Abstract
Conditioned reflex changes of the rate and intensity of the cardiac contractions were altered by the removal of the adrenal medulla. Studies were made on chronic preparations of dogs having a pericardial fistula. The conditioned cardiac reflexes were reduced or disappeared completely at the third, fourth, and fifth postoperative days. The amount by which the amplitude of the contractions changed in response to the stimulus was different on the fifth and sixth postoperative days. The changes were phasic: first there was a reduction, then an intensification, and finally a gradual re-establishment of the preoperative level. In response to an unconditioned stimulus, the failure of the normal increase in cardiac contractions was more marked and prolonged. The removal of the adrenal medulla had no significant effect upon the elicitation of an increased heart rate.
Published Version
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