INTRODUCTORY 3 



and the modification of their mouth-parts to skin 

 of a certain character and thickness. They are 

 also very sensitive to what has been aptly called 

 the climatic conditions of the skin, that is to say 

 its temperature and humidity. There are three 

 kinds of lice found upon man, the head-louse 

 (Pediculus capitis), the body- or clothes - louse 

 (Pediculus corporis, or Pediculus vestimenti, as 

 it is often called), and the crab-louse (Phthirus 

 pubis). It is with these three and mainly with 

 the second that we shall deal in the following 

 pages, and wherever " louse " or " lice " without 

 the prefix " head-" or " crab-" are mentioned, the 

 body-louse must be understood. 



In reference to the systematic names of the 

 head-louse and body-louse, Linnaeus recognised 

 only one species, which he named Pediculus 

 humanus. His species was split up into P. 

 cor ports and P. capitis. Both Nuttall and Bacot 

 consider that these are merely racial varieties of 

 one species, so that the systematic names are 

 really P. humanus var. corporis and P. humanus 

 var. capitis. 



Before the war the head-louse was the only 

 one with which the average person in this country 

 was at all acquainted. It occurs most frequently 

 on children, and they become infested occasion- 

 ally in even the best-regulated schools. The 

 body-louse was almost, though not entirely, con- 

 fined to the poorer, congested parts of towns and 

 to agricultural districts. In such places it was 



