VELOCITY AND PRESSURE OF BLOOD-FLOW. 



505 



side the pressure within its veins will be greater than when the 

 hand is raised to the heart level. The pressure actually measured 

 for any given position of the hand or foot must, therefore, be 

 corrected for the heart level by determining the vertical distance 

 between the vein and the heart (costal angle), and subtracting this 

 distance, expressed in centimeters, from the pressure, also ex- 



A glass capsule, A, is fastened to the skin 



-Hooker's venous pressure apparatu 

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

 with a pressure-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. 



pressed 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 (7.4 to 14.8 mms. of mercury). 

 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- 

 usual or pathological conditions which cause a congestion in the 

 * Hooker, "American Journal of Physiology," vols. 35 and 40, 1914, 1916. 



