320 GENERAL SCIENCE 



Cream is ripened through the aid of bacteria. Sometimes germs 

 or ferments are added to cause the cream to ripen quickly. 



Fresh butter contains a large number of bacteria. When butter 

 is a day old it contains about one-half as many bacteria as when 

 first produced, and by the second day the number of bacteria has 

 been reduced to ^ of the original number. In butter a month old 

 the number of bacteria present has been very greatly reduced. 



Project. Send for pamphlet on " Butter and Cheese Making," U. S. Depart- 

 ment of Agriculture. 



Bacteria in Vinegar. We have learned that the bacteria in bread 

 change the sugar to alcohol, and if bread is not well-baked they 

 will change the alcohol into an acid. Bacteria which change alcohol 

 into acids are used to produce the acid in vinegar. " Mother of 

 vinegar " is a mass of bacteria. 



Bacteria in Textiles and Fibers. Bacteria are often used for 

 rotting the stems of flax, hemp, and many other fibers, until the 

 surrounding tissues are soft. 



Bacteria, Useful for Decomposition. Certain types of bacteria 

 are used to-day to change dangerous sewage into harmless material. 

 Even disease-producing bacteria are killed by such methods. Small 

 private sewage systems allow the sewer to run through porous tile 

 drains around which decomposing bacteria are working, converting 

 the sewage into harmless substances which may be used by the roots 

 of trees and other plants. 



Life which exists upon the earth to-day depends to a great extent 

 upon the decomposing action of bacteria. 



Project i. Make a report on Conn's " Bacteria, Yeast and Mold in the 

 Home." 



Project 2. Lippman's " Bacteria in Relation to Country Life." 



QUESTIONS 



1. Why do we have an impression that most bacteria are harmful? 



2. In what ways are bacteria useful? 



3. W'hy is it necessary to have bacteria in vinegar? 



4. How do bacteria assist in the manufacture of linen? 



5. Why would it be almost impossible for man to live without 

 the aid of bacteria? 



