262 BIOLOGY OF SPECIALIZED GROUPS 



blood serum be added, the bacteria will be markedly effected 

 and killed, and in bacteriolytic serums will be disintegrated. 

 In addition the experiment shows the presence of an extremely 

 labile substance in the bactericidal serum which was replaced 

 by the fresh normal serum. This substance is called the 

 complement. There is present in the serum also a stable sub- 

 stance which resists heat and all external agents. This sub- 

 stance is called the amboceptor or immune body. These 

 chemical substances can be definitely separated from each 

 other. It has been shown by experiment that the chemical 

 group which is called the amboceptor must first unite with 

 the bacterial cell before the complement can combine and 

 destroy it. Anti-complements and anti-amboceptors may be 

 produced on immunizing with these bodies. Complements 

 may also be changed into complementoids by heat. The am- 

 bocep tor-complement reaction will be mentioned later in the 

 consideration of other immune substances. 



Agglutinins. Agglutinins are substances which are found 

 in the blood serum of some normal and immunized animals, 

 and which have the power to produce a clumping of the 

 specific microorganism causing some infections. Group 

 agglutinins, that is, agglutinins for bacteria related to the 

 species producing the agglutinin, may also be present in small 

 amounts in the serum. These may be removed by diluting 

 the serum. The agglutinin in the serum enters into chemical 

 combination with the so-called agglutinogen which is present 

 in the bacterial cell, and the resulting chemical reaction pro- 



