VITALITY. 255 



authorities, the organism remains alive in the gelatin tube 

 for from eight weeks to two years. 



On agar-agar stroke cultures a shining, moist, grayish- 

 white growth develops along the line of inoculation (Fig. 

 112). The growth on blood-serum is exactly like that on 

 agar, but the blood-serum is liquefied. 



Bouillon, even when very dilute, is soon clouded, with the 

 formation of a surface membrane. The culture in^milk is 

 destroyed by the formation of lactic acid. On potgjp a 

 grayish-brown, translucent, very delicate membrane is formed, 

 even when the potato is acid. 



If it is desired to preserve the cholera spirillum for a long 

 time, it should be transplanted into sterilized water, in which 

 it develops quite rapidly and persistently. It also retains its 

 vitality for a long time if wrapped in moist linen. 



The cholera germ also produces mtritcs and indol. The 

 addition of a few drops of sulphuric or hydrochloric acid to 

 cholera cultures containing peptone gives a beautiful red color, 

 the so-called cholera-red reaction, which is characteristic of 

 this organism. The cholera bacillus is one of a very few 

 germs which give the nitroso-indol reaction. This is used as 

 a means of differentiation. 



Vitality : The cholera spirillum possesses little resisting 

 power. A four minute exposure to a temperature of 52 C. 

 is fatal. Drying also destroys it very quickly within a few 

 hours. The addition of a very small quantity of acid to the 

 culture-medium immediately inhibits the growth of the organ- 

 ism. Pettenkofer claimed that when the cholera organism 

 is brought in contact with normal gastric juice it is destroyed 

 immediately. He demonstrated the truth of this by swallow- 

 ing a pure culture of cholera. In the presence of a little 

 moisture the germ retains its vitality for a long time. When 

 associated in culture with saprophytic germs its development 

 ceases. Freezing destroys the germ in a few days. A 10 

 per cent, solution of mercuric chloride or a 3 per cent, solu- 

 tion of carbolic acid is effective immediately. Milk of lime 

 and sulphate of copper are excellent disinfectants for choleraic 

 discharges. High temperatures always favor the development 

 of the germ, 



