26 NATURAL HISTORY OF SLEEPING SICKNESS 



varied, from eighteen to forty-five days, after which 

 time a fly will remain infective and able to introduce 

 the Trypanosome into every animal it bites for as long 

 as seventy-five days ! 



The complete life cycle of the Trypanosome in the fly 

 was worked out fully in Uganda by Miss Robertson 

 in 1913.^ The Trypanosome multiplies in the gut of the 

 fly, but the forms of m^ultiplication are not those which 

 will live in the blood stream of the vertebrate host, and 

 a somewhat different form is developed which finds its 

 way into the " salivary " glands of the fly and is 

 injected with the irritant secretion of the gland which 

 presumably is intended to produce a free flow of blood 

 in the site of puncture. We have now arrived at the 

 most important fact that when once it has acquired 

 the Trypanosome the Tse-tse fly can infect for the rest 

 of its life. 



We must now consider the relations between Tse-tse, 

 Trypanosome, and the " alternative hosts " of the latter 

 from which the fly acquires it. 



It was known from Bruce 's researches on Nagana ^ 

 that Trypanosoma brucei is a natural and harmless inhabi- 

 tant of the blood of various species of big game in the 

 " fly areas," and as soon as Sleeping Sickness was 

 proved to be due to another Trypanosome, efforts were 

 made to discover its natural host or reservoir. The 

 Commission in Uganda made a series of experiments 

 with the blood of such animals and birds that, inhabiting 

 the lake shore, might be justly suspected of harbouring 

 the trypanosome, but with negative results. One impor- 

 tant species of antelope, however, was not at this time 

 (1908-10) examined. The next step was to mfect captive 

 antelope and native cattle by feeding upon them flies 



^ Reports of the Sleeping Sickness Commission, No. XIII, p. 119, etc. 

 - ApjDendix to Further Report on Tse-tse Fly Disease or Nuga7ia in 

 Zululand, 1903, p. 8. London, Harrison & Sons. 



