CIRCULA TIOX. 1 57 



The refractory phase disappears with sufficiently strong stimuli, especially 

 if the heart is warmed. In such a case an artificial stimulus falling in the 

 beginning of a spontaneous contraction produces an extra contraction. This 

 extra contraction, however, comes first after the end of the systole during which 

 the artificial stimulation is made, occurring in fact toward the end of the 



Fig. 28. — The refractory period and compensatory pause. The curves are recorded by a writing lever 

 resting on the ventricle of the frog's heart. They read from left to right. A break in the horizontal line 

 below each curve indicates the moment at which an induction shock was sent through the ventricle. In 

 curves 1, 2, and :; the ventricle proved refractory to this stimulus; in the remaining curves, the stimulus 

 having fallen outside t.he refractory period, an extra contraction and compensatory pause are seen. 

 Many of the phenomena mentioned in the text are illustrated by this figure (Marey, 1876, p. 72 



following diastole. The latent period of such a contraction Lengthens with 

 the length of the interval between the artificial stimulation and the end of the 

 systole. 



A refractory period has been demonstrated in the auricle of the frog 1 

 and dog; 2 in the ventricle of the cat, rabbit, and dog, and in the sinus 

 venosus and bulbus arteriosusof the frog, h is said noi to be present in 

 the lobster. 3 



1 Engelmann: Archiv fitr die gescmmU Physiologic, 1894, li\. p. 322. 



'Meyer: Archives de Physiologic, 1893, p. 185; Cushny and .Matthews: Journal of Physiology, 

 1897, xxi. p. 213. 



8 Hunt, Bookman, and Tierney : Centrcdblatt fur Physiologic, 1897, \i. p. 276. 



