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46                 PATHOGENIC BACTERIA.

isrn found in the blood in the stomach. There seems to
be very little toxin in the blood of patients with yellow
fever, 30-40 of blood being necessary to kill a
guinea-pig when injected subcutaneously. The injection
of 1-2 of blood from the stomach, however, caused
death of the guinea-pig. In its body an almost pure cul-
ture of the bacillus of Havelburg was found. This ex-
periment was repeated twenty-one times without a failure.
The micro-organism is an exceedingly small straight
bacillus i p. in length and o. 3-0.5 fj> in breadth, and may
be single or in pairs, never occurring as filaments. The
stained specimens are more deeply colored at the ends
than at the center, so that the bacillus somewhat resem-
bles the bacillus of fowl-cholera and looks somewhat like
a diplococcus. It has no flagella, is not'motile, and does
not seem to produce spores.

Upon, gelatin plates the colonies appear in twenty-
four hours as small, round, white points, and increase
in size during the next twenty-four hours. The older
colonies are yellowish, finely granular discs, with deli-
cately serrated borders. The gelatin is not liquefied.

In gelatine puncture-cultures a c c nail-growth '' is pro-
duced, consisting of a delicate line of colonies along the
puncture and a broad surface-growth.

The growth on agar-agar is not characteristic, as is that
of Sanarelli's bacillus. Bouillon becomes clouded by the
development of the organism. Rapid fermentation and
gas-production occur in media containing sugar. A
grayish growth occurs on potato. Milk is curdled in
twenty-four hours. The bacillus produces large quan-
tities of indol and sets free H2S. Development in acid
media is rapid. The organism is a facultative anaerobic.
Guinea-pigs and mice are very susceptible: white rats
far less so. Dogs suffer only/rom local abscesses at the
point of injection. The bacillus rapidly alternates in
virulence. No toxin seems to be produced by it.

Havelburg is  of the opinion that tc yellow fever is a
disease of which the specific toxic agent enters the stom-