206 The Animal Mind 



ism's past experience may modify its behavior, asking each 

 time what the possible conscious aspect of the modification 

 may be. 



80. Absence of Modification 



In the first place there presents itself for consideration the 

 case of animals that meet a situation by repeating the same 

 reaction over and over again. For example, Paramecium 

 encounters an obstacle in its path. It performs the only 

 reaction in its power, the avoiding reaction; it darts back- 

 ward, rolls to one side, and proceeds forward at an acute 

 angle to its former course. Suppose that the obstacle is so 

 large that the animal strikes it again. The negative reaction 

 is repeated and again repeated if need be until the course 

 is sufficiently altered to carry the Paramecium clear of the 

 obstacle. To behavior of this sort Jennings has extended 

 the term "trial and error" (206, p. 237). The expression 

 was first used by Lloyd Morgan to distinguish between the 

 human method of solving a problem and the dog's method, 

 the latter being called "trial and error" (282, p. 139). Mor- 

 gan meant that the dog does not attempt to reason the matter 

 out beforehand, making use of his previously acquired knowl- 

 edge before beginning to act ; but that he attacks it at once 

 in some manner derived from individual experience or racial 

 inheritance. If this method fails, he tries another similarly 

 derived, and so on until one method proves successful. 

 Paramecium also tries over and over again, although what 

 it tries is always the same thing. Whether Paramecium's 

 behavior is really shown to be akin to the dog's, by calling 

 both "trial and error," is questionable, however ; the resem- 

 blances between the performances of an animal that invariably^ 

 responds with the same reaction until it chances to be carried 

 beyond the reach of the stimulus, and those of a human being 

 who successively "thinks of," that is, recalls the ideas of 



