432 Bacteria in Relation to Country Life 



With this knowledge came its application. There 

 came the drying or salting of fish and meat; the storing 

 of grain in cool, dry chambers; the pickling of vegetables 

 in tight receptacles. The seasons of plenty were made 

 to contribute to seasons of scarcity, and these contri- 

 butions were made effective largely by the natural re- 

 sistance to decay of dry grains and grasses. 



Modern research has made clear to us the nature of 

 decay, putrefaction and fermentation, and has helped 

 us to account for the instability of vegetable and ani- 

 mal substances. Knowing, as we do, of the universal 

 presence of microorganisms, and of the conditions 

 suitable for their growth and survival, we have gradually 

 perfected the means for excluding them from our food 

 products. We have thus developed important agricul- 

 tural industries. 



The principles of canning. — The successful canning of 

 fruits, vegetables, meat and fish depends upon the de- 

 struction of all of the bacteria present in these materials, 

 and the sealing of the cans so that no new invasion by 

 bacteria or other microorganisms can occur. This is 

 readily accomplished by heating the cans and their 

 contents to a temperature that kills not only the bac- 

 teria themselves, but, also, the most resistant spores. 

 The complete sealing of the cans previous to heating is 

 inadvisable, for the steam pressure inside of the can 

 might lead to the formation of leaks that would en- 

 courage subsequent infection. Hence, a small hole is 

 punched in the cover, through which the air and steam 

 escape during the heating process. After the steriliza- 

 tion, the hole is closed with a drop of solder and, if the 



