The Vectors of Relapsing Fever 531 



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 matur- 

 ity. The full and enipty 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. Pedicidus vestimenti (Nitzsch, i8i8). 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 iheasures 3 mm. in length 

 and I mm. in breadth; tlie 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 Uce have been found to be capable of effecting the transmission 



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



their offspring. 

 II. Phthirius ^each, 1815). In this genus there is only one human parasite. 

 Phthirius inguinaUs (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 

 eyebrows 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 tyhoid fever when lice are present. 



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

 genic bacteria or protozoa. 



