THE CIRCULATION OF THE BLOOD 277 



For the purpose of obtaining the time of all these events, the recording 

 surface was divided into equal spaces by vertically drawn lines. The rate 

 of movement of the surface was such that each division corresponded to 

 one-tenth of a second. The record thus indicates that the auricular con- 

 traction lasted approximately 0.2 second, the ventricular contraction 0.4 

 second, and the pause 0.4 to 0.6 second. 



From similar experiments made on other animals, e.g., the dog, similar 

 results have been obtained; but by reason of the employment of more 

 sensitive and more quickly responsive tambours, the curve of the auricular 

 contraction exhibits variations not recorded by the forms of tambour used 

 in earlier experiments. Reference to these variations will be alluded to in 

 subsequent paragraphs. The results obtained by recent observers now 

 generally accepted are in accord with the results obtained by Chauveau and 

 Marey by means of their cardiac tambours as shown in Fig. 120. 



The Movement of the Blood Dur- 

 ing the Cycle. From the characteris- 

 tic features of the foregoing record it is 

 apparent that with the relaxation of the 

 auricular walls, blood at once flows 

 from the venae cavae and the pulmonic 

 veins into the auricular cavities and 

 continues so to do throughout the entire 

 auricular diastole. With the relaxation 

 of the ventricular walls, however, the 

 blood that has accumulated in the 

 auricles up to this time, or its equiva- 

 lent coming from the venae cavae and pulmonic veins, now flows into the 

 ventricles until they are nearly filled. Before they are filled, however, the 

 auricular diastole comes to an end, the auricular walls again contract and 

 force some of their contained blood into the ventricles and thus rapidly com- 

 plete the filling. The ventricular systole immediately follows, during which the 

 blood is driven into the pulmonic artery and aorta. This having been ac- 

 complished, the ventricles relax, and the blood that has been accumulating 

 in the auricles begins to flow into the ventricles, after which the same series 

 of events follows as in the previous cycle. 



The Curp of the Systole and Diastole of the Heart. In the study 

 of the volume* changes of the heart by means of a specially devised cardi- 

 ometer, Henderson was enabled to record the contraction and relaxation 

 movements of the heart, obtaining thereby a curve that resembled the curve 

 of the contraction and relaxation of a skeletal muscle. If this curve is re- 

 versed and superposed on a curve of the intra-ventricular pressure, their 

 relation one to an other becomes apparent, Fig. 121. 



The chief characteristic of the systolic portion of the curve, viz.: hs 

 ascent, though less than that of the pressure curve, shows that with 

 te opening of the semilunar valves, b, a large portion of the volume of the 

 blood in the ventricles, 90 per cent, according to Henderson, is quickly and 

 in a uniform manner discharged, after which the outflow slows and finally 

 ceases as indicated by the rounded apex of the curve. The chief character- 

 istic of the diastolic portion of the curve, viz. : its steep descent, though less 

 than that of the pressure curve, shows that with the opening of the auriculo- 



FIG. 121. THE VOLUME CURVE OF 

 THE HEART CONTRASTED WITH THE CURVE 

 OF THE INTRAVENTRICULAR PRESSURE. 



