IV 

 YEAST 



[1871] 



IT has been known, from time immemorial, that 

 the sweet liquids which may be obtained by ex- 

 pressing the juices of the fruits and stems of 

 various plants, or by steeping malted barley in hot 

 water, or by mixing honey with water are liable 

 to undergo a series of very singular changes, if 

 freely exposed to the air and left to themselves, in 

 warm weather. However clear and pellucid the 

 liquid may have been when first prepared, however 

 carefully it may have been freed, by straining and 

 filtration, from even the finest visible impurities, 

 it will not remain clear. After a time it will 

 become cloudy and turbid ; little bubbles will be 

 seen rising to the surface, and their abundance will 

 increase until the liquid hisses as if it were sim- 

 mering on the fire. By degrees, some of the solid 

 particles which produce the turbidity of the liquid 



