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.