articles that have come into contact with
persons suffering from the disease may be the means of conveyance to a
distance. There is no reason to suppose that it is air-borne, or that
atmospheric influences have anything to do with its spread, except in so
far as meteorological conditions may be favourable to the growth and
activity of the micro-organisms. Beyond all doubt, the great manufactory
of the poison is the human body, and the discharges from it are the
great source of contagion. They may infect the ground, the water, or the
immediate surroundings of the patient, and so pass from hand to hand,
the poison finding entrance into the bodies of the healthy by means of
food and drink which have become contaminated in various ways. Flies
which feed upon excreta and other foul matters may be carriers of
contagion. Of all the means of local dissemination, contaminated water
is by far the most important, because it affects the greatest number of
people, and this is particularly the case in places which have a public
water-supply. A single contaminated source may expose the entire
population to danger. All severe outbreaks of an explosive character are
due to this cause. It is also possible that the cholera poison
multiplies rapidly in water under favourable conditions, and that a
reservoir, for instance, may form a sort of forcing-bed. But it would be
a mistake to regard cholera as purely a water-borne disease, even
locally. It may infect the soil in localities which have a perfectly
pure water-supply, but have defective drainage or no drainage at all,
and then it will be found more difficult to get rid of, though less
formidable in its effects, than when the water alone is the source of
mischief. In all these respects it has a great affinity to enteric
fever. With regard to locality, no situation can be said to be free from
attack if the disease is introduced and the sanitary conditions are bad;
but, speaking generally, low-lying places on alluvial soil near rivers
are more liable than those standing high or on a rocky foundation. Of
meteorological conditions it can only be said with certainty that a high
temperature favours the development of cholera, though a low one does
not prevent it. In temperate climates the summer months, and
particularly August and September, are the season of its greatest
activity.

Western diffusion.

Cholera spreads westwards from India by two routes--(1) by sea to the
shores of the Re