810 NUTRITION AND HEAT REGULATION. 



the experiment has been accepted as showing conclusively that the 

 total energy of muscular work does not come necessarily from the 

 oxidation of proteid. 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 

 potential energy of the proteid simultaneously oxidized, but that 

 the performance of muscular work within certain limits does not 

 affect at all the amount of proteid 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 soldiers 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 that undoubtedly occurs during muscular activity must affect 

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

 Subsequently the question was reopened by experiments made 

 under 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 proteid 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-proteid 

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

 there would not have been any increase in proteid metabolism. 

 These experiments were repeated in various forms by many ob- 

 servers (Zuntz, Speck, et al.), and the general result has been 

 the abandonment of both the former views, the Liebig theory 

 that the energy comes only from the consumption of proteid, and 

 the Voit theory, that it comes only from the oxidation of non-pro- 

 teid material. It has been found that in muscular work carried to 

 the ordinary extent proteid material, in excess of that destroyed in 

 conditions of rest, may or may not be used according to the amount 

 of fats and carbohydrates in the diet. If these latter elements are 

 in sufficient quantity they furnish the energy required, and proteid 

 metabolism is not increased by work. If, however, the non-pro- 



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

 1890. 



