THE CIRCULATION OF THE BLOOD 



343 



thing, to divide the vessel and insert the horizontal portion of a T-shaped 

 tube into the central and distal ends through which the blood can con- 

 tinue to flow, and to connect the vertical portion with a vertical pressure 

 tube or with a mercurial manometer. The absolute pressure on any given 

 unit of vessel surface e.g., i sq. mm. is obtained by multiplying the height 

 of the column, expressed in millimeters, by the unit of surface, and then 

 determining the weight of this mass of blood. Thus if the height of the 

 column of blood in the carotid artery tube is 2000 mm., then the pressure on 

 i sq. mm. is the weight of 2000 mm. of blood. The weight of 2000 c.mm. 

 of blood is equal to 2.1 grams. 



The Arterial Blood-pressure. For accurate and long-continued ob- 

 servation the arterial blood-pressure is more conveniently studied by means 

 of a U-shaped tube (a manometer) partially filled with mercury. One limb 

 of the manometer is connected by means of a tube and a cannula with an 



^ 



RECORDING BLOOD-PRESSURE. 



artery (Fig 



For the purpose of retarding coagulation of the blood and 

 revenmg escape of a large volume of blood from the vessels the 

 system is filled with a solution of carbonate of soda of sp. gr. 060 558 

 grams per 1000 C.C., or a 25 per cent, solution of magn ^um sulphate 

 sp gr 1060 and under a pressure approximately equal to that in the ves 



of the Wood within, .nd the 



of air 



that 



placed between the two limbs. 



