CHOLERA VIBRIO. 471 



tained by transferring a small amount of the sur- 

 face fluid to tubes of liquefied gelatin, then plating 

 the latter. The colonies appear in a few hours as 

 small translucent points from which pure cultures 

 are made on a suitable medium. For more positive 

 identification agglutination tests are performed 

 with anticholera serum. The Eoyal Institute for 

 Infectious Diseases (Berlin) keeps on hand a dried 

 serum of known strength (1-10,000) for this pur- 

 pose. The tests being made with high dilutions, 

 coagglutinins for other vibrios are practically elim- 

 inated. To the agglutination test may be added 

 the "Pfeiffer experiment," in which the protective 

 power of an anticholera serum is determined when 

 guinea-pigs are infected intraperitoneally with the 

 suspected culture. If the serum shows a protective 

 power against this organism which approximates 

 that shown against a known cholera vibrio, or, if 

 the organisms are dissolved, the diagnosis of chol- 

 era is justified. In performing such experiments 

 the serum is mixed with the culture before injec- 

 tion. 



The resistance of the cholera vibrio is very low. Resistance. 

 It dies in about two hours when dried (Koch) and 

 on this account dust infection is thought not to 

 occur. It is killed instantly by the boiling tem- 

 perature, and in five minutes at 80 C. It is ex- 

 tremely susceptible to carbolic acid (killed by 1 

 per cent, in five minutes), corrosive sublimate (1 

 to 2,000,000 or 3,000,000 in from five to ten min- 

 utes), and to acids. Calcium chlorid is an effi- 

 cient disinfectant when thoroughly mixed with the 

 stools. The micro-organism lives in distilled water 

 not longer than twenty-four hours, in ordinary 

 water for several days to several weeks, and in one 



