BACTERIA. 159 



with serious results, if care is not taken to exclude 

 the air. The outside layer of skin, not being sup- 

 plied with blood vessels, is germ proof, and 

 excludes bacteria from the inner and more delicate 

 parts. In a similar way, fruits and vegetables are 

 covered with skin to keep out decomposition 

 germs. When this skin is once broken germs 

 enter, and decay quickly sets in. 



Fruits and vegetables contain a large amount of 

 water, and for this reason they are more subject to 

 decay than grain, nuts, beans, and their like, that 

 contain but a small amount of moisture. When 

 the water is taken from them, they will keep for a 

 long time, because germs cannot act without the 

 presence of water. From this fact, the drying of 

 fruits and vegetables has come about. Meats are 

 dried for the same reason, and will keep for a long 

 time in that condition. 



The bacteria in vegetables, fruits, and meats can 

 be killed by boiling for an hour or more. If the 

 substances to be preserved are then put in cans 

 which have been thoroughly cleaned and heated so 

 as to kill all germs, and if the cans are hermetically 

 sealed, they will keep their contents sound for an 

 indefinite length of time. The things necessary to 

 do in canning foods so that they will keep, are to 

 kill all germs in the food and the inside of the 

 cans; to seal while hot, so as not to allow other 

 germs from the air to enter, and to keep sealed 

 till the whole contents of a can are to be used. 



