THE CIRCULATION OF THE BLOOD 547 



thyroid cartilage. When the tambour (without 

 rubber membrane) is pressed well down over the 

 artery, let an assistant close the side branch. If 

 the receiving tambour has been properly placed, 

 the recording tambour will write a sharply 

 marked pulse curve. If none such appears, open 

 the side branch and move the receiving tambour 

 into a better position. 



Indicate the primary wave, the predicrotic 

 elevation, and the dicrotic notch. 



2. Cover the thistle-tube with a rubber mem- 

 brane. Cement in the centre of the membrane a 

 bone collar-button. Place the button upon the 

 radial artery at the wrist and record the radial 

 pulse. 



It will be found that the degree of pressure 

 must be carefully regulated in order to secure a 

 satisfactory curve. The blood-pressure in the 

 artery normally is held in equilibrium by the 

 elastic tension of the wall of the artery and the 

 surrounding tissues. The pressure of the sphyg- 

 mograph increases the tension of the peri-arterial 

 tissues and thus assists in holding the blood- 

 pressure in equilibrium. The greater the pres- 

 sure of the sphygmograph, the larger the part of 

 the blood-pressure borne by it and the more com- 

 pletely will variations in the blood-pressure be 

 made visible in the pulse curve. The record, 



