20 
WORLD OF INVISIBLE LIFE 
How do 
microbes 
move about? 
How do they 
grow? 
Some microbes cannot move about at all, 
while others move only when grown in certain 
substances. Their ability to move around de¬ 
pends on their having a tiny hair-like fringe, 
which the microbe waves back and forth and 
so travels through the liquid. These hairs are 
called flagella. Some microbes have many 
more flagella than others. The typhoid bacillus 
has ten or twelve, while the colon bacillus, its 
near relative, has only from two to six. Many 
kinds of microbes have these hairy fringes, and 
so can move about wherever they please. Even 
their rate of speed has been roughly measured. 
The typhoid bacillus can travel about 2,000 
times its own length in an hour, and the cholera 
spirillum, for a short distance, can go as fast 
as seven and a half inches per hour. 
Microbes increase rapidly. A young cell 
grows to full size in less than an hour. That 
is much quicker than any other form of life 
reaches full size. Most microbes multiply them¬ 
selves by simply splitting into two or more 
pieces, which sometimes remain connected in 
