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. Of the hard
and solid homogeneous parts bone, fish-spine, sinew, blood-vessel, are
examples. The last of these points to a sub-division that may be
made in the class of homogeneous parts. For in some of them the
whole and a portion of the whole in one sense are designated by the
same term-as, for example, is the case with blood-vessel and bit of
blood-vessel-while in another sense they are not; but a portion of a
heterogeneous part, such as face, in no sense has the same designation
as the whole.
The first question to be asked is what are the causes to which these
homogeneous parts owe their existence? The causes are various; and
this whether the parts be solid or fluid. Thus one set of
homogeneous parts represent the material out of which the
heterogeneous parts are formed; for each separate organ is constructed
of bones, sinews, flesh, and the like; which are either essential
elements in its formation, or contribute to the proper discharge of
its function. A second set are the nutriment of the first, and are
invariably fluid, for all growth occurs at the expense of fluid
matter; while a third set are the residue of the second. Such, for
instance, are the faeces and, in animals that have a bladder, the
urine; the former being the dregs of the solid nutriment, the latter
of the fluid.
Even the individual homogeneous parts present variations, which
are intended in each case to render them more serviceable for their
purpose
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