544 CIRCULATION OF BLOOD AND LYMPH. 



the apex. Other observers,* in fact, most of the workers in this 

 field, doubt this interpretation, since the T wave may be obtained 

 apparently from any point on the external surface of the heart mus- 

 cle. Einthoven states that this wave may be positive or negative or 

 may be absent. According to him the whole ventricle is in contrac- 

 tion between the R and T wave and there is during this period no 

 difference in potential. The T wave when present indicates 

 simply that the condition of contraction does not cease simul- 

 taneously in all parts of the ventricle. It is evident from these 

 diverging views that it is not possible at present to give a satis- 

 factory interpretation of the electrocardiogram. 



Change in Form of the Ventricle During Systole. Much 

 attention has been paid to the external change of form of the 

 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), 



* For discussion and literature see Kahn, "Ergebnisse d. Physiologic," 14, 

 1914; also Eyster and Meek, "Archives of Int. Medicine," 11, 204, 1913. 



