88 ANTIGENS AND ANTIBODIES 



as they are of protein character, by the production of substances 

 which in a general way tend to antagonize or even to destroy those 

 which indirectly gave rise to their formation. For this altered 

 behavior of the "treated" as compared with the "non-treated" 

 animal, v. Pirquet has proposed the very appropriate and at the 

 same time non-committal term allergia (dtty ip-feca), which merely 

 denotes a state of altered power of reaction on the part of the 

 "treated" organism. 



The reaction products which are formed in the body of the treated 

 animal are conjointly spoken of as antibodies, and the substances 

 whose introduction from without give rise to their formation are 

 similarly termed antigens or allergens.. 



The discovery of these substances and their bearing upon the sub- 

 ject of immunity has opened up an enormous field for fruitful research, 

 not only in the domain of medical science, but in that of general 

 biology as well, and has already led to results which the boldest 

 flight of the imagination would not have thought possible twenty- 

 five years ago. The earliest and, in a manner, the most brilliant 

 investigations in this direction we owe to the genius of Behring and 

 his collaborators, Wernicke and Kitasato. 



Antitoxins. These investigators found that the serum of animals 

 which had been rendered immune to the specific toxins of tetanus and 

 diphtheria had acquired the power of neutralizing the harmful effect 

 of those poisons, and Tizzoni and Catani introduced the term anti- 

 toxin to denote the substance to which this action is due. Here the 

 way was shown for the first time along which it would be possible 

 successfully to combat one of the most common and most dangerous 

 diseases which has threatened the human race since times imme- 

 morial. Scarcely twenty-five years have now passed since Behring's 

 announcement to the world (1890) that it is not only possible to 

 protect the human being against infection with the diphtheria 

 bacillus, but that the disease may be arrested even after it has 

 gained a foothold and all this through the injection of a relatively 

 small amount of serum derived from a horse that has been previously 

 treated with diphtheria bacilli or their specific toxin. How well 

 Behring's discovery has served the human race is already a matter 

 of history. 



For a while hopes ran high that it would only be a matter of time 

 before equally efficacious antitoxins would be discovered for the 



