2 IMMUNE SERA 



was not bactericidal, and retained its therapeutic 

 power for a considerable time. He believed that 

 the action of the serum was effected by a neu- 

 tralization of the bacterial toxin by an " antitoxic 

 serum constituent." The action was strictly specific, 

 an antitoxic serum obtained after a diphtheria 

 infection protected only against diphtheria; one 

 derived from a tetanus animal, only against tetanus. 

 Subsequently Behring and Knorr showed that im- 

 munization could be effected with bacterial-free 

 filtrates of tetanus cultures and that the serum thus 

 produced protected not only against tetanus 

 infection but against poisoning by the toxic prod- 

 ucts of the bacilli. After considerable experi- 

 mental work Behring and his collaborators devised 

 an effective method of immunizing Lheep and 

 certain other animals against diphtheria and against 

 tetanus and so produced antitoxic sera in con- 

 siderable amounts. 



The following account taken from Park shows the 

 present methods of producing diphtheria antitoxin. 



Production of the Diphtheria Toxin. A strong 

 diphtheria toxin should be obtained by taking a very 

 virulent culture and growing it in broth which is about 

 8 cc. normal soda solution per liter above the neutral 

 point to litmus. The culture fluid should be in com- 

 paratively thin layers and in large-necked Erlenmeyei 

 flasks, so as to allow of a free access of air; the tem- 

 perature should be about 35 to 36 C. The culture, 

 after a weeks growth, is removed from the incubator, 



