Metaplasm

Metaplasm, a name (Hanstein, 1868) that, in contrast to proper cytoplasm and so-called deutero-plasmic inclusions of a nutritional nature, encompasses all various fibrillar structures. The main function of M. is supportive. Poorly visible in vivo, metaplasmic intracellular structures are nevertheless easily detected after osmium and bichromate fixatives followed by staining with iron hematoxylin, toluidine blue according to Ikeda, Mallory's stain, or crystal violet by Bend's method. Metaplasmic structures reach their greatest development in the form of supporting fibrils in protozoa, where they have been well studied in recent years (Taylor, Peshkovskaya). In the tissues of multicellular organisms, metaplasmic fibrils are found in the epithelium of coverings and the intestine, in the endothelium, and in reticular cells of lymphoid organs. In covering epithelia, these metaplasmic fibrils pass from cell to cell (Heidenhain) and, with their bases directed toward the basement membrane, form a system of arched fibers. These are undoubtedly mechanofibrils. In cartilage cells, fibrillar structures can also be easily detected. Further, M. includes the fibrils of muscle cells as well as neurofibrils. For a time, it was admitted (Meves) that the metaplasmic structures of muscle and nerve fibers originate from mitochondria, but at present this viewpoint has been abandoned. Most researchers believe that metaplasmic structures arise through the crystallization of micelles. Among the numerous theories of the structure of M., mention should be made of the teaching of Heidenhain, known under the name of the "protomer theory". Heidenhain considers that the smallest particles, "protomers," which form all metastructures, are capable of metabolism, growth, and division; they are variable in form but do not possess polarized conductivity. When monaxial structures are formed from protomers, all fibrillar formations in the organism arise.