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 
