266 ELEMENTS OF GENERAL SCIENCE 



it examined chemically to determine what preservative it 

 may contain. Refrigeration and pasteurization are the safest 

 methods of preserving milk, and these are effective for only 

 a day or two, since they retard but do not prevent the devel- 

 opment of bacteria within the milk. 



Various kinds of chemicals are used in the preservation of 

 meats. These chemicals are sometimes of a poisonous nature. 

 In most cases, however, preserved meats are injured more by 

 excessive quantities of relatively harmless preservatives. An 

 excessive amount of salt hardens the fiber of the meat and 

 destroys its normal taste. Salt, sugar, etc. are used to cure 

 meat because they take up water so rapidly that bacteria are 

 killed by the extraction of the water from the cells of the 

 bacteria. The older practice of smoking meat gave a coated 

 surface of creosote in which destructive organisms could 

 not live. 



293. Food and filth. There is no inherent reason why small 

 particles of earth upon our food should be injurious to our 

 bodies, though they are always unattractive, but dirt of any 

 kind upon our food suggests the possibility of the presence of 

 living organisms that may prove injurious. It is more impor- 

 tant, however, to know that our food has been handled only 

 by persons who are free from disease germs than to know that 

 the food is not conspicuously dirty. Apples which are shipped 

 in barrels may have small particles of dirt adhering to them 

 and may not appear so attractive as when highly polished, 

 but if polished by the use of a soiled and bacteria-laden cloth, 

 the apples may thereafter be infinitely more dangerous as food 

 than when first removed from the shipping barrel. Obviously, 

 great care should be exercised to determine whether vegetables 

 and other foods have been handled in cleanly ways. A syste-j 

 matic examination of the vegetable markets, with reports and 

 discussions in class, will prove instructive. Fortunately, thor- 

 ough cooking will destroy bacteria upon food, and unless it 

 is reasonably sure that there is no contamination, thorough 



