THE CANADIAN ENTOMOLOGIST 269 



INSECTS AND PAIN. 



BY HARRY B. WEISS, NEW BRUNSWICK, N.J. 



In various books on entomology one often comes across the 

 statement that insects do not suffer acute sensations of pain as 

 do the higher animals. Different facts are cited to prove this, the 

 most familiar being the case of a butterfly that was pinned alive, 

 escaped and returned to its feeding among flowers with apparently 

 no inconvenience. Kirby and Spence quote the action of a bee 

 eating honey though deprived of its abdomen. Dr. John B. 

 Smith found that if he cut off the abdomen of a fly it would live 

 for twenty-four hours after, with practically no digestive system, 

 very little nervous system and most of its heart gone and when 

 the head was removed it lived for the same length of time. The 

 interesting feature was that no apparent symptom of pain was 

 developed. 



It is also said that if a dragonfly be captured, held loosely by 

 the wing and the tip of its abdomen presented to its mouth, it will 

 proceed to eat at once as far as it can reach. 



Referring to the human system many experiences commonly 

 called painful are only unpleasant or disagreeable. This con- 

 fusion is due to the fact that painful things are always unpleasant. 

 Painfulness however is quite distinct from unpleasantness. The 

 same stimuli which result in sensations of pressure, warmth and 

 cold may also bring about painfulness if they are long continued 

 or repeated often enough. 



There are various theories accounting for pain sensations, the 

 oldest one teaching that there were no specific pain organs, but 

 that sensations of pain were brought about by continued or ex- 

 cessive reactions of other end-organs especially those of pressure. 

 This theory was disproved by the discovery that certain anaes- 

 thetics destroyed pain sensations independently of pressure sen- 

 sations. For instance if one's tooth is treated with cocaine, no pain 

 is felt upon its removal but one is conscious of the pressure of the 

 dentist's instrument. 



Another theory is that pain is produced only by the excitation 

 of distinct end-organs of pain. This theory is based on the dis- 

 covery of pain spots on the skin. However the spots which are 

 sensitive to pain and not to pressure have been found to occur 



August), 1914- 



