128 l,()(w\I, I ISSUE REACTIVITY 



The ncii(iali/ini> jjotciuy ol sera may be (oiueniciitly titrated 

 against iiieieasiii^ ainoiiiits of reacting factors. 



Tlie acti\e principles of B. typhosus, B. colt, and as will be 

 shown in (Ihajiter xin, those ol meningococcus, possess "strain" 

 and "variant" specificity. 



The passage through mice induces in certain strains a partial 

 loss of neutralizability of reacting factors. This is probaf)ly due 

 to \'ariations to^vards smoothness ^vith an increase in the antigenic 

 cc:)mplexity. Reacting factors deri\ed from rough \ariants accpiire 

 a ne^v specificity. Changes in the neutralizability of the reacting 

 factors cannot be consistently correlated \vith colony morphology, 

 serum agglutinability and virulence of strains, nor with the serum 

 precipitabiHty of the culture filtrates. 



There is an indication that fluctuations in potency of filtrates 

 are accompanied })y formation of "toxoids" retaining their power 

 to comljine Avith the neutralizing antibodies. Meningococcus ac- 

 tive principles can be also detoxified by formalin whereby the 

 antigenicity and the antif^ody-combining capacity remain essen- 

 tially unimpaired. 



It was shown that the neutralization of the active principles 

 of the phenomenon by immune sera is not due merely to the 

 adsorption of active principles but the precipitate formed. The 

 addition of homologous neutralizing antibodies to B. typhosus 

 active filtrates results in processes essentially consisting of two 

 phases: (i) Flocculation of the antigenic components of the 

 bacterial filtrates by immune sera accompanied by adsorption of 

 the active principles by these complexes. (2) Neutralization of 

 the active principles in these precipitates which may or may not 

 follow this adsorption depending whether or not the antibodies 

 pcissess neutralizing po\ver. 



The neutralization of the active princij^les of B. typhosus and 

 B. coli occurs according to the Lnv of "multiple proportions," the 

 reaction closely resembling the neutralization of diphtheria toxin 

 by antitoxin. 



There is demonstrated the existence of an heterologous anti- 

 body auxiliary to the neutralization of meningococcus and B. coli 

 reacting factors. The presence of this antibody facilitates studies on 

 neutralizing potency of anti-meningococcus sera. 



There also appear to exist certain reacti\ating factors in nor- 

 mal and immune blood sera of various animal species. The effect 

 of reacti\ating factors consists in restoration of the toxicity /// vixio 



