DIPHTHERIA ANTITOXIN. 411 



may be saved, or its death postponed, by the subsequent 

 injection of the serum ; the result depending upon the 

 amount of serum used and the lapse of time between 

 inoculation with the bacteria and injection of the serum. 



And, finally, that although this serum has such a 

 marked effect upon the toxins of bacterium diphtherias in 

 a test-tube or in the animal, and so striking an influence 

 upon the course of infection with the living organisms 

 in the animal, it has little or no effect upon the living 

 bacteria either in a test-tube or at the site of inoculation 

 in the living animal body. 



This serum with which we have been experimenting 

 is the so-called " diphtheria antitoxin " or " antidiph- 

 theritic serum." 



For practical purposes, it is obtained from horses, 

 the animals being treated with gradually increasing 

 doses of diphtheria toxin until they are able to with- 

 stand enormous multiples of the ordinarily fatal dose. 

 When this point is reached, the protective body the 

 antitoxin is present in the blood in such large quan- 

 tities that the serum may be successfully employed in 

 the treatment of diphtheria in human beings ?'. e., as 

 an antidote to the diphtheria toxin that is produced by 

 the growing bacteria in the throat, or elsewhere, and 

 distributed through the body by the circulating blood. 



THE STANDARDIZATION OF DIPHTHERIA ANTI- 

 TOXIN. The value of diphtheria antitoxin may be de- 

 termined according to several different standards. Those 

 that are best known have been proposed by Behring and 

 Ehrlich. 



1. Behring' s Method. He designates as a "normal" 

 poison a toxin of which 0.01 c.c. suffices to kill a guinea- 

 pig weighing 250 grammes in four days, Of such a 



