130 PHYSIOLOGY AND NATIONAL NEEDS 



be brought about in quite a small quantity if 

 precautions be taken to prevent the heat from 

 escaping. This can easily be effected by using a 

 Dewar flask, or what is popularly known as a 

 thermos flask, in which, as you know, the dissipation 

 of the heat is reduced to a minimum by means of 

 a surrounding vacuum. 



Two such flasks were each filled with the same 

 sample of wheat moistened until it contained 20'7 

 per cent of water. To assist the process of heating, 

 these flasks were kept in a warm incubator, under 

 exactly the same conditions save only that one 

 was hermetically sealed while the other was merely 

 plugged with cotton- wool, so as to allow of the access 

 of air. Each flask was provided with a thermometer, 

 the bulb of which was plunged in the wheat. 



On March 7th twenty-five days from the com- 

 mencement of the experiment, the thermometer 

 in the sealed flask still indicated only 28*1 C. 

 (82*6 F.), just about the temperature of the incuba- 

 tor, while that in the ventilated flask had risen 

 to 49'4 C. (121 F.). In other words, while the 

 wheat in the ventilated flask had heated so as to 

 cause a rise of temperature of no less than 38'4 F., 

 that in the sealed flask had not heated at all or 

 at any rate not to any extent worth noticing here. 1 



That the moistened grain, as placed in the 



1 This experiment has since been repeated, the flasks being kept at 

 room temperature, and similar results of a highly satisfactory character 

 were obtained. 



