208 INTRODUCTION TO BOTANY 



In the preservation of fruits much progress has been made 

 by improvements in methods of gathering them. Most fruits 

 have a natural covering, which, if unbroken or unbruised and 

 kept clean, will for a long time prevent the entrance of organ- 

 isms of decay. If two sets of ripe apples are gathered one 

 carelessly, so that bruising and scratching of the surface occurs, 

 the other with sufficient care to avoid these injuries and both 

 are kept under similar conditions, an interesting demonstration 

 will be made of the desirability of proper care in handling fruit. 



193. Refrigeration and drying. Long before it was known 

 how decay is produced, it was known that low temperature 

 and drying would prevent decay. Refrigeration has now be- 

 come the chief method of preventing decay, since bacteria do 

 not thrive at or below the freezing point. There is doubt 

 whether bacteria grow at all when at freezing temperature, 

 but this point is not definitely settled. Foods are kept for 

 years by cold or by drying, and are thus shipped all over the 

 world. Fruits, meats, and grains, when completely dried (a 

 natural process of preservation), may be kept for years, since 

 destructive bacteria cannot thrive upon thoroughly dry food. 

 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 proto- 

 plasmic water extracted and therefore cannot grow. Fish, 

 beef, pork, and other meats may be preserved by 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. 



194. Sterilization and canning. High temperature may also 

 prevent the growth of bacteria, and by its use 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 



