IMMUNITY 87 



producing immunity is little used in man. The most 

 important example of its use is in the immunization of 

 the horse against diphtheria for the production of anti- 

 toxin, also in the production of tetanus antitoxin. 

 While the results of this method are usually attributed to 

 the toxin, it is probable that other products of bacterial 

 activity play a part, as the broth upon which the bac- 

 teria have been cultivated is separated from the germs 

 by nitration and injected, and in all likelihood contains 

 other substances besides toxin. The employment of 

 tuberculin for the production of immunity is a combi- 

 nation of this method with the use of the dead germs. 



