CH. XXI.] 



THE KYMOGRAPH 



269 



duced the heavy liquid, mercury, as the substance on which the blood 

 exerted its pressure; and the U-shaped mercurial manometer was 

 connected to the artery by a tube filled with sodium carbonate 

 solution to delay clotting. 



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 hcemodynamo- 

 meter 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. 270. 



B.P. tracing 

 Abscissa 



FIG. 270. Diagram of mercurial Kymograph. 



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 indiarubber 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 mano- 

 meter is not an elastic one, but is made of flexible metal, so that none 



