TRYPANOSOMES ALLIED TO T. EVANSI 573 



Bolivia, Paraguay, Argentine). Mules and donkeys also acquire the 

 disease, but in them it is less acute than in horses. Cattle, sheep, and 

 goats, which usually recover, take the disease in a very mild form, trypano- 

 somes only being demonstrable by inoculation of the more susceptible 

 smaller animals. The duration of the disease in horses varies from about 

 one to four or five months. Voges (1901) quotes an instance in which a 

 regiment received 600 horses, of which 500 died of the disease in the 

 course of the succeeding five months. Inoculated to the smaller laboratory 

 animals, an acute infection is produced comparable with those produced 

 by T. evmisi and T. bnicei. 



T. equinmn is remarkable in that it differs from all known pathogenic 

 trypanosomes in the absence of the kinetoplast, or rather the parabasal 

 body, for the axoneme can still be seen to originate in a minute blepharo- 

 plast, as is well illustrated in the figures of detached flagella depicted by 

 Sivori and Lecler (1902). In length it measures from 22 to 24 microns, 

 of which about five comprise the flagellum (Plate V., i, p. 456). Dividing 

 forms may be as much as 30 microns in length. The breadth of the 

 trypanosome is 3 to 4 microns. The nucleus is central, and there is a 

 well-developed membrane. T. equinum, apart from the condition of the 

 kinetoplast, of which the blepharoplast alone is present, closely resembles 

 T. evansi. 



It has been noted that from time to time epidemics occur amongst the 

 capibaras {Hydrochcprus capibara) in districts in which T. equinum is 

 endemic. Migone (1910) studied one of these outbreaks, found trypano- 

 somes resembling T. equinum in the blood, and noted that the animals 

 died with symptoms which he stated resembled those of mal de Caderas. 

 The evidence, though not absolutely conclusive, seems to suggest that 

 these animals may act as a reservoir for the virus, though the fact that 

 they die of the infection does not support this view. The disease is 

 probably transmitted by species of Tabanus and Stomoxys. Sivori and 

 Lecler (1902) claimed to have obtained mechanical transmission by means 

 of S. calcitrans. 



These various South American trypanosomes resemble T. evansi so 

 closely that it seems more reasonable to regard them as races of T. evansi 

 rather than distinct species. In connection with the absence of the 

 parabasal body in T. equinum, it must be remembered that similar forms 

 in other trypanosomes can be produced experimentally by the action of 

 certain drugs (p. 460). 



