44 



A CHEMICAL SIGN OF LIFE 



state of excitability. On the other hand, if this carbon 

 dioxide increment were not correlated with the vitality 

 of the nerve, and if nerve activity did not involve respira- 

 tion, we expected to find that putting the nerve in 

 hydrogen gas would not affect the output on stimulation. 

 For this experiment the claw nerve of a spider crab was 

 used, and stimulation was effected in the usual manner 

 by a tetanizing induced current of the same strength as 

 that which had been used before and found to increase 

 the output in normal nerves. The results are given in 

 Table VI. It will be seen in this table that the pro- 

 duction of carbon dioxide by this nerve was reduced 



TABLE VI 

 COMPARATIVE RATES OF CO* PRODUCTION IN THE NERVE WITH AND WITHOUT OXYGEN 



almost exactly 50 per cent when the nerve was in hydro- 

 gen, as compared with when the nerve was in the air; 

 and still more remarkable is the fact that stimulation in 

 the hydrogen atmosphere produced practically no 

 change in the carbon dioxide output. We interpret this 

 to mean that the excitability of the nerve had been so 

 reduced by the lack of oxygen that this strength of 

 stimulus was unable to cause any excitation in the nerve. 

 We base this conclusion on the known fact that lack of 

 oxygen lowers considerably the irritability of the nerve 



