FOOD AND FEEDING VALVE, When a section of the potato is carefully examined, it will be seen to consist of three more or less well-defined por tions, namely, the skin, cortical or fibro-vaseular layer, and the flesh, which is made up of the outer and inner medullary layers. The cortical layer, immediately beneath the true skin, and sometimes designated the inner skin, is slightly colored, containing practically all the coloring matter normally present in the potato. As shown by recent analyses. the skin of the potato consti tutes on an average 2.5 per cent. of the whole and the cortical layer S.5 per cent. It is difficult to peel potatoes so that the skin only is removed.
The amount of refuse and edible portion lost by peeling is estimated at 20 per cent. Doubtless, in many cases the rejected portion is very much larger.
The edible portion is made up of 78.3 per cent. water. 2.2 per cent. protein (total nitrogenous matter), 0.1 per cent. fat, 18.4 per cent. car bohydrates (principally starch), and 1 per cent. ash or mineral matter. Of the carbohydrates, 0.4 per cent. is made up of crude fibre and materials which in some of their modifications constitute the cell walls of plants and give them a rigid structure. The fuel value is 3S5 calories per pound. The above figures. like others for eompo ition of food materials, represent genera] aver ages. from which there are wide variations in individual specimens. Though the skin, cortical layer, and flesh differ somewhat in composition, they all resemble more or less closely that of the whole tuber. When potatoes are stored they shrink about 12 per cent. in 7 months.
Although the potato contains some protein, it is chiefly valuable as a carbohydrate food, and, like all such food, is useful for supplying the body with energy. The principal ways of cooking potatoes are baking, boiling, and frying, or sonic modifications of these processes. Just wily cook ing changes the flavor as it does has apparently never been made the subject of investigation. In potatoes, as in other fonds, the cooked starch is more agreeable to the taste than the raw. Pos
sibly also there are volatile bodies of more or less pronounced flavor which are removed or reduced by the heat of cooking. The physical condition of the potato is much affected by heat. In the raw potato the separate starch grains are inclosed in cells with walls composed of crude fibre, a material resistant to digestive juices.' If potatoes were eaten raw, the digestive juices would not reach the starch as easily, unless the cell walls happened to be ruptured mechani cally. as in mastication. Heat, however, expands the water present, ruptures the cells, and breaks up the starch, expanding the granules. which when raw consist of tightly packed concentric layers. Over 00 per cent. of the total nutritive material of potatoes is digestible. According to statistics obtained in the large number of dietary studies made in this country, potatoes constitute about 13.7 per cent. of the total food consumed by the average American family, and furnish not far from 3.9 per cent. of the total protein and 10 per cent. of the total carbohydrates. The potato is a staple article of diet in almost every house hold. The universality and extent of its Con sumption would seem sufficient to prove it to be a wholesome and nutritious food. Scientific in vestigation shows that the practice, which has become so general, of serving potatoes with meat and other similar foods which contain liberal amounts of protein is based upon correct prin ciples, one food supplying the deficiencies of the other.
Evaporated potatoes are on the market, being especially recommended for provisioning camps and expeditions. As compared with fresh, the evaporated potatoes have a high nutritive value in proportion to their bulk. Large quantities of potatoes are used for the manufacture of starch. Potatoes either raw or cooked are sometimes fed to pigs. milch cows. and other farm animals. When fed to pigs it has been found that bushels of cooked potatoes (fed with corn meal) is equivalent to one bushel of corn.