Actively sensitized guinea pig intestine responds, typically, with a large contraction to the first application of antigen (Ag). This is followed by a spontaneous relaxation of the tissue, while still in the presence of the Ag and a rapid desensitization, i.e. further exposures to Ag fail to evoke new contractions. 2. In contrast when the guinea pig was passively immunized with chicken antiserum, the first dose of Ag produced a sustained contraction. The second and third doses elicited contractions of comparable magnitude and no desensitization occurred. 3. In addition, consecutive Schultz-Dale reactions of guinea pig intestine or uterus from animals passively sensitized with chicken antiserum showed a consistent potentiation. They reached a maximal amplitude when the tissue was exposed to the Ag 6-7 times. Such a potentiation is abolished by storing the preparations up to 48 hr at 4 degrees C. 4. The tissues from chickens passively immunized with homologous antisera showed the same behaviour as those taken from actively sensitized chicken, i.e. no desensitization was observed. 5. These results agree with those previously observed in our laboratory suggesting the existence of a special property of the chicken antibodies (Ab). Indeed, the characteristic features of the anaphylactic reaction in actively sensitized chickens were transmitted to both chickens and guinea pigs passively sensitized with chicken Ab's.
