286 THE CIRCULATION IN THE BLOOD-VESSELS. [OH. xxi. 



The study of blood-pressure cannot, however, be considered to 

 have been in a satisfactory condition until the introduction by 

 Carl Ludwig of the Kymograph ; that is to say, Poiseuille's hcenio- 

 dynamometer was combined with apparatus for obtaining a graphic 

 record of the oscillations of the mercury. The name kymograph 

 or wave-writer we shall see immediately is a very suitable one. 



A skeleton sketch of the apparatus is given in fig. 274. 



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 Frauck's) 

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



Fig. 274. Diagram of mercurial kymograph. 



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 

 manometer is not an elastic one, but is made of flexible metal, so 

 that none of the arterial force may be wasted in expanding it. 

 The tube, cannuia 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 



