476 SCIENCE PROGRESS 



nausea, disgust, and rejection from the mouth when tasted, like- 

 wise all foul and many poisonous odours excite nausea, disgust, 

 and aversion ; whereas pleasant tasting and smelling substances 

 found in nature are usually wholesome and nutritious. 



Pain and Pleasure in Relation to Mental Development 



The associative memory of painful and pleasurable feelings 

 plays an important part in mental development. The sense of 

 well-being and pleasurable feeling is a vague state of conscious- 

 ness clothed and enriched by perceptual and intellectual associ- 

 ated memories which we desire to experience again, and they form 

 an accompaniment of the healthy activity of the functions of body 

 and mind when not exceeding the ordinary normal powers of 

 reparation that the organism possesses. The preservation of 

 the individual and the species depends not only upon the gratifi- 

 cation of the desires, but also upon the protection of the body 

 from physical and chemical injury by pain ; moreover, the senses 

 of smell and taste are sentinels to the alimentary and respiratory 

 systems, protecting them from injury, by exciting nausea and 

 disgust or reflex acts such as coughing, sneezing, and vomiting. 

 These are states of consciousness which there is no desire to 

 experience again, and when associated with perceptual and 

 intellectual memories their causes can be avoided. 



There is evidence to show that if pain is felt in the optic 

 thalamus the perceptual concomitants with which it is asso- 

 ciated are registered in the cortex cerebri ; for the optic 

 thalamus is connected with every part of the cerebral cortex, 

 the seat of associative memory and recollection. The cortex 

 is not the perceiver of pain but the perceiver of the causes 

 which produced it and by which it may be avoided. The cortex 

 can be cut and stimulated without producing pain ; not so the 

 optic thalamus. If by associative memory of the conditions and 

 instrument which cause pain, revival of pain occurred, what 

 would our state of mind be normally ? Pain is the great pro- 

 tector of the body from injury. One of the trite sayings of 

 Oliver Wendell Holmes was "That clergymen and persons 

 without wisdom consider pain a mystery ; it is a revelation ! " 

 We can understand therefore the great biological significance of 

 pain in evolution. Richet indeed is right in asserting that 

 instead of considering pain as an evil we ought to consider it 

 fundamental to human progress, for as instinct is blind, intelli- 



