572 FAMILY: TRYPANOSOMIDJE 



T. evansi, from which they have been separated by Laveran and others by 

 cross-immunity tests alone. They resemble T. evansi in that tabanid 

 flies are probably responsible for their transmission. It is therefore 

 a reasonable hypothesis to suppose that they are merely races of T. evansi. 

 The results of inoculation and immunity tests are merely indications of a 

 dift'erence in virulence of various strains of the same trypanosome. 



Forms in Central and South America. 



In America, domestic stock is also liable to infection with trypano- 

 somes of the T. evansi type, and it seems probable that these also may be 

 merely races of T. evansi. 



Trypanosoma hippicum Darling, 1910. — This trypanosome, which very 

 closely resembles T. evansi, was first seen by Darling (1910) in mules arriving 

 in Panama from the United States. It produces in equines a disease which 

 is very like surra. It is inoculable into laboratory animals, in which it 

 gives rise to the same types of infection as those caused by T. evansi. 

 Laveran and Mesnil (1912) state that the large forms sometimes seen in 

 T. evansi infections do not occur in the case of T. kippicufn, and that it can 

 be distinguished from the trypanosome of surra by cross-immunity tests. 



T. venezuelense Mesnil, 1910. — This form, which was first seen by 

 Rangel (1905), is very similar to T. hippicion and T. evansi, and causes a 

 disease of equines and dogs in Venezuela. 



Morphologically it is indistinguishable from either, and as no cross- 

 immunity tests had been carried out at that time, Mesnil (1910), who 

 examined a strain sent to Paris, considered it safer to give it a new name 

 provisionally. Leger and Tejera (1920) have recently investigated this 

 trypanosome, and compared it with T. evansi. They claim that it differs 

 from T. evansi in dimensions, in virulence for laboratory animals, and 

 response to various medicaments and blood-sera. Taking these facts 

 into consideration, together with the results of cross-immunity tests, 

 they conclude that T. venezuelense is a distinct species. The comparisons 

 were made, however, with a strain of T. evansi which had long been 

 maintained in laboratory animals. It is very questionable if the slight 

 differences noted justify the retention of T. vetiezuelense as a distinct 

 species. Rangel (1905) stated that the trypanosome occurs naturally 

 in the domestic dog, the wild dog {Canis azare), capibara {Hydrochcerus 

 capibara), and howler monkeys {Mycetes vrsinus and M. seniculus). 



T. equinum Voges, 1901.— Synonyms : T. equina Yoges, 1901; T. elmassiani 

 Liguieres, 1902; Trypanosoon equinum (Liilie, 1906). 



This is a trypanosome which produces a disease of horses known as 

 mal de Caderas. It occurs in various parts of South America (Brazil, 



