Is yeast 
alive? 
54 WORLD OF INVISIBLE LIFE 
may wonder why we talk about yeast as one 
of the microbes. But yeast is just as much a 
tiny living thing as any of the other microbes. 
What we see in a cake of yeast is a group of 
millions of tiny yeast plants massed together. 
A single yeast plant is much too small to see 
with the unaided eye. It is somewhat larger 
than many other microbes, but it is not much 
more than 1/2800 of an inch across, and so 
can only be seen through a microscope. It is 
an egg-shaped body, quite colorless, and nearly 
transparent under the microscope, though 
whitish when seen in a large group. 
The yeast plants in a yeast cake are in a 
resting state; that is, they are alive but not 
growing. They grow and multiply, in a way 
called budding, when placed in water contain¬ 
ing the proper kind of food. On the sides of 
the egg-shaped plant small buds appear as 
little swellings. They grow until they are as 
large as the original plant, and after a time 
they drop apart. Then all the new cells, or 
plants, grow just as the original one did and 
