296 



THE CIRCULATION IN THE BLOOD-VESSELS [CH. XXII. 



pressure rises the oscillations become more pronounced, and at a 

 certain point they exhibit a greater excursion than they do at any 

 other height ; beyond this point of maximal pulsation, the oscilla- 

 tions diminish in amplitude, and as the distension of the bag is 

 increased still more, the pressure is at last reached, when it is 

 sufficient to obliterate the pulse, and the oscillations of the mercurial 

 column cease, and the pulse is no longer to be felt at the wrist. The 

 pressure necessary to do this is equal to the systolic pressure, and the 

 height of the mercurial column should be noted when the pulse just 

 disappears. The point of maximal pulsation gives a reading of the 



FIG. 264. Martin's Sphygmometer (made by Hawskley, 357 Oxford Street). 



diastolic pressure. The systolic pressure is more easily read than the 

 diastolic pressure, for it is by no means easy to judge accurately 

 where the pulsations are greatest. Moreover, the amount of systolic 

 pressure gives one more useful information of the condition of the 

 circulation than does the diastolic pressure. 



The normal pressure in the radial artery of healthy young adults 

 is 110 to 120 mm. Hg. It appears to be as constant as the body 

 temperature. In the recumbent posture the pressure is slightly 

 lower than in the erect position. This relation is reversed in condi- 

 tions of exhaustion. The pressure in the lower limbs is greater than 

 that in the upper limbs in the standing posture owing to the effect 

 of gravity. During muscular exertion the pressure is raised, while 

 in the subsequent period of rest it is subnormal. Mental work 

 raises the pressure ; during rest and sleep it is lowered. The taking 



