grow. The mind is like everything else in the world. It can grow only by changing.
Don't you like for papa to open the back of his watch so you can see the wheels go 'round? When he does that you want to know what makes them go 'round, don't you? You want to know how and why each part of the watch works for and with the others. A plant or an animal is more wonderful than a watch. A watch runs down, and has to be wound again. But plants and animals have little live wheels that wind themselves, and keep going as long as they live. And before they die they start other plants and animals just like themselves—or even a little better—to going.
To understand it all you will have to go a long way back. There couldn't have been a watch until there was a wheel, then another wheel to turn on that, and a spring to make them turn. So there could never have been a plant or an animal until there was a little living wheel, or cell. Did you know that men of science, who have studied life in plants and animals, have found out what that cell looks like, and what it is made of? It is just a tiny, egg-shaped bag so small that you cannot see it, except under a microscope, and as colorless as a drop of water.
Still, that little living cell has a skin or thin wall around it, and it is filled with a drop of magical jelly. The jelly is alive. What is it to be alive? A bit of sponge can soak up water, but it cannot use it, or make anything out of it. A silk worm eats mulberry leaves, grows larger on this food, makes a silk cradle to go to sleep in, and hatches out into a butterfly that lays more silk worm eggs. To be alive, is to eat and grow, and turn the food into something else and, don't forget this, make more living things like itself. That is why we know that the little drop of jelly is alive. It is the smallest, simplest live thing in the world. Of course, it is so important it has to have a name. It is called Pro'to-plasm.
The wonderful cell full of protoplasm is the fairy godmother of every living thing in the world. It is the "once upon a time" with which the story of life begins. It has done more wonderful things than to turn pumpkins into gilded coaches and mice into horses. It didn't do them all at once, just by waving a wand. It began in a very humble way, and took one small step at a time. At first it was contented to make another little round cell just like itself, then another and another and another, all as alike as so many peas. But each one of those cells full of protoplasm could
