THE SPHYGMOGRAPH. 669 



leaves its tracing upon a piece of smoked glass which is moved for- 

 wards by clockwork, or upon a coil of paper which is constantly being 

 unwound. 



The waved lines traced by such an instrument show, by the number 

 of the undulations in a given space, the frequency of the pulse ; by the 

 length of the up and down strokes, the amplitude of the pulse move- 

 ment, or the force of the pulse ; and by the greater or less inclina- 

 tion of these strokes from the perpendicular, or the horizontal distance 

 between the points of commencement of the upward strokes, the dura- 

 tion of the pulse-waves. Besides this, certain variations in the lines 

 indicate other characters, such as firmness, or tremulousness, and so 

 forth. There is, however, one character of the pulse recognizable by 

 the finger, concerning which the sphygmograph gives information which 

 may be delusive, viz., the volume of the pulse, which may be full in very 

 different conditions of the system. A full pulse is usually slow and 

 strong, but it may be quick ; on the other hand, a small pulse is gen- 

 erally quick and feeble, but not necessarily so. The pulse is wiry, 

 thready, or small, in hemorrhage, or on approaching death. In re- 

 cording the pulse movements, this instrument also indirectly meas- 

 ures the force and duration of the systole of the left ventricle, and the 

 duration of the respiratory movements. 



The sphygmograph has been ingeniously employed by Marey to 

 assist in determining the cause of the pulse itself. An india-rubber 

 cylinder, provided with internal valves, is fitted at one end to a short, 

 and the other to a long, elastic tube. By alternately relaxing and 

 compressing the cylinder, water, under the direction of the valves, is 

 drawn in through the short tube, and pumped intermittently through 

 the longer one. This latter tube is disposed in three loose horizontal 

 coils, each of which is brought in contact with a separate sphygmo- 

 graphic lever, the pencils of all of which rest upon a paper previously 

 ruled with vertical and horizontal lines, and which revolves upon one 

 drum, common to the three pencils. The sphygmographic pencils being 

 placed, at starting, exactly under one another, and the drum being 

 made to revolve, three horizontal lines are first simultaneously traced ; 

 but when the india-rubber cylinder is repeatedly compressed, so as to 

 inject water by separate impulses into the long tube, thus imitating 

 the ventricular propulsion of the blood into the arteries; undulations, 

 resembling the pulse-waves, travel along the coils of the tube, and move 

 the three sphygmographic levers, the pencils of which record the mo- 

 ment of commencement, the extent, and the duration of the movements 

 occurring at three different points of the tube, by up and down lines 

 of corresponding character and form. In the first place, the line cor- 

 responding with the point nearest to the propulsive cylinder, shows a 

 greater amplitude in its undulation, owing to the greater force of the 

 lateral pressure on the walls of the tube at that point ; whilst, in the 

 other two lines, a progressive diminution in the vertical depth of the 

 undulating lines, shows a gradual diminution in the pressure, in pro- 

 portion to the distance from the agent of propulsion. But what is of 

 more interest in relation to the cause of the pulse- wave, is the fact, 

 that though the commencement of the wave, at each of the three points 



