40
MIXTURE OF NEW AND OLD COOLIES.
It is evident that each year every colony in every line throughout
the Duars is liable to receive its annual addition of new arrivals. Hence
new-comers are at once distributed throughout the whole community.
An example of this is shown in the accompanying plan of a line taken
at the end of the recruiting season.
In the year or two following their arrival these new-comers are in
the position of being susceptibles received into a hot bed of infection.
They at once become infected, and in proportion to their susceptibility
become disseminators of infection. They thus tend to raise still higher.
the intensity of malaria in the lines. This process repeated year by
year tends to maintain a permanent condition of exalted epidemic mala-
ria.
In addition to the mixture produced in the ways we have described
there is also a great tendency, for reasons which we need not here
specify, for large numbers of the population to move about from garden
to garden.
Under conditions where the mingling of infected persons and sus-
ceptibles was less complete we might expect that the health of each com-
munity would depend upon its relatively healthy or unhealthy situation,
and its history and constitution; but in the Duars the conditions suit-
able for the spread of infection approximate everywhere so much to
the optimum that, provided there are any anopheles at all, a state of
maximum infection seems everywhere to result.
If under these conditions we wish to reduce disease, it is obvious
that we have to think about trying to protect or render the com-
munity unsuitable to malaria, especially the new-comers. For, given
a moderate degree of infection, the older and more or less immune
coolies will manage to retain their health; it is the new coolies,
those within the first few years of their arrival, who form as it
were the most inflammable fuel, and not only suffer themselves, but
raise the amount of prevailing infection for old and new alike.