SPECIFICITY OF AGGLUTININS 271 



preparation in the form of a precipitate surrounding the bacterial 

 cells. 



3. The presence of some salt is necessary for the occurrence of agglu- 

 tination. Bordet found that if the salts were removed from the serum 

 and from the suspension of bacteria by dialysis and that the two were 

 then mixed, agglutination did not occur, but that if a small amount 

 of sodium chlorid was added, agglutination promptly took place. Ac- 

 cording to this view, therefore, agglutination is a phenomenon of molec- 

 ular physics the agglutinin acts on the bacteria or other cells and 

 prepares them for agglutination by altering the relations of molecular 

 attraction between them and the surrounding fluid, the second phase, 

 the loss of motility, clumping, etc., being brought about by the presence 

 of salt. This second phase, therefore, would be a purely physical 

 phenomenon, the salts altering the electric conditions of the colloidal- 

 like agglutinin-bacterium combination, so that their surface tension is 

 increased. To overcome this the particles adhere together, presenting 

 in a clump less surface tension than if they remained as individual par- 

 ticles. Bordet cites the precipitation of clay as an analogous case: if 

 a little salt is added to a fine emulsion of potters' clay in distilled water, 

 the clay immediately clumps and falls to the bottom, the resemblance 

 between these flakes and the clump of agglutinated bacteria being very 

 striking. 



Specificity of Agglutinins. For a time after their discovery the ag- 

 glutinins were regarded as strictly specific, i. e., a typhoid-immune serum 

 would agglutinate only typhoid bacilli and no others. Gruber early 

 pointed out that an immune serum will frequently agglutinate other 

 closely related organisms, although not usually to so high a degree. 



Group or partial agglutinins, therefore, refer to the presence in a serum 

 of certain agglutinins that agglutinate certain other microorganisms 

 that are morphologically, biologically, and often pathogenetically 

 closely related to the homologous microorganism (the bacterium causing 

 the infection or used in artificial immunization). For example, a ty- 

 phoid-immune serum possesses, besides its greatly increased aggluti- 

 nating power for Bacillus typhosus, some agglutinin for Bacillus para- 

 typhosus, notably above that of normal serum. This is explained by the 

 very close biologic relationship of these bacteria, together with the fact 

 that the agglutinin-producing substance (agglutinogen) is a complex 

 and not a single chemical substance. This has been explained by Dur- 

 ham in the following example: If the typhoid agglutinogen is composed 

 of various elements, A, B, C, D, it is conceivable that the closely related 



