310 THE CAUSES OF THE XI 
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 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 
Fig.z. 
