158 THE MOVEMENT OF THE BLOOD. 



highest elevation is a small notch, which is produced by a slight vibration com- 

 municated to the blood by the partly destroyed semilunar valves in their ineffective 

 effort at closure. The enormous wave of blood that passes through the descending 

 aorta to the iliac artery after the closure of the semilunar valves is the cause of 



FIG. 63. I. Elastic Platform for Registering Vibration-curves. II. Vibration-curves Taken from the Body 

 of a Healthy Individual. III. Vibration-curves Taken from a Man Suffering from Aortic Insufficiency and 

 a High Degree of Cardiac Hypertrophy. 



the lowest drop of the elastic platform. This is followed by a rise caused by 

 the centripetal movement of the wave. The third rise, which then follows and 

 which is relatively low, appears to correspond with the development of the dicrotic 

 wave in the portion of the arterial system that is directed downward. 



THE MOVEMENT OF THE BLOOD. 



The closed system of blood- vessels with its many branches, endowed as 

 its walls are with elasticity and contractility, is not only completely 

 filled with blood, but it is in fact overfilled. The volume of the entire mass 

 of blood slightly exceeds the available space within the entire vascular 

 system. It follows, therefore, that the mass of blood everywhere exerts 

 a pressure on the vessel-walls that causes a corresponding distention of 

 the elastic coats. This is true, however, only during life. After death 

 the muscles of the blood-vessels relax and blood-plasma escapes into 

 the tissues, so that the vessels after death are found partially empty. 



If the volume of blood be conceived as equally distributed in the 

 entire vascular system, and as everywhere subject to the same pressure, 

 it would be in a condition of passive equilibrium, as is the case shortly 

 before death. If, however, the pressure to which the blood is subjected 

 be heightened at one point of the system of tubes, the blood will escape 

 from this point of increased pressure to some point where the pressure 

 is less; the movement (displacement of the blood-column) is, therefore, 

 the result of the existing difference in pressure. If the venae cavae or 

 the aorta in a living animal be suddenly occluded, the blood will continue 

 to flow at a gradually diminishing rate until the differences in pressure 

 in the entire circulation have been equalized. 



The velocity of the blood-stream is directly proportional to the 



