BIOLOGY FOR YOUNG BEGINNERS. 



577 



I will tell you how you can prove that this is not true. These little 

 toruke float about in the air, or sleep in any dry place, never showing 

 that they are alive till they are planted in some nest or nidus. When 

 the cook dries her yeast-cakes, she puts all the little torulae to sleep, 

 and there they go into winter quarters, or hibernate in their cells, 

 like the bears in their caves. 



Fig. 12. Cell and its Bubs. 



Fig. 13. The Baby Torul.e grouped 

 around their mother. 



Fig. 14. Cells linked to- 

 gether in Chains. 



There is still another appearance of yeast. Let your cup of yeast 

 stand long enough, and do not add any more sugar or water to it, 

 you will find that the bubbling or fermentation stops, the torulae settle 

 to the bottom, and the fluid comes to the top. This fluid has a strong 

 or biting instead of a sweet taste, like the fluid into which you first 

 placed the yeast. The fermentation has changed its nature the fairy 

 torulae with their magic wands have turned the sugar into carbonic 

 acid, alcohol, glycerine, and succinic acid. These are called the prod- 

 ucts of fermentation. The carbonic acid, you know, passed off through 

 the bubbles, the other products are still in the fluid. A little of this 

 fluid will make you merry ; if you take much of it, you will become 

 intoxicated. This is due to the alcohol, and the value of yeast de- 

 pends upon its power to make alcohol. You may know that the fluid 

 is alcohol if, when you touch it with a lighted match, it burns with a 

 blue flame. 



Now, I have told you the torula grows it has life ; but how does 

 it grow as a mineral, a vegetable, or an animal ? The mineral grows 

 larger and larger by additions made to its outside. This is called 

 growth by accretion. But the torula or yeast-cell grows by taking 

 in new substance in among the particles of its old substance, and this 

 kind of growth is called by a long name intussusception. This is 

 one of the reasons why it is not a mineral. Is it an animal ? The 

 line that divides the animal from the vegetable kingdom is not very 

 well marked, but there are two reasons why the torula is not an ani- 

 mal. In the first place, its jelly or protoplasm is shut up in a close 

 sac, but the protoplasm-jelly of animal cells forms a wall of itself. In 

 the second place, the torula can make its own food or protein out of 

 the raw material it finds in the liquid, while the animal cells seem to 

 have no such power ; they must have their protein already made, and 

 vol. vi. 37 



