Bacteria, Helpful and Otherwise 447 



less, as this single bacterium will multiply and there will soon 

 be a vast number in the can that will cause the food to spoil. 



Sometimes the material to be canned contains bacteria in the 

 form of spores. These are not easily killed by boiling. They 

 are not commonly present in fruit, but in material like green 

 corn, green peas and green beans they are often found. Only 

 a very high degree of heat will destroy them. 



Drying. Drying is one of the most common methods of 

 preserving food. It is nature's method. You have probably ob- 

 served that seeds will keep for a long time if protected from 

 moisture. You know also that flour, meal and foods made from 

 these seeds will keep in good condition if absolutely dry. Bacteria 

 and other microorganisms will not develop on them if kept dry. 



Material of animal origin also may be preserved by drying. 

 Most kinds of meat may be kept in this way. The Indians 

 understood this and cut the flesh of wild animals into thin strips 

 which they dried by the heat of the sun or otherwise. Meat thus 

 dried will keep for a long time, as bacteria do not develop on it. 

 Apples, peaches, plums, berries and other fruits may be dried and 

 preserved indefinitely, if properly protected from moisture. 



Smoking and Pickling. One of the common methods of 

 preserving fish -and the flesh of animals is by smoking, after the 

 substance has been well pickled, that is, soaked in a solution of 

 salt water. This process is called curing. Hams, bacon and 

 dried beef are preserved in this way. The smoke from burning 

 wood is commonly used. Smoked meat will not be injured by 

 bacteria for three reasons ; it is too dry to support their growth, 

 the smoke itself is not favorable to the development of bacteria, 

 and salt is injurious to them. Certain food material may be 

 preserved by pickling, without smoking. 



Cold Storage. The fact that low temperature will preserve 

 all kinds of food is well known. Cold storage means the keeping 

 of food in a building that is cooled artificially and kept at a low 

 temperature even in the hottest weather. The idea of cold storage 

 is modern. Buildings adapted for this purpose, cold storage plants 

 as they are called, are now found in all large cities and in some 

 small places. In the preservation of apples and similar fruits, 



