566 THE CHOLERA GROUP 
study and speculation. The former fails to agglutinate with a specific 
cholera serum, but is strongly hemolytic; the latter also fails to agglu- 
tinate at high dilution, although it acts as an antigen with cholera 
serum in the complement-fixation test. It produces a thermostabile 
solution toxin. 1 
The organisms are aerobic, facultatively anaerobic. They were 
formerly considered to be strongly aerobic; it is doubtful, however, if 
they are markedly more aerobic than other intestinal bacteria. The 
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,'- 
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.^ Under ordinary conditions, how- 
ever, they remain viable for much shorter periods of time in feces. 
According to Forster,* 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 corroborated 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^ has found that 0.5 per cent carbolic acid will 
always kill cholera organisms after an exposure of an hour. Bichlo- 
ride of mercury in a dilution of 1 to 1000 kills them in ten minutes, 
and 5 per cent carbolic acid 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.'' No other 
enzymes are know^n. 
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 PoehF as a skatol derivative. This view appears to have 
been accepted by Bujwid^ and Dunham. ^ Brieger,^" however, regards 
• Kraus and Pribram: Wieii. klin. Wchnschr., 1905, 18, 999. 
2 Bakteriologie, p. 644. ' Centralbl. f. Bakteriol., orig., 1911, 58, 14. 
* Hyg. Rund., 1893, p. 722. ^ ztschr. f. Hyg., 1890, 9, 395. 
« See Public Health Reports, 1912, 27, No. 11, for full details. 
■ Ber. d. deutsch. chem. Gesel., 1886, 19, 1162. 
8 Centralbl. f. Bakteriol., 1888, 4, 494. 
9 Ztschr. f. Hyg., 1887, 2, 337. " Deutsch. med. Wchnschr., 1887, 13, 303. 
