()2 LOCAL ILSSLE REACTIVITY 



paiatoiy doses. Alter c'stal)lisliiii^ dclmitcly the la(t thai ncutral- 

 i/alioii ol skin-])iej)ar<U()iy laclors by sj)ecihc sera is j)()ssible, it 

 a|))x'are(l desirable to aiialy/e tiie results iurther lor purposes 

 ol titration ol the neutralizing power of the ininiune sera. Stich 

 analysis is illustrated by the lollowing typical example: 



In 6 rabbits receiving antityj)hoid horse seriun complete neu- 

 tralization ^vas obtained in dilution of 1:200, in one rabbit in 

 dilution 1:20, while in two rabbits there was no neutralization. 

 Similar results were obtained with other sera. 



It becomes evident from this example that there is a definite 

 variation in the response of different rabbits to the skin-prepara- 

 tory effect of sernm filtrate mixtures. The rabbits sho\vino these 

 varying responses can be classified under three groups, namely, 

 those which yield completely neutralized reactions ^vith the high- 

 est dilutions of serum (HN) , those which give rise to completely 

 neutralized reactions only \vith serum in louver dilutions (LN) , 

 and those ^vhich show non-neutralized reactions (NN) . The rea- 

 son for the absence of neutralization in some rabbits has not 

 been definitely established as yet. It is likely, however, that it 

 may be due to a partial dissociation of a certain amount of pre- 

 jiaratory factors from their combination with the neutralizing 

 antibodies in the tissue injected. If this dissociation takes place 

 in rabbits of high susceptit^ility, a small non-neutralized or par- 

 tially neutralized amotuit of preparatory factors may then pro\e 

 sufficient to elicit the necessary state of reactivity to the phenom- 

 enon. It appears, liowever, that the potency of a given serum bears 

 a mathematical ratio to the reactions obtained in the three groups 

 of rabbits. Thus, if complete neutralization is obtained in dilu- 

 tion 1:2000 in HN rabbits, namely, those showing highest titer of 

 neutralization, the titer in LN rabbits is likely to be 1:200. In 

 the cases in which the HN is 1:200, the LN titer is likely to be 

 only 1:20. The relative numbers of HN, LN, and NN rabbits also 

 vary. The follow-ing schematic formula has been found useful in 

 recording the varying factors obtained in a typical serum titra- 

 tion: HN,i 2000, LN4 200 LNi 20, NNo. This indicates that 6 rab- 

 bits showed complete neutralization Avith serum diluted 1:2000, 

 4 rabbits sho^ved complete neutralization ^vitli serum diluted 

 1:200, one rabbit with serum diluted 1:20, and 2 rabbits showed 

 no neutralization. For practical purposes the highest dilution of 

 serum Avhich gives complete neutralization of the B. typhosus skin- 

 preparatory factors (HN titer) may be taken as the actual titer of 



