That great excitement is accompanied by sympathetic innervations which increase the contraction of the small arteries, render unusually forcible the heart beat, and consequently raise arterial pressure, has already been pointed out ( see p. 26). Indeed, the counsel to avoid circumstances likely to lead to such excitement, which is given to persons with hardened arteries or with weak hearts, is based on the liability of serious consequences, either in the heart or in the vessels, that might arise from an emotional increase of pressure in these pathological conditions. That great muscular effort also is accompanied by heightened arterial pressure is equally well known, and is avoided by persons likely to be injured by it. Both in excitement and in strong exertion the blood is forced in large degree from the capacious vessels of the abdomen into other parts of the body. In excitement the abdominal arteries and veins are contracted by impulses from the splanchnic nerves. In violent effort the diaphragm and the muscles of the belly wall are voluntarily and antagonistically contracted in order to stiffen the trunk as a support for the arms; and the increased abdominal pressure which results forces blood out of that region and does not permit reaccumulation. The general arterial pressure in man, as McCurdy[80] has shown, may suddenly rise during extreme physical effort, from approximately 110 millimeters to 180 millimeters of mercury. The Effect of Increasing Arterial Pressure What effect the increase of arterial pressure, resulting from excitement or physical strain, may have on muscular efficiency, has received only slight consideration. Nice and I found there was need of careful study of the relations between arterial pressure and muscular ability, and, in 1913, one of my students, C. M. Gruber, undertook to make clearer these relations. The methods of anesthesia and stimulation used by Gruber were similar to those described in the last chapter. The arterial blood pressure was registered from the right carotid or the femoral artery by means of a mercury manometer. A time marker indicating half-minute intervals was placed at the atmospheric pressure level of the manometer. And since the blood-pressure style, the writing point of the muscle lever, and the time signal were all set in a vertical line on the surface of the recording drum, at any given muscular contraction the height of blood pressure was simultaneously registered.