852 MICROBIOLOGY OF DISEASES OF MAN AND DOMESTIC ANIMALS 



singly, occasionally two may be found end to end in the form of an "S." There is 

 no capsule, 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. 180). Concentric rings may appear as 

 liquefaction progresses from day to day. In old cultures the liquefaction assumes a 



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FIG. 179. Micrcspira comma. X 1000. (After Williams ) 



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 probable that organisms grow under practically 

 anaerobic conditions in the intestine. The reaction of all media must be very dis- 

 tinctly 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 bacterium 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. 



