30 LOCAL TLSSUE REACTIVITY 



factors against c:onstant doses (Method II) ; and titration of react- 

 ing factors against constant skin-preparatory doses (Method III) . 

 Method III affords accurate determinations of the plienomenon- 

 producing potency of the material and may be advantageously 

 used for determinations of the neutralizing potency of sera. 



There exists a strict quantitative reciprocity Ijetween the skin- 

 preparatory and reacting factors. If advantage be taken of the 

 fact and several multij)les of the minimal dose of reacting factors 

 be used, a high incidence of positive restdts may be obtained 

 Avhich may reach loo j^er cent ^vith filtrates of some microor- 

 yanisms. 



