CHAPTER XIV. 



THE NATURE OF THE SUBSTANCES CONCERNED IN 

 AGGLUTINATION. 



Two substances are concerned in agglutination: Terms. 

 one, the active or agglutinating substance, exists 

 in the serum, while the other, the substance acted 

 on or the agglutinable substance, is present in the 

 bacteria. The agglutinable substance is generally 

 supposed to be passive in the reaction, while the 

 agglutinating property seems to possess a ferment- 

 like element, which acts on the agglutinable sub- 

 stance. Agglutinin, the term used in the preced- 

 ing chapter, is now generally applied to the sub- 

 stance in the serum. Recently the bacterial con- 

 stituent has been called agglutinogen, because of 

 the belief that the agglutinable substance, when 

 introduced into the animal body, stimulates the 

 latter to the formation of agglutinin; hence ag- 

 glutinogen means, not agglutination-producing, 

 but agglutinin -producing. These shorter terms 

 will be used for the sake of convenience. 



The presence of agglutinogen in an organism \j-i mi no .-. 

 may be demonstrated in three ways : 1. The mere 

 fact of its agglutinability by a serum is evidence 

 of the presence of an agglutinable substance. 2. 

 If during infection or immunization the serum ac- 

 quires agglutinating properties, the bacterium pos- 

 sesses an agglutinogenic substance. 3. If a cul- 

 ture is mixed with a serum containing the specific 

 agglutinin, and after a period of contact is re- 

 moved by centrifugation, the resultant disappear- 



