Effects of Carcinogens on Embryonic Mouse Tissue Transplants, with Special Reference to Lung *

The present series of experiments was undertaken to study the neoplastic potentialities of embryonic tissue, under normal conditions and under influence of carcinogens and other chemicals. This work was the outgrowth of an interest in the problem of the origin of the malignant cell in the adult, and an investigation of the stages in development during which cells may become neoplastic.$ MATERIALS Mice four to six weeks of age of strains A, C, CBA, CsH, and C67 black were used, chiefly because these strains are notably homogeneous. Embryonic tissues used for subcutaneous grafts were limited to tissues from strains A, C, and CBA. Six mice were placed in each cage, and all mice were maintained on stock laboratory chow ("Nurishmix") and water ad libitum. The temperature of the animal rooms was constant at 720 F. Embryonic lung, liver, and gut tissues were obtained from 15-20-day-old embryos and transplanted subcutaneously in the axillary region. Although the exact age of each litter was not determined, in many cases the gestation period was calculated by the vaginal plug method, and in some instances, the age was estimated by crown-to-rump measurements of the embryo. Hysterectomy was performed after each pregnant mouse was killed by cervical vertebral dislocation. The uterus and embryos were placed immediately in a petri dish moistened with isotonic saline to minimize desiccation. Each fetus was removed separately from the uterine wall and decapitated immediately after rupture of the amniotic sac. The lungs were excised and kept moist with isotonic saline solution. From each embryo it was usually possible to obtain four small pieces of tissue for implantation immediately after removal. The same transplantation procedure was used from embryonic liver and gut tissues. A small piece of tissue, about one cubic millimeter in size, was placed in a 13-gauge trocar and subsequently transplanted into the axillary region of the host. Most animals received two transplants, one on each side. Homologous (to the same strain) and heterologous (to a different strain) transplants were made in each case. Transplants were made with untreated tissues and with tissues exposed to carcinogens.