STATES OF THE BODY INFLUENCING THE JÆIND. 791
organisation of the brain or on the matter which enters into its structure.
On the other hand the operations of the mind, with which the organisa¬
tion of the brain keeps, as it were, equal pace, induce changes in the
structure and component matter of that organ, and of all other parts of
the body which are under its influence. The ideas and thoughts are
not themselves composed of parts, but they are developed in matter
which has organisation and parts, and the distinctness of the conceptions
is entirely dependent on the condition of this divisible matter.
Hence we may infer that, whatever changes the mind produces in
the organism generally, are effected through the medium of the brain—
the organ in which alone the mental force, elsewhere latent, is manifest,
and from which its influence radiates, as from a centre, to all other
parts of the body. Every organ, also, by virtue of its power of acting
on the brain itself through the medium of its nerves and of the blood
circulating through the whole organism, must have an influence upon
the ideas and upon the power of mental conception. This influence
may be either exciting or depressing, so that the power of the mind to
conceive ideas may be either increased or impeded. The impressions
communicated from different organs of the body to the brain can, of
course, produce no other distinct ideas than those of the sensations, and
the peculiar import of these sensations. But since local changes of par¬
ticular organs may produce the sensations of pleasure or suffering, or of
the tendency of the organ to its specific function, and may thereby
excite the ideas of the expansion and restriction of self and of desire,
which are associated with those sensations, it is evident that the disposi¬
tion to a state of emotion may be kept up by the state of other organs
than the brain.
1. Influence of states of the body upon the intellect and emotions.
—The excitement of certain organic states of the brain, by the bright
scarlet aerated blood, is a necessary condition for the action of the mind.
Hence the abstraction of blood in large quantity produces syncope and
loss of consciousness. Even the quality of the blood, however, exerts
an influence on the intellectual operations. The most common instance
of an influence exerted on the mental faculties by a cause of this kind,
is afforded in the effects of digestion. The digestion of food introduces
a quantity of imperfectly assimilated matter into the circulation. Until
this new material has undergone the necessary changes, and while cer¬
tain matters, altogether unfit for nutrition, are mingled with it, it is not
adapted to excite those states of the brain which are necessary for the
proper manifestation of mind, and as it is conveyed to that organ by
the circulating blood, it produces an injurious change in it, and impedes
or disturbs the mental functions. Hence the indisposition to mental
labour experienced by some persons after meals. This disturbance of
the intellectual operations is still more evident, as the result of the mate¬
rial changes produced by the alterantia nervina (spirituous liquids and
narcotics). Some “secreta” and “excreta,” as bile and urea, are equally
unfitted for producing the natural organic states of the brain. The
former substance being absorbed into the blood, produces not only indis¬
position to the exercise of the intellect, and diminution of its power, but
also depression of spirits, by disturbing those organic conditions of the
brain which influence the emotionary feelings.