138 A MANUAL OF PHYSIOLOGY 



tion cannot develop itself in the presence of inhibition at 

 least, until the latter is nearly spent. In the frog, at any 

 rate, the two processes can hardly be considered as 

 antagonistic, in the sense that a definite amount of 

 augmentor excitation can overcome a definite amount of 

 inhibitory excitation. Nor is it the case that when the 

 heart is pjayed upon at the same time by impulses of both 



FIG. 49. FROG'S HEART. 



A, auricular ; V, ventricular tracing. Ventricle beating very feebly. Vagus stimu- 

 lated (60 mm. between coils). Marked augmentation of ventricular beat. 



kinds, it pits them against each other and strikes the 

 balance accurately between them. It is possible, however, 

 that when the inhibitory fibres are very weakly, and the 

 augmentor fibres very strongly stimulated, the amount of 

 inhibition may be somewhat diminished. In mammals, on 

 the other hand, a true antagonism seems to exist; and 

 stimulation of the inhibitory nerves is less effective when 

 the augmentors are excited at the same time. 



