THE UNIVERSE OF LITTLE THINGS. 209 
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a 
Another class looks like marbles, and the third 
class has spiral forms. Each class appears to contain 
varieties innumerable, differing 
slightly in shape, but still hav¬ 
ing the general form. The 
rod-shaped forms were prob¬ 
ably the first to he studied, for 
all these organisms have been 
named bacteria (bacterium is 
the Greek for stick). 
You may ask. How do we 
know that they are organisms ? 
It would be an easy matter to 
convince you if you could see 
them through the microscope 
for half an hour. If we take a 
little fine dust from that which 
sticks to the window-pane and 
place it under a magnifier, we might watch it for 
hours, but it would always appear the same. On the 
other hand, if we 
take a drop of milk 
a day old, which 
has been freely ex¬ 
posed, and put it 
under the same 
magnifier, we 
should see some 
little things dan¬ 
cing up and down, others moving in a straight course 
or in a serpentine path, to and fro, in the milk. 
Fig. 101. —General shapes 
of bacteria, a, spher¬ 
ical forms ; b, rod¬ 
shaped forms; c, spiral 
forms. (From Conn’s 
Germ Life.) 
Fig. 102.—Method of multiplication of 
bacteria, a and b, bacteria dividing 
by fission. 
