UNION OF ANTIBODIES WITH ANTIGENS. 345 



by injecting these substances into living animals, 

 and the animal experiment naturally continues to 

 be the means of testing the curative and prophy- 

 lactic values of serums. So long, however, as such 

 experiments were performed exclusively in the liv- 

 ing animal the nature of the action of antitoxin 

 remained to a certain extent in doubt. It re- 

 mained uncertain whether antitoxin is protective 

 because it actually destroys the toxin, because neu- 

 tralization of a chemical nature occurs, or because 

 in some manner it increases the resistance of the 

 inoculated animal. In Chapter XII experiments 

 were cited to show that antitoxin does not destroy 

 the toxin, and this is generally admitted to-day. 

 There continues to be some difference of opin- 

 ion, however, in relation to the two other possibili- 

 ties, i. e., as to whether antitoxin combines chemi- 

 cally with toxin, or is efficacious because of its 

 stimulating power on the tissues of the animal. 

 Behring, the discoverer of antitoxin, was from the 

 beginning an exponent of the chemical theory, even 

 at a time when the conceptions of Ehrlich had not 

 been fully developed. On the other hand, certain 

 noted investigators, especially Eoux and Buchner, 

 and later Metchnikoff, stood for the alternative 

 view. 



Following closely on Behring's great discovery, Ricin and 

 Ehrlich studied the hemagglutinating toxin ricin, 

 from the castor-oil bean, and by immunization 

 with it produced a specific antitoxin, i. e., anti- 

 ricin. Ricin is toxic to erythrocytes both in the 

 animal body and in the test-tube, and if it could 

 be shown that antiricin protects in the test-tube 

 by a direct effect on the toxin, it was highly prob- 



