144 A MANUAL OF PHYSIOLOGY 



sympathetic cord to its junction with the vagus, in which they run, 

 mingled with the inhibitory fibres, down to the heart. 



When the vago-sympathetic in the frog or toad is cut, and its 

 peripheral end stimulated, the heart in the vast majority of cases 

 is stopped or slowed, or its beat is distinctly weakened without, it 

 may be, any marked slowing. In other words, the rate at 

 which the heart was working before the stimulation is greatly 

 diminished, or reduced to zero. Such an effect, a diminution of 

 the rate of working, we call Inhibition. What precise form the 

 inhibition shall take, whether the stoppage shall be complete or 

 partial, appears to depend partly upon the strength of the 



FIG. 59. TRACING FROM FROG'S HEART. 



A, auricular, V, ventricular tracing. Sinus stimulated (primary coil 70 mm. 

 from secondary). Heart at temperature 11*2 C. Complete standstill. The 

 time -tracing between the curves marks intervals of two seconds. 



stimulus used and partly upon the state of the heart itself. 

 Some hearts it may be impossible to stop with weak stimulation, 

 although other signs of inhibition may be distinct, while they 

 are readily stopped by stronger stimulation. In other cases 

 the strongest stimulation may not produce complete standstill. 

 Again, a heated heart may be more readily brought to standstill 

 by stimulation of the vagus than a heart at the ordinary tem- 

 perature or a cooled heart. 



But there are other points of importance to be noted in regard 

 to this inhibition : (i) It does not begin for a little time after 



