FERMENTS AND ARTIFICIAL FERMENTATIONS. 79 
all the ferments, and may be regarded as the type of 
the family. Its cells are round or oval, from eight 
to nine micro-millimetres in their longest diameter, 
isolated or united in pairs (Fig. 35). 
When these cells are deposited in a saccharine 
liquid, which is therefore susceptible to fermentation, 
vesicular swellings, filled with protoplasm at the 
expense of the mother cell, may be observed at one 
Fig. 45. —Yeast of superior beer Fig. 46.—Spores of beer-yeast, in 
budding (x 40v diam.). different phases of development. 
or two parts of the surface of the cell; these swellings 
increase, acquire the size of the mother cell, and then 
contract at their base (Fig. 45). They generally arise 
on the sides of the cell, more rarely on its extremities. 
The new cells thus formed soon separate from the 
mother cell, and the protoplasm given up to its off- 
spring by the latter is replaced by one or two empty 
spaces, termed vacuoles. When yeast is not in a 
liquid susceptible to fermentation, it can remain for 
a longer or shorter time without modification. If 
abruptly deprived of all nutriment, and especially of 
sugar, and placed in a sufficiently moist atmcsphere, 
