n8 MIND IN EVOLUTION CHAP. 



of attacking them that, when the partition was removed, 

 it left them quite unmolested. 



The cases which have been quoted, and which might be 

 indefinitely multiplied, admit of a simple general descrip- 

 tion. A certain stimulus, in the case of the chick some 

 small object within striking distance, evokes a reaction in 

 this case pecking. This reaction has a certain result, con- 

 nected in this case with the swallowing or tasting of the 

 object, and in future the same stimulus evokes a modified 

 reaction. The modification may be in either of two direc- 

 tions. The <c result" the tasting or swallowing maybe 

 to confirm the original mode of reaction, so that in one 

 instance that sort of object is in future preferred for peck- 

 ing at and swallowing to others. This was the case with 

 the yolk of egg and the green caterpillars. Or it may be 

 to prevent or inhibit the reaction, as in the case of the 

 orange-peel or the cinnabar larvae. In either case, we have 

 a sequence of facts which we may symbolise thus : 

 Stimulus Reaction Consequence 



5 r p 



followed by 



5 p 7T 



In this sequence, all the links mentioned but one are 

 matters of direct observation. That one is the consequence 

 which I have called p. Now, in our human experience, we 

 have also direct knowledge of p. It is in such simple 

 cases as those described a feeling, and if its action is con- 

 firmatory of the reaction which caused it, it is a pleasant 

 feeling ; if inhibitory^ a painful feeling. We need not 

 labour this point. The burnt child dreads the fire because 

 it hurts, and continues to steal the sugar with increasing 

 avidity because it is sweet. In the case of the chick we 

 cannot directly observe the feeling. We can, however, 

 be sure that something happens in the place where we 

 have put ^>, otherwise there would be no cause to account 

 for the subsequent change and the action of this some- 

 thing is precisely analogous to the action of pleasure and 

 pain in human experience. 1 



1 We feel sure about the child, first, because we know our own feelings, 

 and it is so like ourselves ; and secondly, because it expresses itself in 

 ways which we understand. The chick is not quite so like ourselves, 



