Facts bearing on acquired immunity 213 



the round granules may be seen swollen vibrios, and others which 

 have kept their normal form, but all are absolutely motionless. Some 

 of these granules are gathered into small 

 clumps, others remain isolated in the fluid. 

 When to the hanging drop containing these 

 transformed vibrios a small quantity of 

 a dilute aqueous solution of methylene blue 

 is added, we observe that certain granules 

 stain very deeply, whilst others take on 

 merely a very pale tint, scarcely visible. 

 Many of these granules are still alive, because 

 it is easy to watch them develop outside 

 the animal and elongate into new vibrios. 

 A large number of the granules, howeTer, **% 

 no longer exhibit any sign of life and are showing Pfeiffer's phe- 

 evidently dead. R. Pfeiffer and certain other nomenon. 

 observers affirm that the granules may be 



completely dissolved in the peritoneal fluid just as a piece of sugar 

 dissolves in water. We have repeatedly sought for this disappearance 

 of the granules in hanging drops of the peritoneal fluid, without 

 being able to find any diminution in the number of these trans- 

 formed vibrios, even after several days ; nor have we been able to 

 observe the phenomenon of the solution of the granules. It is at any 

 rate indisputable that this granular transformation is a manifestation 

 of very profound lesions undergone by the cholera vibrios under the 

 influence of the peritoneal fluid of the immunised animal. 



An attempt has been made to define the mechanism of Pfeiffer's 

 phenomenon more exactly, and Fischer 1 has sought to refer it to 

 osmotic action, exercised by the salts of the fluids in which the [225] 

 vibrios are suspended. These vibrios, under the action of media 

 richer or poorer in salts than is the fluid in which they had developed, 

 are said to present an increase of their internal pressure, in con- 

 sequence of which the vibrios swell up or allow a spherical droplet 

 of protoplasm to escape at one of their poles. This explanation was 

 inadequately supported by its author and cannot be regarded as 

 proved. On the other hand, one is compelled to the conclusion that 

 the granular transformation is due, as we shall see later, to a fermen- 

 tative action of the peritoneal exudation. 



Whilst the vibrios are undergoing this transformation in the 

 1 Zltchr.f. Ht/g., Leipzig, 1900, Bd. xxxv, S. 1. 



