Sect. XX. 10. OF VERTIGO. iS 9 



ly in winter, or by candle light, but are yet able to read without 

 them during the fummer days, when the light is ftronger. Thefe 

 people do not fee objects fo diftinclly as formerly, and by ex- 

 erting their eyes more than ufual, they perceive the apparent 

 motions of objects, and confound them with the real motions 

 of them j and therefore cannot accurately balance themfelves fo 

 as eaiily to preferve their perpendicularity by them. 



That is, the apparent motions of objects, which are at reft, 

 as we move by them, fhouid only excite irritative ideas : but as 

 thefe are now become lefs diftinct, owing to the beginning im- 

 perfection of our fight, we are induced voluntarily to attend to 

 them \ and then thel'e apparent motions become fucceeded by 

 fenfation ; and thus the other parts of the trains of irritative 

 ideas, or irritative mufcular motions, become difordered, as ex- 

 plained above. In thefe cafes of flight vertigo I have always 

 promifed my patients, that they would get free from it in two 

 or three months, as they mould acquire the habit of balancing 

 their bodies by lefs diftinct objects, and have feidom been mii- 

 taken in my prognoftic. 



There is an auditory vertigo, which is called a noife in the 

 head, explained in No. 7. of this fecl:ion, which alfo is very lia- 

 ble to affect, people in the advance of life, and is owing to their 

 hearing lefs perfectly than before. This is fometimes called a 

 ringing, and fometimes a finging, or buzzing, in the ears, and is 

 occafioned by our firft experiencing a difagreeable fenfation from 

 our not being able diftinclly to hear the founds, we ufed former- 

 ly to hear diftinctly. And this difagreeable fenfation excites 

 defire and confequent volition ; and when we voluntarily attend 

 to fmall indiftincl: founds, even the whifpcring of the air in a 

 room, and the pulfations of the arteries of the ear are fucceeded 

 by fenfation ; which minute founds ought only to have produ- 

 ced irritative fenfual motions, or unperceived ideas. See Sec- 

 tion XVII. 3. 6. Thefe patients after awhile lofe this auditory 

 vertigo, by acquiring a new habit of not attending voluntarily 

 to thefe indiftinct, founds, but contenting themfelves with the 

 lefs accuracy of their fenfe of hearing. 



Another kind of vertigo begins with the difordered acYion of 

 fome irritative mufcular motions, as thofe of the flomach from 

 intoxication, or from emetics ; or thofe of the ureter, from the 

 ftimulus of a ftone lodged in it •, and it is probable, that the dif- 

 ordered motions of fome of the great congeries of glands, as of 

 thofe which form the liver, or of the inteftinai canal, may occa- 

 lion vertigo in confequence of their motions being affociated or 

 catenated with the great circles of irritative motions ; and from 



hence 



