440 DISEASES CLASS IV. 3 2. 4. 



distance, or to their apparent or unusual motions. Hence these 

 irritative motions of vision are exercecl with greater energy, and 

 are in consequence attended with sensation; which at first is 

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

 irritative motions of the stomach, and of the absorbent vessels, 

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

 ciations with them by reverse sympathy. 



For the action of vomiting, as well as the disagreeable sen- 

 sation of sickness, are shown to be occasioned by defect of the 

 sensorial power; which in this case is owing to the greater ex- 

 penditure of it by the sense of vision. On the same account the 

 vomiting, which attends the passage of a stone through the 

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

 of some fevers, is caused by the increased expenditure of the sen- 

 sorial power by the too great action of some links of the associa- 

 tions of irritative motions; and there being in consequence a 

 deficiency of the quantity required for other links of this great 

 catenation. 



It must be observed, that the expenditure of sensorial power 

 by the retinas of the eyes is very great; which maybe estimated 

 by the perpetual use of those organs during our waking hours, 

 and during most of our sleeping ones; and by the large diame- 

 ters of the two optic nerves, which are nearly the size of a 

 quill, or equal to some of the principal nerves, which serve the 

 limbs. 



4. Vomitio a ccdculo in urelere. The action of vomiting in con- 

 sequence of the increased or decreased actions of the ureter, 

 when a stone lodges in it. The natural actions of the stomach, 

 which consist of motions subject to intermitted irritations from 

 the fluids, which pass through it, are associated with those of the 

 ureter, and become torpid, and consequently retrograde, by in- 

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

 previous great stimulus from the stone it contains; as appears from 

 the vomiting existing when the pain is least. When the motions of 

 the ureter are thus lessened, the sensorial power of association, 

 which ought to actuate the stomach along with the sensorial 

 power of irritation, ceases to be excited into action; and in con- 

 sequence the actions of the stomach become less energetic, and 

 in consequence retrograde. 



For as vomiting is a decreased action of the stomach, as ex- 

 plained in Section XXXV. 1.3. it cannot be supposed to be pro- 

 duced by the pain of gravel in the ureter alone, as it should then 

 be an increased action, not a decreased one. 



The perpetual vomiting in'ileus is caused in like manner by 

 the defective excitement of the sensorial power of association by 



