CHAPTER IV 



BEHAVIOR OF PARAMECIUM {Continued) 



Special Features of the Reactions to a Number of Differ- 

 ent Classes of Stimuli 



In the preceding chapter the general method of the reactions of 

 Paramecium to most classes of stimuli has been described. In the 

 present chapter certain important details and special peculiarities of 

 the behavior under the different classes of stimuli will be described. 



i. mechanical stimuli 



When Paramecium strikes in its forward course against a solid ob- 

 ject, it responds usually by the avoiding reaction, as described in the 

 preceding chapter. In such cases the stimulus affects the anterior end 

 of the animal. But if mechanical stimuli affect other parts of the body, 

 will this alter the nature of the reaction? This question may be an- 

 swered by drawing a glass rod to an extremely fine point and touching 

 various parts of the body with this point under the microscope. The 

 first discovery that we make by this method of experimentation is that 

 the anterior end is much more sensitive than the remainder of the body 

 surface. If the anterior end is touched very lightly, the animal responds 

 by a strong avoiding reaction, while the same or a more powerful stimu- 

 lus on other parts of the body produces no reaction at all. There is 

 some evidence drawn from other sources 1 that the region immediately 

 about the mouth is likewise very sensitive. 



A second fact brought out by these experiments is that a stimulus 

 on the posterior part of the body produces a different reaction from a 

 stimulus in front. If we touch the anterior end, or any point on the 

 anterior portion of the body back nearly to the middle, the typical avoid- 

 ing reaction is produced. But if we touch the middle or the posterior 

 part of the body of a resting specimen, the animal, if it reacts at all, 

 merely moves forward. 



1 See Chapter V. 

 59 



