Osborne & Mendel (1917) showed that raw soya beans (RS) had a low nutritive value for rats, and that cooking them for 3 h greatly increased this value. They attributed this increase in nutritive value to an increase in food consumption and to improved nitrogen absorption.These findings were confirmed by Hayward, Steenbock & Bohstedt (1936). They showed that for the first 3 days the food consumption of rats was similar on the RS and heated soya-bean (HS) diets. Later the consumption of the HS diet became greater than that of the RS diet. From these observations they concluded that the low nutritive value of the RS diet was not due to unpalatability but was caused by the 'unavailability of some essential protein fraction'; and that application of heat to the RS made this fraction available for absorption and metabolic use.Hayward & Hafner (1941) showed that addition of cystine or methionine, or of the combination of these two amino acids, improved the growth of rats or chicks given RS diets. Growth was even better when HS diets were thus supplemented. These investigators concluded that cooking not only made the sulphur amino acids available, but in addition, 'the heat treatment possibly increased the availability of the entire protein fraction of the soybeans'.Additional information on this problem was furnished by Bouthilet, Hunter, Luhman, Ambrose & Lepkovsky (1950), who showed that there was more methionine and more total N in the faeces of chickens with colostomies on RS diets than of those on HS diets, indicating the presence in the faeces of a complex of protein or methionine resisting digestion. The decrease in the digestibility of the RS protein could have been the result of ( I ) an unavailable protein fraction in the RS, or (2) the conversion of a part of the dietary and endogenous proteins in the intestine into an unavailable protein fraction by the action of the RS, Both these possibilities could operate in reducing the digestibility of the protein.Previously Chernick, Lepkovsky & Chaikoff (1948) showed that the pancreases of the chickens fed on the RS diet hypertrophied and contained more proteases. Since then the RS diet has been used for many years in this laboratory to study pancreatic function. This paper presents the results of experiments in which measurements were made of the nitrogen and proteases of the pancreases and of the corresponding intestinal contents at fasting and after eating, before and after adaptation to these diets. It was found that the protease activity of the pancreas was highest at fasting, but that it almost invariably decreased after eating. The decrease represents the algebraic sum of the proteases lost and those synthesized during the feeding period. The enzymes in the contents of the intestine, caecums and colon represent (I) the proteases secreted into the intestine less those that are inactivated, (2) the enzymes lost with the passage of the faeces, and (3) the proteases that are synthesized or destroyed by the intestinal microflora.The object of the experiments with ...

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