Recovery of crown-gall tumor cells.

nant animal cells are distinguished from healthy or inflaznmstory cells. In emphasizing the perma nency of the cellular alteration, Kidd (6) states that “Cancercells remain such until they die . . they never turn back en masse towards the benign or normal state. . . .“The inability to accomplish a reversal of malignant to normal cells under con trolled conditions has, however, served as a serious barrier to further progress in defining more pre cisely the nature of the proximate cause for the continued abnormal proliferation of certain neo plastic cells. The initiating and continuing factor or factors responsible for the alteration of normal cells to tu mor cells and for the continued abnormal prolifera tion of the tumor cells once the cellular change has been consummated remain uncharacterized in crown gall. The former are clearly associated with the presence of the inciting bacterium during the inception period of the disease. The author has shown (1,4) that this factor is capable of bringing about the cellular alteration as early as 34—36 hours after the bacteria are brought into contact with susceptible tissues. When the inciting bac teria are destroyed by thermal treatment at this early period, very small, extremely slowly grow ing galls are produced. If, on the other hand, the bacteria are permitted to act on the host cells for 4 days before being killed, rapidly growing tumors result. Such tumors are not self-limiting, and when they develop on certain perennial plants they may reach enormous size. The transformation of normal cells into tumor cells appears to take place gradually, leading in a 4-day period to a rapidly growing autonomous type of cell. Essentially two hypotheses have been advanced