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24
Generation is the initial participation, mediated by warm substance,
in the nutritive
soul, and life is the maintenance of this
participation. Youth is the period of the growth of the primary
organ of refrigeration, old age of its decay, while the intervening
time is the prime of life.
A violent death or dissolution consists in the extinction or
exhaustion of the vital heat (for either of these may cause
dissolution), while natural death is the exhaustion of the heat
owing to lapse of time, and occurring at the end of life. In plants
this is to wither, in animals to die. Death, in old age, is the
exhaustion due to inability on the part of the organ, owing to old
age, to produce refrigeration. This then is our account of
generation and life and death, and the reason for their occurrence
in animals.
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It is hence also clear why respiring animals are suffocated in
water
and fishes in
air. For it is by water in the latter class, by air in
the former that refrigeration is effected, and either of these means
of performing the function is removed by a change of environment.
There is also to be explained in either case the cause of the
cause of the
motion of the
gills and of the lungs, the rise and fall
of which effects the admission and expulsion of the breath or of
water. The following, moreover, is the manner of the constitution of
the organ.
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In connexion with the heart there are three phenomena, which, though
apparently of the same
nature, are really not so, namely
palpitation, pulsation, and respiration.
Palpitation is the rushing together of the hot substance in the
heart owing to the chilling influence of residual or waste products.
It occurs, for example, in the ailment known as 'spasms' and in
other diseases. It occurs also in fear, for when one is afraid the
upper parts become cold, and the hot substance, fleeing away, by its
concentration in the heart produces palpitation. It is crushed into so
small a space that sometimes life is extinguished, and the animals die
of the fright and morbid disturbance.
The beating of the heart, which, as can be seen, goes on
continuously, is similar to the throbbing of an abscess. That,
however, is accompanied by pain, because the change produced in the
blood is unnatural, and it goes on until the matter formed by
concoction is discharged. There is a similarity between this
phenomenon and that of boiling; for boiling is due to the
volatilization of fluid by heat and the expansion consequent on
increase of bulk. But in an abscess, if there is no
evaporation
through the walls, the process terminates in suppuration due to the
thickening of the liquid, while in boiling it ends in the escape of
the fluid out of the containing vessel.
In the heart the beating is produced by the heat expanding the
fluid, of which the food furnishes a constant supply. It occurs when
the fluid rises to the outer wall of the heart, and it goes on
continuously; for there is a constant flow of the fluid that goes to
constitute the blood, it being in the heart that the blood receives
its primary elaboration. That this is so we can perceive in the
initial stages of generation, for the heart can be seen to contain
blood before the veins become distinct. This explains why pulsation in
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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