Biochemical and Physiological StudiesThe 1940 developments in the field of fat metabolism were thoroughly reviewed by Eckstein (Ann. Rev. Biachem. 10,18].).The relative nutritive values of various fats have not been clearly established. Investigators at the University of Wisconsin have published data indicating that butterfat has growth-promoting properties superior to vegetable oils. In their latest announcement (Boutwell et al.--J. Dairy Sci. 24, 1027) it was suggested that this superiority was probably due to a long chain saturated fat acid or acids. The unsaturated portion of butter was converted to the active compound by hydrogenation. Certain vegetable oils such as corn, coconut, cottonseed and soybean did not contain the unsaturated form of the compound, for their nutritive value did not improve on hydrogenation. The results of work by Federal Government investigators (U. S. Dept: Agr. B. A. I. Rept. 1941, 12-13) were not in full agreement with the above. Growth experiments with young rats on diets containing 5% fat indicated that soybean oil and corn oil were superior to other fats. At a 15% fat level, butterfat and soybean, corn and linseed oils were superior in growth-promoting properties to other fats. Butterfat, oleo stock, mutton tallow, soybean oil, corn oil, linseed oil, coconut oil and cocoa butter were the fats studied. In digestion studies with diets containing 5% fat, soybean, corn and coconut oils had digestion coefficients of 98 to 99%, butterfat 88, oleo stock 74, mutton tallow 74, and cocoa butter 63. With diets containing 15% fat the soybean, Coconut and linseed oils had digestion coefficients of 97-99%, butterfat 91, oleo stock 87, mutton tallow 85 and cocoa butter 82. Work similar to the above, but with very young calves, by Gullickson et al. (J. Dairy Sci. 24, A315) indicated that butterfat excelled, followed closely by lard and tallow; corn, cottonseed and soybean oils were least satisfactory. A review on the subject was prepared by Munin (Fette u. Seifen 48, 88). His evidence claiming the superior nutritive value of butterfat was taken from work by the Wisconsin investigators and tests on very young calves reported in the Swedish, Danish and Norwegian literature.Hoagland and Snidcr (J. Nutr. 22, 65) fed young rats lard and hydrogenated cottonseed oil at levels of 5, 15, 30 and 54%. The growth properties of the fats were the same at the 5% level, but lard was superior at higher feedingievels. Maximum growth with both fats occurred on the diets containing 30%