512 



Sleeping Sickness 



Yet the disease is infectious, and the transfer of a small quantity 

 of the parasite-containing blood to appropriate experiment animals 

 perfectly reproduces it. 



The present knowledge of the mode of transmission came about 

 through the knowledge of other trypanosome infections that had 

 already been carefully studied and understood. In speaking of 

 nagana, or tsetse-fly disease, Livingstone, as early as 1857, recognized 

 that the flies had to do with it. For years, however, the supposition 

 was that the fly was poisonous and that its venom was responsible for 

 the disease. In 1875 Megnin stated that the tsetse-fly carries a 

 virus, and does not inoculate a poison of its own. In 1879 Drysdale 

 suggested that the fly might be an intermediate host of some blood 

 parasite, or the means of conveying some infectious poison. In 

 1884 Railliet and Nocard, who suspected the same thing, proved 



Fig. 208. — Glossina palpalis. A 

 perfect insect just escaped from the 

 pupa (Brumpt). Showing how the 

 wings close over one another like the 

 blades of a pair of scissors. 



Fig. 209. — Glossina palpalis before 

 and after feeding (Brumpt). 



that inoculations with the proboscis of the tsetse-flies were harmless. 

 The exact connection between the flies and the disease was worked 

 out by Bruce,* who found, first, that flies fed on infected animals, 

 kept in captivity for several days, and afterward placed upon two 

 dogs, did not infect; second, that flies fed on a sick dog, and imme- 

 diately afterward on a healthy dog, conveyed the disease to the 

 latter. The flies were infectious for twelve, twenty-four, and even for 

 forty-eight hours after having fed on the infected animal. It was, 

 therefore, shown that the flies could and did infect, not through 

 something of which they were constantly possessed, but through 

 something taken from the one animal and put into the other; this, of 

 course, proved to be the trypanosome. Further; it was shown that 

 where there were no tsetse-flies, there never was nagana. 



*" Preliminary Report on the Tsetse-fly Disease or Nagana in Zululand, 

 Ubombo, Zululand," Dec, 1895; "Further Report," etc., Ubombo, May 29, 

 1896; London, 1897. 



