134 PHYSIOLOGY AND NATIONAL NEEDS 



C0 2 . At the end of that time they were all quite 

 dead and the gas present in the tube was found to 

 contain 17*72 per cent of C0 2 and only 0*18 per cent 

 of oxygen (in a duplicate experiment 17*97 per cent 

 of C0 2 and 0*12 per cent of oxygen). In other 

 words, very nearly all the oxygen present at the 

 commencement of the experiment had been con- 

 sumed and replaced by carbon dioxide. 



The question now arises Is the death of the 

 insects due to some poisonous action of the carbon 

 dioxide or merely to the deprivation of oxygen ? 

 A number of experiments were made with a view 

 to determining this point. In the first place it 

 was found that weevils are soon killed by keeping 

 them in an atmosphere of moist nitrogen, as pure 

 as could be obtained. At the commencement of 

 this experiment the atmosphere consisted of 98*13 

 per cent of nitrogen and 1*87 per cent of oxygen, 

 no carbon dioxide being present. After being sealed 

 up for 46 hours at 31 C. (88 F.) the weevils were all 

 dead and only 0*89 per cent of carbon dioxide 

 had been produced. We may safely conclude in 

 this case that it was the absence of oxygen which 

 killed the weevils. 



On the other hand we have abundant evidence 

 that carbon dioxide, if present in sufficient quantity, 

 does exercise a poisonous effect. In pure moist 

 carbon dioxide rice weevils are rendered completely 

 motionless in three minutes, and it is interesting to 



