340 



THE FOODS WE EAT 



What is this girl doing ? 



The Value of Sterilization. These experiments show 



rather conclusively that very hot and very cold tempera- 



tures are unfavorable 

 for the growth of 

 bacteria, yeast, and 

 molds. Most bac- 

 teria are killed after 

 boiling for ten 

 minutes, or exposure 

 to dry heat of 212 

 for about the same 

 length of time. Heat- 

 ing substances for a 

 long enough period to 

 kill all bacteria is 



called sterilization. It is a process used in canning vege- 



tables and fruits. We cook our foods, and we put them 



in cold storage or ice boxes in order to keep them. Other 



experiments made with bacteria show that bacteria must 



have moisture in order to grow ; that the bacteria must 



have a moderate temperature ; 



and that food substances must be 



present. Proteins seem to be 



the substances most favorable to 



their growth. It has also been 



found that light is unfavorable 



and darkness is favorable for 



the growth of many microor- 



ganisms. 

 Milk and Bacteria. Milk is 



not only a perfect food for man, 



but it is also a perfect food for 



bacteria. Since it is one of our 



most important foods, and one 



that easily spoils, great care must 



.water 



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one for home use? 



