on which the action of the heart depends , &c. 8 1 
From this experiment it is evident, that the nervous influ-,, 
ence, so far from having a power of preserving the excitability 
of the muscles, exhausts it like other stimuli. The excitabi- 
lity therefore is a property of the muscle itself. Yet we have 
just seen, that it may be wholly destroyed by changes induced 
on the nervous system. On the same principle we explain 
the seeming contradiction respecting the action of the heart. 
We have seen that its power exists as independently of the 
brain and spinal marrow, as the action of the first muscles to 
which the salt was applied, whose nerves had been divided ; 
but, while the brain, and spinal marrow retain their functions, 
and the connection of nerves is entire, the heart, as well as 
the muscles of voluntary motion, may be influenced by agents 
acting through the nervous system. It is not difficult to ac- 
count for the latter being more copiously supplied with nerves 
than the heart, because all the stimuli which affect them, act 
through their nerves, while the heart is only now and then 
influenced through its nerves, its usual stimulus being as im- 
mediately applied to it, as the salt was to the muscles of the 
limb in the above experiment, and acting as independently of 
the nervous system. We do not surely in all this see any 
difference in the nature of the muscular power of the heart, 
and that of the muscles of voluntary motion, except their 
being fitted to obey different stimuli, a difference which we 
find in the two sides of the heart itself. 
It may here be objected, that in apoplexy the power of the 
muscles of voluntary motion is lost, while that of the heart is 
little or not at all impaired. Were such the fact, this objec- 
tion would be unanswerable ; but I have repeatedly examined 
the state of the muscles of voluntary motion in apoplexy, 
MDCCCXV. M 
