434 Dr. Philip’s additional experiments on the 
to the nervous system on the heart, being proportioned to the 
extent of surface to which they are applied. It is evident 
that the stimulus can be applied to a greater extent of surface 
in the fluid than in the solid form. When the effect of the 
mechanical agent is rendered extreme and general on the 
nervous system, we find its influence on the heart far greater 
than that of any chemical agent I tried. From experiments 
I lately laid before the Society, it appears, that suddenly crush- 
ing any considerable part of the nervous system instantly 
destroys the power of the heart. 
The conclusions then at which we arrive, are, — that the 
heart is excited by all stimuli applied to any considerable part 
of the nervous system, while the muscles of voluntary motion 
are only excited by intense stimuli applied to certain small 
parts of this system. 
These facts being ascertained, the other differences observed 
in the effects of stimuli applied to the nervous system, on the 
heart and muscles of voluntary motion, are easily explained. 
Irregular action of a muscle arises from stimuli acting par- 
tially, or at intervals, on its nerves, or on the particular part 
of the brain or spinal marrow, from which its nerves arise. 
But partial action of a stimulus on the nervous system, we 
have just seen, is incapable of exciting the heart, and while 
the stimulus is applied to any part of the nervous system, as 
all parts of this system seem equally to influence the heart, it 
cannot act upon it interruptedly, as an instrument does on the 
muscles of voluntary motion when it is moved from place to 
place in the brain. When the instrument is kept still after it is 
introduced into the brain, the action of the muscles of voluntary 
motion often ceases; its merely being in contact with the parts 
