340 PA THOGENIC BA CTERIA.
growth in bouillon and in peptone solutions is accompa-
nied by the production of indol.
The spirillum is pathogenic for mice, guinea-pigs, and
Spirillum Weibeli.—This spirillum (Fig. 95) was found
in 1892 by Weibel in spring-water which had a long time
FIG. 95.—Spirillum Weibeli, from agar-agar; x 1000 (Itzerott and Niemann).
before been infected by cholera. It is short, rather thick,
and distinctly bent, often forming S-shaped figures.
The colonies before liquefaction sets in are described
as pale-brown, transparent, circular, and homogeneous.
Liquefaction is much more rapid than in cholera, and
causes the borders of the colonies to become irregular.
In the centre of each colony a little depression is ob-
In gelatin puncture-cultures the growth is rapid, be-
ginning first upon the surface, where a large flat, saucer-
shaped liquefaction, extending to the sides of the tube,
forms. Scarcely any growth takes place in the puncture,
but the superficial liquefaction, separated by a horizontal
line from the normal gelatin, descends slowly.
Upon agar-agar a grayish-white layer is formed.
No growth has been obtained upon potato.