60 THE TROPISMS 
inserted in the two sides of a drop of water containing 
Parameecia the infusorians will soon all collect around the 
negative pole. In solutions of sodium chloride and certain 
other salts Paramcecium frequently swims backward 
toward the anode, and Bancroft has found that true anodal 
electrotaxis, in which the infusorians swim forward toward 
the anode, may occur for a short time in solutions of sodium 
chloride, sodium carbonate and other salts if the Para- 
mcecia are washed in distilled water before being placed in 
the solutions. 
Electrotaxis has been observed in ccelenterates, worms, 
mollusks, crustacea, the larve of insects and in fishes, tad- 
poles and salamanders. In general the reaction of worms 
and mollusks is negative and the reaction of crustacea 
positive. In tadpoles which orient their bodies parallel 
with the direction of the current the direction of orientation 
is dependent upon the strength of the current. 
Orientation to the electric current is apparently brought 
about by the polar effect of the current upon the tissues of 
the body. In Paramcecium there is a direct orientation pro- 
duced by the unequal beat of the cilia on the two sides. In 
cathodal orientation the forward phase of the stroke of the 
cilia is accentuated where the current leaves the body so that 
there may be a reversal of the effective stroke; where the 
current enters, the backward stroke continues so the organism 
naturally swings into line with the current. In higher organ- 
isms there is a distinctly evident polar effect upon the 
musculature of the body which can be seen to produce the 
orientation of the organism. The effect of the electric 
current on animals generally is to produce movements 
which are in a certain sense “forced,” and the orientation 
so brought about affords an excellent example of a typical 
tropism as conceived by Dr. Loeb. 
