490 COLLECTED STUDIES IN IMMUNITY 



time I gained the impression that a pure poison must oe so consti- 

 tuted that one I. E. fully neutralizes exactly 200 L. D. 1 Later on I 

 shall show that by means of the "spectrum" analysis I have suc- 

 ceeded in verifying this figure. 2 



The discovery of this number, 200, led me to represent the con- 

 stitution of diphtheria poison by means of a " spectrum" which is 

 divided into 200 segments, each of which corresponds to a toxin, 

 toxoid, or toxon equivalent. This scheme is not, as some have as- 

 sumed, a mere makeshift, but is the expression of knowledge labori- 

 ously attained. This graphic reproduction shows at a glance how 

 much toxin or toxoid is neutralized by each combining unit of anti- 

 toxin. Such a reproduction possesses so many advantages over the 

 curve used by Arrhenius and Madsen that I shall not hesitate a moment 

 in retaining the spectrum method for diphtheria poison. By its 

 means one obtains a view of the entire process of neutralization. 3 



It may be well at this point, by means of a suitable chemical 

 illustration, to elucidate the influence which such admixtures of 

 toxoid exert in the titration of alkaloids. In doing this it will be 

 best to proceed on the following assumptions. An alkaloid acts hsemo- 

 lytically when in the form of free base, but not when in the form of 

 a salt. 4 The base would then correspond to the toxin. The ana- 

 logue of the toxoid would then be an alkaloid which exerts no dele- 

 terious action either as such or in the form of a salt. The antitoxin 

 would be represented by any acid, e.g., hydrochloric acid. Under 

 these conditions the mixture of the two alkaloids can be titrated bio- 

 logically (by determining the haemolytic power at any point) by 

 means of an acid exactly as a toxin solution containing toxoid by 

 means of its antitoxin. 



Let us assume that the toxic alkaloid A as well as the atoxic B 

 possesses so strong an affinity for hydrochloric acid that neutraliza- 

 tion is effected to within a very small fraction. A solution of a mole- 

 cules A would then correspond to the pure toxin, while mixtures of 



1 It is self-evident that each toxin-combining unit can be replaced by an 

 equivalent amount of less toxic or non-toxic substances possessing combining 

 properties (toxones, toxoids). 



' The poison studied by Madsen, therefore, which contained 160 L. D. in 

 Lf, corresponded to a purity of four-fifths. 



3 See also page 552. 



4 This is probably the case with solanin, whose hsemolytic power is inhibited 

 by the addition of acid salts (Pohl) or ot free acids (He"don, Bashford). 



