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Tsetse Flies and Trypanosomiasis 
This provisional conclusion agrees well with the common belief held in 
1906-1907 that trypanosome fever always developed into sleeping sickness. 
Possibly it may have done so in a much greater proportion of cases in the 
earlier stages of the epidemic than in the later years. 
It also adds plausibility to the hypothesis that, at present, the trypanosome 
persisting in fly and game is less virulent toward man than that responsible 
for the decimating epidemic of sleeping sickness: in short, that we have to 
deal with two types of human trypanosomiasis, one chronic and the other 
invariably fatal, caused respectively by two different strains of the parasite. 
The fatal strain naturally burnt itself out. The other, causing a generally mild, 
though possibly sometimes fatal, disease, is relatively widespread and per¬ 
sistent. 
XII. GENERAL CONCLUSIONS. 
In the preparation of a paper of this character we have had three main 
objects in view: 
(1) To call attention to the fact that the bio-economic problem created 
by the tidal wave of sleeping sickness that swept the region of the Upper Nile 
in general and the shore of Victoria Nyanza especially, is not solved, but that 
it has merely passed from the stage which called for measures designed to 
prevent further destruction of life and values into a new stage calling for the 
substitution of reconstructive for preventive measures. The “main and 
most important feature” of the measures adopted in Uganda in 1907 was to 
remove all natives from contact with the fly in order to prevent further spread 
of the disease and further destruction. The main and most important feature 
of the reconstruction measures must be to replace the populations and recover 
economic values, but at the same time to preclude absolutely the possibility 
of another devastating pestilence. This effort toward reconstruction is in every 
respect as important and necessary as the effort to prevent further de¬ 
struction. 
(2) To call attention to the main question raised by the outcome of the 
preventive measures, with a view to determining future policy. Are we 
justified in accepting the most obvious interpretation and proceeding to re¬ 
constructive effort on the assumption that an epidemic of sleeping sickness is 
impossible unless there is sufficiently broad contact between fly and population 
to render possible the development of a virulent, “mechanical transmission,” 
strain. Or must we take also into account the possibility that the patho¬ 
genicity of the trypanosome may be subject, per se, to variations, irrespective 
of the method by which it is transmitted? On this latter explanation the dis¬ 
appearance of acute trypanosomiasis in Uganda is not altogether due to the 
preventive measures, but also in greater or less degree to diminution in 
pathogenicity of the parasite and that the trypanosome is liable to resume a 
virulent state, even in Uganda Protectorate, under existing conditions. 
(3) To present the results of self-questioning along these lines, which has 
resulted in the formation of a working hypothesis supported by considerable 
