VELOCITY OF THE PULSE- WAVE. 237 



LESSON LIV. 



THE PULSE-WAVERIGID AND ELASTIC 



TUBES SCHEME OF THE CIRCULATION 



RHEOMETER. 



1. Velocity of the Pulse -Wave. 



(a.) Take about 3 metres of india-rubber tubing about 

 6 mm. in diameter. To one end of the tube attach an 

 ordinary elastic pump to imitate the heart, while the other 

 end of the tube is left open, with a clamp lightly fixed 

 on it. Arrange to pump water through the tube. Arrange 

 two light levers on one stand, and place a part of the tube 

 near the pump under the lower lever, and resting on a suit- 

 able support, while part of the tube near the outflow end 

 is similarly arranged under the upper lever. Regulate the 

 pressure of the lever upon the tube by means of lead 

 weights. 



(b.) Arrange on the same stand a Deprez* chronograph to 

 record the vibrations of an electro-tuning-fork, vibrating 30 

 or 50 D.V. per second. See that the writing-points of the 

 two levers and the chronograph write upon the drum in the 

 same vertical line. 



(c.) Set the tuning-fork vibrating, allow the drum to move, 

 compress the elastic pump interruptedly to imitate the 

 action of the heart and propel water through the tube. 

 The compression may be done by means of alemon-squeezer, 

 the extent of the excursion being regulated by a screw, and 

 to secure regularity, arrange the number of pulsations to 

 the beating of a metronome. On doing so, as one pumps in 

 the water, the tube distends and raises the lever; in the 

 interval between the beats, as the water flows out at the 

 other end, the tube becomes smaller, and the levers fall. 

 Feel the tube; with each contraction of the heart, a beat 

 the pulse-beat can be felt. 



(d.) Fix and study the tracing. The tracing due to the 

 rise of the lever next the heart begins sooner, and is higher 



