84 OUR BODIES AND HOW WE LIVE 



expense of our fruits ; and another develops itself on 

 paper, on the inside of books, and on their bindings, 

 when they come in contact with a damp wall. Some forms 

 of skin disease, like ringworm, are caused by the growth 

 of this microscopic plant on the skin. 



FIG. 57. A Piece of Bread upon which One of the Common Molds, 

 known as Mucor, is growing. 



125. Different Forms of Fermentation. There is no one 

 particular form of bacteria which can be called the micro- 

 organism of fermentation, but there are a number of fer- 

 mentations each started by some special form of agent. 

 We must remember, however, that fermentation nearly 

 always consists of a process of breaking down of complex 

 bodies, like sugar, into simpler ones, like alcohol and car- 

 bonic acid. Of these fermentations we have the alcoholic, 

 by which alcohol is produced ; the acetous, by which wine 

 absorbs oxygen from the air and becomes vinegar; and the 



