284 AGGLUTININS 



the resistance of Bacillus coli to acid agglutination at any hydrogen ion 

 concentration, and, indeed, he has found certain strains of nearly all 

 species of bacteria to be non-agglutinable within the tested reaction 

 limits. Gillespie 6 found that pneumococci belonging to the serologic 

 types I and II have, as a rule, narrow zones of agglutination. The 

 optimum hydrogen ion concentration was found different in the two 

 cases, while other pneumococci had broad zones or, in a few cases, 

 narrow zones not coincident with those occupied by the typical organ- 

 isms. For a technic of acid agglutination see page 310. 



Mechanism of Agglutination. The true nature of the phenomenon 

 of agglutination is unknown, as is shown by the number of theories ad- 

 vanced. Thus 



1. Gruber's idea of the mechanism of this phenomenon was. that the 

 agglutinin so changed the bacterial membrane as to render it more 

 viscous, and that this increased viscosity caused the bacteria to adhere 

 and form clumps. No visible changes in the organisms or red corpuscles 

 can, however, be seen. 



2. Paltauf's theory is somewhat similar, he believing that the agglu- 

 tinogen is precipitated on the surface of the bacteria by union with the 

 agglutinin, with the formation of a sticky substance. He cites evidence 

 that tends to show that such substances are actually thrown out from 

 the bacteria during agglutination, as may be seen in a properly stained 

 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- 



1 Jour. Exper. Med., 1914, 19, 28 



