500 THE CHOLERA GROUP 



sharply differentiated from the true cholera vibrio with the imperfect 

 methods available in the early days of bacteriology, when these obser- 

 vations were made. It is now universally held that the cholera vibrio 

 is the causative organism of the disease. 



Morphology. The typical cholera vibrio is a distinctly curved rod, 

 the curvature being in three planes of space. It measures 0.5 to 0.6 

 micron in diameter by 1 to 3 microns in length, occurring singly or 

 in pairs, less commonly in longer spiral chains of several elements. 

 Pairs of organisms frequently appear as S-shaped spirilla, the curva- 

 ture being in three planes of space in the living vibrios. Freshly 

 isolated vibrios have slightly but distinctly pointed ends which are 



FIG. 71. Cholera vibrios, showing flagella. 



best observed in stained specimens made directly from cholera dejecta. 

 Cultures grown for some time on artificial media lose their original 

 uniformity of size and shape and tend to become less curved, many 

 individuals even appearing as straight rods. The passage of these old 

 cultures through animals is said to restore their original morphology. 

 Cultures in artificial media several days old frequently exhibit involu- 

 tion forms which are irregularly swollen or even coccoid in outline. 

 Bacillary forms and even true spirillum forms also are not uncommonly 

 seen. 



Cholera vibrios are actively motile and they possess a single polar 

 flagellum monotrichic flagellation. 1 No capsule has been demon- 

 strated and no spores are produced, although involution forms which 

 stain somewhat irregularly may suggest spores. 



The cholera organism stains with ordinary anilin dyes, although less 



1 Loffler, Centralbl. f. Bakt., 1889, vi> 209. 



