THE CIRCULATION OF THE BLOOD 28l 



filling of the ventricles, and hence their effective working as force-pumps is 

 more readily secured. The auricles may therefore be regarded as L/- 

 pumps. For this reason it is probable, notwithstanding the contraction of 

 the circular muscle-fibers at the terminations of the venous system, that the 

 flow of blood into the auricles is never entirely arrested, but merely retarded 

 Regurgitation m these vessels does not occur for the reason that the re- 

 tardation develops a side pressure during the auricular contraction which 

 is equal to if it does not exceed the pressure in the auricle 



Synchronism of the Two Sides of the Heart. If the balance of the 

 circulation is to be maintained, the two sides of the heart must act synchron- 

 ously. That they do so can be shown by attaching levers to their walls, and 

 thus recording their activities. The synchronism is so perfect that until 



S.a.-D.v. 



D.a.-S.v. 



FIG. 123. DIAGRAMMATIC REPRESENTATION OF THE AURICULAR SYSTOLE, S.a., WITH THE 

 VENTRICULAR DIASTOLE, D. v., AND OF THE AURICULAR DIASTOLE, D. a., WITH THE VENTRICULAR 

 SYSTOLE, S.v. C.s. and C.i. Superior and inferior cavae; A.d. (atrium dextrum) right auricle; 

 A,s. (atrium sinistrum) left auricle; V.d. (ventriculus dexter) right ventricle; V.s. (ventriculus 

 sinister) left ventricle; P. pulmonic artery; A. aorta; P.P. papillary muscles. (Landois.) 



recently it was generally believed to be dependent on nerve connections; but 

 Porter has shown that if the ventricles are cut away from the auricles, in 

 which the nerve mechanism seems to lie, the synchronism of the former is 

 not interfered with; that the apical halves of the ventricles will beat syn- 

 chronously if perfused with blood through an artery; that a very small bridge 

 of muscle-tissue will carry the wave of excitation from one part to neighboring 

 parts of the ventricle. It is therefore probable that the synchronism is 

 accomplished through muscle connections only. The left ventricle, in 

 keeping with the greater work it has to do, has a greater development than 

 the right, and therefore contracts more energetically. The ratio between 

 the energy of the left and right sides is approximately 3 to i. 



