heart, which pumps it to all parts of the body. In addition to lacteal radicle; the villus contains long capillary bloodvessels, and the arteriole and venule in which they commence and end. These traverse the lymph-spaces of the connective tissue, which contains, not only the fat which the epithelial cells have passed into it, but the other products of digestion also. None of the fat traverses the walls of the bloodvessels; but the other products diffuse from the lymph, through the walls of the vessels, into the blood. Many nerve-fibres are found in the core of the villus on their way to epithelial cells, or to one or two plain muscle-fibres which are disposed in the direction of its long axis. For each villus is a little pump. By the contraction of the muscle-fibres it is shortened, and the fluid in its lacteal radicle is forced into the submucous vessels. Two problems have to be considered: First, in what form and by what mechanism are the several kinds of food absorbed? Secondly, what becomes of them after they have been absorbed? Clearly, the epithelial cell is the absorbing mechanism. It is not a membrane governed by the laws which regulate diffusion of fluids through membranes, but a living cell. There is hardly any limit to its power of selecting the food which it ingests. It could, and very possibly it does, ingest albumin and fats as such. Still, the elaborate provision which is made for converting albumin into diffusible peptone, and cane-sugar and maltose into easily diffusible dextrose, suggests that substances which will pass through membranes are more readily absorbed than substances which will not. We are justified in looking upon absorption as a physical problem up to a certain point. But we must not dwell too much on the physical aspects of the problem. If the absorption of food were merely a process of diffusion, an enormous quantity of water would be required to carry the diffusible products of digestion into the villi. The passage of the foods is aided by the selective activity of the epithelial cells. Peptonization greatly facilitates the work of the epithelial cells, but it is not a condition essential to absorption, so far as soluble proteins are concerned. It is, however, essential that the proteins should be presented to the epithelial cells in a soluble form. They could do nothing with the solid fibres of meat, however much they might have been disintegrated by mastication and by the action of hydrochloric acid. It is only after digestion by pepsin and by trypsin that all the proteins of food are brought into solution. Digestion is needed to reduce them to a condition in which the epithelial cells can take them up.