500 CIRCULATION OF BLOOD AND LYMPH. 



ventricle. Owing to the whorl made by the superficial fibers at 

 this point as they turn to pass into the interior (see Fig. 208, 7), 

 the systole causes a rotation of the apex, which is thereby 

 forced more firmly against the chest wall. This rotation and 

 erection of the apex during systole may be seen upon the exposed 

 heart of the lower mammals and has been described also for man 

 in cases in which the heart is covered only by the skin, owing to 

 malformation in the chest wall (ectopia cordis) or to surgical 

 operations. 



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 

 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 

 long diameter. The apex beat is proof that the apex remains 

 against the chest wall during systole and in mammals corroborative 

 experiments have been made by running needles through the chest 

 wall into the base and the apex of the heart. Such needles act as 

 levers with a fulcrum in the skin, and from the movement of the 

 projecting portion it has been shown that, while the basal portion 

 of the heart moves downward during systole, the apex remains 

 more or less stationary except for the lateral movements due to 

 the rotation. 



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. 209. 

 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 



