920 PHYSIOLOGY 



where v is the velocity per second, 



g, the acceleration due to gravity, 

 e, the elastic coefficient of the wall, 

 a, the thickness of the wall, 

 d, the diameter of the tube, 

 D, the density of the fluid, 

 Jc. a constant. 



o.i 



5 ovVVTuvVVV\A/V/\AAA/\ Ay 



FIG. 410. Pulse-curves 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-valve 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 

 several primary waves to the tuning-fork curve below, each complete vibration 

 of which occupies -^ sec., 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 (yi) the reflected 

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

 wave, so that the rise of pressure in VI is actually greater than that in V. 

 (From FOSTER, after MABEY.) 



If the end c of the tube is closed, the wave of a positive pressure on 

 arriving at B will be reflected back as a positive reflected wave. If a 



