160 LIFE ON THE FARM. 



If living germs have been allowed to enter the 

 can with the food, and decomposition or fermenta- 

 tion has set in, the fact may at once be known by 

 the escape of confined gas. The principle of can- 

 ning is founded upon the fact that the exclusion of 

 bacteria from organic matter will prevent its 

 decomposition. 



VARIOUS MEANS OF PRESERVING FOOD. 



Another method of controlling the action of 

 germs in food is to reduce the temperature to near 

 the freezing point. The low temperature simply 

 keeps them from growing and multiplying. As 

 soon as the temperature rises, they begin to act and 

 the food spoils. For this reason meats, fruits, and 

 vegetables keep longer during winter and in cold 

 storage. 



Bacteria cannot live in a strong solution of com- 

 mon salt (sodium chloride), and a great deal of 

 meat, and some vegetables, are preserved through 

 this means. The salt solution, however, produces 

 some changes in such foods, so that they lose the 

 flavor of their original freshness. 



Some meats are "cured" with common salt, or 

 other chemicals; some, by smoking. Fish and 

 pork are thus treated. Smoking coats the outside 

 of the meat with a thin layer of creosote (crude 

 carbolic acid), which not only kills all germs pres- 

 ent, but also gives the meat a better flavor. Car- 

 bolic acid is a dangerous substance to take into the 



