DISEASE, INFECTION, AND RESISTANCE 281 



upon the development, in the tissues of the animal, of 

 antagonizing substances termed antibodies. Any substance 

 which, when injected into the tissues or when present in 

 the tissues, causes these tissues to develop an antibody is 

 termed antigen. A consideration of specific immunity, 

 therefore, is primarily a discussion of the various substances 

 or antigens ivhich can incite the tissues of the body to the 

 development of immunizing substances and a study likewise 

 of these immunizing substances or antibodies. 



The following table lists the more important of the anti- 

 gens and their corresponding antibodies, which will be dis- 

 cussed on the succeeding pages : 



ANTIGENS AND THEIR CORRESPONDING ANTIBODIES 



ANTIGENS ANTIBODIES 



Toxin Antitoxin 



Bacterial cell (agglutinogen) Agglutinin 



Soluble protein (precipitogen) Precipitin 



Cells foreign to body: Cytolysin 



Bacteria Bacteriolysin 



Red blood cell Hemolysin 



Bacterial cell Opsonin 



Certain kinds of bacteria capable of producing disease are 

 known to produce poisons termed toxins. The body devel- 

 ops immunity against such by the production of antitoxins. 

 When certain kinds of bacteria or other cells gain access to 

 the body, the latter may sometimes produce substances which 

 will cause these bacteria to clump together or agglutinate. 

 These are termed agglutinins. Foreign proteins, that is pro- 

 teins not native to the body of the animal into which they 

 are injected or coming from another species of animal or 

 plant, will cause an individual injected to develop sub- 

 stances in the blood serum which will precipitate the corre- 

 sponding protein. Such antibodies are termed precipitins. 

 The presence of foreign cells (such as bacteria) may cause 

 the tissues to develop substances which will digest or dis- 



