AGGLUTINATION. 231 



Theories of agglutination have to do, not with 

 the existence of agglutinin and agglutinogen, but 

 rather with the nature of the reaction between the 

 two, and the influences which bring about the 

 clumping after the reaction has occurred. The 

 original theory of Gruber supposed that the serum 

 so affected the bacteria that they became sticky; 

 consequently, as they came in contact, they were, 

 so to say, glued together. Dineur thought changes 

 occurred in the flagellae of the organisms, a theory 

 which is untenable because some bacteria are ag- 

 glutinable which do not possess flagellae. Em- 

 merich and Loew refer agglutination to the action 

 of an enzyme which is produced by the bacterium 

 itself, a theory which is not given general credence. 

 Bordet excludes the vitality or motility of the or- 

 ganisms as factors, and believes that the process is 

 purely a physical one, because of the fact that 

 some known chemical substances may be made to 

 precipitate or to agglutinate certain other sub- 

 stances (precipitation of colloids by salts) ; the 

 theory presupposes some change in the molecular 

 attraction between the microbes and the surround- 

 ing fluid. 



Other theories have to do with the question of 

 precipitation. As previously stated, when the fil- 

 trates of cultures of certain organisms are mixed 

 with their corresponding immune serums, precipi- 

 tates occur in the mixtures. It was mentioned 

 that the substance in the filtrate which takes part 

 in the precipitation may represent, in part, the ag- 

 glutinable substance which has been excreted by 

 the bacteria. Nicolle supposes that the agglutin- 

 able substance resides in the external layer of the 

 bacteria and that when the serum is added a coag- 



