170 BACTERIA, YEASTS, AND MOLDS 



We have already noticed that bacteria are almost uni- 

 versally distributed in earth, air, and water. This fact 

 makes it extremely difficult to protect food from their 

 action, and, indeed, without special devices it is quite 

 impossible to do so. All food material — meats, fruits, or 

 vegetables — is sure to contain bacteria when it reaches 

 the home or the canning factory. From some source, 

 either air, water, or earth, every kind of food material is 

 sure to become contaminated. Every one must recognize, 

 then, that bacteria will be found with absolute certainty in 

 every kind of fresh food. 



Hence the process of keeping food by protecting it from 

 bacteria must consist of two steps : (i) Some means must 

 be devised for removing the bacteria already present in 

 the food, (2) The access of all other bacteria must be 

 absolutely prevented. If these two objects can be accom- 

 plished, the food will be protected from bacterial action 

 and, thus protected, may be preserved mdefiniteiy. Food 

 thus guarded may be kept for any number of months. No 

 limit has ever been found, and we have no reason for ques- 

 tioning that it might be preserved for centuries without 

 any subsequent change, provided it could be kept abso- 

 lutely free from the attack of microorganisms. This 

 method, therefore, offers almost unlimited possibilities in 

 the way of preserving food for future use. It demands 

 care in its application, but the results, when properly 

 obtained, are permanent. 



I. Destroying the Bacteria Present. The removal from 

 any food material of bacteria already present is generally 

 brought about by the action of high heat. We have 

 already noticed that a sufficiently high heat is fatal to all 



