Immunity against pathogenic micro-organisms 165 



When, instead of cholera vibrios of medium virulence, we take 

 a variety completely deprived of pathogenic activity, it is sometimes 

 observed that certain of these organisms, when injected into the 

 peritoneal cavity of the normal guinea-pig, become transformed into 

 spherical granules in the fluid of the exudation without any direct [175] 

 co-operation of the phagocytes. This transformation into granules 

 was first studied by R. Pfeiffer 1 and hence has been termed Pfeiffer's 

 phenomenon. It is of limited occurrence in natural immunity and is 

 produced, as I have been able to demonstrate, only under certain 

 well defined conditions. Pfeiffer's phenomenon is observed in the 

 peritoneal fluid. It commences soon after the injection of the vibrios 

 and takes place during the period of phagolysis. In other parts of the 

 body of the guinea-pig, notably in the subcutaneous tissue and in the 

 anterior chamber of the eye, Pfeiffer's phenomenon does not manifest 

 itself; the animal, none the less, resists the inoculation of the vibrios. 

 Even in the peritoneal cavity, moreover, it is easy to check the 

 granular transformation of the vibrios by means which prevent the 

 production of phagolysis. When we inject into the peritoneal cavity 

 of a guinea-pig a foreign fluid, capable of exciting the phagocytic 

 action, e.g. veal broth, physiological salt solution, urine, etc., we first 

 excite a transitory phagolysis. To this stage succeeds another in 

 which the leucocytes become very numerous and much more resistant 

 than before. If we take advantage of this period of leucocytic 

 stimulation to inject vibrios which have been attenuated as much as 

 possible, we shall observe that they soon become the prey of the 

 peritoneal phagocytes, without manifesting any sign whatever of 

 Pfeiffer's phenomenon. 



It is evident, then, that this extracellular destruction of the 

 vibrios, sometimes observed in the peritoneal cavity, is really the work 

 of the microcytase that has escaped from the phagocytes during their 

 period of transient injury. 



Having analysed the mechanism of natural immunity against 

 certain bacilli, spirilla and vibrios, it will be interesting to determine 

 whether the same rules are to be applied in the case of the cocci. 

 Choice is not difficult since we may equally well fix upon the staphylo- 

 cocci, the pneumococci, streptococci or gonococci. Should we decide 

 upon the streptococcus it is solely because the natural immunity 

 against this micro-organism has attracted the special attention of 



1 Ztschr.f. Hyg., Leipzig, 1894, Bd. xvin, S. 1. 



