BACILLUS COLI COMMUNIS. 391 media. Upon gelatin plates the colonies develop in twenty-four hours. Those situated below the surface appear round, yellow-brown, and homogeneous. As they grow older they increase in size and become opaque. The superficial colonies are larger and spread out upon the surface. Their edges are dentate and resemble grape- leaves, often showing radiating ridges suggestive of the veins of a leaf. They may have a slightly concentric appearance. The colonies rapidly increase in size and become more and more opaque. The gelatin is not liquefied. In gelatin punctures the culture, developing rapidly upon the surface, and also in the needle's track, causes the formation of a nail-like growth. The head of the nail may reach the walls of the test-tube. Not infre- quently gas is formed in ordinary gelatin, and when i per cent, of glucose is dissolved in the medium the gas- production is often so copious and rapid as to form large bubbles, which by their distentioii subsequently break it up into irregular pieces. Sometimes the gelatin becomes slightly clouded as the bacilli grow. Upon agar-agar along the line of the inoculation a grayish-white, translucent, smeary growth takes place. It is devoid of any characteristics. The entire surface of the culture-medium is never covered, the growth re- maining confined to the inoculation-line, except where the moisture of the condensation-fluid allows it to spread out at the bottom. Kruse says that in old cultures crys- tals may form. I have never seen them. Bouillon is soon evenly clouded by the development of the bacteria. Sometimes a delicate pellicle forms upon the surface. There is rarely much sediment in the cul- ture. Wiirtz found that the bacillus produced ammonia in culture-media free from sugar, and thus caused an intense alkaline reaction in the culture-media. The cultures usually give off an odor that varies somewhat, but is, as a rule, unpleasant.