BACILLUS TYPHOSUS. 417 
living germs of the respective diseases. He also de- | 
scribed the occurrence of a peculiar phenomenon when 
a portion of a fresh culture of the typhoid bacillus on 
agar is added to a small quantity of the serum of an 
animal immunized against typhoid and the mixture 
injected into the peritoneal cavity of a non-immunized 
guinea-pig. After this procedure, if from time to time 
minute drops of the liquid be withdrawn in a capillary 
tube and examined microscopically, it is found that the 
bacteria, which were formerly and in control animals, 
which remain, actively motile and vigorous, become 
in a very short time, under the influence of the serum, 
entirely motionless and later dead. They are first im- 
mobilized, then they become somewhat. swollen and 
agglomerated into balls or clumps, which gradually 
become paler and paler, until finally they are dissolved 
in the peritoneal fluid. This process takes place regu- 
larly in about twenty minutes, provided a sufficient 
degree of immunity be present in the animals from 
which the serum was obtained. The animals injected 
with the mixture of the serum of immunized animals 
and typhoid cultures remain unaffected, while control 
animals treated with a fluid containing only the serum 
of non-immunized animals mixed with typhoid cultures 
die. Pfeiffer claimed that the reaction of the serum 
thus employed is so distinctly specific that it may serve 
for the differential diagnosis of the cholera vibrion or 
typhoid bacillus from other vibrions or allied bacilli, 
such as Finkler’s and Prior’s or colon groups. 
In March, 1896, Pfeiffer and Kolle published an 
article entitled ‘‘ The Differential Diagnosis of Typhoid 
Fever by Means of the Serum of Animals Immunized 
Against Typhoid Infection,’ in which they claimed 
27 
