Animal experimenters are prone to overemphasize the importance of the food substances that they regularly use with which to supplement inadequate diets and to ignore, almost wholly, the natural order of feeding. For example, milk is a very handy item of food and is used very much as a dietary supplement in these experiments. It usually suffices to render adequate an otherwise inadequate experimental diet, hence the experimenters are prone to emphasize the "value" of milk and to completely ignore the obvious fact that in nature, animals secure an adequate diet without resort to milk after they are weaned. Their experimental diets are almost never the diets of the people; nor are they the diets of animals in nature. There is a tendency of this class of experiments to mislead both the experimenter and the people as a whole, inasmuch as they ignore the many other food supplements that are equally capable of supplementing the inadequacies of a monodiet or of a deficient but somewhat varied diet.

In experiments on dogs deficient diets were fed to a group of dogs. To this diet was added, for some of the dogs, a given quantity of milk. The dogs that got the milk grew and developed normally. The dogs not receiving the milk were stunted and poorly developed. It would be folly to reason from this that dogs require milk for normal development, for we know that dogs can and do develop normally without getting milk after they are weaned. All that such an experiment proves is that milk added to an otherwise deficient diet will render the diet adequate. But there are hundreds of other ways of rendering the diet adequate as all animals in the wild state are well aware. Indeed, it is probable that many of the other ways of rendering the diet adequate are superior to the milk. Milk after the normal suckling period has ended is far from being an unmixed blessing.

Experiments with the different proteins would easily lead the unwary to believe that the elephant, cow, horse, buffalo, deer, rabbit and other strictly vegetable eating animals cannot live and grow on their vegetable diets, but, actually, we know that they do very well on such diets. This is because they never eat but one kind of protein (never eat individual isolated proteins). Their diet is varied. One protein corrects the defects of another.

Another fact strikes the serious student of dietetics: namely, the experimenters never seem to consider nuts, which are certainly important constituents of man's normal diet, as worthy of their attention; yet most nuts contain complete and high grade proteins. Green vegetables also contain high grade proteins, although in very small amounts. But when these are added to the diet in large quantities, as in consuming large daily salads, they are capable of supplementing the deficiencies in an all-cereal diet and rendering this adequate. The experimenters are fond of comparing legumes and cereals with flesh foods, and neither of these classes of foods form parts' of man's normal diet.

The biological value of the different proteins is tested on animals, commonly on rats. These are rapidly growing animals. A protein may prove to be incomplete or partially complete when fed to animals of rapid growth and may prove to be complete when fed to animals of slow growth. No doubt, too, different species require the different amino acids in varying amounts, even for maintenance. We know that the protein in human milk is especially rich in tryptophan, more so than the protein of cow's milk, an amino acid vitally important in the growth of the infant and young child. No broad generalizations about the value of the different proteins are, therefore, possible. When a protein has been shown to be complete, partially complete or incomplete for a particular species it can be said to be so only for this species. It may prove to be otherwise when fed to another species with different requirements. The underworld notwithstanding, man is not yet a rat, and "rat-pen" results are not fully applicable to his nutrition. The final test must be upon man.

We are frequently told that meat protein is more easily assimilated than vegetable proteins. There is no evidence for this statement, but it may be argued on the other side that the frequency with which allergic manifestations follow the use of animal foods indicates that these are less easily assimilated than vegetable proteins. The assertion is based upon a failure to take into consideration, not the difficulties, but the differences (largely of timing) in the digestion of the various foods: not of various proteins, but of various foods.

Muscle meat, the kind most commonly consumed, is a very poor food. Its inadequacy is made manifest by the failure of captive lions to reproduce themselves on a diet preponderantly of this food. Berg says that the protein of potatoes is more efficiently utilized by the body than that of flesh. Hindhede has also shown the protein of potatoes to be adequate.

On the other hand, we are not concerned so much with the relative values of specific proteins, or even of the proteins of one protein-carrying food, but with the total value of all the proteins contained in our customary diet: and not with the proteins alone, but with the total diet. The whole question involved is best expressed thus: Is meat, as a whole, superior to vegetables as food? When we consume flesh or vegetables, we do not confine ourselves to their protein constituents, but eat the whole of them and they must be considered in their entirety.

There is nothing in the protein of the flesh that the animal did not derive from the plant. Not being able to synthesize amino acids, the animal merely appropriates these, ready-made, from the plant, in the form of plant proteins. Man can do this as efficiently and as easily as the lower animals. Plants yield up their amino acids to man as readily as to the cow.

Green vegetables contain proteins of a very high quality, though in small quantities. Nuts, on the other hand, rank with or even surpass, flesh foods in the quantity of their proteins, while their proteins are of equal rank with those of flesh. At the same time, nut proteins are "free from pathogenic bacterial or parasitical contamination," to use Clendening's words.

It is argued that plant proteins are "poor" because "they contain unnecessarily large amounts of some amino acids and little or none of others." It should not be overlooked, however, that we consume several vegetable protein foods and the deficiencies of one are made up by the richness of another. The excess of amino acids in vegetable proteins is never great.

That the individual proteins in grains and some other plant foods are physiologically inadequate is sufficiently demonstrated, but the sum-total of the various proteins in those foods, or shall we better say, in the diet as a whole, is usually fully adequate.

A protein is said to have higher physiologic or biologic value the smaller the amount of it required to supply the needs of the animal. Based upon this standard, the whole egg is ranked at 94; milk, 85; liver and kidney, 77; heart, 74; muscles meat, 69; whole wheat, 64; potato, 67; rolled oats, 65; whole corn, 60; white flour, 52; navy beans, 38. By this standard, vegetable proteins in general are said to be nearly always inferior to those of animal origin. The proteins of peanuts and soybeans are listed as exceptions, their proteins being complete. There is no appreciable difference between the muscle meat of cow, hog or sheep. These relative values were determined by tests made on rats, dogs, etc., and are not necessarily valid for human nutrition. It will be noted that nuts are again ignored in this classification of biologic values.