WORK PRODUCTION 543 



horn, a Swiss mountain 6418 feet high, after having abstained 

 from nitrogenous food for 17 hours, and found that the amount 

 of protein katabolized during the six hours occupied by the 

 ascent and the seven succeeding hours of rest, as measured by 

 the urea excreted, was insufficient, according to their com- 

 putations, to account for more than about one- third of the energy 

 required to lift their bodies to the height of the mountain, mak- 

 ing no allowance for the work of the internal organs nor for 

 those muscular exertions which did not contribute directly to 

 the work done. They observed no considerable increase in 

 the urinary nitrogen over that excreted before the ascent. 



643. Protein insufficient as source of energy. It is true 

 (637) that with an insufficient supply of non-nitrogenous ma- 

 terials in the feed muscular exertion may lead to an increase in 

 the protein katabolism, but in the many comparisons which have 

 been made since the time of Fick and Wislicenus by far more 

 refined methods than were available to them, this increase has 

 been shown to be entirely inadequate to furnish the energy for 

 the work performed. Moreover, even the supposition that the 

 energy of the total protein katabolized was all applied to work 

 production usually fails to account for the energy expended. 



The facts, then, first, that the chief, and often the only, effect 

 of muscular work is to increase the katabolism of non-nitrog- 

 enous material; second, that even the total protein katab- 

 olism is in most cases insufficient to supply the energy ex- 

 pended in work ; and third, that, as Kellner (637) has shown, 

 the addition of non-nitrogenous nutrients to the ration enables 

 more work to be done ; demonstrate beyond cavil that under 

 ordinary conditions of nutrition it is the non-nitrogenous in- 

 gredients of the body and of the feed which supply most or all 

 of the energy expended in the performance of work. 



644. Functions of proteins. The foregoing statements 

 should not be understood as an assertion that the proteins 

 play no part in the production of muscular work. In the first 

 place, their katabolism furnishes a considerable amount of non- 

 nitrogenous products (229, 233) and that these products are avail- 

 able to supply energy for work has been strikingly shown by 

 Pfluger. He maintained a dog for about nine months on an 

 exclusive diet of almost fat-free meat and showed that on this 

 diet the animal was capable of performing large amounts of 



