IMMUNOLOGICAL BEHAVIOR II3 



tencies of these preparations were titrated by means ol combined 

 intradermal injections of tlie formalinized meningococcns mate- 

 rials Avith intravenous injections of active meningococcus filtrates; 

 or by means of combined intradermal injections of active menin- 

 gococcus filtrates with intravenous injections of formalinized fil- 

 trates. In this manner it was found that the potency of the forma- 

 linized materials, as measured by the titer of the reacting units, 

 was markedly decreased. In contrast the antigenicity and the anti- 

 body-combining capacity remained essentially imimpaired. The 

 antibody-combining capacity of meningococcus toxoids ^vas 

 studied as follows: 



Mixtines of meningocccus active principles with antimeningo- 

 coccus horse serum ^vere titrated for reacting potency. Complete 

 neutralization was obtained with 100 imits of meningococcus re- 

 acting factors. "With the use of an equal amotuit of sertmi, com- 

 plete neutralization was obtained wtih only 1.7 reacting tuiits of 

 meningococcus toxoid. The ratio of the antibody-combining capac- 

 ity of meningococcus toxoid to that of meningococcus active prin- 

 ciples was, therefore, that of 10:14, ^^^^^^ showing in the toxoid a 

 loss of only 28.7 per cent of the antibody-combining capacity asso- 

 ciated with 98.8 per cent loss of toxicity as compared to the mother 

 filtrate. 



It remained to determine whether 1.7 reacting units of menin- 

 gococcus toxoid actually held in combination all of the neutraliz- 

 ing antibody in the serum used for the neutralization titrations. 

 If the mixture contained an excess, i.e., unbound antibody, then 

 complete neutralization should still be obtained after the addi- 

 tion of a small amount of active principles to the mixture. Accord- 

 ingly, the following experiment was performed: 



Each of 4 rabbits received an intradermal injection of 0.25 c.c. of undiluted 

 active meningococcus principles, followed t^venty-foiu' hours later by an in- 

 travenous injection of a mixture of 1 c.c. of meningococcus toxoid diluted 



1:10 (1.75 reacting luiits) plus 1 c.c. antimeningococcus immune horse serinu 

 plus 0.5 c.c. of meningococcus active principles diluted 1:70 (10 reacting 

 imits) per kilo of body weight. Reactions were elicited in 3 of the 4 rabbits 



(no neutralization) . 



The above experiment demonstrated conclusively that 1.7 re- 

 acting units of meningococcus toxoid actually combined ^vith all 

 of the antibodies in 1 c.c. of the immune antimeningococcus 

 serum. It remained to ascertain the antigenicity of meningococcus 

 toxoid. 



