STUDIES ON THE SERUM OF VACCINATED ANIMALS. 65 



V. FACTORS CONCERNED IN THE PRODUCTION OF PFEIFFER'S 

 PHENOMENON IN VITRO. 



Let us consider the experiment for producing the granular 

 transformation of the cholera vibrio in vitro by the combination 

 of normal serum and serum of an immunized goat. We repeat 

 that it is not necessary for cells to be present either in the preven- 

 tive serum or in the normal serum to produce a complete Pfeiffer's 

 phenomenon. 



There are three factors necessary in the experiment ; each of these 

 factors may be studied in turn and we may determine whether there 

 are conditions that render these factors unfit to produce the phe- 

 nomenon and also whether any one of them may be omitted or 

 replaced by any other factor. The first factor is the cholera vibrio. 

 We have already seen that the cholera vibrio from Eastern Prussia 

 which was used in producing the anticholera serum may be replaced 

 by any other of the true vibrios. There are two other factors: the 

 normal serum and the preventive serum. Is the presence of both 

 of these substances necessary? Or may one of them be omitted and 

 the phenomenon still occur? These are the first questions that arise. 

 We already know that the normal serum employed has little or no 

 power in itself to change the form of the vibrios. 



The preventive serum used in these studies was from a goat that 

 had been well vaccinated against the Eastern Prussia vibrio. It 

 produces no transformation of vibrios in any dose when not asso- 

 ciated with normal serum. When used alone the only effect that 

 this serum has on vibrios is to immobilize them. A very small 

 amount of serum rapidly paralyzes their motility. It is also to be 

 noted that the vibrios collect in small clumps in the fluid.* 



The serum we first used had been drawn from the goat three weeks 

 previous to our experiments. It might reasonably be supposed 

 that during this period the serum had lost some of its properties, 

 since it is known that the bactericidal substance is easily affected. 



* We have not been able to decide whether this clumping is an active phenome- 

 non due to the vibrio itself or a purely physical affair. If the red blood cells 

 of a normal guinea-pig are placed in their proper serum, they diffuse uniformly and 

 soon collect at the bottom of the hanging drop. But when our protected goat 

 serum is added to such normal serum the corpuscles collect in small separate 

 clumps and give the drop a granular appearance. 



