SPECIFICITY OF SERUM. 227 



The same line of reasoning would explain the in- 

 creased agglutinating power of an anticolon serum 

 for the typhoid bacillus. 



A further elaboration of this principle may be 

 made in a case in which two different strains of 

 the same organism (typhoid bacillus) have some- 

 what different agglutinogenic molecules; conse- 

 quently the homologous immune serums for the 

 two organisms might not coincide in their ag- 

 glutinating powers for a third strain of the bacil- 

 lus. 



In view of the points mentioned, it is clear that |^JJ^ tancc o 

 specificity of a given serum may be determined 

 only by diluting the serum to such an extent that 

 the coagglutinins practically are eliminated, the 

 chief agglutinin being present in so much greater 

 concentration that it is still able to agglutinate 

 the homologous bacterium. 



Theoretically, it is also important for the spe- 

 cificity of the reaction that the particular strain 

 of the organism to be used for the test correspond 

 in its agglutinogenic molecules or receptors with 

 those of the strain used for the immunization ; the 

 agglutinogenic receptors should be typical for the 

 organism. 



It is doubtful if group agglutination occurs 

 among all closely related bacteria, inasmuch as 

 Kolle found that it did not exist among the vib- 

 rios. 



It is thought possible that the multiple agglu- Dilutions. 

 tinating power of a serum may be caused by mixed infection*. 

 infections in some instances. Although this is to 

 be kept in mind, one should not overestimate its 

 diagnostic importance, because a similar multi- 



