156 



IRRITABILITY 



Fig. 29. 



Eight series of lieart contractions. Tlie dotted lines e sliow tlie moment of an artificial 

 stimulus. Tlie artificial stimulus is ineffective if it is applied before the height of a 

 systole. The artificial stimulus becomes the more effective in producing an extra 

 systole, followed by a compensatory pause, the later it is applied after the height of 

 the systolic contraction. (After Marey.) 



