XIV.] BLOOD PRESSURE. 151 



When there is little or no resistance in the capil- 

 laries, comparatively little distension of the arterial 

 walls is produced at each stroke of the pump. 



b. Close the clamps c, c' and c". 



The lever S^ now describes a well-marked 

 curve with each stroke of the pump. 

 Observe the sudden rise to a maximum, the 

 commencing fall, the break in the fall, fol- 

 lowed by a slight rise (dicrotic wave) and 

 the final descent. 

 The lever S^ describes now a straight line. 



The rise in pressure at each stroke indicated by 

 the mercurial manometer is accoTnpcmied by a 

 distension of the proximal (arterial) part of the 

 tubing, indicated by the rise of the lever. This 

 is the pulse. 



On the distal (venous) side of the resistain,ce no 

 pulse is visible. 



4. Progression of the Pulse-wave. 



Place two levers, one S^, as near as possible to 

 the pump, the other S'^, as near as possible to 

 the resistance. Bring the two levers to mark on 

 the cylinder ^Afi one exactly beneath the other. 

 (The pressure exerted by the two levers must be 

 as nearly equal as possible.) ' 



Observe that each rise of S,, begins a little before, 

 and is over a little before that of S'a- In other 

 words, the pulse of /S'a is a little later than that 

 of-Sf,. 

 (By means of a tuning-fork this interval may be 



