16 
WORLD OF INVISIBLE LIFE 
How can we 
grow them 
for ourselves? 
various stages of development. The separation 
is accomplished by growing our own microbes. 
For instance, we take some of the cloudy water 
which we looked at under the microscope, and 
which we found contained many different kinds 
of microbes. We pour it over some substance 
that contains the proper kind of food for the 
microbes. 
The most common material is a kind of gela¬ 
tin, but we could use slices of raw potato, or 
milk, beef broth, or several other foods just as 
well. The gelatin is poured into a dish where 
it jells. After a few days many spots appear 
on its surface. Then we take a platinum needle 
set in the end of a glass rod and pass it through 
a flame to kill all the microbes on it. We touch 
one of the spots with the point of the needle 
and then touch another dish of gelatin, the sur¬ 
face of which has been sterilized; that is, made 
clean. 
After a few more days, a spot will appear on 
the second gelatin containing only the particu¬ 
lar kind of microbe which formed the spot we 
