THE OXIDIZING SUBSTANCE AND MYOSINOGEN. 



237 



But if we can separate these elements of the process into two 

 distinct parts, viz.: (1) a nervous impulse to the muscular 

 elements themselves, and (2)- a simultaneous change in the 

 caliber of the local arterioles, the fact that as the impulse leaves 

 the end-plate "it is followed by an explosive decomposition of 

 material, leading a discharge of carbonic acid," will stand as 

 the only result to be expected. Such a division becomes neces- 

 sary in the light of our conception of the process. 



While the nerve-impulses only have for their purpose to 

 excite and govern the function, the blood i.e., the blood- 

 plasma mainly through its oxidizing substance becomes the 

 factor through which the chemical process to which contractile 

 work is due is suddenly awakened. A feature of this concep- 

 tion upon which particular stress must be laid since it applies 

 to all organs is that it dissociates from the oxidation process 

 per se a stimulus which does not belong to it and which, there- 

 fore, introduces elements of confusion. "We cannot tell," says 

 Stewart, "in what the 'natural' or 'physiological' stimulus to 

 muscular contraction in the intact body really consists, nor 

 how it differs from artificial stimuli." Eelieved of this au- 

 tonomous agency, the organic physico-chemical processes enter 

 within the limits of exact investigation. 



Oxygen in other fields of thermochemistry is known to 

 constitute the reactionary agent through which "explosive de- 

 composition" is awakened and sustained. That it fulfills the 

 same role in this connection, some complex organic compound 

 in the muscular fibers constituting the primary source of en- 

 ergy or fuel, is probable. Under these circumstances the 

 passive "irritability" of a living muscle would be maintained 

 by a continuous reaction in which the reagents would be these 

 compounds i.e., hydrocarbons and the oxygen held in loose 

 combination in the blood, particularly the blood-plasma, which 

 penetrates the contractile elements themselves. This irrita- 

 bility would then become abruptly converted into contractility 

 when the blood-supply i.e., the plasma in the contractile fibers 

 would be increased through the arrival of more oxygen. 



Considerable familiar evidence besides that already ad- 

 duced is available in support of this conception of the general 

 physiology of muscle-tissue. Although continuous muscular 



