Another function of protein in the diet is that of supplying energy by combustion in the body. The proteins also are con cerned in promoting the oxidation of the carbohydrates and par ticularly of the fats in the body. Thus the inhabitants of very cold climates can withstand the low temperatures on a diet very rich in protein and fat, the high protein content enabling the fats to be oxidized more readily in the body. This action is known as the "specific dynamic action" of the proteins. The inhabitants of the tropics, on the other hand, subsist on a diet that contains a relatively small amount of protein, the energy re quirements for the maintenance of body temperature being very low. It was at one time thought that the muscular energy of the body was obtained from the proteins alone, but it has been found that this is erroneous. Carbohydrates normally function in this way, but the requisite carbohydrates can be supplied from certain of the amino-acids in animals fed on a pure protein diet. Any excess of protein in the diet over the immediate needs of the body is usually oxidized in a few hours, the body being unable to store protein as it can fats or carbohydrates. But within certain limits
it seems that if abundant protein is taken with regular muscular exercise, as in the training diet of some athletes, a small per centage of this protein can be stored for increase in the size of the protoplasmic masses of the individual muscle fibre. The utilization of proteins as food-stuffs is primarily dependent on their digestibility. Proteins like the keratins of hair and horn are not broken down into amino-acids by the enzymes of the alimentary canal and cannot serve as foods. The average amount of protein in the adequate diets of adult inhabitants of the tern perate climes is about ioo grams per diem.
The industrial uses of proteins are dealt with in other articles (see GELATIN, GLUE, CASEIN, HAIR, WOOL, SILK, LEATHER, etc.). Other uses are in the manufacture of water-resisting ad hesives, distempers, small articles, such as buttons, and in the special transparent preparation known as "galalyte" which is used for artificial amber.