112 METABOLISM AND NUTRITION 



hours later they ate the first nitrogenous food after the experiment. The urine 

 was collected from the beginning of the ascent until seven hours after its con- 

 clusion, and was analyzed for nitrogen. Fick's urine contained 5.74 g. N and 

 that of Wislicenus 5.55 g., representing a work equivalent, calculated from the 

 heat value of the proteid burned, of 63,378 and 62,280 kilogram-meters respec- 

 tively. Fick's weight was 66 kg. and Wislicenus's was 76 kg. ; hence the amount 

 of external work actually done in lifting their bodies 1,956 meters was 129,096 

 and 148,656 kg. m. respectively. The work done at the expense of proteid there- 

 fore could not have been more than one-half that expended merely in lifting their 

 bodies, not taking into account the work of the heart, of the respiratory muscles 

 and of the other muscles constantly in use in maintaining equilibrium. 



But it might be argued that the increased excretion of nitrogen corre- 

 sponding to the work of a given day would be eliminated from the body the 

 following day. This idea, first expressed by Liebig, was tested by Argutinsky 

 and Krummacher on themselves., and was reported by them to be correct. 

 The force of their experiments is considerably diminished, however, by the 

 fact that neither of the authors was in nitrogenous equilibrium during the 

 resting days, and that their food was much too poor in absolute quantity of 

 nutrient substances. 



Moreover, Krummacher himself has shown elsewhere that when plenty o 

 energy is supplied, the increased output of nitrogen on the day following work 

 is quite insignificant. Thus a man engaged in hard labor received daily 89.3 g. 

 proteid (=14.3 g. nitrogen), 175 g. fat, and 903 g. carbohydrate (=5,701 Cal.). 

 During rest while on this diet, he excreted on the average 13.46 g. "N in the urine 

 and fgeces. Then followed a workday on which he did 402,000 kg. m. of external 

 work, and excreted 14.05 g. N. The output on the two following rest days was 

 13.70 and 13.47 g. N respectively. Only on the first of the two was there any 

 increase over the elimination previous to the workday, and then it was only 0.24 

 g. !N". This experiment also shows in a particularly beautiful way that muscular 

 work is not done at the expense of proteid when a sufficient supply of nonnitro- 

 genous food is given. The external work of the one day was equivalent to 945 

 Cal., whereas the total metabolism of proteid on the workday plus the excess 

 on the day following (14.05 g. N + 0.24 g. N = 90 g. proteid) was equivalent 

 to only 364 Cal. 



But we are not to suppose that proteid cannot serve as the source of 

 muscular energy. For in extreme cases when there is no fat and no carbo- 

 hydrate at the disposal of the body, if muscular work is done, it can only 

 be at the expense of proteid. 



Pfliiger fed a large dog for a long time on nothing but meat which contained 

 as little fat and carbohydrate as possible. The dog was already very lean before 

 the beginning of the experiment, so that there was no stored fat and glycogen 

 to draw upon. From time to time he was compelled to do severe work varying 

 in amount from 73,072 kg. m. to 109,608 kg. m., and since the fat and carbo- 

 hydrate in the food were far from sufficient to produce this amount of energy, 

 the work must have been done largely at the expense of the proteid. 



It is perfectly easy to show that the nonnitrogenous foodstuffs furnish 

 energy for muscular work. The excretion of carbon dioxide rises almost 



