SUMMARY 353 



bacteria in milk form lactic acid and cans.- the milk to BOlir. 

 Tlie growth of these bacteria can be checked bv pasteuriz- 

 ing the milk. Ice cream, if too old, is dangerous, for the 



slow-growing bacteria have had a chance t<» develop. 



The men who did the most to make the study of bacteria 

 possible were Leeuwenhoek, who improved the microscoj 



Pasteur, who discovered bacteria in milk, and Koch, who 

 found the way to make a pure culture and to tesl cows for 

 tuberculosis. Many students are devoting their lives to 

 finding out about the various bacteria. 



K very one should know the main facts about bacteria 30 

 that he may not have a foolish fear of them, but may be 

 able to take reasonable precautions against the harmful 

 kinds. Since a healthy body is the best safeguard against 

 harmful bacteria, we should, observe the laws of hygiene in 

 order to keep well, and at the same time, avoid, when 

 possible, the bacteria which produce disease. 



QUESTIONS 



What are the main points of likeness between a bacterium and a bean 

 plant? What has the pleurococeus which the bacterium lacks? Bow 

 can food be protected from harmful bacteria? In what respects are 

 bacteria harmful to milk? In what respects helpful? Why are a : 

 harmful bacteria not injurious in a healthy body ? If one bacterium 

 divides every half hour, and all live, how many will there be at the end of 

 twenty-four hours ? (Solve by arithmetic or by algebra.l Why <1» B an 

 apple with a broken skin decay more rapidly than one in which the akin 

 is not broken ? Why should one not put ice into water to cool it '.' 



REFERENCES 



Conn, The Story of Germ Life. 

 Frankland, Our Secret Friends and Foes. 

 Prudden, The Story of the Bacteria. 

 Radot, The Life of Pasteur. 

 Woodhead, Bacteria and Their Products, 



U. S. Bulletin No. 56, Hygienic Laboratory Bulletin. Milk and Its 

 Relation to Public Health. 



