530 THE OUTGO OF ENERGY 



last the bulbus. Note the pallor of the contracted, 

 empty ventricle. 



Graphic Record of Ventricular Contraction. - 

 Pass a fine wire through the tip of the ventricle 

 and fasten the free end to the heart lever (Fig. 53). 

 Let the lever write on a slow-moving drum. 



Note the characteristics of the curve. 



THE HEART MUSCLE 



All Contractions Maximal. Inhibit the heart 

 by a Stannius ligature (see page 562). Find the 

 least strength of stimulus that will cause the ven- 

 tricle to contract. Increase the strength of the 

 stimulus, but do not stimulate oftener than once 

 in ten seconds (to avoid the staircase contractions 

 described below). 



The force of ventricular contraction will re- 

 main the same, notwithstanding the increased 

 stimulus. 



If the heart responds at all to a stimulus, it 

 responds by a maximum contraction. There is 

 no interval between the minimal and maximal 

 value (compare page 175). 



Staircase Contractions. Find the least Stimu- 

 lus that will cause the ventricle to contract. 



