THE CIRCULATION OF THE BLOOD. 



277 



max valve 



to manometer 



mi'n valve 



these vessels does not occur for the reason that the pressure in the auricles 

 is not higher than, if as high as, in the great veins. 



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 

 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. 



Intra-ventricular Pressure. 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 resis- 

 tance, 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 pressure of the blood within 

 the ventricle exceeds that in the arteries. It 

 becomes, therefore, a matter of importance 

 to determine the extent of this pressure as 

 well as its variations during 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 respec- 

 tively, and connecting its free extremity with a mercurial manometer. By 

 the interposition of a double valve such as represented in Fig. 135, it becomes 

 possible, according to the direction in which 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.; in the right ventricle, a pressure of 35 

 to 62 mm. Minimal pressures of 23 to 52 mm. for the left ventricle have 

 also been obtained. 



The maximal pressure in the ventricles during the systole, though always 

 higher than that in the arteries, is neither a fixed nor an invariable pressure, 

 as it rises and falls with the latter from moment to moment. Within limits 

 the cardiac power, and therefore the intra-ventricular pressure, is capable of 

 considerable increase. The function of the heart is to drive the blood 

 through the vessels with a given velocity. This is possible only by first over- 



to heart 



FIG. 127. v. 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 

 manometer according to the tap which 

 is left open. (Starling.) 



