VELOCITY AND PRESSURE OF BLOOD-FLOW. 



511 



the pressure, also expressed in centimeters, which was found, 

 necessary to obliterate the vein. Measurements made by this 

 method and corrected for the heart-level show that in the normal 

 person the pressure within the small veins of the hand or arm 

 varies in general, for the adult, between 10 and 20 cm. of water. 

 The average pressure seems to increase progressively during life, 

 from a value of 8 cm. in early youth to 25 cm. in old age.* Un- 



rig. 207. Hooker's venous pressure apparatus. A glass capsule, A, is fastened to the skin 

 over a vein by means of a solution of collodion. This capsule is connected by rubber tubing 

 with a pressur^bulb, C, and a water manometer, M . By means of the bulb the pressure is 

 raised in A until the vein is obliterated. The pressure at which this occurs is shown by the 

 level of the liquid in the manometer. This pressure, expressed in centimeters of water, is cor- 

 rected by subtracting the distance between the vein and the costal angle, as indicated on the 

 metal rod supporting the hand. B gives an enlarged view of the glass capsule. 



usual or pathological conditions which cause a congestion in the 

 venous side of the heart will raise the venous pressure correspond- 

 ingly, f 



When the venous pressure is measured in the small veins of the feet in a 

 person while standing we should suppose that after a reduction to the heart 

 level it would be about the same as that noted for the veins of the hands, 

 since the vessels are of about the same order with reference to their distance 



loc. 



