists continued to develop the doctrine of tissues with the naked eye; in this way, cellular tissue (tela cellulosa), or connective tissue (having no relation to the discovered cells), and mucous tissue were distinguished. Works in this direction were completed by the French scientist Bichat, who in his "Anatomie generale, appliquee a la physiologie et a la medicine" (t. I-II, Paris, 1802) gave a complete classification of tissues (21 in number) and described their properties in detail. There is no reason to consider Bichat the founder of modern histology; on the contrary, he completes the old histology without a microscope, which disappeared from the scientific horizon in the first half of the 19th century. Only at the end of the 18th century, attempts at microscopic study of tissues (Fontana) resumed, which, however, did not have particular success. The third period - the achromatic microscope; the development of histology on the basis of the cell theory. By the 1820s of the 19th century, when opticians learned to eliminate aberrations, the achromatic microscope was constructed, which quickly gained recognition from scientists. The results were first reflected in plant anatomy; botanists began to study the cell, its structure and role in development. In addition to the shell and contents, the nucleus was recognized as a necessary component of the cell (Brown; 1833), which had been seen by individual researchers earlier. Through the work of Mirbel, Turpin, Meyen and Schleiden (Mirbel, Turpin, Meyen, Schleiden), by 1838 the cell theory of plants was established, according to which all formative elements (fibers, vessels) develop from cells and the cells themselves arise within previously existing ones. Using this theory as a model, Theodor Schwann (Theodor Schwann) in 1839 created the cell theory of the animal organism. He proved that in the animal body there are real cells with a shell, contents and nucleus, which was not known before, and that formations unlike cells, various fibers and vessels develop from cells or with their participation. In conclusion, Schwann established two basic provisions of the cell theory, which long dominated science: 1) the cell is the elementary, simplest form in which life manifests itself, something like an animal crystal, and 2) the organism is a cellular colony, or state. Almost simultaneously with Schwann, the widespread distribution of cells was discovered by the physiologist Valentin. Schwann's ideas quickly gained general recognition and were further developed. It was proved that cells multiply by division, and not arise from blastema (see), as Schwann thought, and that the cell contains a special, living, protein substance - protoplasm (see) (von Mohl). In the 1840s, 1850s, 1860s, a rapid flourishing of histology on the basis of the cell theory begins, the cellular composition of various tissues and organs is studied, their histogenesis is clarified, and in the main outlines the building of modern histology is laid. A number of outstanding scientists, mostly German and English, took part in the development of these issues: Henle, Leydig, Gerlach, Remak, Virchow, Frey, Max Schulze, Brücke, Bowman, Hassall, Beale (Henle, Leydig, Gerlach, Remak, Virchow, Frey, Max Schulze, Brücke, Bowman, Hassall, Beale) and others. The same time includes the founding of the first journal devoted specifically to microscopic research ("Zeitschrift für wissenschaftliche Zoologie", hrsg. v. Siebold u. Kolliker, B. I, 1849), as well as the appearance of a large number of histology textbooks by Hassall, Kölliker, Gerlach, Leydig and others. The fourth period - further improvement of the microscope: immersions and apochromats; development of microscopic technique; cytology (from the 1870s of the 19th century to the beginning of the 20th century). In the 1860s, a new, significant improvement in the microscope occurred: water immersion objectives were constructed, which significantly increased the "resolving power", i.e., the amount of detail given by the objective. In the 1870s, oil, or homogeneous, immersions appeared, which surpassed water ones in this respect. And finally, with the production of apochromats by the firm Zeiss under the leadership of Abbe, the optical part of the microscope reached the highest perfection. All this technical progress could not but affect histology, which, having clarified the structure of the body in outline, now turned to the study of the finest structure of the cell and tissues. At the same time, in the 1870s, the improvement of research technique begins. Instead of alcohol, Müller's fluid, acetic acid and carmine of the previous era, osmic and chromic acids, sublimate, platinum chloride, then formalin and a number of other substances appear on the stage; from them are made fixatives suitable for any occasion. The arsenal of dyes is enriched with hematoxylin and all possible aniline dyes; gilding and silvering are added to them, the technique of injections is perfected. But, most importantly, hand cutting with a razor is replaced by machine technique due to the introduction of the microtome, first manual, then sliding, and the object must first undergo a complex operation of embedding in paraffin or celloidin.

The ideal for the histologist becomes a thin paraffin section of a few microns from material fixed specifically for a particular purpose and selectively stained in several colors; it is examined with Zeiss apochromats. After Max Schultze defined the cell as a clump of protoplasm with a nucleus in the 1860s, the attention of histology focused on protoplasm, and over the last quarter of the 19th century, theories of the structure of protoplasm succeeded one another: Fromann, Heitzmann, Flemming, Altmann, Butschli, not to mention their variants. The second main theme of the work is the structure of the nucleus and the study of the division process; through the work of Schleicher, Schneider, Butschli, Perevyshko, and especially Flemming, the details of karyokinesis were clarified; these were supplemented by the work of van Beneden, Hermann, Driiner, and others. In the 1880s, van Beneden discovered the third necessary component of the cell—the centrosome, which is clearly evident during division; it was thoroughly studied by Boveri and M. Heidenhain, who developed a method for detecting centrosomes in resting cells, and in a short time, the literature on these structures reached enormous proportions. As a result, in the 1890s, the doctrine of the cell emerged as a separate discipline—cytology. Interest in it increased tremendously due to the recognition of the nucleus's primary role in transmitting hereditary properties, and cytology soon became the foundation of general biology. A monument to this time can be the excellent comprehensive works on the cell: German—by O. Hertwig and Verworn, French—by Henneguy and Delage, American—by Wilson, and Russian—by Ognev and Maksimov. Of course, the history of histology during the specified period is not limited to cytology alone; researchers from all countries, whose number has increased enormously, continue to work on clarifying the fine structure of all tissues and organs. Where the structure was already more or less known, efforts were directed toward studying histogenesis; works in this very area are characteristic of the 1890s. But particular successes were achieved in those areas where it was possible to improve research techniques and develop special methods. This applies first and foremost to the nervous system, whose fine structure could only be deciphered thanks to special staining methods: myelin of nerve fibers (Weigert), vital staining with methylene blue (Ehrlich and Dogel), and impregnation with chrome silver (Golgi). The same applies to blood and hematopoiesis, whose study was greatly advanced by Ehrlich, who applied mixtures of acidic and basic dyes for staining granules. During the specified period, many journals specifically for histological works arose; among them, the central place was occupied by: 'Archiv fur mikroskopische Anatomie', founded in 1865 (under the editorship of M. Schultze), and later (1886) 'Anatomischer Anzeiger' (under the editorship of K. Bardeleben), which became international organs; these two journals perfectly reflect all the directions of that time. The Belgian journal 'La Cellule', dedicated to the special study of the cell, was edited by one of the first cytologists, Carnoy (Carneau). In view of the enormously growing literature, periodic publications that provided summaries on individual issues and abstracts became very important: 'Ergebnisse der Anatomie und Entwicklungsgeschichte', under the editorship of F. Merkel, R. Bonnet, and 'Jahresberichte iiber die Fortschritte der Anatomie u. Entwicklungsgeschichte', under the editorship of G. Schwalbe. In 1886, the German Anatomical Society was founded, which held annual meetings in various cities of Germany. The overwhelming majority of reports at these meetings concerned the field of histology; these meetings had an international character, as scientists from all countries, especially from Italy and Russia, gathered in large numbers. Later, following this model, the association of French anatomists was founded. Modern histology. In the first decade of the 20th century, histology continued to develop in the previous direction, incorporating ever larger and smaller details into its study. In cytology, the doctrine of mitochondria came to the forefront, first discovered by Benda by means of specific staining and studied by Meves; they were soon recognized as an essential component of the cell, performing very important functions in the process of secretion and formation of cellular structures, and generated enormous literature. When the wave of enthusiasm subsided, attention turned to intracellular apparatuses: the Golgi reticular apparatus, trophospongiae, and Holmgren's canals, which in turn were recognized as a permanent part of the cell, playing a role in the processes of metabolism and secretion. The study of these structures, to which the so-called vacuome (Parat) has been added in recent times, by means of very complex special methods is currently one of the current topics of modern histology. Another thread connecting the present with the traditions of classical cytology is the study of the nucleus as the morphological substrate of heredity. The rediscovery of Mendel's laws in 1900 revived Weismann's theory of the localization of genes in chromosomes and forced a close study of these structures in the process of development of the sexual elements; in this direction, American histologists worked intensively: Wilson, Sutton, McClung, and especially the school of Morgan. Currently, histology has entered into a firm alliance with genetics, and at congresses it has become customary to hold joint sessions of sections of these two specialties. But although the traditions of the old are still strong, in general modern histology is decisively turning onto a new path, and this new direction threatens to nullify many achievements of the previous period. The prerequisites are, besides the ideological criticism of the cell theory, numerous doubts arising regarding the fine structures visible in fixed preparations. The lack of a decisive authority in disputes between histologists working by different methods has placed a number of questions at a dead point and has discredited pure morphology. The way out could only be provided by vital research, displaced by complex microscopic techniques, to which they turned. The methodology of this research has been significantly improved 1) by the application of the ultramicroscopic method (illumination in the dark field of view), 2) by the well-developed technique of tissue culture in vitro, which gives the researcher definitely living material, and finally 3) by the experimental method of microdissection, which allows penetration with fine instruments into the cell and so to speak probe it through with the help of a micromanipulator. Vital study was introduced into science mainly by American scientists: Kite, Barber, Chambers, Lewises, but it found response in other countries (Speck) and in the USSR (Karpov). The results of this method are reflected in the significant simplification of the confusing morphological scheme developed on fixed preparations. The new direction is also connected with the development of physical chemistry and especially its branch—colloid chemistry. Under their influence, the concepts of protoplasm and the processes of cellular life have changed significantly, and the place of purely morphological observation of the cell has been taken by systematically planned experimental research on the effect of various ions, dyes, etc. on the cell. The change of eras is reflected not only in cytology; histological works concerning tissues and organs are increasingly losing their purely descriptive character and are taking the path of experiment, being planned in close contact with the tasks of physiology and pathology. This is the way the most current topics are being developed, such as in the field of general histology the role of mesenchyme, in particular the reticulo-endothelial system, questions about which were raised by pathologists. The study of these structures is based on methods of vital staining with so-called colloidal dyes, as well as on injections of other blocking substances. On the other hand, the question of the transformations of mesenchymal elements and hematopoiesis, previously studied on sections, is now being attempted to be solved with the help of vital cultures. Another attracting attention topic is the endocrine glands, the enthusiasm for which covers all of medicine. Since direct observation does not resolve old controversial questions, one has to resort to the help of experiments on animals in order to cause enhancement or weakening of the gland's functions and thus obtain a foothold for judgment. The new course in histology manifested itself with particular force after the world war, and recently there has been expressed more than once the conviction that histology should in essence disappear and give way to histophysiology. But it is still premature to speak of this: defenders of purely morphological directions in histology rightly point to the extensive, little-developed field of comparative histology and to the possibility of establishing purely morphological laws in it. In any case, it must be stated that histology is going through a transitional period; externally connected with the death of most of the corifaei of the classical period and with the transfer of the scientific center to America. Development of Russian histology. Russian scientists began to take systematic part in the development of histology only from the beginning of the 4th period, i.e., from the 1860s.

XIX century; earlier, microscopic work was a random phenomenon and was carried out by those physicians who were sent abroad and could become acquainted with the microscope there. Such was the dissertation published in Strasbourg by Shumlyansky on the study of the fine structure of the kidneys, investigated by means of injections ("De structura renum", Argentorati, 1782); this work attracted attention and even went into a second edition (1788). Histology at Moscow University was first introduced by Professor of Anatomy Loder (died in 1832), with whose help the university was gifted "a rich and unique collection of microscopic preparations of the famous Lieberkühn and the illustrious Prochaska," and then Professor of Comparative Anatomy and Physiology Glebov. The latter, during a foreign trip in 1838, took a private course with Schwann, became a supporter of the cell theory, and brought a microscope of the newest construction by Schick. He published (1846) a microscopic investigation of the soft parts of a mammoth found in Siberia. The 1850s saw microscopic works on the nervous system by Ovyanikov (professor of physiology in Kazan and St. Petersburg) and Yakubovich (professor at the St. Petersburg Medico-Chirurgical Academy); both were pupils of the Dorpat University, where German science flourished. Yakubovich was awarded a prize of 10,000 francs by the Paris Medical Academy in 1858 for his discoveries, as reported by Claude Bernard. Only in the 1860s, when intensive trips of young physicians abroad began, and then independent departments of Histology were established at medical faculties, does the systematic development of Russian Histology begin. The first professors of Histology were: Zavarykin (St. Petersburg), Babukhin (Moscow), Peremyzhko (Kiev), Arnstein (Kazan), Khronshchewsky, and then Kuchin (Kharkov), Goyer (Warsaw). All of them studied abroad, published their works in German journals, and immediately became full members of the international scientific family. Of their works, the most outstanding should be mentioned: Zavarykin's work on the absorption of fat, Babukhin's on the development of the retina and electric organs, Peremyzhko's on cell division, Arnstein's on the vital staining with methylene blue, Khronshchewsky's on physiological injection, and Goyer's on the structure of the spleen (based on excellent injections). The second generation of professors grew up in Russian laboratories, while the custom of foreign trips remained and became firmly established. It helped maintain close ties with Western science, and most Russian histological works served as responses to questions posed by German science, which held hegemony; only a few visited France. To the second generation also belonged a number of outstanding histologists who improved teaching and finally consolidated the position of Russian histology. These include: Lavdovsky (St. Petersburg), Ognev (Moscow), Dogel (Tomsk, then St. Petersburg), Kulchitsky (Kharkov), Kolosov (Warsaw, now Rostov), Lominsky (Kiev), Polyakov (Yuryev), Smirnov (Tomsk), Mankovsky (Odessa). Professors of the third generation: Maximov, Martynov, Nemilov, Deineka, Zavarzin (Leningrad), Gardner, Karpov, Gurevich (Moscow), Rubashkin (Kharkov), Chasovnikov (Tomsk), Pavlov (Saratov), Mislavsky (Kazan), Schmidt (Perm). Of these, Maximov became most known abroad for his works on connective tissue and blood formation. At present, the fourth generation of histologists is coming to the fore. In the 1890s, Russian histological schools began to take shape both in methods of work and in choice of topics. Among them, the Moscow school adopted the critical spirit of its founder Babukhin, the study of the microscope as an optical instrument, and work in the field of histogenesis; the Kharkov school (Kulchitsky, Kolosov) developed the finest technique of histological research and applied it in their works; the Kazan school (which moved with Dogel to the St. Petersburg University) gained European fame by studying the nervous system and nerve endings by means of vital staining with methylene blue, and then by its works in cytology (Golgi apparatus); this school has the largest number of students. Among histologists-zoologists, it is necessary to mention: Mitrofanov and Eysmond (Warsaw), Ivan'tsov, Koltsov, Bogoyavlevsky (Moscow), Belousov (Kharkov); among histologists-physiologists-Leontovich (Moscow); among histologists-veterinarians-Yustov and Loginov. Russian histologists always sensitively responded to the demands of the day, and their works cover all departments of Histology; similarly, among them there were representatives of all scientific directions. Most works were and are published in foreign editions; in Russian they appeared in the form of dissertations or articles scattered in the university scientific notes. But already in the 1870s, the "Journal of Normal and Pathological Histology, Pharmacology and Clinical Medicine" (St. Petersburg, ed. Zavarykin and Rudnev) began to be published, which existed until 1878. Then, after a long break, in 1916 was founded: the "Russian Archive of Anatomy, Histology and Embryology" (St. Petersburg, ed. Dogel). There were no societies or associations similar to the German Anatomical Society in which histologists would be members in Russia; works were reported at the congresses of Russian naturalists and physicians (since 1867) or at the Pirogov congresses, but after the revolution, All-Russian congresses of zoologists, anatomists and histologists with a special section of Histology are regularly convened. Such congresses were three: the 1st in 1922 in Leningrad, the 2nd in 1925 in Moscow, and the 3rd in 1927 in Leningrad. These congresses were very lively, with a huge number of reports on Histology; at present, a permanent association of zoologists, anatomists and histologists is emerging. It should be noted that the ranks of histological workers and young specialists after the war and revolution greatly thinned out, and only recently, with the introduction of the graduate student institute, has a new generation begun to be trained. Histological laboratory. The time when a histological laboratory could all fit on one table, on which besides the microscope stood jars with preparations and bottles with reagents and lay slides and cover glasses, and all necessary instruments (needle, scissors, razors) were kept in the table drawer—this time has passed irrevocably. Now a histological laboratory, intended for scientific work, besides a working office must have a whole series of rooms. Well-equipped histological institutes (which in Germany are combined with anatomical institutes) have: 1) working rooms, if possible separate for each scientific worker and common only for beginners, 2) a room for thermostats set at different temperatures, from 37° to 55° and higher, 3) sometimes a separate room for microtomes of various constructions, including large microtomes for the nervous system, 4) a room for a large microphotographic installation and microcinematography with a separate dark room, 5) a room for vital tissue culture, 6) an operating room for animals, 7) a material room, 8) a preparation room, 9) a library, 10) a servant's room, 11) a room for animals. Working offices must have running water, gas, electricity, and the necessary optical equipment for histological research, which includes: 1) a microscope of medium or large stand with an aperture condenser of 1.4, a movable stage, and a set of lenses from weak magnifications to immersion objectives (apochromats are desirable), 2) lamps for microscopy, 3) a binocular, which is extremely useful for many observations, 4) measuring oculars and objective micrometers, 5) a polarization apparatus, 6) a drawing apparatus, 7) a dissecting microscope or magnifier. Other apparatus, e.g., for research in monochromatic light, vertical illuminators, polarizing spectroscope, must be available in the laboratory, but not for each worker, and issued as needed. Furthermore, each worker must have a microtome with razors for ordinary sections, and if there is no special thermostat room, have a small thermostat for paraffin embedding with a thermoregulator at hand, as well as a number of small instruments and apparatus. An essential part of a modern laboratory is the micromanipulator (see), without which experimental work on living cells cannot claim completeness. The laboratory should have stocks of all stains and reagents in sufficient quantity, necessary laboratory supplies, including various kinds of balances (except analytical), apparatus for distilling water and alcohol, and a large supply of glassware. Almost all laboratories have their own libraries with sets of the most common specialized journals, classic monographs, textbooks, and all necessary reference books. The tendency to concentrate all special books in a general fundamental university library is completely irrational, as it hinders work. Most histological laboratories, not only in our country but also abroad, are far from ideal; they are being pushed into the background by biological institutes, in which microscopic research often also occupies a prominent place, but which at the present moment attract much more funds. Histological laboratories of Russian universities as a rule have small, unsuitable premises; the histological laboratory built in 1891 at Moscow University is far from meeting its purpose at present, the others are even worse; better than others is the laboratory in Odessa KELK, a newer one.

The lack of a solid material base strongly hinders the development of histology in the USSR and inevitably gives most Russian works a handicraft character. Teaching of H. In most countries, H. on the medical faculty has been established as a separate department, only in Germany the teaching of H. remains connected with the teaching of anatomy and is carried out by the same professor. Sometimes even the room for practical exercises is common (Marburg), during which in the winter semester corpses are dissected, and in the summer-microscoped. The teaching consists of 1) lectures accompanied by demonstrations of tables, slides and microscopic preparations, the latter being demonstrated either by a projection microscope on the screen to the entire audience at once or exhibited under microscopes after the lecture, which is more rational, and 2) practical exercises of students with the microscope, which are absolutely necessary for mastering the science. In Germany, lectures have always been distinguished by brevity and simplicity (textbooks had the same character); before the war, 5 annual hours per week were allocated for lectures in the 3rd and 4th semesters, and accordingly the course was taught on a large scale. According to the new curriculum, lectures are limited to two hours per week in the 2nd and 3rd semesters, which is insufficient for the presentation of a systematic course, as a result of which lectures must be linked with practical exercises and take on the character of introductory and concluding ones, as well as present those sections that cannot be worked out in class. Practical exercises are now allocated 4 annual hours, which is sufficient. The organization of practical exercises in different universities abroad and in our country has always been different: depending on the resources, equipment and number of workers, varying degrees of independence were provided, ranging from the independent preparation of sections, teasing and preparation of the preparation, which was then studied, and ending with the simple study of ready-made preparations. After the world war, this path had to be taken almost everywhere and in our country as well.

HISTOMERS

which was then studied, and ending with the simple study of ready-made preparations. After the world war, this path had to be taken almost everywhere and in our country as well.