440 Bacteria in Relation to Country Life 



ditions favorable for their development. Hence, by 

 drying vegetable and animal substances, we can pre- 

 vent the multiplication of bacteria in them. The pre- 

 servation by cold and by drying ceases to be effective 

 when, on the one hand, the temperature rises above 

 50 Fahr., as was already noted in the discussion of 

 milk, or when, on the other hand, enough moisture gains 

 access to the dry material to allow bacterial growth. 



Salting, pickling and smoking. Still another method 

 of food preservation is based on the salting or pickling 

 of animal and vegetable substances. It is well known 

 that meat or fish, immersed in very strong brine, is 

 more or less effectively protected from bacterial decom- 

 position. Similarly, meat of healthy animals may be 

 preserved by smoking, as is actually done on a large 

 scale at the meat-packing establishments. 



All these methods are effective and desirable in so 

 far as they permit the exclusion of the destructive bac- 

 teria, or, better still, if they allow the preservation of 

 foods with the retention of the desirable tastes and 

 flavors. Hence, canning, refrigeration, drying, salting 

 and smoking each have a distinct value. From the bac- 

 terial standpoint* however, they aim only at the ex- 

 clusion of microorganisms, or the suppression of their 

 activities. In some of the pickling industries, more than 

 mere suppression of bacterial growth is aimed at. The 

 value of certain fish products and of dill-pickles and 

 sauerkraut is directly dependent upon -certain bacterial 

 changes, which impart to the materials distinct tastes 

 and flavors. 



Pickled fish. Bacteriological and chemical studies 



