There are numerous views as to the nature of the action of roentgen rays on living tissues. In general, it is felt that small doses "stimulate" and large doses "depress." After the therapeutic use of large doses, death or a decrease in the size of the exposed tissue follows. Whether this action is one of a toxic necrosis of tissue directly, a mechanism disturbing the cell division or an increase in the rate and intensity of the normal processes in the life of the cell is a matter of discussion.
For the study of the effect of roentgen rays on living tissue, the blood offers admirable material. The polymorphonuclear leukocytes may be recognized morphologically in twelve or more stages in the course of their life history, and at least five or six definite stages in the maturation of a red blood cell can be identified. This enables one to study