60 SILOS, ENSILAGE AND SILAGE. 



its own processes of nutrition, will serve to check its 

 yital powers, and at the same time prove of immediate 

 advantage to some other species. 



Many illustrations might be given of the well known 

 fact that a repression of the vital powers, and even the 

 death of an organism may be caused as a direct result of 

 the exercise of its own normal activities. In a confined 

 atmosphere animals are killed by the carbonic acid ex- 

 haled in the process of respiration. Yeast is an alcoholic 

 ferment, but its activity as a ferment is checked or en- 

 tirely suppressed by an accumulation of the alcohol re- 

 sulting from its own processes of nutrition. " The wines 

 produced from the rich juices of Southern grapes always 

 contain unfermented sugar," * the alcohol produced be- 

 ing sufficient to stop the process of fermentation before 

 the sugar is all consumed. 



When lactic acid is allowed to accumulate beyond a 

 certain amount, the lactic ferment ceases to perform its 

 function ; the microbes of nitrification are unable to act 

 as ferments in the absence of lime or some other salifi- 

 able base to combine with the nitric acid as it is elabo- 

 rated, and under such conditions they are superseded 

 by other forms that have no such special requirements. 

 One ferment may thus succeed another, as the condi- 

 tions of life are changed to favor it and restrain the 

 activities of its predecessor. The process of putrefaction 

 is not a single fermentation produced by any single spe- 

 cific form, but an indefinite series of fermentative 

 changes brought about by a succession of microbes, 

 each of which, in its processes of nutrition, prepares the 

 way for those that follow, until, by their combined 

 action, the putrefactive materials are reduced to their 

 simplest chemical combinations. 



The temperature most favorable for the activity of 

 bacteria will yary with the species, the conditions of 



* Encycl. Brit. 9th ed. 1 x p. 94. 



