The Physical Basis of Mind: Being the Second Series of Problems of Life and Mind.Lewes, George Henry
Philosophy
The Physical Basis of Mind: Being the Second Series of Problems of Life and Mind.
Lewes, George Henry
Mind and body; Psychophysiology
laugh at Scholasticism?
134. The hypothesis of the nerve-cell as the fountain of nerve-force
is supported by the gratuitous hypothesis of cell-substance having
greater chemical tension and molecular instability than nerve-fibre.
No evidence has been furnished for this; indeed the only experimental
evidence bearing on this point, if it has any force, seems directly
adverse to the hypothesis. I allude to the experiments of Wundt, which
show that the faint stimulus capable of moving a muscle when applied
directly to its nerve, must be increased if the excitation has to pass
through the cells by stimulation of the sensory nerve.[164] Wundt
interprets this as proving that the cells retard every impulse, whereby
they are enabled to store up latent force. The cells have thus the
office of locks in a canal, which cause the shallow stream to deepen at
particular places. I do not regard this interpretation as satisfactory;
but the fact at any rate seems to prove that so far from the cells
manifesting greater instability than the fibres, they manifest less.
135. The hypothesis of nerve-force being developed in the ganglia,
gradually assumed a more precise expression when the nerve-cells were
regarded as the only important elements of a ganglion. It has become
the foundation-stone of Neurology, therefore very particular care
should be taken to make sure that this foundation rests on clear and
indisputable evidence. Instead of that, there is absolutely no evidence
on which it can rest; and there is much evidence decidedly opposed to
it. Neither structure nor experiment points out the cells as the chief
agents in neural processes. Let us consider these.
Fig. 22 shows the contents of a molluscan ganglion which has been
teased out with needles.
[Illustration: Fig. 22.--_Cells, fibres, and amorphous substance from
the ganglion of a mollusc_ (after Bucholtz).]
The cells are seen to vary in size, but in all there is a rim of
neuroplasm surrounding the large nucleus, and from this neuroplasm
the fibre is seen to be a prolongation. The dotted substance in the
centre is the neuroglia. Except in the possession of a nucleus, there
is obviously here no essential difference in the structure of cell and
fibre.
[Illustration:
Fig. 23--_Fibres from the auditory nerve._ _a_, the axis cylinder;
_b_, the cellular enlargement; _c_, the medullary sheath.
]
Now compare this with Fig. 23, representing three fibres from the
auditory nerve.
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