CHEMICAL SIGNS OF IRRITABILITY 25 



will be seen, if the experiments on November 6 and 7 are 

 compared, that i c.c. of gas taken from the respiratory 

 chamber in which the dead nerve had been for a certain 

 length of time contained not enough carbon dioxide to 

 produce a precipitate, while i c.c. of gas from the cham- 

 ber in which the living nerve had been for the same time 

 did produce a precipitate and consequently contained 

 more carbon dioxide. It is clear, then, that a dead 

 nerve gives off less carbon dioxide than the living. 



Comparison of anesthetized and normal nerves. By 

 the use of anesthetics we can diminish the irritability, 

 or, as we may say, the vitality, of the nerve without 

 abolishing it altogether, The nerve, although anesthe- 

 tized, is still alive, but in a condition of suspended 

 animation. When the anesthetic escapes from it, it 

 recovers its normal vitality. If the carbon dioxide has 

 been produced by a vital process and is at all corre- 

 lated with the state of irritability of the nerve, we 

 should expect that a diminution of that irritability by 

 anesthetics would produce a diminution in the carbon 

 dioxide output. If, on the other hand, this carbon 

 dioxide is the result, not of a vital process, but of a 

 fermentation, or of an acid production of some sort, then 

 we should expect that it would be little, if at all, affected 

 by the anesthetic. Accordingly, nerves were anesthe- 

 tized in various ways, for example, by placing them in a 

 solution of urethane, or they were treated with the 

 vapors of ether, or the nerve was isolated from a deeply 

 anesthetized frog, and the quantity of carbon dioxide 

 produced by such nerves was compared with the quantity 

 produced by normal nerves of the same animals. It was 

 found always that the anesthetized nerve gave off 



