181 



The Morphology of Trypanosoma evansi (Steel). 

 By Colonel Sir David Bbuce, C.B., FJi.S., Army Medical Service. 



(Received May 19,— Eead June 1, 1911.) 

 [Plate 5.] 

 LnTEODUCTION. 



In previous papers published in the ' Proceedings,' the morphology of 

 various trypanosomes, such as Trypanosoma pecorum, vivax, uniforrne, nanum, 

 and hrucei, has been described somewhat more fully than is usually done. It 

 is proposed to do the same for Trypanosoma, evansi in this paper. 



This trypanosome causes the disease in elephants, camels, horses, cattle, 

 and dogs, known in India as Surra. It was discovered in 1880, by Evans, in 

 the Punjab. 



A. Living, Unstained.. 



Trypanosoma, evansi is described by Laveran and Mesnil as being more 

 motile than Trypanosoma hrucei, and as sometimes travelling out of the 

 field of the microscope, which is rarely the case with Trypanosoma hrtccei. 



B. Fixed and, Stained. 



The blood films were fixed, stained, and measured as previously described 

 in the 1 Proceedings.'* 



Length. — The following table gives the length of this species as found in 

 the elephant, camel, horse, dog, guinea-pig, and rat. 



It will be seen from the following table that Trypanosoma evansi varies in 

 length between 18 and 34 microns, the average of 820 individuals being 24 - 9. 

 It is true that short, stumpy individuals, without free flagellum, are some- 

 times found, but very few of these rare specimens were met with in the 

 820 trypanosomes taken as they came for the purposes of the table. These 

 short and stumpy forms are so few and far between that this species may be 

 described as monomorphic, whereas Trypanosoma Irucei, which has about 

 40 per cent, of these short, stumpy forms, may be called dimorphic. 



Breadth. — This lies usually between 1*5 and 2 microns. 



Shape. — Trypanosoma evansi resembles very closely the intermediate forms 

 of Trypanosoma hrucei. The posterior extremity is often triangular in 

 shape, the body gradually narrowing towards the anterior extremity 

 (Plate 5). 



* 'Eoy. Soc. Proc.,' 1909, B, vol. 81, pp. 16 and 17. 



