60 



Sir D. Bruce and others. Trypanosome 



It will be noted that there is a great difference between the two positive 

 experiments as regards the time required for the flies to become infective. 

 In the first 50 days elapsed, in the second only 20. This is due to different 

 temperatures under which the experiments were carried out. The first 

 positive experiment was done during the coldest time of the year on Kasu 

 Hill, when the mean temperature was 62° F. (16-6° C), which is much lower 

 than on the plains, the natural habitat of G. morsitcms. The flies in the 

 other experiment were kept in an incubator at a temperature of 83° F. 

 (28 - 3° C), and they became infective much sooner. 



Details of the Two Positive Experiments. 



The following table gives the principal details of the first positive experi- 

 ment : — 



Experiment 754. 



Table II. 



Day of 

 expt. 



Procedure. 



Remarks. 



1-3 

 4 

 5-60 



Flies fed on T. .s£mt'«-infected monkey. 

 Starved. 



Fed on clean monkey 



Trypanosomes first appeared on the 

 57th day. 



It is seen that it was not until the flies had been fed on the clean monkey 

 for 57 days that the animal showed trypanosomes in its blood. If we allow 

 seven days for the average incubation period of the parasite in the mammalian 

 host, then the monkey contracted the disease about the 50th day after the 

 infecting fly had fed on trypanosome-infected blood. 



The following table gives the principal details of the second positive 

 experiment : — 



Experiment 1847. 



Table III. 



Day of 

 expt. 



Procedure. 



Remarks. 



1-10 

 11 



12-27 



Flies fed on T. si'mta-infected monkey. 

 Starved. 



Fed on clean monkey. 



Flies became infective on the 26th 

 day after first infected feed ; 

 16 days after the last. 



Since the flies of this experiment were fed on infected blood for a period 

 of 10 days, the time required for the trypanosomes taken up by the " fly " 



