APPENDIX II. 167 



garded 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, v/hereof 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 de- 

 veloped 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 muscu- 

 lar 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 regard- 

 ing the amount of carbonic acid evolved from his 

 own lungs under different circumstances.* 



Excretion of carbonic acid during rest and mus- 

 cular exertion : 



Carbonic acid 

 per hour. 



During sleep 19'0 grams. 



Lying down and sleep approaching . 23 - 



In a sitting posture 29'0 



Walking at rate of 2 miles per hour . 70*5 



3 . 100-6 



On the treadwheel, ascending at the 



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



* Phil Trans, for 1859, p. 709. (Pettenh offer's experi- 

 ments on the different amounts of carbonic acid thrown out 

 during the day and during the night do not affect the three 

 last numbers in this table.) 



