XI PHENOMENA OF ORGANIC NATURE. 309 
stumps (e e, Fig. 1). Now that is a 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 
on 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, decay- 
ing, 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 
