58 LICE AND THEIR MENACE TO MAN 



reasons given above, be considered the ideal 

 method, among the armies in the field it is not 

 found practicable to use it for the treatment of 

 garments in the winter in Europe, owing to the 

 difficulty of drying them. For this reason hot- 

 air chambers are mainly used now, and an effort 

 is made to raise the temperature in them as high 

 as may be done with safety. One of these is of 

 the form known as the "Russian pit," in which 

 the chamber consists of a large hole dug in the 

 ground in which braziers are placed, the roof 

 being heavily earthed up. Another type con- 

 sists of a chamber of corrugated iron with a 

 double wall and roof which is built over a pit. 

 The braziers are placed in the pit and the hot 

 air passes through holes in the floor up into the 

 chamber. 



The thermometers placed in the chambers 

 record only the highest temperature attained, 

 and not the length of time that the lethal heat 

 has been maintained. Instruments which would 

 do this are too costly and delicate to issue for 

 routine work. There is scope for the ingenious 

 here to invent some simple instrument which 

 would record the necessary data. Bacot has 

 suggested that a piece of paraffin wax of known 

 melting-point and of such a size that it would 

 just entirely melt in the requisite time should be 

 used. Thus if the machine should maintain a 

 temperature of 60 C. for twenty minutes the 

 melting-point of the wax would be 60 C. and a 



