MECHANISM OF ANTIGEN-ANTIBODY REACTIONS 209 



vanced an liy])otliesis which was based upon Kraiis's work but was 

 really the beginning of our knowledge of flagellar agglutinins 

 although Gruber had suggested that flagella might be important. 

 Dineur conceived of the agglutination reaction as due to the forma- 

 tion of an "adhesive" substance on the flagella with the subse- 

 quent interlacing of the latter. 



Bordet's Objections to Current Theories. — Bordet carefully 

 considered Gruber 's hypothesis that bacteria were agglutinated 

 because the agglutinin caused them to become sticky. He could 

 understand how changes in the coll membrane might make them 

 ''adhere" Avhon tliey came in contact wnth each other, but this 

 tlieory did not explain wliy they came together. In fact, there was 

 no experimental evidence to show that a change in the membrane 

 occurred. He knew from experience that hemagglutinins were 

 developed in animals when red cells were injected and he watched 

 the agglutination of red cells by immune serum under the micro- 

 scope and could see no change in the membrane. Since red cells 

 were agglutinated by their immune serum and since they did not 

 possess flagella, he felt that flagella were not necessary factors 

 in the phenomenon of agglutination, as suggested by others. Be- 

 sides, Widal had shown that formalized cultures were agglutinated 

 as readily as living suspensions and this he regarded as additional 

 evidence. He then compared hemagglutination, bacterial agglu- 

 tination, serum precipitation, and bacterial protein precipitation 

 by their respective immune sera and saw that while they differed in 

 that each antigen had in the beginning combined with its specific 

 antibody, yet the end-result was quite similar; i.e., clumping or 

 precipitation. 



Bordet's Two-Phase Theory. — Thus Bordet considered two 

 steps or phases in immunological reactions of this kind: First, one 

 which involves specificity, the union of antigen and antibody, and 

 second, a common mechanism of agglutination or precipitation. It 

 was this second phase, involving a mechanism of agglutination 

 common to all, that he set about investigating. At the beginning 

 of his work he was very much impressed with Duclaux's theories 

 as to the mechanism of coagulation and his conclusion that ag- 

 glutination is a phenomenon of coagulation. 



