The contractions elicited in pieces of small intestine of actively immunized young chickens upon exposure to the specific antigen (Ag), or Schultz-Dale reaction, have been compared to similar responses of sensitized guinea-pig intestine. 2. Guinea-pig intestine responds, typically, with a large contraction to the first application of Ag. This is followed by a spontaneous relaxation of the preparation, while still in the presence of the Ag, and a rapid desensitization; i.e. further exposures to Ag fail to evoke new contractions. 3. In marked contrast, chicken intestine responds to the Ag with a contraction that remains at its maximal initial value for ca 5 min and then declines only slowly. 4. Exposure to the Ag does not desensitize chicken intestine, which relaxes upon washing out the antigenic protein but contracts again when this is re-introduced in the bath. 5. In addition, consecutive Schultz-Dale reactions of chicken intestine showed a consistent potentiation. They reached a maximal amplitude when the tissue was exposed to the Ag 5-7 times. Such a potentiation is abolished by storing the preparations for 24 hr at 4 degrees C. 6. These observations are discussed in terms of the known properties of avian antibodies.
