82 A CHEMICAL SIGN OF LIFE 



While there seems, then, to exist a very close corre- 

 lation between the rate of respiration of resting nerves 

 and the velocity with which they conduct a nerve 

 impulse, the data for the establishment of this generaliza- 

 tion must necessarily be cumulative, and we are not yet 

 able to state positively that all nerves which give off 

 much carbon dioxide in the resting state will be found 

 to conduct the impulse more rapidly than those which 

 give off less. There are, however, several conditions 

 which influence the rate of the nerve impulse, and we 

 have investigated the effect of these conditions on the 

 production of carbon dioxide. Two of these con- 

 ditions are: changes in the salts in the nerves, and 

 temperature. 



a) Changes in salts: Mayer found that the rate of 

 nervous conduction in the sub-umbrella regions of the 

 subtropical jelly fish, Medusa cassiopea, increases about 

 5 per cent in sea-water diluted with distilled water in the 

 proportion of 9:1, while it decreases 50 per cent in sea- 

 water diluted to 50 per cent with fresh water. By sub- 

 stituting 0.9 M dextrose for the distilled water he 

 demonstrated that the change in rate of the impulse in 

 diluted sea-water was not due to the decrease of osmotic 

 pressure, but was due to the change in concentration of 

 the salt. If under those conditions which decrease 

 the rate of the conduction a measurement is made of the 

 amount of carbon dioxide produced from the thin layer 

 of the regenerating ectoderm tissue, it is found that a 

 change in the rate of carbon dioxide production goes 

 parallel with the decrease in the rate of conduction. As 

 a result of using the regenerating tissue just mentioned, 

 the nervous tissue regenerates before the muscular, so 



