220 HANDBOOK OP PHYSIOLOGY. 



jection of blood into the already full arteries, and the gradual fall of 

 the lever signifying the recovery of the arteries by their recoil. These 

 points may be demonstrated on a system of clastic tubes, with a syringe 

 to pump in water at regular intervals, just as well as on the radial 

 artery, or on the more complicated system of tubes in which the heart, 

 the arteries, the capillaries and veins are represented, which is known 

 as an arterial schema. If we place two or more sphygmographs upon 

 such a system of tubes at increasing distances from the pump, we may 

 demonstrate first, that the rise of the lever commences earliest in that 

 nearest the pump, and secondly, that it is higher and more sudden, 

 while at a longer distance from the pump the wave is less marked, and 

 a little later. So in the arteries of the body the wave of blood gradu- 

 ally gets less and less as we approach the periphery of the arterial sys- 

 tem, and is lost in the capillaries. 



The origin of the secondary waves is still a matter of uncertainty. 



Fig. 185. Anacrotic pulse from a case of aortic aneurism. 



The anacrotic wave occurs when the peripheral resistance is high; that 

 is, when, for some time during the systole, the flow from the aorta 

 toward the periphery is slower than the flow from the ventricle into the 

 aorta. Thus, it is seen in some cases of nephritis where the arteries are 

 rigid and the peripheral resistance high. 



The dicrotic wave is the most important of the secondary waves, and 

 has been the subject of much discussion. It is constantly present in 

 pulse-tracings, but varies in height. In point of time the dicrotic wave 

 occurs immediately after the closure of the aortic semilunar valves. In 

 certain conditions, generally of disease, it becomes so marked as to be 

 quite plain to the unaided finger. Such a pulse is called dicrotic. The 

 most generally accepted view of the cause of the dicrotic wave is that it 

 represents a rebound from the closed aortic valves. During systole, as 

 the blood is forcibly injected into the aorta, there is as it were" an over- 

 distention of the artery. The systole suddenly ends, the aorta by rea- 

 son of its elasticity tends to recover itself, the blood is driven back 

 against the semilunar valves, closing them and at the same time giving 

 rise to a wave the dicrotic wave which begins at the heart and travels 

 onward toward the periphery like the primary wave. According to Fos- 



