454 PATHOGENIC BACTERIA. oval spores are found; by their presence they distort the bacilli in which they occur, causing them to assume a spindle shape (clostridium), or, when two are united and a spore occupies one of them, a drumstick shape. In- FIG. .128.—Bacillus of symptomatic anthrax, containing spores, from an agar- agar culture; x. 1000 (Frankel and Pfeiffer). volution-forms are exceedingly common in old cul- tures, and are of enormous size and of granular appear- ance. The bacillus can be stained with the ordinary aqueous solutions of the anilin dyes, but will not retain the color by Gram's method orWeigert's fibrin method. It can be colored in sections of tissue with lyoffler's solution, and can be observed in the blood without staining shortly after death. The spores, which can be stained by ordinary methods, are quite resistant to the action of heat and disinfect- ants, and withstand the effects of drying for a consider- able length of time. The bacillus of symptomatic anthrax (Fig. 129) is a strictly anaerobic, parasitic bacterium. It grows at tem- peratures above 18° C., but best at 37° C.