26 O B S E R V A T I O N S ON T H E
iidcr the brain as a medium between the mind and the reft of the body of
the animal, by the intervention of the machinery of which the intelleftual
powers are influenced, in a way we neither do, nor, probably, ever lliall be
able to comprehend: And that, in man efpecially, a fmall part only of it is
lengthened out, fo as, in the common way of fpeaking, to give origin to
the nerves.
S E C T . III.
NAY we may, perhaps, go a ftep further, and doubt whether, inftead of
confidcring the brain as the origin of the nerves, we ought not to confider
it merely as connected with the nerves; or whether there are better reaions
for fuppofmg the brain to produce the nerves, than for fuppofmg the
nerves to produce the brain. Some fads, at leaft, may be here obferved,
which feem to fliow that the nerves may exift independent of the brain.
1. In childi-en delivered at the full time, plump and well formed in their
trunk and limbs, I have obferved the fubftance which fupplied the place of
the brain not more bulky thMi a fniall nut, and, inftead of containing a
•white medullary fubftance, it was of a red colour refembling a clot of blood:
And Imall cords, occupying the place of the optic nerves, were likewife of
a red colour, 'i'et the fpinal marrow, and all the nerves from it, had the
ordinary fize and appearance.
2. In a monftrous kitten, with two bodies and the appearance of one
head, I found the fpinal marrow of one of the bodies conneSed with a brain
and cerebellum of the common fliape and fize. But the fpinal marrow of
the other body, though equally large, had only a fmall button of medullary
fubftance at its upper end, without a fuitable brain or cerebellum f .
3. In living frogs, I have repeatedly cut acrofs the fpinal marrow, or the
trunk of the fciatic nerve, and fed the animal for upwards of a year thereafter.
• See Tab. VIII. and Tab. VIIl. •
t Sec Tab. XU. f ig. 3. 4.
N E R V O U S S Y S T E M . 27
after. In fome of them, the fciatic nerves were rejoined; but in none of
my experiments did the nerves under the incifion recover their powers ; yet
the nerves under the incifion feemed, at the end of that period, as large in
the limb in which the experiment was made, as they were in the found
limb*.
Whilft thefe fails feem to prove that the nerves may exift without the
brain, and that they are not to be coniidered, according to the common
idea, as being merely duils which convey a fluid from a gland to diftant
parts, they feem alfo to fhow, that there is an energy of the nerves, independent
of the energy of the brain; and, therefore, lead us to attempt to
prove more fully that the nerves poffefs fuch an energy, and to difcover the
ftrufture on which the pofleflion of the energy depends.
Here let us begin by direfting our attention to the ftruflure of the fpinal
marrow.
C H A P .
' Pee Tab. SIV. Fig. i. a.