COLON, that part of the large intestine which extends from the cmcum to the rec tum, the greater part of the large intestine. It consists of three divisions, the ascending colon on the right side of the abdomen, the transverse colon, which passes horizontally from right to left just beneath behind the liver and stomach which cause it to bend slightly in its course, and the descending colon which passes down on the left side of the abdomen to the left iliac fossa where it joins the sigmoid flexure which extends into the rectum. The structure of the colon in comparative forms is dependent upon its function, which varies according to the nature of food. In herbivorous animals, where nutritive material in the food stuffs is enclosed in cellulose walls, the large intestine plays a considerable part in digestion. The dissolving of these cellulose walls is dependent upon the action of bacteria which are present in the large intestine for this purpose. Carnivorous animals possess a short and narrow colon, since their food undergoes practically complete digestion and absorption before it reaches this portion of the intestine. Man occupies an intermediate position in regard to structure and function of the colon. There is properly speaking no in testinal secretion in the large intestine, but the presence of alkaline substances which may favor the growth of bacteria while at the same time they the acid products of bacterial activity. The question of the normal presence
and action of bacteria is a debated one. The excessive action of bacteria leads to disease conditions yet they seem to be necessary, at least in some instances, to complete the digest ive process. Antiperistaltic waves of contrac tion keep the food in the large intestine under a constant mixing and kneading process. Ab sorption from the colon is slow and consists of a variable amount of nutrient material which was not absorbed by the small intestine and of a considerable quantity of water. The excre tory function is of more importance. The waste matter from the small intestine receives here the addition of many decomposition products while a large amount of water is absorbed by the colon, leaving the excretory products in the form of feces. A secretion of mucus aids in the passage of the waste material and perhaps interferes with the excessive propagation of bacteria. Consult Howell, 'A Text-Book of Physiology' ; Starling, 'Human Physiology.)