REFLEX CARDIAC AND RESPIRATORY INHIBITION IN THE ELASMOBRANCH, SCYLLIUM CANICULA

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Abstract
1. Mechanical and electrical stimulation of various parts of the surface of the body and certain viscera resulted in cardiac and respiratory inhibition when the spinal cord was pithed posterior to the second vertebra in Scyllium canicula. 2. Faradic stimulation of the central end of the cut vagus, either the cardiac branches or the visceral ramus, and the central ends of the cut hypobranchial and lateral line nerves produced reflex cardiac and respiratory inhibition. 3. Stopping or starting the perfusion water through the gills or suddenly altering its rate of flow resulted in respiratory inhibition and sometimes cardiac inhibition. 4. Mechanical or electrical stimulation of the surface of the ventricle produced reflex cardio-inhibition and sometimes respiratory inhibition. 5. When stimulation was strong or prolonged, both cardiac and respiratory inhibition occurred, but weak stimulation of the gills or pharynx frequently produced only respiratory inhibition, whereas weak stimulation of the skin or viscera often produced only cardiac inhibition. 6. Both cardiac and respiratory inhibition were obtained for over twenty-four hours when the gills were perfused; for over three and one-half hours without perfusion; and for over one hour with the aorta transected at the heart. These phenomena, therefore, are true reflexes and are not due to alterations in blood pressure in the medulla. 7. The emergency function of the inhibitory responses is pointed out.

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