CHOLERA VIBRIO 503 



limits of growth are 10 C. and 43 to 45 C. respectively, the optimum 

 being 37 C. They are very sensitive to drying; according to Giinther, 1 

 three hours' drying kills them. They remain alive, however, for weeks 

 in culture media. An exposure to 60 C. for thirty minutes usually 

 kills them. Freezing at 10 C. has little effect even if the exposure is 

 prolonged. They will remain viable in impure water for from one to 

 two weeks on the average. 



In feces they may remain alive for seven to nine months if air is 

 excluded, according to Zlatogoroff. 2 Under ordinary conditions, 

 however, they remain viable for much shorter periods of time in feces. 

 According to Forster, 3 the organisms are very sensitive to acids 

 and to germicides. According to his observations, a dilution of 1 

 to 300,000 bichloride of mercury kills them in five minutes, and 

 1 to 3,000,000 in ten minutes. These results have not been corrob- 

 orated and it is very likely that they are not markedly more sensitive 

 to disinfectants than the ordinary pathogenic intestinal bacteria, as 

 the typhoid bacillus. Behring 4 has found that 0.5 per cent, carbolic 

 acid will nearly kill cholera organisms after an exposure of an hour. 

 Bichloride of mercury in a dilution of 1 to 1000 kills them in ten 

 minutes, and 5 per cent, carbolic in less than fifteen minutes. 



Products of Growth. Cholera organisms produce in sugar-free pro- 

 tein media an active soluble gelatinase which dissolves gelatin and also 

 blood serum. Some strains elaborate a soluble hemolysin. 5 No other 

 enzymes are known. 



One of the striking reactions of the organism is the so-called 

 "cholera-red reaction," or the nitroso indol reaction. The addition 

 of acid, either sulphuric or hydrochloric or nitric, to a forty-eight-hour 

 culture of cholera vibrios grown in sugar-free nutrient broth or in 

 peptone solution, will develop the well-known reddish-brown color 

 indicative of the indol reaction. The organisms appear to form 

 nitrites from the protein constituents of the medium. The reactive 

 substance was regarded by Poehl 6 as a skatol derivative. This view 

 appears to have been accepted by Bujwid 7 and Dunham. 8 Brieger, 9 

 however, regards it as an indol derivative. It is probable that Brieger's 

 explanation is the correct one. The substance formed is nitroso indol, 



1 Bakteriologie, p. 644. 2 Centralbl. f. Bakt., 1911, Iviii, 14. 



3 Hyg. Rund., 1893, 722. * Ztschr. f. Hyg., 1890, ix, 400. 



6 See Public Health Reports, 1912, xxvii, No. 11, for full details. 

 6 Ber. d. deutsch. chem. Gesell., 1886, xix, 1162. 



7 Centralbl. f. Bakt., 1888, iv, 494. 



8 Ztschr. f. Hyg., 1887, ii, 340. 9 Deutsch. med. Wchnschr., 1887, No. 15. 



