THE HEART BEAT. 



549 



size of the heart. The arrangement of apparatus for this purpose 

 is designated usually as an orthodiagraph, and the photographic 

 record obtained is spoken of as an orthodiagram. It may be shown 

 by this means, for example, that during muscular exercise there is 

 an increase in the size of the heart owing to the greater venous 

 inflow, while at the end of exercise, with the cessation of respira- 

 tory and muscular activity, the heart becomes smaller than normal, 

 owing to the fact that the faster rate, which is maintained for a 

 while, causes the heart to empty itself more rapidly than it is filled.* 

 The Apex Beat. The apex of the heart rests against the chest 

 wall at the fourth or fifth intercostal space, and here the systole 

 may be seen and felt in consequence of a slight protrusion of the 

 wall. Much discussion has ensued as to why this protrusion 

 occurs during systole, since the apex is drawn toward the base 

 and the volume of the heart is diminished by the output of 



Fig. 228. 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. 



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 

 downward which counteracts the effect of the shortening in the 



* Nicolai and Zuntz, "Berliner klin. Wochenschrift," No. 18, 1914. 



