As a result of the extensive scientific findings recorded in the several chapters of this discussion, this research as a whole, we hope, makes some important contributions not only to abstract science, but certain of the data supply legitimate bases for practical use in periods of stress such as obtained during the recent world war. The fundamental possibility of completely lowering the nutritional level so as to produce profound alterations in the gaseous metabolism, blood pressure, pulse, and practically all physiological functions opens a new field for the study of physiology at a low nutritional level. The fact that the whole picture was presented with striking clearness by Squad B after a relatively few days of low diet makes it not only possible but practicable to duplicate the experimental conditions easily and to refine the study of any one of the many scientific problems presented by this research. Several of these have already been indicated in our text. We regret particularly not having secured some evidence with regard to the stimulating effects of foodstuffs at this lower level, for such study should contribute materially to an explanation of the cause of the excess heat production following food ingestion. It is not impossible that many factors which are now studied on the normal nutritional level would be considerably accentuated by being superimposed on the lower level. A complete study of the character of the blood nitrogen is of course imperative. Further and more intricate studies of pulse and blood pressure, and their reactions to posture and both moderate and severe work, should also prove profitable lines of study.

Without attempting to catalogue any considerable number of these abstractly scientific problems, we would call attention to the possibilities of the therapeutic use of this procedure, since we have here two pronounced factors which are popularly supposed to influence perturbed metabolism. One of these, the removal of an excessive amount of nitrogen by the simple method of producing undernutrition, should have most important bearings upon many pathological conditions. Second, the profound lowering of the total metabolism, which has already been found in the Allen fasting treatment for diabetics to have great therapeutic effectiveness, will doubtless be extended to other pathological cases. These are problems primarily for the clinician. The dietetic procedure is extraordinarily simple, is in no particular sense strenuous or painful, and the condition of lowered nitrogen and lowered metabolism can be rapidly produced in a few weeks. The untoward influence of both procedures upon norma' healthy man is so slight as to indicate that danger, if any exist, must be remote. The beneficial effects in many pathological cases of removing large amounts of surplus nitrogen and of lowering the metabolism perceptibly will, it is confidently believed, be demonstrated in the near future.

The loss in weight of all of our subjects was a resultant of the restricted diet and the relatively active daily program. After the short periods of excess food on the free Sundays or holidays, the loss in weight was accentuated by severe physical exercise. The reduction in body-weight primarily by excessive physical exercise is also a problem that, in the light of the present research, assumes new significance; a complete interpretation of the physiology of weight reduction can not be made unless this factor has been thoroughly tested. A practical application of the principles laid down in this research may be found, however, in the question of moderate reduction cures. With the weight reduction produced by these men, either absolute or percentagewise, no serious physiological effects were noted. A word of caution, however, should be inserted, for, as McKenzie1 has pointed out, weight reduction without accompanying physical exercise is liable to cause a loss of bodily power; furthermore, in connection with the loss of protein, when loss of weight is produced without due regard to keeping up the general tone of the body by muscular activity, constipation, hernia, and gastroptosis, particularly in middle-aged and excessively fat women, may occasionally occur. Although the rapid absorption of fat has occasionally caused displacements of the kidneys and uterus, the resulting symptoms have usually not been more troublesome than the obesity itself. For moderate weight reductions of 10 per cent it is safe to predict that even such rare occurrences may not be noted. Further weight reduction should be carried out only with the constant supervision of a competent physician.

Entirely aside from the laboratory and clinical suggestions arising from this research, we should consider the influence of an observation of this kind upon the feasibility of general dietetic restrictions as a food-conservation measure. Judging superficially from the appearance of these men at the end of their long period of restricted diet and from the amount of their intellectual and physical activity, one could assert almost with certainty that a reduction of total caloric intake of one-third was an assured possibility. Certain objections to this have been cited in our discussion. Of these the picture of secondary anemia indicated by the blood findings, the marked repression of all normal sex expression, the mental unrest and dissatisfaction experienced by many of these men should all be seriously considered. Dr. Minot believes that the anemia would not progress much farther with continuance of this diet. The absence of sex interest has an important bearing on the subject of the propagation of the race. It is possible that nature is insistent that the metabolic level found in practically all normal individuals is that best adapted for propagation and that reduction in this level can only be made at a sacrifice of sex interest and reduction of propagation. These warnings must certainly be heeded. Precisely the same factors that reduced normal sex expression in these men may, however, be of extreme practical importance in pathological phases of sexual perversions.

1McKeniie, Exercise in Education and Medicine, Philadelphia, 1915, 2d ed. p. 530.

The introspection shows clearly that not a little of the mental unrest was caused by the fact that others were eating liberally and freely and the social element was removed or repressed.

Certain possible procedures that in times of stress might be justifiably recommended, at least as war measures, have been considered recently in reporting some of the data from this research.1 This is not the place to enter into any discussion of the practical application of these diets to immediate economic national problems. It is, however, perfectly justifiable to make conclusions as to the practicability of a reduced diet in food stringencies. Entirely aside from war or any factors pertaining thereto, food stringencies will inevitably occur throughout the world as a result of accident, floods, climatic disturbances, etc. To instill into the world at large a belief that a pronounced lowering of rations is not necessarily accompanied by a complete disintegration of the organism and collapse of mental and physical powers may, after all, be of real service. A reduced ration may be a minimum, but this is far from saying that it is an optimum. Experimental evidence has accumulated in sufficient amounts to justify a serious consideration of a material reduction in the intake of protein, which is one of the most expensive factors in human food. It is not clear that a low-protein diet is harmful. Indeed, much of the evidence now points to the fact that a low-protein diet is without harmful effects upon the organism.

One of our unsolved problems in this research is the relationship between body protein and metabolic level. If the lowered general metabolism is due to the absence of protein in the body - and our evidence points strongly towards this - we may then argue that while in times of stress the minimum and lower level is justifiable and reasonably safe, in times of plenty the optimum is a higher protein level. The reduction of body-weight without loss of body-nitrogen is a scientific situation that should be thoroughly investigated. Our data throw no light on this subject. Obviously the diet could be so adjusted as to keep up the supply of body-nitrogen for the most part and still draw from body-fat. Until experiments of this type are made with accuracy and in sufficient numbers to settle this question without doubt, the amount of the optimum protein intake must be held in abeyance. For a tentative war measure the question of low protein need not seriously be contested. The recent marvelous developments as a result of the study of the so-called "food accessory substances" lead us to believe that instead of devoting an undue amount of time to fictitious "nitrogen balances" and an attempt to curtail nitrogen to an extraordinarily low point, the character of the nitrogenous material ingested, including the food accessories, should be carefully considered, and then and not until then can the ultimate reduction of protein be properly studied.

1Benedict, Proc. Am. Phil. Soc., 1918, 57, p. 478.

In connection with the study of low protein and the value of the surplus protein of the body, a complementary condition should be studied in which, after the reduction in protein and its concomitant body-loss, there should be realimentation with low nitrogen intake to minimize nitrogen storage but accentuate the return to normal weight. Under these conditions the true value of the nitrogen storage to the body would be clearly shown. Furthermore, the level of nitrogen equilibrium on a diet with very low nitrogen and the normal calories for weight maintenance should be established and carefully explored. For all practical purposes, however, it is clear that the so-called low-protein diet is perfectly justifiable as a war measure and in all probability is a logical procedure that can not be accompanied with any untoward effects, even by long-continued practice. Just what this level should be remains to be demonstrated.

Our evidence seems to show that, at least with American young men, the nitrogen excretion in urine is much lower than has been commonly supposed. Whether this speaks for a nitrogen metabolism that has always existed, or whether it is due to the fact that the agitation for low protein has been gradually impressing itself upon the American dietetic habits, we can not state. A nitrogen excretion with normal men of 9 grams of nitrogen, i. e., 0.15 gram per kilogram of body-weight, is a minimum level certainly well above any danger-line.

We may say, in summarizing, that protein curtailment is an assured and physiologically sound procedure, and a reduction in calories is possible for long periods, but definite and significant disturbances of blood composition, normal sex expression, and neuro-muscular efficiency, and the appearance of mental and physical unrest are deterrent factors in too sweeping generalizations as to the minimum calories being synonymous with an optimum level.