AGGLUTINATION 187 



also allied species, though usually not to the same extent ; 

 anti- typhoid serum, for example, may agglutinate not 

 only the typhoid bacillus, but also, though to a less degree, 

 members of the paratyphoid group. As the result of 

 infection or of inoculation with an organism, agglutinins 

 may, however, be produced which agglutinate not only 

 the organism of the infection, but also other organisms 

 e.g. typhoid serum may agglutinate the B. coli as well 

 as the B. typhosus and typhus serum B. typhosus and M. 

 melitensis. The agglutinins acting on the infecting organ- 

 ism may be termed primary or homologous, those acting 

 on other organisms secondary or heterologous. In a case 

 of double infection each organism may produce its own 

 primary agglutinin, so that the agglutination of two 

 species by a serum may be due to the presence either of a 

 primary and a secondary agglutinin or of two primary 

 agglutinins. Castellani, 1 by applying the saturation test 

 (p. 193), found that an organism would absorb both its 

 primary and secondary agglutinins, but would not absorb 

 two different primary agglutinins. This test, therefore, 

 would distinguish a double infection from a single one. 

 Thus, if a typhoid serum agglutinated both the B. typhosus 

 and the B. coli, and the serum after saturation with typhoid 

 culture still agglutinated the B. coli, this would point to 

 an infection with the latter as well as with typhoid. The 

 formation of primary and secondary agglutinins may be 

 brought about as follows : In the bacterial cell there are 

 several substances, each of which forms its own agglutinin. 

 The cells of two bacterial species we can imagine both 

 contain three or four substances capable of producing 

 agglutinins, and it may happen that one of these in each 

 species is the same and will produce the same agglutinin 

 the secondary agglutinin and, therefore, the serum 

 produced by each bacterium will agglutinate the other. 

 1 Zeitschr. /. Hy<j., xl, 1902, p. 1. 



