Diseases of Domestic Animals in Nyasaland. 61 



to multiply and regain their virulence cannot be accurately estimated. 

 Allowing seven days for the incubation period it cannot be more than 

 20 days. 



When the healthy monkey became infected, in order to separate the 

 infective flies, those remaining alive were divided into three batches. Eacli 

 batch was put into a cage and fed separately on a healthy monkey. The 

 following table gives the details and results of feeding the three batches of 

 flies : — 



Table IV. 



Expt. 



Batch. 



No. of flies. 



No. of days fed. 



Kesult. 



No. of infected flies 

 found. 



1847 



1 



12 



7 





• ' 0' '' 



1847 



2 



10 



7 



+ 



3 



1847 



3 



13 



7 



+ 



3 



The monkeys on which Batches 2 and 3 were fed showed trypanosomes 

 in their blood on the sixth day after the first application of the flies. It is 

 therefore highly probable that the flies infected the monkeys on the first day 

 of feeding. 



Details of the Six Negative Experiments. 



The following table shows the method of procedure in carrying out the 

 six negative experiments : — 



Table V. 



Expt. 



Day of expt. 



Procedure. 



Remarks. 



502 



1-2 



3-4 

 5-42 



Fed on infected monkey. 

 Starved. 



Fed on clean monkey. 



All flies negative on dissection. 



1477 



1-3 

 4-5 

 6-45 



Fed on infected goat. 

 Starved. 



Fed on clean monkey. 



One infected fly found on the 

 40tli day; proboscis and gut 

 infected. 



1582 



1st 

 2nd 

 3-30 



Fed on infected pig. 

 Starved. 



Fed on clean monkey. 



All flies negative on dissection. 



1602 



1st 



2nd 



3-35 



Fed on infected pig. 

 Starved. 



Fed on clean monkey. 



All flies negative on dissection. 



1622 



1st 



2nd 



3-29 



Fed on infected jjig. 

 Starved. 



Fed on clean monkey. 



All flies negative on dissection. 



1856 



1-7 

 8-26 



Fed on infected monkey. 

 Fed on clean monkey. 



All flies negative on dissection. 



