-An increase of blood pressure in the cephalic end of the carotid arteries of the dog, whose general blood pressure is at or above a normal level, invariably causes a slowing of the heart, in some cases accompanied by a respiratory arrhythmia. After denervating the sinus caroticus according to the method described by Hering, an increase of blood pressure in the cephalic end of the carotid does not affect the heart rate. The slowing of the heart which accompanies, under normal conditions, such an increase of cephalic carotid pressure is a reflex from the sinus caroticus and apparently homolateral. Sudden elevation of blood pressure in the vertebral arteries does not produce a change in heart rate when the sinus caroticus has been denervated. These observations confirm those of Hering, viz., that an increase of pressure in the cephalic end of a carotid or a vertebral artery causes no slowing of the heart by a direct action on the cardio-inhibitory center; but through a reflex from the sinus caroticus. An increase of blood pressure in the body circulation produces a reflex slowing of the heart (pres-sor-vagus reflex). Epinephrin has no direct stimulating action on the cardio-inhibitory center of the dog. The primary slowing of the heart produced by epinephrin is a reflex due to the action of increased blood pressure on the endings of the sinus and depressor nerves. A rise of intracranial pressure causes a slowing of the heart which persists after denervating the carotid arteries.