39 2 



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. 



FIG. 102. Spirillum of cholera, colonies on gelatin plates. (X 100 to 150.) 



(Frankel and P/eiffer.) 

 a. Twenty-four hours old. b. Thirty hours old. c. 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, inj$ 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 of Infectious Diseases. Vol. II. No. 3. June 24, 1905. 

 fKolle in Kolle and Wassermann. Vol. III. 1903. p. 23. 



