44 



STUDIES IN IMMUNITY. 



III. Serum of a guinea-pig immunized against the Vibrio 

 Metchnikovi. 



IV. Serum of a guinea-pig vaccinated against the Cholera 

 Vibrio. (Eastern Prussia.) 



* Innumerable. 



We have not considered it necessary to carry these experiments 

 farther because the results agree wholly with those recently ob- 

 tained by various observers. In fact, we have a method which is 

 much easier to employ than the gelatin plate method to detect 

 whether a given vibrio is susceptible to a given immune serum. 

 This method, which we shall later consider, consists in estimating 

 the susceptibility of the vibrio to granular transformation (Pfeiffer's 

 phenomenon) which occurs when the organism is mixed either with 

 the specific immune serum or the immune serum plus a small 

 amount of fresh normal serum.* It will be seen in the tables which 

 have been given that the bactericidal property of a serum is always 

 more active against the vibrio which has served to vaccinate the 

 animal furnishing the serum, or for those few organisms that are 

 closely allied to the immunizing organism. There is no doubt that 

 the bactericidal effect is highly specialized, since, however similar 

 organisms may be morphologically and culturally, certain of them 

 are wholly unaffected by a serum fatal to others. It is to be noted 



* As will be seen later, the immune serum must have been recently obtained in 

 order to effect a granular transformation of an organism without the addition 

 of fresh normal serum. 



