STUDIES ON THE SERUM OF VACCINATED ANIMALS. 43 



usually considered non-pathogenic, may, after a few passages, 

 infect animals quite as well as the typical cholera vibrio. The 

 cholera red reaction is no certain method of diagnosis. Morpho- 

 logically and culturally, then, the separation of Koch's bacillus 

 from other vibrios is impossible. 



The question arises as to whether these vibrios, which are so much 

 alike, always react in the same manner to the bactericidal sera of 

 vaccinated animals. Is the bactericidal property of the serum of a 

 vaccinated animal active only against the species of vibrio used to 

 vaccinate the animal, or is it, on the contrary, a more general property 

 and active against the majority of organisms belonging to the same 

 group? Pfeiffer states that the bactericidal property in the sera 

 of vaccinated animals is specific. We have made a few experiments 

 along this line. The sera of several guinea-pigs and rabbits, each 

 of which had been immunized against a certain vibrio, were tested 

 for their bactericidal property against several different vibrios. 



I. Serum of a rabbit immunized against the Massaouah Vibrio. 



NUMBER OF COLONIES. 



II. Serum of a guinea-pig immunized against the Massaouah 

 Vibrio. 



* Innumerable. 



