H. L. Duke 
427 
The riparian populations of Uganda possessed many hundreds, probably 
several thousand, canoes, which were in constant use for fishing and com¬ 
merce. They also fished, in parties, from fly infested shore; gathered in 
numbers for repairing canoes, fishing gear, etc., under similar conditions; and 
finally there were market places where islanders met mainlanders for exchange 
of produce, at points on the shore that were well known to be densely and 
dangerously infested by fly. 
PART III. 
XI. CONCLUSIONS TO BE REACHED REGARDING THE TRYPANOSOMES 
PRESENT IN MAN AT THE TIME OF THE EPIDEMIC FROM A CONSIDERA¬ 
TION OF THE MORTALITY STATISTICS. 
It has been shown that the death rate among the surviving island popula¬ 
tions, after their removal in 1909 up to the outbreak of war, was only from 
4 to 6 per cent, of the total number removed. What then are the logical con¬ 
clusions to be derived from this statement? 
They are either that the assumption that 90 per cent, of the population 
were already infected is wrong or that all those infected did not die. 
We have no grounds for discrediting the estimated proportion of infected 
persons and must accept, provisionally at least, the statement of officials who 
were in a position to know the facts. Therefore we must conclude, provision¬ 
ally, that very many infected persons recovered. 
This conclusion is difficult to reconcile with the statement and common 
belief that on some islands the epidemic reached an exterminative culmination 
and left no survivors, or so few as to seem a negligible quantity. On some 
islands, we are informed, there was approximately or actually 100 per cent, 
of infections, and that all persons, old and young, developed sleeping sickness 
and died (13); whereas on other islands, after the climax of the epidemic had 
passed, there were 90 to 95 per cent, of infections but more than 80 per cent, 
of recoveries. 
As before we must, provisionally at least, accept the statements and 
common belief of officials who were in a position to know the facts, and this 
leaves no alternative to the conclusion that the trypanosome was subject to 
great variation in its pathogenicity toward man. 
This conclusion must now be reconciled with the statement and common 
belief of persons in a position to know, that the disease showed no signs of 
diminished virulence in individual cases (14). Reconciliation is only possible on 
the assumption that sleeping sickness showed no signs of diminution in viru¬ 
lence, but that the number of cases of trypanosome fever which failed to 
develop into sleeping sickness was very much greater on some islands, toward 
the close of the epidemic, than on other islands or perhaps generally, during 
the earlier stages of the epidemic. 
