IMMUNOLOGICAL BEHAVIOR 99 



a considerable achantage of the method since the immiuie senmi 

 exercised a definite protection against the mortality induced by 

 intravenous injection of B. tyj)]iosu6 cidttue filtrates. Thus. ])rac- 



t. 



A is C. 



Fig. 10. rhiee labljits \\erc each injected intiadennally with 0.5 c.c. of menin- 

 gococcus active principles diluted 1:2. Twenty-four hours later, mixtures of i c.c. 

 of serum with various multiples of active principles were injected intravenously. 

 Figure A illustrates lack of neutralization of 100 reacting tniits of toxin. Figure B 

 illustrates partial neutralization of 75 reacting units of toxin. Figure C illustrates 

 complete neutralization of 50 reacting iniils of toxin. 



ticafly no animals died from the injection of mixttnes of the 

 filtrate with immune serimi and, therefore, the number of ani- 

 mals necessary for determination of the neutralizing potency 

 could be considerably reduced. In other l^asic studies similar to 

 the foregoing it ^vas possible to obtain consistent specific neu- 

 tralizations of meningococcus, B. coli, B. dysentenae, B. pertussis, 

 and B. i)ifluenzae reacting factors. 



In planning the neutralization experiments with meningococ- 

 cus, the question again arose as to what was the minimal num- 

 Ijer of reactino- units which \\'oidd vield a high percentage of 

 reactions and ^vhich, therefore, could be safely used for these 

 experiments. \'arious mtdtiples of the minimal doses were tested 

 in groups of 6 rabbits each. In this manner it ^vas foinid that 6 

 reactino- units oave a hioh percentaoe of reactions, i.e., never be- 

 lo^v 75 per cent and frequently ranging bet^veen 80 to 100 per 

 cent, depending on the filtrate employed. Amoinits larger than 

 six reacting tuiits gave positive reactions in 90 to 100 per cent of 

 rabbits. Similar to the above described ^vork, immiuie and normal 

 sera Avere tested against various midtiples of the filtrates. Certain 

 antimeninoococctrs immune sera in a dose of o.2r, c.c. were ca- 



