CH. XXL] 



TICK'S KYMOGRAPH 



273 



(which is seen in fig. 275, g), before the clip is removed from the 

 artery. The manometer itself is a hollow C-shaped spring filled with 

 liquid ; this opens with increase, and closes with decrease of pressure, 

 and the movements of the spring are communicated to a lever pro- 

 vided with a writing-point. 



Hurthle's manometer (see p. 242) is also very much used. The 

 advantage of these forms of manometer is that the character and 



FIG. 275. Pick's Kymograph, improved by Bering (after M'Kendrick). a, Hollow spring filled with 

 alcohol, bearing lever arrangement 5, d, c, to which is attached the marker e ; the rod c passes 

 downwards into the tube /, containing castor oil, which offers resistance to the oscillations of c ; 

 g, syringe for filling the leaden tube h with saturated sulphate of sodium solution, and to apply 

 sufficient pressure as to prevent the blood from passing into the tube h at i, the cannula inserted 

 into the vessel; I, abscissa-marker, which can be applied to the moving surface by turning the 

 screw m ; fc, screw for adjusting the whole apparatus to the moving surface ; o, screw for elevating 

 or depressing the Kymograph by a rack-and-pinion movement ; n, screw for adjusting the position 

 of the tube /. 



extent of each pressure change is much better seen. In a mercury 

 manometer the inertia is so great that it cannot respond to the very 

 rapid variations in pressure which occur within an artery during each 

 cardiac cycle. If Tick's or Hiirthle's manometer is employed, and 

 the surface travels sufficiently fast, these can be recorded (see fig. 

 276). These instruments, though useful for recording the complete 

 changes in pressure, require calibration : that is, the extent of move- 

 ment that corresponds to known pressures must be ascertained by 



S 



