THE CIRCULATION OF THE BLOOD. 



303 



and for preventing the escape of a large volume of blood from the 

 vessels, the system is filled with a solution of carbonate of soda of 

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

 vessel of the animal as determined in previous experiments. When 

 communication is established between the vessel and the cannula, the 



FIG. 140. DIAGRAM TO SHOW THE RELATION or THE MERCURIAL MANOMETER TO 

 THE ARTERY, ON ONE HAND, AND TO THE RECORDING CYLINDER, ON THE OTHER 

 HAND, WHEN ARRANGED FOR RECORDING BLOOD-PRESSURE. 



mercurial column adjusts itself to the pressure in the artery. It at 

 once begins to exhibit the same cardiac and respiratory oscillations and 

 undulations as did the column of blood in the previous experiment. 



The height of the mercurial column kept in equilibrium by the 

 pressure of the blood within and the pressure of air without the vessel 



FIG. 141. BLOOD-PRESSURE TRACING. 



is that between the lower level of the mercury in the proximal and 

 the higher level in the distal limb of the manometer, both of which 

 can be read off on a scale placed between the two limbs. 



The height of the mercury as well as its oscillations in the distal 

 limb may be recorded by placing on the top of the mercury a light 



