ELEMENTARY EXPERIMENTAL PHYSIOLOGY 127 



instrument is graduated empirically. While taking the reading the 

 hand of the subject must be placed on the same level as the heart, so as 

 to avoid the influence of gravity. 



Measurement of Systolic Pressure with Hill-Barnard Armlet 

 and Mercurial Manometer. Strap the armlet lightly around the 

 middle of the upper arm. Palpate the radial artery. By working the 

 pump, raise the pressure in the cuff until the radial pulse is imper- 

 ceptible. Now manipulate the exhaust stop cock so that the pressure 

 in the cuff very gradually falls, and observe carefully the height of the 

 mercury in the manometer. Whenever the radial pulse reappears, 

 note the pressure. Continue the decompression (best by slightly 

 lowering it a few mm. at a time), and note the pulsations of the 



J.d. HICKS SOLE MAKER LONDON. PATENT. 

 Fii. 127. Leonard Hill sphygmometer. 



mercury, which became evident at the systolic pressure, get gradually 

 of greater amplitude until, by further lowering of pressure, they become 

 smaller again. The pressure at which the pulsations are of maximal 

 amplitude is the diastolic pressure. 



The difference between the two pressures is the pressure pulse. 



Repeat the above observations until constant results are obtained. 

 Then let the observed person run up and down stairs several times, 

 and repeat the observations. 



Try the effect of putting the hand in very hot water, and palpate 

 the artery at the elbow and wrist. The pulse will disappear earlier at 

 the wrist. A contracted artery conducts the crest of the systolic wave 

 better than a softened artery. The effect of the hot water is more 

 evident after exertion, when the pulse waves are larger. 



The systolic arterial pressure is 100-110 mm. Hg in healthy young 

 men. It may fall during sleep 10-20 mm. Hg, and rises to 130-140 and 

 to even 200 mm. Hg during mental excitement or severe effort. The 

 arterial pressure is as constant as the body temperature from day to 

 day. In the horizontal posture the arterial pressure will be found to 

 be the same in all the big arteries. In the erect posture the pressure is 



