800 Trypan osome Diseases. 



clusively on their occurrence in certain species of animals and in 

 well-defined localities, further on the variance in their pathogeni- 

 city towards the different species of animals; and also on the 

 fact that animals immunized against one type are still suscepti- 

 ble to others. However these differences are not constant, as it 

 is often possible to increase the virulence of one strain of 

 trypanosomes for otherwise slightly susceptible or apparently 

 immune species of animals by passage-inoculations. Morpho- 

 logically the trypanosomes of surra, nagana, and dourine, as 

 well as of sleeping sickness, correspond absolutely, and those 

 of Mai de Caderas are supposed to be different from them 

 only in that their blepharoblast is smaller, and that they are 

 more difficult to stain. 



Distinctly different types are: the relatively large (50:3.5-4.0/^) 

 Trypanosome Theileri, the even much larger Trypanosome giganteuni 

 some non-flagellated trypanosomes, thus especially the Tr. dimorphon 

 (see p. 837), further the Tr. Lewisi occurring in the blood of rats, which 

 has been most thoroughly studied, and in which the nucleus is not in 

 the center, but in the posterior third of the plasma body. 



Pathogenicity. Artificial transmission to susceptible ani- 

 mals succeeds most readily by subcutaneous, intraperitoneal, 

 or intravenous inoculations, with less certainty by applying 

 blood containing trypanosomes to fresh wounds. After a cer- 

 tain time the parasites appear in the blood in large numbers, 

 when in certain species of animals, especially in dogs, cats and 

 rabbits, fever appears as a usual s;^^nptom, in addition to 

 edematous swellings on different parts of the body, resulting 

 sometimes in the loss of hair, emaciation, sometimes also in- 

 flammation of the cornea and of the eyelids, whereupon the 

 anemic animals emaciate rapidly and succumb. If virulent 

 blood is inoculated into an animal of the same species from 

 which it originated, a severe or mild disease results, which is 

 identical with the original affection, 



Dourine may be produced artificially by applyiug material 

 containing trypanosomes on the uninjured mucous membrane 

 (Vrijburg obtained in one case positive results in a horse with 

 surra material). 



The virulence of the trypanosomes varies in diiferent 

 species of animals, and may be increased for certain species 

 and reduced for others by passage experiments. Generally 

 native animals are less susceptible in infected localities than 

 those brought to such places from non-infected countries. 



Natural infection in the domestic animals, exclusive of 

 dourine in which it occurs by coitus, usually results from the 

 stings of flies, namely, Glossinae, Tabanidae and Stomoxys 

 species, they transmit the trypanosomes mainly in a purely 

 niechanical manner by sucking l)lood from affected animals and 

 inoculating it to healthy individuals. If, however, the trypano- 



