60 LICE AND THEIR MENACE TO MAN 



temperature throughout the mass of clothing is 

 more quickly attained. 



Treatment by Chemicals and Greases. 

 Chemicals may be used in relation to lice in two 

 ways : to destroy the lice and nits on clothing 

 and hair, or to repel them and prevent them from 

 establishing themselves. The latter expedient 

 would of course never be used by the person 

 going about in ordinary civil life, as all are dis- 

 agreeable, but may be found of use to those, such 

 as sanitary inspectors and district nurses, who 

 are particularly liable owing to their vocations 

 to come in contact with lousy people. For the 

 poisoning of lice the type of substance most 

 commonly used is either an oil or a grease, with 

 or without some other active ingredient. Any 

 greasy substance which kills lice may be regarded 

 in a way as a repellant, in that it would destroy 

 any louse which obtained access before it could 

 establish a colony, though it might be able to feed 

 first. Strongly smelling oils such as eucalyptus, 

 certain coal-tar products such as naphthalene 

 and carbolic acid, and some creosoty wood oils 

 such as birch tar oil, are all to some extent repel- 

 lant in their action on lice. As Bacot (3) showed, 

 they exert only an effect over quite a small radius, 

 and for this reason the wearing of a belt impreg- 

 nated with such substances, or one or more small 

 bags of them slung in different positions about 

 the body, cannot be expected to be of much use, 

 as their action would be only local and lice could 



