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 



