But as all influences require to be
counterbalanced, so that they may be reduced to moderation and brought
to the mean (for in the mean, and not in either extreme, lies the true
and rational position), nature has contrived the brain as a
counterpoise to the region of the heart with its contained heat, and
has given it to animals to moderate the latter, combining in it the
properties of earth and water. For this reason it is, that every
sanguineous animal has a brain; whereas no bloodless creature has such
an organ, unless indeed it be, as the Poulp, by analogy. For where
there is no blood, there in consequence there is but little heat.
The brain, then, tempers the heat and seething of the heart. In order,
however, that it may not itself be absolutely without heat, but may
have a moderate amount, branches run from both blood-vessels, that
is to say from the great vessel and from what is called the aorta, and
end in the membrane which surrounds the brain; while at the same time,
in order to prevent any injury from the heat, these encompassing
vessels, instead of being few and large, are numerous and small, and
their blood scanty and clear, instead of being abundant and thick.
We can now understand why defluxions have their origin in the head,
and occur whenever the parts about the brain have more than a due
proportion of coldness.
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