934 NUTRITION AND HEAT REGULATION. 



a certain amount of muscular work performed in the move- 

 ments of the arms and in walking upon level ground that was 

 omitted entirely from their calculations. For seventeen hours 

 before the ascent, during the climb of eight hours, and for six 

 hours afterward their food was entirely non-nitrogenous, so that 

 the urea eliminated came entu-ely from the protein of the body. 

 Nevertheless, when the urine was collected and the urea estimated, 

 it was found that the energy contained in the protein destroyed, 

 reckoned as heat energy, was entirely insufficient to account for 

 the work done. Although later estimates would modify somewhat 

 the actual figures of their calculation, the margin was so great that 

 the experiment has been accepted as showing conclusively that the 

 total energy of muscular work does not come necessarily from the 

 oxidation of protein. Later experiments made by Voit upon a 

 dog working in a tread-wheel and upon a man performing work 

 while in the respiratory chamber gave the surprising result that 

 not only may the energy of muscular work be far greater than the 

 heat energy of the protein simultaneously oxidized, but that the 

 performance of muscular work within certain limits does not 

 affect at all the amount of protein metabolized in the body, since 

 the output of urea is the same on working days as during days of 

 rest. Careful experiments by an English physiologist, Parkes, made 

 upon 8okliers, while resting and after performing long marches, 

 showed also that there is no distinct increase in the secretion of urea 

 after muscular exercise. It followed from these latter experiments 

 that Liebig's theory as to the source of the energy of muscular 

 work is incorrect, and that the increase in the oxidations in the 

 body, which undoubtedly occurs during muscular activity, must affect 

 only the non-protein material — that is, the fats and carbohydrates. 

 Subsequent!}^ the question was reopened by experiments made 

 imder Pfliiger by Argutinsky.* In these experiments the total 

 nitrogen excreted was determined with especial care in the sweat 

 as well as in the urine and the feces. The muscular work done 

 consisted in long walks and mountain climbs. Argutinsky found 

 that work caused a marked increase in the elimination of nitrogen, 

 the increase extending over a period of three days, and he estimated 

 that the additional protein metabolized in consequence of the work 

 was sufficient to account for most of the energy expended in per- 

 forming the walks and climbs. A number of objections have been 

 made to Argutinsky's work. It has been asserted that during his 

 experiment he kept himself upon a diet deficient in non-protein 

 material, and that if the supply of this material had been sufficient 

 tliere would not have been an increase in protein metabolism. 

 These experiments were repeated in various forms by many ob- 



* Argutinsky, "Pfluger's Archiv f. die gesammte Physiologie, " 46, 552, 

 1S90. 



