Class IV. i. i. OF ASSOCIATION. 367 



motions of the ftomach and cefophagus are induced, and which 

 it is of confequence to diftinguifh from each other. The firft 

 is the mode above defcribed, where an effort is made to diflodge 

 fomething, which flimulates the ftomach into difagreeable fen* 

 fation ; and which is returned by repeated exertions ; as when 

 a naufeous drug is taken into the mouth, or a bit of fand falls 

 into the eye, or a drop of water into the wind-pipe. In this the 

 periftaltic motions of the ftomach are firft (topped, and then re- 

 verted by painful fenfation ; and the abdominal mufcles and di- 

 aphragm by repeated efforts become affociated with them. Now 

 as lefs fenforial power is expended on the retrograde actions of 

 the ftomach, and of the lymphatics, which open their mouths 

 on its furface, than by their natural motions, an accumulation 

 of fenforial power in the fibres of the ftomach follows the ex- 

 hibition of an emetic, and on that account an emetic will fome- 

 times ftcp a fpontaneous vomiting which was owing to fenfori- 

 al deficiency. See Seel:. XXXV. 1.3. and Art. V. 2. 1. 



As bitters and metallic falts, exhibited in fmall dofes, ftimu- 

 late the ftomach into greater action, as appears by their increas- 

 ing the power of digeftion, and yet become emetic, when given 

 in larger dofes ; one might fufpect, that they became emetic 

 by inducing debility, and confequent retrograde actions of the 

 ftomach, by their previoufly exhaufting the fenforial power by 

 their great ftimulus j which might be effected in a moment 

 without producing pain, and in confequence without our per- 

 ceiving it. But on the contrary, there does not in general ap- 

 pear on the exhibition of emetics to be any previous exhauilion 

 of fenforial power ; becaufe there is evidently an accumulation 

 of it during the ficknefs, as appears from the digeftion being 

 ftronger afterwards ; and from the increafed action of the eel- 

 lular and cutaneous abforbents during its operation. See Art. 

 V. 2. 1. 



Another mode by which vomiting is induced, is owing to de- 

 bility or deficiency of fenforial power, from the previous ex- 

 hauftion of it ; as on the day after intoxication, or which occurs 

 in people enfeebled with the gout, and in dropfy, and in fome 

 fevers with debility. In thefe, when the vomiting ceafes, there 

 is no appearance of accumulation of fenforial power, as the di- 

 geftion (till remains weak and imperfect. 



Another mode by which ficknefs or vomiting is induced, is 

 by defect, of ftimulus, as in great hunger ; and in thole, who 

 have been habituated to fpice and fpirit with their meal?, v 

 are liable to be fick after taking food without thefe additional 

 ftimuli. Other means of inducing ficknefs by vertigo, or by 

 naufeous ideas, will be mentioned below. 



We 



