Control of the Peripheral Circulation, Physiologists’ Bliss and Biophysicists’ Ignorance. More than a century ago, Bernard (1851) discovered the function of the vasomotor nerves to the ear of the rabbit by cutting them and observing the vasodilation. Two years later, 1853, Sequard stimulated the sympathetic nerves in the neck of a rabbit and noted the intense vasoconstriction. It is astonishing that only in the last few years have there been quantitative studies of the control of the caliber of the arterioles by these, or other vasomotor nerves. Due to the recent work of Girling (I), Folkow (2), Folkow and Gernandt (3), Van Bobben-Broekema and Dirken (4), we now know what frequency of impulses in these nerves produces what degree of increase of resistance to flow, and can estimate the physiological range of frequencies in vasomotor nerves, both constrictor and dilator. These frequencies are very low, certainly less than zo/sec. Some details of the transmitter mechanism at the effector smooth muscle of the blood vessel wall are also known (2). It is perturbing to realize that the century of delay in obtaining this information is probably due to the use of improper electrical stimuli, like those of the inductorium or condenser discharges of short duration. To stimulate these nerves without destroying them, a stimulus of at least 15 msec. should be used. This lends weight to the remark of a physiologist at a meeting some years ago, that what physiology needed was a ‘moratorium on the inductorium.’Physiologists can also feel quite complacent about their knowledge of the control of the circulation by vasoactive drugs, though the discovery of the distinction between nor-adrenaline and adrenaline has required a repetition of many classical experiments to re-evaluate our knowledge. The monograph of Barcroft and Swan (5) shows how much has been done in this field. There remains, however, a very great area of ignorance regarding the ‘venimotor system’controlling the tone of the venous