SECT. XXV. 5. AND INTESTINES. -219 



and if one of this chain be difturbed, the whole is liable to be 

 put into diforder. See Sect. XX. on Vertigo. 



5. When the ftomach and inteflines receive a quantity of food, 

 whofe ftimulus is greater than ufual, all their motions, and thofe 

 of the glands and lymphatics, are ftimuhted into (Ironger aclion 

 than ufual, and perform their offices with greater vigour and in 

 lefs time : fuch are the effects of certain quantities of fpice or of 

 vinous fpirit. 



6. But if the quantity or duration of thefe ftimuli are ftili 

 further increafed, the ftomach and throat are ftimulated into a 

 motidt*. whofe direction is contrary to the natural one above de- 

 fcribed ; and they regurgitate the materials, which they contain, 

 inftead of carrying them forwards. This retrograde motion of the 

 ftomach may be compared to the itretchings of wearied limbs the 

 contrary way, and is well elucidated by the following experiment. 

 Look earneflly for a minute or two on an area an inch fquare of 

 pink filk, placed in a ftrong light, the eye becomes fatigued, the 

 colour becomes faint, and at length vanifhes, for the fatigued 

 eye can no longer be ftimulated into direct motions ; then on 

 clofing the eye a green fpedrum will appear in if, which is a 

 colour direftly contrary to pink, and which will appear and dif- 

 appear repeatedly, like the efforts in vomiting. See Seclion. 

 XXIX. ii. 



Hence all thofe drugs, which by their bitter or aftringent ftim- 

 ulus increafe the action of the ftomach, as camomile and white 

 vitriol, if their quantity is increafed above a certain dofe become 

 emetics. 



Thefe inverted motions of the ftomach and throat are gener- 

 ally produced from the ftimulusof unnatural food, and are attend- 

 ed with the fenfation of naufea or ficknefs : but as this fenfation 

 is again connected with an idea of the diftafteful food, which 

 induced it ; fo an idea of naufeous food will alfo fometimes ex- 

 cite the action of naufea ; and that give rife by aflbciation to the 

 inverfion of the motions of the ftomach and throat. As fome, 

 who have .had horfe-flefh or dogs-flefh given them for beef or 

 mutton, are faid to have vomited many hours afterwards, when 

 thev have been told of the impofition. 



I have been told of a perfon, who had gained a voluntary com- 

 mand over thefe inverted motions of the (tomach and throat, and 

 Supported himfelf by exhibiting this cufiofity to the public. At 

 thefe exhibitions he fwallowed a pint of red rough goofeberries, 

 and a pint of white fmooth ones, brought them up in fmall par- 

 cels into his mouth, and reftored them feparately to the fpecta- 

 tors, who called for red or white as they pleafed, till the whole 

 were redelivered. 



7. At 



