THE CIRCULATION OF THE BLOOD. 



125 



the lever writes upon the paper, and a tracing of the heart's impulse or 

 cardiogram, is thus obtained. 



By placing three small india-rubber air-bags or cardiac sounds in the 

 interior respectively of the right auricle, the right ventricle, and in an 

 intercostal space in front of the heart of living animals (horse), and 

 placing these bags, by means of long narrow tubes, in communication 

 with three levers, arranged one over the other in connection with a re- 

 gistering apparatus (Fig. 117), MM. Chauveau and Marey have been able 



FIG. 117. Apparatus of MM. Chauveau and Marey for estimating the variations of endocardia! 

 pressure, and production of impulse of the heart. 



to record and measure with much accuracy the variations of the endocar- 

 dial pressure and the comparative duration of the contractions of the 

 auricles and ventricles. By means of the same apparatus, the synchron- 

 ism of the impulse with the con- 

 traction of the ventricles, is also well 

 shown; and the causes of the several 

 vibrations of which it is really com- 

 posed, have been demonstrated. 



In the tracing (Fig. 118), the inter- 

 vals between the vertical lines repre- 

 sent periods of a tenth of a second. 

 The parts on which any given vertical 

 line falls represent simultaneous events. 

 It will be seen that the contraction of 

 the auricle, indicated by the marked 

 curve at A in first tracing, causes a 

 slight increase of pressure in the ven- 

 tricle, which is shown at A' in the sec- 

 ond tracing, and produces also a slight 

 impulse, which is indicated by A" in 

 the third tracing. The closure of the 

 semilunar valves causes a momentarily 

 increased pressure in the ventricle at D' affects the pressure in the auri- 

 cle D, and is also shown in the tracing of the impulse also, D". 



The large curve of the ventricular and the impulse tracings, between 

 A' and D', and A" and D", are caused by the ventricular contraction, 

 while the smaller undulations, between B and c, B' and c', B" andc", are 



FIG. 118. Tracings of (1), Intra-auri- 

 cular, and (2), Intra- ventricular pressures, 

 and (3), of the impulse of the heart, to be 

 read from left to right, obtained by Chau- 

 veau and Marey's apparatus. 



