Absorption is the process by which the end products of digestion pass through the intestinal epithelium and enter the blood stream. In man there is little absorption in the stomach which can absorb water, alcohol and small amounts of mineral salts. Small intestine is mainly responsible for major absorption, since the intestinal villi contain the absorptive epithelial cells and a network of blood and lymph capillaries which readily pick up the digested materials. The mechanism of absorption has been explained on the basis of several physico-chemical principles. Of them diffusion is the most important.