576 FAMILY: TRYPANOSOMID^ 



infection in horses. Recovery may take place in about a year, or death 

 occurs before this. With virulent strains rats and mice survive from one 

 to three weeks. Guinea-pigs succumb in one to three months. Other 

 animals which have been inoculated generally recover. 



Watson (1920) states that the Canadian strain of T. equiperdum was 

 transmitted to a white mouse after hundreds of unsuccessful attempts 

 with dogs, rabbits, guinea-pigs, rats, and mice. When once established 

 in mice, the trypanosome was readily inoculable to the other animals. 

 Furthermore, after passing through the horse again for several successive 

 passages, it was readily recoverable by inoculation of laboratory animals. 

 Thus its power of infecting laboratory animals was not lost after return to 

 the original host. In the first instance, when the first successful inoculation 

 of a mouse occurred, this animal was the eighty-fourth of a series of rats 

 and mice which had been inoculated during a period of four weeks with 

 fluid rich in trypanosomes which had been collected from the plaques 

 appearing on an infected mare. The remaining eighty-three animals did 

 not become infected. This change in virulence after passage through an 

 animal is perhaps comparable with Bruce's (1914) observation that T. con- 

 golense (T. pecormn) lost its virulence for laboratory rats after passage 

 through the goat (see p. 552). The strain isolated by Watson in mice 

 after many failures behaved in mice and in horses like T. evansi. Though 

 it was actually isolated in the first place from the serum from the oedema- 

 tous swellings, it is just conceivable that the trypanosome which infected 

 the mice was not T. equiperdum, but T. evansi, a trypanosome, however, 

 which is not known to occur in Canada. In any case, the change in 

 character of the trypanosome after passage through mice raises the 

 question of relationship of these two forms. 



Morphology. — T. equiperdum is a trypanosome of the T. evansi type 

 (Plate v., c, p. -ISO). There is always a fiagellum, and the trypanosome 

 varies in length from 25 to 28 microns. Blacklock and Yorke (1913) 

 examined three strains of the trypanosome obtained from various European 

 laboratories. Two of the strains correspond with T. equiperdum, but one 

 was polymorphic in nature and resembled T. brucei. It was concluded 

 that this form was a different type of dourine-producing trypanosome, 

 and it was named T. equi. The strain was said to have originally :come 

 from Algeria, in which country dourine is known to be due to T. equiperdum 

 of the normal type. In the case of a trypanosome so far removed from its 

 original host, quite apart from the possibility of changes in morphology, 

 accidents of interchange with other laboratory trypanosomes may have 

 occurred, a fallacy which certainly cannot be excluded. 



Transmission. — As already remarked, dourine is spread from animal 

 to animal by the direct contact of mucous surfaces. That the disease may 



