THE VENOUS BLOOD-PRESSURE AND CAPILLARY PRESSURE 227 



limb of the artery below the band. The flow of this fluid produces a very 

 definite first sound which is used to determine the moment of systolic 

 pressure. The sounds in the brachial artery, known as Karatkoff sounds, 

 have been described as going through five phases before the circulation is 

 fully established in the cut off artery. The first phase is the initial 

 development of a clear cut and sharp sound. It is the index of the 

 systolic pressure. The first sound is followed by a series of murmurs 

 called the second sound, and that by a more definite tone, the third phase. 

 The third phase will vary in character with certain abnormalities in the 

 vessel wall thickening, sclerosis, etc. 



The fourth phase is the appearance of a duller tone of diminishing 

 intensity which rapidly fades into no sound, the so-called fifth phase. 

 The fourth phase is taken as the index of minimal or diastolic arterial 

 pressure. 



If the ascultatory reading and the palpation reading are made at the 

 same time the latter usually gives a slightly lower systolic pressure than 

 the former. In other words, the stethoscopic reading by the sound is the 

 more accurate. The diastolic reading is far more accurately determined 

 by the ascultatory method. Woley gives the average systolic pressure as 

 127 mm. for all ages. But it is well known that the pressure increases 

 with age from 75 at one year, to 105 in youth and 140 mm. or more at the 

 age of fifty. 



AVERAGE BLOOD PRESSURE MEASUREMENTS or MAN 



The Venous Blood-Pressure and Capillary Pressure. The blood- 

 pressure in the veins is nowhere very great, but is greatest in the small veins, 

 while in the large veins near the heart the pressure may become negative. 

 In other words, when a vein is put in connection with a mercurial manom- 

 eter the mercury may fall in the arm farthest away from the vein and will 

 rise in the arm nearest the vein, the action being that of suction rather than 

 pressure. In the large veins of the neck the tendency to suck in air is espe- 

 cially marked, and is the cause of death in some accidents or operations 

 in that region. The amount of pressure in the brachial vein is said to 



