A general knowledge of the chemical composition of different food products, and the changes effected by each element when introduced into the system is as essential to scientific living as a similar knowledge of drugs in the compounding of medicines. A few years ago it was necessary to depend upon the scientific researches of other countries for such information, but now hundreds of different analyses of the common foods are recorded at Washington, and as they vary but slightly from those of other countries, they are accepted as authentic.

In order to enlighten the general public upon this most important subject, W. O. Atwater, Ph.D., Special Agent in charge of Nutritive Investigations, Office of Experiment Stations, has published a pamphlet entitled "Principles of Nutrition and Nutritive Value of Food," in which he gives much valuable information as well as definite tables of averages of different analyses, arranged in practical form for daily use in regulating the diet to the best advantage.

His propositions are:

1. "Food is that which taken into the body builds tissue or yields energy.

2. "The most healthful food is that which is most fitted to the needs of the user.

3. "The cheapest food is that which furnishes the most nutrition at the least cost.

4. "The best is that which is both the most healthful and the cheapest".

While the question of cheapness is not a vital one after man realises his innate power to attract what he really needs, in the present social conditions it is well for both rich and poor to know that the best nutrition is usually derived from the most inexpensive foods, and that a great variety is not desirable. Because of deluded ideas regarding "the best" the wealthy injure the health by indulging in delicacies that gratify taste but do not nourish the system properly, while the poor cultivate misery because they are deprived of such gratification, entirely unconscious that there is more real starvation or physical suffering because of lack of nutrition among those who live in affluence than among the laboring classes who are obliged to cultivate habits of simplicity. There is much greater need of education in selecting and preparing food to meet the demands of the system as well as to gratify the aesthetic taste, than of greater wealth. The most simple dishes may be attractive, appetizing, and nutritious when prepared with skill and care to save the living cell.

To improve the judgment regarding food values and the necessities to sustain life, Mr. Atwater gives the composition of both body and food, as the chemical substances of which the body is composed are the same as those of the foods which nourish it.

He says, "From fifteen to twenty elements are found in both body and food, among the most abundant of which are oxygen, hydrogen, nitrogen, calcium, phosphorus, and sulphur. The elements are so combined as to form a great variety of compounds in each. The most important kinds of compounds in the body and in foods being proteids, fats, carbohydrates, mineral matter and water. The functions of the compounds in the food are to build and repair the various tissues of the body and to supply it with heat and muscular energy.

"Water forms 60 per cent, of the weight of the body. It is important but does not yield energy as it cannot be burned or oxidized in the system.

"Mineral matter, or ash (in organized condition), forms 5 or 6 per cent, of the weight of the body, and is found in the bones and teeth as well as in solution in the tissues and fluids. It is indispensable but does not yield energy. When food or body material is burned the mineral matter remains as ash (dead or disorganized by the heat).

"Proteids include the principal nitrogenous compounds for tissue building, forming 16 per cent, of the weight of man, and may be divided into three classes:

1. Albuminoid - as white of egg, lean and gristle of meat, curd of milk, gluten of wheat.

2. Gelatinoid - as connective tissue, skin, ossin of bone.

3. Extractive - as extract of meats, beef tea, amids of vegetables.

Albuminoids and gelatinoids together make the basis for the structure of bone, muscle and all the tissues, hence are most important. They may also be burned in the body to produce energy if there is not enough of other energy producing food.

"Extractives contain nitrogen but are not supposed to produce energy or build tissue. They act as stimulants and appetizers, hence are of value,"

This lifeless condition of extractives is a most important discovery and is corroborated by Chambers' Encyclopaedia in the statement that gelatine although a tissue building element, does not seem to serve that purpose. It is generally supposed that extracts of meat and vegetables, especially beef tea, are condensed nutritives, and invalids depend upon them for nourishment in the most critical stages of disease unconscious that they are starving or fasting, being sustained only by stimulant and the subjective forces. The reason that this class of food is so devitalized is that every proteid cell is killed by long boiling.

Continuing Mr. Atwater's analysis of food, he says:

"Fat varies greatly but should form 15 per cent, of the weight of the body. It is a reserve force for supplementary fuel to produce heat or energy in emergencies. Fat is found in meat, butter, olives, cotton seed, oatmeal and corn. The proteid and fat of food may become body proteid and body fat.

"Carbohydrates form only 1 per cent, of the weight of tissue, but they burn in the body, producing energy. They are found in vegetable food like cereal grains and potatoes, milk, sugar, starch, etc.

"Refuse is the part of food that is not used or cannot be appropriated by the body, as seeds, skin, shells, the woody fibre of the wheat kernel, and bones".

This analysis, although about the same as given elsewhere, will aid the beginner in scientific living to understand the tables on the chemical composition of food. Mr. Atwater also explains the process of measuring energy in the following extract by com-paring food with fuel. "When fuel in the furnace or food in the body is oxidized by air the latent energy becomes active, or the potential energy becomes kinetic. It is transformed into heat and power. As various kinds of coal differ in the amount of heat produced, so various foods differ also, yielding different value as fuel in the body. Latent energy in food is measured by the "bomb calorimeter" - food is burned by oxygen - and the result is expressed in its "heat of combustion".