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 



