Chap, xxi.] THE KYMOGRAPHION. 229 



the blood. The oscillations of the mercury tend to 



/ 



maintain themselves, and small variations thus escape 

 record. An arrangement for obtaining tracings with 



O o o 



more minute variations is that of Bourdon, adapted 

 by Fick. It consists of a hollow spring thrown into 

 the form of a curve (GB, Fig. 106). The interior is 

 filled with alcohol. One extremity 

 is sealed, and has passing from 

 it an arrangement of levers GD 

 for amplifying the movement. The 

 extremity of the lever projects, by 

 means of a writing point, against 

 a revolving cylinder. The lower 

 end of the spring communicates 

 with a lead tubing A ; which 

 is filled with bicarbonate of soda Fig. 106. Tick's 

 solution, and is connected with a pblcnf 

 T-shaped tube in the blood- 

 vessel. To damp the oscillations, and prevent 

 them being continued by the mere elasticity of 

 the spring, a prolongation of the writing lever dips 

 below the writing point into a tube of glycerine. 

 Pressure causes the spring to expand, and a movement 

 is communicated to the lever. As soon as the 

 pressure is removed the spring returns to its former 

 position. 



Marey's tambours (page 1 85) have been adapted to 

 register blood pressure. In 1861 Marey and Chauveau 

 obtained tracings of pressure by introducing into the 

 heart itself a sort of catheter carrying a small caout- 

 chouc bag at the heart end. The other end of the 

 sound communicated by means of an indiarubber 

 tube with a registering tambour writing on a revolving 

 cylinder. For the right side of the heart the sound 

 was introduced through the jugular vein, for the root 

 of the aorta and left side of the heart through the 

 carotid. 



