HISTORIC DEVELOPMENT OF IMMUNOLOGY 63 



sera: (1) Antitoxic sera, and (2) Antibacterial 

 sera. The former, represented by Diphtheria 

 Antitoxin and Tetanus Antitoxin, neutralize 

 the toxin in the circulation and in the various 



Paul Ehrlich (1854-). 



tissues and body cavities. In diphtheria and 

 tetanus, the bacteria elaborate a poison or 

 toxin which is absorbed into the circulating 

 blood and is carried to the tissue-cells. This 

 toxin must be rendered inert before it has been 



