Page:Popular Science Monthly Volume 6.djvu/594

576 and brownish, next the wall of the bag, but thinner and more transparent toward the centre (Fig. 8). This jelly (a) is called protoplasm, and the thin space (b) in the centre is an air-cell or vacuole (Fig. 9). If you color the yeast-cells, you can see the different parts much better. A drop of magenta will pass right through the sac without staining it at all. The cell-jelly, or protoplasm, will be quite red, and the vacuole will not be colored, though it may look pinkish, because you see it through a layer of the protoplasm (Figs. 10, 11). Now, if the cell were all made of the same material, it would probably all be colored by the magenta.

These cells are called torulæ—a single one is a torula. The word means a little knobby swelling. You will soon see how it comes to

have this name. If you have followed me carefully, better still it you have seen it all for yourselves under the microscope, you know that the torulæ are alive, and that they grow. Every thing that grows must have food. Now, whence does the torula get its food? From the liquid in which it floats. What is this liquid? The greater part is water, but if you sow yeast in pure water it will hardly grow at all; but if you put in ever so little sugar, it will froth and bubble considerably. If besides the sugar you give it the least bit of ammonia, magnesia, lime, and potash, it will thrive splendidly. The torula takes in this food, and churns it up into that "elixir of life" or protein, woody cells or cellulose, and fat. Then, if you watch carefully, you will see a whole lot of little buds coming out around the edges of the wall (Fig. 12); hence the torula is really a little knobby swelling. Some of the buds have other buds at their edges; all these buds are the little baby-torulæ. By-and-by they break away from the old mother-torula, but they always pay visits back and forth, and sometimes build their houses right next the parental roof in clusters (Fig. 13); at other times they build in long rows, like a chain or a string of beads (Fig. 14). Of this you may be sure, every torula has a mother. People have been trying to prove for two hundred years or more that these little specks of life can make themselves. Some time