404 DISEASES CLASS IV. 2. I. 10. 



It must also be observed, that when the irritative motions are 

 stimulated into unusual action, as in inebriation, they become 

 succeeded by sensation, either of the pleasurable or painful kind; 

 and thus a new link is introduced between the irritative motions 

 thus excited, and those which used to succeed them; whence 

 the association is either dissevered or much weakened, and thus 

 the vomiting in sea-sickness occurs from the defect of the power 

 of association, rather than from the general deficiency of senso- 

 rial 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 sense of touch. A blind man balances himself by the sense 

 of touch, which being a less perfect means of determining small 

 quantities of deviation from the perpendicular, occasions him to 

 walk more carefully upright than those who balance themselves 

 by vision. When he revolves, the irritative associations of the 

 muscular motions, which were used to preserve his perpendicu- 

 larity, become disordered by their new modes of successive ex- 

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

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

 customed to; and in consequence he judges less perfectly of the 

 situation of the parts of the floor in respect to that of his own 

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

 illustrated by the curious experiment of crossing one finger over 

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

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

 from the deception of the sense of touch. 



In this vertigo from gyration, both of the sense of sight, and 

 of the sense of touch, the primary link of the associated irritative 

 motions is increased in energy, and the secondary ones are in- 

 creased at first by direct sympathy; but after a time they become' 

 decreased by reverse sympathy with the primary link, owing to 

 the exhaustion of sensorial power in general, or to the power of 

 association in particular; because in the last case, either pleasur- 

 able or painful sensation has been introduced between the link^ 

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

 feebled them. 



Dr. Smyth, in his Essay on Swinging in Pulmonary Consump- 

 tion, has observed, that swinging makes the pulse slower. Dr. 

 Ewart of Bath confirmed this observation both on himself and 

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

 board, where some degree of vertigo might be supposed previ- 

 ously to exist. Dr. Currie of Liverpool not only confirmed this 

 observation frequently on himself, when he was also phthisical, 

 to found that equitation had a similar effect on hirn 5 uniformly 



