152 S. J. HOLMES 



can explain this in physiological terms we can safely leave the 

 preceding question to one side to be answered in whatever way 

 it may. 



Turning then to the problem of how behavior comes to be mod- 

 ified in adaptive ways by the pleasureable and painful experiences 

 it brings to the animal, it is evident that it can be treated as a 

 problem of physiology. We are dealing with a series of physio- 

 logical reactions and how they come to be modified. We may 

 assume that psychical states enter into the chain of causes and 

 effects that make up an animal's behavior, but it is not clear that 

 such an assumption throws the least light upon our problem, and 

 it is open to serious objections on both scientific and metaphysical 

 grounds. We shall therefore consider the question purely from 

 the physiological standpoint. Viewed objectively we find that 

 in an animal's behavior certain acts when once performed tend 

 to be performed with greater readiness under similar conditions 

 a second time, while other acts once performed tend under sim- 

 ilar conditions to be inhibited. This problem of learning, Bald- 

 win observes "is the most urgent, difficult and neglected question 

 in the new genetic psychology." Spencer with his character- 

 istic insight into fundamental problems has grappled with it and 

 has attempted to give a physiological explanation. Pleasure, 

 according to Spencer, is the concomitant of heightened nervous 

 discharge; pain the concomitant of lessened discharge. In an 

 animal with a diffuse discharge of its nervous energy resulting 

 in random movements, some of these movements bring a height- 

 ened nervous discharge with its psychic accompaniment of pleas- 

 ure. This tends to reinforce the movement that brought the 

 increase of nervous energy and to cause it to be repeated. Re- 

 sponses resulting in pain tend on account of the diminution of 

 nervous discharge that follows to be discontinued, and in this way 

 the organism is kept repeating certain acts and avoiding others. 



"Along with the concentrated discharge to particular muscles," says 

 Spencer, "the ganglionic plexuses inevitably carry off a certain diffused 

 discharge to the muscles at large, and this diffused discharge produces on 

 them very variable results. Suppose, now, that in putting out its head to 

 seize prey scarcely within reach, a creature has repeatedly failed. Sup- 



