There is a lot of sugar in the dough from which bread is made. Sugar contains three things--carbon, hydrogen and oxygen. When sugar is fermented it amounts practically to burning it. To make good bread from the dough it is necessary to ferment the sugar which is in the ingredients from which it is made. Yeast, which is a simple living plant, has the power to ferment sugar. When sugar ferments, two things are produced. One thing is the formation of carbonic acid gas. A great deal of this carbonic acid gas is caught in the dough in the form of large or small bubbles and some of it escapes into the air. The other part tries to escape into the air also but cannot, and causes the dough to rise, which makes the bread light, as we say. The holes you see in the bread after it is baked are the little pockets where the carbonic acid gas was retained in the dough. These bubbles of gas all through the dough act like a lot of little balloons and lift the dough up with themselves as they try to get to the top and escape into the air. What Is Yeast? Yeast is a living plant that is used for the purpose of causing fermentation. The yeast we use in baking bread is an artificial yeast--really a dough made of flour and a little common yeast and made into small cakes and dried. If kept free from moisture it retains the power of causing fermentation for some time. The flour and other matter in a cake of yeast are only used to keep the yeast in a form where it can be preserved. It is necessary to add water to start fermentation and that is why we add hot water when we stir in the yeast for a baking. Is a Moth Attracted By a Light? It seems to be a strange contradiction of the nature of living things that a moth should fly deliberately into a light or dash itself to death against the glass surrounding a strong light. This is contrary to the usual law of nature which gives the living thing an instinct to protect itself against enemies. For a long time we thought that moths did not deliberately burn themselves up by flying right into a light, but our naturalists have proven that not only moths but certain birds, bees, flies and butterflies, burn themselves up by flying into the flame of a light or fire. [Illustration: HOW MAN LEARNED TO MAKE A FIRE SAWING This was probably man’s first method of producing fire. By rubbing two sticks together in this way sufficient heat was produced to set fire to easily burnable material such as dried grass, etc.] [Illustration: DRILLING An improvement came when man learned that by twirling a dry stick in a hole in another piece of dry wood the fire could be started more quickly.] How Man Discovered Fire