33& THE SECRET OF A TERRIBLE DISEASE 



occurred were in persons who had the duty of collecting 

 and disinfecting the clothing of the patients when ad- 

 mitted. This seems to exclude the bug as a carrier. The 

 flea is excluded by the fact that in the phosphate mines of 

 Tunis the flea is abundant, and bites both natives and 

 Europeans. Yet when typhus fever broke out among the 

 miners — although all were equally bitten by the fleas no 

 European was infected. The indication^ therefore, was 

 that if any insect is the carrier, it is neither the flea nor the 

 bug, but probably the clothes-louse. Although the smaller 

 monkeys cannot be directly infected with typhus fever 

 from man, it was found that (as with some other infections) 

 the bonnet monkey was susceptible to the infection after 

 it had passed through the chimpanzee. Experiments 

 were, therefore, made with clothes lice taken from a 

 healthy man, and kept for eight hours without food. They 

 were placed on a bonnet monkey which was in full typhus 

 eruption. A day afterwards they were removed to healthy 

 bonnet monkeys with the result that the healthy bonnet 

 monkeys developed typhus fever. There is thus no doubt 

 whatever that typhus fever can be carried in this way from 

 bonnet monkey to bonnet monkey. The whole history 

 of typhus fever fits in with the carriage of the infection in 

 the same way from man to man, and not with the notion 

 of an aerial dispersion of the infection. 



The fact that typhus only exists in very dirty and 

 crowded populations, and that it has disappeared where 

 even a moderate amount of cleanliness as to person and 

 clothing has become general, coincides with the possibility 

 of the body louse as carrier. This little parasite is known 

 to be a wanderer, and is gifted with a very acute sense of 

 smell. An individual placed in the centre of a glass table 

 invariably walked, guided by the scent, towards the 

 observer, at whatever position he placed himself. Sul- 

 phurous acid is a violent repellant of these creatures. Not 



