60 A CHEMICAL SIGN OF LIFE 



ishes as the nerve approaches death. The point of 

 minimum production of the gas corresponds approxi- 

 mately to the point where an electrical response ceases 

 (see p. 28). 



b) Although the nerve remains active for some time 

 without oxygen, it is known that the absence of oxygen 

 diminishes the excitability of the nerve. This diminu- 

 tion of the excitability when in hydrogen is accompanied 

 with a lowering of carbon dioxide production in the nerve. 



c) Further facts showing the relation between 

 excitability and metabolic activity are brought out by 

 the study of the effects of narcotics on the nervous 

 metabolism. There are several compounds which alter 

 the state of excitability of nerves to a considerable 

 degree. The discovery of just what happens to respira- 

 tion during anesthesia will throw much light on the 

 nature of irritability. It is this which we shall now 

 study in detail. 



In recent years many experiments have been per- 

 formed which are supposed to prove that oxygen con- 

 sumption can go on uninterruptedly during narcosis, and 

 the consequent conclusion has been that narcosis is not 

 produced by asphyxiation. This is not the place for us 

 to weigh the merit of these arguments, nor are we con- 

 cerned here with the question of how narcotics act on 

 protoplasm, but it is very important to know whether or 

 not metabolic activity in nervous tissue can go on undis- 

 turbed while the tissue is unable to perform its own 

 function. Are respiration and irritability independent 

 processes ? To show that they are dependent we shall 

 cite in detail experiments on the effects of anesthetics on 

 respiration. 



