PRODUCTION OF THE PULSE 53 



contraction of the ventricles, which forces the blood onward in the inter- 

 vals of the heart's action. This recoil produces what is known as the 

 dicrotic pulse. It is in this way that the physical property of elasticity 

 of the vessels favors the blood-current The arteries are not only elastic 

 but contractile ; and this property, which gives tonicity to the vessels, 

 aids in adapting them to the quantity of blood which they contain and 

 regulates the arterial pressure as well as the supply of blood to different 

 parts of the capillary system. 



A study of the elasticity and contractility of the arteries naturally leads 

 to a consideration of the pulse. With each ventricular systole there is 

 a wave of dilatation which extends from the aorta to the smallest arteries. 

 There is, however, a slight delay in the pulse in the smaller vessels. The 

 difference in time between the ventricular systole and the pulse in the 

 feet is about one-seventh of a second. 



Locomotion of the Arteries and Production of the Pulse. With each 

 contraction of the heart, the arteries are increased in length and many of 

 them undergo a considerable locomotion. This may be readily observed 

 in vessels that are tortuous in their course and is frequently quite 

 marked in the temporal artery in old persons. The elongation may also 

 be observed by watching attentively the point where an artery bifurcates, 

 as at the division of the common carotid. It is simply the mechanical 

 effect of sudden distention, which, while it enlarges the calibre of the 

 vessel, causes an elongation that is even more distinct. 



The finger placed over an exposed artery or one that lies near the 

 surface experiences a sensation at every beat of the heart as though the 

 vessel were striking against it. Ordinarily this is appreciated when 

 the current of blood is subjected to a certain degree of obstruction, as 

 in the radial, which can readily be compressed against the bone. In an 

 artery imbedded in soft parts which yield to pressure, the actual dilata- 

 tion of the vessel being very slight, pulsation is felt with difficulty if at all. 

 When obstruction of an artery is complete, as after tying a vessel, the 

 pulsation above the point of ligature is quite marked and can easily be 

 appreciated by the eye. The explanation of this exaggeration of the 

 movement is the following : Normally, the blood passes freely through 

 the arteries and produces, in the smaller vessels, very little movement or 

 dilatation ; when, however, the current is obstructed, as by ligation or 

 even compression with the finger, the force of the heart is not sent 

 through the vessel to the periphery, but is arrested and therefore be- 

 comes more easily appreciated. In vessels that have become undilatable 

 and incompressible from calcareous deposits, the pulse cannot be felt. 

 The character of the pulse indicates, to a certain extent, the condition of 

 the heart and vessels. 



