Description of a Strain of T. brucei from Zululand. 527 



Three hundred and eight flies were used and 47 infected flies were found — 

 15 - 3 per cent. 



It is difficult or impossible to explain the difference in the ratio of 

 infected flies. Experiment 1857 has only one infected fly in 58; Experi- 

 ment 1988, 20 in 45. There is no record as to whether Cage 1857 was kept 

 in the incubator or not, but it is to be presumed that it was, as was the 

 habit at that date. From Table III it will be seen that the flies in 

 Experiment 1988 were feci for eight days on an infected dog, monkey, and 

 goat. It is possible that this had something to do with the high rate of 

 infection, but it is impossible to say with certainty. The scarcity of 

 laboratory-bred flies made it out of the question to pursue this line of 

 inquiry. Experiment 2188 has also only one infected fly in 30, but this is 

 capable of explanation. Experiments 2188 and 2188a were carried out for 

 the sake of economy with the same cage of flies. It having become evident 

 (see Table IV) that the flies after their first feeding on an infected rat had 

 failed to infect Monkey 2203, the 20 remaining flies were again fed on an 

 infected guinea-pig, with the result tbat eight of them became infected. 



Table II.— Wild Flies. 



Date. 



Expt. 



No. of 

 flies 

 used. 



Experiment 

 positive or 

 negative. 



No. of infected 

 flies found. 



No. of days 

 before flies 

 became infective. 



Temperature 

 at which flies 

 kept. 



1913. 

 July 22 

 „ 26 



2309 

 2313 



50 

 50 



+ 

 + 





 5 



34 

 24 



84° P. (29° C.) 

 84° P. (29° O.) 



In Experiment 2309 none of the flies were dissected, hence no infected 

 flies were found. In Experiment 2313, only 21 flies out of 50 were 

 dissected. These experiments are tabulated here as they give the number of 

 days before the flies became infective, and thus afford data as to the length 

 of time the cycle of development runs in the fly. 



Details of the Five Positive Experiments. 



The following table gives the principal details in the carrying out of the 

 five positive experiments. The first three were carried out with laboratory- 

 bred flies, the last two with wild flies. 



It would appear from these five experiments that an average period of 

 21 days 4 elapses before the cycle of development of T. brucei, Zululand, 1913, 

 is complete in G. morsitans and the fly becomes infective. 



2 s 2 



