i 5 2 AIDS TO BACTERIOLOGY 



nitrites has proceeded sufficiently far to cause the appear- 

 ance of the indole reaction (a distinct rose-madder 

 tint) on the addition of a few drops of pure sulphuric 

 acid. 



Many other organisms besides Koch's comma also 

 produce indole and nitrites in sufficient quantities to 

 yield the indole reaction, but not in this time (twelve 

 hours it can often be obtained in five or six). The 

 commas tend to form a delicate film on the surface of 

 the medium. This should be examined, care being taken 

 not to shake the flasks, so that the film may be preserved. 

 In cases of true cholera the organism frequently cannot 

 be demonstrated in the stool when the patient is on the 

 way to recovery, so that the inability to demonstrate the 

 organism in cases three or four days from the commence- 

 ment of the attack must not be taken as evidence that 

 the disease was not true cholera. 



An agglutination reaction may be performed with the 

 isolated vibrio. (Agglutination reactions with the patient's 

 serum on a pure strain of the vibrio are said to be of 

 doubtful value.) 



Major Glen Liston (Kept. Bombay Bact. Lab., 1913) 

 says the distinction between cholera and ' cholera-like ' 

 vibrios is based solely on their behaviour with a standard 

 agglutinating cholera serum, as no morphological or 

 cultural differentiation was discovered that could dis- 

 tinguish in a trustworthy way between the cholera and 

 the ' cholera-like ' strains. 



Hccmolysis Test. True cholera vibrios do not hacmolyse 

 apparently even after prolonged contact, while several 

 similar vibrios are ha3molytic. An emulsion of a young 

 agar culture in 5 c.c. of normal salt solution is. made, 

 O'l c.c. of which emulsion is mixed with - 9 c.c. of normal 

 salt solution, and then a drop of a suspension of well- 

 washed rabbit corpuscles added. Haemolysis is gener- 

 ally apparent in twe e to twenty-four hours if the 

 organism produces a haemolysin, but some of the cholera- 

 like vibrios described by Ruffer require forty-eight 

 hours. 



Saturation Test. The saturation of a specific agglu- 

 tinating scrum with the homologous organism removes 

 most or all of the specific agglutinin. (a) Ten loopfuls of 

 a young agar culture of the isolated vibrio are mixed with 



