OUR DRINK FILLING THE BOILER OF THE BODY-ENGINE The Need of Water in the Body-Engine.

If you have ever taken a long railway journey, you will remember that, about every two or three hours, you would stop longer than usual at some station, or switch, for the engine to take in water.

No matter how briskly the fire burns in the furnace, or how much good coal you may shovel into it, if there be no water in the boiler above it to expand and make steam, the engine will do no work.

And an abundant supply of water is just as necessary in our own bodies, although not used in just the same way as in the engine.
The singular thing about water, both in a locomotive and in our own bodies is that, absolutely necessary as it is, it is neither burned up nor broken down in any way, in making the machine go; so that it gives off no energy, as our food does, but simply changes its form slightly.
Exactly the same amount of water, to the ounce, or even the teaspoonful, that is poured into the boiler of an engine, is given off through its funnel and escape-pipes in the form of steam; and precisely the same amount of water which we pour into our stomachs will reappear on the surface of the body again in the form of the vapor from the lungs, the perspiration from the skin, and the water from the kidneys.

It goes completely through the engine, or the body, enables the one to work and the other to live, and yet comes out unchanged.
Just how water works in the engine we know--the heat from the furnace changes it into steam, which means that heat expands it, or makes it fill more space.