The transitory nature of a transmissible entity controlling the growth of a spontaneous tumor in mice

Two hundred and sixty‐three control mice of the C 3 H/ST inbreds bearing spontaneous tumors of mammary gland origin have been studied in reference to the injection of a specially prepared liver extract into one or more of their ancestors. Of these, 24 mice were from the original inbred strain in which no liver extract had ever been injected. Two hundred and thirty‐nine mice were among the descendants of a mouse that had received an intraperitoneal injection of a liver emulsion. These 239 mice were spread over 15 generations of lineal descent. All mice (263) of this experiment were kept as “controls” when their spontaneous tumors arose. The evidence obtained with the analysis of the growth rate of these tumors indicated the activity of a “transmissible entity” which increased in potency in suppressing these cancerous growths. The new evidence, obtained after six generations of lineal descent separation from the original injection of the liver extract, demonstrated quite convincingly that the amount of tumor inhibition became erratic and finally disappeared. The value of growth rate of tumors in mice of the 15th generation returned to the original rate obtained in mice of the 0 class in which there had been no treatment with liver extract in their ancestry.