CIRCULATION OF THE BLOOD. 



535 



a wave. The rise of each lever is abrupt ; its fall is more gradual, and usually 

 marked by secondary fluctuations. 



If two levers, separated by a considerable length of tube, be allowed to 

 record their movements on a rapidly traveling surface, it will be found that on 

 working the pump the movements described by the levers will not be synchronous ; 

 in other words, an appreciable interval of time will be required for the trans- 

 mission of the wave through the length of tube separating the two levers. In 



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Fig. 222.— Pulse-Waves Described by Levers Placed at Intervals of 

 Twenty Centimeters on an Elastic Tube, into which Fluid is 

 Forced by the Sudden Stroke of a Pump. {Foster.) 



The pulse-wave is traveling from left to right ; A, primary, and B C secondary waves. The intervals 

 between the dotted lines each correspond to 1-50 second, determined by the tuning-fork curve V, and 

 permit measurement of the velocity of the wave. At A' are reflected waves from the closed end of the tube. 



such an apparatus the statement already made as to the conditions governing the 

 rapidity of transmission of the wave-impulse may be readily demonstrated. The 

 more rigid the tube, the more rapid the movement of the wave ; the more exten- 

 sible the tube, the slower the wave travels. It will also be noticed that the 

 nearer the levers are to the pump, the greater will be their excursion, indicating a 

 greater expansion of the tube at that point, while in very long tubes the wave 

 gradually decreases in intensity until it often becomes scarcely distinguishable. 



