444 FAMILY: TRYPANOSOMID^ 



Though it was long known that the diseases caused by trypanosomes in 

 man and domestic animals in Africa were transmitted by flies belonging 

 to the genus Glossina, the role of these blood-sucking diptera was not 

 properly understood till Kleine (1909, 1909a) proved that a period of about 

 twenty days was required for development of the trypanosome in the fly 

 before the latter was able to bring about infection. Before Kleine's 

 discovery in 1909, the repeated failure to transmit infections by tsetse 

 flies had led observers to hold the view that they acted merely in a 

 mechanical manner in carrying infective blood from one animal to 

 another, with a lapse of a minimal interval of time between the two bites. 



The work of Rabinowitsch and Kempner, Swingle, Noller, the writer, 

 Minchin and Thompson, and others established the role of the flea in 

 transmitting T. lewisi from rat to rat, and proved that a development 

 took place in the flea, leading to the appearance of infective forms of the 

 trypanosome in the flea fseces which were eaten by other rats. 



Brumpt, Robertson, Noller, and others demonstrated the develop- 

 ment of trypanosomes of fish and frogs in leeches, and the part they play 

 in handing on the infection from one animal to another. The work of 

 Chagas, Brumpt, and others has proved the role of Triatoma megista and 

 other reduviid bugs in the transmission of the human trypanosome, Try- 

 panosoina cruzi, of South America, while, finally, the observations of 

 Noller, Kleine, and Hoare have proved the transmission of T. melophagium 

 of sheep by the sheep ked {Melophagus ovinus). 



METHODS OF DISTINGUISHING TRYPANOSOMES. 



The number of trypanosomes which have been named is very great, 

 and the list is constantly being extended. It becomes of importance, 

 therefore, to be able to distinguish one from another, and it has resulted 

 that, quite apart from morphological details, various methods of separating 

 the species have been devised. In many quarters, the discovery of a 

 trypanosome in a new host has been taken as sufficient ground for the 

 creation of a new species. Though this procedure is not in accordance 

 with the rules of nomenclature, there is something to be said in favour of 

 it. for the trypanosome of a particular host will be referred to by its name 

 till it has been definitely proved to be identical with some other previously 

 named type. This is likely to lead to less confusion in the literature than 

 if workers had to deal with a large number of unnamed trypanosomes, 

 or trypanosomes which had received already existing names because of 

 certain resemblances they might have to these. Scientifically, it is just 

 as incorrect to group together under one name without sufficient evidence 

 what may eventually prove to be distinct species as to give dift'erent 

 names to forms which ultimately may be found identical. 



