The intravenous injn. of small vols. of strongly hypertonic solns. (10-20% NaCl, 50% glucose) results in marked changes in the heart rates of cats and dogs. In nembutalized cats and unan-esthetized or decerebrated dogs cardiac irregularities occur at first, and are followed by transient but profound bradycar-dia which is absent after bilateral cervical vagotomy. Relatively slight and variable changes in heart rate, without characteristic vagal bradycardia, occur following these injns. in dogs anesthetized with nembutal. The variability in the effects of nembutal upon the cardiac slowing mediated by the vagi obscures the fundamental similarity of the phenomenon as seen in cats and dogs, for it can be demonstrated in both spp. under specifically defined conditions.