270 THE CIRCULATION IN THE BLOOD-VESSELS [CH. XXI. 



of the arterial force may be wasted in expanding it. The tube, 

 cannula, and proximal limb of the manometer are all filled with a 

 saturated solution of sodium carbonate, sodium sulphate, or other salt 

 which will mix with blood and delay its clotting. Before the clip is 

 removed from the artery, the pressure is first got up by a syringe (or 

 pressure bottle containing the same saline solution suspended at a 

 good height above the apparatus and connected to it by a tube), so 

 that the mercury rises in the distal limb to a height greater than that 

 of the anticipated blood-pressure ; this prevents blood passing into 

 the cannula when the arterial clip is removed. 



In the distal limb of the Ll'tube, floating on the surface of the 



FIG. 271. The manometer of Ludwig's Kymograph. It is also shown in fig. 272, D, c, E. The 

 mercury which partially fills the tube supports a float in the form of a piston, nearly filling the 

 tube ; a wire is fixed to the float, and the writing style or pen fixed to the wire is guided by passing 

 through the brass cap of the tube ; the pressure is communicated to the mercury by means of a 

 flexible metal tube filled with fluid. 



mercury, is an ivory float, from which a long steel wire extends 

 upwards, and terminates in a writing-point. The writing-point may 

 be a stiff piece of parchment or a bristle which writes on a moving 

 surface covered with smoked paper, or a small brush kept full of ink 

 which writes on a long strip of white paper made to travel by clock- 

 work in front of it. When the two limbs of the mercury are at rest, 

 the writing-point inscribes a base line or abscissa on the travelling 

 surface ; when the pressure is got up by the syringe it writes a line 

 at a higher level. When the arterial clip is removed it writes waves 

 as shown in the diagram (fig. 270), the large waves corresponding to 

 respiration (the rise of pressure in most animals accompanying 



