CHEMICAL SIGNS OF IRRITABILITY 25 
will be seen, if the experiments on November 6 and 7 are 
compared, that 1 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 1 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 
