384 INFECTION AND RESISTANCE 



that successful accomplishment of such experiments depends largely 

 upon the properties of the sensitive sera, for they say : 



"We, too, often had sera which would sensitize guinea pigs only 

 after an interval of 24 hours and produced no effects when injected 

 simultaneously with the antigen." It is in this difficulty probably 

 that we must seek the discrepancy between these later results and 

 those obtained in the earlier investigations, and it is upon this point 

 that many of the later controversies concerning the intravascular 

 or cellular localization of the anaphylactic reaction have turned. It 

 will find further consideration in a later paragraph. 



