THE CIRCULATION OF THE BLOOD. 



139 



which will write the effect on a smoked card, which is made to move by 

 clockwork in the direction of the arrow. Thus a tracing of the pulse is 



FIG. 124. The Sphygmograph applied to the arm. 



obtained, and in this way much more delicate effects can be seen than 

 can be felt on the application of the finger. 



The tracing of the pulse (sphygmogram), obtained by the use of the 

 sphygmograph, differs somewhat according to the artery upon which it 

 is applied, but its general characters are much the same in all cases. It 

 consists of: A sudden upstroke (Fig. 125, A), which is somewhat higher 

 and more abrupt in the pulse of the carotid and of other arteries near 

 the heart than in the radial and other arteries more remote; and a 

 gradual decline (B), less abrupt, and therefore taking a longer time than 

 (A). It is seldom, however, that the decline is an uninterrupted fall; it is 

 usually marked about half-way by a dis- 

 tinct notch (c), called the dicrotic notch, 

 which is caused by a second more or less 

 marked ascent of the lever at that point 

 by a second wave called the dicrotic 

 wave (D); not unfrequently (in which 

 case the tracing is said to have a double 

 apex) there is also soon after the com- 

 mencement of the descent a slight 

 ascent previous to the dicrotic notch: 

 this is called the pre- dicrotic ivave (c), 

 and in addition there may be one or more 

 slight ascents after the dicrotic, called post-dicrotic (E). 



The explanation of these tracings presents some difficulties, not, how- 

 ever, as regards the two prirnary factors, viz., the Upstroke and down- 

 stroke, because they are universally taken to mean the sudden injection 

 of blood into the already full arteries, and that this passes through the 

 artery as a wave and expands them, the gradual fall of the lever signi- 

 fying the recovery of the arteries by their recoil. It may be demonstrated 

 on a system of elastic tubes, where a syringe pumps in water at regular 

 intervals, just as well as on the radial artery, or on a more complicated 

 system of tubes in which the heart, the arteries, the capillaries and veins 

 are represented, which is known as an arterial schema. If we place two 



FIG. 1 5 Diagram of pulse-tracing. 

 A, upstroke; B, downstroke; c, pre-di- 

 crotic wave; D, dicrotic; E, post-dicrotic 

 wave. 



