CHAPTER II 



THE STRUCTURE OF THE BODY-LOUSE 



THE louse is an elongated oval creature, varying 

 in colour from white to brown, while the red or 

 black colour of the blood in the gut can be seen 

 through the skin. When young and newly fed 

 it appears to be bright red and is then known 

 in the soldier vocabulary as a " red-back." As 

 the blood becomes darker in digestion it is called 

 a " black-back " or " grey-back " and is often 

 thought to be a different kind. The full-grown 

 female louse measures about one-sixth of an 

 inch in length and one-fifteenth of an inch in 

 breadth, while the newly hatched one is about 

 the size of a pin's head, all intermediate stages 

 existing. Its skin is leathery, and it is not very 

 easily crushed, except when quite young or just 

 after it has " cast its skin." It is covered all 

 over with a smooth coat of a substance known 

 as chitin, which corresponds to the dead horny 

 layer of our own skin. It is sparsely covered 

 with fine hairs. In the young stages a fresh 

 layer of chitin grows under the old layer, which 



