THE CIRCULATION OF THE BLOOD AND LYMPH 91 



and registering the movement of the pulse, as is Marey's 

 Dwn ' sphygmograph of transmission.' 



In a normal pulse-tracing (Fig. 27) the ascent is abrupt 

 and unbroken ; the descent is more gradual, and is inter- 

 rupted by one, two, or even three or more, secondary 

 wavelets. The most important and constant of these is the 

 one marked 3, which has received the name of the dicrotic 

 wave. Usually less marked, and sometimes absent, is the 

 wavelet 2 between the dicrotic elevation and the apex of 



i, Primary elevation; 

 2, predicrotic or first tidal 

 wave ; 3, dicrotic wave. 

 The depression between 

 2 and 3 is the dicrotic or 

 aortic notch ; 3 is better 

 marked in B than in A. 

 C, dicrotic pulse with low 

 arterial pressure ; D, pulse 

 with high arterial pressure 

 summit of primary ele- 

 vation in the form of an 

 ascending plateau. E, sys- 

 tolic anacrotic pulse ; the 

 secondary wavelet a occurs 

 during the upstroke corre- 

 sponding to the ventricular 

 systole. F, presystolic 



anacrotic pulse; a occurs r- T ~ ,, P T TTC TUA/-TV/-C 



just before the systole of FlG ' 27 '~ L ULSE TRACINGS - 



the ventricle. In this rarer 



form of anacrotism, a may sometimes be due to the auricular systole when the aortic 

 valves arc incompetent. 



the curve. It is generally termed the predicrotic wave. 

 Following the dicrotic wave are sometimes seen one or more 

 ripples, which have been called by some elastic elevations. 



In the explanation of the pulse-tracing, a fundamental fact to be 

 borne in mind is the elasticity of the vessels. When an incompressible 

 fluid like water is injected by an intermittent pump into one end of 

 an elastic tube a wave is set up, which is transmitted to the other 

 end of the tube. It is a positive wave that is, it causes an increase 

 of pressure and an expansion of the tube wherever it arrives ; and if 

 a series of levers be placed in contact with the tube, they will rise 

 and sink in succession as the wave passes them. After the passage of 

 this primary wave the walls of the tube, instead of coming instantlv to 

 rest in their original position, regain it by a series of oscillations, first 

 shrinking too much, then expanding too much, but at each move- 

 ment coming nearer to the position of equilibrium. Each vibration 

 of the elastic wall is of course accompanied by a change of pressure 

 in the contents of the tube. This change of pressure runs along the 

 tube as a wave ; and such waves, succeeding the primary one, may 

 be called secondary waves of oscillation. These secondary waves will 

 be set up in an elastic system whether the distal end of the system 



