1 86 



THE CIRCULATION OF THE BLOOD 



against the wall of the chest. When the ventricles contract, their walls 

 suddenly become firm and tense. Being firmly attached to the base the 

 effect of the movement is to press the hardened ventricle against the 



Screw to adjust the lever 



Writing lever Tambour Tube to the cardiograph 



FIG. 156. Marey's Tambour, to which the Movement of the Column of Air in the 

 Cardiograph is Conducted by a Tube, and from which it is Communicated by the Lever 

 to a Revolving Cylinder so that the tracing of the movement of the cardiac impulse is 

 obtained. 



chest wall. The discharge of the contents of the ventricle into the curved 

 aorta intensifies this pressure by its mechanical effect in tending to 

 straighten the curve of that vessel and thus holds the ventricle in firm 

 contact with the chest. It is this sudden pressure of the contracting 

 heart against the chest wall that is felt on the outside. The impact or 



FIG. 157. Typical Cardiogram (upper trace) from the Dog. Taken simultaneously 

 with the aortic pressure (middle) and intraventricular pressure (lower) tracings. Time 

 in o.oi of a second. (Hiirthle.) 



shock is possibly more distinct because of the partial rotation of the 

 whole heart toward the right and front along its long axis. The move- 

 ment of the chest wall produced by the ventricular contraction against 

 it may be registered by means of an instrument called the cardiograph; 



