546 THE OUTGO OF ENERGY 



rubber membrane) to the sphygmograph (Fig. 

 70) and adjust the tube upon the aorta. Close 

 the side branch of the sphygmograph tube. Bring 

 the writing point of the sphygmograph lever 

 against a slow-moving, lightly-smoked drum. 

 Record a series of pulse curves. 



Note the quick upstroke, corresponding to the 

 quick distention of the artery by the emptying 

 of the ventricle, and the gradual downstroke, 

 corresponding to the gradual emptying of the 

 artery through the resistance during the diastole 

 or interval between two beats. Near the apex 

 of the more delicately written curves may be 

 seen a slight depression, the dicrotic notch. 



It is obvious that the changes observed in the 

 size of the artery are the expression of changes 

 in the blood-pressure. The pulse is a function 

 of the blood-pressure at the point observed. 

 Hence the term pressure-pulse. 



The Human Pressure-Pulse Curve. 1. Adjust 

 the lever of the recording tambour so that it. shall 

 write with the least friction possible on a thinly 

 smoked drum. Let the drum revolve slowly 

 (two revolutions a minute). Be sure that the 

 side branch is open. Place the larger thistle- 

 tube, which serves as a "receiving tambour," 

 over the carotid artery, anterior to the stern o- 

 cleidomastoideus muscle, about the level of the 



