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Our Surroundings 



subjected to a high degree of heat in order to kill all microscopic 

 forms of life; second, the vessels or cans in which the material 

 is to be placed are thoroughly sterilized; and third, the ma- 

 terial, while highly heated, is put into the vessels or cans and 

 sealed hermetically, that is, so that no air can get into the can. 

 In sealing fruit jars, a rubber ring is inserted between the 

 jar and the cover, which is clamped or screwed down. As the 



SHUTTING OUT HARMFUL BACTERIA 



The vegetables are preserved by heating in the boiler to destroy germs and by 

 sealing in sterilized glass jars. 



jar cools the air inside contracts, forming a partial vacuum. Out- 

 side air pressure aids in forcing the rubber tightly into every 

 crevice. 



If even a single bacterium chances to survive the heating 

 process and gets into the can, the work of canning will be use- 



