CHOLERA BACILLUS 183 



phuric acid. Dextrorotatory lactic acid is produced from all the 

 sugars. Gases are not formed. Yields alkali in culture; causes 

 slight coloration of potato, and produces a disagreeable odor in 

 bouillon; also yields H 2 S, and ferments that liquefy gelatine. 

 Bacteriolysins and invertin are also produced, as well as a toxin 

 which is soluble in water. The most powerful toxin, by far, is 

 contained in the cells of the vibrio themselves. This causes death 

 after intra-peritoneal injection in guinea pigs. 



Oxygen Requirements. It is a facultative aerobe; its growth, 

 however, without oxygen is slow, while powerful toxins are formed. 



Temperature. Grows best at 37 C., but very well at 23 C. 

 Does not grow below 8 C. 



Cultures. On gelatine plates the growth is characteristic. 

 Small yellowish-white colonies, which rapidly liquefy the gelatine, 

 appear in twenty-four hours. As the colony increases in size it 

 becomes more and more granular, and finally the whole medium is 

 liquefied. In gelatine tube stab culture, the growth, at first, is 

 not characteristic; but, after a few hours, a semi-spherical depres- 

 sion appears, which extends downward, and resembles a large 

 bubble of gas. As liquefaction progresses, the whole line of punc- 

 ture disappears, and the excavation looks cylindrical. This area 

 becomes cloudy. On agar plates the colonies are elevated, round 

 and white, with a moist lustre. Deep colonies are whetstone shape. 

 Old agar colonies become yellowish-brown. Coagulated blood 

 serum is rapidly liquefied at 37 C. Milk, at times, is coagulated. 

 No curdling ferment is formed; the acid produced is thought to be 

 sufficient. On potato the growth is slow, or not at all, if the medium 

 is acid. If the potato is rendered alkaline, growth occurs, with a 

 moist lustre, slightly elevated; white at first, later becoming brown. 

 On acid fruits it will not grow. In bouillon, after sixteen hours, 

 a diffuse cloudiness occurs, with the formation of a stiff pellicle, 

 which in some cultures becomes wrinkled. In peptone, abundant 

 growth takes place, with the production of indol and nitrites. If a 

 few drops of H 2 SO 4 are added, a beautiful red appears if nitrites are 



