268 



MANUAL OF PHYSIOLOGY. 



FIG. 121. 



doubt helps to make the sudden tenseness 

 more distinctly felt through the wall of the 

 chest. 



The point at which the impulse is best 

 felt coresponds to the anterior surface of 

 the ventricles some distance above the apex ; 

 it is therefore erroneous to call it the " apex 

 beat." 



Moreover, the motion of the apex is so 

 slight when the wall of the chest is removed, 

 that its "tilting forwards" can have no 

 share in causing the impulse : the thoracic 

 wall being always in contact with the apex, 

 it can only move laterally, and cannot ham- 

 mer against it so as to cause a shock. The 

 "recoil of the ventricles" caused by the 

 blood leaving them, which some think aids 

 in producing the impulse, obviously owes its 

 supposed existence to the confusion of cause 

 and effect. 



The cardiac impulse is a valuable measure 

 of the strength of the systole, and hence is 

 of great importance to the clinical physician. 

 It may be registered by means of an instru- 

 ment called the Caliograph. Many such 

 instruments have been devised, most of 

 which work on the same principle, and write 

 a record on a moving surface with a lever 

 attached to a tambour, to which the move- 

 ments of the chest wall are transmitted from 

 a somewhat similar drum by means of air 

 tubes. In using this plan, so generally em- 

 ployed by Marey, one air-tambour (fig. 120) 

 is applied over the heart, the motions of 

 which cause a variation in the tension of 

 the air it contains ; these variations are 

 transmitted by a tube (/, Fig. 121) to the 

 other tambour (6), where they give rise to 

 a motion in its flexible surface to which a 

 delicate lever is attached at (a). 



Writing Lever and 

 Tambour. (a) Joint 

 of the lever; (6) Air 

 chamber; (/) Rubber 

 tubing connecting it 

 with cardiac tambour. 



