70 LICE AND THEIR MENACE TO MAN 



and vice versa. This is evidence of their close 

 relationship. 



The curious scientist is able to distinguish 

 between them by breeding them in pill -boxes 

 under control, and for the rest it is sufficient to 

 know their distribution on man and to name 

 them one or the other according to their obvious 

 habits. If the lice are found on the garments, 

 and not, or only a few, on the body hair, they are 

 body-lice. If they are in the hair of the head 

 or in that of the body, with none, or very few, on 

 the clothing, they are head-lice. Any on the 

 body hair should, of course, be first distinguished 

 from crab-lice, and this is easily done by the 

 shape. Thirdly, if the lice are numerous on both 

 the clothing and the hair, an infestation by 

 both races is indicated. As with the lice, so with 

 the eggs : if these are few on the body hair and 

 numerous on the clothing they are probably 

 those of the body -louse. If they are numerous 

 on the body hair they are almost certainly those 

 of the head-louse. Nuttall (2) showed that under 

 artificial conditions, if both hair and cloth are 

 available, the head-louse relatively infrequently 

 lays on the cloth, while the body-louse seems to 

 have little preference for one or the other. 



Under normal conditions, far and away the 

 most common site in which the head-louse is 

 found is the head. Children are the most fre- 

 quent sufferers, and, after these, old people. 

 These are the two classes of the community who 



