2
briefly, be said to be those associated with the " labour camp " in
the tropics.
Labour camps, such as we refer to, must be familiar to almost every-
one. They are seen in a very typical form on railways under con-
struction, on almost all engineering projects-notably great excava-
tion works, on operations involved in the opening up of tropical country
such as clearing, road-making, laying-out and working plantations;
and they are very characteristic of many tropical industries, notably,
in India, coal and tea in Mauritius, sugar, and so on. The Duars-
almost exclusively dependent on the tea industry-contains some
thousands of labour camps, the tea coolie lines, and the conditions on
a single one of these camps is representative of the whole Duars.
Without at the present going into details, we may say that in our
researches on malaria we have for some time recognised the almost
constant association of labour camps with severe malaria; and, what-
ever be the cause of this association, we believe that in it lies the expla-
nation of the association of outbreaks of malaria with soil disturbance,
opening up of new country and so on. It is not the soil disturbance,
we believe, but the occurrence of labour camp conditions, or what
we shall call for convenience of description THE TROPICAL AGGREGA-
TION OF LABOUR, in association with these enterprises which has
given them their evil reputation.
Anopheles under such conditons are often plentiful, especially as
squalor and aggregation of human beings undoubtedly tends to
foster anopheles. Not only so but the work in hand often increases
facilities for breeding, and may even lead to " importation " of ano-
pheles, a factor we believe which comes into play much more than
has been supposed. But a condition of increased anopheles preva-
lence is not necessary for intense malaria under such conditions, and
very frequently anopheles are so few in a malaria-stricken camp that
it is difficult to detect their presence. The existence of extensive breed-
ing places is even less necessary; and the common idea that these
camps are malarious, because of the formation of borrow-pits and
hollows is, when one has seen and studied many of them, found to
be quite erroneous. The peculiar prevalence of malaria in labour