496 COLLECTED STUDIES IN IMMUNITY. 



tritotoxid of exactly toxicity was found. It should be emphasized 



that the fatal doses which disappeared in the deterioration were found 

 in the form of toxoids in the tritotoxoid zone. 



These investigations show that these changes are due exclusively to 

 the fact that a part of the toxin has become transformed into toxoids ; 

 in fact into toxoids which are neutralized after the main portion of 

 the toxin, and which, therefore, must possess less affinity. If we were 

 to represent this phase by means of a curve according to the method 

 of Arrhenius and Madsen, we should observe a marked flattening 

 of the curve in the tritotoxoid zone. This, however, is not the expres- 

 sion of the weak affinity of the diphtheria toxin, or of the neutraliza- 

 tion dependent thereon. It is to be ascribed with absolute certainty 

 solely to the presence of toxoids and their appearance in place of toxin 

 molecules which have disappeared. 



I shall discuss phase III later, merely remarking at this time that 

 in this phase, 80 out of 100 parts toxon have disappeared. The L 

 dose of 0.125 cc. now contains only 120 combining units instead of 

 the 200 units (toxin and toxon) originally present. Corresponding 

 to this, therefore, the L dose, which must contain 200 combining units, 

 increases from 0.125 cc. to 0.21 cc. In this third phase the toxin 

 zone has not suffered any essential change. The L-j- dose has accord- 

 ingly remained constant at 0.26 cc. Because of the new L dose made 

 necessary by the loss of toxon, the spectrum representing this phase 

 shows a much wider toxin zone than the previous one. The toxin- 

 toxon boundary has been moved from 100 to 166. - 



In phase IV, L-j- remained 0.26 cc., but the toxicity decreased, 

 the L. D. increasing gradually from 0.003 cc. to 0.004 cc. During the 

 course of these changes 22 L. D. had disappeared from the L dose of 

 phase III. 



The fate of these 22 L. D. is made plain by the spectrum which 

 I constructed at that time. In this I found an extended prototoxoid 

 zone which included the first 40 combining units of the spectrum, 

 sufficient, as can be seen, to explain the loss of toxin which had oc- 

 curred. I desire to call particular attention to the fact that no loss 

 of combining groups had occurred despite the slight increase of the 

 L dose. 1 



1 A superficial glance might lead one to suppose that the fact that the Lf 

 dose of 0.25 cc. in the first phase had become increased to a little over 0.26 cc., 



