

460 THE EXPENDITURE OF ENERGY. [BOOK n. 



from the metabolism of the proteid constituents of muscle. We 

 have already seen (p. 70) that when the muscle itself is examined, we 

 find no proof of nitrogenous waste, but, on the other hand, clear 

 evidence of the production of non-nitrogenous bodies, such as 

 carbonic acid. And when we ask the question, Does muscular 

 exercise increase the urea given off by the body as a whole ? for 

 this, according to Liebig's theory, it certainly ought to do, the 

 evidence we can obtain, though somewhat conflicting, gives on the 

 whole a decidedly negative answer. Exercise, even severe, appears 

 not necessarily to increase the urea of the urine. 



More than this, the experience of Fick and Wislicenus lands us 

 in an absurdity if we suppose the whole energy of muscular work 

 to arise from proteid metabolism. These observers performed a 

 certain amount of work (an ascent of the Faulhorn) on a non- 

 nitrogenous diet, and estimated the amount of urea passed during 

 the period. Assuming the urea to represent the oxidation of so 

 much proteid matter, which oxidation represented in turn so much 

 energy set free, they found that whereas the actual work done 

 amounted to 129026 and 148-656 kilogram. -kilometres, for each 

 respectively, the total energy available from proteid metabolism 

 during the period was in the case of the first 68'69, and of the 

 second 68'376 kilogram.-ldlometres. That is to say, the energy 

 set free by the proteid metabolism of the muscles engaged 

 in the work was at the most far less than that necessary to 

 accomplish the work actually done, besides having to provide 

 for the movements of respiration and circulation. Their muscular 

 energy therefore must have had other sources than proteid meta- 

 bolism. 



That on the contrary the production of carbonic acid is at once 

 and largely increased by muscular exercise is beyond all doubt, 

 One hour's hard labour will increase fivefold the quantity of 

 carbonic acid given off within the hour. And in an experiment 

 directed to this point it was found that a man in 24 hours con- 

 sumed 954 grms. oxygen and produced 1284 gims. carbonic acid 

 when doing work, as against 708 grms. oxygen consumed and 

 911 grms. carbonic acid produced when remaining at rest, the 

 quantity of urea secreted being in the first case 37 grms., in the 

 second 37' 2 grms. 



It is evident that the conclusions arrived at by the statistical 

 method entirely corroborate those gained by an examination of 

 muscle itself, viz. that during muscular contraction an explosive 

 decomposition takes place, the non-nitrogenous products of which 

 alone escape from the muscle and from the body, any nitrogenous 

 products which result being retained within the muscle. We must 

 therefore reject the second as well as the first division of Liebig's 

 view; not only is the muscle not fed exclusively on proteid 

 material, but also its energy does not arise from an exclusively 

 proteid metabolism. 



