ultraviolet rays of low intensity with wavelengths from 1,900 to 3,250 angstroms; they are produced by cells and tissues in plants and animals.

Mitogenetic rays were discovered in 1923 by A. G. Gurvich, who demonstrated the capacity of mitogenetic rays to stimulate cell division—mitoses (hence the name). The biological action of mitogenetic rays is caused by the development of chain chemical processes within the cells under their influence. Mitogenetic rays are detected during fermentative reactions in the organism and in noncellular systems by means of biological indicators (according to intensification of cell division) and by means of highly sensitive photomultiplier tubes.

Analysis of the spectra of mitogenetic rays reveals their dependence on the physiological state of the objects investigated; in certain pathological states of the body, the intensity of mito-genetic rays changes. Because of the contradictory results obtained from the experimental study of mitogenetic rays, their existence is not generally acknowledged.