582 BACTERIOLOGY. 



The serum is now known to be feebly antitoxic and 

 strongly bactericidal. This specific change in the blood 

 is observed to take place from eight to ten days after 

 the termination of an attack of cholera and reaches its 

 maximum during the fourth week of convalescence, 

 after which it declines rapidly and disappears entirely 

 in about two or three months. Similar antitoxic or 

 bactericidal substances exist also in the serum of guinea- 

 pigs, rabbits, and goats, when these animals are immu- 

 nized artificially against cholera by subcutaneous or 

 intraperitoneal injections of living or dead cultures. 

 These specific substances present in the blood of chol- 

 era-immune men and animals act only upon organisms 

 similar to those with which they were infected ; but, 

 as Pfeiffer showed, this specific relation, which is found 

 to exist between the antibacterial and protective sub- 

 stances produced during immunization and the bacteria 

 employed to immunize the animals, is not confined 

 alone to cholera. The discovery, moreover, of this 

 specific reaction of the blood-serum of immunized men 

 and animals when brought in contact with the spirilla, 

 has given us an apparently reliable means of distin- 

 guishing the cholera from all other vibrios, and the 

 disease cholera from other similar affections, both of 

 which have proved to be of great value, particularly in 

 obscure or doubtful cases, in which heretofore the only 

 method of differential diagnosis available viz., by 

 cultural tests was often unsatisfactory. 



Cholera in man is an infective process of the epithe- 

 lium of the intestine, in which the spirilla clinging to 

 and between the epithelial cells produce a partial or 

 entire necrosis and final destruction of the epithelial 

 covering, which thus renders possible the absorption of 



