298 



MANUAL OF PHYSIOLOGY. 



which consists of a column of mercury in a U-shaped tube. To 

 prevent coagulation, the tube between the mercury and blood is 

 filled with a solution of sodium carbonate, the pressure being regu- 

 lated to equalize as nearly as possible that of the blood. A rod 

 is made to float upon the mercury, in the open side of the tube, 

 and to the upper extremity of this a writing apparatus can be 

 attached, so that by the movements of the mercury, a graphic 



FIG. 132. 



The ordinary modern form of rotating blackened cylinder (R), which is moved by the 

 clock-work in the box (A) by means of the disk (D) pressing upon the wheel (n), which can 

 be raised or lowered by the screw (L), so as to rub on a part of the disk more or less near 

 the centre, and thus rotate at different rates. The cylinder can be raised by the screw 

 (v), which is turned by the handle (u). (Hermann.) 



record of the blood pressure and its variation can be traced on a 

 regularly moving surface. This instrument, known as Ludwig's 

 Kymograph, is that used in all ordinary measurements and ex- 

 periments on blood pressure. In order to overcome the inertia 

 of the mercurial column, another instrument has been devised, 

 which will be mentioned in speaking of the character of the curve 

 (p. 302). When an experiment of long duration has to be made, 



