YEASTS, OR SACCHABOMYCETES 235 



YEASTS, OE SACCHAROMYCETES. 



The yeasts, or Saccharomycetes, are a group of organisms 

 of the greatest importance on account of their connection 

 with the great process of fermentation. They are round 

 or oval cells, which generally multiply by gemmation or 

 budding. Eeproduction by gemmation consists of the 

 budding out of daughter-cells in different places from the 

 gradually enlarging parent-cell. The buds formed become 

 divided from the parent-cell by a diaphragm, but some- 

 times they remain adherent, forming a chain. The cells 

 containing granular protoplasm are surrounded by a thin 

 membranous wall, and often exhibit in their interior one 

 or more colourless lacunae, known as vaciioles, which 

 probably consist of fat globules. So long as the conditions 

 remain suitable, the saccharomycetes invariably multiply 

 by gemmation, but in presence of lack of nourishment, 

 such as, for instance, if the cells are washed free from 

 nutrient material, or are placed on a moist porcelain or 

 plaster of Paris surface, a most remarkable change in the 

 constitution of the cells is seen to take place. In about 

 twelve hours or so, the time varying with different species, 

 the cells will be seen to have increased in size, their con- 

 tents to have become homogeneous, and in the course of a 

 few more hours such cells are found to contain two to four 

 shining spots, which become more spherical and surround 

 themselves with a thick membrane. In the course of time 

 these new cells or ascospores, as they are called, become 

 liberated by dissolution of the mother-cell. On introducing 

 these spores, which are 4 to 5 m in diameter, into a sac- 

 charine liquid, they germinate and multiply, as usual, by 

 gemmation. Sometimes the growth of the saccharomycetes, 

 especially on solid media, by the growth of the cells in the 

 form of chains, gives rise to a misleading appearance re- 



