EFFECTS OF DIFFERENT GASES 91 



in the growing amplitude of successive responses till a limit 

 was reached. 



Carbonic-acid Gas 



The effect of undiluted carbonic-acid gas is a depression 

 of excitability. This is seen in the present record (fig. 47), 

 where on the application of this gas the amplitudes of suc- 

 cessive responses are seen to undergo a decline. Another 

 noticeable fact is the incompleteness of recovery after each 



Fig. 48. — Effect of vapour of alcohol ; note alternating 

 character of response after application. 



excitation. The plant-chamber was next refilled with 

 fresh air, and we observe the restoration of normal 

 excitability. 



Vapour of Alcohol 



The immediate effect of dilute vapour of alcohol is 

 sometimes a transient enhancement of excitability. But 

 continued action of the vapour induces a depression. In 

 the accompanying record (fig. 48) there was little immediate 

 effect ; but after an application of 15 minutes there was 

 induced a depression of response ; another effect also 



