338 THE FOODS WE EAT 



know that bacteria present in the air under certain con- 

 ditions will grow in foods and will cause foods to decay. 



SELF-TESTING EXERCISE 



Select from the following list those words which best fill the blank spaces* 

 in the sentences below and arrange the words in proper numerical order. 

 A word may be used more than once. 



grow vacuum dark dryness 



light plants excessive circulation 



odor moderate animals ferment 



moisture vitamins decay appearance 



Foods spoil because tiny (1) , yeasts, bacteria, and mold, 



grow in them. Experiments have shown that (2) and (3) 



temperature as well as some protein food, which is living or dead, are 

 all factors favorable to the growth of bacteria. Bacteria grow more 



rapidly in the (4) . than in the (5) Microorganisms cause 



food to spoil. Bacteria cause it to (6) , yeast causes it to 



(7) , while molds may change its (8) and give it an unpleas- 

 ant (9) 



STORY TEST 



ROY MAY BECOME A BIOLOGIST 

 Read carefully and critically. List all the errors and suggest corrections. 



I used to think it rather funny that they called bacteria and 

 yeast, plants when you couldn't even see them. Molds seem like 

 plants, at least you can see them. I made some root beer by 

 putting yeast into a prepared sugar solution, with some root 

 extracts. I could see bubbles of gas as it worked. This is the 

 same kind of change that occurs when bacteria in milk cause it 

 to sour. The same gas is given off in both cases. Plants that 

 we can barely see with the unaided eye are called microorganisms. 

 When microorganisms take root and grow in our foods, the food 

 may acquire a changed and more pleasing taste as is the case, 

 sometimes, with cheese and butter. Or it may produce an offen- 

 sive odor and taste. Bacteria are seen under the microscope to 

 have three common forms or shapes. They are rods, circular, 

 and ball shaped. 



