The Response of the Dogfish to Anoxia

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Abstract
1. Curves relating the cardiac and respiratory rates of Squalus acanthias L. to the minute volume of water passing through the pharynx are presented; decreased minute volume caused respiratory and cardiac slowing. 2. The change in heart rate was dependent on anoxia; the respiratory response was largely independent of the oxygen content of the inspired water. 3. The respiratory and cardiac changes caused by deoxygenated water flow are described. Anoxia produced cardiac inhibition and a fall in blood pressure; respiration slowed at first and then accelerated to a level above the resting rate. 4. Gill deafferentation distinguished a short-latency reflex cardiac inhibition from a weaker long-latency slowing of central origin. The reflex, it is suggested, was mediated by branchial chemoreceptors. The existence of the central response was confirmed by occluding the conus with a clamp. 5. It is suggested that bradycardia in response to anoxia has a significance in relating cardiac output to the minute volume of water flow, thus ensuring adequate loading of the haemoglobin in the blood leaving the gills.

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