272 



THE CIRCULATION IN THE BLOOD-VESSELS [CH. XXII. 



point, it oscillated with the heart-beats, each cardiac systole causing 

 a rise, each diastole a fall. Hales also noted a general rise during 

 each inspiration. The method taught Hales these primary truths in 

 connection with arterial pressure, but it possesses many disadvan- 

 tages ; in the first place, the blood in the glass tube very soon clots, 

 and in the second place, a column of liquid 8 feet high is an 

 inconvenient one to work with. 



The first of these disadvantages was overcome to a great extent 

 by Vierordt, who attached a tube filled with saturated solution of 

 sodium carbonate to the artery, and the blood-pressure was measured 

 by the height of the column of this saline solution which the blood 

 would support. 



The second disadvantage was overcome by Poiseuille, who intro- 

 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 



A 



B 



FIG. 239. Diagram of mercurial Kymograph. 



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

 mometer 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. 239. 



