ASIATIC CHOLERA AND THE CHOLERA ORGANISM 583 



periods without passage through the animal body have a tendency to 

 lose the curve, assuming a more bacillus-like appearance. The spirilla 

 are stained with all the usual aqueous anilin dyes. They are decolor- 

 ized by Gram's method. In histological section they are less easily 

 stained, but may be demonstrated by staining with alkaline methylene 

 blue. 



Cultivation. The cholera spirillum grows easily upon all the usual 

 culture media, thriving upon meat-extract as well as upon meat-infusion 



FIG. 126. CHOLERA SPIRILLUM. (After Frankel and Pfeiffer.) 



media. Moderate alkalinity of the media is preferable, though slight 

 acidity does not prevent growth. 



In gelatin plates growth appears at room temperature within twenty- 

 four hours as small, strongly refracting yellowish-gray, pin-head colonies. 

 As growth increases the gelatin is fluidified. Under magnification these 

 colonies appear coarsely granular with margins irregular because of 

 the liquefaction. Liquefaction, too, causes a rapid development in 

 such colonies of separate concentric zones of varying refractive power. 

 Old strains, artificially cultivated for long periods, lose much of their 

 liquefying power. 



In gelatin stab cultures fluidification begins at the surface, rapidly 

 giving rise, to the familiar funnel-shaped excavation. 



Upon agar plates, within eighteen to twenty-four hours, grayish, 

 opalescent colonies appear, which are easily differentiated by their 



