XVIIl] GENERAL ACCOUNT 343 



The name T. dimorphon, therefore, is only applicable to the 

 trypanosome which reached Europe and was described by 

 Laveran and Mesnil. This parasite, as pointed out by the 

 authors, differs considerably from Button and Todd's description 

 of the " Horse trypanosome," especially in the absence of any 

 forms provided with a free flagellum. T. dimorphon Laveran and 

 Mesnil, is the ordinary dimorphon of the laboratories of Europe, 

 and it is important that the use of this name should be abso- 

 lutely restricted to trypanosomes agreeing with Laveran and 

 MesmTs original description (1904). Montgomery and King- 

 horn wish to reserve the name T. dimorphon for the forms 

 described by Button and Todd and apply the term T. confusum 

 to the parasite described by Laveran and Mesnil. Such a 

 course, however, is illegitimate, for the name dimorphon was 

 only applied to the latter, and never to Button and Todd's 

 original description. 



The occurrence of mixed infections in many animals is a 

 source of great difficulty in identifying the species of trypano- 

 somes, for Yorke and Blacklock have shewn that dimorphon 

 and cazalboui may occur side by side in horses from the 

 Gambia. 



T. dimorphon is widely distributed throughout West Africa 

 and has been recorded from the following localities : Gambia, 

 Senegal, Casamance, Upper Gambia, French Guinea, Sierra 

 Leone, Ivory Coast, Togoland, Bahomey, French Sudan and 

 French Congo. In the Congo Free State, Rhodesia, Zululand, 

 Portuguese East Africa, Zanzibar, Bahr el Ghazal, and Somali- 

 land, trypanosomes of the dimorphon type have been observed, 

 but it is difficult to say whether they should all be referred to 

 T. dimorphon Laveran and Mesnil. 



Horses, mules, cattle, goats, sheep, pigs, dogs, cats, mon- 

 keys, and all the smaller laboratory animals are susceptible to 

 infection with T. dimorphon. As a rule, in the larger animals, 

 the course of the disease is slow, and death only occurs after 

 trypanosomes have been present in the blood for several months. 

 In some cases the animals recover and trypanosomes may be 

 present in the peripheral circulation for some years, without 

 apparently producing any pathogenic symptoms. 



