Diet and azo dye tumors; effect of diet during a period when the dye is not fed.

1. m 'Methyl p -dimethylaminoazobenzene was fed to rats for 8 weeks, either continuously or interrupted for periods of 2 to 12 weeks. Tumors developed in the livers of all groups, the number depending on the length of the period of interruption. 2. When 0.064 per cent of the dye was fed for two 4 week periods separated by a 4 week period during which various dye-free diets were fed, the final incidence of tumors depended upon the diet fed during the intermediate period. Tumor incidence was increased by diets containing 0.29 per cent of nicotinamide or 20 per cent of corn oil or when the amount of basal diet fed during this period was restricted to 63 per cent of the calories consumed by the control group. Tumor incidence was decreased by a diet containing 5 parts per million of selenium. A diet containing 24 per cent of casein and 20 mg. of riboflavin per kg. during the period of interruption reduced the incidence of tumors in one experiment and had no effect in two others. Choline or methionine fed during the intermediate period had no effect on tumor incidence. 3. Homogenates of livers from rats fed the dye for 4 weeks failed to coagulate with heat. This decreased coagulability persisted for at least 4 weeks on most of the dye-free diets fed. The percentage of tumors that developed on the various diets did not appear to be related to the coagulability of the liver homogenates when the feeding of azo dye was resumed nor to the concentration of hepatic riboflavin at this time.