136 PHYSIOLOGY AND NATIONAL NEEDS 



Much lower percentages of carbon dioxide, how- 

 ever, are sufficient to kill the weevils even in the 

 presence of plenty of oxygen. For example, let 

 me quote one of a series of experiments conducted 

 at 31° C. (88° F.). Ten rice weevils were sealed 

 up in an artificial atmosphere containing 56*42 per 

 cent of nitrogen, 20*36 per cent of oxygen and 

 23*22 per cent of carbon dioxide. The weevils 

 were all motionless in 43 hours. After 91 hours 

 the flask was opened and the gas in it was found to 

 consist of 56*30 per cent of nitrogen, 19*09 per 

 cent of oxygen and 24*61 per cent of carbon dioxide. 

 Hardly any of the oxygen had been used up, but 

 all the weevils were dead beyond the possibility 

 of revival. 



These experiments serve to show that pure carbon 

 dioxide gas is actually less fatal than carbon dioxide 

 with a moderate admixture of oxygen. I think 

 the explanation is probably that in pure carbon 

 dioxide all metabolism is completely suspended, 

 the machinery of life is stopped short, so that the 

 carbon dioxide cannot exercise its lethal effects, 

 while, if there is enough oxygen present to maintain 

 a certain amount of metabolism — though the insects 

 remain apparently lifeless — the poisonous action of 

 the carbon dioxide takes place. 



I fear that I have wearied you too long with the 

 dry details of experimental evidence, and will pass 

 on at once to my concluding remarks. 



