Increased effect of a transmissible entity on the control of cancer in C3 H/St mice

Three hundred and seventy-one mice of the C3H/St inbreds bearing spontaneous tumors of mammary gland origin have been used in this experiment. All mice studied were lineal descendents of a tumor-bearing mouse which had been injected with a liver extract. In this descent there appears to be a transmissible entity presumably induced by the injection of the liver extract. Following 15 generations of inbreeding after the appearance of a transmissible entity, a second sudden reversal of effect on cancer growth in mice has been indicated. This change has progressively altered the growth of cancer from a very low effect to a maximal effect, i.e., to a complete regression of a high percentage of the tumor. The maximal effect of the transmissible entity is the complete suppression of the growth of cancer during, at least, through the 25th period of observation, thus producing negative values of tumor growth. All these effects of the growth and fate of spontaneous tumors of mammary gland origin in mice have been obtained in a single lineal descent of C3H/St inbreds without resorting to any outcross.