274 MANUAL OF PHYSIOLOGY. 



FIG. 121. 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 movements of the 

 chest wall are transmitted from a somewhat 

 similar drum by means of air tubes. In using 

 this plan, so generally employed 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 (>), where they give 

 rise to a motion in its flexible surface to which 

 a delicate lever is attached at (a). 



HEART SOUNDS. 



The heart's action is accompanied by two 

 distinct sounds, which can be heard by 

 bringing the ear into firm, direct contact 

 with the precordial region, or indirectly by 

 the use of the stethoscope, an instrument of 

 which there are many varieties to suit the 

 taste of clinical observers.* 



*A flexible stethoscope to listen to one's own 

 heart sounds can easily be made by fitting to one 

 end of a piece of rubber tubing about 18 inches 

 long the mouth piece, and to the other end the bowl 

 of a wooden pipe. The bowl is applied over the 

 d fferent regions of the heart, and the mouth-piece 

 firmly fitted in the ear. 



Writing Lever and Tambour. (a) Joint of the lever; (&) Air chamber; (/) Rubber 

 tubing connecting it with cardiac tambour. 



