548 CIRCULATION OF BLOOD AND LYMPH. 



ventricle during systole. Does it diminish in size in all diameters 

 or only in certain diameters? The question is one that cannot 

 be answered definitely for all normal conditions, owing to the 

 fact that the form of the heart during diastole varies with the 

 posture of the body. During diastole the heart muscle is 

 quite soft and relaxed, and consequently its shape is influenced 

 by gravity. The exact change of form that it undergoes in 

 passing from diastole to systole will vary with its shape, what- 

 ever that may happen to be, in diastole. During systole the 

 musculature, on the contrary, is hard and resisting and the form 

 of the heart in this phase is probably constant. The change 

 from the variable diastolic to the constant systolic form will natu- 

 rally be different in different positions. With an excised frog's 

 heart one can show that the ventricle is elongated in passing from 

 diastole to systole or one can show the reverse. If the heart is laid 

 upon its side it flattens in diastole so as to increase in length, 

 and systole causes a shortening. If the heart is held or placed 

 with its apex pointing upward it flattens during diastole so as 

 to shorten the diameter from base to apex and during systole 

 this diameter is lengthened. In ourselves the exact change of 

 shape is probably different in the erect from what it is in the 

 recumbent posture. Speaking generally, the accounts agree in 

 stating that the long diameter of the heart is decreased, base and 

 apex are brought closer together, and the diameter from right to 

 left is also decreased, while the anteroposterior or ventrodorsal 

 diameter is increased. That is, the outline of the base of the heart 

 during diastole is an ellipse with its short diameter in the ventro- 

 dorsal direction. During systole this outline approaches that of a 

 circle. A more interesting change is described for the apex of 

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

 at this point as they turn to pass into the interior (see Fig. 223), 

 fche 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 respects under various normal and patho- 

 logical conditions may be studied quite successfully by means of 

 the z-rays. When the arrays 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 



