204 THE MECHANISM OF THE BEAT. [BOOK i. 



of the " differential manometer," the changes of pressure in the 

 ventricle and in the aorta at the same time. 



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FIG. 49. SIMULTANEOUS TRACINGS OF VENTRICULAR AND AORTIC PRESSURE. 



HURTHLE. 



On the left side the recording surface is travelling slowly, on the right more 

 swiftly, the tuning-fork vibrations, t, being 100 a second. 



A. aortic. V. ventricular curve, x x base line to each. The vertical lines 

 1 , 2, 3, 4, 5, cut each curve at exactly the same time. 



In the differential manometer, Fig. 50, the two tamhours of two 

 membrane manometers T and Tj (the mouths of the tubes opening into 

 each are seen in section) are arranged so that the central discs of both, 



FIG. 50. DIAGRAM OF THE DIFFERENTIAL MANOMETER OF HURTHLE. 



d and d v work on a balance above them. When the pressure in the 

 two tambours is equal, the balance is horizontal ; any difference of 

 pressure between the two leads to an upward or downward movement 

 of one or other arm, and this working against the light steel spring s, by 

 means of e and e 1 moves the lever I. 



In Figs. 51, 52 we give simultaneous tracings of the pressure 

 in the left ventricle V, and in the aorta A, and of the movements 

 of the lever of the balance indicating differences of pressure D 

 between the ventricle and the aorta. At the base line x x of D the 

 two pressures are equal. The course of the curve below this base 

 line indicates that the pressure in the ventricle is below that of the 

 aorta ; as the curve approaches towards the base line the pressure 

 in the ventricle becomes more and more nearly equal to that in 

 the aorta ; and such part of the curve as lies above the base line 

 indicates (except in so far as it may be due to the inertia of the 



