THE HEART BEAT. 



543 



blood. The fact seems to be explained satisfactorily by two con- 

 siderations: The heart during diastole rests against the chest wall 

 at its apex and a portion of its anterior surface, but causes no pro- 

 trusion of the wall because the tenseness of this latter is sufficient 

 to flatten or deform the softer heart muscle. During systole the 

 hardened heart muscle, on the contrary, overcomes the now rela- 

 tively less resistant integument. The rotation of the apex tends 

 also to maintain the contact; so that, although the heart is short- 

 ened in its long diameter, the extent of the movement is not 

 sufficient to draw it away from the chest wall. In the second place, 

 the discharge of the heart contents into the curved aorta by tending 

 to straighten this tube causes a movement of the whole heart 



FiK. 229. — Marey's cardiograph. The button on the tambour is pressed upon the 

 chest over the apex. The movements are transmitted through the tube to the right to a 

 recording tambour. 



downward which counteracts the effect of the shortening in the 

 long diameter. 



The Cardiogram. — The apex beat may be recorded easily by 

 means of appropriate tambours. Several instruments have been 

 especially devised for this purpose and are designated as cardio- 

 graphs. The cardiograph described by Marey is shown in Fig. 229. 

 It consists essentially of a tambour inclosed in a metal box. The 

 rubber membrane of the tambour carries a button which can be 

 brought to bear, under a suitable pressure, upon the apex of the 

 heart. The movements of this button cause pressure changes in 

 the air of the tambour which are transmitted through tubing to a 

 recording tambour and recorded on a kymographion. A simple 

 and effective cardiograph may be made by pressing a funnel 

 against the skin over the apex and connecting the stem of the 

 funnel by tubing to a suitable recording tambour. The car- 

 diograms obtained by such methods have been the subject of 

 much discussion. The form of the curve varies somewhat with 



