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 minute drops of the liquid be withdrawn in a capillary 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 



