PATHOGENIC BACTERIA. 399 



sists in testing the suspected organism with serum from an 

 animal immunized with cultures of cholera bacilli, as already 

 explained above. 



The serum employed in this test must of course be prepared 

 by injecting the animal furnishing the serum with pure cultures 

 of a strain of undoubted origin. The potency of the serum 

 itself must be determined by trial upon cultures of known 

 identity. This is done* by preparing a series of dilutions of 

 the serum with normal salt solution in test-tubes, each test-tube 

 to contain i c.c. of the diluted serum. To each of the series 

 of tubes one loopful from an eighteen-hour agar culture is 

 added, and the tubes so prepared are placed in the incubator 

 at 37° C. for one hour. The strength of the serum is denoted 

 by the dilution which causes an agglutination which can be 

 seen with the naked eye. Thus a serum of the strength 

 i-iooo is such that i c.c. of a dilution of i part of serum to 

 999 parts of normal salt solution causes a visible clumping 

 of I loopful of the cholera spirillum taken from an i8 hour 

 agar culture. If the strength of the serum is thus determined, 

 and if a culture obtained from the stool of a person presenting 

 suspicious symptoms of cholera, it is safe to make a positive 

 diagnosis. 



For examining suspected water for the spirillum of cholera 

 Kollef advises the following method: An enriching fluid 

 is first prepared which consists of i liter of distilled water 

 in which are dissolved by warming loo grams Witte's peptone, 

 100 grams salt, i gram potassium nitrate, and 2 grams crys- 

 tallized carbonate of sodium. The solution is filtered, and 

 distributed into flasks, 100 c.c. in each flask, and sterilized. 



At least I liter of the water to be examined is taken, and to it 

 is added the contents — 100 c.c— of one of the flasks of enrich- 

 ing fluid. It is then distributed into flasks, 100 c.c. in each 



*Kolle and Wassermann. Bd. III. 1903. p. 39. 



fKoUe and Wassermann's Handbuch. Vol. III. 1903. pp. 44-45. 



