Protozoology

PROTOZOOLOGY, the study of Protozoa (see), a branch of zoology that has developed into an independent discipline similar to entomology or helminthology. Along with taxonomy, morphology, physiology, and genetics of Protozoa, protozoology also studies their ecology and in particular the phenomena of parasitism of Protozoa in humans, animals, plants, and even in other Protozoa. Due to their practical importance, parasitic Protozoa have become the object of special attention from researchers, many of whom were not zoologists, particularly medical and veterinary physicians—the study of parasitic Protozoa began to show a tendency to separate into an independent branch alongside the so-called general P. and the study of free-living Protozoa. Both branches of P., however, are closely interconnected. The study of parasitic Protozoa is possible only on the basis of a deep knowledge of zoology in the broad sense and in particular of general protozoology, since parasitic Protozoa originated from free-living forms and are connected with them by a series of transitional forms. Sufficient information about free-living Protozoa is necessary for the protozoologist-parasitologist also because into the body of an animal or plant, into their secretions and excretions along with parasitic forms, free-living organisms, so-called transit forms, passants, coprozoic organisms, can also enter, which may cause confusion with parasitic species. On the other hand, the enormous number of studies devoted in recent decades to parasitic Protozoa has led to the fact that many questions of general P., for example many aspects of the life cycles of Protozoa, have been best studied on parasitic objects. For this reason, sufficient familiarity with this branch of P. is necessary for all those working with free-living forms. In the study of free-living Protozoa, chapters on Protozoa of bodies of water and soil are particularly distinguished according to chorological and ecological principles. The study of parasitic Protozoa is divided into medical and veterinary P. and the less developed phytopathological. The above-mentioned branches of the study of parasitic forms are closely intertwined. Many species of parasitic Protozoa parasitize at different stages of development in hosts belonging to widely separated divisions, classes, types, and even kingdoms of organisms; for example, some stages develop in a worm, others in a vertebrate, one cycle is completed in a plant, another in an insect. The study of parasitic Protozoa of humans or animals that are transmitted through insects or other arthropods is inseparable from the study of the life cycle of these same parasites in the corresponding insects, ticks, etc. The latter in turn requires comprehensive familiarity with all sorts of parasitic Protozoa found in these arthropods. The study of parasitic Protozoa of insects also has independent practical importance, since some diseases of economically important insects, for example the silkworm or bees, are caused by parasitic Protozoa. The role of arthropods and worms as intermediate and definitive hosts of parasitic Protozoa closely connects parasitic P. with other branches of parasitology, arthropodology and helminthology. The study of a parasitic protozoan is inseparable from the study of the host organism, its histology, physiology and pathology, from questions of ecology. Thus, P. is closely connected with all branches of zoology, botany, microscopy, anatomy of animals and plants, pathology, etc. For medicine, P. has enormous importance as the study of the causative agents of so-called protozoan diseases of humans (see Protozoa). Many parasitic and free-living Protozoa are objects for testing pharmacological preparations and poisonous substances. A. Leeuwenhoek, who gave the first description of free-living Protozoa, can also be called the father of the second branch of P.—the study of parasitic Protozoa: he discovered in the excretions of a flagellate parasite, later identified as Giardia intestinalis. However, only in the middle of the 19th century, along with the development of microscopy, on the one hand, and the cell theory on the other, discoveries in the field of medical and veterinary P. begin to follow one after another. In 1839, Hake describes the intracellular parasite Eimeria Stiedae in rabbits. In 1849, G. Gros in Moscow discovers Entamoeba gingivalis in humans. In 1854, Davaine describes under the name Cercomonas hominis types A and B of flagellates

PROTOZOOLOGY

intestinal parasites, which were later named Chilomastix Mesnili and Trichomonas hominis. In 1856, Malmsten discovered the parasitic infusorian Balantidium coli. In 1875, Loesch in St. Petersburg described the dysentery ameba. In 1880, Laveran discovered the causative agent of human malaria; blood parasites of animals had been discovered much earlier, in the 1840s by Gross. In 1885, Marchiafava and Celli studied the morphology of malaria plasmodia in stained smears. Golgi established the differences between 3 species of malaria plasmodia. In 1893, Smith and Kilborne described the causative agent of Texas fever of cattle and its transmission through ticks. In 1895, Bruce discovered the causative agents of African cattle disease nagana and established the role of tsetse flies in the transmission of this infection. In 1898, Borovsky in Tashkent discovered the causative agent of Pian (Saratov) ulcer. From 1895 begins the brilliant series of works by Ross, Grassi and others (Ross, Grassi) on the study of the transmission of the causative agents of human and bird malaria through mosquitoes. In 1900, Leishman discovered the parasite of kala-azar (visceral leishmaniasis). In 1901, Dutton and Dutton discovered the causative agent of African sleeping sickness. In 1909, Chagas establishes the pathogenic role of Schizotrypanum Cruzi, the causative agent of South and Central American human trypanosomiasis, and the role of kissing bugs in its spread.' The first quarter of the 20th century brought a series of works by Schaudinn, Pro-wazek, Dobell, Wenyon. In 1925, Boeck and Drbohlav obtained a culture of human parasitic amebas. In 1926, Adler and Theodor established the transmission of Leishmania tropica through phlebotomus flies. In 1932, James established the independence of the 4th species of human malaria plasmodium, Plasmodium ovale, described in 1922 by Stephens. Among Russian protozoologists, Mitrofanov (cytology of trypanosomes), Danilevsky (trypanosomes, blood parasites of birds), Mechnikov, Sakharov, Gabrichevsky, Shevyakov, Averintsev, Ilovaisky, Bogoyavlensky should also be noted. The problems of general protozoology, developed in modern scientific institutes, revolve primarily around questions of taxonomy, morphology, life cycle, and physiology of Protozoa. Special attention is drawn to the genetics of Protozoa, their variability and heredity. The methodology of P. until recently was largely reduced to their microscopic study, establishing cytological and karyological details, reconstructing the life cycle mainly from fixed preparations. Recently, the method of cultures, initially introduced in P. mainly for the purpose of studying the reproduction processes of Protozoa, is beginning to be applied to the study of the properties and functions of a community of Protozoa, their collective metabolism, the nature of growth on solid nutrient media, similar to how this method is applied in other branches of protistology (see), bacteriology and mycology. Nevertheless, unlike these disciplines, as Yollos rightly points out, in P. the study of the Protozoan organism as an individual comes first. In this respect, P. is closer to zoology than to the aforementioned branches of protistology adjacent to it. Parasitic P. above all continues the search for new species of causative agents of diseases of humans, animals and plants, reviews the taxonomic position of already known species, establishes their life cycles, vectors, control and preventive measures. Along with these questions, parasitic P. widely raises questions of the relationship and interaction between host and parasite, the influence of the host's life rhythm on the development of the parasite (malaria of birds and monkeys), immunity in protozoan diseases. Finally, P. is one of the cornerstones of the new discipline created by Ehrlich in the first two decades of the current century-chemotherapy. The main model for chemotherapy was trypanosomes, the study of which made it possible to establish the general principles of this discipline and extend its influence to other groups of protists. The study and teaching of P. at present is carried out very intensively in all corners of the globe, in biological, medical, veterinary, agricultural institutions, in Pasteur institutes in Paris, Tunis, Algeria, in tropical colonial institutes in London, Liverpool, Hamburg, Paris, Amsterdam, Brussels, Berlin, Rome, in universities of Cambridge, Lisbon, California, in Africa, Australia, in Manila (Philippines), in Rio de Janeiro and in a number of other cities and countries. In the Soviet Union, parasitic P. is specially developed and taught in special institutes: the Tropical Institute in Moscow, the Protozoan Institute in Kharkov, tropical institutes of union republics, protozoological departments of medical and veterinary sanitary-bacteriological institutes, the All-Union Institute of Experimental Medicine, the Microbiological Institute of Narkompros, the All-Union Institute of Experimental Veterinary Science. Extensive work and teaching of P. are carried out at Leningrad University and a number of other biological higher educational institutions.

S. Moshkovsky.