BACTERIUM XEROSIS 505 



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 diphtherise 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 " antidiphtheritic 

 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 withstand 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 quantities that the serum may be 

 successfully employed in the treatment of diphtheria in 

 human beings i. 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 cir- 

 culating fluids. 



The Standardization of Diphtheria Antitoxin. The value 

 of diphtheria antitoxin may be determined according to 

 several different standards. Those that are best known 

 have been proposed by Behring and by 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 weigh- 

 ing 250 grams in four days. Of such a normal diphtheria 

 toxin 1 c.c. will be sufficient to kill 100 guinea-pigs weigh- 



