34 



IMMUNE SERA 



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. f&$ is added to 

 the amount of toxin in question, the result will be 

 just complete neutralization. If the toxin is entirely 

 pure, i| of the antitoxin unit would neutralize all 

 but vhv of the initial toxicity and M&, or ^ or >/&, 

 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 

 found it convenient to express them graphically in 

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



Toxon 



I 10 20 30 40 50 60 70 80 90 100 



FIG. 2. 



150 



200 



going much deeper into the subject the point may be 

 illustrated by the appended diagrams or " spectra." 



Fig. 2 shows the simplest conceivable diphtheria 

 poison. In this case the following values would 

 be obtained. 



x cc poison (100 fatal doses) + }#$ antitoxin 

 units = o, i.e. absolutely neutral. 



