THE HEART BEAT. 545 



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 exact position and size of the heart in man and 

 its variations in these respecte under various normal and patho- 

 logical conditions mjay be studied quite successfully by means of 

 the z-rays. When 'the x-rays are passed through the chest, the 

 heart forms a shadow which may be seen with the aid of the fluor- 

 escent screen and which may also be photographed. The appa- 

 ratus used for this purpose may be so arranged that the rays pass 

 through the chest in parallel lines and give a shadow of the exact 

 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 

 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 



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

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