PLEASURE, PAIN AND INTELLIGENCE 159 



In the reinforcement or stamping in of a reaction to a particu- 

 lar stimulus that brings pleasure, it certainly seems as if pleasure 

 or its physiological correlate in some way serves to cement more 

 firmly the association between the stimulus and the response. 

 Let us consider, however, the case in which the chick pecks at a 

 caterpillar which has a good taste; the presence of the caterpillar 

 in the mouth excites the swallowing reflexes; in the presence of 

 a similar caterpillar the pecking response is made more readily 

 than before and whatever hesitation there may have been at first 

 disappears. Is not the difference from the pain response due to 

 the fact that there is an organic incompatibility between the first 

 and second responses in the pain response, while there is an 

 organic congruity or mutual reinforcement of these responses 

 in the other? Pecking and swallowing form the normal elements 

 of a chain reflex; when one part of the system is excited it tends 

 to excite the rest, to increase the general tonus of all parts con- 

 cerned in the reaction. Many reflexes instead of being mutually 

 inhibitory, tend to reinforce one another's action. According to 

 Sherrington, 



When in the spinal animal the one fore foot is stimulated, flexion of the 

 hind leg of the crossed side is often obtained. Stimulation of that hind 

 foot itself also causes a like reflex of that limb. When these two are con- 

 currently stimulated, the flexion movement is obtained more easily than 

 from either singly. These widely separate reflex-arcs therefore reinforce 

 one another in their action on the final common paths they possess in com- 

 mon. Similarly with certain reflex-arcs arising from the skin of the pinna 

 of the crossed ear. In them excitation reinforces that of the just men- 

 tioned arcs from the fore foot and opposite hind foot. 



The presence of savory food in a dog's mouth causes the secre- 

 tion of saliva and the movements of chewing and swallowing, and 

 the stomach at the same time may be stimulated to secrete gas- 

 tric juice. These activities are organically associated and they 

 are usually preceded bv seizing acts of various kinds. A particu- 

 lar object, then, which evokes the seizing response and which is 

 of a character to set up these other reactions becomes more readily 

 responded to again. The seizing reaction becomes assimilated 

 to the other reactions which dispose of the food. 



