560 Sleeping Sickness 



and those in the country less than a year frequently died of it, 

 there was no spread of the affection to those that were ac- 

 climated. The Europeans that carried the disease from 

 Africa to England and were the first in whose bloods the 

 trypanosomes were found, did not spread it among their fel- 

 low countrymen. A case from the Congo that died in a 

 hospital in Philadelphia and came to autopsy at my hands, 

 did not spread the disease in this city. 



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 sug- 

 gested 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 that inoculations with the proboscis of 

 the tsetse-flies were harmless. The exact connection be- 

 tween 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 immediately afterward on a healthy dog, conveyed the 

 disease to the latter. The flies were infectious for twelve, 

 twenty-four, and even 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. 



So soon as African lethargy was shown to be a form of 

 trypanosomiasis, the question arose, Was it spread by tsetse- 



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

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

 Ubombo, May 29, 1896; London, 1897. 



