CH. XXII.] THE KYMOGRAPH 273 



The artery is exposed and clamped, so that no haemorrhage 

 occurs ; it is then opened, and a glass cannula is inserted and firmly 

 tied in. The form of cannula usually employed (Francois Franck's) 

 is shown on a larger scale at A ; the narrow part with the neck in it 

 is tied into the artery towards the heart ; the cross piece of the T is 

 united to the manometer; the third limb is provided with a short 

 piece of india-rubber tubing which is kept closed by a clip and only 

 opened on emergencies, such as to clear out a clot with a feather 

 should one form in the cannula during the progress of an experiment. 



The tube by means of which the cannula is united to the man- 



FIG. 240. The manometer of Ludwig's Kymograph. It is also shown in fig. 241, 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 iixed 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 fille 



led with fluid. 



ometer is not an elastic one, but is made of flexible metal or thick 

 rubber, so that none 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 sus- 

 pended 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 pass- 

 ing into the cannula when the arterial clip is removed. 



In the distal limb of the (J'tube, floating on the surface of the 



s 



