FERMENTATION 329 



The ferment remains the same, qualitatively, both before 

 and after the reaction. Hence we may class many bodies 

 as ferments to which the word ' ferment,' as meaning a 

 / boiling,' is misapplied. 



All ferments possess three properties : 



1". They are nitrogenous organic bodies. 



2. They are unstable ; that is to say, they are destroyed 

 by reagents, such as heat, acids, etc. 



3. A relatively small quantity of the ferment is capable 

 of producing great changes in the body acted upon, especi- 

 ally if the products of the change be removed as they are 

 formed. 



Ferments can be divided into two classes, as follows : the 

 formed or organised ferments, and the unformed, ' soluble ' 

 ferments, or enzymes. 



(a) The Formed or Organised Ferments. — These have a 

 definite organized structure, and are capable of indepen- 

 dent growth and multiplication. They include : 



1. The yeasts, or saccharomycetes. 



2. The moulds, or fungi. 



3. The bacteria proper, or schizomycetes. 

 Fermentation by Yeasts. — From time immemorial brewers 



have been famihar with the art of preparing beer from an 

 infusion, or 'wort,' of malted barley. This infusion, or 

 'wort,' if left alone, soon putrefies, becomes muddy and 

 covered with a floating film, emits a disagreeable smell, 

 and assumes an offensive flavour. Experience has, how- 

 ever, shown that the wort can be made into excellent 

 beer by the addition of a little yeast, the remains of a 

 previous operation, which the brewer can always find in 

 the receptacles in which new beer is kept. Under the 

 influence of this yeast an internal working in the mass 

 occurs, gas is disengaged, producing effervescence, the sweet 

 taste disappears, and is replaced by the characteristic 



