646 MICROBIOLOGY OF THE DISEASES OF MAN AND ANIMALS. 



and no spore formation. There is a single terminal flagellum, and the organism is 

 exceedingly motile. Does not stain as readily with the ordinary aniline dyes as many 

 other bacteria. Fuchsin gives the best result. It is Gram-negative. The optimum 

 temperature for growth is 37 with a minimum of 8 and a maximum of 42. Plain 

 agar moist, shining, grayish-yellow, and rather thin and transparent as compared 

 with the colon type of colony. A rapid growth takes place in broth, causing a uniform 

 clouding with a more or less well-developed pellicle. In gelatin plates colonies are 

 visible in twenty-four hours and are round, even, and yellowish-white, later they 

 become irregular and their surface presents fine refractile granules; within forty-eight 

 hours the colonies are found to be sinking into a small round pit due to liquefaction of 

 the medium (Fig. 114). Concentric rings may appear as liquefaction progresses from 

 day to day. In old cultures the liquefaction assumes a funnel or turnip shape with an 

 air bubble at the surface due to evaporation. Growth in milk occurs without any 

 visible change in the medium. At 37, on potato, an abundant moist brownish growth. 

 Blood serum is liquefied rapidly. The vibrios prefer the presence of oxygen, yet it is 



FIG. 113. Microspira comma. Xiooo. (After Williams.') 



probable that organisms grow under practically anaerobic conditions in the intestine. 

 The reaction of all media must be very distinctly alkaline and even very small amounts 

 of acid are inhibitive. Neither gas nor acid is formed. The production of indol and 

 the formation of nitrites from nitrates occurs regularly. The addition of sulphuric acid 

 is sufficient to give the nitroso-indol reaction, which from its association with this bac- 

 terium has been called the cholera red reaction. No pigment is produced. Majority 

 of freshly isolated cultures have haemolytic powers. It is generally considered that there 

 is only an endotoxin, but it is strongly asserted by some that a soluble toxin is formed. 

 Thermal death-points are 60 for ten minutes, 95 to 100 for one minute. Vibrios 

 are quite sensitive to low temperature and at most have been found viable in ice only 

 after a few days. The vibrios are quite susceptible to the ordinary disinfectants. 



