This explains why
the blood diminishes in quantity when no food is taken, and
increases when much is consumed, and also why it becomes healthy and
unhealthy according as the food is of the one or the other
character. These facts, then, and others of a like kind, make it plain
that the purpose of the blood in sanguineous animals is to subserve
the nutrition of the body. They also explain why no more sensation
is produced by touching the blood than by touching one of the
excretions or the food, whereas when the flesh is touched sensation is
produced. For the blood is not continuous nor united by growth with
the flesh, but simply lies loose in its receptacle, that is in the
heart and vessels. The manner in which the parts grow at the expense
of the blood, and indeed the whole question of nutrition, will find
a more suitable place for exposition in the treatise on Generation,
and in other writings. For our present purpose all that need be said
is that the blood exists for the sake of nutrition, that is the
nutrition of the parts; and with this much let us therefore content
ourselves.
4
What are called fibres are found in the blood of some animals but
not of all. There are none, for instance, in the blood of deer and
of roes; and for this reason the blood of such animals as these
never coagulates.
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