226 THE POPULAR SCIENCE MONTHLY. 



bonic acid, it appears that any vegetable cells which are capable of 

 extracting their needed supply of oxygen from organic combinations 

 may, by this manifestation of their vital activity, act as ferments, 

 and the true ferments are distinguished from these, not by a differ- 

 ence in their specific action, but from the fact that they are capable 

 of carrying on the functions of nutrition and assimilation with much 

 greater activity without a supply of atmospheric oxygen. Pasteur 

 has likewise proved that the alcoholic ferments develop rajjidly im 

 the presence of air, but that their function as ferments is impaired by 

 this ready supply of oxygen. In the absence of air, on the other hand, 

 as in an atmosphere of carbonic acid, they take their supply of oxygen 

 from organic substances, as sugar, and their function as ferments is 

 increased. When the life of the bacteria or other organized fer- 

 ments is destroyed, the processes of fermentation and putrefaction 

 cease, and this takes place at a temperature of from 122° to 140°, 

 according to observations made in the course of the controversy in 

 regard to spontaneous generation. After the organized ferments are 

 killed, fermentation or putrefaction can not take place until the living 

 ferments are asjain introduced. The canned articles of food which 

 are now so common in the markets are an illustration of the applica- 

 tion of this principle. In their preparation heat is applied, which 

 kills the bacteria — the active agents of fermentation — and the cans are 

 then sealed to prevent the introduction of a fresh supply of germs 

 from the atmosphere. The popular notion that canned articles of food 

 are preserved by excluding the atmospheric oxygen, which has been 

 derived from the application of Liebig's chemical theory of fermenta- 

 tion, is without foundation. The experiments of Schwann, Pasteur, 

 and Tyndall conclusively prove that articles which are peculiarly lia- 

 ble to undergo putrefactive changes, as urine, and an endless variety 

 of vegetable and animal infusions, can be kept without change for 

 months and years when abundantly supplied with free oxygen, if 

 proper precautions are taken to exclude the living organisms that are 

 the real cause of fermentation. These experiments have likewise 

 proved that the germs of the bacteria of fermentation and putrefac- 

 tion are widely distributed in the air, and the supposed cases of spon- 

 taneous fermentation, or putrefaction, are readily explained by the 

 " seeding " of the fermenting substances with germs derived from the 

 atmosphere. 



As fermentation is strictly a physiological process, the fermented 

 product may be looked upon as the residuum of what is required in the 

 nutritive processes of the bacteria of fermentation. 



The variations in the quality of ensilage, to which attention has 

 already been dii'ected, are readily explained by differences in the con- 

 dition of the crops, as to maturity and development, and the manner 

 in which it is packed in the silo, all of which must have an influence 

 on the performance of the nutritive functions of the bacteria, and cor- 



