ELEMENTAEY EXPERIMENTAL PHYSIOLOGY 



85 



artery are the same. If the pressure of the instrument be made greater 

 than the mean, the artery will not expand to its fullest in systole. 

 Similarly, if the pressure be made less than the mean the artery will 

 not completely collapse in diastole. 



FIG. 85. Arrangement of levers in 

 Dudgeon's sphygmugraph. 



FIG. 86a. Sphygmometer. 



The mean 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 

 mm. Hg during mental excitement or severe effort. It is normally 

 higher in the erect than in the horizontal position. The effect of 

 gravity is over-compensated. The reverse is the effect in states of 



FIG. 866. iSphygmometer. The leather armlet encloses a rubber bag. The bicycle 

 pump is used to raise the pressure. The spring manometer indicates the maximal 

 pulsation and the pressure. 



debility, and the pulse frequency is then greatly accelerated in the 

 vertical posture. 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 higher in the femoral than in the carotid 

 by the height of the column of blood which separates the two arteries. 



