ANA" 
red parts of the blood. The remaining part of the cortex, 
which is not filled by any injection, is probably either an 
aflemblage of veins, or of yet more tender velfels ; for no 
diffiniilar parts are apparent in the cortex, whilft it is in an 
entire or natural ftate; and hence we are not permitted to 
conclude that part of it is tubular, and part folid. As to 
glandules making the fabric of the brain, that notion has 
been difcarded by univerfal confent, as not being founded 
on the lead probability. 
The nerves of the brain, as well as of the fpinal marrow, 
divide into branches like the blood-veffels, but in acute 
angles, and often in a courfe manifeflly retrograde, they ge¬ 
nerally, but not always, gradually become fofter, and iefs 
bulky, as they recede from the brain, till at length their 
ultimate extremities, which are feldom vilible, feem to 
terminate in a pulp, by depofiting the firm integuments 
with which they were covered, as we obferve in the optic 
nerve. The refti-lineal courfe of the fibres, continued 
from the brain itfelf, is never broken olf by tlie divilion or 
fplitting of a nerve into fmalier threads ; but the fibres 
themfelves recede from eacli other by an opening of the 
cellular fubfiance that tied them together. This appears 
from the dil'orders which are determined not to all, but 
only to fume lingle parts of the body, by injuries of the 
brain; as a lofs of the voice, deafnels, dumbnefs, and pal- 
lies of particular mufcles. The nerves are connected in 
their courfe by the cellular fubftance to the adjacent parts, 
but have hardly any elafticity ; whence they do not fly 
back after being cut, but only expel, by the contraction 
of their integuments, the foft medulla which they include. 
Though they be ever fo much irritated, they are neither 
contracted, nor rendered fhorter during the mufcular mo¬ 
tion which they produce. A great many nerves, fays 
Haller, are fent into the mufcles; many of them go to 
the fkin; fewer to the vifeera, and very few to the lungs. 
Wrifberg, however, obferves, that more nerves manifeflly 
enter the organs of fenfe than the mufcles ; and that the 
lungs are fupplied with more nerves than the fpleen, ute¬ 
rus, and other vifeera. Haller alfo afferts, that no nerves 
go to the dura and pia mater, arachnoides, tendons, cap- 
fules, and ligaments. That thefe parts have few nerves 
is certain; but that nerves can be traced into fome of them, 
efpecially into ligaments, cannot now be denied. 
Thus much we are taught by anatomy concerning the 
brain and nerves ; it now remains that we explain the phy- 
fiological ufes of thefe parts. Every nerve that is irritated 
by any caufe produces a fharp fenfe of pain. To feel or 
perceive is to have the mind changed or affeCted by a 
change or attention of the body. It is the medullary part 
of the nerve that feels. If the nerve was endowed with 
any peculiar fenfe, that fenfe perifhes when the nerve is 
comprefled or cut through ; the feni’es of the whole body 
are loft by a compreffion of the brain, and a preffure of 
the fpinal marrow deprives only thofe parts which are be¬ 
low it of fenfation. If a preffure be made on the brain 
where particular nerves arife, then only thofe fenfes de¬ 
pending on thefe nerves are loft. Thofe parts of the body 
that are furnifhed with nerves, are the only parts endued 
with fenfation, which is greater in proportion to the quan¬ 
tity of nerves fent to the parts, of which we have exam¬ 
ples in the eye and the penis; thofe have lefs fallibility 
which receive few nerves, as the vifeera; and thole which 
have feweft nerves, as the dura mater, tendons, ligaments, 
fecundines, bones, and cartilages, have little or no fen¬ 
fation in the found (fate. It is therefore evident, that all 
fenfation arifes from the impreflion of an aftive fubftance 
on fome nerve of the human body; and that the fame is 
then reprefented to the mind by means of that nerve’s 
connection with the brain. It feems to be falfe, that the 
mind perceives immediately by means of the fenforia and 
branches of the nerves. For this opinion is refuted by 
the pains felt after amputation, by the celfation of all pain 
when the nerve is comprelfed, and by defefts or faults of 
the fenfes in confequence of difeafes of the brain. And 
that the effeft of the fenfes is preferved in the brain, is 
O M Y. 59j 
evident from the lofs of memory which follows an injury 
or comprefiion of the brain ; and alfo from the . delirium 
which happens in fome difeafes, and the (lupor and lleepi- 
nefs which happen in others. 
Another office of the nerves is to excite motions, even 
the moll violent, in the mufcles. When a nerve is irri¬ 
tated, every nuifcle to which it goes is immediately con- 
vull'ed ; or, if it fends branches to feveral mufcles, they 
are all convulfed at the fame- time. This happens both 
during the life of the animal, and a little after its death, 
while all the parts remain moift. By a great irritation 
other mufcles, belides thofe to which it lends branches, 
are thrown into convullions, and afterwards the whole 
body. Nor is it necelfary that the nerve thould be whole; 
for even when it is cut, an irritation of it will excite limi- 
lar motions in the mufcles. On the other hand, when a 
nerve is comprelfed or tied, a pally follows; that is, the 
mufcles which have their nerves from it lie unmoved, 
when they are commanded by the will to aft ; but they re¬ 
cover their motion when the comprefiion is iemoved, pro¬ 
vided the nerve has received no hurt. 
But the medulla of the brain being vellicated, or irrita¬ 
ted deeply in its crura, dreadful convullions enfue through¬ 
out the whole body ; and tills elieft is univerlally produced, 
what part of the brain foever be irritated ;- whether it be 
the brain itfelf, the cerebellum, or the corpus callofum:. 
The fame confequences alfo follow, if the fpinal marrow 
be irritated. But if the encephalon itfelf be comprelfed 
in any part whatever, there follows thence a lofs of fenfe 
and motion in that part of the body whole nerves come 
from the affefted or comprelfed quarter of the brain. This 
fact is proved by experiments made in difeafes of the brain, 
where the origin of particular nerves have been com- 
prelfed ; thus the voice, the power of deglutition, the mo¬ 
tion of an arm or a leg, are loft, if the origin of the nerves, 
on which thefe faculties and motions depend, be com- 
prelfed. This is (till more evident in irritations or com- 
prellions of the fpinal marrow, which produce refpeftively 
convullions or paliies of thole parts that receive nerves 
from or below the place injured. If any large portion of 
the brain be comprelfed by an extravafation of blood, by 
a collection of water, by a fchirrhus, or by an impafted 
bone, or by any mechanical caufe whatever, then, in pro¬ 
portion to the violence of the compreffion, there will follow 
either a partial or a total lofs of the power of motion, 
thofe organs obedient to the will being affefted in confe¬ 
quence of a flighter compreffion; but all the organs, if 
the preffure be great. The effects above recited ceafe 
when the caufe is removed. It may be proper to add, that, 
if the fpinal marrow be hurt in the neck, death immedi¬ 
ately follows, probably becaufe the nerves of the heart 
chiefly arife from that part. 
From thele confiderations, we cannot doubt that the 
caufe of all morion in the human body arifes from the 
brain, and its annexed cerebellum and fpinal marrow ; 
and that it thence proceeds through the nerves to all the 
mufcular parts of the body. Belides, the caufe of this 
motion cannot refide in the parts themfelves, becaufe other- 
wife the moving caufe would continue to aft after being 
feparated from the brain; nor would it be increafed by 
irritating the brain, or weakened by a compreflure of it. 
Is there in the brain any principal part, in which the origin 
of all motion and the end of all the fenfations relide, and 
where the foul has its feat ? Is this opinion proved by the 
frequent obfervation, that the fenfes are fometimes entire, 
and that motion likewife remains, though the brain be 
materially injured ? Is the feat of the foul in the corpus 
callofum ? Is this opinion fhewn by the greater fatality of 
wounds or difeafes in the corpus callofum ? Is this body 
fufficiently connefted with the nerves ? Are there any ex¬ 
periments which prove that from thence the fifth, feventh, 
and other, nerves arife ? Dotli not the fame, or even great¬ 
er, mortality of wounds in the medulla fpinalis, prove the 
fame thing? Yet this is not the feat of the foul, fince 
though it is compreffed, or even deftroyed, the perfon will 
2 furvive 
