110 AGGLUTINATION 



Group Agglutination. 



On testing the titer of a strongly agglutinating typhoid serum, and a 

 strongly agglutinating cholera serum, against typhoid, paratyphoid, colon 

 and cholera bacteria, the results will be the following : 



The cholera serum acts strictly in accordance with the rules stated 

 above for specific agglutinins, i.e., marked agglutination with homologous 

 bacteria; very weak, with heterologous. The typhoid serum on the other 

 hand, although it fulfills the same requirements in the main, nevertheless 

 it manifests some important differences when mixed with heterologous 

 bacteria. It has practically no influence upon the cholera vibrio with which 

 the typhoid bacillus is not at all related; agglutination of i :io can be 

 attained even by a normal serum. The colon bacillus which closely re- 

 sembles the typhoid, morphologically, but which has very different bio- 

 chemical properties, is more strongly agglutinated, i 125; while the para- 

 typhoid bacillus, very much like the typhoid bacillus both morphologically 

 and biologically, is agglutinated even in larger dilations, i : 100. This entire 

 phenomenon is an expression of the biological relationship of the various 

 bacterial groups and is known as group reactions. 



An understanding of group reactions is to be found in a more 

 Partial Ag- complete conception of specificity. From this source we have 

 glutination. learned that the difference in antibodies is influenced by the 

 dissimilarity of the injected antigen. For example, the differ- 

 ence between the cholera and typhoid agglutination is caused by the differ- 

 ence existing in the protoplasmic structure of the respective bacteria. As 

 these bacteria, however, are not constituted of a distinct chemically de- 

 fined substance, but made up of a mixture of various substances, there 

 may be a number among them which can act as antigens. If, figuratively 

 speaking, there are five different elements in the body of the typhoid bacillus 

 which can act as agglutinogens, i.e., antigens, these should be able to form 

 according to the law of specificity five different agglutinins. On mixing a 

 typhoid serum with typhoid bacilli, one brings together five distinct antigen 

 antibody combinations and consequently complete and thorough action 

 results of this union. A biological relationship of bacteria implies the exist- 



