HYPERSENSITIVENESS 563 



7. The injection of an atopen into an atopically sensitive in- 

 dividual may lead to an increase in the reagin content of the 

 blood. 



8. A few cases are on record where reagin was detected in the 

 blood of an individual before he became clinically sensitive. 



9. Multiple sensitization is quite commonly observed. 



10. Among individuals sensitive to food Rowe estimates that only 

 50 or 60 per cent will give positive skin reactions to the exciting 

 agent. 



Comparison op Reagin With Antibodies. — It seems to us that 

 these results are not necessarily incompatible with the view that 

 reagin is an antibody. 



According to the present concept of antigen-antibody union it is 

 a partial filming of dispersed particles of antigen by antibody 

 globulin; therefore, it is conceivable that the toxic property of 

 atopen (antigen) might be retained after partial filming with 

 reagin protein (antibody globulin). In the case of the neutraliza- 

 tion of toxin by antitoxin the properties of the toxin are not 

 destroyed since the antigenic property is unimpaired and the toxic 

 property is demonstrable after dissociation occurs. 



In regard to the reaction between reagin and atopen not leading 

 to the formation of a visible precipitate, it is of interest to recall 

 that Coca described an antibody which interferes with the ag- 

 glutination of E. typhosa by its specific agglutinin. In toxin- 

 antitoxin neutralization experiments a precipitate is formed only 

 under certain specific conditions. In the case of syphilitic reagin 

 a precipitate is formed when it is brought into contact with a 

 lipoid hapten only under certain conditions. Furthermore, the 

 suppression phenomenon of Landsteiner involves the participation 

 of an antibody in a reaction characterized by the absence of a 

 visible precipitate. It may be that the proper conditions for a 

 precipitin or flocculation test for atopic reagins may at some future 

 time be discovered. In any event, it should be remembered that the 

 phenomena of precipitation and agglutination are secondary and 

 not primary ones in antigen-antibody reactions. 



Since it has been established that immune serum from one species 

 of animal is not always capable of passivel}' sensitizing another 

 species or, for that matter, every individual of the same species, it 



