24 IMMUNE SERA 



antitoxin, would require the addition of but one 

 fatal dose of toxin in order to regularly kill the test 

 animal. In the above table, however, we see that 

 this difference ranges from six to fifty fatal doses. 



Partial Saturation Method - - Toxons, Toxoids. 

 Ehrlich obtained considerable additional informa- 

 tion by means of his " partial saturation " method. 

 Certain experiments had led him to believe that the 

 original antitoxin on which he had based his " unit " 

 determinations, while able to neutralize 100 fatal 

 doses (per unit) really represented 200 " binding 

 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, ^{jf of the antitoxin unit would neutralize all 

 but ?hu 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 



