440 DISEASES Class IV. 3. 2.4. 



tance, or to their apparent or unufual motions. Hence thefe 

 irritative motions of vifion are exerted with greater energy, and 

 are in confequence attended with fenfation ; which at firft is 

 agreeable, as when children fwing on a rope ; afterwards the 

 irritative motions of the ftomach, and of the abforbent veffels, 

 which open their mouths into it, become inverted by their af- 

 fociations with them by reverfe fympathy. 



For the action of vomiting, as well as the difagreeable fen- 

 fation of ficknefs, are fhewn to be occafioned by defect of the 

 fenforial power ; which in this cafe is owing to the greater ex- 

 penditure of it by the fenfe of vifion. On the fame account the 

 vomiting, which attends the pafTage of a (tone through the ure- 

 ter, or an inflammation of the bowels, or the commencement of 

 fome fevers, is caufed by the increafed expenditure of the fen- 

 forial power by the too great action of fome links of the aflbci- 

 ations of irritative motions ; and there being in confequence a 

 deficiency of the quantity required for other links of this great 

 catenation. 



It muft be obferved, that the expenditure of fenforial power 

 by the retinas of the eyes is very great ; which may be eftimated 

 by the perpetual ufe of thofe organs during our waking hours, 

 and during mofl of our fleeping ones ; and by the large diam- 

 eters of the two optic nerves, which are nearly the fize of a 

 quill, or equal to fome of the principal nerves, which ferve the 

 limbs. 



4. Vormtio a calculo hi uretere. The action of vomiting in con- 

 fequence of the increafed or decreafed actions of the ureter, 

 when a (lone lodges in it. The natural actions of the ftomach, 

 which confift of motions fubject to intermitted irritations from 

 the fluids, which pafs through it, are affociated with thofe of the 

 ureter ; and become torpid, and confequently retrograde, by in- 

 tervals, when the actions of the ureter become torpid owing to 

 previous great ftimulus from the (tone it contains ; as appears 

 from the vomiting exifting when the pain is leaft. When the 

 motions of the ureter are thus leffened, the fenforial power of 

 affociation, which ought to actuate the ftomach along with the 

 fenforial power of irritation, ceafes to be excited into action ; 

 and in confequence the actions of the ftomach become lefs en- 

 ergetic, and in confequence retrograde. 



For as vomiting is a decreafed action of the ftomach, as ex- 

 plained in Sect. XXXV. 1. 3. it cannot be fuppofed to be 

 produced by the pain of gravel in the ureter alone, as it fhould 

 then be an increafed action, not a decreafed one. 



The perpetual vomiting in ileus is caufed in like manner by 

 the defective excitement of the fenforial power of affociation by 



the 



