Certainly as yet, there is no evidence that the amino-acids, as such, go through the epithelial cells of the intestine; they are not found in the blood or lymph to any appreciable extent, yet the proteids of the blood are reinforced in some manner by the products of proteid digestion. Whichever view is correct, one thing is perfectly obvious, viz., that in the act of absorption the products resulting from the gastric and pancreatic digestion of proteid foods are exposed to some influence, presumably in the epithelial cells of the intestinal wall, by which there is a reconstruction of proteid. Further, the proteid substances so formed are of the type peculiar to the blood of that particular species of animal. The proteids of beef, mutton, chicken, oatmeal, or bread go to make the proteids of human blood. From these statements, it is obvious that what we term absorption is something more than a simple diffusion of soluble substances from the alimentary tract into the blood current. The process is much more complex than appears on the surface, and our lack of definite knowledge, in spite of numerous efforts to unravel the mystery, merely strengthens the view that we are dealing here with an obscure physiological problem, and not a simple physical one. Digestion induces a splitting up of the food proteid into fragments, large or small, while incidental to absorption there is apparently a reconstruction, or synthesis, of proteid from the fragments so formed. The process seems somewhat costly, physiologically speaking, yet when one considers the variety of proteids consumed as food, it is easy to comprehend how essential it is that in some manner, as in absorption, there be opportunity for construction of the specific proteids of the blood and lymph.