242 



PHYSIOLOGY 



CHAP. 



of the mercury column on a rotating cylinder. This is another 

 immense advance, as the recording manometer was the first 

 application of the automatic graphic method, which has since 

 been employed in the most various directions, and has rendered 

 signal service to physiology. (Fig. 91 ; and Fig. 68, p. 207.) 



FIG. 91. Lud wig's kymograph. (Baltzar's type.) The movements of the drum are rendered 

 uniform by the clockwork of a Foucault regulator. The velocity of rotation is altered either 

 by pushing the little wheel on the axis of the drum nearer to or farther from the centre 

 of the vertical metal disc, which drives the drum by simple friction, or by adjusting the 

 clockwork of the regulator. 



Ludwig's writing manometer or Kymograph is the classic 

 instrument by which the absolute value of the average blood pressure 

 of any artery can be directly obtained under natural conditions. 

 An anti- coagulant alkaline or peptone solution is introduced 

 between the blood and the mercury. If the manometer is con- 

 nected by a T-cannula with the artery, the flow of blood through 

 the vessel is not interrupted, and the resulting value gives 

 the lateral pressure obtaining in the branch vessel. For greater 



