94 ANTIGENS AND ANTIBODIES 



or vegetable nature, or of the products of foreign cells, insofar at 

 least 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 alter gia (SAfoj />?*), which merely 

 denotes a state of altered power of reaction in 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 

 subject 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 

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

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

 sible successfully to combat one of the most common and most 

 dangerous diseases which has threatened the human race since times 

 immemorial. 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 diph- 

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

 has gained a foothold and all this through the injection of a rela- 

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

 previously treated with a culture of 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 hope ran high that it would only be a matter of time 



