174 BEGINNINGS OF INTELLIGENCE 
ment, a discharge which finds its way to the same channels 
as before, and so makes it likely that the same movement 
will be repeated, the external conditions remaining the same. 
Pleasure and pain can be agents of accommo- 
dation and development only if the one pleasure, carry 
with it the phenomenon of ‘motor excess,’ and the other, 
pain, the reverse—probably some form of inhibition or of 
antagonistic contraction.” 
The theories of Spencer, Bain and Baldwin are physio- 
logical since they attempt to explain the modifications of 
behavior, not through the influence of certain psychic states, 
but as the effect of the physiological conditions of which these 
states are the concomitants. The theories are all open to the 
objection that pleasure is by no means the constant con- 
comitant of heightened nervous discharge. Laughing and 
crying are very similar in their physiological expression, 
though they go along with very different psychic states, 
A child who burns his hands and writhes about in agony 
certainly manifests a heightened nervous discharge, but he 
shows no tendency to put his hands again into the fire. 
Another outreaching movement of the child brings his hands 
toward a pleasant degree of warmth. The movement 
tends to be repeated. The nervous discharge in the first 
case is much greater than in the second, but in both cases 
it goes to the arm, though along somewhat different nerves. 
It is obvious, I think, that we cannot account for the differ- 
ence: between the responses to pleasurable and painful 
stimuli on the basis of any quantitative difference in the 
discharges to the part affected. It is a matter of nervous 
connection rather than quantity of nervous energy. 
Pain-giving stimuli, owing to the arrangement of an animal’s 
reflex arcs, are generally followed by a withdrawing move- 
ment of the part stimulated, but that there is a tendency 
