1 88 OF VERTIGO, Sect. XX. i* 



and the difordered irritative mufeular motions, as thofe of th« 

 ftomach in vomiting, follow. 



10. "When thefe irritative motions are diflurbed, if the de- 

 gree be not very great, the exertion of voluntary attention to 

 any other object, or any fudden fenfation, will disjoin thefe new 

 habits of motion. Thus fome drunken people have become fo- 

 ber immediately, when any accident has ftrongly excited their 

 attention ; and fea-ficknefs has vanifhed, when the (hip has been 

 in danger. Hence when our attention to other objects is molt 

 relaxed, as jufl before we fall afleep, or between our reveries 

 when awake, thefe irritative ideas of motion and found are moft 

 liable to be perceived ; as thofe, who have been at fea, or have 

 travelled long in a coach, feem to perceive the vibrations of the 

 fhip, or the rattling of the wheels, at thefe intervals ; which 

 ceafe again, as foon as they exert their attention. That is, at 

 thofe intervals they attend to the apparent motions, and to the 

 battement of founds of the bodies around them, and for a mo- 

 ment miftake them for thofe real motions of the- fhip, and noife 

 of wheels, which they had lately been aceuftomed to : or at thefe 

 intervals of reverie, or on the approach of deep, thefe fuppofed 

 motions or founds may be produced entirely by imagination. 



We may conclude from this account of vertigo, that fea-ilck- 

 nefs is not an effort of nature to relieve herfelf, but a neceffary 

 confequence of the affociations or catenations of animal motions. 

 And may thence infer, that the vomiting, which attends the 

 gravel in the ureter, inflammations of the bowels, and the com- 

 mencement of fome fevers, has a fimilar origin, and is not al- 

 ways an effort of the vis medicalrix naturae. But where the ac-; 

 tion of the organ is the immediate confequence of the ftimula- 

 ting caufe, it is frequently exerted to diflodge that ftimulus, as in 

 vomiting up an emetic drug ; at other times, the action of an 

 organ is a general effort to relieve pain, as in convulfions of the 

 locomotive mufcles ; other aclions drink up and carry on the 

 fiuids, as in abforption and fecretion ; all which may be termed, 

 efforts of nature to relieve, or to preferve herfelf. 



1 1. The cure of vertigo will frequently depend on our previ- 

 oufly inveftigatmg the caufe of it, which from what has been 

 delivered above may originate from the diforder of any part of 

 the great tribes of irritative motions, and of the affociate m 

 tions catenated with them. 



Many people, when they arrive at fifty or fixty years of age, 

 are affected with flight vertigo ; which is generally but wrongly 

 afcribed to indigeftion, but in reality arifes from a beginning de- 

 fect, of their fight ; as about this time they alfo find it neceffary 

 io begin to ufe fpectacles, when they read imall prints, efpecial- 



