METABOLISM. 73 



oxygon must be derived from some component of muscle; 

 it results that the energy must be obtained by decomposi- 

 tion of a nitrogenous body. To this reasoning it may be 

 objected, in the first place, that the conditions specified are 

 abnormal, and that it is dangerous to assume that what 

 takes place under abnormal conditions takes place also under 

 normal ones. In presence of blood and oxygen the process 

 may possibly, or even probably, be unlike that which arises in 

 their absence : the muscular substance may begin consuming 

 itself when it has not the usual materials to consume. Then, 

 in the second place, and chiefly, it may be replied that the 

 difficulty raised in the foregoing argument is not escaped 

 but merely obscured. If, as is alleged, the carbon and 

 oxygen from which carbonic acid is produced, form, under 

 the conditions stated, parts of a complex nitrogenous sub- 

 stance contained in muscle, then the abstraction of the 

 carbon and oxygen must cause decomposition of this nitro- 

 genous substance; and in that case the excretion of nitro- 

 genous waste must be proportionate to the amount of work 

 done, which it is not. This difficulty is evaded by supposing 

 that the " stored complex explosive substance must be, in 

 living muscle, of such nature " that after explosion it leaves 

 a " nitrogenous residue available for re-combination with 

 fresh portions of carbon and oxygen derived from the blood 

 and thereby the re-constitution of the explosive substance." 

 This implies that a molecule of the explosive substance con- 

 sists of a complex nitrogenous molecule united with a 

 molecule of carbo-hydrate, and that time after time it sud- 

 denly decomposes this carbo-hydrate molecule and thereupon 

 takes up another such from the blood. That the carbon is 

 abstracted from the carbo-hydrate molecule can scarcely be 

 said, since the feebler affinities of the nitrogenous molecule 

 can hardly be supposed to overcome the stronger affinities 

 of the carbo-hydrate molecule. The carbo-hydrate molecule 

 must therefore be incorporated bodily. What is the implica- 

 tion? The carbo-hydrate part of the compound is relatively 

 stable, while the nitrogenous part is relatively unstable. 



