36 IMMUNE SERA 



fairly resistant substances which withstand heat- 

 ing to 60 0., and lose their power only on heating 

 to 65 C. It is possible, therefore, to make a serum 

 bacteriolytically inactive by heating to 55C., and 

 still preserve its agglutinating power. Corres- 

 ponding to the specific combining power of these 

 agglutinins, they possess a haptophore group which 

 effects the combination, and a second group, easily 

 decomposed by acids, which effects the clumping. 

 In the bacterium as well as in the blood cell there 

 exists a substance not yet closely studied, called 

 the agglutinable substance. This also has two groups, 

 a haptophore, which combines with the hapto- 

 phore group of the agglutinin; and a second, more 

 delicate group, which is acted on by the functional 

 group of the agglutinin. 



Nature of the Agglutination Reaction. The union 

 of agglutinin with the agglutinable substance is a 

 chemical reaction, and is quantitative. The amount 

 of bacteria in the emulsion used to test the amount 

 of agglutinin must, therefore, be known. An 

 emulsion one hundred times as dense as another 

 would require one hundred times as much agglu- 

 tinin to give an equally complete reaction. Agglu- 

 tinin acts both on living and on dead bacteria. 



The influence of salts upon agglutination is in 

 a sense comparable to their action upon the pre- 

 cipitins. Joos found that antityphoid serum did 

 not agglutinate typhoid bacilli in the absence of 



