THE WILD FAUNA OP THE EMPIEB 



47 



THE TSETSE PLY AND SLEEPING SICKNESS. 



' Chelsea Gardens, Chelsea Bridge Eoad, London, 

 December 18, 1906. 



' Dear Sir,— My friend Mr. Gillett, F.Z.S., has asked me to 

 Write to you on the subject of the relation of big game in Africa to 

 sleeping sickness and other " tsetse-fly diseases." In discussing 

 this subject, it is necessary first of all to be quite clear about the 

 facts, and at the risk of giving you information about things you 

 know already, I will begin by setting forth as briefly as possible 

 the principal facts known about these diseases. 



' Sleeping sickness and similar maladies are caused by the 

 presence in the blood, or other body-fluids of the affected subject,, 

 of a minute organism with very definite peculiarities, belonging to 

 the genus of protozoa termed by zoologists Trypanosoma. Hence 

 these organisms are commonly called "trypanosomes," and the 

 diseases which they cause " trypanosomiasis." Many species of 

 trypanosomes are known, parasitic on vertebrate animals of all 

 kinds, from fish to man, and the majority of them are quite harm- 

 less to the animals they infest, but there is a group of pathogenic 

 or disease-producing trypanosomes which cause trypanosomiasis 

 of several kinds. In the African continent there are two 

 trypanosomiases of importance : (1) that of cattle and horses, com- 

 monly known as the " nagana " disease ; (2) human trypanosomiasis, 

 which manifests itself as (a) Gambia fever, so called, (b) sleeping 

 sickness. It is probable that (a) is simply the early stage of (b), 

 though it may not get beyond the earlier stage in all cases. These 

 two trypanosomiases ars caused by different species of Trypanosoma; 

 the parasite of nagana is named T. Brncii, after its discoverer, Col. 

 Bruce ; the trypanosome of sleeping sickness is named T. 

 gambiense. 



' These two species are distinguished mainly by their effects. 

 When one injects a given speces of trypanosome, say T. gambiense, 

 into various animals, some, like the monkey or rat, take the infec- 

 tion and are susceptible ; others, like the baboon, do not take it, and 

 are refractory. It is highly probable that man is refractory to 

 i 7 . Brncii of nagana ; the experiment has never been made directly, 

 but it is common for people, in a given region of Africa, to have all 

 their cattle, horses, and dogs killed by it, while no human being 

 has ever been known to contract the disease. And on the other 



