9
hear of the occurrence among such people of cases of Black water
Fever. It often happens that the effects upon the actual labour
forces and the neighbouring native populations may pass unnoticed
and unrecorded, only the outbreak of disease among Europeans
attracting attention; but there can be little doubt that were such
cases investigated it would be found that the infection of Europeans,
troops, and well-to-do natives was only a concomitant and a result
of a vastly greater amount of malaria among the poorer population,
and especially among the labour force itself.
In the case of railway construction we have, then, to deal not
alone with the formation of borrow-pits and the interference with
surface drainage, but with a peculiar set of conditions mainly associated
with the human host which are probably more or less identical through-
out the tropics. In canal construction, too, we have other considerations
involved beside the mere formation of water channels, which, though
they may undoubtedly assist in increasing malaria, are probably not
the sole cause of canal epidemics. We have labour communities engaged
in the primary excavation of the main channels and subsequently
drafted off throughout the district for the purpose of cutting the dis-
tributing branches, and in addition the influx of immigrants seeking
to find employment and to secure land in the newly irrigated area.
All these things point to a complex of factors, which it is impossible to
dismiss without serious thought if we wish to understand the natural
history of great outbreaks of malaria. It is obvious that in the clear-
ing of jungle, the making of roads, and all such operations as are requir-
ed in the opening up of new countries, labour is necessary; and one has
only to visit a large road under construction in forest country. or
a tea garden being laid out, to realise that the malaria associated with
such undertakings is merely the result of the conditions we have
termed tropical aggregation of labour.
Quite recently we have had the opportunity of seeing at Bombay
a typical example of the malaria of tropical aggregation of labour.
With the inauguration of large harbour works there has recently
appeared a serious outbreak of malaria. The epidemic, we are inform-
ed, came with the works and has got progressively worse year by year
1 SC B