How do they 
multiply? 
52 WORLD OF INVISIBLE LIFE 
When the mold changes color from the first 
white growth, to blue-green, brown, black, or 
red, it is forming the seeds or spores by which 
it multiplies itself. The tiny seeds or spores 
grow on the surface of the mold; they are so 
small and light that they are blown into the 
air by the lightest air current. As a result, 
they are nearly always floating in the air, and 
may drop upon any substance that contains food 
material for them. There they will grow into 
molds again, if the proper conditions of damp¬ 
ness and warmth exist. 
The sour taste of vinegar is due to large 
quantities of a substance called acetic acid . 
This acetic acid is produced from alcohol by 
the activity of a special group of microbes. 
Vinegar usually comes from cider, which is 
apple juice that has been fermented, and so 
contains a small amount of alcohol. The 
change is brought about by the growth of 
microbes forming a slimy brownish mass, 
known as “mother of vinegar,” on the surface 
of the cider during the change. When this 
Apple juice with the 
help of certain microbes 
will form vinegar 
