FOODS AND NUTRITION 385 



could be kept in this way as long as desired. These 

 methods are still used in rural communities with good 

 results. 



All foods are subject to the attack of destructive bac- 

 teria. The changes produced in food by these bacteria 

 usually render them less palatable and often destroy 

 their value as foods. The various methods of preserving 

 foods may be classed under the general heads of physical 



FIG. 343. Drying Codfish, Provincetown, Mass. 



and chemical methods. To the first class belong such 

 methods as canning, refrigerating or cooling, and drying 

 or evaporating. These methods are applicable to all 

 kinds of foods and are highly efficient, since they make 

 very slight changes in the flavor, appearance, and com- 

 position of the foods. The chemical methods of preserv- 

 ing foods involve a change of chemical conditions in the 

 foods of such a character that decomposition takes place 

 very slowly. Chemicals used as preservatives include 



