302 



MANUAL OF PHYSIOLOGY. 



increased action of the heart ; (2), increased contraction of the 

 muscular coat of the arteries ; (3), sudden increase in the quan- 

 tity of blood. When the change is gradual, the vessels adapt 

 themselves to the increase. The opposite of these conditions 

 may be said to have an opposite effect. 



The character of the change in pressure which accompanies 

 the heart's systole is not exactly shown in the tracing obtained 



FIG. 135. 



Blood-pressure Curve, drawn by mercurial manometer. O x = zero line, y y' = 

 curve with large respiratory waves and small waves of heart impulse. A scale is intro- 

 duced to show height of pressure in c c of Hg. 



by the mercurial manometer, owing to the sluggishness of the 

 movement of the mercurial column, which, as it were, rubs off 

 the apices of the curves. But with the spring Kymograph of 

 Fick the details of these oscillations are marked. They are, of 

 course, synchronous with the arterial pulse, and follow the vari- 

 ations of tension, as will be described when treating of that sub- 

 ject. (See Figs. 136 and 137.) 



