278 



TEXT-BOOK OF PHYSIOLOGY. 







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 synchronously. That they do so can be shown by attaching 

 levers to their walls and thus recording their activities. The syn- 

 chronism is so perfect that until 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 mechan- 

 ism seemed to lie, the synchronism of the former is not interfered 

 with; that the apical halves of the ventricles will beat synchronously 

 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 neigh- 

 boring parts of the ventriclelj It is therefore probable that the syn- 

 ch ron ism 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 



he e^ejgy_gf jjie left an 



energetically. TJ^gjaJjgJjiS^ 



sides is approximately 3 to i. 

 Intra-cardiac Pressure. 



max valve 



to manometer 



mm valve 



It has been stated that during the 

 pause of the heart when its cavities are 

 filling with blood the semilunar valves 

 are kept closed by the pressure of the 

 blood in the pulmonary artery and 

 aorta, a pressure due to the resistance, 

 as will be explained later, offered to 

 the flow of the blood mainly by the 

 smaller arteries and capillaries; that 

 they are opened only when the press- 

 ure of the blood within the ventricle 

 exceeds that in the arteries. It be- 

 comes, therefore, a matter of impor- 

 tance to determine the extent of this 

 pressure as well as its variations dur- 

 ing the course of a cardiac cycle. 

 This can be done by inserting a long 

 catheter into either the right or left 

 ventricle, through the jugular vein or 

 the carotid artery respectively, and 

 connecting its free extremity with a 

 mercurial manometer. By the inter- 



position of a double valve such as represented in Fig. 122, it 

 becomes possible, according to the direction the blood is permitted 

 to flow, to obtain either the maximal or the minimal pressure that 

 occurs in the heart during a series of cycles. Thus Goltz found in 

 the left ventricle of the dog a maximal pressure of 114 to 135 mm 

 m the right ventricle, a pressure of 35 to 62 mm. Minimal pres- 



FIG. 



122. V. 



1 'to heart 



FRANK'S VALVE. 

 This is placed in the course of 

 the tube between heart and 

 manometer, so that the latter 

 may be used as a maximum, 

 minimum, or ordinary man- 

 ometer according to the tap 

 which is left open. (Starling.') 



