CHAP, iv.] 



THE VASCULAR MECHANISM. 



339 



recording tambour, were enabled to take simultaneous tracings 

 of changes occurring in the two cavities. These results are 

 embodied in Fig. 21, of which the upper curve is a tracing taken 



TC 



V 



FlG. 21. SIMULTANEOUS TRACINGS FROM THE INTERIOR OF THE RIGHT AURICLE, FROM 

 THE INTERIOR OF THE RIGHT VENTRICLE, AND OF THE CARDIAC IMPULSE, IN THE 



HORSE. (AFTER CHAUVEAU AND MARF.Y.) To be read from left to right 1 . 



The upper curve represents changes taking place within the auricle, the middle 

 curve changes within the ventricle. The lower curve represents the variations of 

 pressure transmitted to a lever outside the chest and constituting the cardiac 

 impulse. A complete cardiac cycle, beginning at the close of the ventricular 

 systole, is comprised between the thick vertical lines I and II. The thin vertical 

 lines represent tenths of a second. The explanation of the letters is given in 

 the text. 



from the auricle, the middle curve a similar tracing taken from 

 the ventricle, while the lower curve is a cardiographic tracing 

 of the cardiac impulse. All these curves were taken simultaneously 

 on the same recording surface. 



Method. A tube of appropriate curvature is furnished with two 

 small elastic bags, one at the extreme end and the other at such a 

 distance that when the former is within the cavity of the ventricle the 

 latter is in the cavity of the auricle ; such an instrument is spoken of 

 as a ' cardiac sound.' Each bag (Fig. 22 A) or 'ampulla' communicates 

 by a separate air-tight tube with an air-tight tambour (Fig. 22 B) on 

 which a lever rests so that any pressure on either bag is communicated 

 to the cavity of its respective tambour, the lever of which is raised in 



1 It must be remembered that the curves in the diagram are intended merely 

 to illustrate the changes occurring at different times in the same chamber, 

 or to shew what changes in the one chamber are coincident in point of time with 

 changes in the other. They in no way indicate the amount of pressure exerted in the 

 auricle as compared with that in the ventricle. 



