TRYPANOSOMA EVANSI 569 



intestinal contents of various species of Tahanus (T. orientis, T. tropicus, 

 T. subcallosus) and Stomoxys calcitrans into guinea-pigs at varying 

 intervals after feeding on infected horses. Up to twenty-four hours the 

 animals became infected, but not later. Bouet and Eoubaud (1912a), 

 working with a Sudan strain {T . soiidatiense), effected transmission with 

 S. calcitrans. Mitzmain (1913) conducted very careful experiments in 

 the Philippines with T. striatus, which were bred in the laboratory. In 

 these experiments the trypanosome was transmitted by the method of 

 interrupted feeding, where only a short interval intervened between the 

 two feeds. It was further shown that the contaminated labellum did not 

 appear to be a factor in the conveyance of the trypanosomes, which were 

 present in the gut of the fly up to thirty hours after feeding. Transmis- 

 sion was also effected with S. calcitrans, and in one instance by means of 

 the louse, Hcematopinus tuberculatus. Sergent and Donatien (1922), 

 working with the strain known as T. herberum, again obtained a mechanical 

 transmission with Stomoxys, while Donatien and Lestoquard (1923) 

 observed that dogs which frequented the stables occupied by infected 

 dromedaries became infected through the numerous Stoinoxys which were 

 always present. It will thus be seen that up to the present the only 

 known method of transmission of Trypanosoma evansi in nature is a 

 mechanical one, in which various biting insects inoculate healthy animals 

 within a short time of their having fed on infected ones. It would seem 

 very probable, however, that this is not the whole of the story, and that 

 further research will reveal some form of development in the fly, leading to 

 a permanent infection similar to that which occurs in various species of 

 Glossina in Africa. 



Cross and Patel (1921) in India claim to have transmitted T. evansi 

 from camels to healthy rabbits by means of ticks. A number of ticks 

 (Ornithodonis crossi and 0. laborensis) were fed on camels. Some were 

 allowed to complete their feed, while others were interrupted before this 

 was finished. Those which had not completed their feed were allowed 

 to finish it upon healthy animals from one to twenty minutes later. The 

 others were similarly fed again five to twenty-two days later on healthy 

 animals. In no case did infection result. After forty-six days the result 

 was again negative, but after sixty-seven days forty-two of the ticks, 

 together with two others which had fed on an infected camel twenty-two 

 days before, produced an infection in a healthy rabbit. After a further 

 interval of sixteen days thirty-six ticks were fed on a clean rabbit, and 

 again after eighteen days on another rabbit. Both these animals became 

 infected. It is concluded that ticks can harbour the virus for long periods 

 (67 to 101 days), and then produce outbreaks of surra. Trypanosomes 

 first appeared in the rabbits eight to ten days after the ticks had fed, 



