The subject of salt in food has received considerable attention and discussion by scientific investigators, and many theories have been advanced by those interested in hygiene as to the effect of common salt used in food. The tissues and organs of the body contain certain salts, without which life could not exist, but it does not follow that these salts need to be supplied in mineral form. Common table salt is an inorganic substance, while the mineral salts in green and fresh vegetables are organic, and readily convertible, therefore a valuable aid in the digestion of other foods. A diet of sugar, pure oil, and artificially prepared proteids would be absolutely unwholesome and would fail to nourish the body for any length of time because of the lack of mineral salts. All natural food products, whether of vegetable or animal origin, contain a limited but ever-present amount of mineral salts. This is especially true of milk, eggs, and the seeds and green portion of plants. The amount of salts in the human body is considerable, especially the calcium phosphates of the bones, but the salts that need to be supplied daily in food is small because the salts are not consumed as rapidly as are other elements of nutrition. [Sidenote: Grains deficient in salt] Some grains, especially rice and corn, are somewhat deficient in salts. At the Kansas Experiment Station some pigs were fed exclusively on corn, and others on grain and green forage. At a certain age the pigs were killed, and the bones weighed and tested for strength. The bones of the pigs which had been fed on a corn diet, which is deficient in mineral salts, were about half as heavy and strong as the bones of the pigs fed in a more natural way. LESSON V CHEMISTRY OF DIGESTION DIGESTIVE ORGANS AND DIGESTIVE JUICES FIRST--THE MOUTH: The three salivary glands of the mouth secrete the saliva, which is an _alkaline_ substance containing a digestive enzym called ptyalin. The saliva begins the digestion of starch and moistens food to facilitate swallowing. SECOND--THE STOMACH: The gastric juice secreted by the mucous lining of the stomach is an _acid_. It contains hydrochloric acid and pepsin, which act on proteids, changing them to _proteoses_ ("intermediate products formed naturally in the process of digestion") and peptone. The gastric juice also contains _rennet_, which acts directly on milk, and indirectly on all proteids. THIRD--THE LIVER: The liver secretes a digestive fluid called bile, which is an _alkaline_ substance. Its chief purpose is to emulsify fats and to supply the alimentary tract with the requisite amount of moisture. FOURTH--THE PANCREAS: The pancreatic juice, secreted by the pancreas, is an _alkaline_ and slightly _acidulous_ substance. It contains three enzyms, the names and action of which are as follows: Amylopsin completes the digestion of starch.