As some of these salts are constantly being eliminated from the body, there must be a constant supply to keep the tissues in equilibrium.
Vitamines are elsewhere considered in this booklet, hence only a very brief summary here. The chemistry of these products is very little understood at present. They were so named by Funk because of their nitrogen content and similarity to ammonia, the name really meaning _vital ammonias_. The term "vital" carries with it the idea of their importance to life. Some persons have questioned this name; but up to the present, it seems to be the best suggested.
The importance of the vitamines in nutrition has been very clearly demonstrated in experiments upon animals, and these experiments have been repeated a sufficient number of times to be conclusive. Animals have been fed upon pure protein, fat, carbohydrate, and salts, but with vitamine removed or destroyed; and although receiving calories enough, they fail to keep up their nutrition. With a simple change of dietary to include a small amount of food containing the vitamine, without any change in the total calories eaten, their nutrition improves quickly, and they come back to a normal state.
Foods rich in vitamine are represented by milk, fresh vegetables, fresh fruits, and whole grain products. Foods poor in these substances are represented by sterilized and preserved milks, dried fruits, dried vegetables, white flour, and polished rice.
Vitamines are reduced or lost by the following processes in the preparation of foods: taking off the coating of grain, overheating, washing out in cooking, and drying.
Water, although not a food in the sense of yielding fuel value to the body, is a most important agent in all the various chemical processes taking place in the tissues.
Water is the universal solvent; and because of this property, it carries both food and waste to and from the tissues. The average person needs from three to five quarts a day, a part of which is taken as a portion of the food eaten. This leaves from three to five pints to be taken as a drink. Good drinking water should be colorless, odorless, and of an agreeable taste; should be free from organic matter, poisonous metals, and the bacteria of disease; and should be low in nonpoisonous mineral salts--that is, should be reasonably soft.