The conception now held of the amino-acid structure of proteins, and the specific need of certain amino-acids in the construction of tissue components, has lent a new interpretation to the purpose of proteolytic digestion in the alimentary tract. There is no longer any question regarding the possibility of an extensive cleavage of proteins during their sojourn in the gastro-intestinal canal. Considerable quantities of amino-acids have actually been isolated from the intestinal contents during the progress of digestion of proteins in the body. Furthermore, the researches of Folin, Van Slyke and others in this country have left little doubt that amino-acids are actually absorbed as such during the digestive cycle; for, by the use of microchemical methods, a noteworthy increase of amino-acids circulating in the blood can be discovered during the period at which the height of digestion may be expected to occur.
Shall we assume, on this account, that proteins