fragments, many of them crystalline bodies; such as leucin, tyrosin, glutaminic acid, aspartic acid, arginin, lysin, histidin, etc., known chemically as monoamino-acids and diamino-acids. We have no means of knowing to how great an extent these more profound disruptive changes of the proteid molecule take place in the intestine. Whether practically all of the ingested proteid food is broken down into these relatively simple compounds prior to absorption, or whether only a small fraction suffers this change, cannot be definitely stated. A few years ago, the majority of physiologists held to the view that in the digestion of proteid food all that was essential was its conversion into soluble and diffusible forms which would permit of ready absorption into the blood. The belief was prevalent that, since the proteid of the food was destined to make good the proteid of the blood and through the latter the proteids of the tissues, any change beyond what was really necessary for absorption of the proteid would be uneconomical and indeed wasteful. On the other hand, due weight must be given to the fact that in trypsin digestion, proteid can be quickly broken down into simple nitrogenous compounds, and that in the enzyme erepsin, present in the mucous membrane of the intestine, we have an additional ferment very efficient in bringing about cleavage of proteoses and peptone into amino-acids. From these latter facts it might be argued that, in the digestion of proteid foodstuffs by the combined action of gastric and pancreatic juice in the alimentary tract, a large proportion of the proteid is destined to undergo complete conversion into amino-acids, and that from these fragments the body, by a process of synthesis, can construct its own peculiar type of proteid.