410 Col. Sir D. Bruce and others. Hie Development of [July 5, 



Remarks on the Experiment. 



Everyone will agree that this is a most interesting experiment. It is 

 evident that a single infected fly did all the mischief, and by good luck this 

 fly was detected. Captain A. E. Hamerton, D.S.O., had charge of the 

 experiment at first, and on his leaving Mpumu about the beginning of May, 

 it fell to Sergeant A. Gibbons, Koyal Army Medical Corps. Both are 

 to be congratulated on the results, which are the outcome of care and 

 thoroughness. Captain F. P. Mackie had the good fortune to dissect the fly 

 which did the injury, and which will be fully described later. 



Incubation Period. 



From the experiment may be drawn the incubation period in monkeys 

 bitten by a late-infected fly. 



It is remarkable how regular this is in those monkeys which gave a 

 positive result. This shows how very infective Fly 866 was. Apparently 

 each time it bit it infected. 



The following table gives the period of incubation in each case : — 



Table III. 









Trypanosomes 



Number of days 



Date. 



Experiment. 



Flies first fed. 



appeared in 



before trypanosomes 







blood. 



appeared, in blood. 



1909. 





1909. 



1909. 





March 19 



652 



March 19 



March 30 



11 



„ 24 



653 



„ 24 



April 2 



9 



„ 29 

 April 3 



654 



„ 29 



„ 6 



8 



655 



April 3 



„ 13 



10 



„ 8 



672 



„ 8 



„ 15 



7 



„ 13 



722 



„ 13 



„ 20 



7 



„ 18 



727 



„ 18 



„ 24 



6 



„ 28 

 May 5 



735 



„ 28 



May 5 



7 



749 



May 5 



„ 11 



6 



„ 12 



765 



„ 12 



. » 17 



5 



Leaving out the first experiment, 652, as it is doubtful as to the exact day 

 Fly 866 became infective, this gives an average incubation period of seven 

 days. It would therefore appear that Fly 866 probably infected each 

 animal on the first day it bit it, showing how dangerous such an infected 

 fly is. 



