KEEPING WELL 419
It may be interesting at this point to consider briefly the nutritive value of some of the substances which are commonly used for food. Of these substances milk is first in importance, for it is not only a product which is derived from all mammals, but it is a universal article of food with the entire human race. It is the typical food substance, because it contains water, which is the most essential element in the body; caseine (cheese), which is the albuminoid element, and fat (butter) and sugar, which are the hydrocarbons. These essential elements are always found in milk, no matter whether it be obtained from human beings or from any other variety of mammals.
Wheat is perhaps next in importance to milk, and has often been termed, in the form of bread, " the staff of life." It contains albumen, starch, and mineral substances, and is therefore perfectly adapted to sustain life. One could live indefinitely on bread and water, even though such a diet might be very monotonous.
Eggs form an important portion of human food, but they consist largely of albumen, and, therefore, are not suited exclusively for a substance of food. They are important and almost indispensable as an element in diet. It should be remembered that eggs cooked are more difficult to digest than eggs uncooked. The error is often made of giving cooked eggs to the sick, or to those who are beginning to convalesce from severe illness. At such a time the gastric juice is deficient in quality and quantity, as a rule, and is unable to attack this concentrated mass of albumen successfully. Hence it must not cause surprise if it is brought up again in a hard lump, or after causing abundant pain, passes downward and is finally expelled from the lower end of the alimentary canal, still practically undigested.
Meat, or muscular tissue (and this includes the muscular tissue of fish), is quite essential as an article of diet. It is not indispensable, for many human beings do not use it and thrive without it. Lean meat is classed among the albuminoids; animal fat is, of course, a hydrocarbon. The digestibility of different kinds of meat varies greatly. Beef, mutton, and the white