170 THE KINGDOM OF MAN 



the sleeping sickness trypanosome when this was intro- 

 duced by means of injection through a syringe. Such 

 monkeys were found to develop the chief symptoms of 

 sleeping sickness, and ultimately died of the disease, 

 their cerebro-spinal fluid being invaded by the parasites. 

 Accordingly it was possible to use monkeys as test 

 animals. It was found by Colonel Bruce that tsetze flies 

 (Glossina palpalis) which had been made to bite infected 

 negroes could carry the infection to the monkeys ; and 

 it was also found that even when a number of tsetze flies, 

 not specially prepared, were allowed to bite a monkey, 

 the latter eventually developed the trypanosome in its 

 blood and cerebro-spinal fluid, thus showing that the 

 tsetze flies, as naturally occurring in the country around 

 Entebbe, contain many of them, the trypanosome ready 

 to pass from the fly to a human or simian victim, when 

 casually bitten by the fly. 



Experiments such as these of infection by the fly, and 

 the use of monkeys in the research, require very great 

 care ; and it is quite reasonable to ask that they shall be 

 repeated and most carefully checked before they are 

 considered as demonstrative and absolutely certain. It 

 may, however, be considered as practically certain that the 

 sleeping sickness is due to the presence in the cerebro- 

 spinal fluid of quantities of a minute parasite, the Trypano- 

 soma Gambiense, which is carried from man to man by the 

 palpalis tsetze fly, which sucks it up from the blood of 

 an infected individual and conveys it to previously unin- 

 fected individuals. The natives in Uganda lie about and 

 sleep under the shade of trees where the tsetze flies 

 are especially abundant ; and they are quite indifferent to 

 the bites of flies of one kind and another. 



It is the dislike to the mere touch of a fly, still more 

 to its bite, which has protected Europeans almost entirely 



