THE CIRCULATION OF THE BLOOD AND LYMPH 105 



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 communicates (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 adjusted the stopcock is 

 turned so that the rubber bag 

 is in communication 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 adjust- 

 ment. The stopcock is now 

 rotated so as to cut off the 

 armlet from the exterior 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 ex- 

 terior. When the de- 

 sired pressure has been 

 reached, the stopcock is 

 turned into an interme- 

 diate position, which 

 cuts off both the armlet 

 and the space TS from 

 the exterior, and the 

 pulse is then trans- 

 mitted to the tambour 

 and recorded on the 

 drum. By certain ad- 

 justments of the stop- 

 cock air can be 

 allowed to es- 

 cape more or 

 less rapidly 

 from the armlet. 

 To determine 

 the maximum 

 or systolic 

 blood - pressure, 

 the air-pressure 

 in the armlet is 

 raised consider- 

 ably (about 50 

 mm. Hg) above 

 what it is ex- 

 pected to be. 



While the lever is writing on the drum the small oscillations due 

 to the impact on the bag of the pulse-waves in the central portion 

 of the obliterated artery, the pressure is gradually diminished by 

 allowing air to escape. At the moment when the pressure upon the 



FIG. 37. SPHYGMOMANOMETER OF ERLANGER. 



