that it is impossible, under circumstances as trying as those in which Private Mulvaney and his companions were placed, for all the cutaneous constrictor nerves to let go their grip at the same time. Terror heightens the control of the vaso-motor centre over the vessels of the skin; it increases vagus inhibition of the heart. Even disgust evoked by a revolting sight or a foul smell may call the vagus so forcibly into action as to bring the heart to a standstill. =The Pulse.=—The arterial system is always distended. The pressure in the largest arteries amounts to about 140 millimetres of mercury. The source of pressure is the beat of the heart pushing the blood forward against the resistance offered to its flow by the smallest vessels. At every stroke another 3 ounces is added to the already overfull vessels. In the aorta, therefore, the blood moves forward with jerks, but by the time it reaches the capillaries the intermittent accessions of force have been taken up by the elastic walls of the vessels and returned to the stream in the form of constant pressure. In the very smallest arteries the blood flows in a steady stream. If the corpuscles in a capillary vessel are watched under the microscope, they show no variations in rapidity synchronous with the beat of the heart. The “pulse” in the larger arteries is the push given to the column of blood by the sudden contraction of the left ventricle. Its propagation along the arteries will be understood if it is remembered that the blood is contained within elastic tubes. The first effect of the ejection into the aorta of an additional quantity of blood is the distension of its wall. The wave of distension travels down all the arteries of the body with gradually decreasing force. [Illustration: FIG. 14.—SPHYGMOGRAPH. A, An ivory button which is pressed on the skin over the radial artery by a metal spring. B, A continuous screw which works against the cogwheel C. By rotating B, the lever D is raised to a position in which its point scratches the travelling-plate E (covered with blackened paper). F, A box containing clockwork which moves E. G, A screw by means of which the pressure of the spring is adjusted to the force of the pulse.] [Illustration: FIG. 15. A, A cardiogram, or tracing of the impulse of the heart, recorded on a blackened plate borne on the end of a vibrating tuning-fork; _a-b_, the systole of the auricles; _b-e_, the ventricular systole. From _c-e_ the heart is shrinking as blood leaves it by the aorta and pulmonary artery. B, C, D, E, F, Sphygmograms. B is shaded to show the portion of the pulse-wave which corresponds to the systole of the heart. C, High-tension pulse of vigorous health. D, Low-tension pulse. E, Dicrotic pulse of fever. F, Hog-backed pulse of hardened (atheromatous) arteries.]