Food serves three great purposes in the physical body and is divided into three general classes so far as digestive nutriments are concerned.

1. The proteid or body building element, as found in eggs, meat, nuts, milk, cheese, cereals, beans, peas, etc.

2. The fat or reserve force element, as found in fat of meat, vegetable oils, butter, etc.

3. The carbohydrates or heat and energy producing element as found in starch foods, like potatoes and rice, also in the sugar and starch of cereals, fresh vegetables and fruit.

Other essential elements are present in all food, as mineral matter, water, and refuse which will be considered later, but at present only the great value of the proteid, or tissue building element is to be established, as no other kind of substance except a small amount of proteid, that is reorganised by the constructive ferments, can take its place. Both fat and proteid may be burned or oxidized in the system to produce energy if the carbohydrates are lacking. Carbohydrates and proteid may produce fat if not exhausted in energy, but neither fat nor carbohydrates can be used to reproduce the body cells, hence the necessity of intelligently selecting enough of the proteid foods and protecting this element from being destroyed by excessive heat, as it is the only source of prepared material to sufficiently reconstruct the body cells to prevent the first encroachment of old age.

Many other conditions are sustaining and protective to a degree, as when fat is stored and of a healthy quality it is drawn upon in cases of emergency for heat or energy that otherwise must be supplied from the latent forces of the body cells, but an increase in fat is not always an indication of health and strength of the real physical tissues or body substance. In fact the amount of fat often becomes excessive in old age and diseased conditions after the body cells are too weak to prevent its accumulation.

This is because the cells are not properly nourished for reproduction, and the food that should be used for this purpose, being devitalized or dead from the heat of cooking must be passed off as refuse, be stored as fat, or be oxidized for energy and heat, all of which tends to overwork the constructive ferments and the cells that are already weakened. An increase in fat indicates health only when the cells are perfectly sustained and repro-duced. While the lymphatic temperament which takes things easy is subject to excessive fat, the opposite extreme is seen with the nervous temperament, where incessant mental or physical action causes thinness, as the surplus energy is used, instead of being allowed to accumulate as fat. Health cannot be maintained unless the vitality of the cells enables them to regulate the energy instead of being ruled by it. Many people are living entirely beyond their capacity, while others are stupid and plodding from a clogged and burdensome physical condition. When the value of the proteid and organized chemical elements in food is realized and the amount of food is better proportioned to sustain its natural purposes, the life will be more perfectly balanced, maintaining the freshness of youth for a much longer time than is possible with the present conditions of extremes and friction. The body cells utilize the water, and some of the organized chemical substances in constructing the intercellular tissue of both muscle and bone in which the cells are imbedded, but the cells themselves upon which all life action depends can only be quickened to reproduce themselves or multiply in natural growth when nourished by the "living mass of protoplasm" or nucleated proteid cells - the only substance endowed with organized life.

Blaisdell says many of the cells of the body live only for a few hours, especially those of the lining membrane of the intestines, while others, as those of the bones, exist for several years. All authorities agree that in a few years' time, from five to seven years as the longest estimate, every atom of the human body is entirely changed - new cells replace the old ones. As this is the case, "perpetual youth," or at least the retaining of youth for many years, is not a mysterious or unnatural condition. It may be enjoyed by all who use good judgment in nourishing the cells of the body, avoid excesses which exhaust them, and the indulgence of thoughts that impress diseases and age upon them. The living proteid element in food is essential to long life, but qualities of mind and regulated activities must go with it - "we do not live by meat alone".