4 o 4 DISEASES Class IV. 2. 1. 1 • 



It mull alfo be obferved, that when the irritative motions are 

 flimulated into unufual action, as in inebriation, they become 

 fucceeded by fenfation, either of the pleafurable or painful kind ; 

 and thus a new link is introduced between the irritative mo- 

 tions thus excited, and thofe which ufed to fucceed them ; 

 whence the aflbciation is either diflevered or much weakened, 

 and thus the vomiting in fea-ficknefs occurs from the defect of 

 the power of aflbciation, rather than from the general deficiency 

 of fenforial power. 



When a blind man turns round, or when one, who is not 

 blind, revolves in the dark, a vertigo is produced belonging to 

 the fenfe of touch. A blind man balances himfelf by the fenfe 

 of touch, which being a lefs perfect means of determining fmall 

 quantities of deviation from the perpendicular, occafions him to 

 walk more carefully upright than thofe, who balance themfelves 

 by vifion. When he revolves, the irritative aiToeiations of the 

 mufcular motions, which were ufed to preferve his perpendicu- 

 larity, become difordered by their new modes of fucceflive ex- 

 ertion \ and he begins to fall. For his feet now touch the floor 

 in manners or directions different from thofe they have been ac- 

 cuftomed to \ and in confequence he judges lefs perfectly of the 

 iituation of the narts of the floor in refpecl: to that of his own 

 body, and thus lofea his perpendicular attitude. This may be 

 illullratcd by the curious experiment of crofling one finger over 

 the next to it, and feeling a nut or bullet with the ends of them. 

 When, if the eyes be cloied, the nut or bullet appears to be two, 

 from the deception of the fenfe of touch. 



In this vertigo from gyration, both of the fenfe of fight, and 

 of the fenfe of touch, the primary link of the aflbciated irritative 

 motions is increafed in energy, and the fecondary ones are in- 

 creafed at firfl by direct fympathy ; but after a. time they become 

 decreafed by reverfe fympathy with the primary link, owing to 

 the exhauilion of fenforial power in general, or to the power of 

 aflbciation in particular ; becaufe in the laft cafe, either pleafur- 

 able or painful fenfation has been introduced between the links 

 of a train of irritative motions, and has diilevered, or much en- 

 feebled them. 



Dr. Smyth, in his EfTay on Swinging in Pulmonary Confump- 

 tion, has obferved, that (winging makes the pulfe flower. Dr. 

 Ewart of Bath confirmed this obfervation both on himfelf and 

 on Col. Cathcart, who was then hectic, and that even on fhip- 

 board, where fome degree of vertigo might be fuppofed previ- 

 oufly to exift. Dr. Currie of Liverpool not only confirmed this 

 obfervation frequently on himfelf, when he was alfo phthifical, 

 but found that equitation had a fimilar effect on him, uniform- 

 ly 



