PLANTS THAT CHANGE FOOD 



435 



Plants That Change Food. If it were not for microscopic 

 plants (page 398), food would keep indefinitely without 

 change. These little plants are, however, present every- 

 where and if conditions are suitable for their growth they 

 begin at once to change or to " spoil " all foods they can 

 reach. Some of the bacterial changes make food more 



BREAD MOLD. (Greatly magnified.) 



palatable, for it is bacteria that give the fine flavors to' the 

 best butter and cheeses and the gamy flavor to certain kinds 

 of meat. Bacteria also change cider into vinegar. 



Experiment 143 (Teacher's Experiment). Make a solution of 

 molasses and water. Place some yeast in it and put the mixture 

 away in a warm place. Watch it for a few days, and after gas 

 bubbles have been coming off for some time put the solution in a 

 flask connected with a distilling apparatus, as shown in Figure 136. 

 Gently heat the solution and collect the distillate. Smell of the 

 distillate. What does it smell like? Dip a piece of cotton cloth 

 in it and touch a lighted match to it. If the experiment has been 

 successful, the distillate will burn. If not, distill some of the 

 distillate again. Alcohol and carbon dioxide are produced by the 

 action of the yeast on the molasses and the alcohol is evaporated 

 by low heat and condensed in the still. 



