72 MICKOBES, FEKMENTS, AND MOULDS. 



ganized ferment has been ascertained, that ferment is 

 necessary. This minute being produces the transforma- 

 tion which constitutes fermentation by breathing the 

 oxygen of the substance to be fermented, or by ap- 

 propriating for an instant the whole substance, then 

 destroying it by what may be termed the secretion 

 of the fermented products. Three things are necessary 

 for the development of the ferment: nitrogen in a 

 soluble condition, phosphoric acid, and a hydrocarbon 

 capable of fermentation (such as grape sugar). Finally, 

 every organized ferment of fermentation or putrefac- 

 tion is borne about in the air, as may be shown by 

 experiments. 



II. VEGETABLE NATUEE OF FERMENTS OR YEAST. 



Yeast, or ferments, are in their organization 

 closely allied to the fungi of which we spoke in the 

 preceding chapter under the name of Microsporon. 

 Many botanists still assign them to the class of fungi 

 under the name of Saccharomycetes ; yet, as they live 

 in liquids, or at any rate on damp substances, like the 

 Algse, which are species of water-fungi, it is now 

 almost agreed to place them in the same category as 

 the latter, which they resemble in their whole organi- 

 zation, except in the absence of chlorophyl. This 

 last characteristic, the only one by which they ap- 

 proximate to fungi, is common both to them and to 

 microbes or bacteria, which are only ferments of 



