2 



1 "* <""V 



> 'flie celebrated discoveries of Surgeon-Major (now Major-General 

 Sir David) Bruce in Zululand, in 1895-96, resulted in the dissemination 

 of these two diseases by Tsetse-flies being placed beyond doubt. Since 

 the present work is limited to a study of the insects themselves, we 

 cannot here enter into a detailed description of the mechanism of the 

 transmission of trypanosomes by Tsetse-flies. Suffice it to say that 

 the trypanosome that is the cause of nagana exists in the blood of 

 many species of African big game, without apparently doing these 

 animals much harm, and that when a Tsetse-fly bites one of these 

 creatures it sucks up the micro-organisms in question with the blood. 

 The trypanosomes then undergo a developmental cycle in the body of 

 the insect, and when, after the lapse of a certain time, the fly bites a 

 healthy domestic animal, such as a horse, ox, dog, etc., the parasites 

 escape into its blood, multiply there, and set up the disease. In a 

 similar manner the trypanosome of sleeping sickness is transmitted 

 from man to man by certain species of Tsetse-flies. 



The trypanosomes that are conveyed by Tsetse-flies belong to a 

 number of different species. Their study, which belongs to the domain 

 of medical and veterinary science and cannot be touched upon here, 

 is a most complicated subject, to which many observers are devoting 

 their attention. 



Excluding races or varieties, nineteen species of Glossina all confined 

 to the African continent, with the exception of one which also occurs 

 in Arabia (in the Aden Hinterland) are at present known. Some of 

 these species are very widely distributed and very abundant in many 

 countries ; others are more local, and yet others are very rare and 

 but little known. 



These nineteen species of Tsetse, while agreeing in essential characters,, 

 differ in details of structure, habitat and habits, as also, which is more 

 important, in their ability to transmit trypanosomes. 



Until some ten years ago it was believed that Glossina palpalis f 

 Rob.-Desv., and Glossina morsitans, Westw., the two most widely 

 distributed and best known species of their genus, were alone respon- 

 sible, the former for the transmission of sleeping sickness, the latter 

 for that of nagana or Tsetse-fly disease of domestic animals. In reality, 

 however, the matter is much more complicated, since it has been 

 discovered that in Nyasaland and Northern Rhodesia, where G. palpalis. 

 does not occur, G. morsitans transmits a trypanosome known as 

 Trypanosoma rhodesiense, which produces a form of sleeping sickness 

 in man and is very closely allied to T. gambiense, the cause of sleeping 

 sickness in other parts of Africa. Similarly it appears that nagana, 

 or other closely related trypanosomiases of domestic animals, are 

 disseminated by the bites of several kinds of Tsetse-flies, including 

 G. palpalis, so that it may be said that at the present time all the 

 species of Glossina are suspected of conveying trypanosomes. 1 



The study of Tsetse-flies is of the utmost importance to the future 

 of Tropical Africa, and the discovery of effective means of combating 

 these insects, especially G. palpalis and G. morsitans, would render 

 an immense service to its development. 



Within the last twenty years entomological science has made great 

 progress as regards knowledge of the specific characters of the various 



1 On the other hand it is by no means proved that Tsetse-flies are the only 

 insects capable of infecting an animal with trypanosomiasis (see p. 106). 



