96 THE CIRCULATION OF THE BLOOD AND LYMPH 



This conclusion is essentially in accordance with the results of 

 Chauveau and Marey, obtained long ago by means of their ' cardiac 

 sound,' which was in principle an elastic manometer. 



It consisted of an ampulla of indiarubber, supported on a frame- 

 work, and communicating with a long tube, which was connected with 

 a recording tambour. The ampulla was introduced into the heart (of 

 a horse) through the jugular vein or carotid artery in the way already 

 described. Sometimes a double sound was employed, armed with 

 two ampullae, placed at such a distance from each other that when 

 one was in the right ventricle the other was in the auricle of the same 

 side. Each ampulla communicated by a separate tube in the common 

 stem of the instrument with a recording tambour, and the writing 

 points of the two tambours were arranged in the same vertical line. 

 When any change in the blood-pressure takes place, the degree of 

 compression of the ampullae is altered, and the change is transmitted 

 along the air-tight connections to the recording tambours. 



On most of the endocardiac pressure tracings taken with modern 

 manometers, whether the curves belong to the type of the peak or of 

 the plateau, no sudden change of curvature, no nick, or crease, or 

 undulation reveals the moment of opening or closure of any valve. 

 This has been considered by some writers a striking tribute to the 

 smooth working of the cardiac pump. There is reason to think, 

 however, that the smoothness of the curve is still in some degree 

 artificial, and on some of the records obtained by optical methods 

 (Fig. 32) indications of changes of curvature, associated with the 

 action of the valves, may be observed. But even in the absence of 

 such indications, by experimentally graduating a pair of elastic 

 manometers, and obtaining with them simultaneous records of the 

 pressure in auricle and ventricle, or by using a ' differential ' mano- 

 meter, in which the pressures in two cavities are opposed to each 

 other, so that the movement of the membrane corresponds to their 

 difference, we can calculate at what points of the ventricular curve 

 the pressure is just greater than and just less than the pressure in the 

 auricle. The first point, it is evident, will correspond to the instant 

 at which the mitral or tricuspid valve, as the case may be, is closed, 

 and the second to the instant at which it is opened. And in like 

 manner, by comparing the pressure-curve of the aorta with that of 

 the left ventricle, the moment of opening and closure of the semi- 

 lunar valves may be determined (Figs. 33 and 34). According to the 

 best observations, the closure of the semilunar valves takes place at 

 a time corresponding to a point on the upper portion of the descend- 

 ing limb of the intraventricular curve. 



On the blood-pressure curve of the aorta, simultaneously registered, 

 the corresponding point is near the bottom of the so-called ' aortic ' 

 notch (p. 105) which precedes the dicrotic elevation. For clinical 

 purposes, in man the moment of closure of the semilunar valves 

 (denoted by the abbreviation S.C. point) may be taken as 0-03 second 

 before the bottom of the aortic notch in sphygmo graphic tracings 

 from the carotid, this being approximately the average time occupied 



