LUDWIG'S KYMOGRAPH. 



163 



pressure tracing range. [Briefly, it is the average elevation of the 

 mercurial column.] 



Fig. 72. 

 I, Scheme of C. Ludwig's kymograph ; II, Fick's spring-kymograph. 



In a blood-pressure tracing, such as Fig. 74, each of the smaller waves corre- 

 sponds to a heart-beat, the ascent corresponding to the systole and the descent to the 

 diastole. The large undulations are due to the respiratory movements. It is clear 

 that the heart-beat is expressed as a simple rise and fall (Fig. 74), so that the curve 

 of the heart-beat obtained with a mercurial kymograph differs from a sphygmo- 

 graphic curve. A perfect recording instrument ought to indicate the height of the 

 blood-pressure and also the size, form, and duration of any wave-motion com- 

 municated to it. The mercurial manometer does not give the true form of the 

 pulse-wave, as the mercury, when once set in motion, executes vibrations of its 

 own, owing to its great inertia, and thus the finer movements of the pulse-wave are 

 lost. Hence a mercurial kymograph is used for registering the blood-pressure, and 

 not for obtaining the exact form of the pulse- wave. Instruments with less inertia 

 and with no vibrations peculiar to themselves, are required for this purpose. [The 

 theory of the mercurial manometer has been carefully worked out by Mach and 

 also by v. Kries.] 



[Method. Expose the carotid of a chloralised rabbit, and isolate a portion of 

 the vessel between two ligatures, or two spring clamps. With a pair of scissors 

 make an oblique slit into the artery, and into it insert a straight glass cannula, 

 directing the open end of the cannula towards the heart. Fill the cannula 

 with a saturated solution of sodium carbonate, taking care that no air-bubbles 

 enter, and connect it with the lead tube which goes to the descending limb 

 of the manometer. The tube which connects the artery with the manometer must 

 be flexible and yet inelastic, and a lead tube is best. It is usual to connect a 

 pressure-bottle, containing a saturated solution of sodium carbonate, by means of an 

 elastic tube, with the tube attached to the manometer. This bottle can be raised 

 or lowered. Before beginning the experiment, raise the pressure-bottle until there 

 is a positive pressure of several inches of mercury in the manometer, or until the 

 pressure is about equal to the estimated blood-pressure, and then clamp the tube 



