394: BACTERIA PATHOGENIC TO MAN 



that none of them is affected by the specific serum of animals immu- 

 nized to cholera. After a time, therefore, the exclusive association of 

 Koch's vibrio with cholera became almost generally acknowledged until 

 now it is regarded by bacteriologists everywhere to be the specific cause 

 of Asiatic cholera. Certain sporadic cases of cholera-like disease, how- 

 ever, are undoubtedly due to other organisms. 



Morphology. Curved rods with rounded ends which do not lie in 

 the same plane, from 0.8/* to 2ju in length and about QAp in breadth. 

 The curvature of the rods may be very slight, like that of a comma, 

 or distinctly marked, particularly in fresh unstained preparations of 

 full-grown individuals, presenting the appearance of a half-circle. By the 

 inverse junction of two vibrios S-shaped forms are produced. Longer 

 forms are rarely seen in the intestinal discharges or from cultures grown 

 on solid media, but in fluids, especially when grown under unfavorable 

 conditions, long, spiral filaments may develop. The spiral forms are 

 best studied in the hanging drop, for in the dried and stained prep- 

 arations the spiral character of the long filaments is often obliterated. 

 In film preparations from the intestinal contents in typical cases it 

 will be found that the organisms are present in enormous numbers, 

 and often in almost pure culture (Figs. 120 and 121). In old cultures 

 irregularly clubbed and thickened involution forms are frequent, and 

 the presence in the organisms of small, rounded, highly refractile bodies 

 is often noted. 



Staining. The cholera spirillum stains with the aniline colors usually 

 employed, but not as readily as many other bacteria; a dilute aqueous 

 solution of carbol-fuchsin is recommended as the most reliable staining 

 agent with the application of a few minutes' heat. It is decolorized by 

 Gram's method. The organisms exhibit one long, fine, spiral flagellum 

 attached to one end of the rods, or, exceptionally, to both ends. (Cholera- 

 like spirilla often have 1, 2, or 3 end flagella.) 



Biology. An aerobic (facultative anaerobic), liquefying, very motile 

 spirillum. Grows readily in the ordinary culture media, best at 37 C., 

 but also at room temperature (22 C.); does not grow at a temperature 

 above 42 or below 8 C. and does not form spores. 



In gelatin-plate cultures at 22 C. the colonies are quite character- 

 istic; at the end of twenty-four hours, small, round, yellowish-white to 

 yellow colonies may be seen in the depths of the gelatin, which later 

 grow toward the surface and cause liquefaction of the medium, the 

 colonies lying at the bottom of the holes or pocket thus formed. The 

 zone of liquefaction, which increases rapidly, at first remains clear, 

 then becomes cloudy, mostly gray, as the result of the growth of the 

 colonies. In many cases after a time concentric rings, increasing from 

 day to day, appear in the zone of liquefaction. (See Figs. 122 and 123.) 

 Examined under a low-power lens, at the end of sixteen to twenty- 

 four hours, the colonies appear as small, light-yellow, round, coarsely 

 granular disks, with a more or less irregular outline. In many cases 

 at this stage an ill-defined halo is seen to surround the granular colony. 

 As the colonies become older the granular structure increases, until a 



