The frequency of the heart beat, which expresses itself in the pulse rate, is one of the various vital phenomena over which conscious control is not ordinarily exercised. There may be marked differences in the pulse rate found in different individuals without their having any pathologic significance attached to them, although the newer studies in nutrition, notably those of F. G. Benedict at the Boston Nutrition Laboratory of the Carnegie Institution of Washington, have tended to show a surprising parallelism between pulse rate and the intensity of metabolism. It is well known that the heart beat is quickened by warmth and diminished by cold applied to the surface of the skin of the vagus. The act of swallowing causes a reflex increase in heart rate by inhibition of the tonic action.
The function of the nervous system in the control of the frequency of the heart beat is familiar to