XI PHENOMENA OF ORGANIC NATURE SLL 
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 
munching 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 soon as that 
operation has taken place, the food is passed down 
to the stomach, and there it is mixed with the 
chemical fluid called the gastric juice, a substance 
which has the peculiar property of making soluble 
and dissolving out the nutritious matter in the 
grass, and leaving behind those parts which are 
not nutritious; so that you have, first, the mill, 
then a sort of chemical digester; and then the 
food, thus partially dissolved, is carried back 
by the muscular contractions of the intestines into 
the hinder parts of the body, while the soluble 
portions are taken up into the blood. The blood 
is contained in a vast system of pipes, spreading 
through the whole body, connected with a force- 
pump,—the heart,—which, by its position and by 
