EFFECTS OF DIFFERENT GASES 95 



of 15 minutes, proved to be quite ineffective (fig. 54). The 

 action of this gas was so poisonous that restoration of fresh 

 air did not bring about any revival. The plant was subse- 



Fig. 53. — Abolition of excitability under the action 

 of ammonia. 



Fig. 54. — Total abolition of excitability and death of plant 

 under the action of sulphuretted hydrogen. 



quently found to have died under the poisonous effect of 

 this gas. 



Nitrogen Dioxide 



Nitrogen monoxide or laughing-gas has but little effect : 

 there may, however, be a slight excitatory action. Nitrogen 



