NUTRITION 
147 
the action of the 
cilia, the direc¬ 
tion being due 
to the angle at 
which the cilia 
are held. It can 
be observed that 
the animals move 
backward and 
forward, and that 
they also rotate 
on the long axis. 
Paramecia de¬ 
fend themselves 
by discharging 
their trichocysts. 
This discharge 
occurs either as a result of certain strong artificial stimuli, 
such as electric currents or chemicals, or naturally because of 
collision with certain other Protozoa. If attacked by some 
animal which feeds upon 
them, they discharge the 
trichocysts in the region 
of the attack (Figure 
136). 
120. Nutrition. — The 
paramecium, like all 
other living things, re¬ 
quires food, which con¬ 
sists mostly of bacteria. 
These are collected by 
means of the cilia located 
on each side of the fold or 
depression called the 
gullet. At the inner end 
' * % - 
% , 5* - 
v y/" \f i 
** f • 
- $ * * ;■ 
Figure 137 . — Paramecium Stained to 
Show the Nucleus (Photomicrograph). 
Figure 136 . — Paramecium. 
Being attacked by another protozoon that fe'eds 
upon it. The trichocysts are discharged, and they 
force the foe away. 
