112 LOCAL TISSUE REACTIVITY 



till at ions it was loiind that 0.25 c.c;. of the serum neutralized c:on- 

 sistently 150 reacting units ot tlie filtrate. This serum was selected 

 as the standard. In subsequent work, in addition to direct titra- 

 tions of the reacting jjotency of the filtrates, there was also deter- 

 mined the maximum amount of each filtrate completely neutral- 

 ized by 0.25 c.c. of the standard serimi. This amoimt was then 

 considered as containing 150 reacting units and the titer for one 

 c.c. of the filtrate Avas derived by multiplying the dilution of the 

 filtrate by 150. Thus, if a dilution 1:5.25 was the maximum 

 amount completely neutralized by 0.25 c.c. of the standard seriuii 

 the filtrate was considered as containing 750 reacting imits. When 

 the direct and indirect titrations just descril)ed ^vere carried out 

 Avith a large group of filtrates prepared under identical condi- 

 tions and from the same strains, the following was foinid: 



There ajjpeared to exist no constant ratio between the direct 

 and indirect titers, i.e., toxicity and antigen-combining titers. The 

 ratios varied ^vithin the following range: 1:1, 1:1.5, i'^. i:'^ 1:4 

 and 1:6. Fresh filtrates ^vere likely to sho^v ratios of 1:3, 1:4, and 

 1:6. The louver the reacting potency, the greater ^vas the discrep- 

 ancy between the reacting titers and the titers deri\'ed from in- 

 direct neutralization titrations. After the filtrates were stored for 

 t^vo to three ^veeks the reacting potency frequently increased. In 

 these instances, the direct and indirect titers coincided more 

 closely, sometimes changing from 1:5 to 1:1.5 and 1:2 ratios. On 

 storage extending for sexeral months a sudden drop in potency 

 occurred. In such cases the ratios became approximately tfie same 

 as those Avhich existed soon after preparation of the filtrates, i.e., 

 before the rise in the direct titer took place. 



When the indirect titers of many preparations were compared 

 it became obvious that the antibody-combining power fluctuates 

 within a considerably narrower range than the reacting potency 

 and moreover, the antibody-combining power remains stationary 

 in spite of the wide fluctuations of the reacting potency. These 

 facts can be safely interpreted as toxoid formation ^vith retention 

 of the antibody-combining power. 



This is further substantiated by the following observations of 

 Klein made in my laboratories (1932) . 



Meningococcus "agar Avashings" filtrates were mixed ^vith for- 

 malin in a final concentration of 0.4 per cent, placed in ground 

 glass stoppered bottles, sealed with paraffin and kept in an in- 

 cubator at 37° c. for 5 days. The skin-preparatory and reacting po- 



