EXCITATION AND CONDUCTION 61 
We have already mentioned the effect of ether on 
nerves and demonstrated that lowering the excitability of 
a nerve is accompanied by a lowering of ‘carbon dioxide 
production. For the quantitative experiments, carried 
out in conjunction with Dr. Adams, we used chloral 
hydrate and ethyl urethane in preference to the ordinary 
volatile narcotics. If we anesthetize a nerve with the 
lowest concentration of ether or chloroform that pro- 
duces a reversible loss of irritability, then the anesthe- 
tized nerve regains its excitability during the course of the 
experiments, for in order to make the apparatus free 
from carbon dioxide after introducing the nerve we have 
to wash it with carbon-dioxide-free air several times. 
By so doing the most volatile narcotics are removed 
from the nerve. On the other hand, if we use higher 
concentrations, which, as we know, lower carbon dioxide 
production, we may be subject to the criticism that the 
lowering of metabolism may be due partly to death or 
injury. It is therefore essential that we should investi- 
gate the effect of various concentrations, from such as 
have apparently no narcotic effect to those from which ' 
recovery is doubtful or absent. Thus the use of suitable 
narcotics as well as concentrations seems to be of prime 
importance. For even those who consider that narcosis 
is not due to an asphyxiation admit that the oxygen 
consumption is greatly depressed if the narcosis is pushed 
too far, although such depression in the rate of oxidation 
may have nothing to do with the cause of the narcosis. 
With a view to studying the effect of various con- 
centrations of anesthetics, the claw nerve of a crab was 
isolated, its excitability tested by electrical stimulation, 
and, without being cut off from the claw, it was immersed 
