CHEMICAL SIGNS OF IRRITABILITY 27 



we should expect to find that less carbon dioxide was 

 produced by nerves in an atmosphere of hydrogen than 

 in normal air. On the other hand, if the carbon dioxide 

 was due to some fermentation, or non-vital process, then 

 it should not be influenced by the absence of oxygen. 



When, with Dr. Adams, we determined the rate of 

 carbon dioxide production in nerves placed in an atmos- 

 phere of hydrogen gas, care having been taken to insure 

 the gas being perfectly pure, we found .that the rate was 

 only about half that of the normal nerve. It appears 

 from this determination that in a medium deficient in 

 oxygen the claw nerve of the spider crab gives off less Y 

 carbon dioxide than in an ordinary atmosphere. The 

 effect cannot be due to the hydrogen, since that gas has 

 no physiological action, but is quite inert, and we may 

 conclude that the lowering of the carbon dioxide is due 

 to the lack or absence of oxygen. This is additional 

 evidence that the lowering of the gaseous output is a 

 physiological phenomenon, and that the carbon dioxide 

 measured in normal isolated nerves is a product of normal 

 metabolism, and is not the mere diffusion outward of the 

 gas which is present in the tissue, being produced there 

 by other than living processes. 



Carbon dioxide production of the isolated nerve at suc- 

 cessive time intervals. If the carbon dioxide production 

 is due to a vital process, it might be expected to diminish 

 gradually in the isolated nerve as its vitality diminishes. 

 On the other hand, there was a possibility that the iso- 

 lated nerve had become infected with bacteria and that 

 the carbon dioxide might be due to their action. If 

 this were the case, it \vould be expected that the carbon 

 dioxide would gradually increase. Accordingly, experi- 



