TYPHUS FEVER, TRENCH FEVER, ETC, 953 



LICE AND DELOUSING 



The sanitation of typhus fever, of trench fever and of some forms 

 of relapsing fever is so definitely dependent upon processes of louse 

 extermination that a few paragraphs on the habits of lice and the 

 means for their destruction will contain the most important prin- 

 ciples upon which sanitary efforts in the prevention of these diseases 

 must be based. The lice which infest the human body are of two 

 types, the Pediculus humanus which includes the body louse and the 

 head louse, and the Phthyrius pubis, or the pubic or crab louse. It 

 is the first two of these, the body louse and the head louse with which 

 sanitarians are most concerned. 



For an anatomical description of lice we must refer the reader 

 to Nuttall's comprehensive Monograph in the British Journal of 

 Hygiene of 1917, and to textbooks on medical entomology. The 

 following facts, important for the sanitarian, are compiled from 

 various sources. 



The ordinary life of a louse is about four to six weeks. The 

 female louse begins to lay eggs about eight or nine days after 

 hatching. It is stated that such lice, well fed, and in normal en- 

 vironment, will lay altogether about 300 eggs at the rate of ten 

 or so a day. It takes about one week to eight days for these eggs 

 to hatch. On this basis, a single generation of lice takes about 

 sixteen to eighteen days. 



The louse prefers to lay its eggs upon little threads or hairs, 

 more readily upon rougher cloth than upon silk. It was suspected 

 in the early part of the war that silk underclothing gave some 

 protection, but apparently this is not of very much use. The body 

 louse prefers to lay its eggs on the inner surfaces of underclothing 

 and other clothing, preferably along the seams, and on blankets, 

 though most of the louse eggs are probably laid on underclothing. 

 It should not be forgotten that in arranging for disinfestation, the 

 outer clothing, overcoats, blankets, etc., may also be infested. In 

 addition to this, both the head louse and the body louse may lay 

 their eggs on the hairs of the body. The louse, being an habitual 

 parasite on animals and man, prefers to lay its eggs at a temperature 

 little below that of the body, a temperature which is stated as 

 ranging about 30 C. If the temperature is lower than that, it 

 takes them two weeks or more to hatch. According to studies made 

 by British Army sanitarians, they will not hatch below 22 C. and 



