i68 'INFINITE TORMENT OF FLIES' 



inoculation of the beasts with a minute parasitic 

 organism conveyed from host to host by the fly. The 

 disease is known as ' nagana/ and the organism that 

 causes it is a species of Trypanosoma, a flagellate 

 Protozoon or unicellular organism, which moves by 

 means of the lashing of a minute, whip-like process. 

 Since Bruce's researches a number of Trypanosomas 

 have been found causing diseases in various parts of 

 the world. Thus T. evansii causes the ' surra ' disease 

 of cattle, horses, and camels in India. T. equinum 

 produces the ' mal de caderas ' of the horse-ranches of 

 South America, and T. equiperdum. is responsible for 

 the North African disease called by the French the 

 ' dourine.' T. theileri causes the gall-sickness, and there 

 are others. These parasites were first seen by Gruby, 

 who named them in 1843, in the bloo(^ of a frog; 

 they live, not as does the malaria parasite, in the 

 blood-cells, but in the fluid of the blood. The par- 

 ticular species of Trypanosoma which causes nagana 

 is Trypanosoma brucei, and it does not attack man, and 

 some goats and donkeys seem also immune ; but, with 

 these exceptions, all domesticated animals suffer, and 

 in a great percentage of cases the disease terminates 

 in death. Just as the native children in Africa form 

 the source of the supply of the malarial parasite with- 

 out appearing to suffer much, so the big game of the 

 country abound in Trypanosoma without appearing to 

 be any the worse. They are, in Lankester's phrase, 

 ' tolerant ' of the parasite, and a harmony between 

 them and the parasite has been established, so that 

 both live together without hurting one another. 

 Under a more natural condition of things than at 

 present obtains in South Africa, the big game formed 

 the natural prey of the tsetse; and, indeed, so 

 dependent is the fly on the antelopes, etc., that, in 

 places where the game has Ibeen exterminated, the fly 

 has also disappeared. It is from the big game that 



