PRESERVATIVES 17:> 



placed in kegs and thus k<-|>1 from the air, no mold growth 

 can take place. The action of acid-forming bacteria is also 

 important in the preservation of certain pickles, especially 

 cucumber pickles made in brine. 



Silage. The preservation of green fodder, especially 

 corn, has become of great economic importance. It is 

 customary to cut the material to be ensiled into short pieces, 

 so that it may be closely packed. This process perm its 

 the sap to exude, and gives the bacteria that were on the 

 surface of the tissue access to it. Bacterial growth is 

 rapid; lactic ami acetic acids soon accumulate to such an 

 extent as to exclude the growtli of putrefactive forms. The 

 fresh vegetable tissue carries large numbers of acid-form- 

 ing bacteria on its surface, so that no inoculation is nec- 

 essary. 



The oxygen of the air between the pieces of ensiled ma- 

 terial is soon exhausted by the respiratory processes of the 

 cells of the plant tissue. The result is that the air consists 

 of carbon-dioxide and nitrogen. No molds can grow under 

 these conditions. If the wall of the silo is so constructed 

 that no air can pass through it, and if the silage is closely 

 packed, so that air can not penetrate deeply into it from 

 the surface, the acid mass will keep for an indefinite time. 



In those areas in which molds grow, as near the surface, 

 the acid will be destroyed and conditions thus established 

 that will permit the growth of putrefactive bacteria. The 

 >ilage in these places will be dark in color and will have an 

 of Tensive odor, and the tissues will have disintegrated, 

 while that in which the growth of molds and putrefactive 

 bacteria has been prevented will show none of these 

 changes. 



Preservation by low temperature. The use of low tem- 

 peratures to restrain or prevent the growth of microor- 

 ganisms is of the greatest importance. The methods in- 



