Mechanical principles are operative in every part of the body--in the heart, in the arteries, in the limbs, in the joints, in the bowels, in the muscles; and chemical principles are operative in the lungs, in the stomach, in the liver, in the kidneys; but to all these things do we not have to add something that is not mechanical or chemical to make the man, to make the plant? A higher mechanics, a higher chemistry, if you prefer, a force, but a force differing in kind from the physical forces. The forces of life are constructive forces, and work in a world of disintegrating or destructive forces which oppose them and which they overcome. The mechanical and the chemical forces of dead matter are the enemies of the forces of life till life overcomes and uses them; as much so as gravity, fire, frost, water are man's enemies till he has learned how to subdue and use them. IV It is a significant fact that the four chief elements which in various combinations make up living bodies are by their extreme mobility well suited to their purpose. Three of these are gaseous; only the carbon is a solid. This renders them facile and adaptive in the ever-changing conditions of organic evolution. The solid carbon forms the vessel in which the precious essence of life is carried. Without carbon we should evaporate or flow away and escape. Much of the oxygen and hydrogen enters into living bodies as water; nine tenths of the human body is water; a little nitrogen and a few mineral salts make up the rest. So that our life in its final elements is little more than a stream of water holding in solution carbonaceous and other matter and flowing, forever flowing, a stream of fluid and solid matter plus something else that scientific analysis cannot reach--some force or principle that combines and organizes these elements into the living body. If a man could be reduced instantly into his constituent elements we should see a pail or two of turbid fluid that would flow down the bank and soon be lost in the soil. That which gives us our form and stability and prevents us from slowly spilling down the slope at all times is the mysterious vital principle or force which knits and marries these unstable elements together and raises up a mobile but more or less stable form out of the world of fluids. Venus rising from the sea is a symbol of the genesis of every living thing.