Preservation of Foods. 229 



vative effect which is made use of in the preparation of 

 such foods as mince-meat, sausage, etc. In the first, the 

 preservative effect is aided by the sugar present and in 

 the case of sausage by the salt. 



Fodders such as corn, clover, and other leguminous 

 plants may be preserved by placing them under such 

 conditions that the air can not reach them, as in a silo. 

 In such cases the preservation is accomplished by virtue 

 of the acid which is formed in the tissues as a result of 

 the continued action of the plant cells in the absence of 

 air. 



The material to be ensiled must have the plant cells in 

 an active condition. Silage can not be made from ripe 

 or frozen corn. In the ensiling of clover it is necessary 

 to place it in the silo before much wilting of the plants 

 has occurred. 



The living plant cells continue to respire after they are 

 placed in the silo. The supply of free oxygen is soon 

 exhausted and the interspaces filled with nitrogen and 

 the carbon dioxide formed by the respiring plant cells. 

 The cells in their effort to keep alive draw on the oxygen 

 that is found in the sugars and starches of their contents. 

 They are then acting exactly as the anaerobic bacteria 

 when they obtain their supply of oxygen from the sugar 

 in the culture medium. In the effort of the plant cells 

 to obtain oxygen from the materials of the cells, they de- 

 compose the sugar with the formation of lactic and acetic 

 acids and carbon dioxide. These acids are formed in 

 such amounts as to prevent all bacterial growth. The 

 silage of course contains many bacteria that were present 

 on the fodder ensiled, which continue to exist in the si- 

 lage but are unable to grow. The mold spores are also 

 present in the silage but they are likewise unable to grow 



