in its broadest signification includes all those substances which when taken into the body build tissues, restore waste, furnish heat and energy, and provide appropriate condiments. The building of tissues is especially an important function during the early life of animals as it is through this building of tissues that growth takes place. The restoration of waste of tissues assumes special importance during that period of life when the weight of the body is supposed to be reasonably constant. At this time the waste of tissue in the natural processes is restored by the assimilation of new material in the same proportion.

If the assimilation of new material goes on at a greater rate than the waste of old material it manifests itself during the period of expected equilibrium in the deposition of adipose tissue and a consequent abnormal increase in weight.

In the after period of life the process of waste is naturally more vigorous than that of assimilation, and the tendency is manifested, which is wholly in harmony with the laws of Nature, to gradually diminish the weight of the body, and this continues to the extreme emaciation of old age.

It is evident, therefore, that the food consumed should be adapted to these changing periods. The growing animal needs a larger quantity of food in proportion to its actual weight than the animal which is in a state of equilibrium, that is, of mature age, and the animal which is entering upon the period of old age needs a less quantity of food in proportion to its weight than in either of the other periods of life. Thus, the rations of infants and children should be generous, the rations of mature man sufficient, and the rations of old age limited.

The food should also contain the various elements which enter into nutrition in the proper quantity. The nitrogenous constituents in food, when subjected to the ordinary process of digestion, yield a certain quantity of heat and energy but their more important function is to nourish the nitrogenous elements, of the body of which the muscles, hair, skin, and fingernails are types. The mineral constituents of food, especially phosphorus and lime, have a general utility in promoting the metabolic functions, especially in the movement of the fluids of the body through the cells walls, and at the same time are actual nourishing materials, entering particularly into the composition of the bones and teeth.

The fats and oils which are present in the foods have the capacity of producing large quantities of heat and energy during their combustion in the body, and thus serve as a source of animal heat and muscular activity.

The starches and sugars which are the most abundant elements of our food, although they have a heat-forming power of less than one-half that of fats, are largely utilized in the production of heat and energy and in the formation of animal fat.

SOCIAL FUNCTIONS OF FOOD.

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To secure a proper and complete nutrition of the body it is desirable that all these elements should be so adjusted as to provide for complete nourishment without having any one of them in great excess. It is evident that an excess of any one or more of these nutrient materials must necessarily impose on the organs of the body an additional work in securing their proper elimination. This tends to overburden the excretory organs and to cause a premature breakdown thereof. This giving away of the organs may not come for many years, not, perhaps, until advanced life, but when it comes it necessarily shortens the period of human existence.

The term "balanced ration" means the adjustment of nutrients in the food in such a way as to secure complete and perfect nutrition without loading the body with an excess of any one element. This is also an important point on the score of economy. A large percentage of all the earnings of man is expended for food products, and hence these products should be used in a manner to secure the best results possible. If, by a practice of scientific nutrition, 10 percent of the value of foods could be saved it would create a fund which, could it be utilized, would minister in the highest degree to the comfort and welfare of the human family and form an abundant pension for old age.

SOCIAL FUNCTIONS OF FOOD.

In the above paragraphs attention has been directed particularly to the nutritive and economic properties of food. It must not be considered that mere nutrition is the sole object of foods, especially for man. It is the first object to be conserved in the feeding of domesticated animals, but is only one of the objects to be kept in view in the feeding of man. Man is a social animal and, from the earliest period of his history, food has exercised a most important function in his social life. Hence in the study of food and of its uses a failure to consider this factor would be regrettable. For this reason it is justifiable in the feeding of man to expend upon the mere social features of the meal a sum which often is equal to or greater than that expended for the mere purpose of nutrition. This part of the subject, however, belongs especially to the kitchen and dining room, and, therefore, will not be discussed at greater length at the present time.

It is believed that a more careful study of the food he consumes will benefit man in many ways. It will lead to a wider public interest in the problem of the purity of food and the magnitude of the crime committed against mankind in the debasement, adulteration, and sophistication of food articles.

This study will impart to the social function of food an additional charm, in that the origin and character of the material consumed will be known and the properties which they possess for nourishing the body understood. This will enable man, as a social animal, to so conduct himself at table as

to secure the greatest possible pleasure and social benefit therefrom and at the same time avoid any injury which ignorance might permit and invite.

It may appear that the inartistic treatment of a subject of this kind, as indicated in the following pages, is not one which is calculated to excite any sympathetic interest or appeal to the natural desire for literary and artistic expression. Yet the importance of the subject is so great as to warrant the experiment of presenting the matter in this form rather than in any more elaborate and connected way.

DEFINITION AND COMPOSITION OF FOODS.

Food, in its general sense, is that which nourishes the body without regard to its physical state, that is, it may be solid, liquid, or gaseous. More particularly defined, food is that material taken into the body in the ordinary process of eating which contains the elements necessary for the growth of tissues, for the repair of the destruction to which the tissues are subjected during the ordinary vital processes and for furnishing heat and energy necessary to life. Incident to the utilization of these elements there is consumed, also, a considerable quantity of matter inextricably mingled with food in a natural way, which takes no direct part in nutrition and yet which is useful, as a mass, in promoting the digestive processes. These bodies are certain indigestible cellular tissues which are present in foods, mineral matter, and other materials which are naturally found in food products. Included in this broad definition, therefore, are many substances which are usually not thought of in the sense of food; among these are water and air. Air, however, would probably be excluded because it is not introduced into the stomach, that is, not in quantities which have any significance in the vital processes. Water, on the contrary, is one of the most indispensable constituents of food and is also used in considerable quantities as a beverage. The water, itself, is indispensable to nutrition and is also one of those bodies mentioned above which are necessary to secure the proper conduct of the digestive processes.

By means of the oxygen in the air the combustion of food in the various parts of the body is secured, and thus animal heat and energy developed. In this respect the combustion of a food product is similar in every way to the burning of coal in the production of heat and motion. The same calorific laws which govern the steam-engine are applicable, in all their rigidity, to the animal engine. The quantity of heat produced by the combustion of a certain amount of fat or sugar is definitely measured in a calorimeter and is found to correspond exactly to the quantity of heat produced by the ordinary combustion of such bodies. The term "food," therefore, in this respect, would include the oxygen of the air without which the development of animal heat and energy would be impossible. It also includes those bodies of a

CLASSIFICATION OF FOODS.

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liquid character which are classed as beverages rather than as foods. All of these bodies have nutritive properties, although their chief value is condimental and social.

That large class of food products, also, which is known as condiments is properly termed food, since they not only possess nutritive properties but through their condimental character promote digestion and by making the food more palatable secure to a higher degree the excellence of its social function.

It is now possible to condense into a distinct expression the definition of food in the following language: Food in a general sense embraces those substances taken into the body which build tissues, restore waste, and furnish heat and energy.

CLASSIFICATION OF FOODS.

Foods may be considered under different classifications. First, as to general appearance and use three classes may be made,-foods, beverages and condiments. As types of the first division of these foods may be mentioned cereals and their preparations, meat and its preparations (except meat extracts), fish, fowl, and game. Beverages are those liquid food products which are more valued for their taste and flavor than actual nutritive value. As types of beverages may be mentioned wines, beers, distilled spirits and liquors of all characters, tea, coffee, cocoa, chocolate, etc. Under wines, in this sense, may be included the fermented beverages made of fruit juices, such as cider, perry, etc. Types of condiments are salt, pepper, spices, vinegar, etc. Milk, although a liquid substance, is hardly to be considered a beverage, and on account of its high nutritive properties may be classed, together with its preparations, under the first head.

Foods may also be classified as nitrogenous, starchy, oily, and condimental. Nitrogenous foods are those in which the proportion of their material containing nitrogen is large. Lean meat may be regarded as a type of nitrogenous food, since it consists almost exclusively of tissues known as protein and contains nitrogen and sulfur as essential ingredients. The white of an egg is also a typical nitrogenous food and, to a less extent, the yolk. Among vegetables, peas and beans are typical foods containing large percentages of nitrogenous matter. The gluten of wheat is also a typical nitrogenous food and the zein of Indian corn, corresponding to gluten, is a nitrogenous material. Practically all the vegetables used as foods contain more or less protein in their constituents. Among the cereals oats has the largest quantity and rice the smallest of this valuable food material. Of oily foods the fat of animals, including butter, is a typical representative. All meats, fish, fowl, and game contain more or less fat. Of vegetables and fruits there are many

which contain large quantities of fat, such as nuts, oily seeds, etc. All vegetables contain more or less fat, although the succulent vegetables usually contain but little thereof. Of starchy foods there are no types in animal food, the quantity of carbohydrate material therein being extremely limited. The lobster and horse-flesh contain perhaps a little more than 1 percent of carbohydrate food, but most meats contain much less than that. Sugar and starch are typical carbohydrate foods.

The cereal grains are composed largely of starchy foods, and so are certain tubers, such as the potato, cassava, etc. Of the common cereals rice contains more starch than any other and oats the least. Sugars are intimately related to starch and are included under the term starchy food or carbohydrate food. The carbohydrate matter in the flesh mentioned above, namely glycogen, is of the nature of a sugar. Among the typical sugar foods are beets, melons, and fruits, some of which contain large percentages of sugar. All fruits contain greater or less quantities of sugar, and that is true, also, of all vegetables.

Of the plants which produce the sugar of commerce there may be mentioned the sugar-cane, the sugar-beet, the maple, and palm trees. The principal sources of the sugar of commerce are the sugar-cane and the sugar-beet.

Of the condimental foods may be mentioned spices, including pepper, mustard, cinnamon, allspice, and other foods of this class. Common salt occupies a unique position in food products. It is the only mineral substance which has any value as a condiment in human food. But it also has a more important function than its condimental character, namely, it furnishes the supply of hydrochloric acid without which digestion in the stomach could not take place. For this reason common salt must be regarded as an essential food product as well as a condiment.

EXPLANATION OF CHEMICAL TERMS.

Inasmuch as this manual is not solely intended for expert chemists and physiologists but also for the general public, a simple explanation of the use of the terms used in analytical data and tables is advisable.

Under the term moisture is included all the water which is present in a free state, that is, not combined in any way with the ingredients of the material, and other substances volatile at the temperature of drying. The water is determined by drying to a constant weight at the temperature of boiling water or slightly above. In bodies which are easily oxidized this drying takes place in a vacuum or in an inert gas like hydrogen or carbon dioxid.

Protein. Under this term is included all the nitrogenous compounds in a food product which contain in their composition sulfur, nitrogen, car