horse--as mathematicians would say--reduced to its most simple
expression. Carry that in your minds, if you please, as a simplified
idea of the structure of the Horse. The considerations which I have
now put before you belong to what we technically call the 'Anatomy' of
the Horse. Now, suppose we go to work upon these 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 (Fig. 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