CHOLERA 59 



rapidly on gelatine plates at 22 C. (71.6 F.), forming, within twenty- 

 four hours, colonies visible as small bright points. 



Under a low power the colonies appear like fine bits of glass 

 strewn over the gelatine. They are easily distinguished from colonies 

 of Bacterium coli, found in normal stools, by their greater refraction. 

 After forty-eight hours the gelatine under and about the colony begins 

 to liquefy, forming a small funnel or crater in the bottom of which 

 lies the colony. Old subcultures develop colonies on gelatine plates 

 which are less characteristic than those freshly obtained from cholera 

 stools. In gelatine stick cultures the bacillus grows along the line and 

 looks like a white thread. Liquefaction begins at the top and extends 

 downward forming a funnel-shaped depression. Colonies grown on 

 agar plates are also quite characteristic. On other media it grows 

 quickly, especially so in alkaline 1 per cent, peptone solution. The 

 cholera bacillus does not grow in the absence of air and consequently 

 is known as an obligate aerobe. 



The cholera bacillus grows most abundantly at or a few degrees 

 above body temperature and does not wholly cease to multiply until 

 the temperature is at or below 8 C. (46.4 F.). Freezing does not 

 destroy it and it retains its virulence after having been frozen in 

 ice for several days. It is quickly destroyed by drying. A drop of a 

 bouillon culture placed on glass and allowed to dry in the diffuse 

 light of a room shows no growth when placed in proper medium after 

 two hours. When exposed to direct sunlight life is destroyed in even 

 less time. This indicates that the bacillus does not form spores and 

 that the disease is not air borne. 



Boiling destroys the bacillus instantly; at 80 C. (176 F.) five min- 

 utes is long enough to destroy its vitality and a temperature as low 

 as 55 C. (131 F.) has the same effect after half an hour. It is also 

 highly susceptible to chemical agents. One per cent, carbolic acid, 

 1 : 3,000,000 corrosive sublimate and feebly acid solutions kill it within 

 a few minutes. According to Harding one part of chlorin to one mil- 

 lion parts of water destroys the bacillus within fifteen minutes. In 

 distilled water it soon dies but in ordinary drinking-water or tank- 

 water, such as is used in India, it may retain its vitality and virulence 

 for weeks and even months. According to Hankin the organism soon 



