312 PATHOGENIC BACTERIA.

year when there are not at least some cases of cholera
in the city.

The frequent pilgrimages and great festivals of the
Hindoos and Moslems, by bringing together an enormous
number of people who crowd in close quarters where filth
and bad diet are common, cause a rapid increase in the
number of cases during these periods and the dispersion
of the disease when the festivals break up. The disease
extends readily along the regular lines of travel, visiting
town after town, until from Asia it has frequently ex-
tended into Europe, and by the steamships plying on
foreign waters has been several times carried to our own
continent and to the islands of the seas. Many cases are
on record which show conclusively how a single ship,
having a few cholera cases on board, may be the cause
of an outbreak of the disease in the port at which it
arrives.

It seems strange to us now, with the light of present
information illuminating the pages of the past, to observe
how the distinctly infectious nature of such a disease
could be overlooked in the search for some atmospheric
or climatic cause, some miasm, which was to account
for it.

The discovery of the organism which seems to be the
specific cause of cholera was made by Koch, who was
appointed one of a German cholera-commission to study
the disease in Egypt and India in 1883-84. Since his
discovery, but a decade ago, the works upon cholera and
the published investigations to which the spirillum has
been subjected have produced an immense literature,
a large part of which was stimulated by the Hamburg
epidemic of a few years ago.

The micro-organism described by Koch, and now gen-
erally accepted to be the cause of cholera, is a short
individual about half the length of a tubercle bacillus,
considerably stouter, and distinctly curved, so that the
original name by which it was known was the " comma
bacillus" (Figs. 80, 81).