I 
2 6 Dr. Fordyce^s Letture 
produced by fomething palling by the nerves, from the brain to 
the moving part. Three doctrines have been fet forth ; one, 
that there is a fluid palling along the nerves ; a fecond, that 
there is a vibration ; and a third, that the nerves are furrounded 
with fomething like eledlric matter, in which motion runs 
from the brain to the moving parts. Thofe who have conli- 
dered this fubjedt mult be tired of the arguments which have 
been brought to refute each of thefe ; for no argument from 
fact has been employed to prove any one of them : I lhall 
therefore leave them as mere chimeras of the brain. I 
have taken notice, that it is not requiftte for any motion to 
pafs between tw r o bodies, exciting in each other an original 
motion, through or by any other matter : I have alfo (hewn, 
that mufcular motion is an original motion : it follows, that it 
is not neceflary for any motion, or communication, to pafs 
through any other matter, in order to bring the mufcular fibres 
into adtion. 
One cafe of mufcular motion is, when a ftimulus is applied 
to fome part of the body, and a mufcle at a diftance imme- 
diately contradls. It has been fuppofed in this cafe, that fome. 
influence was communicated to the nerve of the part where the 
ftimulus w’as applied, and through it to the brain, and from 
the brain through the nerves of the contradling mufcle. 
Granting, for a little, that fome motion may pafs along the 
nerves, and therefore that the end of the nerve, where the 
application was made, may be the part- in which the original 
motion began, the ftimulus frequently does not touch the end 
of the nerve; for if vapour of volatile’alkali be applied to the 
loftrils, an univerfal glow of heat, and inCreafed circulation, 
will conftantly take place ; but the vapour of the volatile alkali 
could not touch the nerves of the noftrils, the membrane 
4 being 
