In both the stomach and the intestine bacteria cause more or less putrefaction or abnormal fermentation of foods. Among the compounds thus formed from proteins in the intestines, indol and skatol are especially well known. They are produced most abundantly when protein digestion is slow or ceases, and when proteins remain undigested and unabsorbed for a long time in the intestine. Therefore, disturbances of pancreatic secretion and imperfect or very slow peristalsis are conditions that contribute to their formation. The discovery of these substances in the urine in unusually large quantities is indicative of such disturbances of protein digestion.

The movements of the intestines, or peristalsis, are quite as essential to rapid digestion of food in them as are the churning movements of the stomach. As the food is moved through the intestine its digestion is completed and it is absorbed.

Normally the products of protein digestion are not absorbed from the stomach. Most of them are absorbed from the small intestine; probably more than 80 per cent, is taken up by its villi.

1 Chemistry of Food Nutrition, by H. C Sherman page 116.

Inflammation of the intestines often hinders or prevents absorption. This will necessarily interfere with the maintenance of strength and flesh. Disturbances of circulation, destruction of epithelium, the obstruction of lymph-spaces with inflammatory exudates, and the formation of a covering of mucus, all take part in the causation of such an interference with absorption.

Pathologic processes sometimes give rise to the appearance of peptone in the urine. Often, they prevent, as in fevers, for example, the appropriation of food by tissue cells. When this happens, the cells can no longer develop a normal degree of energy, and may waste, atrophy, or die.

Meat is the chief source of proteins. Beefsteak, for example, contains 20 per cent, of it. In foods of vegetable origin a variable amount is found. For instance, bread contains 8 per cent.; arrow-root, 0.8 per cent.; potatoes, 2 per cent.; and dried peas, 22 per cent. Although dried peas are as rich in proteins as is beefsteak, they contain only 2 per cent, of fat and 53 per cent, of carbohydrates, while the flesh contains 3.5 per cent, of fat and no carbohydrates.

If meat be the chief food consumed by a man, the quantity of urates, urea, phosphates, and sulphates in his urine will be increased. Animal food requires a considerable quantity of oxygen for its utilization by the tissues. Therefore, a diet composed largely of meat increases the demand for oxygen. Most persons are more energetic and active when they eat meat freely than when they live chiefly upon vegetables. But if digestion is disturbed, or if there is a tendency to gout, this is not the case. Meat better satisfies hunger than will the same bulk of carbohydrate food. It is very agreeable to most persons, and its aroma and flavor stimulate appetite and gastric secretions. For these reasons most persons are tempted to eat too much meat. If, by an abundance of outdoor exercise, sufficient oxygen is not furnished to utilize it and a need for it is not also thereby created, an excess of protein waste will accumulate in the blood and tissues and cause biliousness, gout, and other disorders.

Meat is not a necessity of life. Nitrogenous food is a necessity, but it can be obtained in sufficient quantities from vegetables, certainly from vegetables supplimented by milk and eggs. An exclusively vegetable diet will enable a person to do as much, and at times even more work, as a diet containing an excessively large amount of meat, but it will not fit one as well to meet sudden demands for great exertion. A mixed diet is undoubtedly the most desirable: but one that contains a very moderate amount of meat is best. A diet rich in meat and relatively poor in carbohydrates is less fattening than one with these conditions reversed.

When carbohydrates and fats are eaten abundantly less protein is required to maintain a protein balance than when less is taken, therefore, they are called protein savers. Exercise or muscular work does not increase the breaking down of tissues in proportion to its increase, on the contrary muscles grow larger by use not smaller, therefore there occurs an appropriation and storage of nitrogen from protein food. There is, however, enough protein in an ordinary mixed diet always to supply this need.

How much protein is required to maintain health when an abundance of fuel in the form of carbodydrates and fat is eaten is a problem which has long vexed dietitians and physiologists. Voit observing the habits of large numbers of individuals concluded that 118 grams of protein were needed. Playfair recommended 119 grams, Gautier 107 and Atwater in our own country 150 for a man at hard work and 90 to 100 when at rest. More recently Chittenden has studied the subject exhaustively. By practical experiments on groups of men following different vocations and doing various grades of work, he found that they remained in good health, were well nourished and strong on a diet which afforded an average of 50 grams of protein and enough of other foods to supply the needed energy. Therefore he concludes that the old standards are much larger than they should be. This is doubtless true at least in adult life. Infants get in the milk which is their only food an amount of protein which would be equivalent to 140 grams for an adult. But it must be remembered that their cells are multiplying with rapidity and for this a large amount of protein is needed. As a child develops into manhood or womanhood gradually less is needed.