343 PATHOGENIC BACTERIA. growth of the organism sulphuretted hydrogen gas is produced. The spirillum does not grow at all upon potato. Giinther did not find the organism to be pathogenic. Spirillum Terrigenus.—This species, also discovered by Giinther, was secured from earth. It generally occurs in a slightly curved form, but sometimes is spiral. It is actively motile and has a terminal flagellum. The colonies, which appear in twenty-four hours, are small, structureless, and transparent, and later take on a " fat-drop " appearance. Upon agar-agar a thin white coating is formed. Milk is coagulated by the growth of the organism. No indol is produced. The organism does not stain by Gram's method, and is said not to be pathogenic for guinea-pigs or for mice. FIG. 97.—Spirillum aquatilis, from an agar-agar culture; x 1000 (Itzerott and Wipmjmn^ Niemann). Vibrio Schuylkiliensis.—This form, closely resembling the cholera spirillum, was found by Abbottl in sewage- polluted water from the Schuylkill River at Philadelphia. The colonies upon gelatin plates resemble very closely those of Spirillum Metschnikovi. In gelatin puncture- cultures the appearance is exactly like the true cholera spir- 1 Jour, of Exper. Med^ vol. i., No. 3, July, 1896, p. 419.