72 THE BEHAVIOR OF PROTOZOA 
By the action of its cilia Paramecium swims through the 
water in a spiral course, rotating on its long axis to the left 
and keeping the oral side facing the center of the spiral. 
At times Paramcecium may swim backward, by reversing 
the effective stroke of the cilia, although the direction of 
rotation is unchanged. 
Paramcecium is a common organism in vegetable infu- 
sions, where it subsists upon bac- 
teria which are swept by cilia into 
its gullet. There seems to be little 
power of choice as to what sub- 
stances are taken in; particles of 
India ink and carmine are swept in 
and swallowed in the same way as 
its normal food, and the organism 
selects its food only by swimming 
elsewhere when the materials swept 
in are unsuitable. Metalnikow, 
however, states that when Par- 
amoecia are fed with carmine for 
fifteen days they gradually take 
in less of this substance and finally 
refuse it. Metalnikow’s experiments 
were repeated by Schaeffer who 
: failed to confirm these results when 
ee area the carmine was kept in a condi- 
: “tion such that it could be readily 
ingested. Occasional individuals, however, failed to take 
in any of the substance, but examination showed that they 
were deformed or had recently divided so that the oral ap- 
paratus was not capable of sweeping in food. After thirty- 
three days the Parameecia failed to show any appreciable 
diminution in the carmine ingested. 
