ONE THE SOURCE OF MUSCULAR POWER. 259 



cause, as they say, these substances are more nourishing than meat. 

 They doubtless find that in fat and sugar they can most conveniently 

 carry with them a store of force-producing matter. The above tables 

 affirm the same thing. They show that "55 lb. of fat will perform 

 the work of 1-15 lb. cheese, 5 lbs. potatoes, 1-3 lb. of flour or pea- 

 meal or of 3|- lbs. of lean beef. Doaders, in his admirable pamphlet 

 ' On the Constituents of Food and their Relation to Muscular Work 

 and Animal Heat,' mentions the observations of Dr. M. C. Verloren 

 on the food of insects. The latter remarks, " Many insects use du- 

 ring a period in which very little muscular work is performed food 

 containing chiefly albuminous matter ; on the contrary, at a time 

 when the muscular work is very considerable, they live exclusively, or 

 almost exclusively, on food free from nitrogen." He also mentions 

 bees and butterflies as instances of insects performing enormous mus- 

 cular work, and subsisting upon a diet containing but the merest 

 traces of nitrogen. 



"We thus arrive at the following conclusions : — 



1. The muscle is a machine for the conversion of potential energy 

 into mechanical force. 



2. The mechanical force of the muscles is derived chiefly, if not 

 entirely, from the oxidation of matters contained in the blood, and 

 not from the oxidation of the muscles themselves. 



3. In man the chief materials used for the production of muscular 

 power are non-nitrogenous ; but nitrogenous matters can also be em- 

 ployed for the same purpose, and hence the greatly increased evolution 

 of nitrogen under the influence of a flesh diet, even with no greater 

 muscular exertion. 



4. Like every other part of the body, the muscles are constantly 

 being renewed ; but this renewal is not perceptibly more rapid during 

 great muscular activity than during comparative quiescence. 



5. After the supply of sufl5cient albuminized matters in the food 

 of man to provide for the necessary renewal of the tissues, the best 

 materials for the production, both of internal and external work, are 

 non -nitrogenous matters, such as oil, fat, sugar, starch, gum, &c. 



6. The non-nitrogenous matters of food, which find their way into 

 the blood, yield up all their potential energy as actual energy ; the 

 nitrogenous matters, on the other hand, leave the body with a portion 

 (one-seventh) of their potential energy unexpended. 



