THE PREPARATION OF FARM PRODUCTS. 303 



What then is the cause of the fermentation ? A partial 

 answer has been given as follows : The living plant cell is 

 always carrying on the physiological process of respiration, a 

 process quite similar to respiration in animals, and resulting in 

 the use of oxygen and the evolution of carbon dioxide. In 

 this respiration carbohydrate bodies are used, with some 

 albuminoids as well, and a certain amount of heat is evolved. 

 Now the plant cells do not die when the plant is cut down, 

 but continue for some considerable time to carry on this process 

 of respiration. Cutting the plant to pieces appears, indeed, to 

 increase temporarily, rather than to decrease, the respiratory 

 changes. These may go on for several days, until, indeed, 

 the plant cells are fully dead. These are well-known facts, 

 recognized by botanists for a long time. 



To these respiratory changes is due part of the fermentation 

 of silage. After the material is packed in the silo the plant 

 cells remain alive for several days and carry on these respira- 

 tory changes as long as they are alive and have oxygen at 

 their command. This results in the gradual oxidation of the 

 carbohydrate material and the evolution of carbon dioxide. 

 A study of the gas evolved from the silo while it is undergo- 

 ing the preliminary heating, shows it to be almost pure car- 

 bon dioxide. This fact clearly indicates that the fermentation is 

 not putrefactive and probably is not due to microorganisms, 

 since they would almost always give rise to other gases along 

 with the carbon dioxide, ammonia or some other nitrogen-hold- 

 ing gas being commonly the result of bacterial fermentation. 

 These respiratory changes are thought to be fully sufficient to 

 explain the initial changes in the silage, with the initial heat- 

 ing and evolution of gas. 



In regard to the later changes in silage we can say less. 

 The formation of acid, hitherto attributed to acid bacteria, is re- 

 garded by Babcock and Russell as wholly independent of these 

 organisms. They regard it as due to some changes which 



