viz.] Relation to the substratum. Fermentation. 67 



is a Sprouting Fungus, a Fission-fungus, that is a Bacterium, or 

 a Filamentous Fungus, it is shortly termed Sprouting Yeast, 

 Fission Yeast, or Filamentous Yeast. The French system of 

 terminology limits the application of the French word levure, 

 which had originally the same meaning as the German Hefe and 

 English yeast, to the Sprouting Fungi which excite fermentation. 

 It is essential to the understanding of the literature to observe 

 that the German Hefe, English yeast, is used in quite different 

 senses ; it must be added also, that the same word is applied not 

 only to the ferment- organism simply, or to the particular form 

 of Sprouting Fungus which excites fermentation, but also to all 

 forms of Sprouting Fungi whether they excite fermentation or 

 not, thus often causing very needless confusion. 



We shall speak again presently of the different meanings of 

 the word ferment. 



Since the vegetation of organisms sets up fermentation, the 

 substratum in which the fermentation is to take place must 

 contain all the nutrient substances necessary for the process of 

 vegetation. A pure saccharine solution, for example, does not 

 ferment if a small quantity of fermentation-exciting Fungi or 

 Bacteria also in a pure state is introduced into it. The sugar, as 

 we have seen, is a good nutrient material for these organisms. 

 But it only supplies the necessary amount of carbon, the elements 

 of water, and free oxygen, and is therefore imperfect as food. It 

 is only when the compounds which supply the nitrogen men- 

 tioned above and the ash-constituents are added to the solution 

 that it is rendered capable of fermentation, and fermentation 

 commences as soon as the conditions favourable to vegetation 

 are secured. Bodies which in the natural course of things or 

 when artificially prepared have finished fermenting, such as 

 must or brewers' mash, are proper food for ferment- 

 organisms. 



In every process of fermentation there is first of all a growth, 

 a multiplication of the exciting organism at the expense of the 

 fermenting substance. This can be seen by direct observation 



F 2 



