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 
