416 PATHOGENIC BACTERIA.

be circular and rounded, or irregular. They are said
rarely to reach a greater diameter than 2 mm. The gela-
tin is not liquefied. There is nothing distinctly charac-
teristic about the appearance of the colonies.

Upon agar-agar the superficial colonies attain a diam-

FIG. 114.—Ulceration of the intestine in a typical case of swine-fever
(Crookshank).

eter of 4 mm. and have a gray translucent appearance with
polished surface. They are round and slightly arched.

In gelatin punctures the growth takes the form of a
nail with a flat head. There is nothing characteristic
about it. The growth in the puncture shows it to be an
optional anaerobe.