442 THE PRESIDENTS ADDRESS. 



simongst its victims. I do not propose here to enter into the 

 •distressing symptoms of this deadly disease, but only to deal 

 with what may be termed its natural history. 



Before it is possible to understand clearly the nature of sleeping 

 sickness it is necessary to say a few words about similar diseases 

 in animals. It was well known to all African travellers from 

 the time of Livingstone that domestic animals, especially cattle, 

 horses, and dogs, were liable in Africa to a peculiar fatal disease 

 known as nagana, caused by the bite of blood-sucking flies of the 

 genus Glossinctj the tsetse-flies, of which there are several species 

 abundant in various parts of Africa. It was supposed that the 

 fly produced and injected a virus which caused the disease. 



The nature of nagana was first made clear by Sir David 

 Bruce, who found that the cause of the disease was the presence 

 in the blood of a minute flagellate or trypanosome, since named 

 Trypanosoma brucii, and that the tsetse-fly did not generate the 

 parasite, but was merely the unwitting agent in transmitting it 

 from infected to healthy animals. 



When the epidemic of sleeping sickness broke out in Uganda, 

 the Royal Society, at the request of the Government, appointed a 

 commission to investigate it, and Sir David Bruce was sent out 

 as a member of the commission. A trypanosome w T as found by 

 Castellani in the cerebro-spinal fluid of sleeping-sickness patients, 

 and it was shown by Bruce and his assistants that this trypano- 

 some was the cause of the disease, and that it was transmitted 

 from sick to healthy persons by the bite of the local species of 

 tsetse-fly, Glossina palpalis. It was proved by subsequent re- 

 searches that the trypanosome causing sleeping sickness was 

 identical with one that had been discovered previously in the blood 

 of negroes in Gambia and named T. gambiense by Dutton. In 

 short, it was proved that sleeping sickness of man is a trypanosome- 

 disease similar to nagana of animals, but produced by a different 

 species of trypanosome, transmitted by a different species of tsetse- 

 fly, and running a somewhat different course. Whereas Trypano- 

 soma brucii remains in the blood of its victims until their death, 

 T. gambiense is found in the blood in the early stages of the 

 disease, but spreads, probably through the lymphatic channels, 

 into the cerebro-spinal fluid, and then causes the peculiar nervous 

 symptoms which give the disease its name. The rapid spread of 

 sleeping sickness into regions where it was previously unknown 



