THE CIRCULATION. 237 



movements of the auricles, ventricles, and the beating of the heart 

 against the walls of the chest. There are, to-day, numerous cardio- 

 graphs, all of them, however, being only modifications of Marey's 

 tambours. 



Sanderson's instrument consists of' a hollow disc, the rim and 

 back of which are of brass, while the front is of thin rubber. On 

 its back is a flat steel spring bent at right angles, and its unattached 

 end is provided with an ivory button which is directly over the cen- 

 ter of the rubber membrane. The ivory button is applied over the 

 point where the apex-beat is most plainly felt. During the applica- 

 tion of the apparatus the ivory button is kept continually in motion 

 by the surface pulsations. Each movement of the button sets the 



i 



Fig. 71. Cardiogram (B) with Simultaneous Record of Heart- 

 sounds (A). (HuBTHLE, STARLING.) 



1, Position of first sound. 2, Position of second heart-sound. The first heart- 

 sound corresponding to the systole of the ventricle begins at the notch in the 

 cardiogram near the top of the ascent; hence the ascent of curve preceding 

 this notch is due to auricular systole forcing blood into the ventricle, and the 

 ventricular systole is indicated by the notch. 



rubber membrane in motion, and, as the drum is airtight and in 

 communication with a second drum with a recording lever, the 

 diminution of air in the first causes an increase in the content of 

 air in the second, and an elevation of its recording lever on a 

 smoked drum. Each systole of the ventricle causes a sudden rise 

 of the lever, and the end of the systole is noted by a marked gradual 

 descent of it. 



The cardiogram is read from left to right, and normally shows 

 a small elevation, corresponding to auricular systole, immediately 

 succeeded by a very abrupt rise which marks ventricular systole. 

 This is held for 0.3 of a second and presents small vibrations, which 

 are attributed to the closure of the semilunar valves. The very 

 abrupt, downward stroke marks the pause, or diastole. 



