3
undoubtedly that cholera had become in those years completely extinct over
very large tracts of Southern India, and was renewed only by a distinct new
invasion of cholera contagium from the true endemic province in Lower Bengal.
Physical conditions
of districts in which
cholera lingers, similar
to those of the true
endemic province.
5. There are in the south of India certain localities which, as before observed,
do undoubtedly tend to harbour cholera, and the physical
conditions of such districts in some respects resemble those of
the Gangetic delta. Thus the delta of the Cauvery river is
proved to be a favourite haunt of cholera, and in this district
we find a deep alluvial subsoil, permeable by water at all seasons of the
year, and often for months together completely saturated by irrigation
from innumerable streams. As the river channels cease their supply,
the water recedes from the surface and falls to a lower level in the
subsoil, which soil is subjected to a process of desiccation in its upper strata.
It is usually during the earlier period of this drying up of the land that the
seasonal reproduction of cholera in Tanjore and Trichinopoly is most active,
and it is under precisely similar conditions that cholera re-appears year after year
in the endemic province of Lower Bengal. But the cholera thus bred or fostered
in the localities of Southern India, hitherto regarded as endemic centres, never
diffuses itself widely. If left to itself, it would soon die out. It is the importation
of new seed, so to speak, into these localities that gives strength to the cholera and
causes them to be reputed as cholera centres. For all practical purposes localities
like the districts of Tanjore, Trichinopoly, and the valley in which the town of
Salem stands, may be considered places in which cholera re-appears year after
year, though for scientific accuracy, it would hardly be fair to speak of them as
endemic sites. Cholera is like a foreign plant in them, that has found a fairly
congenial, but not a wholly natural soil, so that after a certain definite time the
plant dies, and has to be replaced by fresh seed brought from a foreign locality.
Although the soil conditions of our southern river deltas are very similar to those
of Lower Bengal, the climatic conditions as regards rain-fall and humidity are
very different. The climate of the southern delta districts is hot and dry with but
little variation in temperature, while that of Lower Bengal is especially remark-
able for a combination of heat and moisture and a wider therniometrical range.
The movement of
cholera
is
1818,
repeated more or less
completely in all subse-
quent invasions.
6. The history of the epidemic advance of cholera in 1818, as detailed in Scott's
narrative, is, in point of fact, the history for all time of the
mode in which the peninsula and Southern India are invaded.
In every new invasion there are sure to be some minor
differences, as to the rapidity of movement of, and the extent
of country covered by, cholera, but the main facts are unalterable. The broad
truth in regard to invasion to be borne in view is, that the great body of cholera
which invades Southern India leaves its natural territory in Lower Bengal, by
what Bryden terms "the southern epidemic highway" across the Central
Provinces, and southward through the Deccan and Bombay Presidencies towards
Madras territory, which in a longer or shorter space of time is occupied. Nor
does cholera terminate with the extreme southern limit of the peninsula. In all
true epidemic invasions, from 1818 down to 1870, it has been carried on to the
neighbouring Island of Ceylon. In this southern progress of cholera, a period of
two years may elapse (as in the latest invasion) before the
epidemic has travelled its southern course from Bengal to
Ceylon, or, as in 1818, the whole journey may be completed
B
Period of time occu-
pied in the movement
of cholera from Bengal
to Ceylon.