MECHANICS OF THE CIRCULATION IN THE VESSELS 103 



Fig. 37. Scheme of Marey's Sphygmo- 

 graph. A, toothed wheel connected with 

 axle H, and gearing into toothed upright 

 B; C, ivory pad which rests over blood- 

 vessel and is pressed on it by moving G, 

 a screw passing through the spring J ; 

 E, writing-lever attached to axle H, and 

 moved by its rotation. E writes on D, a 

 travelling surface moved by clockwork F. 



to magnify the movements of the pulse was made by loosely attaching 



a thin fibre of glass or wax to the skin with a little iard, in order to 



demonstrate the venous pulse which appears under certain conditions. 



In all modern sphygmographs there is a part, usually button-shaped, 



which is pressed over the artery by means of a spring, as in Marey's 



and Dudgeon's sphygmographs, 



or by a weight, or by a column of 



liquid. In Marey's instrument, 



the button acts upon a toothed 



rod gearing into a toothed wheel, 



to which a lever, or a system of 



levers, is attached. The lever has 



a writing-point which records the 



movement on a smoked plate, or 



a plate covered with smoked 



paper, drawn uniformly along by 



clockwork (Figs. 37, 100). Special 



forms of sphygmographs (poly- 

 graphs) have been devised, which, 



by the addition of one or more 



recording tambours, permit the 



simultaneous record of movements from two or more points of the 



vascular system for example, the radial artery and the jugular vein, 



or the radial or carotid artery, jugular vein, and the apex of the heart. 



In rare cases, with de- 

 fect of the chest wall, 

 a tracing may be ob- 

 tained even from the 

 aorta (Fig. 40). 



In a normal arterial 

 pulse-tracing (Fig. 38) 

 the ascent or ana- 

 erotic limb is abrupt 

 and unbroken ; the 

 descent or katacrotic 

 limb is more gradual, 

 and is interrupted by 

 one, two, or even 

 three or more, second- 

 ary wavelets. The 

 most important and 

 constant of these is 



Fig. 38. Pulse-Tracings, i, primary elevation ; 2, predi- 

 crotic 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 elevation in the 



the one marked 3, 

 which has received the 

 name of the dicrotic 

 wave. Usually less 

 marked, and some- 

 times absent, is the 

 wavelet 2 between the dicrotic elevation and the apex of the curve. 

 It is generally termed the predicrotic wave. Oscillations, due to 

 vibrations of the recording apparatus, appear on many pulse- 



form of an ascending plateau. E, systolic anacrotic 

 pulse; the secondary wavelet occurs during the 

 upstroke corresponding to the ventricular systole. 

 F, presystolic anacrotic pulse; a occurs just before 

 the systole of the ventricle. In this rarer form of 

 anacrotism, a may sometimes be due to the auricular 

 systole when the aortic valves are incompetent. 



