GRAIN CONSERVATION 119 



markedly accelerated. Increasing temperature also 

 causes increase in the rate of "respiration" until 

 55 C. (131 F.) is reached. Accumulation of carbon 

 dioxide decreases the rate of " respiration." " Ee- 

 spiration " is also reduced in an oxygen-free atmo- 

 sphere, the ratio to that occurring in a normal 

 atmosphere being about 1-2-5. I need not remind 

 you that the rise of temperature or heating of the 

 grain depends upon the rate of " respiration," or, 

 as I should prefer to put it, upon the rate at which 

 destructive metabolism takes place. 



Their knowledge of the physiology of the organ- 

 isms concerned, imperfect though it still is, has 

 enabled scientific experts to suggest various ways of 

 combating the diseases to which stored grain is 

 subject. Insect-infested grain can at least tem- 

 porarily be cured by fumigation with poisonous 

 gases of various kinds, such as carbon disulphide, 

 hydrocyanic acid, and carbon dioxide. A better 

 and safer method, now much used in America, 

 depends upon the extraordinary susceptibility of 

 grain insects to changes of temperature. Professor 

 Chittenden pointed out more than twenty years ago 

 that a temperature of from 125 to 140 F., continued 

 for a few hours, is fatal to grain insects, while wheat 

 can be subjected to a temperature of even 150 or 

 more for a short time without destroying its germi- 

 nating power. The heat may be applied by means 

 of steam pipes, whereby the whole of the building 



