176 THEPHILOSOPHY 



examine a mite, or any very minute obje£i:, by the naked eye, a 

 pain is propagated over every part of that organ. Several caufes 

 may concur in producing this pain, fuch as the dilating of the pupil, 

 and the adjufting the chryftalline lens ; but the chief caufe mufl be 

 afcribed to the preternatural intumefcence and extenfion of the pa- 

 pillae of the retina, the fubftance of vyhich is a mere congeries of 

 nervous terminations. This circumflance confirms a former re- 

 mark, that the immediate organs of fenfation were more copioufly 

 fupplied with nervous papillae than thofe parts v;hofe ufes require 

 not fuch exquifite fenfibility ; for a diftindion in this refpeft is ob- 

 fervable even among the fenfitive organs themfelves. They are 

 furniflied with nerves exadly proportioned to the fubtility of the 

 objeds whofe imprcflions they are fitted to receive. The eye pof- 

 fefl'es by far the greateft number. The particles of light arc fo mi- 

 nute, that, had not this wife provifion been obferved in the con- 

 ftrudion of the eye, ic could never have been able to diftinguifli ob- 

 jedls with fuch accuracy as at prefent it is capable of performing. 

 When an infipid body, or a body which conveys but a very feeble 

 fenfation of tafle, is applied to the tongue, we are confcious of aa 

 effort which that organ makes in order to difcover the quality of the 

 body thus applied. This effort is nothing but the ftretching of the 

 nervous papillae, that they may enlarge the field of contaft with the 

 body under examination. 



The pleafure or pain produced by the fenfe of touch depends 

 chiefly on the fridion, or number of impulfes, made upon the pa- 

 pillae. Embrace any agreeable body with your hand, and allow it 

 to remain perfedlly at reft, and you will find the pleafure not half 

 fo exquifite as when the hand is gently moved backward and for- 

 ward upon the furface. Apply the hand to a piece of velvet, and 

 it is merely agreeable : Rub the hand repeatedly on the furface of the 

 cloth, and the pleafant feeling will be augmented in proportion to 



the 



