158 MICRO-ORGANISMS AND FERMENTATION. 



The whole behaviour suggests the zoogloea-formation of 

 bacteria. 



The Microscopic Appearance of a Yeast-cell. As an 

 introduction to the systematic description of the separate 

 species of Saccfiaromyces, we give the following general 

 description of the Saccharomyces cell. 



The microscopic appearance of a yeast cell as it most 

 frequently occurs in a fermenting liquid is a spherical or oval 

 figure, which, by the swelling out of its wall, gives rise to one 

 or more buds, which detach themselves sooner or later from 

 the mother cell. This cell is consequently surrounded by a 

 membrane which can vary somewhat in the different stages 

 of the development of the cell, but rarely in a noticeable 

 degree. It is otherwise, however, with the contents of the 

 cell. The contents present the simplest appearance when the 

 cell is observed in its most vigorous state of growth. The cell- 

 contents then consist of clear homogeneous plasma. As the 

 processes of multiplication and fermentation continue, different 

 bodies appear in this plasma; partly clear portions filled with 

 sap (vacuoles), partly larger and smaller particles, some of 

 which can be shown to be fat globules, whilst others appear to 

 be of a similar nature to the plasma. These granules have been 

 minutely described by Raum. This granular appearance of the 

 plasma increases with the further development of the cell, and 

 at a very advanced stage of the fermentation, when the cell has 

 almost come to a state of rest, the plasma may become reduced 

 to a thin layer on the inner side of the wall, whilst a large 

 vacuole occupies the remaining space, and contains numerous 

 small and large grains, many of a fatty nature. If such cells 

 are again brought into a fermentable liquid, they soon exhibit 

 a highly characteristic appearance during the period which 

 precedes the macroscopic phenomena of fermentation. The 

 grains disappear, and numerous fine plasma-threads appear in 

 the clear cell-sap, and gradually circumscribe rounded 

 vacuoles ; finally these disappear, and the cell again becomes 

 filled with clear homogeneous plasma- 



