Blastema

BLASTEMA (from Greek blastema—sprout, offshoot), a term occasionally used to denote the rudimentary mass from which parts of living beings are formed, e.g., renal blastema (Nierenblastem). In 19th-century science, the term was introduced by Schwann, the founder of the cell theory of animal organisms (in the doctrine of cellular blastema—cytoblastema, 1839). Schwann rejected the doctrine of Schleiden, the founder of the plant cell theory which served as his model, regarding the formation of cells within pre-existing cells, and hypothesized that they arise in a structureless, liquid or semi-liquid substance found in various parts of the animal organism, which he called cytoblastema. Consistent with his view of the cell as an animal crystal, Schwann saw cell formation as a process analogous to crystallization. First, a nucleus arises (on this point Schwann agrees with Schleiden, for whom the nucleus is cytoblastus—the cell germ) in the following manner: a cluster of granules appears in the cytoblastema, which becomes surrounded by a thin, transparent, structureless membrane; around the nuclear membrane a new membrane—the cell membrane—arises; it first adheres tightly to the first, and then liquid seeps through it from the surrounding environment and it stretches in the form of a bubble, forming a cell, with the seeped liquid forming the cell contents. The remainder of the cytoblastema not consumed in cell formation constitutes the intercellular substance, either liquid or hardening. Such a mode of cell generation is usual, while their formation within pre-existing cells is, conversely, an exception. Schwann did not explain how the cytoblastema arises, since the very nature of the egg remained unclear to him. Schwann's doctrine held sway in science until the mid-1850s in connection with the recognition of the membrane as an essential part of the cell; Kölliker in the first edition of his classical textbook (Gewebelehre, 1852) admits the formation of a number of cells according to Schwann; C. Ludwig (1856), describing the formation of cells in a liquid mass, notes that the explanation of this process from ordinary molecular forces does not encounter fundamental difficulties. An opponent of this doctrine was Remak, who was the first to trace the process of animal cell division under the microscope (1852); he resolutely rejected the existence of cytoblastema, but the doctrine of cytoblastema was finally banished from science by R. Virchow, who in his cellular pathology (1855) put forward the principle: every cell arises from a cell (omnis cellula e cellula). However, even at a later time, individual authors returned to the hypothesis of the free formation of cells; for example, Arnold (1869 and later) claimed that upon the destruction of the epithelium on the cornea and tongue of a frog, the wound is filled with a fine-grained mass in which cells arise. At present, the doctrine of cellular blastema has been completely abandoned, but the free generation of cells is defended by the Russian zoologist S. A. Usov.