STRUCTURE OF PROTOPLASM OF PARAMCECIUM 25 



extreme delicacy of the adjustment between the physical structure 

 of the protoplasm and the external conditions has hardly been 

 recognized. For example, the smallest perceptible elevation of 

 temperature above the normal results in a decided increase in the 

 fluidity of the protoplasm, and it is probable that this structural 

 change explains the extreme sensitiveness of the paramcecia, 

 judged by their thermotropic reactions, to these same variations 

 in the temperature. 



2. Gafaanotaxis. It has been well known that paramcecia 

 normally react to the electrical current in a vigorous and definite 

 manner by orienting themselves with their anterior end toward 

 the cathode, and swimming rapidly in this direction, so that 

 eventually a dense gathering of the organisms occurs about the 

 negative electrode. In other words they collect at that point in 

 the electrical field where the conditions are such as to induce a 

 liquefaction of the protoplasm. After a weak current has been 

 passed through the preparation for from thirty minutes to one 

 hour, it will be seen that the dense gathering at the cathode 

 begins to break up and a reverse movement toward the anode 

 sets in. The number of paramcecia that exhibit this reverse 

 movement varies with the conditions of the organisms at the time 

 of the experiments, as will appear later ; but with paramcecia 

 from alkaline cultures only a small proportion of the entire num- 

 ber will be seen to swim toward the anode at any one time. At 

 first the paramcecia swim only a short distance toward the anode 

 and then immediately dart back to the cathode, but the length of 

 the reverse reaction increases until a few reach the anodal end of 

 the dish. Having arrived at the anode, they immediately swim 

 back to the cathode again, and no gathering occurs at the anode 

 except in rare cases after the current has been passed for about 

 two hours. The paramcecia normally keep the anterior end 

 pointed always toward the cathode, so that they swim backwards 

 toward the anode. But this is not always the case. 



After a large number of experiments with paramcecia under 

 various conditions, I find that the relations between this initial 

 and secondary reaction to the current may be greatly modified. 

 With paramcecia from alkaline cultures, the secondary reaction 

 begins only after the current has been passed for thirty minutes 



