208 IMMUNO-CATALYSIS 



inactivation of the enzymes or toxins, one cannot define what con- 

 figurational and other more critical changes in the whole molecule 

 precede or follow such reactions. We must, therefore, inquire into 

 other possibilities which may account for the above mentioned dis- 

 crepancy. 



Second: The second possibility is the reactivation in vivo of the 

 in vitro inactivated enzymes and toxins, etc. The amount of the 

 reactivated molecules produced at a given time might be insufficient 

 to produce noticeable toxic effects but sufficient to produce specific 

 antibodies. The data concerning this point are not as yet adequate, 

 but whatever can be cited is strongly suggestive of this process. For 

 example, urease oxidized with dilute iodine is inactive. This inactiva- 

 tion, probably involving the oxidation of SH groups, is reversed by 

 sulfhydryl groups. 



As discussed above, Pillemer, et al. (1938) showed that although 

 oxidized urease has lost its specificity to react with antiserum to crys- 

 talline active urease, both the oxidized and the reduced urease produced 

 a similar antibody. The ability of the oxidized urease to produce such a 

 specific antibody was attributed to the fact that tissue extracts were ca- 

 pable of reactivating oxidized urease, showing that the oxidized urease 

 regains its lost specificity in the animal system. Similarly, the detoxifi- 

 cation of snake venom involves the reduction of di-thiol groups into 

 sulfhydryl groups. In vivo the reduced molecule can regain to some 

 degree the original form. The reaction of formaldehyde Math the 

 imino, amino, amide, hydroxyl and sulfhydryl groups are reversible 

 reactions, though some are more stable than others. Which of these 

 reactions predominate in the conversion of toxin into toxoid is not 

 known. It is assumed, but contested, that formaldehyde reacts prin- 

 cipally with amino groups. If this is the predominant reaction the 

 resulting hydroxymethyl compounds are unstable and reversible. The 

 toxoid molecules can be considered subject to reversion in vivo to the 

 original molecular form. Acetylation with ketene likewise would seem 



tralizing power fell rapidly on stirring. All heterologous antisera reduced infectivity 

 more than normal sera stored similarly. 



Precipitating antibodies did not appear to be responsible for neutralization. No 

 correlation was found between precipitation titre and neutralization power, and 

 removal of precipitins did not affect neutralization power. Only quantitative differ- 

 ences were found in behavior between homologous and other sera; the infectivity of 

 all virus serum mixtures was regained by dilution. 



