THE BACTERIA (SCHIZOMYCETES) 169 



Foods are thereby kept for years, and shipped all over the 

 earth. Drying is proportionately less used than formerly, since 

 this process causes most foods to lose some desirable qualities. 

 Destructive organisms cannot thrive upon thoroughly dry food. 

 Dried fruits, dried meats, and dried grains (a natural process 

 of preservation) may be kept for years. Preservation in salt 

 and sugar or their strong solutions serves the same purpose as 

 drying, since salt and sugar have such avidity for water that 

 destructive organisms have their protoplasmic water extracted 

 and therefore cannot grow. Fish, beef, pork, and other meats 

 may be preserved by thoroughly smoking with wood smoke. 

 The creosote that is carried into the meat by this process helps 

 to prevent the growth of destructive organisms. This method 

 of preservation, though thoroughly wholesome, requires long 

 exposure to the smoke. It is not so extensively used for beef 

 and pork as formerly, though large quantities of fish are still 

 preserved in this manner. 



Sterilization and canning have recently offered very great 

 opportunities for food preservation and shipment. By means 

 of heat properly applied all bacteria and other organisms of 

 decay may be killed. If such thoroughly sterilized food is 

 hermetically sealed in vessels that have been similarly steri- 

 lized, it will not decay. It is difficult, but entirely possible, to 

 sterilize thoroughly both food and sealing appliances so that 

 absolutely no organism will grow. 1 Other methods of preser- 

 vation by introduction of chemicals that prevent growth of 

 bacteria are sometimes used. These chemical preventives are 

 poisons. If eaten by men in very small quantities, injurious 

 results are not immediately noticeable, but their use is at- 

 tended by constant danger. Milk, meats, and confections that 

 are so preserved should always be avoided. 



1 Sometimes in canned goods, stale meats, and other foods, poisonous 

 ptomaines are formed. They are probably secretions from bacteria, results 

 of chemical change or decay of such foods as meats and fruits, or originate 

 from the disorganization of bacteria. For means of prevention, see "Care 

 of Food in the Home," Farmers' 1 Bulletin 375, U. S. Dept. Agr., 1909. 



