124 The 
and mufcles, except this ftimulus? for I have 
conftantly found, by all the experiments that I 
made, that the mufcles are contracted when the 
beginning of the marrow, or the nerves iffaing 
from thence, are moved. 
Hence I propofe it, asa matter worth confi- 
dering, whether we fhould not rejeét that opi- 
nion, which fuppofes a fpirituous matter to be 
neceflary to excite mufcular motion, and that it 
flows out of the brain; and that this influx hap- 
pens with fuch great rapidity and velocity, that 
thefe new {pirits conftantly propel the former, 
and in an inftant of time, at the leaft intimation 
of the will, or otherwife f{pontaneoufly fhould, 
and may, be in the moft remote extremes of the 
body. . 
Iam perfuaded, thofe who derive the con- 
traction of the mufcles from inflation, fermenta- 
tion, or a kind of explofive motion, will differ 
from meas to this matter: they will object, that 
the inflation or expanfion of the moving fibres, 
is evident even to the eyes, in the contrac- 
tion of the mufcles; and befides, that all the 
mufcular parts are filled with {pirits: and there- 
fore, that only a {mall quantity of animal fpirits 
is requifite to inflate either thefe, or thofe mutcles, 
and to expand them by contraction, as is evident 
to the fight. 
But all thefe opinions are certainly deftroyed, 
if it be confidered, how often the motion of each 
mutcle is reftored by only ftimulating, provok- 
ing, or irritating the nerve in my experiment be- 
fore mentioned: and this, when the nerve hath 
been for a long time cut off, and the requifite 
animal fpirits diffipated, or grown weak, after 
many times difcharging their duty ; and when 
there is no further communication between the 
nerve, brain, and marrow. ‘Therefore, I would 
have it ferioufly confidered, that it cannot be 
demonftrated by any experiments, that any mat- 
ter of fenfible or comprehenfible bulk flows 
through the nerves into the mufcles. Nor does 
any thing elfe pafs through the nerves to the 
mufcles: all is a very quick kind of motion, 
which is indeed fo rapid, that it may be pro- 
perly called inftantaneous. Therefore the {pirit, 
as it is called, or that fubtile matter, which fiies 
in an infant through the nerves into the mutcles, 
may with the greateft propriety be compared to 
that moft fwift motion, which, when one extre- 
mity of a long beam or board is ftruck with the 
finger, runs with fuch velocity along the wood, 
that it is perceived almoft at the fame inftant at 
the other end; nay, that it is further propagated 
through the nerves into our mufcles; and thus 
produces various motions in them, as thofe who 
attentively confider this fingular, though plain 
experiment, well know. 
Add to thefe another argument of yet greater 
weight, which is, that the mufcles themfelves, 
when contracting, are not in the leaft inflated or 
fwollen, but rather they lofe their thicknefs ; 
though the moving fibres in the mean time ac- 
quire a different fituation; or, to exprefs the 
matter more exactly, they are prefled clofer to 
each other. We obferve fomething like this in 
a long piece of {punge, made even and fmooth, 
I 
BOOK off NATUR E: 
or, 
which becomes thicker and more folid by force 
of compreflion; though in reality it poffeffes a 
much lefs fpace. Therefore, for the many rea- 
fons which fhall be mentioned hereafter, J think 
it may be rightly inferred, that the fhortening 
and clofer compaction of the moving fibres, by 
reafon whereof they are contraGed into a lefs 
{pace, is really the true action or contraction of 
the mufcle; and which is therefore erroneoufly 
called inflation, tumefaction, &c. : 
For what reafon can any one imagine it. pof- 
fible for the mufcle to be inflated? fince it con- 
fifts of fuch fubtile flaments, as are almoft invi- 
fible ; though even thefe are finally compofed of 
globules. What matter can effect this inflation ? 
Is it not neceflary, that it fhould pafs throug! 
thofe very fine fibrille, which conftitute the 
nerves, and when curioufly examined, without 
hurting them, are likewife fo {mall as to be al- 
moft invifible? Certainly, if the nerves be con- 
fidered to have their origin from the marrow, it 
is very evident, that they are fo fubtile there, 
and fo clofely furrounded by the meninges, that 
the fmalleft briftle, or thread of fpun glafs, can 
fcarce pafs through the aperture. How fine 
therefore muft that {pirit be, which can penetrate 
into this very cavity, which is likewife ftopt up 
by the nervous filament that iffues out of, and is 
contained in, it? Yet authors eftablifh fuch no- 
tions; nay, they proceed fo far, as to imagine, 
that the nutritious matter, to which fome attri- 
bute the thicknefs of the white of an egg, pafles 
through thefe very nerves: but this opinion is fo 
idle and abfurd, that it does not defervea ferious 
refutation. In the fame light I confider the 
imaginary fermentation between the {pirits and 
blood, by which the mutfcle is faid to be in- 
flated; though the very method of this infla- 
tion is contrary to the known conftruction of the 
mufcles. 
Another thing that plainly contradi@s the in- 
flation and influx of the fuppofed fpirit into the 
mufcles, is that we clearly fee, tho’ the mufcle 
be cut, and its moving fibres feparated from each 
other, all thefe parts move again, as it were na~ 
turally, as foon as the nerve which belongs to 
them is irritated: and this experiment, as well 
as others, may be made on the Frog, and feveral 
other water-animals, and it fucceeds very partt- 
cularly in the Duck. 
From thefe experiments therefore, it may, I 
think, be fairly concluded, that a fimple and 
- natural motion or irritation of the nerves alone is 
neceflary to produce mufcular motion, whether 
it has its origin in the brain, or in the marrow, 
or elfewhere. 
Therefore, we likewife obferve in many ani- 
mals, that as foon as the béginning of the fpinal 
marrow is moved in the brain, all the fubjacent 
mufcles are fuddenly contraéted. And this hap- 
pens in the fame manner with refpect to all thofe 
branches of the nerves which arife out of the 
marrow, at leaft whilft they are handled; tho’ 
only fome of the mufcles, or perhaps that only, 
through which the irritated nerve is diftributed, 
are put in motion, . We muft alfo take particu- 
lar notice, that in this experiment, it is never ob- 
ferved, 
x 
