CHAPTER VI 



PRODUCTION OF WORK, MILK, AND WOOL 



I. PRODUCTION OF WORK 



It has long been known that muscular exertion or external body work 

 greatly increases the amount of food material burned or broken down 

 in the body, but scientists have disagreed as to whether one or all of the 

 nutrients protein, carbohydrates, or fat furnishes the energy. 



139. The source of muscular energy. Because external work is brought 

 about by contractions of the muscles, it was perhaps natural that early 

 scientists believed the muscles, which are composed of protein tissues, 

 were themselves broken down to furnish the energy used in the work. 

 For instance, Liebig, the "father of agricultural chemistry," maintained 

 that the protein of the muscle tissues was the only material used up in 

 producing voluntary or involuntary motions, whether of the limbs, heart, 

 or other parts of the body. When metabolism trials were carried on by 

 various scientists to study the production of work by animals, the results 

 disagreed. In some cases, the amount of nitrogen excreted in the urine 

 was much greater when work was performed, indicating that protein had 

 been broken dow T n in the body in the production of the muscular energy. 

 However, in other trials no more nitrogen was excreted during work than 

 during rest. 



The first clear light was thrown on this matter by Fick and Wislicenus, 1 

 who in 1865 ascended the Faulhorn, an Alpine mountain 6,418 feet high, 

 to study the effect of the work of climbing upon their own bodies. While 

 ascending the mountain they consumed only non-protein food; i. e., 

 starch, sugar, and fat, and during this time they collected all the urine 

 passed. Had the muscles or other protein tissues of the body been 

 broken down in producing the muscular labor involved in climbing the 

 mountain, there would have been a large increase in the amount of nitrog- 

 enous waste material excreted in the urine during and immediately after 

 the climb. But this was not the case. On analysis, it was found that no 

 more nitrogen was excreted than before the climb when no work was 

 being done. Measured by the nitrogen in the urine, the protein broken 

 down during the trial could not possibly have furnished energy for more 

 than one-third of the work done by these men in lifting their bodies to 

 the top of the mountain, making no allowance whatsoever for the work 

 of the internal organs of the body, P' for the muscular exertions which 

 did not contribute directly to the work of climbing. 



J U. S. Dept. Agr., Office of Expt. Sta., Bui. 22, p. 307. 



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