THE MECHANISM OF AOGLUTINATIOy 185 



It is believed that ag'glutiMins are eell receptors, wliich have a group 

 n'itli a chemical affinity for the agglutinogen of the bacterial proto- 

 plasm, and also another group which brings about the agglutination. 

 They are, therefore, more complex than the simple receptors that 

 unite with toxins, and are called receptors of the second order. Ac- 

 cording to Ohno **' the reaction of agglutinin and antigen is in con- 

 stant proportions, and seems to be a chemical rather than a physical 

 reaction. Coplans '^^ finds this reaction associated with an increase 

 in conductivity in the solutions, but whether this depends upon the 

 agglutinin reaction itself, or upon associated processes, is question- 

 able. 



Just what constituent of the bacteria acts as the stimulus to the 

 production of the agglutinin is unknown. Apparently, there are 

 at least two bacterial substances with this property, one of which 

 seems not to be a protein, since it is soluble in alcohol and gives no 

 biuret reaction, and resists temperatures up to 165°. The other gives 

 all protein reactions, and is destroyed by heating to 62°. We con- 

 sider, therefore, that there are two agglutinogens in the bacterial 

 cell, one, thermostable, the other, thermolabile. The difference in the 

 function of these two agglutinogens is still a matter of dispute. 

 Likewise, the question as to whether they occur in the membrane or 

 within the bacterial cell is still open, but Craw found that the insolu- 

 ble residue of crushed typhoid bacilli, after being washed free of all 

 soluble constituents, was but slightly agglutinated by active serum; 

 therefore, the agglutinogens are probably soluble intracellular sub- 

 stances. 



Agglutinated bacteria can be again separated from one another by 

 the action of organic and inorganic acids, alkalies, acid salts, and 

 by heating to 70° or 75°, and after once being separated they can- 

 not be reagglutinated by fresh semm.®^ 



The Mechanism of Agglutination. — Tliis has been a fruitful field 

 of research, in which the application of physical chemistry has been 

 very profitable. At first it was believed that the clumping was 

 brought about by loss of motility, until it was found that non-motile 

 bacilli were equally affected. Similarly, the hypothesis of adhesion of 

 the flagellfe was disposed of. Gruber'" and others supposed that a 

 sticky substance, " glahrificm,'" was absorbed from the senim by the 

 bacilli, which caused them to adhere on contact with one another; 

 but this does not explain the flocking together of non-motile bacilli. 

 Paltauf considered that the specific precipitin (see next section) pro- 

 duced by immunization carried the bacilli down in the precipitate 

 formed, and there is reason to believe that this reaction is of im- 



67 Philippine Jour. Sci., 1008 (3). 47. 



fiSJour. Path, and Bact., 1912 (17). 130. 



eoEisenberg and Volk, Zeit. f. Infektionskr., 1002 (40). 102. 



"0 For complete bibliojrraphy, see Craw, Jour, of Hygiene. 1005 (.">). 113. 



