PROTOZOA 



397 



British Burma with that described by Evans and named it 

 Trypanosoma Evansi. Tr. Evansi is the cause of a very de- 

 structive disease of animals in Africa, India and Indo-China. 

 The species susceptible to this parasite are the horse and the 

 horse kind, cattle, camels, elephants and dogs. Dogs are espe- 

 cially easily infected with surra by subcutaneous inoculation. 

 Rabbits and guinea pigs are also susceptible. When the latter 

 are inoculated subcutaneously, trypanosomes appear in the 

 blood on the sixth or seventh day. Apart from the enlarge- 

 ment of the spleen, the morbid changes are not well marked. 

 Morphology. Tr. Evansi has an average length of about 

 25 fji and about 1.5 ^ in width. The free 

 flagellum measures about 6 /*. In length 

 it varies from 25 to 30 /x. It reproduces 

 by simple division as the centrosome 

 nucleus and flagellum divide into two 

 parts and finally the protoplasm itself 

 divides. Laveran and Mesnil 3 attempted 

 to cultivate the organism after Novy's 

 method but succeeded only once in six 

 experiments. 



The means by which surra is trans- 

 mitted are not definitely determined. A 

 large horse fly, probably Tabanus, has 

 been thought to be a possible carrier. 

 Deixonne in a letter to Laveran, refer- 

 ring to an outbreak of surra in Mauritius, 



said that it occurred simultaneously with 



the appearance of stomaxys. According 



to Schat, Stomaxys calcitrans is chiefly 



concerned in the propagation of surra in 



Java. This fly attacks cattle as well as 



horses. Rogers 4 shows that the horse 



flies in India can convey surra to the dog 



and rabbit. He points out that the latent cases of surra in 



:! Laveran and Mesnil. loc. eft. 



4 Rogers. Brit. Med. Jour., 1904 ii, p. 1454. 



Fig. 86. Trypano- 

 soma Evansi from 

 rat's blood. (After 

 Nocht and Mayer). 



