ON THE MODE OF ACTION OF PREVENTIVE SERA. 87 



well produce slight hemorrhages, and we know that even a small 

 amount of blood serum will affect vibrios in presence of the pre- 

 ventive substance. 



Pfeiffer, moreover, was unable to find the almost instantaneous 

 occurrence of phagocytosis in animals prepared by a previous 

 injection of bouillon, under which conditions it will be recalled the 

 vibrios immediately encounter a large number of phagocytes. It 

 may be that if one injects a large amount of bacterial emulsion 

 at a low temperature a momentary paralysis of the phacocytes 

 may be caused and an extracellular transformation may therefore 

 occur. It does not seem evident that Pfeiffer's conditions were 

 essentially different, which fact renders his results still more inex- 

 plicable, as we regularly obtain rapid phagocytosis under these 

 conditions. 



Pfeiffer mentions the case of a goat that had been well immunized 

 and that died of intoxication following a subcutaneous injection of 

 vibrios ; in this instance the destruction of the culture was brought 

 about, according to Pfeiffer, entirely without the aid of phagocytes; 

 no white cells were found at the point of inoculation, although the 

 cultures were negative. When dealing with well-immunized animals 

 a few scattered leucocytes may be sufficient to give the body fluid 

 a distinct bactericidal power. What is more, it is quite probable 

 that in a dead animal the diffusion of bactericidal substances does 

 not follow the laws that obtain in a living animal. We know, indeed, 

 that when leucocytes are taken out of the animal body they liberate 

 certain substances more readily than they do under normal condi- 

 tions, and the leucocytes in a dead or dying animal can scarcely be 

 considered to be under normal conditions. 



II. THE EFFECT OF SERA ON BACTERIA IN VITRO. THE 

 DIAGNOSIS OF BACTERIA BY SERUM. 



Before endeavoring to determine the mechanism of passive 

 immunity more exactly we must consider the exact effect of 

 serum on vibrios in vitro. To be perfectly clear, we must consider 

 this subject from the beginning, which will necessitate the repeti- 

 tion of certain details that have already been published. 



In the first place we may recall that the serum of an immunized 

 animal causes the granular transformation of the vibrio used for 



