SECT. XXXV. 1.3. OF ASSOCIATION. 345 



3. An inftance of the third circumftance, where the primary 

 part of a train of irritative motions ats with lefs, and the fec- 

 ondary part with greater energy, may be obferved by making 

 the following experiment. If a perfon lies with his arms and 

 (boulders out of bed, till they become cold, a temporary coryza 

 or catarrh is produced ; fo that the pafTage of the noftrils be- 

 omes totally obftrufted ; at leaft this happens to many people j 

 and then on covering the arms and (boulders, till they become 

 warm, the paflage of the noftrils ceaies again to be obftru&ed, 

 and a quantity of mucus is difcharged from them. In this cafe 

 the quiefcence of the veflels of the fkin of the arms and ilioul- 

 ders, occafioned by expofure to cold air, produces by irritative 

 aflbciation an increafed aHon of the veflels of the membrane of 

 the noftrils ; and the accumulation of fenforial power during 

 the torpor of the arms and (boulders is thus expended in produc- 

 ing a temporary coryza or catarrh. 



Another inftance may be adduced from the fympathy or con- 

 fent of the motions of the ftomach with other more diftant links 

 of the very extenfive tribes or trains of irritative motions aflbci- 

 ated with them, defcribed in Sedt. XX. on Vertigo. When 

 the adlions of the fibres of the ftomach are diminifhed or invert- 

 ed, the actions of the abforbent veflels, which take up the mucus 

 from the lungs, pericardium, and other cells of the body, be- 

 come increafed, and abforb the fluids accumulated in them with 

 greater avidity, as appears from the exhibition of foxglove, anti- 

 mony, or other emetics, in cafes of anafarca, attended with un- 

 equal pulfe and difficult refpiration. 



That the aft of naufea and vomiting is a decreafed exertion 

 of the fibres of the ftomach may be thus deduced ; when an 

 emetic medicine is adminiftered, it produces the pain of ficknefsj 

 as a difagreeable tafte in the mouth produces the pain of naufea ; 

 thefe pains, like that of hunger, or of cold, or like thofe, which 

 are ufually termed nervous, as the head-ach or hemicrania, do 

 not excite the organ into greater aHon ; but in this cafe I im- 

 agine the pains of ficknefs or of naufea counteract or deftroy 

 the pleafurable ferifation, which feems neceflary to digeftion, at, 

 (hewn in Seft. XXXIII. i. i. The periftaltic motions of the 

 fibres of the ftomach become enfeebled by the want of this 

 ftimulus of pleafurable fenfation, and in confequence itop for a 

 time, and then become inverted ; for they cannot become invert- 

 ed without being previoufly flopped. Now that this inverfion 

 of the trains of motion of the fibres of the ftomach is owing to 

 the deficiency of pleafurable fenfation is evinced from this cir- 

 cumftance, that a naufeous idea excited by words will produce 

 vomiting as effectually as a naufoeus drug. 



VOL. I. W w Hence 



