130 PHYSIOLOGY AND NATIONAL NEEDS 



be brought about in quite a small quantity if 

 precautions be taken to prevent tbe 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.^ 



That the moistened grain, as placed in the 



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

 room temperature, and similar results of a highly satisfactory character 

 were obtained. 



