THE SOURCE OF MUSCULAR POWER. 731 



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, accord- 

 ing 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 with- 

 out 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 experi- 

 ments 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 muscu- 

 lar 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 elimina- 

 tion 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 ai'ticle of 

 food was weighed or measured, and its nitrogen carefully estimated, 

 as was the nitrogen excreted. The variations in body-weight, tem- 

 perature, etc., were also taken. No accident occurred, and the obser- 

 vations 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 



