FERMENTATION. 381 



do so on the application of a small amount of some fer- 

 ment. This ferment may be either of the albuminous sub- 

 stances gluten, albumen, or casein. 



The manner in which these bodies act in exciting fer- 

 mentation is very imperfectly understood; "they neither 

 add any thing to the fermenting body nor take any thing 

 away from it, but the motion or disturbance of their par- 

 ticles, while undergoing putrefaction, is supposed to be 

 communicated to the particles of the fermenting body with 

 which they are in contact, and thus induce decomposition." 

 Fermentation is always accompanied by the growth of 

 organized bodies called fungi when vegetable, and infu- 

 soria when animal. In fact, their development is regarded 

 as the exciting cause of fermentation and putrefaction. 



537. The Chemical Change in Alcoholic Fermentation. 

 Alcohol is composed of the same elements as sugar, but 

 in different proportions. The production of alcohol by the 

 fermentation of sugar is not really a conversion of sugar 

 into this substance, but a splitting up of the sugar into al- 

 cohol and carbonic anhydride. Cane-sugar does not thus 

 break up, but is converted first into glucose, or grape-sug- 

 ar, and this is decomposed in the following manner: 



Grape-sugar. Alcohol. Carbonic anhydride. 

 C 6 H la O 6 = 2C 2 H 6 O + 2CO 3 " 



Some other substances are formed at the same time, but 

 only in small quantity ; and their production has been dis- 

 regarded in the equation. 



538. Yeast. What is commonly called yeast is really a 

 growth, for yeast is a collection of very minute plants ; so 

 minute that it is estimated that a cubic inch contains twelve 

 hundred millions of them. This plant, revealed to us by 

 the microscope, multiplies itself with exceedingly great 

 rapidity, and will continue to do so as long as there is ni- 

 trogenized matter to supply it with the means of growth. 



