EXTERNAL ANATOMY OF PEDICULUS 529 



Mackie, working in India in 1907, showed the close relations between the 

 prevalence of lice and the incidence of the disease, and found spirochaetes 

 in lice taken from infected persons. In the following year Ed. Sergeant 

 and Foley, working in Algeria, succeeded in transmitting the disease to 

 monkeys by the inoculation of the body juices of infected lice. Many 

 other observers have noted and recorded the close relations existing 

 between the presence of a large number of lice and infection by the 

 spirochaete, though until the present year the exact method of trans- 

 mission was not known. Nicolle, Blaizot, and Conseil, however, have 

 recently published a series of observations and experiments, made 

 during the course of an epidemic in Tunis, which go far to clear up the 

 question. They confirmed the close association of lice and the disease, 

 but failed after a large number of experiments to transmit it either to 

 man or to monkeys by means of the bite of the insect ; they found, 

 however, that the spirochaetes were not present in the alimentary 

 tract of the louse, but were confined to the body cavity. By rubbing 

 the debris from pounded lice into an abrasion of the skin they were, in 

 two experiments, able to produce the disease in man. They have also 

 produced some evidence which indicates that the offspring of an infected 

 female may be infective. 



Several cases are known in which lice act as the invertebrate hosts of 

 blood parasites of mammals. Haemogregarina gerbilli, from the jumping 

 rat, Gerbillus indicus, was shown by Christophers to pass a part of its 

 life cycle in Haematopiniis stephensi ; the vermicules of H. funambuli 

 were seen in a louse from the Indian palm squirrel by Patton. As 

 regards natural parasites, a Herpetomonas, first seen by Mackie in India, 

 and subsequently described by Fantham in England as H. pediculi, 

 occurs in the alimentary tract of both the body and head lice. It was 

 found by Fantham to occur in circumstances which precluded the 

 possibility of its being a stage in the life history of a vertebrate trypano- 

 some. 



EXTERNAL ANATOMY 



The body of the louse is flattened dorso-ventrally, is roughly oval in 

 shape, and is distinctly divided into three parts, the head, thorax and 

 abdomen. Of these only the abdomen is distinctly divided into 

 segments. 



The head is usually more or less conical and pointed, though great 

 differences are found in the several genera in this respect ; in Phthirus, 

 for instance, it is distinctly four-sided and squat, while in Haematomyzus 

 67 



