The one path leads directly to the liver, and substances taking this course, are exposed to the action of this organ, before they enter into the general circulation. The other path is through the lacteal or lymphatic system, and constitutes a roundabout way for substances to enter the blood stream, since they must first pass through the thoracic duct before entering the main circulation. As a general truth, it may be stated that fats are absorbed through the latter channel, while carbohydrates and proteids follow the first path. The innumerable blood capillaries in the villi of the intestine take up the products resulting from the digestion of proteids and carbohydrates, through which they are passed into the portal vein, and thereby distributed throughout the liver. This means that both carbohydrates and proteids - or their decomposition products - are exposed to a variety of possible changes in this large glandular organ, before they can enter into the tissues of the body." 13

12See Lectures of Dr. W. B. Cannon: "The A. B. - Z. of Our Own Nutrition," pp. 285-388.

The residue of the food material that reaches the large intestine is made up chiefly of waste-products, which are more or less a source of danger to the body, since, before being excreted, they are attacked by bacteria and broken down by the process of putrefaction into poisonous or "toxic" substances.

13 Chittenden: "Nutrition of Man," pp. 30-45.

These substances, passing into the blood and lymph through the walls of the intestine, are distributed throughout the entire system, where they give rise to the condition known as "auto-intoxication" or self-poisoning. Scientists nowadays are giving a great deal of attention to this phenomenon. Elie Met-chnikoff, of the Pasteur Institute at Paris, has actually suggested the possible advantage of removing some eighteen feet of the intestine by surgical operation to save the body from the evil effects of the decomposing waste products stored in its convoluted folds; or, since this seems hardly a practical measure, the drinking of sour milk, which, it seems, is endowed with certain properties that are capable of killing off the intestinal bacteria.14 Physicians, recognizing the truth of Metchnikoff's claims for sour milk, but knowing also that they could never get their patients to adopt it as an article of diet, have learned how to take the bacteria-killing principle out of the milk and put it into capsules, that can be administered as medicine.

The leaders of modern medicine and modern physiology alike seem to be impressed with the dangers to the body arising from the waste products in the lower intestines and with the necessity of finding some means of doing away with these dangers.

14 Elie Metchnikoff: "The Nature of Man," p. 70. G. P. Putnam's Sons, New York.

After having been digested and absorbed, food must be "metabolized" - that is to say, built up into living tissue or broken down into excretory products with liberation of heat and energy.

The digested food material, after having been absorbed into the blood and lymph, is circulated throughout the entire body. As it passes along, the tissues seize upon whatever they need of proteid, carbohydrates or fats - and proceed to build it up into living tissue. However, even after the tissues have taken up all the materials they need both for repairs and for growth, a certain amount of food material is still left floating about in the blood and lymph. This material coming into contact with the oxygen furnished to the blood by the lungs, is "oxydized" that is to say it is literally burned up, and as it burns it gives off the heat and energy that result from any form of combustion.

The first of these processes is known as "anabolism," or building up, and the second as "katabolism," or breaking down; but they are both comprehended under the broad term "metabolism" - which is applied to all the chemical changes that take place in living tissue.

During this process certain decomposition products are formed which must be excreted through the lungs, skin or kidneys or they become a menace to the well-being of the organism. Professor Chittenden says, "The human body is a maelstrom of chemical changes; chemical decompositions are taking place continuously at the expense of the proteids, fats and carbohydrates of the tissues and of the food, the stored-up energy of these organic compounds being thereby transformed into the active, or kinetic, forms of heat and motion; while carbon dioxide, water, urea and some few other nitrogenous substances are being continu ally formed as the normal waste products of these tissue changes, and constantly or intermittently excreted. In other words, the body is in a perpetual condition of chemical oscillation, constantly consuming its own substance, rejecting the waste products which result, and giving off energy in the several forms characteristic of living beings." 15

It is therefore of the highest importance that the body should maintain an even balance between its income and its outgo. If it continually pays out more than it takes in, its stores become exhausted and it starves. If, on the other hand, it takes in more than it gives out, the excess of food material is deposited in the tissues as cumbersome fat, or else the whole bodily organism is whipped up to abnormal exertions to get the over-supply out of the way. In either event, the body suffers - from overfeeding even more than from underfeeding.

"It is self-evident," says Professor Chittenden, "that the smallest amount of food that will serve to keep the body in a state of high efficiency is physiologically the most economical and hence the best adapted to the needs of the organism."16

15 Chittenden: "Nutrition of Man," pp. 77-78.

For many years the dietary standard of Carl Voit, the famous Munich physiologist, has been accepted as giving the minimum food requirements for a healthy man. This standard calls for 118 grams or 4 ounces of proteid, 56 grams or two ounces of fat, and 500 grams or 16§ ounces of carbohydrates with a total fuel value of 3,055 large calories 17 daily for a man doing moderate work. For a man doing hard work, the daily requirement is increased to 145 grams or 45/6 ounces of proteid, 160 grains or 51/3 ounces of fat, and 450 grams or 15 ounces of carbohydrates with a fuel value of 3,370 large calories.