Prof. Frankland on the Origin of Muscular Power. 193 



Thus, even under the extremely unfavourable conditions of 

 these determinations, the actual work performed exceeded that 

 which could possibly be produced through the oxidation of the 

 nitrogenous constituents of the daily food by more than 30 

 per cent. 



We have seen, therefore, in the above four sets of experiments, 

 interpreted by the data afforded by the combustion of muscle 

 and urea in oxygen, that the transformation of tissue alone can- 

 not account for more than a small fraction of the muscular 

 power developed by animals ; in fact this transformation goes 

 on at a rate almost entirely independent of the amount of mus- 

 cular power developed. If the mechanical work of an animal 

 be doubled or trebled, there is no corresponding increase of 

 nitrogen in the secretions ; whilst it was proved, on the other 

 hand, by Lawes and Gilbert as early as the year 1854, that 

 animals under the same conditions as regarded exercise, had 

 the amount of nitrogen in their secretions increased twofold by 

 merely doubling the amount of nitrogen in their food. Whence, 

 then, comes the muscular power of animals ? What are the 

 substances which, by their oxidation in the body, furnish the 

 actual energy whereof a part is converted into muscular work ? 

 In the light of the experimental results detailed above, can it be 

 doubted that a large proportion of the muscular power developed 

 in the bodies of animals has its origin in the oxidation of non- 

 nitrogenous substances ? For, whilst the secretion of nitrogen 

 remains nearly stationary under widely different degrees of mus- 

 cular exertion, the production of carbonic acid increases most 

 markedly with every augmentation of muscular work, as is 

 shown by the following tabulated results of E. Smith's highly 

 important experiments upon himself, regarding the amount of 

 carbonic acid evolved under different circumstances*. 



Excretion of carbonic acid during rest and muscular ex- 

 ertion : — Carbonic acid 



per hour. 



During sleep 19*0 grams. 



Lying down, and sleep approaching . 23'0 „ 

 In a sitting posture ...... 29*0 „ 



Walking at the rate of 2 miles per hour 70'5 „ 

 Walking at the rate of 3 miles per hour 100*6 „ 

 On the tread wheel, ascending at the 



rate of 28'65 feet per minute . . . 189*6 „ 



It is admitted on all hands that food, and food alone, is the 



ultimate source from which muscular power is derived ; but the 



above determinations and considerations prove conclusively, 



first, that the non-nitrogenous constituents of the food, such as 



* Phil. Trans, for 1859, page 709. 

 Phil. Mag. S. 4. Vol. 32. No. 215. Sept. 1886. 



