Herrick, Corollaries of Neurological Discoveries. 1 59 



The Summation- Irradiation Theory of Pain- Pleasure. The 

 writer has been accustomed for several years to call especial at- 

 tention of his psychology students to a peculiar analogy be- 

 tween the conditions of pleasure and pain in the bodily sphere 

 and the psychical pleasures and pains. It is easily seen that 

 the purely physical pains have the common character of involv- 

 ing a disproportionateness of stimulus to the conveying power 

 of the organ. In other words summation is a dominant neural 

 note in pain. The apparent exceptions are not really so. Thus 

 the observed fact that a depressed nervous state is conducive to 

 painful impressions (as is also fatigue) is but the opposite way 

 of creating the disproportion between stimulus and conveying 

 (or receiving) power from that of rapidly augmenting the stim- 

 ulus. Central states which impair the viability of tracts have 

 the same effect. Monotony is a mode under fatigue. In all 

 the recent discussions of pain nerves and painful sensations one 

 very obvious consideration is strangely overlooked. It is this : 

 in the majority of cases the interval noticed to intervene be- 

 tween the tactile and the painful sensation is the measure of the 

 time necessary for certain vascular changes to occur. The close 

 relation between pain and vascular change has often been noted. 

 The writer has given special illustrations of this relation in the 

 Psychological Review. Now it is easy to trace the connection 

 between the after-pain of a blow (on the toe for example) and 

 the ensuing nervous congestion. It will be found that in less 

 conspicuous instances the same is true. Even in burns, where 

 the slow conduction of heat in the skin is often ignored, there 

 is the after pain due to the vascular change following. The 

 congestion of local capillaries is a condition especially adapted 

 to produce summation, just as the later stages of repair are pro- 

 ductive of irradiation. It is not necessary to seek special pain 

 nerves if the clue here pointed out be followed up. The slow- 

 ness of the pain current, as so often noted, is seen to rest in 

 the prerequisites of summation processes. On the other hand 

 the simplest form of pleasure — that of tickling or the satisfac- 

 tion growing out of tactile contact — rests upon irradiation. The 

 anatomical basis for peripheral (as contrasted to central) irradia- 



