184 THE CIRCULATION OF THE BLOOD 



three small india-rubber air-bags or 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 the horse. These bags were connected by 

 means of long narrow tubes with three levers arranged one over the other 



FIG. 161. Apparatus of MM. Chauveau and Marey for Estimating the Variations of Endo- 

 cardiac Pressure, and Production of the Impulse of the Heart. 



in connection with a registering apparatus, figure 161. The synchronism 

 of the impulse with the contraction of the ventricles is also well shown by 

 means of the same apparatus, and the causes of the several vibrations of 

 which it is really composed have been demonstrated. 



FIG. 162. Tracings of i, Intra-auricular; 2, Intraventricular Pressures; and 3, of 

 the Cardiac Impulse of the Heart. To be read from left to right. Obtained by Chauveau 

 and Marey. 



In the tracing, figure 162, the intervals between the vertical lines rep- 

 resent 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 the first tracing, causes 

 a slight increase of pressure in the ventricle which is shown at A ' in the second 



