CHANGE IN SHAPE OP HEART. 



65 



greater blood-pressure there. Complete diastolic relaxation of the ventricle occurs 

 from e to / in the curve. 



It is clear, then, that the cardiac impulse is caused chiefly by the contraction of 

 the ventricles, while the auricular systole and the vibration caused by the closure 

 of the semi-lunar valves are also concerned in its production. 



[Change in Shape of Heart. The experiments of Ludwigand Hesse on the heart 

 of the dog show that the shape of the ventricles varies remarkably in systole and 

 diastole, and that the shape of the heart as found post-mortem is not its natural shape.] 



[Method. Bleed a dog rapidly from the carotids, defibrinate the blood, expose the heart, tie 

 graduated straight tubes into the pulmonary artery and aorta, and ligature the auricular vessels. 

 Pour the blood into the heart until it is dilated under a pressure equal to the mean arterial pres- 

 sure (150 mm.). The ventricles are in the diastolic phase, the auricles still pulsate. A plaster 

 cast is now rapidly made of the ventricles. This represents the diastolic phase. To obtain what 

 may be regarded as the systolic phase, a heart, similarly prepared but emptied of blood, is 

 suddenly plunged into a hot (50 C. ) saturated solution of potassic bichromate, when the heart 

 gives one rapid and final contraction and remains permanently contracted owing to the heat- 

 rigor, its proteids being coagulated ( 295). This is the systolic phase. Little pins with twisted 

 points are previously inserted in the organ to mark certain parts of both hearts for comparison. ] 



[In diastole, the shape of the ventricle is hemispheroidal, the apex being rounded, 

 while the posterior surface is flatter than the anterior (fig. 41). In the plane of 

 the ventricular base, the greatest diameter is from right to left, and the shortest 

 from base to apex. The conus arteriosus is above the plane of the base. During 



Fig. 41. 

 Projection of a dog's heart. 

 Posterior surface. 



Fig. 42. 

 Anterior surface. 



Fig. 43. 

 Left lateral surface. 



systole, the apex is more pointed, the ventricle more conical, while all the diameters 

 in the plane of the base are equally diminished, hence the vertical measurement 

 from base to apex is longer now than either of the diameters at the base (fig. 43). 

 The conus arteriosus sinks towards the plane of the base, while the base of the 

 ventricle becomes more circular, so that the difference of the curvatures of the 

 anterior and posterior surfaces van- 

 ishes (fig. 42). In all these figs, the 

 shaded part represents diastole and 

 the clear part systole. The most re- 

 markable point is that the vertical 

 measurement remains unchanged. 

 This refers to the left ventricle, which 

 of course forms the apex; the right is 

 shortened. The plane of the ven- 

 tricular base in systole is about one- Fig. 44. 

 half of what it is in diastole, as is Projection of the base in 

 shown in fig. 44. Thus the heart is systole and diastole, RV, 

 diminished in all its diameters except fW' and LV > left ven " 



triplp 



one, the arterial orifices are scarcely 

 affected, while the area of the auriculo-ventricular orifices (M, T) is diminished 

 about one-half (fig. 45). This is most ^important in connection with the closure of 



E 



Fig. 45. 

 A, aorta ; PA, pulmon- 

 ,., ary artery ; M, mitral, 

 and T, tricuspid ori- 

 fice. 



