In a large number of cases, as with the salivary and lacrymal glands,
intestinal canal, &c., the power of attention seems to rest, either
chiefly, or as some physiologists think, exclusively, on the vaso-motor
system being affected in such a manner that more blood is allowed to
flow into the capillaries of the part in question. This increased
action of the capillaries may in some cases be combined with the
simultaneously increased activity of the sensorium.
The manner in which the mind affects the vasomotor system may be
conceived in the following manner. When we actually taste sour fruit,
an impression is sent through the gustatory nerves to a certain part of
the sensorium; this transmits nerve-force to the vasomotor centre,
which consequently allows the muscular coats of the small arteries that
permeate the salivary glands to relax. Hence more blood flows into
these glands, and they secrete a copious supply of saliva. Now it does
not seem an improbable assumption, that, when we reflect intently on a
sensation, the same part of the sensorium, or a closely connected part
of it, is brought into a state of activity, in the same manner as when
we actually perceive the sensation. If so, the same cells in the brain
will be excited, though, perhaps, in a less degree, by vividly thinking
about a sour taste, as by perceiving it; and they will transmit in the
one case, as in the other, nerve-force to the vaso-motor centre with
the same results.
To give another, and, in some respects, more appropriate illustration.
If a man stands before a hot fire, his face reddens. This appears to be
due, as Mr. Michael Foster informs me, in part to the local action of
the heat, and in part to a reflex action from the vaso-motor
centres.[1346] In this latter case, the heat affects the nerves of the
face; these transmit an impression to the sensory cells of the brain,
which act on the vaso-motor centre, and this reacts on the small
arteries of the face, relaxing them and allowing them to become filled
with blood. Here, again, it seems not improbable that if we were
repeatedly to concentrate with great earnestness our attention on the
recollection of our heated faces, the same part of the sensorium which
gives us the consciousness of actual heat would be in some slight
degree stimulated, and would in consequence tend to transmit some
nerve-force to the vaso-motor centres, so as to relax the capillaries
of the face. Now as men during endless generations have had their
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