46 
these were wanting altogether. We may therefore assume that this 
tissue can contract. If we could ascertain that this bundle is inner- 
vated by the vagus nerve, we should have precisely similar circum- 
stances as in the tortoise-heart. This however cannot be ascertained. 
The distribution of sympathetic and vagus nerve in the heart seems 
histologically uncertain. 
I should think that for the mammalian heart we have reason to 
assume the possibility that here too the inhibition must be ascribed 
to simultaneous efferent impulses, in analogous manner as described 
for the knee jerks. Even if the vagus stimulus elicits but a slight 
contraction of the muscle bundle of His-Tawara, it is still very well 
possible, that this is the reason to which inhibiting influence upon 
the contraction of the heart is due. 
