LACTIC ACID FEEMENTATION 205 



Most of the difficulties in the preparation of satisfactory 

 ensilage are due to defects of one of the first three factors. 

 The suitable lactic acid bacteria are usually present. How- 

 ever, certain investigators have found increased uniformity 

 of results when the silage is inoculated with suitable mix- 

 tures of lactic acid bacteria at the time of preparation. 



Usually the materials placed in the silo are green, that is, 

 they contain many living cells. Among the first changes 

 which occur, therefore, in the silo are those due to the 

 activity of these living cells and of the enzymes present in 

 them. Certain of the earlier investigators of silage con- 

 cluded that these changes were by far the most important. 

 More recent investigations, however, have shown that the 

 bacteria are responsible for most of the fermentative 

 changes. Yeasts, which are usually present, may bring 

 about some alcoholic fermentation. The lactic acid bacteria, 

 however, usually overgrow and outgrow the other organisms 

 present and produce sufficient lactic acid to inhibit their 

 development completely. Eventually the growth of the 

 lactic acid bacteria is likewise stopped, and the food 

 material or silage will then usually keep almost indefinitely, 

 providing air does not gain access. 



A considerable rise in temperature may take place in the 

 silo during the process of fermentation. If this increase 

 is excessive it usually indicates that there is not sufficient 

 moisture present and the material has not been tightly 

 enough packed. The lactic acid fermentation does not give 

 rise to quantities of heat comparable with the amount 

 developed during oxidative changes occurring due to the 

 growth of molds and bacteria in the presence of atmos- 

 pheric oxygen. The surface layers of silage usually become 

 quite warm, for air can penetrate to the depth of several 

 feet. These, therefore, can be preserved only by covering 

 the surface carefully with something which will exclude the 

 air. 



