Yrinttd in Great Britain THE RELATIVE IMPORTANCE OF NERVOUS, HUMORAL AND INTRINSIC MECHANISMS IN THE REGULATION OF HEART RATE AND STROKE VOLUME IN THE DOGFISH SCYLIORHINUS CANICULA

Experiments involving supra-maximal electrical stimulation of the vagus have indicated that the stimulation of the peripheral cut ends of the branchial cardiac branches produces a more intense cardio-inhibition than the stim-ulation of visceral cardiac branches. It is suggested that the visceral cardiac branches may have a mainly sensory function. In no case could cardio-acceleration be obtained during vagal stimulation either before or after injection of atropine, and any increases in stroke volume that occurred accompanied reductions in heart rate. This relationship was considered to be a manifestation of Starling's Law of the heart and it has been concluded that there is no augmentary sympathetic innervation to the dogfish heart. Evidence also indicates that the Starling relationship is responsible for the increase in stroke volume which accompanies the bradycardia during hypoxia. Circulating catecholamines do not appear to be of importance in this response although they are concerned in cardio-vascular regulation during normoxia