METABOLISM. ^1 



developing muscles for subsequent use in the completion of 

 their structures. 



§ 23c. We come now to the supreme and all-pervading 

 metabolism which has for its effects the conspicuous manifes- 

 tations of life — the nervous and muscular activities. Here 

 comes up afresh a question discussed in the edition of 1864 

 — a question to be reconsidered in the light of recent knowl- 

 edge — the question what particular metabolic changes are 

 they by which in muscle the energy existing under the form 

 of molecular motion is transformed into the energy mani- 

 fested as molar motion? 



There are two views respecting the nature of this tra^is- 

 formation. One is that the carbo-hydrate present in muscle 

 must, by further metabolism, be raised into the form of a 

 nitrogenous compound or compounds before it can be made 

 to undergo that sudden decomposition which initiates mus- 

 cular contraction. The other is the view set forth in § 15, 

 and there reinforced by further illustrations which have 

 occurred to me while preparing this revised edition — the 

 view that the carbo-hydrate in muscle, everywhere in contact 

 with unstable nitrogenous substance, is, by the shock of a 

 small molecular change in this, made to undergo an extensive 

 molecular change, resulting in the oxidation of its carbon 

 and consequent liberation of much molecular motion. Both 

 of these are at present only hypotheses, in support of which 

 respectively the probabilities have to be weighed. Let us 

 compare them and observe on which side the evidence prepon- 

 derates. 



We are obliged to conclude that in carnivorous animals the 

 katabolic process is congruous with the first of these views, 

 in so far that the evolution of energy must in some way 

 result solely from the fall of complex nitrogenous compounds 

 into those simpler matters which make their appearance 

 as waste; for, practically, the carnivorous animal has no 

 carbo-hydrates out of which otherwise to evolve force. To 



