The Vectors of Relapsing Fever 505 



II. LICE 



Lice are apterous insects formerly classed in the order Hemiptera, but now 

 placed in a separate order, the Anoplura. Two genera, and three species are 

 common upon human beings. 



I. Pediculus (Linn, 1758). In this genus there are two species: 



1. Pediculus capitis (de Geer, 1778). This is the head-louse. It is of a 



gray color. The abdomen is composed of eight and not of seven 

 segments as was stated by Piaget, and is blackened along the edges. 

 The males and females look much alike, but the male measures 1.8 mm. 

 in length and 0.7 mm. in breadth, while the female measures 2.7 mm. 

 in length by i mm. in breadth. 



These parasites live in the hair, close to the scalp. Rarely they 

 pass from the scalp to the beard. Still more rarely do they occur 

 upon other hair-covered surfaces. The female produces large eggs, 

 one at a time, which are firmly anchored to the hairs by a mucilaginous 

 secretion. In them the embryo develops in about sixteen to eighteen 

 days then escapes as a nymph with proportionally smaller body and 

 larger legs than the adult. There are three molts before the insect 

 reaches maturity. The full and empty eggs occur in great numbers 

 upon the hairs and are known as "nits." 



The insects are sometimes present on the head in great numbers and 

 cause intolerable itching. 



2. Pediculus vestimenti (Nitzsch, 1818). This is a larger louse of much the 



same appearance and structure as P. capitis. Indeed there are such 

 minute differences between the two that there is some dispute as to 

 whether they should not form subspecies of the same insect instead 

 of different species of insects. 



The size is, however, larger. The male measures 3 mm. in length 

 and i mm. in breadth; the female 3.3 mm. in length and 1.14 in 

 breadth. 



The "body louse" as this is commonly called, lives in the clothing, 



and passes to the skin to feed, then returns again to the seams of the garments. 



Its eggs are fastened to the fabric of the clothing, not to the skin or hairs. It is 



sometimes present in great numbers and its bites cause much annoying itching. 

 Both of these lice have been found to be capable of effecting the transmission 



of the spirochaeta of relapsing fever. The infection in the lice is transmitted to 



its offspring as in the case of Ornithodorus moubata. 



II. Phthirius (Leach, 1815). In this genus there is only one human parasite. 

 Phthirius inguinalis (Ridi, 1668). This pubic louse or "crab louse " is 

 often incorrectly called Pediculus pubis. It is a shorter, stouter- 

 bodied creature with more powerful legs terminating in large tarsal 

 hooks that give it a crab-like appearance. The thorax and abdomen 

 are compressed and shortened to a heart-like body. The abdomen is 

 composed of six segments, each of which has a pair of stigmata, but 

 the stigmata of the first, second, third, fourth, and fifth segments ap- 

 pear to be in one broad segment. The males measure i mm. in length, 

 the females 1.5 mm. These lice live chiefly in the pubic hair and that 

 of the perineum. Rarely they are found in the axilla, the beard, the 

 eye-brows and even upon the eye-lashes. The eggs are fixed to the 

 bases of the hairs as in P. capitis. They hatch in about seven days and 

 the nymphs grow to maturity fifteen days later. 



The bites of these lice are very irritating and cause severe itching and 

 the eruption of pink papules that sometimes become bluish spots 

 nearly a centimeter in diameter. Such spots known as " "taches 

 ombrees" are frequent in typhoid fever when lice are present. 



It is not known that this louse can harbor spirochseta or any patho- 

 genic bacteria or protozoa. 



