141
CHAPTER VIL
THE MOVEMENT OF CHOLERA VIEWED IN RELATION
TO RECENT THEORIES.
187. There are at present two very contradictory theories entertained in
regard to the phenomena of cholera movement. The one of most general
acceptance perhaps is that formulated by the International Sanitary Conference
at Constantinople in 1866, as follows :—
" No fact has hitherto been brought forward to prove that cholera is spread abroad
by the atmosphere alone, whatever may be its condition ; and that, moreover, it is a laiv
without exception, that an epidemic of cholera has never spread from one place to
another in a shorter time than that necessary for man to journey between both places"
The other theory has been lately (1869) put forward by Dr. Bryden in an
official report published by the Government of India.
The prevailing wind is the agency which directs the course of an advancing
epidemic and determines its limitation in geographical distribution ; the assertion that
cholera may advance against a prevailing wind is contrary to fact."
188. Dr. Bryden's chief field of observation, whence he has drawn the above
inference, has been the northern and central parts of India, subjected to the south-
west monsoon rains, and here he has traced an apparent connexion between the
advance of cholera and the direction of monsoon winds. He looks upon cholera
indeed as a soil-bred miasrn, not necessarily dependent upon man for renewal
or propagation, but as a soil emanation that is borne aloft by prevailing winds,
and carried by them out of the endemic area to localities more or less distant.
Hence an endeavour is made to establish the proposition that cholera cannot
move against a monsoon wind. However the facts coming immediately under
Dr. Bryden's observation may seem to support such a conclusion, it is only
necessary that I should refer to Scott's narrative of the cholera invasion of 1818,
to prove, beyond the possibility of a doubt, that cholera did in that period traverse
the Peninsula from east to west, and for many hundredsof miles from north to south,
during the season of prevalence of the south-west monsoon, or, in other words,
that an invading cholera advanced in opposition to a prevailing wind. There is
also to be noted the remarkable fact that the change of monsoon from south-
west to north-east did not hurry the advance of cholera over the Southern
Districts. With the north-east monsoon wind blowing in its favour, it took
nearly four months for cholera to travel from the latitude of Madras to the
northern coast of the island of Ceylon. This one instance is, I think, quite
sufficient to prove that Dr. Bryden's theory, in regard to monsoon agencies, does
not rest on the firm basis of fact which he supposes. Nor does the theory of
cholera distribution by monsoon winds in any way account for the circum-
stance that, simultaneously with the movement of a new epidemic out of Bengal
in a north-west or south-west direction, a corresponding movement is going on
to the south and south-east. If the monsoon winds of India blew in circles
continually widening, or from a central point in radiating lines, it would be
easy to understand how they might propagate cholera ; but, as matter of fact,
we know that the two great winds from the south-west and north-east prevail
with great regularity, and that during their seasons of prevalence, atmospheric