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On The Generation Of Animals   

must become of necessity bitter and ill-flavoured. As the embryo is
perfecting, the residual matter left over increases in quantity
because the part consumed by the embryo is less; it is also sweeter
since the easily concocted part is less drawn away from it. For it
is no longer expended on moulding the embryo but only on slightly
increasing its growth, it being now fixed because it has reached
perfection (for in a sense there is a perfection even of an embryo).
Therefore it comes forth from the mother and changes its mode of
development, as now possessing what belongs to it; and no longer takes
that which does not belong to it; and it is at this season that the
milk becomes useful.

The milk collects in the upper part of the body and the breasts
because of the original plan of the organism. For the part above the
hypozoma is the sovereign part of the animal, while that below is
concerned with nourishment and residual matter, in order that all
animals which move about may contain within themselves nourishment
enough to make them independent when they move from one place to
another. From this upper part also is produced the generative
secretion for the reason mentioned in the opening of our discussion.
But both the secretion of the male and the catamenia of the female are
of a sanguineous nature, and the first principle of this blood and
of the blood-vessels is the heart, and the heart is in this part of
the body. Therefore it is here that the change of such a secretion
must first become plain. This is why the voice changes in both sexes
when they begin to bear seed (for the first principle of the voice
resides there, and is itself changed when its moving cause changes).

At the same time the parts about the breasts are raised visibly
even in males but still more in females, for the region of the breasts
becomes empty and spongy in them because so much material is drained
away below. This is so not only in women but also in those animals
which have the mammae low down.

This change in the voice and the parts about the mammae is plain
even in other creatures to those who have experience of each kind of
animal, but is most remarkable in man. The reason is that in man the
production of secretion is greatest in both sexes in proportion to
their size as compared with other animals; I mean that of the
catamenia in women and the emission of semen in men. When,
therefore, the embryo no longer takes up the secretion in question but
yet prevents its being discharged from the mother, it is necessary
that the residual matter should collect in all those empty parts which
are set upon the same passages. And such is the position of the mammae
in each kind of animals for both causes; it is so both for the sake of
what is best and of necessity.

It is here, then, that the nourishment in animals is now formed
and becomes thoroughly concocted. As for the cause of concoction, we
may take that already given, or we may take the opposite, for it is
a reasonable view also that the embryo being larger takes more
nourishment, so that less is left over about this time, and the less
is concocted more quickly.

That milk has the same nature as the secretion from which each
animal is formed is plain, and has been stated previously. For the
material which nourishes is the same as that from which Nature forms
the animal in generation. Now this is the sanguineous liquid in the
sanguinea, and milk is blood concocted (not corrupted; Empedocles
either mistook the fact or made a bad metaphor when he composed the
line: 'On the tenth day of the eighth month the milk comes into being,
a white pus', for putrefaction and concoction are opposite things, and
pus is a kind of putrefaction but milk is concocted). While women are
suckling children the catamenia do not occur according to Nature,

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