CHAPTER IX 



BACTERIA AND FOOD. HOW TO KEEP FOOD WHOLESOME 



Bacteria spoil food and cause disease. Milk sours because 

 minute plants called bacteria live, grow, and reproduce in it; 

 meats decay, eggs rot, canned tomatoes sour, and fruits 

 spoil for the same reason. Diseases, such as diphtheria, 

 grippe, pneumonia, typhoid fever, tuberculosis, and diarrhea 

 are caused by bacteria which develop and reproduce in our 

 bodies. But not all bacteria are undesirable and harmful. 

 Certain kinds live in the soil and keep it fertile enough to grow 

 the grains and vegetables on which we depend for food ; other 

 kinds grow in milk and cream and give a pleasing flavor to butter 

 and cheese. Bacteria are good or bad according to their work. 

 Those that cause disease and decay of food are often called 

 germs. 



Bacteria are hundreds of times smaller than the tiniest fleck of 

 dust, and are so minute that 

 thousands of them could find 

 standing room on the point 

 of a needle, and hundreds of 

 thousands swimming room in 

 a drop of water. Although 

 bacteria are almost unthink- 

 ably small, we can see them 

 with the microscope and can 

 study their structure (Fig. 



OcP 



43). They have many differ- 

 ent shapes, some are spherical 



FIG. 43. Various forms of bacteria, highly 



magnified. 



105 



