518 



Sir D. Bruce and others. Trypanosome 



appearance of trypanosomes in the blood of the experimental animal. Seven 

 days is put down as the average number of days between the infection of the- 

 animal and the appearance of the trypanosomes in its blood — the incubation 

 period. It is probably a day or two shorter. 



The number of flies used in each experiment was small, due to the difficulty 

 of obtaining laboratory-bred flies. They were kept during the experiment in 

 the incubator at a temperature of 84° F. (29° C). 



In Experiment 1723 the number of days which elapsed before the flies 

 became infective is only 14. This number is obtained, as mentioned above, 

 by deducting seven days for the incubation period, but this may have been 

 a day or two less. The flies were kept at an evenly warm temperature, which 

 would tend materially to shorten the period of development. Still, 14 days 

 seems a short time to elapse between the first feed on the infected animal 

 and the appearance of an infective fly in the cage. 



Two hundred and eighty-seven laboratory-bred flies were used and 25 

 infected flies were found — 8"7 per cent. 



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. 



1912. 

 Dec. 11 

 „ 13 

 „ 18 



1680 

 1688 

 1705 



80 

 40 

 45 



+ 

 + 

 + 



8 

 6 

 7 



18 



3 

 1 



84° F. (29° C.) 

 84° F. (29° C.) 

 84° F. (29° C.) 



1913. 

 Jan. 9 

 ,» 14 



1748 

 1729 



70 

 20 



+ 

 + 



1 

 1 



25 

 30 



84° F. (29° C.) 

 84° F. (29° C.) 



Experiments 1688 and 1705 are evidently cases of infection by naturally- 

 infected wild flies which had escaped detection. They are included in the 

 table as they both show invasion of the salivary glands and so help to throw 

 light on the mode of development of this trypanosome in G. morsitans. The 

 other three pass through an interval of 18, 25, and 30 days before the cages- 

 became infective. These are probably cases where there was no naturally- 

 infected fly in the cage, and these periods therefore represent the usual length 

 of time required for the cycle of development of this trypanosome to take 

 place in G. morsitans. The wild flies were also kept in the incubator at 

 a temperature of 84° F. 



Two hundred and fifty-five flies were used and 23 infected flies were found 

 — 9 per cent. 



