THE ARTERIAL PRESSURE 189 



gists of an armlet, a rubber bag encased in soft leather, connected bj 

 tubing and T-piece to a syringe bulb for raising the pressure, and a 

 mercury manometer or spring gauge for registering the same (Fig. 95). 



After the armlet is buckled on, the pressure is gradually raised in 

 the armlet by means of the syringe. A reading is taken when the 

 pulse in the artery is obliterated below the armlet (the systolic pressure). 

 The disappearance and reappearance of the pulse may be felt with 

 the fingers, or heard by placing a stethoscope over the artery at the 

 elbow. When, as the pressure ir, reLxed, the pulse comes through 

 under the armlet, a loud sound is heard synchronous with each systolic 

 wave. As the pressure is further relaxed, the sound undergoes 

 variation in tone, but at a certain point suddenly diminishes or dis- 

 appears. If the pressure be read at this point, it denotes the diastolic 

 pressure. It has been proved by experiments on animals that the 

 systolic and diastolic pressures, so measured, agree with measurements 

 made directly by connecting the artery with a spring manometer. 



The pocket sphygmometer shown in Fig. 96 consists of a rubber 





J.J. HICKS SOLE MAKER LONDON. PATENT. 

 FIG. 90. LEONARD HILL POCKET SPHYGMOMETER. 



bag covered with silk, which is filled with air, and connected by a short 

 length of tube to a manometer. This manometer consists of a gradu- 

 ated glass tube open at one end. A small hole is in the side of the tube 

 near this end. A meniscus of coloured Ikalino water is introduced up 

 to the side hole the zero mark on the scale by placing the open end 

 of the tube in water. The bag is now connected to the gauge, so that 

 the side hole is closed by the rubber tube. To take the arterial pres- 

 sure the rubber bag is covered with the hand, and pressed on the 

 radial artery until the pulse (felt beyond) is obliterated, the height 

 to which the meniscus rises in the manometer being read. This gives 

 the systolic pressure in the artery. The air above the meniscus acts 

 as a spring, converting the instrument into a spring manometer. It 

 is graduated empirically in millimetres of mercury.* 



The systolic pressure of young men, taken in the radial artery 

 with the arm at the same level as the heart, may be taken to be about 

 100 to 110 mm. of Hg. In men of forty to sixty years the systolic 

 pressure is often about 140 millimetres, but in some robust men it is 

 no higher than in youth. 



It is very necessary to remember that the blood-pressures, taken 



* The graduation is at sea-level. A correction would be necessary for high altitudes. 



