BLOOD-PRESSURE MEASUREMENTS IN MAN 



225 



small percentage of the pressure, an error which may be ignored for all 

 comparative purposes. 



Erlanger has perfected a form of sphygmomanometer which contains a 

 very ingenious and compactly arranged recording device, figure 189. This 

 instrument has a mercury manometer from which the pressures are read off 

 directly. On a side limb of the manometer there is a rubber bag enclosed 

 in a glass bell. The cavity of the bell outside of the rubber bag is connected 



FIG. 189. Erlanger's Sphygmomanometer, Shown with the Rubber Bag Attached to 

 the Arm. The picture is taken at the end of an experiment after the pressure in the instru- 

 ment is run up again to above the systolic pressure. The upper part of the cylinder shows 

 a sphygmogram taken with the instrument. (Experiment and photo by Hill and Watkins.) 



with a recording tambour, the entire apparatus being fully supplied 

 with the necessary valves and adjusting devices which make it 

 mechanically very perfect. The instrument is mounted on a stand with a 

 small clock and recording cylinder adapting it to convenient clinical use. 

 The brachial arterial pressure of man when taken by this form of 

 apparatus has been found to vary greatly, but Erlanger gives no mm. of 

 mercury as the average of observations on young adults in the determi- 



