HOW TO KEEP GERMS FROM SPOILING FOODS 121 



Experiment. What effect have different preservatives upon bacteria ? 



Materials: Beans. Test tubes. Salt. Sugar. Vinegar. Boric acid. 



Method: Soak beans in water overnight and crush them. Put a portion 

 into each of seven test tubes. Add water to cover. Set one tube 

 aside; add preservatives as follows: No. i, untreated; No. 2, one 

 fourth teaspoonful of salt; No. 3, one fourth teaspoonful of sugar; 

 No. 4, one teaspoonful of sugar; No. 5, one fourth teaspoonful of 

 vinegar; No. 6, one teaspoonful of vinegar; No. 7, a pinch of boric 

 acid. Leave these tubes open in a warm room. A bad odor will 

 result from bacterial growth. Test for odors every two days for 

 two weeks. Make tabulated form for recording the result of the test. 



Preservatives and their use. Foods are often protected 

 against bacteria by adding substances in which bacteria 

 cannot live and develop. Such materials as salt, sugar, 

 vinegar, and some 

 spices are harmless 

 preservatives. In re- 

 cent years, other sub- 

 stances, such as ben- 

 zoate of soda, borax, 

 or boracic acid have 

 come to be used 

 as preservatives, but 

 the latter materials 

 are harmful, espe- 

 cially when used in 

 large quantities. 



How may we keep 

 germs from spoiling 

 foods ? From the 



Cold storage meat warehouse. 



experiments that we 



have performed, we 



find that intense heat and intense cold prevent the growth 



of germs. Bacteria are prevented from growing in foods 



