CHAPTER XXI 



The Life History of Human Lice ^ 

 R. H. Hutchison and W. Dwight Pierce 



Until the outbreak of the great war there had been a great mass of 

 desultory writing upon the three species of human lice, but this was in 

 all languages and few had made any attempt to classify and arrange 

 the knowledge thus obtained. Since the beginning of the war, however, 

 the louse has been a major problem and there have been more titles pub- 

 lished on it than on any other disease-carrying insect. The first compre- 

 hensive work was published by Hase (1915-1916) in a series of papers. 

 These were followed by several excellent monographs by Professor Nut- 

 tall (1917-1918), the second of which gives a complete bibliography of 

 the literature on human lice, a summary of the evidence of disease trans- 

 mission, exclusive of the recent work on trench fever, and extensive 

 biological studies. With the large number of students recently concen- 

 trating on these vermin, we may expect that our literature will be 

 greatly enriched with many more fine contributions. 



The human lice have generally been regarded as belonging to three 

 different species, Pediculus humanus Linnaeus (^capitis DeGeer), P. cor- 

 poris DeGeer {vestimenti Nitzsch) (plate XXI), and Phthirus pubis 

 Linnaeus {imguinalis Redi). Bacot carried out hybridizing experiments 

 with humanus {capitis), and corporis, carrying the offspring to the third 

 generation. It is on the strength of such studies that Nuttall united the 

 two under the name humanus, and for convenience, designated one capitis 

 (head louse), and the other corporis (body louse) as varieties of this 

 species. Other writers are not wholly convinced in regard to the union 

 of the two species and we shall await further studies with interest. 



The true P. humanus, or head louse, is usually confined to the head, 

 mostly about the occiput and ears, but it may spread over the body, 

 establish itself on other hairy parts, and may be confined to the pubic 

 hairs and multiply there. The body louse, P. corporis, lives usually on 

 the body and in the clothing and is very rarely found on the head. 

 The pubic louse, Phthirus pubis, is usually found on the hairs in the 

 pubic region but may occur in other hairy parts of the body. 



^ This. lecture was presented June 17, 1918, and distributed the same day. It has 

 been greatly revised. 



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