CH. XXL] 



CARDIOGRAPHS 



239 



recorded as in the next figure (fig. 216) 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 forms of cardio- 

 graph devised for this purpose are modi- 

 fications of Marey's tambours. One of 

 those most frequently used is depicted in 

 the next two diagrams. 



It (fig. 217) 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 communi- 

 cates 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 (fig. 218), also closed, 

 and through the elastic and movable lid of the latter to the lever, which is placed in 

 connection with a registering apparatus, which consists of a cylinder covered with 



Tube to communicate 

 with tambour. 



FIG. 216. Cardiogram of frog's 

 heart C, showing auricular, 

 followed by ventricular beat; 

 T, time in half seconds. 



Tambour. 



Ivory Tape to attach the instru- 

 knob. ment to the chest. 



FIG. 217. Cardiograph. (Sanderson's.) 



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. 



Fig. 219 represents a typical tracing obtained in this way. The 

 first small rise of the lever is caused by the auricular, the second 

 larger rise by the ventricular systole ; the downstroke represents the 



