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THE BEGINNINGS OF LIFE. 



421 



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absent, occasional instruments, or necessary conco- 

 mitants in processes of fermentation. Thus there are 

 [a] chemical changes which are essentially fermentative 

 in nature, with which organisms are never known to 

 be associated : to this class belongs the conversion of 

 cellulose into dextrine and glucose under the influence 

 of heat and sulphuric acid. There are other {b) fermen- 

 tations that may be initiated by ordinary physical or 

 chemical agencies alone, or which may be brought about 

 by the agency of living organisms. Examples of such 

 changes are the conversion of salicin into glucose 

 and saligenin, which may be produced either by con- 

 tact with dilute sulphuric acid or by the influence of 

 yeast {Torula) ^ and also the acetous fermentation, 

 which may be induced either by bringing alcohol 

 into contact with certain dead oxidising agents, or 

 by subjecting it to the influence of a living fungus 

 [Mycoderma). Whilst there is a third set {c) of changes 

 in which the transformative processes are invariably 

 associated with the presence of organisms ; the most 

 familiar examples of this class being the putrid and 

 vinous fermentations. Although these latter may be 

 initiated by the agency either of dead or of living 

 ferments, living matter is one of the invariable products 

 of the fermentative changes 1 : during their progress 



^ ' ScUossberger observed that many juicy fungi (for example Agarkns 

 rnssiila, &c.), when kept in narrow-mouthed, open flasks, underwent 

 vinous fermentation spontaneously, and that alcohol could be obtamed 

 from the expressed liquid on distillation ; meanwhile true yeast-cells were 



