348  Infectiwty of Glossina palpalis in Trypanosomiasis. 
after the flies had fed on infected blood, 249 of them were inoculated; the result was 
negative in every case, although 15 of these flies proved, by microscopical examination, to be 
swarming with living Trypanosoma gambiense at the time of inoculation. In 13 experiments, 
14 flies proved, microscopically, to be infected, were inoculated, between the 24th and 53rd days 
after they had fed upon an infected animal, and in five of these a positive result was obtained. 
The following table shows the result of subcutaneous injections of washed 
salivary glands dissected from laboratory-bred flies whose intestines contained 
swarms of 7rypanosoma gambiense :— 
Table III.—Glossina palpalrs (Salivary Glands) and Trypanosoma gambiense. 
| 
| Nis cor da earapies No. of | Incubation 
Date. Expt. No. ae F y flies from which| Result. | period. 
infected feed. ae : 
glands injected. in monkey. 
1910. 
Hae 0 han) a 2376 2 days 3 — 
ee lo ee 2376 See 1 _ 
Ties 2376 6 ,! 2 te 
kee STIS ie on 2376 ie: 3 as 
ee 2394 ee 2 x 
5 5696. ae 2394 es 2 ri || 
Jan; 26 <n 2099 14 ,, 2 _ 
27 SS Sas | 2114 21, 1 = 
Heb 2 ee 2114 Dane 1 a 
3, ae 2148 28, 1 2 
i. ae 2148 30, © 1 ts 
55 piSiee ese PALEY 36 Cs, 4 + 8 days. 
Remarks.—The results of the microscopical examination of the salivary glands show that 
trypanosomes do not appear in the glands until about the 30th day. Out of 12 experiments 
11 were negative, and one was positive. The glands from 19 infected flies were injected 
subcutaneously, between the 2nd and 30th days after the flies had fed upon an infected animal ; 
the results were all negative. In the positive experiment the salivary glands from 4 infected 
flies were injected into a healthy monkey 36 days after the flies had fed on a monkey suffering 
from Sleeping Sickness, with the result that the former animal contracted the disease. 
Conclusions. 
1. Trypanosoma gambiense may retain their virulence, as ascertained by 
direct inoculation. into susceptible animals, for a period of two days after 
they are ingested by Glossina palpalrs. 
2. After the trypanosomes have been within the gut of the fly for two days 
the power of infecting animals with Sleeping Sickness, when inoculated 
subcutaneously, is lost for a period of 22 days. 
3. Trypanosoma gambiense regains the power of infecting by direct 
inoculation after it has been about 24 days within the intestine of the fly. 
4. The number of days, during which the virulence of the trypanosomes 
contained in the fly is lost, roughly coincides with the time that the infected 
fly is incapable of transmitting Sleeping Sickness by biting susceptible animals. 
5. There is some evidence that the salivary glands of the fly are invaded by 
virulent forms of the parasite 36 days after the fly has fed upon infected blood. 
