SECT. III. 5. MOTIONS OF THE RETINA, 25 



years : he appeared to be a man of good under- 

 ftanding, and amufed himfelf with reading, and by 

 converfine: either by the ufe of the pen, or by figns 

 made with his fingers, to reprefent letters. I ob- 

 ferved that he had' ib far forgot the pronunciation 

 of the language, that when he attempted to fpeak, 

 none of his words had diftinct articulation, though 

 his relations could fometimes underftand his mean- 

 ing. But, which is much to the point, he allured 

 me, that in his dreams he always imagined that 

 people converfed with him by figns or writing, and 

 never that he heard any one fpeak to him. From 

 hence it appears, that with the perceptions of founds 

 he has alfo loft the idea of them ; though the or- 

 gans of fpeech dill retain fomewhat of their ufual 

 habits of articulation. 



This obfervation may throw fome light on the 

 medical treatment of deaf people ; as it may be 

 learnt from their dreams, whether the auditory 

 nerve be paralytic, or their deafnefs be owing to 

 fome defect of the external organ. 



It. rarely happens that the immediate organ of 

 vifion is perfectly deftroyed. The moft frequent 

 caufes of blindnefs are occaiioned by defects of the 

 external organ, as in cataracts and obfufcations of 

 the cornea. But 1 have had the opportunity of 

 converfing with two men, who had been fome years 

 blind; one of them had a complete gutta ferena, 

 and the other had loft the whole fubftance of his 

 eyes. They both told me that they did not re- 

 member to have ever dreamt of vifible objects, fmce 

 the total lofs of their fight. 



V. Another method of difcovering that our ideas 

 are animal motions of the organs of fenfe, is from 

 confidering the great analogy they bear to the mo- 

 tions of the larger mufcles of the body. In the 

 following articles it will appear that they are ori- 

 ginally excited into action by the irritation of ex- 

 ternal 



