The bile exercises an important influence upon digestion, any disturbance in the flow of this greenish-brown secretion being very quickly shown both in stomach and intestinal digestion. It emulsonizes and saponifies the fats, it aids in their absorption, and it lubricates the intestinal mass, facilitating its passage through the entire length of the intestines. Thus, it is a very potent agent in regulating the bowel movements. A diminution in the flow of bile quickly expresses itself in constipation. Fats are almost entirely digested in the small intestine. The presence of fat stimulates the flow of pancreatic juice, which, in turn, stimulates the flow of bile from the liver. For this reason, if the liver is sluggish, fatty foods are desirable. Olive oil is prescribed for gall stones to stimulate the action of the bile ducts. Before the fat molecules can be absorbed, they must first be broken up into glycerin and fatty acids and further changed to a fine emulsion, which gives the contents of the small intestine a milky appearance. After they are broken up into these fatty acids and thus brought to the finest state of emulsion, they are readily saponified, being then soluble in water and in a state to be absorbed by the walls of the intestines. The fats are absorbed almost entirely in the small intestine,—mostly in the duodenum. As a rule, the starches, or dextrin, will not be fully digested by the saliva and those which have failed of salivary digestion are acted upon by amylase (one of the solids of the intestinal juice) and changed to maltose, while the trypsin from the pancreas, together with the intestinal juice, acts upon any protein which has failed to be fully digested in the stomach, changing it into peptone. In the form or peptone it is absorbed through the “sucking” villi of the intestinal walls. The food is forced along the intestinal tract by peristaltic or muscular relaxation and contraction waves, as in the stomach. As it is so forced, the nutrient elements, after being put into condition for absorption, are taken up through the villi of the intestinal walls by the portal veins and the lacteals of the sub-mucous lining. (See page 78). It is now believed that a larger proportion of food is digested and absorbed than was heretofore realized, and that the excretions from the intestines are, in many cases, made up almost entirely of refuse, and of the catabolic waste of the system. In an ordinary, mixed diet, it is stated that about ninety-two per cent of the proteins, ninety-five per cent of the fats, and ninety-seven per cent of the carbohydrates are retained by the body.