HEART'S IMPULSE. 267 



ing of the muscle. The mass of the ventricles, from being 

 quite soft and compressible during diastole, suddenly acquires a 

 wooden hardness, owing to the tightness with which the mus- 

 cle grasps the fluid, and the greater firmness of the contracting 

 tissue. 



This hardening gives the sensation of a sudden enlargement in 

 all directions. No matter on what surface the finger be placed, 

 the heart seems to move in that direction, so as to give a slight 

 knock or impulse. Thus, when grasped between the forefinger 

 placed below the diaphragm and the thumb on the antero-supe- 

 rior aspect, the impulse is equally felt by each digit. 



The heart-beat communicates its motion to the chest, and this 

 impulse can be seen over a limited area, which varies with the 



FIG. 120. 



Cardiac Tambour, which can be strapped on to chest-wall, so that the cen- 

 tral button lies over the heart-beat, and the pressure may be regulated by 

 the screws at the side. To the tube bent at right angles is attached the rub- 

 ber tube which connects the air cavity with that of the writing tambour 

 shown in Fig. 119. 



thinness of the individual. This cardiac impulse, as the stroke 

 is called, can be best felt in the fifth intercostal space, a little to 

 the median side of the left nipple. It is found to be synchronous 

 with the ventricular systole. The more important item in causing 

 the impulse is the hardening of the ventricles, while their simul- 

 taneous change in shape, from a flattened to a rounded cone, no 



