» EXCITATION AND CONDUCTION 83 
that we can in this way eliminate the effect of the salt on 
the muscles. 
b) Temperature: It is well known that a change in 
temperature affects the speed of the nerve impulse; an 
increase of 10° C. increases the velocity of the impulse by 
four-fifths, or even more. This is very significant in 
view of the fact that for most physical processes the same 
increase in temperature increases the velocity of the 
process by at most one-fifth. Chemical processes are 
accelerated about 100 per cent. While the magnitude 
and variation of the temperature coefficient of velocity 
of a physiological process do not necessarily tell us what 
kind of reaction is involved in the process, they never- 
theless indicate in this instance very clearly that con- 
duction by a nerve is not a purely physical process, as 
some have imagined it. It is very important, evi- 
dently, that we should compare the effect of temperature 
on the carbon dioxide output with its effect on speed 
of conduction. 
We have made studies of the metabolic rate of the 
nerve of the king crab at different temperatures, such as 
naturally occur at Woods Hole and at Dry Tortugas, and 
we have discovered that the temperature coefficient of the 
production of carbon dioxide by the resting nerve is 
just about the same as the temperature coefficient of 
the speed of conduction. A similar result was obtained 
with a sciatic nerve of a frog under experimental changes 
of temperature. We thus have this additional point of 
parallelism between the rate of conduction and the pro- 
duction of carbon dioxide in the resting nerve. 
It is extremely interesting and significant that the 
fundamental condition for the conduction of a nerve 
