180 



THE VASCULAR MECHANISM. 



so that their curves can be more easily compared, the following facts may be 

 observed when the pump is set to work regularly. 



At each stroke of the pump, each lever rises until it reaches a maxi- 

 mum (Fig. 64, la, 2a, etc.) and then 'falls again, thus describing a curve. 



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Pulse-curve described by a series of Sphygmographic Levers, placed at intervals of 20 cm. 

 from each other along an elastic tube into which fluid is forced by the sudden stroke of a pump. 

 The pulse-wave is travelling from left to right, as indicated by the arrows over the primary (a) 

 and secondary (b, c) pulse-waves. The dotted vertical lines drawn from the summit of the sev- 

 eral primary waves to the tuning-fork curve below, each complete vibration of which occupies 

 1-50 second, allow the time to be measured which is taken up by the wave in passing along 20 cm. 

 of the tubing. The waves a' are waves reflected from the closed distal end of the tubing ; this is 

 indicated by the direction of the arrows. It will be observed that in the more distant lever VI, 

 the reflected wave, having but a slight distance to travel, becomes fused with the primary wave. 

 (From Marey.) 



The rise is due to the expansion of the part of the tube under the lever, 

 and the fall is due to that part of the tube running after the expansion to 

 its previous calibre. The curve is, therefore, the curve of the expansion 

 (and return) of the tube at the point at which the lever rests. We may 

 call it the pulse-curve. It is obvious that the expansion passes by the lever 



