252 



THE HAEMOFLAGELLATES 



in various unaccustomed animals, for which they are more or less 

 lethal. The important immunisation experiments first carried out 

 by Laveran and Mesnil, and since then by other workers, have 

 shown, however, that several of the parasites causing the different 

 trypanosomoses now known are distinct species. 



A full description of all the known forms and tlieir characteristics is 

 impossible within the limits of this article. It must suffice to mention 

 some of the more important and better-known parasites, arranged under 

 the different classes of Vetebrate hosts ; for fuller details regarding them, 

 reference should be made to the writer's previous account, or to Nabarro's 

 revised edition of Laveran and Mesnil's treatise, which is most useful in 



A. 



B. 



C. 



FIG. 33. 

 A and B, T. theileri; C-E, T. "transwalien*:." x 1250. (After L. and M.) 



this connection. A list of known hosts and their Trypanosomes is given 

 at the end of this chapter. 



(a) Parasitic in Mammals. Trypanosoma lewisi, Kent, the common 

 natural parasite of rats (Figs. 7, A ; 20, A). Length * 24-25 p., breadth 

 l|-2 p.. This species is characterised by its narrow and pointed aflagellar 

 extremity, and by the position of the trophonucleus in the flagellar half 

 or third of the body. The cytoplasm is usually free from granules. T. 

 Irudi, Plitnmer and Bradford. Length 28-30 p., breadth 2-2| //. The 

 anterior end is usually bluntly rounded (Figs. 7, B ; 17, A). The cytoplasm 

 often contains granules in the posterior half. Natural hosts probably 

 various Antilopidae (e.g. gnu, " koodoo," etc.), and buffaloes. The cause of 

 Nagana or Tsetse-fly disease in cattle, horses, etc., in South Africa. T. 

 gambiense, Button (Syn. T. ngandense, Castell). Length 21-23 fj., breadth 

 1^-2 /JL. This species (Fig. 32, A), according to its average size, is one of 

 the smallest known. The cause of human trypanosomosis in West and 



1 The dimensions given are intended to indicate the average size of the parasite in 

 each case, but can only be considered as approximate. The length is inclusive of the 

 flagellum, unless otherwise stated. 



