I.— PHYSIOLOGY. 169 



Diseases due to protozoa have an especial significance in Africa, and 

 it is appropriate that in this meeting some reference should be made to 

 that area of tropical Africa occupying more than a million square miles 

 in which one form of these, namely, trypanosomes, produce their ravages. 



Disease of man produced by trypanosomes is confined to tropical 

 Africa and some of the adjacent islands. But an enormous belt of country 

 stretching from Rhodesia northward to the Bahr el Ghazal, and from 

 the Cameroons westward to Tanganyika is inhabited to a greater or less 

 degree by the infected tsetse fly. Two forms of trypanosomes are known 

 to infect man, T. Gamhiense, which is especially common in the neigh- 

 bourhood of the two great lakes, Victoria and Tanganyika, and northward 

 ■of these to the tributaries of the Nile. The other, T. Rhodesiense, is 

 mainly found in the country surrounding Lake Nyasa, Portugese East 

 Africa, Nyasaland, and Rhodesia : this form is more rapidly fatal than 

 T. Gamhiense, and its treatment is less satisfactory. Epidemics may 

 occur in different districts from time to time : thus in 1900 an epidemic 

 occurred in the Belgian Congo in the neighbourhood of Kisantu, in which 

 two-thirds of the population succumbed within ten years. It is probable 

 that the population on the northern border of Lake Victoria Nyanza 

 had existed for generations without trypanosomes (sleeping sickness), 

 although Glossina, the carrier, was plentiful. It then happened that 

 some migration of natives, possibly caravan porters from the Congo, 

 introduced the trypanosome, and a terrible epidemic of T. Rhodesiense 

 swept the country in 1898, spread round the Lake and killed about 

 300,000 natives. The natives and their cattle were removed in 1909 and 

 the infested district was left to the fly. Dr. Duke points out that the 

 Glossina Palpalis had hardly diminished in the succeeding eight years, 

 and he regards wild game as a trypanosome reservoir ; he showed in 1911 

 that the situtunga serves as a mammalian host for the trypanosome as 

 well as man, in the same way as N'gana is carried by many species of 

 game ; in this way the fly retains the trypanosome which causes sleeping 

 sickness. In Uganda, at any rate, lizards and crocodiles form the chief 

 sources of food for G. Palpalis. 



T. Gamhiense is transferred by Glossina Palpalis, T. Brucei by G. 

 Morsitans and Pallidipes, and T. Rhodesiense by G. Morsitans. Innumer- 

 able other instances might be given of its ravages in the whole of the 

 Congo, Cameroons, and other parts of Africa. Besides the human form 

 •of the disease, another tsetse fly is responsible for the trypanosomes of 

 domestic animals, including horses and cattle, T. Brucei, which produces 

 the disease N'gana, so that in infected districts draft animals and dairy 

 ■cattle cannot exist. 



Trypanosomiasis is one of the most serious of all tropical diseases and 

 affects both man and beast ; it is a scourge which renders vast tracts of 

 land practically uninhabitable, and which takes its death toll often in 

 thousands and occasionally even in hundreds of thousands, and yet it is 

 a disease which I believe should be curable if not preventable. The 

 problem is one of wide interest and importance — scientific, humanitarian, 

 and economic. The members of two groups of chemical substances excel 

 all others in their curative value in trypanosomiasis and spirochaetosis ; 

 these are the organic arsenical compounds and the dyes. 



