Some years later, however, McCollum of Johns Hopkins, then of Wisconsin University, demonstrated conclusively that by making a proper selection of vegetable foodstuffs, rats may live and thrive indefinitely on a diet wholly derived from the vegetable kingdom. In connection with this and other similar experiments, McCollum made the interesting discovery that when an animal's bill of fare is to be wholly drawn from the products of plant life it is necessary, in order that the animal shall be fully nourished, that all parts of the plant should be eaten. His experiments demonstrated that if animals are fed upon seeds, alone they undergo physical depreciation, do not obtain full growth, are unable to reproduce or nourish their kind, and ultimately perish. In like manner, roots are found to be incapable of bringing an animal to full development and sustaining its life indefinitely. It was found that to be well nourished the animal must eat in suitable proportions, variable within considerable limits, seeds or fruits and leaves. The great importance of the green leaf as a complement of other foods has been clearly shown.
Experiments by McCollum, as well as those of Osborne, Mendel, and numerous other investigators in the same line of research, have made clear several new and highly important facts in the physiology of feeding.
They find that foods contain certain subtle elements known as vitamines which are absolutely essential to the full development and prolonged life of an animal. These elements are not found equally distributed in the parts of plants and animals. In seeds they are found chiefly in the outer layers or envelope which is commonly rejected as bran. A certain vitamine especially concerned with growth and development, the fat soluble B, is found in the green leaf along with lime and iron, all of which are deficient in seeds. Roots especially supply an abundance of alkaline salts which are highly necessary to balance up an excess of mineral acids found in seeds.
Ignorance respecting these highly important facts has been responsible for a great number of failures in attempts to adopt a non-flesh dietary. A diet consisting of cereals and fruits, as for example a bread and fruit diet, while apparently satisfactory for a brief period, must inevitably result in failure because of lack of lime, iron and special vitamines found in the green leaf. The same deficiency exists in flesh foods. The soft parts of an animal, fat and lean meat, are almost wholly lacking in lime and vitamines. They contain a great excess of mineral acids. Even a carnivorous animal fed on such a diet soon shows evidence of failure. The lime in the animal body is found almost wholly in the bones, and the vitamines are concentrated in the liver and other glands, so that in the case of flesh foods, as well as vegetable foods, for complete nutrition it is necessary that the whole animal or its essential parts should be eaten. Wild carnivorous animals do this as do also wild men who live largely upon flesh foods. The cave men crushed and ate the bones of the animals upon which they fed, and the Indian tribes of Texas and the Northwest have long practiced the grinding up of the bones of fishes to eat with their food.
Dr. Treves, one of London's most eminent surgeons was called upon by the head keeper of the animals of the London Zoological garden for advice respecting the condition of the lions. It was noted that the cubs bred in captivity were club-footed and variously deformed, and in many cases were either born dead or survived but a few weeks. His investigation showed that the fault was wholly in the diet. The lions received only the soft parts, lean and fat, of animals. When given bones and bone meal the difficulty speedily disappeared. Stefansson reports that, when living upon an Eskimo diet it is necessary to take the whole bill of fare, including the raw frozen liver of the seal, otherwise serious illness intervenes.
Hindhede, by arranging a dietary based upon these principles, has demonstrated that a man may be perfectly sustained on a diet which contains no animal product of any sort. In a letter received by the writer from this able Danish physiologist, the statement is made that a strong laboring man was maintained for 23 months in perfect health and vigor on a diet into which no animal products entered.
Another important fact developed by Rubner, Mendel, McCollum and other investigators which is of fundamental importance in animal nutrition, is that proteins differ in their value as tissue builders. Proteins differ from the starches and fats in the great complexity of their composition. Instead of being simple compounds or mixtures of a few simple compounds, proteins, as found in nature, consist of several sorts of highly complex molecules which vary greatly in their composition.
The protein molecule is made up of a number of organic units known as amino acids. There are 30 or 40 different kinds of amino acids of which less than 20 enter into the formation of the proteins of the human body. These 18 or 20 different amino acids are absolutely essential for the formation of body proteins, and are produced by plants, hence if they are not found in the food the body cannot produce them and the material necessary for tissue building or repair will be lacking.
Proteins which contain all the amino acids essential for tissue building are known as complete proteins. Other proteins, lacking in certain essential constituents, are designated as incomplete: Flesh foods necessarily furnish complete proteins. The proteins of milk and eggs are also complete proteins. The proteins met in the vegetable world are exceedingly varied in character. Each species of plant produces its own kind of proteins. Vegetable proteins differ greatly among themselves. Complete proteins are comparatively rare. The proteins of cereals, for example, have been shown to be deficient in some of the essential amino acids. The deficiency is still greater in the proteins of beans. In fact, the proteins of vegetable foods in general may be said to be deficient.
The necessity for providing the body with complete proteins was doubtless the original cause which led men under circumstances of privation and emergency to resort to the use of animal flesh for food. The cows of Nantucket, the ponies of Alaska, and I have recently been informed by Mr. Goddard, curator of anthropology in the American Museum of Natural History, the rabbits of northern Canada, in times of great scarcity of food, also resort to the eating of flesh. The necessity for complete protein to maintain physical fitness is so great that animals by nature the farthest removed from the carnivorous class resort to flesh eating when this is the only source of the needed element.