Relative influences of natural and semipurified diets on tumor formation in mice.

For a number of years this laboratory has been engaged in examining the influence of nutrition on the formation of tumors in mice. Before 1945 these studies were conducted with rations composed of natural foodstuffs, the principal basic components being either wheat grain or Purina Fox Chow meal and milk powder. To these were added cornstarch and partially hydrogenated cottonseed oil, which were varied depending on whether the experiment was concerned with the influence of caloric intake or the proportion of dietary fat. Investigations dealing with the roles of proteins, vitamins, and minerals were initiated in 1945. For these purposes diets of more definitive composition were required, a condition that was met by the use of semipurified diets composed of casein, cornstarch, partially hydrogenated cottonseed oil, supplements of vita mins, and a complete salt mixture. The first of such experiments dealt with the formation of skin tumors in strain DBA male mice. One hundred twenty-six of the animals lived until they were 14-16 months old; and, in 31 per cent, benign tumors of the liver were observed. Grossly and histologically, the neoplasms were of the same type that occur spontaneously in strains C3H and CBA mice (4, 8). The high incidence of hepatomas in DBA males that had consumed semipurified rations contrasted strikingly with the infrequent occurrence of this tumor in comparable mice of the same strain, sex, and age, but fed diets of natural foodstuffs. Our experience with females of this strain was of a parallel nature: Hepatomas had