OF ORGANIC NATURE 15 



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 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 Fig. 1, so we may reduce the FIG. 2. 



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 (Fig. 1), 

 so the primary structure of every tissue may be represented 

 by a mass of cells (Fig. 2). 



Having thus, in this sort of general way, sketched to you 

 what I may call, perhaps, the architecture of the body of 

 the Horse (what we term technically its Morphology), I 

 must now turn to another aspect. A horse is not a mere 

 dead structure : it is an active, living, working machine. 

 Hitherto we have, as it were, been looking at a steam- 

 engine with the fires out, and nothing in the boiler ; but 

 the body of the living animal is a beautifully-formed active 

 machine, and every part has its different work to do in the 

 working of that machine, which is what we call its life. 

 The Horse, if you see him after his day's work is done, 

 is cropping the grass in the fields, as it may be, or munch- 

 ing the oats in his stable. What is he doing ? His jaws 

 are working as a mill and a very complex mill too 

 grinding the corn, or crushing the grass to a pulp. As 



