158 



Dr. H. L. Duke. 



[Feb. 26, 



places where fly abound. In the immediate vicinity of the fly ground the 

 thick forest absolutely precludes shooting. The results obtained on Damba 

 by Hammerton and Bateman in 1910, and again by Carpenter in May, 1911, 

 showing that the flies on this uninhabited island are apparently maintaining 

 their infectivity undiminished, suggested the scene for the experiments. The 

 only species of antelope found upon the islands of Lake Victoria Nyanza is 

 the Situtunga (Tragelaphus spekei). Since the removal of the natives from 

 Damba, these animals have increased greatly in numbers, and at present 

 their tracks may be seen at almost any suitable point on the shore of the 

 island. As will be seen below, events justified the experiment and revealed 

 the parallel in nature to the infections induced in the laboratory. 



These investigations include, in addition to antelope, all other available 

 vertebrates whose habits bring them into contact with the fly. In every case 

 where possible the citrated .blood was injected into a monkey and a goat and 

 smears prepared. On rare occasions fresh preparations were examined. 

 Certain mammalian trypanosomes other than T. gambiense were obtained in 

 the experimental goats, and these are also discussed below. 



The following is a brief summary of the experiments on the infectivity of 

 the wild flies for T. gambiense, carried out during the period April, 1911, to 

 January, 1912, covered by the paper: — 



Table I. 



Date. 



Experiment. 



No. of flies used. 



Eesult. 



Source of flies. 



1911. 











Apr. 3— May 10 





6144 



+ 



Kibanga. 



May 15—28 



56 



1050 









113 



5385 



+ 





July 31— Aug. 31 



234 



6360 







Sept. 10—22 





3310 





Lwagi Island. 



„ 10—22 



387 



3250 









459 



6150 





Kibanga. 



Dec. 11—27 



563 



3190 



+ 



Remarks. — Four and a half years after the removal of the natives from the Chagwe coast line, 

 and two years after the final clearing of the neighbouring islands, there is a percentage of "014 

 infective flies in a total of 28,279 caught at Buka Point, assuming that there is only one infective 

 fly to each positive experiment. On Lwagi Island, where there are no antelope, it was impossible 

 to obtain a sufficient number of fly to constitute evidence on the subject of T. gambiense. It 

 will, however, be seen below that there are some grounds for believing that the negative results 

 obtained with Lwagi flies are due to the absence of antelope from this island. 



The actual injection experiments will now be considered. Each species of 

 antelope is dealt with in a separate table, the remaining animals being 

 grouped together. A blank space occurring in any column of the tables 

 indicates that there is nothing to record under that heading. 



