12 4 THE CIRCULATION OP THE BLOOD AND LYMPH 



Fick, from a comparison of sphygmographic and plethysmographic 

 tracings (p. 128), taken simultaneously from the radial artery and 

 the hand, has demonstrated that in man the velocity-pulse exhibits 



Fig. 52. Fig. 53- 



Fig. 52. The highest of the three curves is a plethysmographic record taken from 

 the hand; the second curve is a sphygmogram taken simultaneously from the 

 corresponding radial artery; the lowest (interrupted) curve is the curve of velocity 

 deduced from a comparison of the first two (Fick). 



Fig. 53- Simultaneous plethysmographic and sphygmographic tracings. 



the same general characters as in animals (Figs. 52 and 53). And 

 v. Kries has confirmed Fick's conclusions by actual records of the 

 velocity-pulse obtained by means of an arrangement called a gas 

 tachograph (Fig. 55). 



Fig. 54. Simultaneous Tracings of the Velocity (Upper Curve) and Pressure (Lower 

 Curve) (Lortet). The tracings were taken from the carotid artery of a horse. 

 The curve of velocity was obtained by the dromograph. The dicrotic wave is 

 marked on it. The slightly curved ordinates drawn through the curves indicate 

 corresponding points. 



This consists of a plethysmograph connected with the tube of a gas- 

 burner. When the part enclosed in the plethysmograph expands, air 

 issues from the connecting tube, and causes an increase in the height of 

 the flame. When the part shrinks, air is drawn in from the flame, 

 which is depressed. Since the speed of the blood in the veins may be 

 considered constant during the time of an experiment, the rate at which 



