24 NATURAL HISTORY OF SLEEPING SICKNESS 



and afterwards by Bruce and Nabarro in every case of 

 Sleeping Sickness examined. Thus was made clear the 

 fact that *' Trypanosome fever " is the early stage of 

 the fatal disease, and the next step was to find out how 

 the disease was transmitted. 



At this step a comparison of what was known about 

 Nagana with what has been found out about Trypano- 

 somiasis aids in the understanding of further developments. 

 In the former case investigation commenced with strong 

 presumptive evidence that a Tse-tse fly was the agent 

 through which the disease was acquired ; in the latter 

 case the germ was discovered and it became necessary 

 to ascertain how it was transmitted. Since Nagana had 

 been proved to be due to a Trypanosome carried by the 

 blood-sucking fly Glossina morsitans, and Sleeping Sickness 

 had now been shown to be due to another species of 

 Trypanosome, evidence pointed to a blood-sucking fly 

 as the carrier of this new species Trypanosoma gambiense, 

 and requests were made to officials in the Sleeping Sick- 

 ness area.s fo send specimens of all biting flies in the 

 neighbourhood to the laboratory in Entebbe. It very 

 soon became clear that one fly was found throughout 

 the areas being ravaged by the disease, that is the shaded 

 margins of the great lakes and rivers ; this fly was 

 Glossina palpalis. Accordingly experiments were made 

 to test whether the fly can be the carrier, and specimens 

 captured on the shores of the lake were fed upon monkeys 

 whose blood was examined daily, the procedure being 

 the same as in Bruce's classical work on Nagana. Con- 

 clusive proof was obtained when the Trypanosome was 

 found in the blood of the monkeys, and the discovery 

 was announced by the Commission in 1903.^ Further 

 proof was obtained by feeding bred flies on monkeys 

 which had been already infected by wild flies, and then 

 making them feed upon another monkey ; the second 

 ^ Reports of the Sleeping Sickness Commission, No. IV, pp. 5G-65. 



