The Metaphysics of a Naturalist 
9 
The most localized forms of pleasure are accompanied by a 
peculiar nervous diffusion, as in tickling and the genial effect 
of warmth. This effect is known as irradiation and is also 
characteristic of higher states of pleasurable feeling. Both pain 
and pleasure depend on exalted stimuli, but the reaction of the 
system toward the stimuli largely determines their pleasurable- 
ness or painfulness. The same excitation may excite one or the 
other feeling at different times.* 
This last statement contains an important thesis of the doc- 
trine, namely, that summation or irradiation is painful or pleasur- 
able only under certain conditions of intensity. As in the general 
statement of the equilibrium theory of consciousness of which 
this is a corollary, the condition of pain and pleasure is a state 
of relative tension or equilibrium. If pleasure meant merely ease of 
adjustment and pain difficulty of adjustment, then habit would 
carry with it the greatest pleasure and pain would be in direct 
ratio to the difficulty of adjustment, neither of which is uniformly 
the case. Up to the limit of normal functioning only, does 
pleasure increase with summation and subsequent irradiation. 
Beyond this point pain supervenes. It is only the relatively 
free discharge that is pleasurable. Supernormal irradiation is 
painful as well as supernormal summation. The limits vary from 
individual to individual. But the general principle holds that 
when the summation or resistance lies between certain limits 
of intensity determined by the structure and inheritance of the 
organism, the subsequent discharge or irradiation is pleasurable; 
if the summation is below or above these limits the discharge 
is painful. The apparent incompetence of the theory to explain 
^The pains of negative states, as ennui, etc., is only apparent. 
Whether a stimulus is painful or not depends not on the absolute 
intensity of the irritation, but on the capacity of the mechanism 
to transmit it. In ennui the sluggish system is incapable of 
reacting against the slight stimuli and their monotonous char- 
acter causes a summation and intermittent discharge. 
Sensation differs from feeling in the more definite localization 
of the stimulus, either by eccentric projection upon the periph- 
^ Journal of Comparadve Neurology, vol. 5, p. 18 (March, 1895). 
^ Journal of Comparative Neurology, vol. 5, 1895, p. 212. See also article, “Sum- 
ir.ation,”in Baldwin’s Dictionary of Psychology and Philosophy. 
