5qS A NATO M Y. 
furvive a long time with the perfect ufe of all his mental 
faculties. Laftlv, this opinion is oppofed by numerous 
fafts: birds'have no corpus callofum, and wounds in that 
body are not more mortal than thofe in other parts of the 
brain, as appears from undoubted experiments. 
The prerogative of exciting vital motions, is not mere 
-peculiar to the cerebellum than to the other parts of tire 
encephalon ; nor does it fuffrciently appear, that the vital 
and animal fundbions are diftincl: for the cerebellum does 
not produce tiie nerves of the heart and of the other vital 
organs, and the brain thofe which go to tiie organs of 
fenfe and voluntary motion. From the cerebellum the fifth 
nerve is mod evidently produced; but that-goes to the 
tongue, pterygoid, buccinator, temporal and frontal muf- 
cles, to the ear, the eye, the noftrils; parts which are 
either moved by the will, or deftined for fenfe. Again, 
the fame nerve, like the eighth, fends vital brandies to 
the heart and lungs, animal and voluntary ones to the 
larynx, and fenfitive Ones to the ftomach. Again, it is 
not even true that diforders of the cerebellum bring on fo 
certain and fpeedy death as is generally imagined ; for 
fome experiments, even of our own making, (hew that it 
has born Wounds and fchirrhi, without taking away life. 
Laftly, it is not much different from the brain, only that 
it is foftcr and more tender ; and we have often known 
wounds of the cerebellum cured. The power, however, 
.of this part, in exciting convulfions, is fomevvhat greater 
than that of the brain. 
We mult inquire experimentally concerning the feat of 
the foul. Tn the firft place it muft be in the head, and not 
in the fpinal marrow : for, though this is obftrriufted, the 
conltancy of the mind remains the fame. Again, from the 
experiment of convulfions arifing when the imnoft parts 
of the brain are irritated, it appears to be feated, not in 
the cortex, but in the medulla ; and, by a probable con- 
jefture, in the crura of the medulla, the corpora ftriata, 
thalami, pons, medulla oblongata, and cerebellum. And 
again, by another not abfurd conjecture, it is perhaps feat¬ 
ed at the origin of every nerve, as the firft origin of all 
the nerves taken together make up the cenforium com¬ 
mune. Are the fenfations of the mind reprefented there, 
-or do the voluntary and necelfary motions arife in that 
place ? This feems very probable ; for it is fcarcely poffible, 
that the origin of motion can lie below that of the nerve, 
fmee the nerve is fimilar throughout its whole length. The 
-origin of motion cannot be in the arteries, which have nei¬ 
ther the faculty of fenfation nor that of voluntary motion. 
It therefore follows, that the feat of the foul muft be where 
the nerve firft begins its formation or origin. 
We come now to explain the manner in which the nerves 
become the organs of fenfe or motion, which, lying hid 
in the ultimate elementary fabric of the medullary fibres, 
I'eem to be placed above the reach both of fenfe and rea- 
fon. We fhall neverthelefs endeavour to make this as 
plain as experiments will enable us. And firft, it is de- 
monftrated, that the fenfation does not come through the 
membranes from the fentient organ to the brain, nor that 
motion is fent through the coverings from the brain into 
the mufcle ; for the brain itfelf lies deeper than thefe mem¬ 
branes, and receives the imprellions of fenfe, and, when 
hurt, throws the mufcles into convulfions. Moreover it 
is certain, that the nerves arife from the medulla of the 
brain; for, by ocular infpeftion, we fee that to be the cafe 
in all the nerves of the brain, more efpecially in the olfac¬ 
tory, optic, fourth, and feventh, pair of nerves, which 
continue their medullary fabric a long way before they put 
on the covering of tiie pia mater. 
We muft therefore next inquire what this medulla is. 
It is a very loft fubftance; its compofition is fibrous, as 
appears from innumerable arguments: its fibres are vifible 
in the corpus callofum, in the ftriatum, in the thalami of 
■the optic nerves, and fpinal marrow ; and ftill more evi¬ 
dently in the brains of filh, and efpecially in their thalami 
optici; but in no part of the human brain does the fibrous 
nature of the medulla more evidently appear than in the 
fornix, efpecially when immerfed in feme, of the acids. 
Again, that the fibres of the brain are continuous with 
thole of the nerves, fo as to form one extended and open 
continuation, appears very evidently in the feventh, fourth, 
and fifth, pair of nerves. There is a great deal of oil in 
the medulla, upwards of a tenth part of its whole weight. 
But here a controverfy begins concerning the nature of 
thefe fibres, a congeries of which compotes the fubftance 
of the medulla and of the nerves. That this is a mere fo- 
lid thread, and only watered by a vapour exhaling into the 
cellular fabric which furrounds the nervous fibres, lias 
been afterted by many of the moderns ; but that, when it 
is ftruck by a fenfible body, a vibration is excited, which 
is then conveyed to the brain. But the phenomena of 
wounded nerves will not allow us to imagine the nervous 
fibres to be folid : for, if irritation caufes a nerve to (hake, 
(ill a manner fomewliat fimilar to an elaftic cord, which 
trembles when it is taken Hold of,) the nerve ought to be 
made of hard fibres, and tied by their extremities to hard 
bodies: they ought alfo to be tenfe ; for neither loft cords, 
nor fuch as are not tenfe, or fuch as are not well faftened, 
are ever obferved to tremulate. But all the nerves at their 
origin, are medullary, and very foft, and exceedingly far 
from any kind of tenfion. Where they pafs through chan¬ 
nels, and are well guarded, they retain the fame foft tex¬ 
ture, and are not covered with membranes; as the inter- 
coftal nerves, and the fecond nerves of the fifth pair. 
Some alfo are foft throughout their whole length, what¬ 
ever their fize be. For example, the foft olfactory and 
acouftic nerves, from which laft we would moft readily 
expect a tremor produced by found. Again, though the 
nerves are hard, they are foftened in the vifeera, mufcles, 
and fenforia, before they exert their operations. The ner¬ 
vous fibres, being neither firmly fixed at each end, nor 
tenfe, cannot therefore tremulate like a tight ftretched 
cord. Another argument againft their tremulation is, that, 
through their whole length, the nerves are firmly attached 
to the folid parts by the cellular fabric. An example of 
this fa ft is feen in thofe very material nerves, the nerves 
of the heart, which are tied to the great arteries and peri¬ 
cardium. Finally, that the nerves are deftituteof all elafti- 
city, is demonftrated by experiments, in which the nerves 
cut acrofs neither (horten, nor draw back their divided 
ends to the folid parts ; but are rather more elongated by 
their laxity, and expel their medulla in form of a protu¬ 
berance. Again, the extreme foftnefs of the medulla in 
the brain, with all the phenomena of pain and convullion, 
leave no room to fufpedl any fort of tenfion concerned in 
the effects or operations produced by the nerves. Add to 
this, that the force of an irritated nerve is never propa¬ 
gated upward, fo as to convulfe the mufcles that are feat¬ 
ed above the place of irritation. This is a confequence 
altogether difagreeing with elafticity ; for an elaftic cord 
propagates its tremors every way, from the point of per- 
cufTion to both extremities. But, if neither phenomena of 
fenfe nor motion can be explained from the nature of elaf¬ 
ticity, the moft probable fuppolition that remains is, that 
there is a liquor lent from the brain, which, defeending 
through the nerves, flows out at their extremities; the 
motion of which liquor, quickened by irritation, operates 
only according to the diredtion in which it flows through 
the nerve ; fo that convulfions cannot thereby afeend up¬ 
wards, becaufe of the refiftance made by the frelh afflux 
of the fluid from the brain. But the fame liquid, being 
put in motion in an organ of fenfe, can carry that fenfation 
upwards to the brain; fince it is refitted by no fenfitive 
torrent coming from the brain in a contrary direction. It 
is therefore probable, that the nervous fibres, and thofe of 
the medulla of the brain, which are of the fame nature, 
are hollow. The objeftions againft this doftrine are fo 
few, and at the fame time fo frivolous, that they need not 
be mentioned. If they are tubes, it is very probable that 
they have their humours from the arteries of the brain. 
There are many doubts concerning the nature of this 
nervous liquid. Several of the moderns will have it to 
be 
