physiologists, that the muscular system is a machine which consumes food as fuel, and does not wear its own substance to any very great extent in the production of force. Fick and Wislicenus advanced the view that "the substances, by the burning of which force is generated in the muscles, are not the albuminous constituents of the tissues, but non-nitrogenous substances, either as fats or hydrates of carbon."
Such a doctrine as that advanced by Fick and Wislicenus, according to Prof. Flint, is not logical and is opposed to many well-known physiological facts. The arguments he advances against it are the following;
1. Physiological experiments should be made under strictly natural or physiological conditions of the system. A non-nitrogenized diet is not natural. No man would attempt to perform a feat of muscular endurance under a diet composed exclusively of fat, starch, and sugar, which was the exclusive diet of Fick and Wislicenus.
2. Lehmann has shown that an exclusively non-nitrogenized diet, of itself, without any variation in muscular exercise, will reduce the excretion of nitrogen by the kidneys more than one-half. Pavy has shown the same effects of non-nitrogenized food upon the system without any variation in muscular exercise.
3. Fick and Wislicenus do not show that extraordinary muscular exertion, with a non-nitrogenized diet, diminishes the excretion of nitrogen below the point to which it would be reduced by the diet itself, without muscular work; for they made no comparative experiments with a non-nitrogenized diet and no unusual exercise.
In view of these facts, the conclusion arrived at by Prof. Flint is, that the experiments of Fick and Wislicenus fail to show that muscular exercise diminishes, or even does not increase, the elimination of nitrogen, which is the very essence of their argument.
In 1870, Prof. Flint made a series of elaborate experiments upon Weston, during a walk of three hundred and seventeen and one-half miles in five consecutive days. Recognizing the fact that the elimination of nitrogen bears a certain relation to the nitrogen of the food, in these experiments, Prof. Flint estimated the nitrogen of the food and calculated the proportion of nitrogen excreted to the nitrogen ingested, which had never been done in any previous experiments upon the physiological effects of muscular exercise. His observations were continued for five days before the walk, the five days of the walk, and five days after the walk. Prof. Flint, or his assistants, were with Weston, day and night, for the entire fifteen days. Every article of food was weighed or measured, and its nitrogen carefully estimated, as was the nitrogen excreted. The variations in body-weight, temperature, etc., were also taken. No accident occurred, and the observations were absolutely complete. The most important general results of these experiments were the following:
For the five days before the walk, the average daily exercise being