58 STUDIES IN IMMUNITY. 



that body fluids have upon it and acts therefore as an index of 

 bactericidal properties of these fluids. 



We have done a number of experiments with Pfeiffer's phenome- 

 non for various purposes which we shall consider collectively for the 

 purpose of exposition. The method employed was uniform and 

 may be detailed once for all. 



II. THE PRODUCTION OF PFEIFFER'S PHENOMENON IN VITRO 

 THROUGH THE COMBINED ACTION OF PREVENTIVE SERUM 

 AND NORMAL SERUM. 



Metchnikoff produced Pfeiffer's phenomenon in vitro by mixing 

 the cholera vibrio with preventive serum and then adding leu- 

 cocytes drawn from the peritoneal cavity to this mixture. These 

 leucocytes may, however, come from another source. We have 

 found that the cholera vibrio (Oriental Prussia) is rapidly changed 

 into rounded granules when placed in a mixture of preventive serum 

 and defibrinated blood of a normal guinea-pig. The control of de- 

 fibrinated blood without preventive serum gave a negative result. 

 When the specific serum is absent the great majority of the vibrios 

 remain quite motile and extracellular changes only rarely occur. 

 The leucocytes of the defibrinated blood, to be sure, take up a few 

 vibrios that become transformed within the protoplasm of the 

 leucocyte, but the preventive serum is necessary to produce trans- 

 formation in the surrounding fluid. 



Metamorphosis takes place under these conditions quite as well as 

 in the animal body, but more rapidly at body temperature than at 

 room temperature. The defibrinated blood used in the experiment 

 may be obtained from various animals; guinea-pig, rat, rabbit, or 

 goat, but human or guinea-pig blood gives the most distinctive and 

 demonstrable granulations. In preparations with rat or rabbit 

 blood it is rather difficult to find the vibrios, as the bactericidal 

 effect is apparently so intense that the granules rapidly lose their 

 staining reaction. 



The preventive serum used may have been kept for some time, 

 but the defibrinated blood from the normal animal must have been 

 obtained recently. When kept for a few days, even if protected 

 from strong light, it loses some of its properties. 



