PRESERVATION OF FOOD PRODUCTS FROM BACTERIA. 317 



Where such low temperatures are not feasible, a moderate 

 degree of cold will greatly check bacterial growth and prevent 

 decay. The ice chest keeps the food a few degrees above 

 freezing. At this temperature the ordinary bacteria do not 

 grow, and the food will not undergo a typical decay, but there 

 are some species of bacteria which can grow at these tempera- 

 tures and gradually ruin the food substances. The use of low 

 temperatures is, however, of great assistance to the agricul- 

 turist in preserving many of his fruits. These are frequently 

 ruined by freezing, but may be kept in perfectly good con- 

 dition for many months if they are kept as cool as possible, 

 avoiding actual freezing. The cold cellar thus serves the 

 farmer's purpose by checking the growth of the common bac- 

 teria in his fruits without lowering the temperature to freezing. 



PRESERVATION BY THE USE OF CHEMICALS. 



Many chemical substances are destructive to bacteria and 

 foods may frequently be prevented from bacterial action by the 

 addition of small quantities of some material, harmless in itself, 

 yet having a checking action upon bacteria. Such agents are 

 called preservatives. If they are to be used in the preserva- 

 tion of food products it is, of course, necessary that they 

 should not be deleterious to health, and also that they should 

 not impart disagreeable flavors to the food. It is, therefore, 

 impossible, or at least, illegimate, to use for such purposes 

 many of the best antiseptics which are used elsewhere ; and 

 the number that can be used without hesitation is not very 

 great. 



The most common substance thus used is salt. Salt is not 

 an antiseptic in any proper sense and it does not destroy bac- 

 teria. But it may be a preservative and, when it is present in 

 quantity in a solution, it will have a decidedly repressing action 

 upon bacterial growth and may stop the ordinary putrefactive 

 changes. It is the common method in use for the preserva- 



