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which have appeared to bear such a diet well in early life are found to break down in middle life or to become prematurely old.

Vitamin A differs strikingly from vitamins B and C in that it can be stored in relatively large amounts in the body for future use. The liver appears to be especially adapted to the storage of vitamin A ; but it has also been found that the lung tissue is richer in vitamin A when the food has furnished it more abundantly. Thus a diet poor in vitamin A leads to a lower proportion of this vitamin in lung tissue, and lung tissue thus depleted becomes more susceptible to infection. These facts strongly suggest that vitamin A here plays the part of an important constituent of the tissue.

All three of the vitamins plainly have important functions in regulating certain conditions in the body, and it here appears that vitamin A may be important as a tissue-building material as well. Hence vitamin values as well as the older aspects of food values will enter into our studies of food products in the chapters which follow.

Summary of the Functions of Food Much the largest part of the total solids of the food is burned in the body and yields energy for the support of its activities. Even during growth most of the fat and carbohydrate and the greater part of the protein is so used.

Part of the protein of the food is used as a source of body protein, or, as it is often expressed, is used to build tissue. Several elements not contained in most proteins are also essential to the tissues of the body and these are derived from the so-called ash constituents of the food. The calcium and phosphorus of the bones, the potassium and phosphorus of the soft tissues, the iron of the red blood cells are just as necessary “ building materials” as are the proteins, though the amounts required are much smaller.

Upon the presence in the body of salts derived from the food, either directly or as the result of its oxidation in the tissues, depend such important properties and processes as the solvent power and osmotic pressure of the body fluids, the elasticity of the muscles, the maintenance of the normal reaction of the blood and tissues, and in recent years it has been strikingly shown that many body processes are dependent upon vitamins as well.

Many functions which might be mentioned as primarily dependent upon water, salts, and vitamins are hardly suggested by the phrase "tissue building,” since they have to do not so much with the actual construction or repair of the tissues as with the regulation of the processes on which the nutrition of the body depends. It may

therefore be said that the functions of food are (1) to yield energy, (2) to build tissue, (3) to regulate body processes.

It is not to be inferred that any given food substance can be assigned once for all to some one of these three general functions. Thus the protein digestion products may serve both to build tissue and to yield energy; phosphates may serve both to build tissue and to assist in regulating the neutrality of the blood and tissues.

Since the same kind of foodstuff may function in more than one way and since more than one kind of foodstuff may contribute to the meeting of certain of the nutritive requirements - proteins, fats, and carbohydrates all serving as sources of energy, for example — there is often wide scope for the exercise of knowledge and judgment in the choice of articles of food to meet the needs of nutrition.

The food as a whole must furnish:

1. Enough of the digestible organic foodstuffs to supply the body's needs for energy, usually measured in terms of Calories.

2. Enough protein of suitable sorts to meet all needs for essential amino acids.

3. Adequate amounts and proper proportions of the mineral elements or ash constituents of the food.

4. Enough of each of at least three kinds of vitamins.

Modern commerce offers us a bewildering array of articles of food ranging from those which contribute to only one of the nutritive needs to those which supply them all. Only by applying a fairly comprehensive knowledge of food products may one hope to be able to make such use of what the market offers as to provide the most satisfactory food supply to the best advantage of health and purse. Any adequate conception of food study must consider the contribution which food makes both to the immediate satisfaction and to the ultimate health of the consumer; it should also hold in due regard the conservation both of the financial resources of the individual and the food resources of the community or of the race as a whole.

REFERENCES

AMERICAN PUBLIC HEALTH Association, Report of Committee on Nutri

tional Problems, American Journal of Public Health, Vol. 10, pages 86

88 (1920). ARMSBY. The Conservation of Food Energy.

The Modern Science of Food Values. The Yale Review, Vol. 9, pages 330-345 (1920). ARMSTRONG. The Simple Carbohydrates and the Glucosides. ATWATER. Methods and Results of Investigation on the Chemistry and

Economy of Food. Bulletin 21 of the Office of Experiment Stations

of the United States Department of Agriculture.
CHITTENDEN. The Nutrition of Man.
Eddy. The Vitamin Manual.
Ellis and MACLEOD. Vital Factors in Food.
FUNK. The Vitamins.
HOPKINS. Influence of Accessory Constituents of Diet upon Growth.

Journal of Physiology, Vol. 44, pages 425-460 (1912).
Howell. Textbook of Physiology.
LEATHES. The Fats.

LEWKOWITSCH. Chemical Technology and Analysis of Oils, Fats, and Waxes.
LUSK. Elements of the Science of Nutrition.
McCOLLUM. Some Essentials to a Safe Diet. Annals of the American
Academy of Political and Social Sciences, Vol. 74, pages 95-102 (1917).

Nutrition and Physical Efficiency. Journal of the Franklin Institute, Vol. 189, pages 421-440 (1920).

Series of Articles in Hygeia, the Journal of Individual and Community Health, published by the American Medical Association, Vol.

I (1923). MENDEL. Nutrition, the Chemistry of Life. OSBORNE. The Vegetable Proteins. OSBORNE and MENDEL. Feeding Experiments with Isolated Food Substances. PEARL. The Nation's Food. PLIMMER. The Chemical Constitution of the Proteins. Rose. Feeding the Family.

Laboratory Handbook for Dietetics. SHERMAN. Chemistry of Food and Nutrition.

Food Chemistry in the Service of Human Nutrition. Journal of Industrial and Engineering Chemistry, Vol. 10, pages 383–390 (1918).

Permanent Gains from the Food Conservation Movement. Columbia University Quarterly, Vol. 21, pages 1-14 (1919); Reprinted as Lesson 139 in the Cornell Reading Course for the Home (July, 1921).

Protein, Phosphorus and Calcium Requirements of Maintenance in Man. Journal of Biological Chemistry, Vol. 41, pages 97-109 and

173-179; Vol. 44, pages 21–27 (1920). SHERMAN and SMITH. The Vitamins.

CHAPTER II

THE FOOD INDUSTRY AND ITS CONTROL

The purpose of this chapter is to consider briefly the economic status of the food industry as a whole, the importance of food as a factor in the cost of living, the reasons for legal control of the food industry in behalf of the consuming public, the chief features of the food laws and the methods and standards which have been adopted for their enforcement, and the marked tendency to standardization and scientific control on the part of trade organizations within the food industries themselves.

The individual foods and food industries discussed in subsequent chapters can be studied with most interest against a background of general survey of the food industry as a whole, of the principles underlying our food laws and standards, of the extent to which such laws can and cannot insure the nutritive value of the food, and of the general safety and wholesomeness from the sanitary standpoint of the foods now offered to the consumer.

Some Economic Features of the Food Supply More than half the total value of natural products of the United States is represented by the food products, whose annual value is about twice that of all other farm products and over twice that of the combined products of the mines and forests.

The products of the mines and forests may be subjected to more elaborate processes of manufacture and so may be increased in value in greater ratio before reaching the consumer than are the food products; but even so we find from the census

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