HANDBOOK OF PHYSIOLOGY. 



contents into the arteries is a distinctly laborious action, as it is resisted 

 by the elasticity of the vessels. It is to this sudden hardening that the 

 impulse of the heart against the chest- wall is due, and the shock of the 

 sudden tension may be felt not only externally, but also internally, if the 

 abdomen of an animal be opened and the finger be placed upon the 

 under surface of the diaphragm, at a point corresponding to the under 

 surface of the ventricle. The shock is felt, and possibly seen more dis- 

 tinctly because of the partial rotation of the heart, already spoken of, 

 along its long axis towards the right. The movement produced by the 

 ventricular contraction against the chest-wall may be registered by means 

 of an instrument called the cardiograph, and it will be found to corre- 

 spond almost exactly with a tracing obtained by the same instrument 

 applied over the contracting ventricle itself. 



The Cardiograph (Fig. 115) consists of a cup-shaped metal box 

 over the open front of which is stretched an elastic india-rubber mem- 

 brane, upon which is fixed a small knob of hard wood or ivory. This 

 knob, however, may be attached instead, as in the figure, to the side of 



the bt>x by means of a spring, and may be 

 made to act upon a metal disc attached to the 

 elastic membrane. 



The knob (A) is for application to the 

 chest-wall over the place of the greatest im- 

 pulse of the heart. The box or tympanum 

 communicates by means of an air-tight elastic 

 tube (/) with the interior of a second tym- 

 panum (Fig. 116, b), in connection with 

 which is a long and light lever (a). The 

 shock of the heart's impulse being communi- 

 cated to the ivory knob, and through it to 

 the first tympanum", the effect is, of course, 

 at once transmitted by the column of air in 

 the elastic tube to the interior of the second 

 tympanum, also closed, and through the 

 elastic and movable lid of the latter to the 

 lever, which is placed in connection with a registering apparatus. This 

 generally consists of a cylinder or drum covered with smoked paper, 

 Tevolving according to a definite velocity by clock-work. The point of 



FIG. 115. -Cardiograph. (San 

 derson's.) 



Fia. 116 Marey's Tambour (6), to which the movement of the column of air in the first tympa- 

 num is conducted by the tube, /, and from which it is communicated by the lever a, to a revolving 

 cylinder, so that the tracing of the movement of the impulse beat is obtained. 



