Cytology (the science of the structure and vital activity)

Cytology, the science of the structure and vital activity of the cell, a branch of histology that has grown in recent years into an independent area of biology with its own research methodology and specific problems. The origin of Cytology dates back to the 1840s, when the discoveries of Schleiden and Schwann drew the attention of scientists to the cell as the structural unit of an organism. The first period in the development of Cytology, coinciding with the second half of the 19th century, is characterized by the flourishing of the morphological method (see Cell, historical sketch). The favored objects of cytological research during this period are the large eggs of certain animals (for example, sea urchins). The morphological method in Cytology proved extremely fruitful in resolving a number of biologically important questions; thus, processes such as karyokinesis, fertilization, reduction of chromosomes, spermatogenesis, and others were described and explained morphologically, which undoubtedly placed Cytology among the most important biological disciplines. The shortcomings of the morphological method, determined by the limited resolving power of the microscope and the impossibility of judging the significance of infinitesimally small structures (grains, vacuoles) in the absence of data on their function, led to the flourishing of the speculative direction in Cytology, to various hypothetical constructions concerning the submicroscopic structure of the cell from elementary particles that are carriers of vital properties (Heidenhain's histiomeres, M. Fervourn's bionts, etc.). Finally, the last decades are characterized by a sharp change in the entire direction of Cytology, the appearance of new problems and essentially new methods. Cytology ceases to be a purely morphological discipline, becomes imbued with physiology, to a large extent becoming the physiology of the cell; many of its new methods are completely unrelated to morphological research. Another essential feature of modern Cytology is the sharp predominance of the experimental method, which has almost entirely displaced the descriptive method. The main methods of modern Cytology are: 1) the histological method (experimental cell morphology, the study of the cell as a whole and its individual parts—the nucleus, chondriosomes, Golgi apparatus, etc.—under various experimental influences, and upon changes in external and internal environmental conditions). Here, the study of the influence of radiant energy on the cell (X-rays, radium, ultraviolet rays, etc.) has received extremely great development in recent years. In addition to the histological method, the following should be noted: 2) the micromanipulation method (microsurgery), which received special development after the works of Chambers, Peterfi, and others: by means of an ingeniously constructed system of very thin, glass-drawn instruments connected to a microscope, the researcher has the opportunity to perform various delicate manipulations on the cell, continuously observing it, for example, cutting it into parts, removing the nucleus, pricking its membrane, stretching chromosomes, etc.; this method has yielded a number of valuable results, allowing one to judge the physicochemical state of the cell, the significance of its various components, etc.; 3) the tissue culture method—the placement of cellular complexes (or in some cases even individual cells) on a nutrient medium in which they continue to live, exhibit metabolism, growth, the ability to divide, differentiation, etc. The doctrine of tissue culture has grown in our time into an independent large discipline with its own printed organ (Arch. f. exper. Zellforsch.), a large number of researchers in all countries. 4) The method of vital (living) stains, which has extremely great significance in a number of problems, such as questions of metabolism, permeability, the cell's ability to deposit reserve substance grains, etc. The cell's reaction to the stain allows us to form an idea of the speed of penetration of various substances through the cell surface (the submicroscopic surface film, hypothetically accepted by most researchers until recently, the deposition of the stain in the cell, its excretion outward, i.e., the problem of microphysiology of excretion, etc.). 5) Finally, a significant number of researchers, grouping around the international journal 'Protoplasma', devote their works to a special physicochemical department of Cytology—the study of the cell as a physicochemical system. Research in this direction is very diverse—the colloidal state of the cell at different moments is studied (Heilbrun's works), the adsorptive capacity of its surface layers (for example, in recent times the works of D. N. Nasanov's school), the electrical charge of the cell (the works of Prague biologists Keller and Gicklhorn), the concentration of hydrogen ions in the cell, etc. All the methods listed can be subject to a general criticism—the specific conditions of the experiment sometimes fundamentally change the reaction of the biological system; therefore, all data obtained by experimental Cytology must be accepted with a certain caution and, if possible, verified by several paths. Otherwise, there is a danger of Cytology moving into a new extreme—physiological mechanism, which many contemporary cytologists are guilty of. The main problem of modern Cytology is reduced to the study of the cell as a whole—in the sense of its physicochemical properties (colloidal state, electrical charge, permeability), as well as understanding the basic biological processes occurring in the cell: metabolism, growth, division, contractile and nervous activity; in particular, the resolution of some questions related to the latter two problems is also largely given by Cytology (the doctrine of synapses, histophysiology of contractile activity). Researches connected with biological Cytology, which remains the most important part of the doctrine of heredity, variability, etc., have not lost their significance. One can mention a special area of Cytology, karyology—the doctrine of the structure of the nucleus, mainly in relation to the chromosomal complement. The problem of the relationship of cells is resolved in Cytology by the method of culturing tissues outside the organism. Cytological data are of value for general physiology, as well as for general pathophysiology, some branches of which (the doctrine of tumors) make significant use of Cytological methods, and their conclusions are based on the comparative study of the morphology and physiology of the normal and cancer cell, S. Zalkind. Lit.-see the bibliography to the articles Histology and Cell.