SECT. XIV. 6. PRODUCTION OF IDEAS. 129 



thefe organs of fenfe do not perceive fmall exceffes 

 or deficiencies of heat ; and as heat has no greater 

 analogy to the folidity or to the figures of bodies, 

 than it has to their colours or vibrations ; there 

 feems no fufikient reafon for our afcribing the per- 

 ception of heat and cold to the fenfe of touch ; to 

 which it has generally been attributed, either be- 

 caufe it is diffused beneath the whole fkin like 

 the fenfe of touch, or owing to the inaccuracy of 

 our obfervations, or the defect of our languages. 



There is another circumftance would induce us 

 to believe, that the perceptions of heat and cold 

 do not belong to the organ of touch ; fi.nce the 

 teeth, which are the leaft adapted for the percep- 

 tions of folidity or figure, are the mod fen Able to 

 heat or cold ; whence we are forewarned from 

 fwallowing thofe materials, whofe degree of cold- 

 nefs or of heat would injure our ftomachs. 



The following is an extract from a letter of Dr. 

 R. W. Darwin, of Shrewfbury, when he was a 

 fludent at Edinburgh. " I made an experiment 

 yefterday in our hofpital, which much favours 

 your opinion, that the fenfation of heat and of 

 touch depend on different fets of nerves. A man 

 who had lately recovered from a fever, and was 

 Hill weak, was feized with violent cramps in his 

 legs and feet ; which were removed by opiates, 

 except that one of his feet remained infeniible. 

 Mr. Ewart pricked him with a pin in five or fix 

 places, and the patient declared he did not feel it 

 in the leaft, nor was he (eniible of a very (mart 

 pinch. 1 then held a red-hot poker at fome dif- 

 tance, and brought it gradually nearer till it came 

 within thr< e inches, when he afierted that he felt 

 it quite diftindly. I fuppofe fome violent irrita- 

 tion on the nerves of touch had caufed the cramps, 

 and had left them paralytic ; while the nerves of 

 heat, having fuffered no increased ftimulus, re- 

 tained their irritability." 



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