CIRCULATION OF THE BLOOD. 149 



arteries against their elasticity, it must be subjected to the pressure of 

 the arterial walls, the elastic recoil sending on the blood after the imme- 

 diate effect of the systole has passed; so that, when an artery is cut across, 

 the blood is projected forward by this force for a considerable distance; 

 at each ventricular systole, a jet of blood escaping, although the stream 

 does not cease flowing during the diastole. 



The relations which exist between the arteries and their contained 

 blood are obviously of the utmost importance to the carrying on of the 

 circulation, and it therefore becomes necessary to be able to gauge the 



range 



ported ,, 



to it; D, c, E, represent mercurial manometer, a somewhat different form of which is shown in next 



figure. 



alterations in blood-pressure very accurately. This may be done by 

 means of a mercurial manometer in the following way: The short hori- 

 zontal limb of this (Fig. 132, 1) is connected, by means of an elastic tube 

 and cannula, with the interior of an artery; a solution of sodium or po- 

 tassium carbonate being previously introduced into this part of the appa- 

 ratus to prevent coagulation of the blood. The blood-pressure is thus 

 communicated to the upper part of the mercurial column (2); and the 

 depth to which the latter sinks, added to the height to which it rises in 

 the other (3), will give the height of the mercurial column which the 



