TRYPANOSOMA 435 



These results have been corroborated by Kempner and Rabinowitsch, 

 Laveran and Mesnil, and by ourselves. 



Trypanosoma Evansi (Steel). 



The next trypanosome of importance studied, and the first of the 

 more pathogenic trypanosomes, is trypanosoma Evansi, Steel. This 

 species was discovered by Evans in 1880 in the blood of horses suf- 

 fering with the disease known as surra, in India. Lingard's important 

 work on this disease in 1893 led, in a way, to all the subsequent work 

 on diseases caused by trypanosomes. In general the descriptions given 

 of the symptomatology of trypanosomiasis in various animals show 

 a great similarity, though there is much variation in individual cases. 

 In a well-established infection the clinical picture- according to Mus- 

 grave and Clegg is as follows : After an incubation period which varies 

 in the same class of animals and in those of different species, as well as 

 with the conditions of infection, and during which the animal remains 

 perfectly well, the first symptom to be noticed is a rise of temperature; 

 and for some days a remittent or intermittent fever may be the only 

 evidence of illness. Later on the animal becomes somewhat stupid; 

 watery, catarrhal discharges from the nose and eyes appear; the hair 

 becomes roughened and falls out in places. Finally the catarrhal dis- 

 charges become more profuse and the secretions more tenacious and 

 even purulent; marked emaciation develops; oedema of the genitals 

 and dependent parts appears ; a staggering gait, particularly of the hind 

 parts, comes on, and is followed by death. There may be various 

 ecchymoses and skin eruptions. Parasites are found in the blood more 

 or less regularly after the appearance of the fever. 



The autopsy generally shows anaemia, an enlarged spleen with hyper- 

 trophied follicles, more or less gelatinous material in the adipose tissue, 

 the liver slightly enlarged, a small amount of serous exudate in serous 

 cavities, oedematous condition, and small hemorrhages in various tissues. 



The duration varies from a few days to many months. The prognosis 

 seems to be influenced to a certain extent by the species of host. It is 

 probably always fatal in horses. Some cattle recover. The cause of 

 death is possibly a toxic substance, though no definite toxin has been 

 isolated. Mechanical disturbances (emboli, etc.) also probably play a 

 part in producing death. The hosts of trypanosoma Evansi are horses, 

 mules, cattle, camels, elephants, buffaloes, and, according to Musgrave 

 and Clegg, rats. After experimental inoculation this trypanosome is 

 infectious for dogs, monkeys, rabbits, guinea-pigs, mice, and cats. 

 Man seems to be immune. It is without doubt transmitted from animal 

 to animal by the bites of insects (flies and fleas). 



Besides the differences in virulence, the trypanosoma Evansi is dif- 

 ferentiated morphologically from the trypanosoma Lewisi by a larger 

 average length (20// to30/^ long and !/> to 2// wide). It differs from 

 the trypanosoma Brucei in having a more pointed posterior end. Many 

 authors, however, consider it identical with the latter species. 



