several parts,--flesh and hair, and skin and
bone,--and lay open these various organs with our scalpels, and examine
them by means of our magnifying-glasses, and see what we can make of
them. We shall find that the flesh is made up of bundles of strong
fibres. The brain and nerves, too, we shall find, are made up of fibres,
and these queer-looking things that are called ganglionic corpuscles.
If we take a slice of the bone and examine it, we shall find that it is
very like this diagram of a section of the bone of an ostrich,
though differing, of course, in some details; and if we take any part
whatsoever of the tissue, and examine it, we shall find it all has a
minute structure, visible only under the microscope. All these
parts constitute microscopic anatomy or 'Histology.' These parts are
constantly being changed; every part is constantly growing, decaying,
and being replaced during the life of the animal. The tissue is
constantly replaced by new material; and if you go back to the young
state of the tissue in the case of muscle, or in the case of skin, or
any of the organs I have mentioned, you will find that they all come
under the same condition. Every one of these microscopic filaments
and fibres (I now speak merely of the general character of the whole
process)--every one of these parts--could be traced down to some
modification of a tissue which can be readily divided into little
particles of fleshy matter, of that substance which is composed of the
chemical elements, carbon, hydrogen, oxygen, and nitrogen, having such
a shape as this (Figure 2). These particles, into which all primitive
tissues break up, are called cells. If I were to make a section of a
piece of the skin of my hand, I should find that it was made up of these
cells. If I examine the fibres which form the various organs of all
living animals, I should find that all of them, at one time or other,
had been formed out of a substance consisting of similar elements; so
that you see, just as we reduced the whole body in the gross to that
sort of simple expression given in Figure 1, so we may reduce the
whole of the microscopic structural elements to a form of even greater
simplicity; just as the plan of the whole body may be so represented
in a sense (Figure 1), so the primary structure of every tissue may be
represented by a mass of cells (Figure 2).

Having thus, in this sort of general way, sketched to you what I may
call, perhaps, the architectur