94 RESEARCHES ON IRRITABILITY OF PLANTS 



much reduced immediately after application ; the power 

 of recovery was also abolished. Subsequent application 

 of stimulus did not result in any sign of response. Even 

 on blowing off the vapour there was no restoration of 



excitability for a very consider- 

 able period. In the present 

 case the period of total insen- 

 sibility lasted for six hours, 

 after which the excitability was 

 slowly restored. 



Ammonia 



The vapour of ammonia is 

 found to cause an abolition of 

 excitability in a very short 

 time. On the introduction of 

 ammonia there is produced an 

 excitatory fall. This may be 

 avoided, however, by introducing this vapour immediately 

 after the excitation induced by the testing stimulus. 

 In the record here given (fig. 53), the first two are the 

 normal responses. Introduction of ammonia is seen to 

 induce an abolition of excitability, three successive stimula- 

 tions, represented by thick dots, at the usual intervals of 

 15 minutes proving to be quite ineffective. On blowing 

 off the vapour the excitability is seen to be very gradually 

 restored. If stronger vapour of ammonia be employed, 

 then the loss of excitability lasts for several hours. 



Fig. 52. — Abolition of excita 

 bility under chloroform. 



Sulphuretted Hydrogen 



The effect of this gas is not merely depressing but 

 extremely toxic. It can be seen from the record that the 

 introduction of this gas caused the period of recovery to be 

 very protracted. The abolition of excitability is evidenced 

 by the fact that successive stimulations at the usual interval 



I 



