A deficiency disorder induced in suckling young rats bred on a purified synthetic diet with "Glaxo casein" (caseinogen) as sole source of protein.

IN a former communication [Mapson, 1932] the stimulating effect on growth of small amounts ofmammalian liver fed as supplement to a purified basal synthetic diet containing all hitherto known dietary principles was demonstrated. It was shown that young rats when transferred from the stock diet to the synthetic ration and fed in addition on small amounts of fresh ox-liver showed a greatly accelerated growth over control animals. Evidence was submitted of the nonidentity of this growth-promoting factor with any of the better-known vitamins. This growth-promoting principle was provisionally named physin. During the course of this work the anomalous behaviour of a small number of litters was observed. The addition of small amounts of liver to the diet failed to give the usual acceleration in growth seen in the majority of the litters. These variable results were in contradistinction to the very uniform and consistent responses obtained when liver was fed not directly to the offspring but by transmission from the parent animal. These results were explicable on the assumption of a seasonal variation in the content of physin in the stock dietary. This assumption was supported by the fact that control offspring from litters showing little or no effect of the liver feeding displayed an absolute growth rate of a higher magnitude than that of control animals from litters in which the acceleration effect of the liver feeding was apparent. Moreover, the growth rate of control animals in the first group was approximately the growth rate given by the liver-fed offspring of the second group. An attempt has been made in the more recent work to eliminate as far as possible the effect of a stock dietary and to render the young animals more uniformly deficient in this growth-promoting factor. The further possibility had to be borne in mind that the actual synthetic diet originally used was not entirely deficient in physin. The existence of such a dietary principle had been demonstrated in the former work merely by its stimulating effect on growth, it was hoped by using a completely deficient diet, that animals might show definite pathological symptoms of such a deficiency. With the latter consideration in mind the synthetic diet used in the former work has been modified in various respects. The results of these experiments here recorded indicate in a striking manner the nutritional differences existing