In 1931 two male and two female albino rats of unknown heredity were mated. Their offspring were bred without any regard to age or blood relationship, the only rule being to select the larger and more healthy animals of the litter for breeding and use the rest in experiments. The present colony, numbering 750 members, consists entirely of the descendants of the four original rats. In 1934, three years after the establishment of the colony, an old rat developed a tumor of the uterus (Fig. 1), and this has since been transplanted through 55 generations into 600 animals without a single instance of spontaneous regression. If the inoculation is made in the axillary space, about one-third of those surviving three weeks have metastases in the lungs. The only agent which has halted the growth of the tumor is radiation. After eight days there is little or no difference between tumors which spring from 0.1 c.c. and 0.2 c.c. of inoculum. Even with 0.00001 c.c. tumors grew in 31 per cent of animals inoculated. With 0.1 c.c. the growth is so rapid that experiments have been terminated fourteen days after transplantation because of the fact that the animals begin to die. Fig. 2 shows tumors arising from 0.01 and 0.001 c.c. fourteen days after inoculation.

A Transplantable Uterine Rat Sarcoma of 100 Per Cent Transmissibility

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