AGGLUTINOIDS. 223 



with its binding power for agglutinogen practi- 

 cally unaltered; these are agglutinoids, just as 

 toxins when changed in a similar way are called 

 toxoids. A serum which is rich in agglutinin may 

 be changed into one rich in agglutinoid by expo- 

 sure to a temperature of from 60 to 75 C., and by 

 the action of acids or alkalies; the change also 

 takes place spontaneously in the course of time, 

 when the agglutinin is in solution. 



Agglutinoids are detected by methods analogous 

 to those used in the recognition of toxoids. If 

 toxoids unite with all the antitoxin in a solution, 

 there naturally remains no antitoxin to unite with 

 true toxin which may be added subsequently. Sim- 

 ilarly, if all the agglutinogen in a mass of micro- 

 organisms has united with inactive agglutinoid, 

 agglutinin which is added subsequently would have 

 no point of attack and the reaction of agglutina- 

 tion would not occur. So we may say that when 

 bacteria are treated with a serum which has lost 

 its original agglutinating power, and the bacteria 

 are thereby made insusceptible to the action of a 

 fresh agglutinating serum, the former serum con- 

 tains agglutinoids. 



Sometimes it is found that even a fresh serum, 

 when concentrated, will cause less agglutination sllltinold ' 

 than when diluted. This has been referred to the 

 presence of agglutinoids which have a stronger 

 affinity for agglutinogen than has the agglutinin; 

 when of this character they are called proagglu- 

 tinoids, and accordingly are analogous to the pro- 

 toxoids mentioned earlier. As the serum is diluted 

 the concentration of the pro-agglutinoids becomes 

 less, and at a time when they are so dilute that they 

 have no influence on the reaction, the agglutinins 



