VEGETATION OP YEAST. 51 



55. Another very curious example of vegetation of a fungous 

 character, in a situation where its existence was not until recently 

 suspected, is presented in the process of fermentation. It ap- 

 pears from microscopic examination of a mass of yeast, that it 

 consists of a number of minute disconnected vesicles, which 

 closely resemble those of the Red Snow, and appear to consti- 

 tute one of the simplest possible forms of vegetation. These, 

 like seeds, may remain for almost any length of time in an 

 inactive condition, without losing their vitality ; and their power 

 of growing, when placed in proper circumstances, is not destroyed 

 by their being entirely dried up, nor by their being exposed to 

 such extremes of temperature, as the boiling point of water and 

 seventy-six degrees below zero. When these bodies are placed 

 in a fluid, in which any kind of sugary matter is contained, they 

 commence vegetating actively, provided the temperature be 

 sufficiently high ; and the decomposition which they effect in the 

 fluid, the nature of which will be presently explained, is that 

 which constitutes its fermentation. 



56. If a small portion of a fluid in this state be examined at 

 intervals, with a powerful microscope, it is observed that each of 

 the little vesicles contained in it puts forth one or more pro- 

 longations or buds, which in time become new vesicles like their 

 parents ; these again perform the same process ; so that, within a 



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FIG. 18. DIFFERENT STAGES OF THE VEGETATION OF YEAST ; a, single cells of which it 

 at first consists ; 6, cells with buds ; c, the same more advanced ; d, rows of cells 

 corresponding to those of Fig. 9. 



few hours, the single vesicles have developed themselves into 

 rows of four, five, or six. This is not the only way, however, 

 in which they multiply ; for sometimes the vesicles are observed 

 to burst, and to emit a number of minute granules, which are the 

 germs of new plants, and which soon develop themselves into 



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