143
the rapidity of movement of the air. The monsoon winds, at certain periods of
the year, travel at the rate of from 200 to 300 miles in twenty-four hours, but I
am not aware of a single fact which shows that cholera can advance, epidemically,
at the same rate.
192. An attentive consideration of the tacts embodied in the district tables
of this report will show, I think, very clearly that the localisation of cholera in
certain places, and the slow movement of an epidemic, the intensity varying
greatly even in adjoining talooks, or in the same district, is very adverse to any mere
theory that the cholera germ is dependent upon a moist monsoon wind for its
transport.
193. The other theory of Dr. Bryden's, that the cholera miasm is in its nature
wholly independent of man, is, I need hardly observe, without any trustworthy
evidence in its favour, and until the actual condition of the population within the
endemic field of cholera is known, we have not the means of profitably pursuing
this branch of the inquiry.
194. To sum up the facts as ascertained regarding the movement of cholera,
I think it must be admitted—
1st.—That an epidemic wave from the natural home of cholera reaches the
Madras Presidency, after affecting the Central Provinces, a portion of
the Bombay Presidency and the Deccan, and rarely, if ever, by the
shorter route along the Coromandel Coast.
2nd.—That these epidemic waves of cholera recur at uncertain intervals, but
generally once in four or five years.
3rd.—That the direction of the line of cholera advance in this Presidency
is, generally, from north to south, and that the invading epidemic never
entirely halts until the extreme southern limit of territory (including
the Island of Ceylon) has been reached.
4th.—That the south-west winds do not stop or retard this southern
advance, nor do the north-east winds hasten it.
5th.—That monsoon moisture has some relation to the seasonal intensity,
and possibly also to the movement of cholera, although prevailing
winds do not harry or check its advance into unoccupied territory.
6th. —That the period of time occupied in the invasion of Southern India,
has varied from six months to two years.
7th.—That increased rapidity of communication by railways and steamboats
has not hastened the advance of cholera, the last epidemic in 1869-70
having taken four times as long to reach Ceylon as did the great
enidemic of 1818.
195. Although Dr. Bryden's theory, in regard to the movement of cholera by
aerial currents, does not seem to me to be warranted by ascertained facts, I am
by no means prepared with a counter theory to explain why cholera should
periodically move out of the land of its birth, radiating in every direction in
which physical obstacles to its progress do not exist.
196. The phenomena oí epidemic movement, as 1 understand them, may in
some respects be likened to the circular waves which follow the displacement of
water in a pool, when a stone is flung into the middle of it. Troubled water is first
seen in the neighbourhood of the disturbing cause, and in a cholera epidemic, it
is the tract immediately outside of the endemic area that is first troubled,
whether that tract lie to the south-east, south-west, or the north-west. The fact
that the sea lies to the south of the endemic area, and a mountain barrier to
o o