O B S E R V A T I O N S ON THE
C H A P T E R XX V I .
O f Senfation.
T T A V I N G endeavoured to prove that the nerves ferve only for fenfation
and motion, I iliall next treat of circumftances "which relate to
the excrcife of each of thefe two funaions: And firft, of Senfation.
. When an imprcflion is made on any organ, the nerves of which are en-
^tire and connefted with the brain, we feel, and are confcious of the impreflion:
But if a nerve is cut, even at its exit from the cranium, or if the
ftrudure of the fpinal maiTow is injured at its upper end*, we are not confcious
of any injury done to our organs beyond the place where the nerve
is divided. Hence authors, not without the appearance of reafon, have
fuppofed, that the livuig and feeling principle, which we commonly call
the mind of the animal, is feated within the head, and occupies there a
fenforium commune.
But although, beyond the place at which a nerve is cut, or in a member
amputated, a wound does not excite pain ; yet, in confequence of that
wound, effeds follow which we cannot account for on mechanical
principles.
Thus, a flight punflure of the heart of a frog, feparated from its body,
throws all its fibres into violent motion. Such a caufe appears fo difproportionate
to its effeds, that we cannot help conceiving that fome living
principle has been influenced: Or that there arc two kinds of feeling, one
. with, and another without confcioufnefs; the latter, perliaps, refembling
that
* Of this I have feen one remarkable example.
N E R V O U S S Y S T E M . 89
that kind of feeling which we muft fuppofe inherent in vegetables, and iii
confequence of which their veflcls ai'e fo adluated as to produce ftiU more
numerous and wonderful changes on the fluids they convey and fecrete,
than are to be obferved in the animal kingdom.
Before venturing to be more explicit, we ihall proceed to confider the other
primary office of the nerves, to wit, their enabling the mufcular organs
to adl.
C H A PItt!
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