568 CIRCULATION OF BLOOD AND LYMPH. 



bered (p. 29) that, according to some authors, the difference in 

 this respect between skeletal muscle and heart muscle is only ap- 



Fig. 237o. —To show the effect of a short electrical stimulus apphed at different times 

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

 stimulus (e) falls into the heart durina; 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 followecf by an extra systole and corresponding compensatory pause. It will be 

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

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



