52 



The only remaining ectoparasites are lice, Pedioulus oapitis 

 and Pediculus vestimenti. The general bionomics of these 

 insects has been dealt with, and it only remains to point out 

 that their prevalence is not confined to the warmer months, 

 but is greatest during the winter (Hamer, 1910), when clothes 

 are least changed and washed. 



Mackie (1907), in an investigation of an outbreak of 

 relapsing fever in a mission school in India, brought forward 

 some rather striking epidemiological facts pointing to lice 

 rather than bugs as being concerned with the epidemic. He 

 found spirochaetse in 14 per cent, of the lice taken off the 

 boys. They were present in the alimentary canal, ovary, 

 and Malpighian tubes of these insects. From his observations 

 he came to the conclusion that spirochsetae multiplied greatly 

 in the stomach of the insect, reaching their maximum on the 

 third day. Jackie fed lice from the patients upon monkeys, 

 but he failed to transmit the disease. 



In two experiments by Sergent and Foley (1910) relapsing 

 fever followed the infection of the clothing by lice from 

 patients. 



The spirochgetse of relapsing fever infect rats, and 

 Manteufel (1908) made some excellent observations on the 

 capacity of the rat louse (Hsematopinuss) to transmit the 

 disease. He first ascertained by 40 experiments that when 

 free from lice sick and healthy rats could be caged together 

 without the latter contracting the disease, and then repeated 

 the experiments with the addition of lice. Two infected 

 rats were caged together with seven healthy ones. The sick 

 animals were killed by ether at the height of the disease 

 and then put back into the cage in order that the lice upon 

 them might crawl off the cadaver and attach themselves to 

 the living animals. Three of the seven became infected. 

 In another similar experiment with Spiroohceta duttoni one 

 out of eight rats became infected. Manteufel could not find 

 spirochsetEe in the louse outside the alimentary canal, nor in 

 the eggs. 



These experiments were confirmed by Neumann (1909) so 

 that it seems highly probable that relapsing fever is spread 

 by lice as well as by the tick Ornithodoros moubata. 

 Although the former agent may not be nearly so efficient 

 as the latter, it may make up by its greater numbers and 

 persistency. 



The details of transmission by lice are still unknown, but 

 from the habits of these insects to freely discharge the 

 contents of their alimentary canal during feeding, and the 

 readiness with which spirochaetae can penetrate uninjured 

 epithelium, it is not difficult to imagine how this may 

 happen, even supposing the salivary secretion does not 

 contain the infection. 



