94 A MANUAL OF PHYSIOLOGY 



arteries, or by muscular exercise (Fig. 69, p. 183), running, for 

 instance, which is supposed to lower the arterial pressure, partly by 

 dilatation of the muscular and cutaneous arterioles, and partly by 

 accelerating the venous flow (p. 121). The increase in the pulse- 

 rate may also have something to do in this case with the exaggeration 

 of the dicrotism, which is very frequently, although by no means 

 invariably, associated with a rapidly-beating heart, and therefore is 

 often seen in fever. On the other hand, in certain diseases asso- 

 ciated with a high arterial pressure the dicrotic elevation almost 

 disappears. Atheromatous arteries, being very inextensible, do not 

 allow a dicrotic pulse. 



Since the pulse represents a periodical increase and diminution in 

 the amount of distension of an artery at any point, the line joining 

 all the minima of the pulse-curve will vary in its height above the 

 base-line, or line of no pressure, according to the amount of per- 

 manent distension, i.e., permanent blood-pressure, which the heart in 

 any given circumstances is able to maintain. Any circumstance 

 that tends to lessen the permanent distension will cause a fall of the 

 line of minima, and any circumstance tending to increase the 

 distension will cause that line to rise. If, for example, the arm be 

 raised while a pulse-tracing is being taken from the wrist, the line of 

 minima falls because the permanent pressure in the radial artery is 

 diminished. 



The form of the pulse-curve varies in the different arteries, 

 and therefore in making comparisons the same artery should 

 be used. When the wave of blood only enters an artery 

 slowly, the ascending part of the curve will be oblique. 

 This is normally the case in a pulse-curve of a distant artery, 

 such as the posterior tibial. The height of the wave is also 

 less than in an artery nearer the heart, such as the carotid, 

 or even the axillary, where the primary elevation is rela- 

 tively abrupt (Fig. 71, p. 183). 



Anacrotic Pulse. As a rule, the ascent of the tracing is 

 unbroken by secondary waves, but in certain circumstances 

 these may appear on it. This condition, which, when well 

 marked at any rate, may be considered pathological, is 

 called anacrotism (Fig. 27). It is seen when the discharge 

 of the left ventricle into the aorta is slow and difficult e.g., 

 in old people whose arteries have been rendered less 

 extensible by the deposit of lime-salts in their walls 

 (atheroma), and in cases where the orifice of the aorta has 

 been narrowed from disease of the semilunar valves (aortic 

 stenosis). Since these conditions are in general associated 



