ECONOMIC IMPORTANCE OF FUNGI 305 



series of operations intended primarily to kill all germs of 

 bacteria and fungi. The sterilized fruit is then sealed 

 from the air and from access of other germs while it is 

 still hot. The ''keeping" of canned goods depends upon 

 the successful exclusion of every living spore or other 

 germ. If goods preserved in tin cans have been im- 

 perfectly sterilized the gases produced by fermentation 

 will exert a pressure upon the can from the inside, often 

 strong enough to cause a bulging of the ends. 



COLD STORAGE 



Just as canning has for its object the preservation of 

 vegetable or animal tissues by killing the germs with 

 heat, so cold storage accomplishes the same end by means 

 of extreme cold. Most germs remain inactive below a 

 certain temperature, which may be readily ascertained 

 by experiment. The spoiKng of eggs is caused by the 

 presence within the egg of a germ-" flora," which lives 

 upon the yolk and white, producing by its life proc- 

 esses, the noxious gases of stale eggs. At certain low 

 temperatures most of the life-processes of the germs 

 are either stopped entirely, or greatly retarded. In the 

 colonial days of America, and later, it was common for 

 dwellers on farms and in villages to preserve meat by 

 burying a quantity of it in the snow during the winter 

 season — a primitive cold storage. During cold storage, 

 however, certain chemical changes take place in the 

 preserved tissue, due to enzyme action. As a result 

 there is a limit to the period that food can be kept in cold 

 storage without deteriorating. All cold-storage plants 

 and refrigerator cars are evidence of the fact that our 

 own lives are profoundly affected by the existence and 

 activity of microscopic forms of plant life. 



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