Modification by Experience 



211 



occur too rapidly to make fatigue of the motor apparatus 

 probable. The most natural analogy to the phenomenon in 

 our own experience is sensory adaptation, such as we find, for 

 instance, in the fact that a moderate weight laid on the skin 

 ceases after a time to be felt. The psychic accompaniment 

 of such modification of behavior is probably, if it exists, 

 merely the gradual disappearance of all sensation. 



Another case of the cessation of reaction to a repeated stim- 

 ulus is reported by Wasmann of ants in an artificial nest, 

 which assumed the fighting attitude in response to the move- 

 ment of a finger outside the nest, but after two or three repeti- 

 tions of the motion were no longer disturbed (426). Where 

 animals as high in the scale as the ant and spider are con- 

 cerned, it is possible that this process of getting used to a 

 stimulus may involve rather a dulling of emotion than a dis- 

 appearance of sensation. 



That adaptation is itself adaptive hardly needs to be empha- 

 sized. As Jennings suggests, if the sea-anemone that con- 

 tracts at the first ray of light were to remain contracted in 

 steady illumination, it would lose all chance of getting food 

 under the new conditions (207). The negative reactions 

 ordinarily involve interruption of the food-taking process, 

 and it is important that they should not be continued in re- 

 sponse to stimulation that is relatively permanent. Hargitt 

 thinks that the loss of reaction to repeated shadows which he 

 observed in marine worms may be an adaptation to the vary- 

 ing illumination caused by ripples at the surface of the water 



(158). 



Does such loss of reactive power ever occur in connection 

 with a positive or food-taking reaction? One would expect 

 that a single condition would bring it about under such cir- 

 cumstances ; namely, loss of hunger. And, as a matter of 

 fact, observers of the feeding processes in many lower forms 



