=The Pulse.=--The _pulse wave_ is characterized by a quick rise and a slow fall, though this cannot ordinarily be distinguished by the finger. In some slow fevers, however, the fall is very long and distinct ripples can be felt. This is known as the _dicrotic pulse_. With age the arterial walls grow stiffer and more rigid and less adapted to their work. In certain cases of heart disease the heart does not transmit all the beats to the pulse and to get the true rate the heart must be listened to. The rate at which the pulse wave travels varies with the size of the artery and the force of the heart beat but is about 15 to 20 feet a second. The flow is most rapid in the arteries because they are nearest the heart, where the pressure is greatest, and slowest in the capillaries, where the area is greatest, the sectional area of the capillaries, known as the _peripheral area_ because it is farthest from the heart, being larger than that of the large arteries. Thus rapidity of flow varies with pressure and with area. =Blood Pressure.=--Liquids, moreover, are incompressible and exert pressure on the walls of the tubes through which they pass. The amount of pressure depends upon the inflow and outflow, increasing directly with the inflow and inversely with the outflow, that is, the smaller the outlet the greater the pressure, and _vice versa_. The pressure is also greatest nearest to the inflow and gradually decreases with distance until at the point of outflow there is practically no pressure. So, in the arteries the blood pressure is greatest in the large vessels nearer the heart and gradually decreases as they branch into smaller and smaller vessels. In passing through the capillaries, owing to their small size and resultant increased friction, the blood meets with more resistance, the peripheral resistance, and this resistance usually regulates the pressure in the arteries. The greater the peripheral resistance, as a rule, the greater the arterial pressure. The pressure in the capillaries is very slight and in the veins there is practically no pressure. In fact, in the large veins near the heart the pressure is negative and the blood is almost sucked into the heart. Pressure, then, is greatest in the arteries and least in the veins, while the rate of flow is fastest in the arteries--300 to 500 millimeters a second--and slowest in the capillaries--75 millimeters a second--being a little faster again in the veins--200 millimeters a second. Blood pressure is gauged by opening a vessel and inserting a _manometer_, the pressure being determined by the height to which the mercury is raised. In man the pressure in the arteries is 120 to 160 millimeters. It is considerably heightened during inspiration by the increased pressure of the lungs on the heart and great vessels. In pericarditis the opposite is true.