132 CONTEMPORARY SCIENCE 



while the sensitive state arises from the interaction of the 

 animal body with any native protein substance what- 

 ever which finds its way directly or indirectly into the 

 blood. 



From the many investigations which now ensued, it 

 appeared that while many kinds of warm-blooded ani- 

 mals are subject to the condition, yet the most striking, 

 because most uniform and dramatic effects are yielded 

 by the guinea pig, which has since become, as it were, the 

 "classical" animal for observing and studying anaphylaxis. 

 The reason for this choice arises from the circumstance 

 that in the guinea pig a sensitization of the smooth muscle 

 fibers occurs, so that in reinjection of the original pro- 

 tein, among other effects, a contraction of the lining mem- 

 brane of the bronchi takes place, which by closing their 

 lumina and excluding air, quickly causes death from 

 asphyxiation. Moreover, the guinea pig has proved ex- 

 quisitely responsive to sensitization, so that minute quan- 

 tities, measured even in fractions of milligrams, of pure 

 native proteins suffice to induce a specific hypersensitive 

 condition, whence it has followed that the prepared guinea 

 pig has been found suitable for the investigation of the 

 ultimate chemical relationships, not otherwise observable, 

 which subsist between native proteins. 



Profoundly different as are the obvious features of the 

 anaphylactic and immune reactions, yet certain of the 

 fundamental conditions governing both coincide. It will 

 be recalled that in arousing immunity in animals by arti- 

 ficial means, certain new substances of the general nature 

 of antipodes, or as technically named, antibodies, are 

 made to arise in the blood of the treated animal ; and it 

 now appears that in the course of sensitization of animals, 

 antibodies to the proteins injected also develop. In both 

 instances the material originally injected, whether pri- 

 marily poisonous or not, if active, belongs to a class now 

 called antigens, that is generators of antibodies. The ex- 

 pression of the immunity reaction, in its simplest terms, 



