Mitochondria

Mitochondria, a cellular organelle that is part of all animal and plant cells and of the protoplasm of protozoa. Mitochondria were first described by Benda in 1898 in the spermatozoa of the mouse, and then in other cells. Subsequent research by later authors (chiefly Meves, Dtisberg, Faure-Fremiet, and others) established the presence of these formations in all cells of the plant and animal world without exception. M. can be observed both in living cells and on fixed preparations. They appear either as grains or as threads or rods, sometimes breaking down into grains. Meves proposed retaining the term M. for the granular form, naming the rod-shaped and thread-like forms "chondrioconta," and all varieties of these formations together as "chondriosomes." For the aggregate of all chondriosomes of a given cell, Meves introduced the term "chondriom" of the cell. At present, Meves' terminology is accepted by the majority of authors. The chemical composition of M. is not precisely known, however all data point to the fact that proteins and lipoids are included in their composition. The lipoid nature of M. is demonstrated, among other things, by their solubility in exactly those substances that dissolve fats and fat-like bodies (in alcohol, ether, chloroform, acetic acid, etc.). In some cases it is possible to stain M. by microchemical methods used specifically for detecting lipoids (e.g., the Sudan method of Ciaccio). Various mixtures containing formalin, chromic acid, potassium dichromate, osmic acid, and other substances are used as fixatives for M. The best results are obtained with Benda's, Meves', Regaud's, and Champy's mixtures. For staining mitochondrial preparations, iron hematoxylin according to Heidenhain, the methods of Altmann, Benda, and Kull, as well as impregnation with silver and osmium, are employed. Despite the vast literature on M., nothing reliable is yet known about their biological significance. The majority of authors recognize them as a living component of protoplasm playing some very important role in the life of the cell, i.e., recognize their organelle nature; but what this role is is still unknown; there is only a series of more or less probable hypotheses. Benda thought that M. constitute part of the motor apparatus of flagella and cilia. Meves (1918) in a whole series of thorough works proved the participation of M. in the transmission of hereditary properties of cells. He opposed the view of the nucleus as the sole bearer of hereditary traits. Meves traced the fate of the paternal and maternal M. during the fertilization of the egg of the horse ascarid, and it turned out that after the penetration of the spermatozoon into the egg, the M. of the spermatozoon emerge into the surrounding egg plasma, where they mix with the M. of the female sex cell. Meves' theory is based on the assumption that M. do not arise anew from the plasma, but are transmitted successively from cell to cell by division. This point of view was supported by many researchers. However, in recent years a number of works have appeared indicating the possibility of the appearance of M. anew directly from indifferent protoplasm. These include the observations of Levi on tissue cultures outside the organism and the research of Wasserman, showing that in the cells of the pea embryo there are no mitochondria and that they arise only at the beginning of seed germination. These observations undoubtedly contradict Meves' theory. According to another theory (Meves, Duesberg, Gowen, and others), M. are not only bearers of the hereditary properties of the plasma, but as it were participate in the realization of these hereditary potentials, transforming during the development of the organism into various specialized organelles. Thus, Duesberg described the direct transformation of M. into myofibrils in the myoblasts of the chick embryo, Gowen attempted to explain the origin of neurofibrils in the same way, and Meves (1910) the development of collagen fibers of connective tissue. Based on the assumption of such a plastic role of M., this researcher proposed calling M. plastosomes, plastokonta, and plastochondria. Nevertheless, this theory also found no confirmation in the works of later researchers. Finally, a whole series of authors (Gowen, Metzner, Duesberg, Prénan, and others) described the direct transformation of granular M. into granules of the most diverse secretions and inclusions, attributing to them a secretory role. Among attempts of this kind, the most reliable and well-founded are the observations of Lewitsky, Guilliermond (1912), Nasonov (1918), and others on the participation of M. in the production of starch by plant cells. According to these authors, the M. of plant cells can either directly produce starch grains inside themselves or, upon increasing, first transform into leucoplasts and chlorophyll grains. In recent years, for the study of M., Dr. Canti applied the method of accelerated cinematography. With the aid of such microphotography of tissue cultures growing outside the organism, this researcher succeeded in proving the ability of M. to active amoeboid movement. These movements are so slow that at ordinary observation they are completely unnoticeable, but the accelerated film allows observing this phenomenon with remarkable clarity. Canti's film was first demonstrated at the Congress of Zoologists in Budapest (1927) and at the All-Union Congress of Zoologists, Anatomists, and Histologists in Kiev (1930).