74 



STANDARDIZATION OF DIPHTHERIA TOXIN 



with it, and so render it incapable of neutralizing the true toxin. 

 The spectrum of this solution will be represented thus : 



Pntto- 

 toxoid 



Toxone 



FIG. 9. SPECTRUM OF TOXIN. 



In this, as in the other diagrams, the lethal portion of the mixture 

 is shaded, the non-lethal portion left blank. 



Ehrlich found on actual experiment that the constitution of the 

 solution was even more complex than this, and had to assume the 

 existence of yet other bodies. Thus, if the spectrum above were 

 a true representation of the constitution of i c.c. of the solution, it 

 follows that the first quarter and the last quarter of the antitoxin 

 added were without effect, so that the middle \ c.c. completely 

 neutralized the whole of the TOO lethal doses. Now let us 

 imagine this i c.c. of standard antitoxin divided into 200 equal 

 parts, and added part by part to the i c.c. of standard toxin, or 

 100 lethal doses. Then 



The first 50 parts added will combine with prototoxoid, and will 



not affect the toxicity of the mixture ; 

 The next 100 parts added will neutralize 100 lethal amounts 



of true toxin ; and 

 The last 50 parts will combine with toxon. 



Now if the spectrum were as simple as is shown above, and if 

 the toxin were quite uniform in its combining capacity and its 

 toxicity, it would follow that the first -^^ part added after the 

 addition of ^^ part would just neutralize one lethal dose and leave 

 99 lethal doses over. Again, the addition of the amount necessary 

 to neutralize all the prototoxoid ( = -f^ c.c.) + -$ c.c., which would 

 neutralize all the prototoxoid and all the toxin except yj^ part 

 (=i lethal dose), and all the toxon, should leave i lethal dose 

 of toxin free, and the animal should die in the limit of time for 

 i lethal dose. We might represent this as follows : 



149 unnc'jfralised 

 'Toxin ( 



