The Development of Trypanosomes in Tsetse Flies. 369 



The method of carrying out these experiments was always the same. The 

 flies were fed for some days on a highly infected monkey, whose blood on 

 microscopical examination was seen to contain numerous trypanosomes of 

 Sleeping Sickness, and afterwards on a series of healthy monkeys. 



The following table gives the number of flies used in each experiment, the 

 number of days they were fed on a monkey whose blood contained Trypano- 

 soma gamhiense, the number of days which elapsed before the flies became 

 infective, and the number of days the flies remained infective. The minus 

 signs signify that the flies failed to become infected, or at least failed to 

 infect ; or, in other words, that the experiment was negative. 



Table I. — Development of Trypanosoma gamhiense in Lake-shore Glossina 



palpalis. 



Experiment. 



No. of flies. 



No. of 

 days fed on. 



No. of days before 

 flies became infective. 



No. of days flies 

 remained infectiTC. 



624 



60 



3 







656 



280 



3 







663 



60 



2 



18 



75 



6Y6 



500 



3 



29 



47 



721 



50 



3 







980 



350 



3 







986 



100 



2 



19 



35 



987 



50 



2 



40 



51 



989 



50 



2 



45 



45 



1020 



100 



3 







1023 



50 



3 



37 



51 



1026 



70 



3 



34 



48 



1198 



20 



40 







1372 



100 



3 







Of these 14 experiments, seven are positive and seven negative. In the 

 positive experiments 880 flies were used, an average of 126; in the 

 negative 960, an average of 137. The shortest time which elapsed before 

 a fly became infective was 18 days, the longest 45 days, and the average 

 32 days. 



It may be well to give some of these experiments more in detail, in order 

 to show the methods used, and draw attention to various interesting points. 



Experiment 624. 



To ascertain if development of Trypanosoma gamhiense takes place in the alimentary 

 canal of Wild or Lake-shore Glossina palpalis. 



March 31, 1909. — Two batches of Glossina palpalis, caught on the Lake-shore, consisting 

 of 30 flies in each batch, were fed to-day on a monkey whose blood 

 contained numbers of T rypanosoma gamhiense. 



