would make us suspect that the different proteins might have different food values, and experiments have shown this to be true. Certain proteins when used alone seem insufficient. While some will perfectly support life and growth, others will support life, but not growth, and still others will not support life at all. Casein is a good example of the first, while it has been known for a long while that gelatine had the characteristics of the third class. For a while gelatine was not called a protein at all. Now it is known by analysis that the difficulty with gelatine is that certain of the amino acids found in casein are absent. This does not make the acids which are present of no value, but means that gelatine is incomplete by itself and needs to be supplemented by proteins which contain the missing amino acids. As the body proteins are many, and also varied in the kinds and amounts of amino acids they contain, it will easily be seen why it is so difficult to state an exact amount of protein which is needed daily in the diet. It undoubtedly makes a difference what the proteins are that are eaten. Since so little really is known about the whole matter, we have here one of the best arguments for variety in diet, that all the needed substances may be present. Until more is known, it will be impossible to settle the question whether a vegetarian diet is superior to one which contains animal protein. Many people who argue for vegetarian- ism are advocates of it only in its modified form, that is, they believe in the use of milk and eggs, but not in the use of meat and fish which involves the sacrifice of life. So far as is known, there is no essential difference be- tween proteins from vegetable sources, and from animal sources, but it is true that because of the way they are combined, the latter are often much more completely absorbed and, perhaps, are more quickly digested as well. PROTEINS 187 Vegetarians are apparently proving that meat-eating is not essential to life. Still it is true that people like meat, and that the dominating races of the world are meat eaters, although we are not sure whether that is true be- cause of, or in spite of, that fact. On the other hand, there is little evidence that the vegetarians are really any better off physically than the meat eaters. There is some evidence that endurance is better in those who eat less protein than in those who eat much, but this is entirely aside from the source of the protein. Fisher, at Yale University, has tried experiments in which people who ate less protein showed much greater ability to carry on given exercises than did those who habitually used more protein. Such tests as deep knee-bending, leg-raising, and holding the arms out horizontally, were tried. Not only could the low-protein consumers hold out longer, but they were less exhausted afterwards and suffered less from sore muscles. Whether this effect is due to the lack of alkaline salts in meat, or to some other cause, is not known. However, considering all the evidence, it would seem as if Americans at least would do well to lessen the amount of meat they habitually consume. As we are the greatest meat eaters among the civilized nations, it would seem that this could be done with perfect safety and possible benefit. REFERENCES As in previous chapter.

AI-modernized reading of the original text

would make us suspect that the different proteins might have different food values, and experiments have shown this to be true. Certain proteins when used alone seem insufficient. While some will perfectly support life and growth, others will support life, but not growth, and still others will not support life at all. Casein is a good example of the first, while it has been known for a long while that gelatine had the characteristics of the third class. For a while gelatine was not called a protein at all. Now it is known by analysis that the difficulty with gelatine is that certain of the amino acids found in casein are absent. This does not make the acids which are present of no value, but means that gelatine is incomplete by itself and needs to be supplemented by proteins which contain the missing amino acids. As the body proteins are many, and also varied in the kinds and amounts of amino acids they contain, it will easily be seen why it is so difficult to state an exact amount of protein which is needed daily in the diet. It undoubtedly makes a difference what the proteins are that are eaten. Since so little really is known about the whole matter, we have here one of the best arguments for variety in diet, that all the needed substances may be present. Until more is known, it will be impossible to settle the question whether a vegetarian diet is superior to one which contains animal protein. Many people who argue for vegetarianism are advocates of it only in its modified form, that is, they believe in the use of milk and eggs, but not in the use of meat and fish which involves the sacrifice of life. So far as is known, there is no essential difference between proteins from vegetable sources, and from animal sources, but it is true that because of the way they are combined, the latter are often much more completely absorbed and, perhaps, are more quickly digested as well. Vegetarians are apparently proving that meat-eating is not essential to life. Still it is true that people like meat, and that the dominating races of the world are meat eaters, although we are not sure whether that is true because of, or in spite of, that fact. On the other hand, there is little evidence that the vegetarians are really any better off physically than the meat eaters. There is some evidence that endurance is better in those who eat less protein than in those who eat much, but this is entirely aside from the source of the protein. Fisher, at Yale University, has tried experiments in which people who ate less protein showed much greater ability to carry on given exercises than did those who habitually used more protein. Such tests as deep knee-bending, leg-raising, and holding the arms out horizontally, were tried. Not only could the low-protein consumers hold out longer, but they were less exhausted afterwards and suffered less from sore muscles. Whether this effect is due to the lack of alkaline salts in meat, or to some other cause, is not known. However, considering all the evidence, it would seem as if Americans at least would do well to lessen the amount of meat they habitually consume. As we are the greatest meat eaters among the civilized nations, it would seem that this could be done with perfect safety and possible benefit. As in previous chapter.

Food study