With these marked effects on strength and fatigue, it is reasonable to assume that some corresponding action may be exerted on physical endurance. As is well known, strength and endurance, though related, are quite distinct and can be separately measured. Strength tests, however, as usually carried out in gymnasium work, do involve in considerable degree the question of endurance, since it is customary to use as one of the factors in estimating total strength the number of times the man can pull up, or push up, his body on the parallel bars. Strictly speaking, however, the strength of a muscle is measured by the maximum force it can exert in a single contraction, while its endurance is estimated from the number of times it can contract well within the limit of its strength.

It is well known that endurance, both physical and mental, is one of the most variable of the human faculties, and it is usually considered that exercise or training is the chief cause of the differences so frequently seen. The Maine guide will row a boat or paddle a canoe for the entire day without undue fatigue, while the novice, though he may have the necessary strength, lacks the endurance to continue the task longer than a few hours. As expressed by Professor Fisher, " Some persons are tired by climbing a flight of stairs, whereas the Swiss guides, throughout the summer season, day after day spend the entire time in climbing the Matterhorn and other peaks; some persons are ' winded' by running a block for a street car, whereas a Chinese coolie will run for hours on end; in mental work, some persons are unable to apply themselves more than an hour at a time, whereas others, like Humboldt, can work almost continuously through eighteen hours of the day." Again, Fisher states that "among some 75 tests of different persons holding their arms horizontal, many were found whose arms actually dropped against their will inside of 10 minutes, whereas several were able to hold them up over 1 hour, and one man held them 8 hours and 20 minutes, or a round 200 minutes, and then dropped them voluntarily. Similarly with deep knee-bending, some persons were found physically unable to rise again from the stooping posture after accomplishing less than 500 bend* ings, whereas several succeeded in stooping 1000 times, and in one case, 2400. " Here, we have inherent differences in endurance not associated with training or exercise, and the question may well be asked, What is the cause of these radical variations in the ability to repeat a simple muscular exertion?

Hitherto, little attention has been paid to the possible influence of diet upon this faculty. It has always been assumed that endurance, like physical strength, is augmented by a rich proteid diet, but it has never been considered that diet by itself was a factor of any great moment as compared with training or persistent exercise. It is true that claims have been advanced from time to time concerning the beneficial effects on endurance of a vegetable diet, and vegetarians have frequently presented glowing reports of the great increase in endurance they have experienced, but little attention has been given to such statements, and the matter has remained more or less in obscurity.

Recently, Professor Irving Fisher,1 of Yale, has conducted an interesting experiment on the influence of a change in diet on endurance, having the co-operation of nine healthy students as subjects. The experiment extended through five months, with endurance testa at the beginning, middle, and end of the period. At the outset, the men consumed daily an average of 2830 calories, of which 210 were in the form of flesh foods, such as meats, poultry, fish and shell-fish; 2.6 calories of proteid being ingested for each pound of body-weight. At the close of the experiment, the per capita calories had fallen to 2220 of which only 30 were in flesh foods, and the proteid had fallen to 1.4 calories per pound of KpHy-wpjpht. In other words, the total calories of the daily ration had dropped off about 25 per cent, the proteid about 40 per cent, and the flesh foods over 80 per cent, or to about one-sixth of their original amount.

1 Through the kindness of Professor Fisher, the writer has had the opportunity of reading the report of this work, which at this writing is not published, and he has drawn upon it freely for the following statements of fact

To determine the endurance of the subjects, six simple gymnastic tests were employed, and one of mental endurance. The physical tests consisted of (1) in rising on the toes as often as possible; (2) deep knee-bending, or stooping as far as possible and rising to the standing posture, repeating as often as possible; (3) while lying on the back, raising the legs from the floor to a vertical position and lowering them again, repeating to the point of physical rxh.ius-tiou; (4) raising a 5-lb. dumb-bell (with the triceps) in each hand from the shoulder up to the highest point above the head, repeating to the point of physical exhaustion; (5) holding the arms from the sides horizontally for as long a time as possible; (6) raising a dumb-bell (with the biceps) in one hand from a position in which the arm hangs free, to the shoulder and back, repeating to the point of physical exhaustion. This test was taken with four successive dumbbells of decreasing weight, viz., 50, 25, 10, and 5 pounds respectively. The mental test consisted in adding specified columns of figures as rapidly as possible, the object being to find out whether the rapidity of performing such work tended to improve during the experiment.

The following table shows the results of the three sets of physical tests made in January, March, and June:

Tests Of Physical Endurance With The Nine Subject

The data presented show a marked improvement in March and June over the record made at the beginning of the experiment in January, except in the case of one subject, E. As Fisher states, the increased endurance observed can be ascribed only to dietetic causes, since no other factors of known significance could have aided in the result. The dietetic changes, as we have seen, consisted in a slight reduction of the total amount of food consumed daily, but with a large reduction of the proteid element, especially from flesh foods. It is significant, says Fisher, that the only man whose strength and endurance showed any decrease was E, "whose case was exceptional in almost all respects. His reduction in quantity of food, except for a spurt at the end, was less than of most of the men; his reduction in proteid, with the same exception, was the least of all; his reduction in quantity of flesh foods was the least of all." He stands out conspicuously as the one man whose endurance failed to improve. The mental test carried out with the subjects pointed to "a slight increase in mental quickness," but the adding test was too short to be of great value.