The production of tumors in the livers of rats fed in-methyl-para-dimethylaminoazobenzene.

Miller and Baumann (3) and Giese, Miller and Baumann (1) studied the carcinogenicity of various methyl derivatives of dimethylaminoazobenzene and found that the m'-methyl-p-dimethylaminoazobenzene was the most potent of the azo dyes for the production of liver tumors in rats, being even more active than ~-dimethylaminoazobenzene itself. As we were interested in studying conditions of rapid carcinogenesis, m'-methyl-~dimethylaminoazobenzcne was selected as the carcinogenic agent. In most of the early studies on the production of liver tumors, the investigators fed the dye continuously to the rats until the tumors appeared. Kinosita (2) mentioned in one of his reports that if animals were fed ~dimethylaminoazobenzene in the rice-carrot diet for only 50 days, and then returned to a normal diet without the dye, some of the rats would develop tumors in 150 days. Sugiura and Rhoads (9) fed p-dimethylaminoazobenzene to rats for 30, 45, 60, and 85 days in the rlce-carrot diet, and then withdrew the dye from the diet, continuing the animals on the rice-carrot diet alone. Only those animals which received the dye foi" 60 and 85 days later developed tumors. Reimann, Stimson, and Medes (8) fed rats p-dimethylaminoazobenzene in a rice diet supplemented with fresh vegetables for 75 days and then returned them to the stock diet. One hundred and thirty days later they found that 5 out of 15 animals had developed tumors. Giese, Miller and Baumann (1) fed the m'-methvl?-dimethylaminoazobenzene at a level of 0.056 per cent in a semi-synthetic diet for 2 ~ months and then continued the animals on the semi-synthetic diet alone. Two months later there was a 100 per cent incidence of liver tumors. In the studies reported here, the animals were fed the azo dye for different lengths of time in an effort to determine the minimum possible exposure to the