The inspection of these values affords an opportunity for the comparison of different foods. The author in discussing energy points out that it is important also to distinguish between the heat produced when substances are burned in the calorimeter, and the heat or energy that is available when used in the body, as it never happens that the combustible portion of a ration is entirely consumed in the body. This is the case because the food is never all digested, the digested proteins are never fully burned, and there is usually an escape of unconsumed gases from the alimentary canal, especially in the case of farm animals. As actual work is performed in the process of digestion, the term "net energy" has been introduced to apply to that amount of energy which is available, after that used up in the digestion and preparation of the food for use in the body has been subtracted.

Newer Knowledge of Nutrition

Although it is not the province of this work to discuss at length dietetic topics, something should be said in regard to the newer knowledge in regard to nutrition. From the researches of Fischer, about the year 1900, it was shown that there is a great difference in the composition of proteins from different sources. We now regard most proteins as bodies capable of being resolved into at least 18 simple digestive products, called amino-acids, which may be absorbed into the blood.1 There are some foods 1 The Newer Knowledge of Nutrition, p. 5.

which appear to be lacking in one or more of these indispensable constituents of an adequate diet. The Vitamin hypothesis of Eijkman, and later of F. G. Hopkins and of Funk has led to a further study of malnutrition as referred to a faulty diet. The subject has developed very rapidly in recent years and there are may points still under discussion.

Vitamins

At least three vitamins are at present fairly well recognized. The first of these, called for want of a better name, "Fat-soluble A" was some years ago found to be present in cod-liver oil, green leaves, milk, butter fat, fat fish, liver and kidney tissues, oleo oil, palm oil, and many vegetables. This substance seems to be essential for the normal growth of animals, and if not present in the diet, a disease of the eyes will appear, and the patients, especially children, will be liable to be sickly and under-developed. Experiments on the lower animals have shown that growth could be maintained when butter-fat or egg-fat was contained in the food, but not so satisfactorily on that from lard or from some of the vegetable oils. Cod-liver oil is almost a specific for the disease known as rickets. Vitamin "A" is not as readily destroyed by high temperatures in cooking as are some of the others.

A second vitamin has been called "Water-soluble B," and is fairly widely distributed, in plants especially in the germs of cereals, in spinach, potatoes, carrots, the juice of citrus fruits, nuts, yeast and vegetables and fruits in general. This vitamin is necessary for growth and as a preventive of polyneuritis or “beri-beri," one of the so-called "deficiency” diseases. Cooking temperatures do not seriously diminish the dietetic value of this substance, if not above the boiling point, and if not carried on in the presence of an alkali.

The third vitamin known as "Water-soluble C," prevents the disease known as scurvy. It is found in living vegetable and animal tissues and in largest amounts in fresh fruits and green

vegetables. It occurs also to a less extent in root vegetables and tubers, and in small amounts in milk, and fresh meat, but has not been found in yeast, cereals, fats or pulses. Orange juice is one of the best sources of this vitamin. Fresh lemon juice is excellent as an antiscorbutic, but lime juice is of little value. Raw cabbage is even better than orange juice, and the raw juice of turnips, beets or carrots may be used. Cooking, especially long cooking, very much lessens the value of these foods. Commercially canned vegetables, with the exception of canned tomatoes, are of little value as a source of this vitamin.

Our knowledge of the quantities of these substances advisable for human beings of different ages, is still very incomplete. Most of our people in comfortable circumstances use enough milk and leafy vegetables, to supply a sufficient quantity of "A," vegetables and whole—not finely-ground-cereals to furnish the "B," and uncooked foods and salads in sufficient quantity to furnish all the "C" we need. Persons with limited incomes, in times of food scarcity, invalids and children and those in some of our large institutions, may often be inadequately supplied with these very essential dietary substances.

Sources of Food

From the table which follows, showing the source of the average diet of the people of the United States, it is evident that more than one third of the weight of the food used is meat and dairy products. During the Great War, partly from selfdenial of the people, and partly from necessity, the per cent. of meat used was much decreased, but recently the amount has increased to nearly normal proportions.

CHAPTER II

THE COMPOSITION OF CEREALS AND THE MANUFACTURE OF STARCH

The term cereals includes the plants of the grass family (Graminea) which are used as food. Wheat, rye, oats, barley, rice, corn (maize) and millet belong in this class, and buckwheat and quinoa, although not grasses, are here considered. The grain consists of the germ, and the endosperm with its coverings, which are the parts most utilized for human food.

WHEAT (Triticum vulgare)

Considered from the viewpoint of general use, there is no cereal of so great importance as wheat, for not only does it grow readily in the temperate climate where the active peoples of the world are found, but its products are peculiarly adapted for the food of man.

The origin of wheat is lost in antiquity. Wheat was cultivated by the ancient Egyptians and Chinese, was grown in Mesopotamia and has been found in the pre-historic lake-dwellings of Switzerland and Italy. The present form of wheat may be as naturally found, or it may be derived from a wild plant some varieties of which, improved by cultivation, are still found. It was introduced into Great Britain by the Romans.

Varieties

The botanist recognizes three species which he calls the grain wheat, Polish wheat, and common wheat, and of each of these, there are numerous varieties. Although the quality is much

modified by the soil and climate yet we commonly speak of wheat as

1. Soft, starchy or winter wheat, which is sown in the fall and harvested in June or July, and,

2. Hard, glutinous or spring wheat, which is sown in March or April, and harvested in late July or August. The climate, of course, determines which of these can be cultivated to best advantage, in each particular locality, but in general the winter wheat is grown in the more temperate climates, and the spring wheat in the north where the summer

is shorter. On the Continent. the upland steppes of Russia furnish the greatest quantity of wheat, although large quantities are grown in India, Siberia, South America, and Central Europe. In the United States of America1 the prairies of the middle west and northwest, which are in many respects similar to the steppes of Russia, are best adapted to the growing of wheat. This is especially true of Minnesota, Wisconsin, Nebraska, the Dakotas, Illinois, Ohio, Missouri, Kansas, Indiana and New York. It is interesting to note that this cereal is grown successfully in Canada, as far north as Manitoba, and Assiniboine. In some countries as Bohemia, parts of Russia, France and Germany, Scotland and Ireland, on account of the cost of wheat, it is partly replaced as food by rye, barley or oats.

FIG. 4.-Structure of the wheat grain. a, Wall of the ovary; b, testa; c and ƒ embryo; d, starchy endosperm; e, aleurone layer. By permission U. S. Dept. Agric.

Structure of the Wheat Kernel

The wheat kernel, or berry, when seen through the microscope has the structure as shown in Fig. 4.

1 References to the "United States" in the following pages are understood to mean "United States of America."