THE CIRCULATION OF THE BLOOD. 



347 



the manner of using it and the results that can be obtained with it will be 

 found in the Johns Hopkins Hospital Reports, Vol. XII. 



With this apparatus, the lever often exhibits a considerable oscillation 

 even when the pressure exerted on the arm exceeds the systolic pressure. 



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



FIG. 162. ERLANGER'S SPHYGMOMANOMETER. 



It is difficult therefore to determine at times the moment at which the pres- 

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

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

 tion 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 ijto 2 mm. of smoked 



