452 rRlNClPLES OF GENERAL /'// YS/OLOGY 



(|iirstion of the origin and regulation of the beat, will be described in 

 Chapter XXIII. 



"All or Nothing." This fact was discovered by Bowditch (1871) in the heart 





FIG. 138. REFRACTORY PERIOD IN FROC'S VENTRICLE. Spontaneous con- 

 tractions with artificial stimulus applied at various intervals after a con- 

 traction, as indicated by a rise in the signal line. 



In lines 1, 2, and 3 the second stimulus has no effect. 



The succeeding lines show gradual decrease of latent period (shaded part) of the extra contraction 



which takes place at this period. 

 The "compensatory pause," after the extra systole, is shown in lines 4, 5, 6, 7, and 8. 



(Marey, 1885, p. 417.) 



of the frog. On account of its interest and importance, the words used by the 

 investigator himself may be given, in translation, thus : " An induction shock 

 produces a contraction or fails to do so according to its strength ; if it does so at 

 all, it produces the greatest contraction that can be produced by any strength of 

 stimulus in the condition of the muscle at the time" (p. 687). 



