THE BEHAVIOR OF INFUSORIA; PARAMECIUM 47 



methyline blue, or by using in the same way water containing India 

 ink. Or if a cloud of India ink, with a definite boundary, is produced 

 in the water containing swimming Paramecia, a cone of the ink is seen 

 to move out to meet the advancing animals (Fig. 35). Thus Parame- 

 cium is continually receiving " samples " of the water in front of it. 

 Since in its spiral course the organism is successively pointed in many 

 different directions, the samples of water it receives likewise come suc- 

 cessively from many directions (Fig. 33). Thus the animal is given 

 opportunity to "try" the various different conditions supplied by the 

 neighboring environment. Paramecium does not passively wait for 

 the environment to act upon it, as Amoeba may be said, in com- 

 parison, to do. On the contrary, it actively intervenes, determining 

 for itself what portion of the environment shall act upon it, and in 

 what part of its body it shall be primarily affected by the varying con- 

 ditions of the surrounding water. By thus receiving samples of the 

 environment for a certain distance in advance, it is enabled to react 

 with reference to any new condition which it is approaching, before it 

 has actually entered these conditions. 



4. Reactions to Stimuli 



Let us suppose that as Paramecium swims forward in the way just 

 described, it receives from in front a sample that acts as a stimulus, — 

 that is perhaps injurious. The ciliary current brings to its anterior 

 end water that is hotter or colder than usual, or that contains some 

 strong chemical in solution, or holds large solid bodies in suspension, or 

 the infusorian strikes with its anterior end against a solid object. What 

 is to be done? 



Paramecium has a simple reaction method for meeting all such 

 conditions. It first swims backward, at the same time necessarily / 

 reversing the ciliary current. It thus gets rid of the stimulating agent, 

 — itself backing out of the region where this agent is found, while it 

 drives away the stimulus in its reversed ciliary current. It then turns 

 to one side and swims forward in a new direction. The reaction is 

 illustrated in Fig. 36. The animal may thus avoid the stimulating 

 agent. If, however, the new path leads again toward the region from 

 which the stimulus comes, the animal reacts in the same way as at first, 

 till it finally becomes directed elsewhere. We may for convenience 

 call this reaction, by which the animal avoids all sorts of agents, the 



"avoiding reaction." 



In the foregoing paragraph we have given only a general outline of 

 the behavior. The avoiding reaction has certain additional features, 



