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youth exceeds that in older people, for in the young the formation
of vapour is more abundant.
All the veins pulse, and do so simultaneously with each other, owing
to their connexion with the heart. The heart always beats, and hence
they also beat continuously and simultaneously with each other and
with it.
Palpitation, then, is the recoil of the heart against the
compression due to cold; and pulsation is the volatilization of the
heated fluid.
27
Respiration takes place when the hot substance which is the seat
of the nutritive principle increases. For it, like the rest of the
body, requires nutrition, and more so than the members, for it is
through it that they are nourished. But when it increases it
necessarily causes the organ to rise. This organ we must to be
constructed like the bellows in a smithy, for both heart and lungs
conform pretty well to this shape. Such a structure must be double,
for the nutritive principle must be situated in the centre of the
natural force.
Thus on increase of bulk expansion results, which necessarily causes
the surrounding parts to rise. Now this can be seen to occur when
people respire; they raise their chest because the motive principle of
the organ described resident within the chest causes an identical
expansion of this organ. When it dilates the outer air must rush in as
into a bellows, and, being cold, by its chilling influence reduces
by extinction the excess of the fire. But, as the increase of bulk
causes the organ to dilate, so diminution causes contraction, and when
it collapses the air which entered must pass out again. When it enters
the air is cold, but on issuing it is warm owing to its contact with
the heat resident in this organ, and this is specially the case in
those animals that possess a full-blooded lung. The numerous
canal-like ducts in the lung, into which it passes, have each a
blood-vessel lying alongside, so that the whole lung is thought to
be full of blood. The inward passage of the air is called respiration,
the outward expiration, and this double movement goes on
continuously just so long as the animal lives and keeps this organ
in continuous motion; it is for this reason that life is bound up with
the passage of the breath outwards and inwards.
It is in the same way that the motion of the gills in fishes takes
place. When the hot substance in the blood throughout the members
rises, the gills rise too, and let the water pass through, but when it
is chilled and retreats through its channels to the heart, they
contract and eject the water. Continually as the heat in the heart
rises, continually on being chilled it returns thither again. Hence,
as in respiring animals life and death are bound up with
respiration, so in the other animals class they depend on the
admission of water.
Our discussion of life and death and kindred topics is now
practically complete. But health and discase also claim the
attention of the scientist, and not mercly of the physician, in so far
as an account of their causes is concerned. The extent to which
these two differ and investigate diverse provinces must not escape us,
since facts show that their inquiries are, to a certain extent, at
least conterminous. For physicians of culture and refinement make some
mention of natural science, and claim to derive their principles
from it, while the most accomplished investigators into nature
generally push their studies so far as to conclude with an account
of medical principles.
-THE END-
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