218 THE HUMAN MECHANISM 



on chemical -analysis, large quantities of protein and only 

 traces of carbohydrates and fats, believed that the energy 

 for muscular contraction comes entirely from the consump- 

 tion of the protein of the muscle substance. If this were 

 true, it would necessarily follow that protein is the proper 

 food to yield the energy for muscular contraction, while fats 

 and carbohydrates would simply be oxidized to give heat. 



This view was disproved by the following epoch-making 

 experiment of physiology: Two observers determined for 

 three successive days the nitrogen excreted by themselves; 

 since almost all this nitrogen comes from protein, this gave 

 the amount of protein consumed by the body. On the first 

 and third days no vigorous muscular work was done ; on the 

 second day they climbed a mountain 1956 meters (6415 ft.) 

 high. As one man weighed 66 kilograms and the other 

 76 kilograms, the work done in lifting the body to the top 

 of the mountain in the two cases was 129,096 and 148,656 

 kilogrammeters respectively. The protein which was oxidized 

 in this time could in the two cases have yielded power for 

 only 68,690 and 68,376 kilogrammeters of work. In other 

 words, the protein did not begin to yield sufficient power 

 for the muscular work done in lifting the body to the top 

 of the mountain ; something else than protein must have 

 been oxidized for that purpose, and that something must 

 evidently have been carbohydrate or fat, or both. 



Again, it was noticed that there was no increase of pro- 

 tein disintegration on the day of work; this remained 

 practically unaffected by muscular contraction. Numerous 

 other experiments made since that time have shown the 

 same thing. Muscular exercise does not necessarily increase 

 protein disintegration, and the power for it can be obtained 

 from fats and carbohydrates. 



In the experiment above referred to no determinations 

 were made of the excretion of carbon dioxide. Since then 

 numerous experiments have been made in which, on an 



