THE CIRCULATION OF THE BLOOD 



with i 



357 



eve^^^^ 



It is difficult, therefore, to dateline atti^ 



COPYRIGHT 1906, Br SCHNEIDER BROS., N.Y. 



FIG. 165. ERLANGER'S SPHYGMOMANOMETER. 



sure indicated by the mercurial column just falls below the systolic pressure 

 and allows the blood to pass through. A new criterion for this determination 

 has been furnished by Erlanger. With a given speed of the drum, the up and 

 down strokes of the lever practically coincide. But if the speed of the drum 

 be slightly increased "so that each wave subtends about i Jto 2 mm. of smoked 

 paper (this speed is attained merely by removing the governor), the change 



