PATHOGENIC BACTERIA 265 



In the chemical reaction the precipitin of the serum must 

 enter into chemical combination with a substance in the fil- 

 trate derived from the bacteria called precipitinogen, and, by 

 thus combining, a definite chemical precipitate is formed. 

 Precipitation, like agglutination, does not take place in the 

 absence of salts (electrolytes). Nothing definite is known in 

 regard to the chemical structure of the precipitins. They 

 are probably protein substances. They are precipitated in 

 the euglobulin part of the serum, like most antibodies, and 

 cannot be separated from the serum proteins. On heating 

 serums containing precipitins they are changed into precipi- 

 toids. The combining group is uninjured, but the active 

 group (zymophore), which causes the precipitation, is de- 

 stroyed. 



Antienzymes. Some pathogenic bacteria produce en- 

 zymes (M. pyogenes var. aureus, etc.) in small amounts. Im- 

 munization of animals with these enzymes produces antien- 

 zymes in the serum of the animal. Little is known in regard to 

 the antienzymes. There is a possibility that in certain cases 

 they may inhibit bacterial growth. The subject of bacterial 

 enzymes has been considered in another chapter (Chap. XV). 



Table of Antibodies which may be produced by Immunization 



Antitoxins for bacterial toxins of : 

 Bact. diphtheriae (Diphtheria). 

 B. tetanus (Tetanus). 

 B. botulinus (Botulism). 



