168 BOTANY 



enzyme into carbon dioxide and alcohol. This may be expressed by the 

 following chemical formula: C6H12O6 =2 (C2H60) + 2 (CO2). This means 

 that the sugar forms alcohol and carbon dioxide. This process, which we 

 call fermentation, is of the greatest importance in the brewing industry. 



Beer Making. — Brewers' yeasts are cultivated with the greatest care; 

 for the different flavors of beer seem to depend largely upon the condition 

 of the yeast plants. Beer is made in the following manner: Sprouted 

 barley, called malt, in which the starch of the grain has been changed to 

 grape sugar by a process of digestion, is killed by drying in a hot kiln. 

 Then hops are added to give the mixture a bitter taste. Now comes the 

 addition of the yeast plants, which multiply rapidly under the favorable 

 conditions of food and heat. Fermentation results on a large scale from 

 the breaking down of the grape sugar, the alcohol remaining in the fluid, 

 the carbon dioxide passing off into the air. The process is stopped at the 

 right instant, and the beer is stored either in bottles or casks. 



In bread making the rapid growth of the yeast plants is facilitated by 

 placing the pan containing the mixture in a warm place over night. Fer- 

 mentation results from the rapid growth of the yeast in the dough; the 

 carbon dioxide remains as the bubbles so familiar to the bread maker, 

 making the bread light and more digestible; the alcohol produced is evapo- 

 rated during the process of baking. 



Bacteria. — The bacteria are found in the earth, the water, 

 and the air. '' Anywhere but not everywhere," as one writer 

 has put it. They swarm in stale milk, in impure water, and in 

 any decaying material. 



These tin}^ plants, " man's invisible friends and foes," are of 

 such importance to mankind that thousands of scientists devote 

 their whole lives to their study, and a science called bacteriology 

 has been named after them. 



Size and Form. — In size, bacteria are the most minute plants 

 known. A bacterium of average size is about -^-^0 of an inch in 

 length, and perhaps ysiro o" ^^ ^^ ^^^^ i^ diameter. Some species 

 are much larger, others smaller. A common spherical form is 

 .^oVo ^^ ^n ii^ch in diameter. It will mean more to us, perhaps, 

 if we remember that several millions of bacteria of average size 

 may be placed within the area formed in this letter 0. Three 

 well-defined forms of bacteria are recognized: a spherical form 

 called a coccus, a rod-shaped bacterium, the bacillus, and a spiral 

 form, the spirillum. Most bacteria are capable of movement 



