82 



A MANUAL OF PHYSIOLOGY 



second is ' diastolic,' beginning at the commencement of the 

 diastole. 



The Cardiac Impulse. A surface-movement is seen, or an 

 impulse felt, at every cardiac contraction in various situations 

 where the heart or arteries approach the surface. The pulsa- 

 tion, or impulse, of the heart, often styled the apex-beat, is 

 usually most distinct to sight and touch in a small area lying in 

 the fifth left intercostal space, between the mammary and the para- 

 sternal line,* and generally, in an adult, about an inch and a half 

 to the sternal side of the former. It is due to the systolic 

 hardening of the ventricles, which are here in contact with the 

 chest- wall, the contact being at the same time rendered closer 

 by their change of shape, and by a slight movement of rotation of 

 the heart from left to right during the contraction (Practical Exer- 

 cises, p. 191). When 

 the left ventricle is in 

 contact with the chest 

 at the position of the 

 apex-beat, as is usually 

 the case, an important 

 element in the impulse 

 is the actual forward 

 thrust of the apex. 

 When the apex - beat 

 corresponds in position 

 with the right ventricle, 

 there is no actual for- 

 ward movement, al- 

 though the hardening 

 FIG 22 .-DiAGRAM OF MAREY'S CARDIOGRAPH, of the ventricle may be 



felt as a thrust by the 



finger. Even in health the position of the impulse varies some- 

 what with the position of the body and the respiratory move- 

 ments. In children it is usually situated in the fourth intercostal 

 space. In disease its displacement is an important diagnostic 

 sign, and may be very marked, especially in cases of effusion of 

 fluid into the pleural cavity. It is sometimes, though not in- 

 variably, a little lower in the standing than in the sitting position, 

 and shifts an inch or two to the left or right when the person lies 

 on the corresponding side. 



Various instruments, called cardiographs, have been devised for 

 magnifying and recording the movements produced by the cardiac 

 * The mammary line is an imaginary vertical line supposed to be drawn 

 on the chest through the middle point of the clavicle. It usually, but not 

 necessarilv passes through the nipple. The parasternal line is the vertical 

 line lying midway between the mammary line and the corresponding 

 border of the sternum. 



