218 STUDIES IN IMMUNITY 



it would have been hasty to assert that specific sensitizers are present 

 in antimicrobial sera in general. Hitherto these bodies have been 

 demonstrated with certainty only in the specific antisera for the 

 true cholera or other similar vibrios. 



This is quite understandable when we come to consider the known 

 method of demonstrating the sensitizing substance. This method 

 described by one of us in the case of cholera serum, and later applied 

 to hemolytic sera, is as follows: 



Mixtures are made in suitable proportions of cholera vibrios 

 with normal serum and specific serum respectively. In the second 

 mixture an intense destruction of the bacteria occurs, as is evidenced 

 by their complete granular transformation. In the first mixture, 

 on the contrary, a morphologically similar, but relatively insignifi- 

 cant, change takes place. Both cholera serum and normal serum 

 lose their bactericidal power completely on being heated to 55 de- 

 grees. But the addition of a trace of heated cholera serum to 

 unheated normal serum forms a mixture that is as strongly bac- 

 tericidal as fresh cholera serum; it enables it to produce granules 

 in the vibrios. This proves that heated cholera serum, although 

 harmless alone, still favors the bactericidal energy of the alexin of 

 normal serum. 



This method, then, of demonstrating a sensitizer depends on the 

 presence of some microscopically detectable lesion of the bacterium 

 affected; bacteriolysis must occur. With hemolytic sera the cri- 

 terion is the occurrence of hemolysis. 



Not all bacteria, however, fulfill this condition. Many of them 

 not only are undestroyed, but remain apparently unchanged in 

 the presence of serum from highly immunized animals. In such 

 cases the method described is of no avail and should be replaced by 

 another. 



We have, indeed, another method to offer for the demonstration 

 of sensitizers in the sera of animals immunized against such bacteria 

 as B. pestis, first anthrax vaccine, B. typhosus, the bacillus of 

 swine plague, and B. proteus vulgaris. 



But first we must recall an experiment described a year ago in 

 the Pasteur Annals * the essentials of which follow : 



If well-sensitized rabbit blood corpuscles (that is, corpuscles 



* See p. 186. 



