CLASS IV. 2.1. OF ASSOCIATION. 399 



ORDO II. 



Decreased Associate Motions. 



GENUS I. 

 Catenated with Irritative Motions. 



As irritative muscular motions are attended with pain, when 

 they are exerted too weakly, as well as when they are exerted 

 too strongly; so irritative ideas become attended with sensation 

 when they are exerted too weakly, as well as when they are ex- 

 erted too strongly. Which accounts for these ideas being at- 

 tended with sensation in the various kinds of vertigo described 

 below. 



There is great difficulty in tracing the immediate cause of the 

 deficiencies of action of some links of the associations of irrita- 

 tive motions; first, because the trains and tribes of motions, 

 which compose these links, are so widely extended as to embrace 

 almost the whole animal system; and secondly, because when 

 the first link of an associated train of actions is exerted with too 

 great energy, the second link by reverse sympathy may be affected 

 with torpor. And then this second link may transmit, as it were, 

 this torpor to a third link, and at the same time regain its own 

 energy of action; and it is possible this third link may in like 

 manner transmit its torpor to a fourth, and thus regain its own 

 natural quantity of motion. 



I shall endeavour to explain this by an example taken from 

 sensitive associated motions, as the origin of their disturbed ac- 

 tions is more easily detected. This morning I saw an elderly 

 person, who had gradually lost all the teeth in his upper jaw, 

 and all of the under except three of the molares; the last of 

 these was now loose, and occasionally painful; the fangs of 

 which were almost naked, the gums being much wasted both 

 within and without the jaw. He is a man of attentive obser- 

 vation, and assured me, that he had again and again noticed, 

 that, when a pain commenced in the membranes of the alveolar 

 process of the upper jaw, opposite to the loose tooth in the under 

 one, (which had frequently occurred for several days past,) the 

 pain of the loose tooth ceased. And that, when the pain after- 

 wards extended to the ear and temple on that side, the pain in 

 the membranes of the upper jaw ceased. In this case the mem- 

 branes of the alveolar process of the upper jaw became torpid, 

 and consequently painful, by their reverse sympathy with the 



