IMMUNE SERA 



units," and that the toxic bouillon really contained 

 several kinds of poisonous substances able to com- 

 bine with antitoxin. 



He now believes that the diphtheria bacilli excrete 

 at least two such poisons, " toxins " and " toxons ; " 

 that these very quickly decompose to a greater or 

 less extent forming various " toxoids." 



In the case of a hypothetically pure toxin Ehrlich 

 believes that one antitoxic unit would correspond 

 to 200 fatal doses or 200 binding units. If the 

 entire amount of antitoxin, i.e. ! is added to 

 the amount of toxin in question, the result will be 

 just complete neutralization. If the toxin is entirely 

 pure, JJ of the antitoxin unit would neutralize all 

 but ?A(j of the initial toxicity and M, or {$ or /A, 

 etc. of the antitoxin added would permit correspond- 

 ing degrees of toxicity to be demonstrated through 

 animal inoculations. It was found, however, that 

 neutralization according to this simple scale did not 

 take place. The results were complicated and Ehrlich 



Toxon 



10 20 30 40 50 60 70 80 90 100 



FIG. 2. 



150 



200 



found it convenient to express them graphically in 

 the form of the so-called " toxin spectra." Without 



