238 



PHYSIOLOGY OF THE HEART 



[CII. XX. 



and levers placed in connection with its various parts may be 

 employed to write on a revolving blackened surface. 



A simple instrument for the frog's heart is the following : 



FIG. 243. Simple Cardiograph for frog's heart. 



The sternum of the frog having been removed, the pericardium 

 opened, and the fraenum (a small band from the back of the heart 



to the pericardium) divided, the heart is 

 pulled through the opening, a minute hook 

 placed in its apex, and this is fixed by a 

 silk thread to a lever pivoted at F as in 

 the figure. The cardiac wave of contrac- 

 tion starts at the sinus, this is followed 

 by the auricular systole, and that by the 

 ventricular systole and pause. This is 

 recorded as in the next figure (fig. 244) 

 by movements of the writing point at the 

 end of the long arm of the lever. Such 

 apparatus is, however, not applicable to 

 the human heart, and all the various 



FIG. 244. Cardiogram of frog's ,. i -i ' -i <> ,1 



heart, c, showing auricular, torms or cardiograph devised tor this pur- 



**' pose are modifications of Marey's tambours. 

 One of those most frequently used is 

 depicted in the next two diagrams. 



It (fig. 245) consists of a cup-shaped metal box over the open front of which is 

 stretched an elastic india-rubber membrane, upon which is fixed a small knob of 

 hard wood or ivory. This knob, however, may be attached, as in the figure, to the 

 side of the box by means of a spring, and may be made to act upon a metal disc 

 attached to the elastic membrane. 



The knob is for application to the chest-wall over the apex beat. The box or 

 tambour communicates by means of an air-tight tube with the interior of a second 

 tambour, in connection with which is a long and light lever. The shock of the 

 heart's impulse being communicated to the ivory knob and through it to the first 

 tambour, the effect is at once transmitted by the column of air in the elastic tube 

 to the interior of the second tambour, also closed, and through the elastic and 

 movable lid of the latter to the lever, which is placed in connection with a register- 

 ing apparatus, which consists of a cylinder covered with smoked paper, revolving 

 with a definite velocity. The point of the lever writes upon the paper, and a tracing 

 of the heart's impulse or cardiogram is thus obtained. 



