94 THE CIRCULATION OF THE BLOOD AND LYMPH 



acts on a writing lever. The instrument is so constructed that for a 

 given change of pressure the quantity of liquid displaced is as small 

 as possible, and it is on this that its capacity to follow sudden varia- 

 tions of pressure chiefly depends. The manometer is connected with 

 the cavity of the heart by an appropriately curved cannula of metal 

 or glass, which, after being filled with some liquid that prevents co- 

 agulation (Practical Exercises, p. 211), is pushed through the jugular 

 vein into the right auricle or ventricle, or through the carotid artery 

 and aorta into the left ventricle. Some observers fill only the cannula 

 with fluid, and leave the capsule of the elastic manometer and as much 

 of the connections as possible full of air. Others fill the whole system 

 with liquid. And around the question of the relative merits of ' trans- 

 mission ' by liquid and by air has raged a controversy which, however, 

 now shows signs of coming to an end. For there is reason to suppose 

 that the character of the curves obtained is modified among other 

 circumstances by the manner in which the pressure is transmitted, as 

 it is certainly modified by the dimensions and mass of the moving parts 

 and the method of recording. As Wiggers has pointed out, the differ- 

 ences in the records obtained by different observers, even with the latest 

 methods of optical registration, are determined largely by the sensitive- 

 ness and degree of damping of the manometer. 



The Ventricular Pressure-Curve. Thus, the pressure-curve of the 

 ventricle, according to most of those who have employed mano- 

 meters with liquid transmission and small inertia of the moving 

 parts (Fig. 33), remains after the first abrupt rise, which undoubtedly 

 corresponds to the ventricular systole, well above the abscissa line 

 for a considerable time, and then 'descends somewhat less suddenly 

 than it rose. This systolic ' plateau,' although usually broken by 

 minor heights and hollows, which may be partly due to inertia oscilla- 

 tions of the liquid or the recording apparatus, would indicate that 

 the ventricular pressure, after its first swift rise, maintained itself at 

 a considerable height throughout the greater part of the systole. 

 The tracings yielded by most of the manometers with air trans- 

 mission show the same suddenness in the first part of the upstroke 

 and the last part of the descent that is, the same abruptness 

 in the beginning of the contraction and the end of the relaxa- 

 tion. But they differ totally in the intermediate portion of the 

 curve, which, climbing ever more gradually as it nears its apex, 

 remains but a moment at the maximum, then immediately descend- 

 ing forms a ' peak/ and not a plateau. It ought to be distinctly 

 understood, however, that the use of the term ' plateau ' must not be 

 taken to imply that the pressure remains constant and the curve 

 parallel to the abscissa during this interval. 



Wiggers, using the optical method of recording the pressure- 

 curve in the right ventricle (p. 93), finds that when the auricular 

 pressure and the pressure in the pulmonary artery are normal the 

 curve of intraventricular pressure may be divided into (i) an auric- 

 ular period; (2) a period of rising pressure while the ventricle is 

 contracting and its cavity is closed by the auriculo- ventricular and 

 semilunar valves; (3) an ejection period during which the pressure 



