72 MODERN BIOLOGIC THERAPEUSIS 



into a series of guinea-pigs. That amount of 

 toxin thus administered which causes death of 

 the guinea-pig in 96 hours is called the L+dose. 

 An antitoxic serum is standardized by mixing 

 graded amounts of it with the L+dose of toxin 

 and injecting the mixtures into a series of 

 guinea-pigs. The smallest amount which suf- 

 fices to protect the animal for 96 hours is re- 

 garded as the unit of antitoxin. 



Tests Having ascertained the potency of 

 the refined antitoxin solution, sterility tests 

 and safety tests are applied to it. For the 

 safety test, the antitoxin is injected into white 

 mice which are kept under observation for 

 seven days. Sterility tests are carried out by 

 placing some of the antitoxin into sterile bouil- 

 lon which is placed in the incubator for five 

 days. Absence of microorganisms is indicated 

 by the bouillon remaining clear. 



Refining Process In 1905 Robert B. Gibson, 

 working under the direction of Dr. William H. 

 Park in the Research Laboratories of the De- 

 partment of Health of New York City, per- 

 fected a practical method for separating diph- 

 theria antitoxin in a refined and concentrated 

 form from the blood-serum of an immunized 



