CHAPTER II.

THE CHEMISTRY AND ECONOMY OF FOODS.*

It is an interesting fact that, although the cost of food makes up the larger part of the living expenses of ordinary people, even the most intelligent know less of the actual value of their food for fulfilling its purposes than of that of almost any other of the staple necessities of life. The man who buys a coat has generally a pretty fair idea as to the relation between its value and its cost, and if he is getting material to have it made, he knows about how much of each kind is wanted, and does not fall into the error of buying a great deal more cloth than he needs for the outside and using part of the excess for lining when cheaper material would do as well or better, nor does he try to economize by buying poor buttons and too little thread. But for his food he is very apt to select materials which furnish some of the nutritive ingredients at needlessly high cost, and in excessive amount, while they supply others in insufficient quantity and in very uneconomical ways.

If I succeed in making clear to you the points which I am here to urge, I believe you will be persuaded that not only our so-called laboring classes, but all who desire or are compelled to economize, would be greatly benefited by a better understanding of the principles on which the economy of food is based, and by the application of those principles in the purchase and use of their aliment.

I think a careful study of the subject will show that among the many ways in which our American habits of wastefulness manifest themselves, one of the worst is in the waste of food, and that this wastefulness is practiced by the poor as well as by the rich. It manifests itself in purchasing more than is needed, in using part of the excess to overload the alimentary organs and throwing the rest away, in using costly materials where less expensive ones would serve as well, in purchasing materials that are really dear but seem to be cheap, and in the false economy of using too little of one material and too much of another, and thus losing where there is an earnest attempt to save. And it is not only the loss to the purse from wrong selection of food in the market, but the loss to both purse and health by wrong keeping and cooking and using at home that is to be deplored, and ought to be avoided.

Then, too, we have to remember that it is the ignorant, and that means the poor, that suffer most from this improvidence, and when we consider still further the suffering that is endured from wrong use of food-and some of our wisest students of physiology and hygiene are persuaded that improper eating, and especially overeating, is a source of more disease than any other one thing; that what we may call the eating habit does, on the whole, more harm to health than the drinking habit-I think we

Paper read by Prof. W. O. Atwater, at the third annual session of the National Convention of Chiefs of the Bureaus of Labor Statistics, held at Boston, Mass., June 29th to July 1st, 1885.

shall be persuaded that the subject of the nature and uses of food is one worthy of our most careful consideration.

A pound of lean beef, round steak freed from fat, for instance, and a quart of milk, both contain about the same quantity, say a quarter of a pound, of actually nutritive material. But the pound of beef costs more than the quart of milk and it is worth more as a part of a day's supply of food. The nutritive materials or nutrients, as we call them, in the lean meat, though the same quantity as in the milk, are different in quality, and of greater nutritive value.

We have here an illustration of a fundamental fact in the economy of foods, namely, that the differences in the values of different foods depend upon both the kinds and the amounts of the nutritive material which they contain. If, then, we would understand the nutritive value of foods, we must know, first of all, what they are composed of. Knowing this, we must next consider what the several food ingredients do in the body; what is the special work which each one of the different nutrients has to perform in building up our bodies and in supplying their wants. When, in addition to all this, we know how much of each class of nutrients our bodies require and our foodmaterials contain we shall be in condition to economize our foods as we do the other necessaries of life.

Twenty five years ago, indeed I might say fifteen years ago, but comparatively little was known about these things, and for that matter our knowledge of them is still very far from complete. But, nevertheless, we do know to-day about how much of the different nutritive ingredients, or nutrients as they are called, our ordinary food materials contain, and we have a tolerably clear conception of the functions of these different ingredients in the nutrition of our bodies; and finally, a large amount of observation and experiment has told us about what proportions of the several classes of nutrients are required to meet the needs of people in different conditions of life.

LATER RESEARCH IN THE SCIENCE OF FOOD AND NUTRITION.

Among the numerous branches of biological research by no means the least interesting and important is the study of foods and nutrition. Within the past fifteen years especially, a very large amount of scientific labor has been devoted to the investigation of the composition of foods and the functions of their ingredients in the animal economy. Indeed, very few persons this side of the Atlantic have any just conception of the magnitude of this work and its result. And, though the most important problems are still unsolved, and must, because of their complexity, long remain so, yet enough has been done to give us a tolerably clear insight into the processes by which the food we eat supplies our bodily wants.

The bulk of our best definite knowledge of these matters comes from direct experiments, in which animals are supplied with food of various kinds, and the effects noted. The food, the excrement, solid and liquid, and in some cases the inhaled and exhaled air, are measured, weighed and analyzed. Many trials have been made with domestic animals-horses, oxen, cows, sheep, goats and swine-with dogs, rabbits, birds, and the like; and a large number also with human beings of both sexes and different ages. In the philosophical planning of the researches in the ingenuity manifested in devising apparatus; in accuracy, thoroughness, patience and persistence in the work, as well as in the distinguished genius of many of the workers, chemicophysiological science has assumed the highest rank among the sciences of our time; with the rest it has brought us where we can estimate the nutritive values of foods

from their chemical composition, with so near an approach to accuracy that in Germany, where the best research is done, tables, giving in figures the composition and nutritive valuations of foods, have been prepared by eminent chemists and physiologists and are coming into general use.

HOW OUR FOOD SUPPLIES THE WANTS OF OUR BODIES.

Our food supplies the wants of our bodies in four ways:

Food Furnishes,

1. The material of which the body is made.

2. The material to repair the wastes of the body.

Food is Consumed in the Body to

3. Produce heat to keep it warm.

4. Produce muscular and intellectual strength for work.

To understand how food does its work in the nourishment of our bodies we must recall the fact that our bodies and the materials that nourish them are both composed of a certain list of chemical elements which are combined in a great variety of compounds. These compounds we may divide into three groups:

A. Water.

B. Organic Compounds.

C. Mineral Compounds.

About water we need here say very little. Of the mineral compounds, one of the most important is the phosphate of lime which makes the basis of bone. Phosphates, sulphates, and chlorides of potassium and sodium, and other mineral salts likewise, occur in our bodies and are essential not only to health, but even to life itself. But in studying food from the standpoint of its nutritive value, that is, value for supplying bodily wants, we have to do, chiefly, with the organic compounds. These we may roughly divide into three principal classes, and this classification will do for the organic compounds of both our food and our bodies.

I. Protein Compounds, otherwise known as albuminoids, flesh formers, or "flesh substance."

II. Fats.
III. Carbohydrates.

This division answers very well so long as we are only making approximate estimates of the nutritive values of our foods, but when we study foods very accurately, and more especially when we come to the chemistry of the body, we find compounds which cannot very well be placed in either of these classes. Fortunately for our purpose, however, the proportion of these latter compounds in our foods and in our bodies is very small.*

We have not as yet sufficiently accurate analyses to tell in just what proportions these compounds occur in the body. Very probably the body of an average healthy

This classification leaves out of account numerous compounds of minor importance, includ ing the so-called "nitrogenous extractives," which are the essential constituents of "extract of meat." See beyond.

man, weighing 148 pounds, or with clothing 156 pounds, would contain something like the following quantities:

Of course I do not mean to say that this is an exact statement of the amounts of these compounds in the body of any given man or of an ideal man. These figures are simply an attempt to show, in a general way, in about what proportions the compounds probably occur.

Such then is the composition of the body. These elements and compounds must come from the food. It is the food that furnishes the material of which the growing body of the child is built up, and as our tissues are being continually consumed by work, and thought, and worry, it is by food that they are restored; and finally it is our food that supplies the fuel by whose consumption the heat and strength of the body are maintained. Viewed from the standpoint of their uses in the nutrition of man, the constituents of ordinary foods may be succintly classified as follows:

1. Edible Substance, e. g., the flesh of meats and fish, the shell contents of oysters, wheat flour.

2. Refuse, e. g., bones of meat and fish, the shells of oysters, bran of wheat.

The edible substance consists of

1. Water.

2. Nutritive Substance or Nutrients.

Of the meat my butcher sends me, the fish I find in the market, and the other food. upon my table, only a part serves to fulfill these purposes. The bone of my roast beef I do not use for food at all, and that of shad is worse than useless, because of the bother it makes me to get rid of it; it is only the edible portion that is of actual value to me as food, the rest being merely refuse. And when we come to consider the edible portion, the meat freed from bone and gristle, the flesh of the fish, or the flour as it is baked in bread, we find that these consist largely of water. And although water is indispensable, that in the meat or the potatoes on my table is of no more value for the support of my body than the same amount in milk, or in the glass of water by my plate.

Leaving out of account, then, the refuse and the water, we have the nutritive materials, or, as we may call them, the nutrients of our foods. Speaking as chemists and physiologists, we may say that our food supplies, besides mineral substances and water, three principal classes of nutritive ingredients or nutrients, viz., albuminoids, carbohydrates, and fats; and that these are transformed into the tissues and fluids of the body, muscle and fat, blood and bone, and are consumed to produce heat and force.

Let me speak in a little more detail of the compounds of which our foods are composed:

Protein, so called, "flesh formers," or "flesh substance."-The terms protein, proteids, and albuminoids, are applied somewhat indiscriminately, in ordinary usage, to several or all of certain classes of compounds characterized by containing carbon, oxygen,

hydrogen, and with them, nitrogen. The most important are the proteids, or albuminoids, of which albumen, the white of egg, fibrin of blood, casein of milk, myosin, the basis of muscle, and gluten of wheat, are examples. Allied to these, but occurring in smaller proportions in animal tissues and foods, are the gelatinoids, the nitrogenous compounds that make the basis of connective and other tissues. Gelatin, whence the name gelatinoid (gelatin-like), is derived from some of these tissues, and may be taken as a type of the compound of this class. As these constituents are of similar constitution, and have similar, or nearly similar, uses in nutrition, it is customary to group them together as protein. What we should especially bear in mind, then, is that protein is a term applied to the nitrogenous constituents of our foods, and we shall see these are, in general, the most important, as they are most costly, of the nutrients.

The muscular tissues of animals, and hence, the lean portions of meat, fish, etc., contain small quantities of so-called nitrogenous extractives-creatin, carnin, etc.which are the chief constituents of meat extract. These contribute materially to the flavor, and somewhat to the nutritive effect, of the foods containing them. They are not usually deemed of sufficient importance, however, to be grouped as a distinct class in tabular statements of the composition of foods.

Fats. We have familiar examples of these in the fat of meat (tallow, lard), in the fat of milk, which makes butter, and in olive, cotton seed, and other animal and vegetable oils. The fats consist of carbon, oxygen, and hydrogen, and contain no nitrogen. In nutritive value, as in cost, they rank next to the protein compounds. For some of the nutritive functions, indeed, the fats equal or exceed protein in importance.

Carbohydrates.-Starch, cellulose (woody fiber), sugar, and inosite ("muscle sugar"), and other similar substances, are called carbohydrates. Like the fats, they consist of carbon, oxygen and hydrogen; but they have less carbon and hydrogen, and more oxygen than the fats.

Mineral Matters, or Ash.-When vegetable or animal matters are burned, more or less incombustible material remains as ash. The ingredients which make the ash are called mineral matters, or sometimes, salts. They are, for the most part, compounds of the elements, potassium, sodium, calcium and iron, with chlorine, sulphuric acid and phosphoric acid. Sodium, combined with chlorine, forms sodium chloride, or common salt. Calcium, with phosphoric acid, forms calcium phosphate, or phosphate of lime, the mineral basis of bones.

Our bodies, as I have already said, contain scores of compounds, many of which cannot be included in either of the above four classes. But the bulk of the compounds, exclusive of water, in the bodies of animals, as well as those in the food by which they are nourished, may be classed with either protein, fats, carbohydrates, or mineral

matters.

Animal foods, as meats, fish, etc., contain but little of carbohydrates, their chief nutrients being protein and fats. Milk, however, and some shell-fish, as oysters, scallops, etc., contain more or less of carbohydrates. Vegetable foods, as wheat, potatoes, etc., contain less protein, and consist largely of starch, sugar, cellulose and other carbohydrates, though nearly all contain more or less of fats.

HOW THE NUTRITIVE INGREDIENTS OF THE FOOD NOURISH THE BODY.

These different nutrients, as we have seen, have different offices in nourishing the body, in building up its tissues, repairing its wastes, and serving as fuel to produce