For the settlement of this problem the evidence at our disposal is fairly extensive. If the flesh-abstainer would only be satisfied to go on utilising the unquestionable advantages of the animal proteins in milk and eggs, there is little doubt that his diet would be quite as satisfactory as that of the mixed feeder. But although he supports his fleshless propagandism by appealing to the health and vigour capable of being maintained on the lacto-vegetarian system, he never ceases to insist that eggs and milk are not a wholesome source of protein, but that vegetable proteins are much more wholesome and safer. Now this is a question upon which there is a decided difference of opinion; for assuming that the attractiveness, and hence, according to Pavlov, the digestibility of the lacto-vegetarian system be equal to that of a mixed diet, it is quite certain that the absorbability of vegetable protein is much inferior to that of animal protein. We have already in Chapter II (Theories Of Metabolism - Continued). quoted Voit's statement that quite 42 per cent. of the nitrogen present in a vegetarian's food is evacuated in the faeces, chiefly because vegetable protein is encased in an insoluble cellulose envelope, and we have also seen that on a mixed diet only 1.2 per cent. of the carbohydrates is lost, whereas on a coarse diet the loss is as much as 5 per cent. The dry substance in the faeces of a vegetarian is more than double that of one living on a mixed diet, the difference being accounted for chiefly by cellulose containing protein, so that in the former case it is evident that the body loses energy in two ways, first by actual loss of food, and second by excretory effort.

We have seen that proteins are broken down in the intestine into their final cleavage products, the amino-acids, which in all probability pass directly into the blood in this form, as the amount of non-protein nitrogen in the circulating fluid is increased during absorption. We have already seen that there exist a multiplicity of proteins with varied and complex compositions, and as without doubt some of them have specific functions of an important, not to say absolutely essential character, it is certainly unwise to exclude from the diet any protein-containing substances, especially those whose value has been proved in nutrition. The study of the vegetable proteins is still in its infancy, but it is already known that they possess characteristics clearly differentiating them from animal proteins, which unquestionably correspond more closely to the proteins in our own tissues. Gowland Hopkins found that mice can live longer on zein - a protein obtained from maize, containing leucin, tyrosin, and abundant glutaminic (glutamic) acid, but destitute of lysine and tryptophane - with the addition of tryptophane than on zein alone. But neither zein alone nor with the addition of tryptophane could enable the animals to maintain their growth. The tryptophane is not therefore likely to be an actual building stone of the body, but it is suggested by Hopkins is a normal precursor of some specific "hormone" or other substance essential to the processes of the body; yet without it nitrogen equilibrium cannot be maintained.

Gelatine, again, which lacks tyrosin, tryptophane and cystine, cannot repair tissue waste, but can replace protein in so far as the latter functions as a source of energy, sharing with it in this capacity some inexplicable advantage over fats and carbohydrates. It is evident therefore that proteins may function in other still unknown ways than those with which we are familiar, and as it is yet impossible to say at present just what function they subserve in the human economy, it may be risky to deprive the body of any of them, as we may thus be denying it some important source of nutrition.

The growth and maintenance of the body may thus be compared to the building of a house, the whole of the details of which are derived from one form of structural material, viz., amino-acids. In the building of a house many kinds of structural materials - wood, bricks, glass and slates, etc. - are employed, and hence the two conditions are not quite analogous. It is futile, therefore, to compare vegetable protein to new bricks from a kiln, and animal protein to brick which has been built into complicated structures, so that when the edifice is disrupted, quantities of rubbish which the body cannot utilise are found mingled with the brick. There is, indeed, some justification for the belief that some of the waste matters introduced with flesh food, so far from being detrimental to, actually subserve, the best interests of the body. It is therefore injudicious for the flesh-abstainer to maintain his uncompromising attitude of hostility towards the moderate flesh-eater, especially when in his capacity of lacto-vegetarians he himself utilises some forms of animal proteins and so shares with the meat-eater the responsibility for killing animals.

We shall shortly deal with some of the more specific objections to a flesh diet; but at this juncture one may fairly argue that given a personal liking for eggs, milk, and milk products, and the opportunity to obtain them in the best possible circumstances, the crux of the whole problem rests with the capacity of the individual to cope with the digestion of lactc-vegetarian foods. Granted such a capacity - and it may be at once conceded that it exists permanently in some - there appears to be no reason why a man should not be as healthy on such a system as on a mixed diet. The problem is one which can easily be, and has been, put to the test, and there is little doubt that many people, both in this country and America, exist in a high degree of physical and mental efficiency on such a diet. If we are to trust to the testimony of many of these individuals that their health and comfort have been immensely benefited by their change, it can hardly longer be contended that the highest degree of physical and mental health cannot be obtained on a lacto vegetarian diet, and that it is often indeed much more suitable than a mixed diet for a large proportion of town-dwellers.

The Irving Fisher Experiments

A considerable amount of evidence has recently been advanced to prove that flesh-abstainers, whilst no stronger than those living on a mixed diet, are on the other hand capable of a much greater degree of endurance. This has been frequently demonstrated by many long-distance walks, but more recently by a careful set of experiments instituted by Professor Irving Fisher at Yale. The subjects of the experiment fell naturally into three groups - (1) Athletes accustomed to a high-protein and full-flesh dietary; (2) athletes accustomed to a low-protein and non-flesh dietary; (3) sedentary persons accustomed to a low-protein and non-flesh dietary. The test employed consisted of (1) holding the arms horizontally as long as possible; (2) deep knee-bending; (3) leg-raising with the subject lying on his back. Although the third item appeared to show the superiority of the flesh-eaters, the result of the other two was a distinct triumph for the flesh-abstainers. In particular, comparing fifteen of the latter with fifteen flesh-eating athletes, the average length of time the arms were held extended horizontally by the flesh-abstainers was nine times that of the flesh-eaters, or 90 minutes compared with 10 minutes.

Irving Fisher draws the following conclusions: (1) Large flesh-eaters, even when trained, show far less endurance than flesh-abstainers, even when the latter are leading a sedentary life. (2) In view of (a) the great extent of the superiority shown; (b) the heavy handicap imposed upon the abstainers; (c) the absence of other known factors to account for their superiority, it is improbable that this superiority can be explained away by adventitious circumstances. (3) It is possible that the superiority of the abstainers was due to the absence of flesh-foods or to a smaller quantity of protein or to both, as well as to the abstention from tea, coffee, and condiments.

I am personally acquainted with some of the flesh-abstainers who were subjects of the experiment, and their appearance would not warrant one in anticipating any such marvellous results, and it is fair to add that physiologists in America think that because Professor Irving Fisher is not a medical man or a trained physiologist, he is hardly competent to carry out in a proper physiological way experiments in endurance such as he reported. But I am not at all inclined to doubt the accuracy of these results, and I believe, were the experiments repeated, the results would not differ in any important degree from those just detailed.

In a paper published since the date of this experiment Professor Fisher gives some details of some tests applied at Brussels by Mile. Dr. J. Ioteyko and Mlle. Kipiani on forty-three vegetarians, the results being quite on a par with those already quoted. "So far as strength is concerned," he says, "very little difference could be discovered between vegetarians and 'carnivores.' In endurance, on the other hand, a very remarkable difference was found, the vegetarians surpassing the carnivores from 50 to 200 per cent., according to the method of measurement." It was also found that the vegetarians recovered from fatigue more quickly than meat-eaters, again corroborating the Yale experiment. As Mosso's ergograph was used, an interesting mathematical study of the fatigue curve was made, in which the equation

η = H - at' + bt2 - ct was employed.

η as height of contraction. t = time. H = height of initial or maximum contraction. a = the measure of the toxicity of albuminoids on muscles. b = the excitability of the central nervous system. c = the utilisation of carbohydrates.

It was found after laborious computation that the average of the co-efficient a for carnivores was .00305 and for vegetarians .00015. The average co-efficient b for the carnivores was .086 and for the vegetarians .023. The average co-efficient c for the carnivores was 1.94 and for the vegetarians 1.46. The average of the constant H was 38.7 for carnivores and for vegetarians 31.7.

It appears therefore to be not now a question of simply admitting that flesh-abstinence is consistent with health, but the question is whether it may not really be conducive to superior health. This, of course, is maintained by the vegetarians, and they attribute their improvement in health to many factors, such as the low protein content of their diet and its freedom from so-called toxicity, with neither of which statements I am prepared to quarrel, although I believe two other factors are of much greater import, viz., its great simplicity and its association with more hygienic surroundings.