to assist us.
In an argument of this kind we must go further and dig deeper into the
matter; we must endeavour to look into the foundations of living Nature,
if I may so say, and discover the principles involved in some of her
most secret operations. I propose, therefore, in the first place, to
take some ordinary animal with which you are all familiar, and, by
easily comprehensible and obvious examples drawn from it, to show what
are the kind of problems which living beings in general lay before us;
and I shall then show you that the same problems are laid open to us by
all kinds of living beings. But first, let me say in what sense I have
used the words "organic nature." In speaking of the causes which lead
to our present knowledge of organic nature, I have used it almost as an
equivalent of the word "living," and for this reason,--that in almost
all living beings you can distinguish several distinct portions set
apart to do particular things and work in a particular way. These are
termed "organs," and the whole together is called "organic." And as it
is universally characteristic of them, this term "organic" has been very
conveniently employed to denote the whole of living nature,--the whole
of the plant world, and the whole of the animal world.

Few animals can be more familiar to you than that whose skeleton is
shown on our diagram. You need not bother yourselves with this "Equus
caballus" written under it; that is only the Latin name of it, and does
not make it any better. It simply means the common Horse. Suppose we
wish to understand all about the Horse. Our first object must be to
study the structure of the animal. The whole of his body is inclosed
within a hide, a skin covered with hair; and if that hide or skin be
taken off, we find a great mass of flesh, or what is technically called
muscle, being the substance which by its power of contraction enables
the animal to move. These muscles move the hard parts one upon the
other, and so give that strength and power of motion which renders the
Horse so useful to us in the performance of those services in which we
employ him.

And then, on separating and removing the whole of this skin and flesh,
you have a great series of bones, hard structures, bound together with
ligaments, and forming the skeleton which is represented here.

(FIGURE 1. Section through a horse.

FIGURE 2. Section through a cell.)

In that skeleton there are a number of parts to be recognized