24 THE MICROSCOPE. Fab. 



the daughter-cell, eventually separating from the larger 

 one, the mother cell. This separation may not occur until 

 after the daughter-cell or "bud" has begun to produce 

 daughter-cells itself. The connection between the mother 

 and daughter cells may persist for several generations if 

 the yeast be growing actively. Size ? S. cerivisisB 6-8 

 microns in diameter, 5-11 long. S. pastorianus T 8 microns 

 in diameter. 



Another method of reproduction is possessed by yeast : 

 that of endogenous division or formation of ascospores. 

 Under certain conditions the protoplasm within the cells 

 divides into two, three, or four rounded bodies, that be- 

 come surrounded by a cell-wall, thus giving rise to a num- 

 ber of cells within the original cell; this latter is called 

 an ascus, the contained cells, ascospores. 



In brewing there are two varieties of yeast employed 

 which produce charcteristically different fermentations, 

 and are known as top and bottom yeasts. The top yeast 

 works at a comparatively high temperature ; the action 

 is rapid, and the yeast is at the surface of the liquid. 

 This top yeast is used in the brewing of ale and porter. 

 The bottom yeast works at low temperature, the action 

 is slow, and the yeast is at the bottom of the liquid. The 

 bottom yeast is used in the brewing of lager beer. 



There are also what are known as " wild " yeasts in dis- 

 tinction from those that are cultivated. To the wild yeasts 

 are due the fermenting of fruit juices ; as, grape and 

 and apple. Sweet cider Avill always shoAv, under the 

 microscope, one of these characteristic forms. The yeast 

 is found on the skin of various fruits, and on the ground 

 under the trees ; from here it can be carried as a fine 

 dust by the wind. It is supposed that the cultivated 

 varieties of yeasts originated from these wild forms, 

 though notwithstanding their frequency, I have never 

 been able to get one from flour, but have gotten the hay 

 bacillus, B. subtilis, in large quantities. 



