Sect. XX. i. OF VERTIGO. 175 



SECT. XX. 



OF VERTIGO. 



I . We determine our perpendicularity by the apparent motions of ob- 

 jeBs. A perfon hood-winked cannot walk in a flraight line 

 Dizzinefs on looking from a tower , in a ropm flamed with uni- 

 form lozenges, on riding over f new, 2. Dizzinefs from moving 

 objects. A whirling wheel. Fluctuations of a river. Experi- 

 ment with a child. 3. Dizzinefs from our own motions and 

 thofe of other objecls; Riding over a broadflream. Seaflcknefs. 

 5. Of turning round on one foot. Dervifes in Turkey. Atten- 

 tion of the mind prevents flight feci -f chiefs . After a voyage ideas 

 of vibratory motions are fill perceived on fhore. 6. Ideas con- 

 tinue fome time after they art excited. drcumflances of turning 

 on one foot, flanding on a tower, and walking in the dark, explain- 

 ed. 7. Irritative ideas of apparent motions . Irritative ideas of 

 founds. Battemens of the found of bells and organ-pipes. Ver- 

 tiginous noife in the head. Irritative motions of the flomach, in- 

 teflines, and glands. 8. Symptoms that accompany vertigo. Why 

 vomiting comes on inflrokes of the palfy. By the motion ofafhip. 

 By injuries on the head. Why motion makes flck people vomit, 

 9. Why drunken people are vertiginous. Why afllone in the ure- 

 ter, or bile-duel, produces vomiting. 10. Why after a voyage 

 ideas of vibratory motions are perceived on fhore. 1 1. Kinds oj 

 vertigo and their cure. I2« Definition of vertigo. 



1. In learning to walk we judge of the diftances of the ob- 

 jects, which we approach, by the eye ; and by obferving their 

 perpendicularity determine our own. This cfrcumftance not 

 having been attended to by the writers on vifion, the difeafe 

 called vertigo or dizzinefs has been little underftood. 



When any perfon lofes the power of mufcular aclidn, wheth- 

 er he is erect or in a fitting pofture, he finks down upon the 

 ground; as is feen in fainting fits, and other inftances of great 

 debility. Hence it follows, that fome exertion of mufcular pow- 

 er is neceiTary to preferve our perpendicular attitude. This is 

 performed proportionally exerting the antagonift mufcles of the 

 trunk, neck, and limbs ; and if at any time in our locomotions 

 we find ourfelves inclining to one fide, we either reflore cur 

 equilibrium by the efforts of the mufcles on the other tide, or 

 by moving one of our feet extend the bafe, which we reft upon^ 

 to the new centre of gravity. 



But the rncfl eafy and habitual manner of determh.Mog out 



ws 



■ 



