IMMUNOLOGICAL BEHAVIOR II5 



comparable loss of antibody-combining capacity is associated with 

 the decrease in toxicity occmring on standing. It was the detoxi- 

 fying alteration of the sort undergone by diphtheria toxin that 

 lead Ehrlich to the description of diphtheria toxoid. Since menin- 

 gococcus active principles can spontaneously or artificially be 

 modified in a similar manner, it appears justifiable to consider 

 such modified meningococcus active principles of the phenomenon 

 under discussion as meningococcus toxoids. 



, In further attempts to determine the effect of immune sera 

 upon the active principles of the phenomenon, it seemed im- 

 portant to investigate ^vhether this ^vas in the nature of 

 neutralization similar to the kno^vn toxin -|-antitoxin reactions. 

 The other possibility still remained that precipitates, formed on 

 addition of the specific antisera to the active bacterial filtrates, 

 may remove the acti\e principles from the solutions by a process 

 of adsorption. In the ^vork about to be described it ^vas sho^vn, 

 ho^vever, that the inactivation of reacting factors occtns in "mul- 

 tiple proportions"; that the precipitates formed do not inactivate 

 the active principles; that the protection against the active prin- 

 ciples may also be obtained in vivo; that the protection ifi vivo 

 also occurs in multiple proportions; and, finally, that specific 

 active acquired immunity can be demonstrated. 



REACTING POTENCY OF PRECIPITATES AND SUPERNATANT FLUIDS 



DERIVED FROM MIXTURES OF ACTIVE BACTERIAL FILTRATES 



WITH IMMUNE SERA 



As already noted, when a B. typhosus "agar washings" culture 

 filtrate is mixed with an immune anti-typhoid horse serum in 

 necessary proportions, there occurs complete inactivation of 

 B. typhosus reacting factors. The mixtures usually form 

 abundant precipitates. In order to determine whether the in- 

 activiation of active principles was not merely due to their adsorp- 

 tion by the precipitate formed, various numbers of B. typhosus 

 reactino- factors were mixed Avith a constant amount of anti- 

 typhoid horse serum. The mixtures made in the proportions in- 

 dicated in Table v, precipitates and the supernatant fluids 

 derived from these mixtures, Avere all tested for reacting potency. 

 As may be seen from Table v, 1 c.c. of the immune serum com- 

 pletely neutralized 750 B. typhosus reacting iniits. Precipitates 

 derived from the mixtures ^vere respecti\ely dexoid of reacting 

 potency. When an amount of B. typJiosus reacting factors exceed- 



