II 



ANTIGENS AND ANTIBODIES 



TOXINS AND ANTITOXINS— AGGLUTININS— PRECIPITINS— 

 LYSINS—ISOCYTOLYSINS— OPSONINS— ANTIFERMENTS— 

 AUTO-ANTIBODIES— ALLERGY AND ANAPHYLAXIS 



We will now discuss briefly the various defensive 

 properties of the fluids and tissues of the body in re- 

 sisting the invasion of disease-producing substances. 

 The latter are usually termed antigens, while the spe- 

 cific substances produced by the body-cells to neu- 

 tralize and thus render the antigens innocuous are 

 termed antibodies. By the term antigen, therefore, is 

 meant an organic foreign substance, usually protein 

 in nature, the product of animal or vegetable cells, 

 which on being introduced into the body has the prop- 

 erty of stimulating the production by the body-cells of 

 a specific substance or antibody which unites chemi-^jjn^^,,^^^^^^^ 

 cally with it and thus neutralizes it. Antigens may be 

 of various types. They may consist of the soluble 

 products of bacterial growth, of substances bound up 

 in the bodies of the bacteria themselves, of protein and 

 lipoid extracts of animal tissues, etc. These different 

 forms of antigens produce corresponding types of 

 antibodies which differ in their methods of attacking 

 the antigens. Antibodies thus specifically produced, 



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