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CHOLERA.                               323

clothing, etc. are readily rendered harmless by the proper
use of disinfectants. Water and foods are rendered in-
nocuous by boiling or cooking. Vessels may be disin-
fected by thorough washings with jets of boiling water
.thrown upon them through hose. Baggage can be steril-
ized by superheated steam.

It often becomes a matter of importance to detect the
presence of cholera in drinking-water, and, as the dilu-
tion in which the bacteria exist in such a liquid may be
very great, much difficulty is experienced in finding them
by ordinary methods. One of the most expeditious meth-
ods that have been recommended is that of L,6ffler, who
adds 200 c. cm. of the water to be examined to 10 c. cm.
of bouillon, allows the mixture to stand in an incubator
for twelve to twenty-four hours, and then makes plate-
cultures from the superficial layer of the liquid, where,
if present, the development of the spirilla will be most
rapid because of the presence of air. A similar method
can be used to detect the spirilla when their presence is
suspected in feces.

Gruber and Wiener, Haffkine, Pawlowsky, and Pfeiffer
have all succeeded in immunizing animals against the
toxic substances removed from cholera cultures or against
living cultures properly injected. There seems, accord-
ing to the researches of Pfeiffer, to be no doubt that in
the blood of the protected animals a protective substance
is present. In the peritoneal infection of guinea-pigs
the spirilla grow vigorously in the peritoneal cavity, and
can be found in immense numbers after twelve to twenty-
four hours. If, however, together with the culture used
for inoculation, a few drops of the protective serum be in-
troduced, Pfeiffer found that instead of multiplying the
organisms underwent a peculiar granular degeneration
and disappeared, the unprotected animal dying, the pro-
tected animal remaining well.

Pfeiffer and Vogedes1 have suggested the application
-of this " immunity-reaction n for the positive differentia-

1 Centralbl.fur Bakt. imd Parasitenk., March 21, 1896, Bd. xix., No. II.