392 



MANUAL OF BACTERIOLOGY. 



peptone solution in the incubator the addition of sulphuric 

 acid develops a red color, owing to the presence of indol and 

 nitrites— the so-called ''cholera red" reaction. Considerable 

 doubt has recently been cast upon the formation of nitrites by 

 the cholera spirillum.* The cholera-red reaction is not 

 confined to this organism, and is said to differ from the nitroso- 

 indol reaction. 





Kj 



'^i,-' 



Q 



% 



u 



^ 



..1<S 





9i)^ 







Fig. 102. — Spirillum of cholera, colonies on gelatin plates. (X 1°° to 150.) 



{Frdnkel and Pfeiffer.) 

 a. Twenty-four hours old. 6. Thirty hours old. i,. Forty-eight hours old. 



The spirillum of cholera is said to be very sensitive to dry- 

 ing, and, provided the drying be complete, is usually killed 

 within twenty-four hours. It is killedf immediately by the 

 temperature of boiling water, in 5 minutes with certainty at 

 80° C, in one hour at 56° C. It may retain its vitality in water 

 for a long time; observations vary widely in respect to deter- 



*Wherry. Journal oj Infectious Diseases. Vol. II. 

 tKolle in Kolle and Wassermann. Vol. III. 1903. 



No. 3. June 24, 1905. 

 p. 23. 



