226 INFECTION AND IMMUNITY. 



habit of attributing to the reactions of immunity ; 

 yet a reasonable explanation has been offered for 

 the occurrence. It is probable that the proto- 

 plasms of all cells have certain constituents in 

 common, and that the closer the relationship be- 

 tween two different cells the greater is the simi- 

 larity of their constituents. In view of this prob- 

 ability, Durham has used the following illustra- 

 tion in the explanation of group agglutinations: 

 The typhoid bacillus contains certain constituents, 

 agglutinogenic molecules, which one may desig- 

 nate as a, b, c, d, and e ; these differ among them- 

 selves in unknown respects, but each is able to 

 stimulate to the formation of a corresponding ag- 

 glutinin. The serum, then, would have the ag- 

 glutinin molecules A, B, C, D and E, also differing 

 among themselves, but having at least one property 

 in common that of causing agglutination of the 

 typhoid bacillus by uniting with the correspond- 

 ing agglutinogenic molecules. In this sense noth- 

 ing could be more specific. The Bacillus enteri- 

 tidis, closely related to the typhoid organism, may 

 possess the agglutinogenic molecules c, d, e, f, g, 

 and h, and following the principle expressed above 

 would stimulate, in the body, to the formation of 

 the agglutinin molecules C, D, E, F, G and H. 

 Inasmuch as the agglutinogens c, d and e are com- 

 mon to the two bacilli, the agglutinins C, D and E, 

 which are present in both serums, would affect 

 either of the two organisms. The typhoid serum, 

 however, would contain five agglutinins for the 

 typhoid bacillus and only three for the Bacillus 

 enteritidis, consequently the action would be 

 stronger against the typhoid bacillus; mutato mu- 

 tandis, the same applies to the enteritidis serum 



