34 O B S E R V A T I O N S ON THE
trunk of the fckitic nerve in a living frog, that the lower part of the nerve
was fcnfibly diininilhed in its bulk.
T. V.
I HAVE found, after the fciatic nerve had been cut, and the member was
infenfible and motionlefs, that the circulation of the blood remained, for a
year thereafter, rapid and free in the hind leg of a frog; nay, that, when I
had broken the bones and wounded the flefli, an inflammation was excited;
and, at lart, the Avounds were clofed with new matter, and the broken bones
reunited. Yet we have the ilrongeil reafons for believing, that the fmall
vcilels, in circulating the blood, in inflammation, and in the produdion of
new matter, are actuated by a nervous energy, which, in the cafes before
lis, could only have been furnillied to the nerves by the vefTels of the pia
mater which inclofes them and the cineritious fubftance it produces.
E T . VI.
AMONGST other experiments I made, of which I read an account to the
Philofophical Society of Edinburgh in 1761 I found, that, when I poured
a folution of opium under the ikin of the thigh and leg of a living frog,
not only the leg itfelf was very foon affected, but the affeilion was communicated
to the moil diftant organs of the body, by a fynipathy of the
nerves; but if, previous to the application of the opium, I cut out the heart,
or cut acrofs the femoral blood-vellels, the ciFeds of the opium were not
communicated from that limb to diftant parts, which proves that the arteries
accompanying the nerves, or the arteries of the pia mater of the nerves,
have great eife£t in fitting the nerves to receive and to communicate impreffions.
C H A P .
' See Edinburgh Phil, and Liter. Eflays, Vol. 3. Art. 13. Exper. 6. and 9.
N E R V O U S S Y S T E M . 3S
C H A P T E R XI.
Conclufions drawn from the Three laft Sedtions.
WH E N we review the three lalt fedions, there appear to be juil
reafons for believing, that a fmall portion only of the brain, efpecially
of the human, is elongated in order to form the nerves and fpinal
marrow.
2. That the refl of it, as a medium between the living principle and the
other parts of the body, performs offices which are proper to it.
3. That the oppofite fides of the encephalon are joined by bundles of
fibres, fo that we feem, in a certain degree, to perceive the caufe of the
fufFerance of all parts of the nervous fyftem with that of any one part of it,
or of the general fympathy of nei-ves.
4. We have obferved, that the right and left fides of the fpinal marrow
are divided from each other by deeper fiiTures than have been defcribed by
many late writers, or that the right and left fides of it are lefs intimately
connefted than is commonly imagined. From attention to this circumftance,
wc are, in fome degree, enabled to explain the caufe why one fide
of the body is much palfied, whilft the other preferves its powers unimpaired,
or to underiland the caufe of hemiplegia.
5. We feel and can aft with our mufclcs only when the brain and the
nei'ves of the organs employed are connefted together. But, for the reafons
given in laft fcdion, I have long thought and endeavoured to prove,
that our nerves, independent of the encephalon, poflefs an energy or principle
of life, which they derive from their proper pia mater and its veiTels:
Or that the limb of a frog, in which the circulation continues, after the
fciatic