CIRCULATION OF THE BLOOD. 



121 



of the contractions of the auricles and ventricles. By means of the same 

 apparatus, the synchronism of the impulse with the contraction of the 

 ventricles, is also well shown; and the causes of the several vibrations of 

 which it is really composed, have been discovered. 



In the tracing (Fig 105), the intervals between the vertical lines rep- 

 resent periods of a tenth of a second. The parts on which any given 



FIG. 104. Apparatus of MM. Chauveau and Marey for estimating the variations of endocardia! 

 pressure, and production of impulse of the heart. 



vertical line falls represent, of course, simultaneous events. Thus, it 

 will be seen that the contraction of the auricle, indicated by the upheaval 

 of the tracing at A in first tracing, causes a slight increase of pressure in 

 the ventricle (A' in second tracing), and produces a tiny impulse (A" in 

 third tracing). So also, the closure of the 

 semilunar valves, while it causes a momen- 

 tarily increased pressure in the ventricle at D', 

 does not fail to affect the pressure in the auri- 

 cle D", and to leave its mark in the tracing of 

 the impulse also, D", 



The large upheaval of the ventricular and 

 the impulse tracings, between A' and D', and 

 A" and D", are caused by the ventricular con- 

 traction, while the smaller undulatitfns, between 

 B and c, B' and c', B" and c", are caused by 

 the vibrations consequent on the tightening 

 and closure of the auriculo- ventricular valves. 



Although, no doubt, the method thus de- 



., , , , i - impulse of the heart, to be read 



Scribed may show a perfectly Correct View of from left to rieht, obtained by 

 , i , , . . , . .,11-iT Chauveau and Marey's apparatus. 



the endocardiac pressure variations, it should be 



recollected that the muscular walls may grip the air-bags, even after the 

 complete expulsion of the contents of the chamber, and so the lever might 

 remain for a too long time in the position of extreme tension, and would 



FIG. 105. Tracings of (1), In- 

 fra-auricular, and ( 2 ), Intra-ven- 

 tricular pressures, and ( 3 ), of the 



