56 Sir D. Bruce and others. Trypanosomes of 



" fly "-bitten goats and only one became infected ; the other nine remained 

 negative although the trypanosome had only been in the goats an average 

 of 23 days. From this it would appear that T. simice loses its virulence 

 for the monkey if exposed to the action of the living goat's blood for even 

 so short a period as 12 or 14 days. 



Action of T. simiae on the Dog. — The dog appears to be immune to this 

 species of trypanosome. Many experiments were made by feeding wild 

 G. morsitans on dogs and by inoculating the blood of infected goats and 

 monkeys. In not a single case did the trypanosomes appear in the blood 

 nor did the dogs appear to be affected in any way. But in two " fly "- 

 feeding experiments (211 and 436), although T. simice did not appear in 

 the blood of the dogs on microscopical examination, yet the injection of 

 their blood into monkeys gave rise to an infection with T. simice, showing 

 that the parasite was present although in numbers too small to be detected 

 by the microscope. It is possible, then, that the dog may act as a 

 reservoir of this disease, but most improbable that it does so to any practical 

 extent. 



Action of T. simise on Rabbits. — The rabbit seems also to be practically 

 immune to this disease. The injection of blood from infected goats, pigs, 

 and monkeys has no effect. But on two occasions after feeding wild 

 G. morsitans on rabbits, T. simice appeared in their blood, in one case 

 (Experiment 1714) in large numbers, in the other (Experiment 1827) 

 only rarely. Both these were examples of mixed infection, the former of 

 T. simice and T. pecorum, the latter of T. simice, T. pecorum, and T. brucei. 

 It was attempted to infect a rabbit by feeding ou it a fly which was known to 

 be infective with pure T. simice, but with no result. 



This susceptibility, or non-susceptibility, of rabbits to T. simice is perhaps 

 not a very important matter, but the experiments go to show that the 

 natural mode of infection of trypanosome diseases by means of the " fly " is 

 probably the most effective. 



Action of T. simiae on Guinea-pigs and Rats. — Both these species of 

 animals appear to be refractory. 



