238 BACTERIOLOGICAL EXAMINATION OF WATER. 



peritoneal contents is withdrawn with a glass capillary tube 

 and examined in hanging-drop and " cover-glass " preparation. 

 If the vibrios injected have been true cholera spirilla, they will 

 become swollen up into round motionless masses which eventu- 

 ally become broken down into granular masses and disappear. 

 If at the end of twenty minutes the peritoneal contents show 

 unaltered and motile vibrios, they cannot be true cholera spirilla, 

 but belong to some other species. If, however, the vibrios are 

 dead but otherwise unchanged, two conditions of things are 

 possible, viz., either the bacilli are true cholera vibrios which 

 have been acted on by the specific bactericidal substances, or they 

 are saprophytic vibrios which, without any question of a specific 

 action, have been acted on by the bactericidal substances 

 present in the normal guinea-pig. In order to diagnose between 

 these two possibilities, one loopful of the suspected culture 

 must be added to 1 c.c. of bouillon containing O'Ol c.c. of normal 

 serum, and the mixture then injected into the peritoneal cavity 

 of a guinea-pig. If the vibrios are found alive and motile at 

 the end of the time when, in the cholera serum experiment, they 

 were completely dissolved, then it is probable that they belong 

 to the cholera bacilli species. Unfortunately it is possible that 

 vibrios which appear to be killed by normal serum may still be 

 true cholera spirilla, for it has been shown that Koch^s vibrios 

 which are enfeebled and have lost their virulence, may be 

 destroyed by normal peritoneal fluid. If, therefore, the sus- 

 pected vibrios disappear in the control experiment, Pfeiffer 

 recommends that the suspected culture be used to immunise a 

 guinea-pig. The serum from this animal must then be tested 

 as to its bactericidal action on true cholera vibrios. Do'mtx, 

 acting on Pfeiffer's suggestion, showed that an old culture of 

 cholera from Calcutta produced a serum which had a specific 

 bactericidal effect on cholera vibrios. 



The agglutination test (or Durham-Gruber reaction) may.be 

 performed in the same manner as described under B. typhosus. 

 The serum is generally used in dilutions varying from 1-10 to 

 1-120. This test is more suitable for general hygienic work 

 than Pfeiffer's reaction. It requires to be performed with care, 

 and, as in the case of the B. typhosus, the dilution of the serum 

 employed is a matter of great importance. Durham prepared 



