Class IV. i. i. OF ASSOCIATION. 363 



Thus when vomiting occurs with cold extremities, a blifter on 

 the back in a few hours occafions univerfal warmth of the fkin, 

 and flops the vomiting. And when a diarrhoea occurs with pale 

 fkin and cold extremities, the pricking of the points of a flannel 

 fhirt, worn next the fkin, occafions univerfal warmth of it, and 

 checks or cures the diarrhoea. 



In fome aflbciate trains of action neverthelefs reverfe fympa- 

 thies more frequently occur than direct ones, and in others di- 

 rect ones more frequently than reverfe ones. Thus in continu- 

 ed fever with debility there appears to be a reverfe fympathy be- 

 tween the capillary vefTels of the ftomach and thofe of the fkin ; 

 becaufe there exifts a total averfion to folid food, and conftant 

 heat on the furface of the body. Yet theie two fyftems of vef- 

 fels are at other times actuated by direct fympathy, as when 

 palenefs attends ficknefs, or cold feet induces indigeflion. This 

 fubject requires to be further inveftigated, as it probably depends 

 not only on the prefent or previous plus or minus of the fenfo- 

 rial power of aflbciation, but alfo on the introduction of other 

 kinds of fenforial power, as in Clafs IV. 1. i.D; or the in- 

 creafed production of it in the brain, or the greater mobility of 

 one part of a train of actions than another. 



Thus when much food or wine is taken into the ftomach, if 

 there be no fuperfluity of fenforial power in the fyflem, thac is, 

 none to be fpared from the continual actions of it, a palenefs and 

 chillnefs fucceed for a time j becaufe now the expenditure of 

 it by the increafed actions of the ftomach is greater than the 

 prefent production of it. In a little time however the flimulus 

 of the food and wine increafes the production of fenforial pow- 

 er in the brain, and this produces a fuperfluity of it in the fyf- 

 tem ; in confequence of which the fkin now becomes warm 

 and florid, which was at fir ft cold and pale ; and thus the reverfe 

 fympathy is fhortly converted into a direct one ; which is prob- 

 ably owing to the introduction of a fecond fenforial power, that 

 of pleafurable fenfation. 



On the contrary, when an emetic drug produces ficknefs, the 

 fkin is at firfl pale fOr a time by direct fympathy with the capil- 

 laries of the ftomach ; but in a few minutes, by the accumula-, 

 tion of fenforial power in the ftomach during its lefs active ftate 

 in ficknefs, the capillaries of the fkin, which are affociated with 

 thofe of the ftomach, act with greater energy by reverfe fympa- 

 thy, and a florid colour returns. Where the quantity of action 

 is diminifhed in the firft part of a train of motions, whether by 

 previous diminution of fenforial power, or prefent diminution' 

 of ftimulus, the fecond part of the train becomes torpid by di- 

 rect fympathy. And when the quantity of action of the firft 



part 



