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 ====II. How the Yeast Plant Grows in a Loaf of Bread==== Which would you rather do, get inside a loaf of bread, or put the bread inside of you?

That makes you laugh. But you never tried getting inside a loaf of bread. If you get inside before it is baked, you will find plenty of playmates. Bread dough is just full of little living cells of protoplasm. They eat the bread before you do. They eat and eat and grow, and make millions of other cells like themselves. Let us watch them. They are very active little plants so they can easily be studied.

Your mama buys a yeast cake when she wants to make bread. It may be dry and hard, or it may be a soft paste wrapped in tin foil. It has an odd smell, and does not seem alive at all. Mama isn't sure that it is alive. She takes a half cup of warm water, and a little flour and a tiny bit of sugar and mixes them. Then she breaks her yeast cake into the cup, stirs them all together and stands the cup in a warm place. If you ask her why she does that, she may say: "I want to see if that yeast is alive."

Now you watch it! Soon little bubbles begin to burst. The batter swells and foams, and rises to the top of the cup. Study it with a microscope. The whole mass is in motion. Mama says the yeast ferments, but that is just another name for growing, for yeast plants. There, the secret is out. Mama made a garden. The flour and water and sugar are soil. In the soil she scattered yeast plants-just as a farmer scatters wheat seeds in a field. The yeast is a water plant and will grow in warm water alone, but it will grow faster if given the starch in flour. And it likes sugar, too, just as you do. It uses these things to grow on and, in using them, it changes them. It turns the starch and sugar sour, and gives off the same gas-carbon dioxide—that animals give off in breathing. This gas is what puffs the bread so it rises to the top of the pan. There is very little food in the cup. Soon the yeast plants will stop growing and making gas. Then the paste will fall flat. Mama must hurry and get a big pan full of dough ready, to give the yeast plants more food.

This time she takes a quart of water, and a lot of flour, and the foaming yeast in the cup. She beats the batter with a big spoon to scatter the yeast plants all through the soil and to beat in air, too.