COURSE OF CIRCULATION IN MAMMALS 



rate of beat is increased by taking exercise and also how quickly 

 the normal rate of beat is resumed after such exercise. By palpa- 

 tion, with the hand over the region of the heart, its stroke, the 

 cardiac impulse, can be felt; by percussion, the anatomical limits 

 of the organ can be defined; by auscultation with the ear directly, 

 or with use of the stethoscope, the sounds of the heart can be heard. 

 The cardiac impulse can be recorded by the tambour method of 

 registration; the heart -sounds by means of the microphone and 

 string galvanometer; while the volume and movements of the heart 

 can be studied with the help of the Rontgen rays. 



Aortic 



( Pulmonary 



Tricuspid 



Mitral 



FIG. 60. DIAGRAM SHOWING SURFACE RELATIONS OF LUNGS, HEART, AND CARDIAC? 



VALVES. (Cowan.) 



The Cardiac Impulse. The impulse is caused by the sudden harden- 

 ing of the muscular mass of the ventricles against the chest wall. It 

 coincides with the beginning of systole. The position at which the 

 impulse is felt varies with the position of the body. Normally, with the 

 body in the supine position, the impulse is visible in the fourth or fifth 

 intercostal space 2 inches below the nipple and 3i inches from the mid- 

 sternal line (Fig. 60). In rising to the standing posture, the impulse shifts 

 its position downwards and to the left for | to 1 inch. When a man 

 rolls over on to his right side, the impulse may shift from 3 to 4 inches 

 to the right, and disappear beneath the sternum. Similarly, on rolling 

 on to the left side, the impulse shifts to the left of the nipple line. 



