. CHOLERA. 319

ance. The existence of cholera organisms in milk is,
however, rather short-lived, for the occurrence of any
acidity at once destroys them.

Wolffhugel and Riedel have shown that if the spirilla
are planted in sterilized water they grow with great ra-
pidity after a short time, and can be found alive after
months have passed. Frankel points out that this ability
to grow and remain vital for long periods in sterilized
water does not guarantee the same power in unsterilized
water, for in the latter the simultaneous growth of other
bacteria in a few days serves to extinguish the cholera
germs.

One of the characteristics of the cholera spirillum is
the metabolic production of indol. The detection of this
substance is easy if the spirilla are grown in a transparent
colorless solution. As the cholera organisms also produce
nitrites, all that is necessary is to add a drop or two of
chemically pure sulphuric acid to the culture-medium
for the production of the well-known reddish color.

Several toxic products of the metabolism of the spirilla
have been isolated. Brieger, Frankel, Roux and Yersin
have isolated toxalbumins; Villiers, a toxic alkaloid fatal
to guinea-pigs; and Gamal£ia, two substances about
equally toxic.

The cholera spirilla can be found with great constancy
in the intestinal evacuations of all cholera cases, and can
often be found in the drinking-water, milk, and upon
vegetables, etc. in cholera-infected districts. There can
be little doubt that they find their way into the body
through the food and drink. Many cases are reported
in the literature upon cholera that show how the disease-
germs enter the drinking-water, and are thus distributed ;
how they are sometimes thoughtlessly sprinkled over veg-
etables, offered for sale in the streets, with water from
polluted gutters; how they enter milk with water used
to dilute it; how they are carried about in clothing and
upon foodstuffs; how they can be brought to articles of
food upon the table by flies which have preyed upon