42 PHYSIOLOGY CHAP. 



elimination of CO 2 and absorption of O 2 are increased; but the 



CO 

 value of the respiratory quotient -^ increases also, because the 



U 2 



output of C0 9 is greater than the intake of 2 (Ludwig and 

 Sczelkow, 1862, Ludwig and Schmidt, 1868, v. Frey, 1885). 



Hans Winterstein (1907) demonstrated that the rigor mortis 

 of mammalian muscle is essentially due to the loss of oxygenation, 

 owing to arrest of the vascular circulation ; it is thus an asphyxia 

 phenomenon. In fact, if a mammalian muscle, excised from the 

 body, is kept in Kinger's solution at an oxygen pressure of 2-4 

 atmospheres, at a temperature of 36-38 C., its excitability may 

 be preserved for twenty-seven hours after dissecting it out, with 

 no appearance of rigor. If rigor sets in, it may be kept off by 

 successive strong doses of oxygen. When it is once established, 

 however, further oxygenation is useless. 



VIII. There can be no doubt that the chemical processes 

 which come into play during the activity of muscle are the source 

 of the physical energy which the muscle develops, and the external 

 mechanical work which it performs. This is a direct corollary to 

 the law of the conservation of energy. Muscular excitation is the 

 most classical instance in the living world of the explosive dis- 

 charge of energy, i.e. the rapid transformation of potential chemical 

 energy into kinetic energy, in the form of work, heat, and 

 electricity. As in the steam-engine the mechanical work depends 

 on the combustion of coal, so the mechanical work of the muscular 

 machine results from the katabolic processes of disintegration and 

 oxidation of the organic compounds which build up the muscle. 



Having now discussed the chemical changes that go on in 

 living muscle during rest and in activity, we must next turn to 

 the problem of the origin of muscular energy, that is, which of the 

 food stuffs introduced into the body and assimilated by the muscles 

 furnishes the necessary energy for their activity. 



Starting from the fact that proteins represent the chief con- 

 stituents of muscle, and that a full meat-diet increases the work- 

 capacity of muscle, while a diet poor in protein depresses it, 

 Liebig (185*7-70) assumed that the source of muscular energy 

 must be sought in the proteins. There can be no doubt that the 

 nitrogenous exchanges of muscle are very active, much protein 

 being consumed both in rest and in activity ; but Liebig showed 

 .no direct experimental proof that the activity of muscle depends 

 mainly upon increased protein metabolism. 



Bischoff and Voit (1860) thought the question could be solved 

 by comparing the urea content and the total nitrogen content 

 of urine during hard muscular work, with that eliminated during 

 rest, the same quantity and quality of food stuffs being ingested. 

 In both man and dogs they obtained a nitrogenous equilibrium after 

 a few days of uniform dieting, i.e. equivalence between the nitrogen 



