26 A CHEMICAL SIGN OF LIFE 



decidedly less carbon dioxide than the nerves of normal 

 frogs or nerves taken from frogs whose circulation had 

 been suspended for a period of time equal to that of 

 etherization. A perfect parallelism was found to exist 

 between the carbon dioxide production and the state 

 of excitability of the nerve. Thus small quantities of 

 anesthetics have often the effect of increasing at first 

 the excitability of the nerve, and it was found that such 

 quantities also produced at first an increase in the carbon 

 dioxide. A further consideration of the effects of 

 anesthetics on the metabolism of the claw nerve of the 

 spider crab will be found in chapter iv. The important 

 fact is that since these agents are known to affect the 

 normal uncut nerve in situ and also to modify carbon 

 dioxide production in an isolated nerve, and in a manner 

 parallel with their known actions on irritability, it is 

 certain that at least the larger part of the carbon dioxide 

 we measure in an isolated resting nerve must have been 

 produced by a physiological process. 



Carbon dioxide production in a hydrogen atmosphere. 

 Although many nerves remain alive for a long time in an 

 atmosphere free from oxygen, they generally exhibit a 

 lowered irritability when compared with nerves in normal 

 air. It has been found, for example, that if nerves 

 remain in the body after the circulation of a frog has 

 ceased, so that they have not been supplied with oxygen 

 for some time, they are by no means so easily stimulated 

 by a salt solution as are normal nerves. Their vitality 

 is reduced. A similar change occurs in nerves taken 

 out of the body and put in hydrogen gas. In them, also, 

 irritability is decidedly diminished. If, now, carbon 

 dioxide is produced in these nerves by a vital process, 



