ii 4 THE CIRCULATION OF THE BLOOD AND LYMPH 



graphic records of the pulse, from which both the maximum and the 

 minimum blood-pressures may be deduced. The mean pressure 

 cannot be directly measured, but must lie much nearer to the mmimur 

 than to the maximum, since the line of mean pressure bisects the area 

 ^ - enclosed by the pulse-curve, and 



this area is broad at the base and 

 narrow at the apex. The rubber 

 bag is applied in the form of a cuff 

 or armlet to the arm above the 

 elbow over the brachial artery. 

 It communicates with a mercury 

 manometer, which gives the pres- 

 sure exerted upon the arm. It is 

 also connected with a rubber bulb, 

 B, enclosed in a glass bulb, G, and 

 through a stopcock with a syringe 

 bulb, V, provided with a valve. 

 The space between B and G com- 

 municates (i) with the tambour; 

 (2) with the exterior through the 

 stopcock by the tube E, and also 

 through a pin-point opening in 

 the membrane of the 

 tambour. While the 

 armlet is being ad- 

 justed the stopcock is 

 turned so that the 

 rubber bag is in com- 

 munication with the 

 external air through 

 F. The same is true 

 of the space TS in the 

 glass bulb. The tam- 

 bour is thus protected 

 against undue strain 

 during adjustment. 

 The stopcock is now 

 rotated so as to cut 

 off the armlet 

 from the ex- 

 terior and to 

 permit the 

 entrance of 

 air through F from V, 

 which is used as a pump 

 to raise the pressure, the 

 space TS and the tam- 

 bour being still in com- 

 munication with the 

 Fig. 45. Sphygmomanometer of Erlanger. exterior. When the de- 



sired pressure has been 



reached, the stopcock is turned into an intermediate position, which 

 cuts off both the armlet and the space TS from the exterior, and the 

 pulse is then transmitted to the tambour and recorded on the drum. 

 By certain adjustments of the stopcock air can be allowed to escape 

 more or less rapidly from the armlet. 



To determine the maximum or systolic blood-pressure, the air- 



