CHEMICAL SIGNS OF IRRITABILITY 53 



irrespective of the stimulus, and accordingly excitation 

 appears to generate no heat and there appears to be no 

 fatigue, unless we deprive the nerve of oxygen for some 

 time, and yet we have a copious production of carbon 

 dioxide which is increased on stimulation. The fact, 

 therefore, that there is no increased heat production in a 

 stimulated nerve is by no means contrary to our results, 

 although it is certainly surprising. It indicates, perhaps, 

 that the act of excitation is not primarily an oxidation, 

 but that the oxidation is concerned in the processes of 

 repair. There are several facts which might be cited, 

 were the space at our command, which would lead to the 

 same conclusion. There are also other suggestions which 

 might be made to account for this seeming incompatibil- 

 ity, but it would be useless to do so without experiments. 



We may therefore close this brief discussion with the 

 statement that the failure to detect heat production in 

 nerves during excitation is no evidence of value against 

 the occurrence there of chemical changes resulting in 

 carbon dioxide production and correlated with the irri- 

 tability. The conclusion drawn from it by some authors 

 that the nerve impulse does not, on this account, involve 

 any chemical processes is entirely unwarranted. 



We may in this connection stop for a moment to 

 consider what is known of the oxygen consumption of 

 nerves, for while we have ourselves as yet carried out 

 no experiments in this line, yet there have been some 

 observations made which can be correlated with the 

 carbon dioxide production. In the first place, it may 

 be noted that there is no immediate dependence of some 

 nerves, at least, on atmospheric oxygen for their activity. 

 In this respect the carbon dioxide production , and the 



