558 Dr. H. L. Duke. Some Observations on [Aug. 16, 



on the part of the flagellates in reaching the proboscis became evident during 

 the dissection of the earlier experiments and led to the carrying on of the 

 later boxes for a considerably longer period. In spite of this, however, 

 although four flies were obtained showing a good infection of the proboscis, 

 none of these proved capable of transmitting the trypanosome to a healthy 

 monkey. The only successful transmission, as has been pointed out above, 

 was apparently caused by Fly 9, which showed a swarming infection of the 

 sucking stomach and its duct. This inability on the part of the proboscis- 

 infected flies to infect a monkey is remarkable. On several occasions the 

 flies were starved for short periods and then again fed upon the monkey ; also 

 with negative results. 



In the case of Fly 9, supposing it to be the infecting agent, two possibilities 

 must be considered. Either the flagellates of the sucking stomach were 

 responsible for the infection, or the proboscis may have shown a temporary 

 infection which at the time of dissection had disappeared. 



From the above experiments it will be seen that Bushbuck 55 was still 

 capable of infecting laboratory-bred G. palpalis some three months after its 

 original infection with T. pecorum. 



The following experiments were carried out 10 months after the original 

 infection of the bushbuck. 



Date. 



Expt. No. 



Quantity of blood. 



Eesult. 



Animal used for 



Pure. 



Citrated. 



injection. 



21.3.12 



670 

 678 

 688 



c.c. 

 2* 

 6 



3£ 







Monkey. 



Calf! 



23.3.12 



3.4.12 





+ 



In considering the positive result of Experiment 688 the following facts 

 may be quoted as excluding any source of error : — 



(1) Since my arrival in Mpumu in September, 1910, there has been no 

 case of spontaneous infection with this trypanosome among the laboratory 

 cattle. 



(2) The cattle in the neighbourhood of the hill are apparently free from 

 the disease. 



(3) A calf of about the same age as Experiment 688 (both were born at the 

 laboratory) has been under daily blood examination from the beginning of 

 April until the date of writing, and has never developed trypanosomes. These 

 two animals have never been allowed to leave the hill top, and have always 

 been stalled together. 



