Transmission 513 



So soon a? African lethargy was shown to be a form of trypano- 

 fomiasis, the question arose, Was it spread by tsetse-flies? Sambon* 

 and Brumptf both suggested it, but it was soon discovered that the 

 geographic distribution of the tsetse-fly, Glossina morsitans, that 

 distributes nagana, does not coincide with the geographic distribu- 

 tion of sleeping sickness. There are, however, different kinds of 

 tsetse-flies, and Bruce and NabarroJ first showed that it was not 

 Glossina morsitans, but a different tsetse-fly, Glossina palpaUs, that 

 is the most important source of the spread of human trypano- 

 somiasis. They submitted a black-faced monkey (Cercopithicus) 

 to the bites of numerous tsetse-flies caught in Entebbe, Uganda, and 

 found trypanosomes in its blood. Bruce, Nabarro, and Greig§ 

 allowed Glossina palpalis to suck the blood of negroes affected with 

 sleeping sickness and afterward to bite five monkeys (Cercopithicus). 

 At the end of about two months trypanosomes appeared in the blood 

 of these monkeys. They also made maps showing the geographic 

 distribution of African lethargy and of Glossina palpalis, which 

 were found perfectly to correspond. 



But thenaturalhistory of sleeping sickness is less simple than these 

 facts make it appear. Elinghorn and Yorke|| observed that in 

 the Luangwa Valley where tsetse-flies (Glossina morsitans) abound, 

 there is much game but few domestic animals. This led them to 

 study the bloods of all the game animals in an attempt to discover 

 how many harbored trypanosomes and what kind they were. The 

 results are interesting, but two are of great importance in the present 

 connection. They discovered that antelopes harbored Trypano- 

 soma rhodesiense, and that it could be transmitted by Glossina 

 morsitans. As Trypanosoma rhodesiense is the more virulent 

 parasite, and as the antelope regularly harbors it and the widely 

 distributed Glossina morsitans distributes it, the likelihood of 

 an early and successful outcome of the campaign against sleeping 

 sickness becomes improbable. 



The flies are found to become infective in from eleven to twenty- 

 five days after consuming infected blood, and to remain so as 

 long as they continue to live. 



Bruce, Hamerton, Bateman and Mackie, the members of the 

 "Royal Society Sleeping-sickness Commission" for 1908-9** have 

 found that under experimental conditions the development of the 

 parasites takes place only in about 5 per cent, of infected flies. 

 The shortest time in which their flies became infective was 18 days, 

 the longest 53 days, the average 34 days. An infected fly was kept 



* III 



"Jour. Trop. Med.," July i, 1903. 

 t "C. R. Soc. de Biol.," Jan. 27, 1903. 



i "Reports of the Sleeping Sickness Commission of the Royal Society," 

 1903, 1, II, II. 



§ Ibid., 1903, No. 4, vni, 3. 

 J „ Brit. Med. Jour.," 1912, n, 1186. 



Bntish Medical Journal," 1910, i, 1312. 

 33 



