984 



PHYSIOLOGY 



two vertical limbs about eighteen inches in height, which is half -filled 

 with clean mercury. On the surface of the mercury of one limb is 

 a float of vulcanite from which a stiff fine rod of straw, glass, or steel 

 rises, bearing on its upper end the writing- point. This point may be 

 adjusted so as to write on the blackened glazed surface of a moving sheet 

 of paper (Fig. 370). (The arrangement for imparting a continuous move- 

 ment to a sheet of glazed paper is known as a kymograph.) Instead 

 of smoking the paper a pen may be fitted to the end of a rod and 

 its excursions recorded in ink on a moving band of white paper. 

 The other limb of the manometer is connected by a flexible inex- 

 tensible tube with a small tube or cannula which is tied into the 



FIG. 370. Arrangement of apparatus for taking blood-pressure tracing. 



a, artery (carotid) ; c, cannula ; d, three-way cock ; ra, mercurial manometer ; 



b, drum covered with smoked paper ; x, tube to pressure bottle. 



central end of an artery, a clip being previously placed on the artery 

 so as to prevent the escape of blood during the insertion of the cannula. 

 To the manometer is connected a three-way tap by means of which 

 the manometer can be placed in communication with the artery alone, 

 or with the artery and a pressure bottle. By means of the latter the 

 whole system is filled with magnesium sulphate solution (25 per cent.) 

 or a half-saturated solution of sodium sulphate, at a pressure of 

 150 mm. Hg. The pressure bottle is then cut off so that the manometer 

 remains in connection only with the cannula, the mercury in one limb 

 being 150 millimetres above that in the other. The clip is then taken 

 off the artery. The pressure in the cannula being greater than that in 

 the artery, a small amount of the fluid used to fill the tubes runs into 



