A CARDIOGRAM 



145 



the tambour. Fixed to the end of a spring d is an ivory button, c, furnished 

 above with a pin which comes into contact with the disc on the tambour. 

 Expose the chest and mark the spot at which the heart's impulse is best felt. 

 Fit the tambour on the chest, so that the tambour rests on the three feet, with 

 the ivory button over the marked spot. It is held in position by the bands 

 e 1 and e-. Now vary the pressure of the button on the skin by altering the 

 position of the three feet until the lever of the recording tambour gives a 

 good excursion. Record a few beats on a drum revolving | cm. per second, 

 taking a seconds time tracing under the record. 



The form of curve so obtained is shown in fig. 115. It is termed a 

 cardiogram. The moment of hardening is indicated by a sudden 



Fig. 115. — A Cardiogram taken upon a Man. The Contraction of the 

 Heart is recorded by the Up-stroke of the Record. 



ascent of the lever and the end of the ventricular systole by a sudden 

 fall of the lever. The chief value of such a tracing is to give us 

 reliable information as to the time at which the heart contracts and 

 relaxes when we wish to compare it with other phenomena occurring 

 at the same time. 



