52 



EXERCISE YIII 



rest upon it. Adjust the pivot of the lever so that the lever inclines down- 

 ward, its writing-point being rather lower than its pivot. Bring the lever 

 to the recording-paper of the kymograph and see that its writing-point keeps 

 in light touch with the paper when it rises and falls. This can be tested by 

 squeezing the rubber tube and so driving the membrane upward. See that 

 the free end of the connecting-tube reaches well to the upper part of the chest, 

 suitably for the left subclavian artery, into which the arterial cannula will be 

 inserted. 



By adopting certain conditions which slightly increase the manipulative 

 difficulties but enhance the value of the features of the record, the membrane 

 manometer provided can be made to exhibit approximately the form of the 



Test-fig. 25. Simple form of membrane manometer. — 1, small-scale view ; 2, plan from above ; 

 3, brass ring-washer ; 4, elevation section. 2, 3, and 4 are actual scale, a, slotted adjustable 

 piece carrying the pivot-bearings ; m, the body containing the chamber and tube-boi*ings ; 

 r, the ring-washer fixing the rubber disk-membrane when c, the cover-nut, is screwed down ; 

 &, aluminium button secotined to top surface of the rubber membrane ; the light grass-stem 

 writing-lever rides in a notch cut in the ridge of the button-top. 



individual pulse-waves. For this a reduction is required, as far as practicable, 

 of the inertia of the moving parts in the recording system, namely, of the 

 writing-lever, and especially of the junctional fluid column between artery and 

 writing-lever. The free-vibration period of the system is thus shortened. 

 Sufficient reduction can be obtained by employing for the junction between 

 arterial cannula and manometer a pressure-tubing of not more than 2 mm. 

 bore and a length of not more than 20-25 cm. ; and for writing-lever a grass- 

 stalk not more than 10 cm. long inclusive of a small thin oil-paper style tied on 

 with fine silk and not glued, the lever resting on the aluminium saddle about 

 •5 cm. from the lever's axle, i. e. multiplying amplitude of displacement of 

 membrane-centre about 20 times. 



