?MALARIA IN THE DUARS.
I.-INTRODUCTION.
It is a very common assumption that, just as an epidemic outbreak
of malaria must, it is thought, be due to some unusual prevalence of
anopheles or to the introduction of some species especially favouring
the transmission of the disease, so an intensely malarious area must
be so by reason of the existence of special facilities for the breeding
of anopheles, or the presence of particularly dangerous species.
Under such an assumption the prevalence of malaria in the Duars
might be put down to the particular physical features of this country
especially favouring the breeding of anopheles, or to the existence of
a particular species, M. listoni, a species which it was suggested by the
Royal Socěety's Commission might be a factor in bringing about a
condětěon of intense malaria.
But the facts given in the body of this report suggest that the
extraorděnary prevalence of malaria in the Duars-for we may state
without going into details that we found malaria extraordinarily pre-
valent and peculiarly intense throughout the whole area-is not solely,
or even maěnly, the result of special facilities for the breeding of ano-
pheles, or of the existence of a partěcular species, but on the contrary
is bound up in what we shall call the "human factor," an increased or
diminished supply of anopheles, so long as there are any at all present,
appearing to exert little or no influence upon the prevalence of the
disease.
The Duars, with its 150,000 immigrant coolies aggregated in its
numerous labour camps, is an example on a great scale of conditions
that in our experience are practically always associated with an extra-
ordinary prevalence of malaria. These conditions, though hitherto
they have not been recognised in their bearing upon malaria, are
nevertheless very distinct and important. They may, speaking
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