FACTORS CONCERNED IN DIGESTIBILITY AND ABSORPTION.-Digestibility and absorption of vegetable foods in the intestine are governed by two factors: first, the bulk, and second, the amount of cellulose which they contain. If the former be small and the latter scanty, digestion is very complete, as will be observed from a glance at the above table, where bread, macaroni and rice were almost completely digested and absorbed.

DIGESTION AND ABSORPTION OF BULKY VEGETABLE FOODS.-The contrary is the case where the food is bulky and full of cellulose. The majority of vegetable foods correspond more or less to this description, hence the dictum "vegetable foods are not so completely digested as animal foods." When we stop to consider that four-fifths of the weight of green vegetables and fruits is due to water, and that even the drier vegetables, such as legumes, take up three times their weight of water in the process of cooking, it will be readily seen that vegetable foods must be bulky out of proportion to their nutritive value. This bulkiness of vegetable foods retards digestion (a) by hindering the free admixture of the digestive juices with the food mass, thereby lessening the conversion of the nutrient constituents for ease of absorption; (b) the bulky mass in the intestine stimulates contractions, which hasten the contents along, allowing less time for absorption.

CELLULOSE AS A FACTOR IN DIGESTION AND ABSORPTION OF VEGETABLE FOODS.-Another obstacle to digestion and absorption of vegetable foods in the alimentary canal is the presence of cellulose and the formidable barrier which it presents to digestion. (Reference has already been made to cellulose and its extraordinary insolubility pointed out.) Indeed, it is only when the plant is very young and tender that it is at all possible for cellulose to be successfully attacked by the digestive apparatus of man or other carnivorous animals.

While the insolubility of cellulose presents barriers to the digestive process, it serves a valuable purpose to the human economy by adding

to the bulkiness of the unwieldy mass which vegetable foods form in the intestine and thereby stimulates the movements of the bowel. For this reason foods rich in cellulose, such as whole wheat bread, fruits and green vegetables, are prescribed as useful adjuvants in the dietetic treatment of those who suffer from sluggish actions of the bowels.

A moderate amount of cellulose in the dietary of healthy persons is advisable for its stimulating action on the alimentary canal. Strictly carnivorous animals have little use for it, while in the herbivora, owing to their long and sluggish intestine, its presence is a necessity.

EFFECT OF INCOMPLETENESS OF ABSORPTION ON NUTRITIVE VALUE. -The incompleteness of absorption, characteristic of most vegetable foods, affects in different measures their varied nutritive elements. The vegetable fats, such as cocoa butter and olive oil, seem to be as readily absorbed as butter and cod liver oil. Starch and sugar are readily digested and carried into the circulation almost to the last atom. It is only when enormous quantities of green vegetables or other carbohydrates of the leguminous variety are ingested that undigested starch is found in the excreta of healthy persons. It is a well-known physiological fact that a larger amount of nitrogen is excreted by the bowel on a vegetable diet than when animal foods are ingested. Just why vegetable protein should be less completely absorbed than the other nutritive constituents of vegetable foods is hard to explain. The following table from Hutchison gives a résumé of a series of experiments carried out on healthy individuals, showing the percentage of protein which escaped in the excreta, the loss of protein from meat being remarkably less than the protein waste from vegetable foods:

39.0

40.0

Carrots and Fat (412 grams dried).................

Lentils (250 grams, simply soaked and boiled till soft)......

It is difficult to account for the large amount of vegetable protein. which escapes in the excreta. Doubtless, the effects of cooking are less favorable to the digestion and absorption of vegetable protein than to that

of starch. The effects of heat and moisture cause the starch grains to swell, rupture and burst through the cell walls composed of cellulose which enclose them, but this same heat and moisture cause the protein in the vegetable cells to coagulate and shrink away from its wall of cellulose and in this way, possibly, remain unruptured.

Some authorities hold that the large amount of nitrogen found in the intestinal excreta on a vegetable diet does not come from unabsorbed protein, but rather from the residue of the digestive juices. Reasoning on this analogy, it will be seen that vegetable foods must require a more thorough admixture and a larger amount of digestive juices for their breaking down than is required by animal foods. This explanation, plausible at least in part, does not satisfactorily explain why more nitrogen is lost from the bowel on a vegetable than on an animal diet.

The Nutritive Value of Vegetable Foods. After considering the chemical constituents of vegetable foods-the proteins, carbohydrates and fats -severally and collectively, we may safely assert that they are equal in fuel value to the corresponding food elements obtained from the animal kingdom. We have already learned that vegetable protein contains a smaller amount of carbon than animal protein and, according to some investigators, the former is therefore of less nutritive value than the latter. The high energy value of starch and sugar is without question. They are fuel foods, and have no nutritive value as tissue formers. Vegetable fats, such as olive oil and cocoa butter, which form a large part of the diet of the inhabitants of some of the southern European countries, are also fuel foods. Fats to some extent are tissue formers of high nutritive value.

PROTEIN VALUE: THE VEGETARIAN QUESTION.-After all is said and done, there remains the fact that the vegetarian question is a question of protein alone. Protein may be obtained from either the animal or vegetable kingdom. Shall we eat our protein in an animal or vegetable form, taking it for granted that the vegetable foods are relatively poorer in this element than the animal foods? Typical examples of both kingdoms will show beyond question that even the fattest meats contain more protein than the most nitrogenous forms of vegetable foods.

It is therefore beyond question that vegetable foods, unless eaten in very large quantities, will not yield a sufficiency of protein for the wear and tear of the human body. This brings us to the question: how much protein does a healthy man require in his food daily?

This most important and momentous question will be elaborated on in Volume II, in the chapter on "Protein and Nutrition."

RELATIVE COST OF ANIMAL AND VEGETABLE FOODS.- The relative cost of animal and vegetable foods is an economic question in which the vegetarian has the best of the argument. Although succulent vegetables are expensive, there is no doubt that cereals are cheap. Then, too, while the nutritive substances in vegetables are not quite so abundant as in animal foods, yet vegetables play an important part in the nourishment of the body, due in part to their attractive flavor, their freshness and the variety they add to the dietary. Personal experiment at the market will show that one dollar expended for bread, peas or potatoes yields a far larger amount of fuel for the body than a dollar invested in eggs, fish, beef, or even in cheese and milk, which are comparatively cheap animal foods.

VARIETIES OF VEGETABLE FOODS

For convenience of description, we will consider vegetable foods in the following order:

Cereals:

Wheat (Flour, Bread), etc.

Breakfast Foods.

Roots and Tubers.

Green Vegetables.

Dried Legumes or Pulses.

Fungi, Lichens and Algæ.

CEREALS

Cereals. Cereals belong to a type of grasses of the natural order Graminacia. They are cultivated at the present time in all parts of the world, but it is questionable whether the cereals so much esteemed at the present day have been evolved by natural selection and cultivation from wild grasses now known, or whether they are distinct species, having their origin in grasses which no longer exist. The term cereal dates back to mythological times. The goddess Ceres is supposed to have been the first to cultivate these wild grasses and gather their seed for food. We gather from the Holy Writ the fact that cereal had been used as a foodstuff many centuries before Joseph, under Pharaoh, secured his famous "corner on wheat" and for seven years monopolized the grain market of the world. In fact, we may safely say that man's use of cereals as a foodstuff antedates history and that its origin is lost in the mists of antiquity.

Among the (grass) cereals, wheat, rice, corn, oats, rye, barley and millet are the most important, and are named in the order of their importance. Other cereals, although not grasses, may be mentioned here as buckwheat and quinoa. As a rule, these grains are ground into meal or flour. However, rice and barley are usually offered in the markets with the hulls removed, though rice flour and barley meal are also used to a limited extent.

COMPOSITION OF FLOUR AND CEREALS.-The following analysis, taken from Lawes and Gilbert and quoted by Tibbles (1), shows the relative percentage composition of flours made from the principal cereals:

COMPOSITION OF FLOUR AND OF CEREALS

WHEAT. Wheat is by all odds the most important cereal used in American and European countries, where it occupies the same position as a dietetic article that rice fulfills among Oriental peoples. It grows readily, producing beautiful crops throughout the temperate zone, where the active peoples of the earth reside. Its origin as a foodstuff is unknown, but profane history tells us of its cultivation by the ancient Egyptians and Chinese. It was grown in Mesopotamia 2,000 years B. C. The present varieties of wheat are, no doubt, the result of careful selection extending for centuries back. Possibly, the modern wheat may be derived from a wild plant, some varieties of which, improved by cultivation, are still found. Wheat as we know it today was introduced into Britain by the Romans. The wheat crop of the United States in 1915 was 1,011,280,000 bushels.

ELEMENTS OF THE COMPONENT PARTS OF WHEAT GRAINS.-The grain of wheat consists of various parts arranged in concentric layers. Since these are important from a dietetic point of view, we shall briefly consider the elements forming the component parts of the grain. The wheat berry has an external covering or skin, an internal substance or kernel and a germ. The external covering, skin or hull, consists of five