STROyCr hniNK and tobacco smoke. 49 



temperature of 77° appears to be most favom*al»le to 

 its oTowtli. Bottom yeast does not present tliis appear- 

 ance of budding, tlie cells multiplying most rapidly at 

 a temperature between 32° and 48° F. 



Ale yeast is generally considered the l)est and 

 strongest, and is preferred by bakers. Porter yeast is 

 used in distilleries. There is a very curious fact vouched 

 for by the importers of German and Dutch yeast, and 

 that is that mechanical injury kills or destroys it ; it is 

 for this reason imported in bags placed in baskets, and 

 if these be allowed to fall violently on the ground the 

 yeavSt is spoiled. Yeast thus injured may be distin- 

 guished by its dark colour ; and from being crumbly 

 or powdery, it becomes soft and glutinous, and sticks 

 to the fingers like flour-paste. Its appearance under 

 the microscope remains unaltered. 



When yeast, or the yeast plant, is added to a saccharine 

 solution, such as brewers' worts, a singular and violent 

 action takes place, during which the plant multiplies 

 itself, as we have seen, prodigiously. At the same time, 

 the saccharine matter of the worts becomes decomposed 

 during the growth and multiplication of the plant ; and 

 its elements, carl3on, hydrogen, and oxygen, re-arrange 

 themselves and become alcohol, carbonic acid gas, and 

 water. This process is known as fGrmentation, and 

 requires simply the addition of yeast to a saccharine 

 solution to produce it. 



No very satisfactory solution has yet been arrived at 

 of the exact nature of the forces set in motion by the 



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