578 



CIRCULATION OF BLOOD AND LYMPH. 



is maximal for that condition, that is, does not vary with the 

 strength of the stimulus. As was said above, this property is not 



Fig 236. To show the effect of a short electrical stimulus applied at different times 

 in the heart beat. (Marey.) The record is taken from the frog's heart. In 1, 2, and 3 the 

 stimulus (e) falls into the heart during systole (refractory period) and has no effect. In 

 4, 5, 6, 7, and 8 the stimulus falls into the heart toward the end of systole or during diastole, 

 and is followed by an extra systole and corresponding compensatory pause, 

 noted that the latent period (shaded area) between the stimulus and the extra systole w 

 ahorter the longer the diastole has preceded before the stimulus is applied. 



