CH. XX.] 



CARDIOGRAPHS. 



239 



A simple instrument applicable to the frog's heart is the 

 following : 



Fig. 2 36. 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 contraction 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. 

 237) by movements of the writing 

 point at the end of the long arm 

 of the lever. Such apparatus is, how- 

 ever, not applicable to the human 

 heart, and all the various forms of 

 cardiograph devised for this purpose 

 are modifications of Marey's tambours. One of those most 

 frequently used is depicted in the next two diagrams. 



It (fig. 238) consists of a cap-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 registering 



Fig. 237. Cardiogram of frog's 

 heart, c, showing auricular, 

 followed by ventricular beat; 

 T, time in half seconds. 



