THE CIRCULATION. 



291 



impulse, and another caused by the oscillation of blood in the feebly 

 distended artery. This is the dicrotic pulse, often present in diseases 

 of a typhoid character. 



FIG. 72. 



DICBOTIC PULSE OF TYPHOID PNEUMONIA. (Marey.i 

 FIG. 73. 



DICKOTIC PULSE OF TYPHOID FEVER. (Marey.) 



It is evident that the dicrotic character of the pulse is not altogether 

 peculiar to diseased conditions, since it exists in some degree, as shown 

 by the preceding figures, even in health. But it is usually too slight 

 to be perceptible by the finger unless exaggerated from morbid causes. 



The mechanism of the dicrotic pulse has been demonstrated by 

 Koschlakoff.* If a liquid be driven by a sudden impulse through 

 an elastic tube, connected with two separate pressure gauges, one 

 near the point of entrance of the liquid, the other near its exit, 

 the liquid will rise in the first gauge before the increased pressure 

 reaches the second; it then falls while the second is rising, and again 

 rises while the second falls ; showing an alternate increase and 

 diminution of pressure in the two extremities of the tube. This 

 alternation continues until the pressure is equalized, or until the tube 

 is again distended by a new impulse. 



Pulsating Flow of Blood in the Arteries. Owing to the alternate 

 contraction and relaxation of the heart, the blood moves through the 

 arterial system in a series of impulses ; and in hemorrhage from a 

 wounded artery the blood flows in successive jets, as well as more 

 rapidly than if it came from veins or capillaries. If a slender canula 

 be introduced through the walls of the left ventricle, in the exposed 

 heart of a living animal, the flow of blood from its orifice is inter- 

 mittent. A strong jet takes place at each ventricular contraction, and 

 is interrupted at the time of relaxation. But if the puncture be made 

 in a large artery near the heart, the blood is discharged from it in a 

 continuous stream ; only its flow is abundant at the time of ventricular 

 contraction, and more scanty at the time of relaxation. The disten- 

 sion and elasticity of the arterial walls modify the effects of the separate 

 arterial pulsations, and partially fuse them with each other ; produc- 

 ing, in the larger and medium-sized arteries, a movement of the blood 



* In Lorain, Etudes de Medecine Clinique. Paris, 1870, p. 7o. 



