43° Dr. Philip’s additional experiments on the 
effect, but continued to stimulate the heart as long as they 
were applied, produced a much greater degree of excitement 
than tobacco, whose slight stimulant effect was quickly suc- 
ceeded by a powerfully sedative one. 
It appears from these experiments, that chemical stimuli, 
applied to the nervous system, exert a greater power over 
the heart than mechanical stimuli, while the latter exert a 
greater power over the muscles of voluntary motion than 
chemical stimuli ; that both chemical and mechanical stimuli, 
applied to the nervous system, excite the heart, after they 
cease to produce any effect on the muscles of voluntary 
motion ; that stimulating every part of the brain and spinal 
marrow equally affects the action of the heart, while the 
muscles of voluntary motion are only excited by stimuli 
applied to those parts of the nervous system from which the 
spinal marrow and nerves originate ; that stimuli applied to 
the nervous system never excite irregular action of the heart, 
while nothing can be more irregular than the action they 
excite in the muscles of voluntary motion ; that their effect 
on these muscles is felt chiefly on their first application, but 
continues on the heart as long as the stimulus is applied. 
These differences in the effects of stimuli applied to the 
nervous system, on the muscles of voluntary and those of in- 
voluntary motion, which seem involved in so much obscurity, 
must be explained before we can be said to understand the 
relation which subsists between that system and the heart. 
In the following part of this paper, I shall, in the first 
place, endeavour to trace the causes from which these dif- 
ferences arise ; and afterwards to ascertain whether the 
power of the blood-vessels, like that of the heart, is indepen- 
