ENTOMOLOGY

CHAPTER XXIThe Life History of Human Lice 1R. H. Hutchison and W. Dwight PierceUntil the outbreak of the great war there had been a great mass ofdesultory writing upon the three species of human lice, but this was inall languages and few had made any attempt to classify and arrangethe knowledge thus obtained. Since the beginning of the war, however,the louse has been a major problem and there have been more titles publishedon it than on any other disease-carrying insect. The first comprehensivework was published by Hase (1915-1916) in a series of papers.These were followed by several excellent monographs by Professor Nuttall(1917-1918), the second of \vhich gives a complete bibHography ofthe literature on human lice, a summary of the evidence of disease transmission,exclusive of the recent work on trench fever, and extensivebiological studies. With the large number of students recently concentratingon these Yermin, we may expect that our literature will begreatly enriched with many more fine contributions.The human lice have generally been regarded as belonging to threedifferent species, Pediculus humanus Linnaeus (capitis DcGeer), P. corporisDeGeer (vestimenti Nitzsch) (plate XXI), and Plztltirus pubisLinnaeus (inguinalis Redi). Bacot carried out hybridizing experimentswith humanus (capitis), and corporis, carrying the offspring to the thirdgeneration. It is on the strength of su·ch studies that Nuttall united thetwo under the name humanus, and for convenience, designated one capitis(head louse), and the other corporis (body louse) as varieties of thisspecies. Other writers are not wholly convinced in regard to the unionof 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 pubichairs and multiply there. The body louse, P. corporis, lives usually onthe 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 thepubic region but may occur in other hairy parts of the body.1 This lecture was presented June 17, 1918, and distributed the same day. It hasbl'en greatly revised.301