CLASS IV. i.i. OF ASSOCIATION. 365 



ienforial powers, as with pain or pleafure, which are in this cafe 

 not the proximate caufe of motion, but which, by becoming a 

 link of catenation, excite the fenforial power of aflbciation into 

 action j as the pain at the neck of the gall-bladder occafioned 

 by a gall-ftone is transferred to the other end of that canal, and 

 becomes a link of catenation between the aft ion of the two ex- 

 tremities of it. 4. The influence of ethereal fluids, as of heat 

 and gravitation. To which laft perhaps might be added moif- 

 ture and oxygen gas as conftituting neceflary parts of the fyf- 

 tem, rather than ftimuli to excite it into action, 



H. The Origin of AJJbciations. 



Some trains or circles of aflbciate motions muft have been 

 formed before our nativity, as thofe of she heart, arteries, and 

 capillaries ; others have been aflbciated, as occafion required 

 them, as the mufcles of the diaphragm and abdomen in vomit- 

 ing ; and others by perpetual habit, as thofe of the ftomach with 

 the heart and arteries directly, as in weak pulfe during ficknefs \ 

 with the capillaries directly, as in the flufhed Ikin after dinner ; 

 and laftly, with the cellular abforbents reverfely, as in the in- 

 creafed abforption in anafarca during ficknefs ; and with the ir- 

 ritative motions of the organs of fenfe reverfely, as in vertigo, 

 or fea-ficknefs. Some of thefe aflbciations fnall be here ihortly 

 defcribed to facilitate the inveftigation of others. 



Firft, other congeries of glands occupy but a particular part 

 of the fyftem, or conftitute a particular organ, as the liver, or 

 kidneys ; but thofe glands, which fecrete the mucus, and per- 

 fpirable matter, which are called capillaries, are of very great 

 extent ; they receive the blood from the arteries, feparate from 

 it the mucus, which lines every cell, and covers every cavity of 

 the body ; and the perfpirable matter, which foftens and lubri- 

 cates the whole furface of the fldn, and the more extenfive fur- 

 face of the air-veflels, which compofe the lungs. Thefe are 

 fupplied with blood by the perpetual action of the heart and ar- 

 teries, and have therefore their motions aflbciated with the form- 

 er, and with each other, by fympathy, which is fometimes di- 

 rect, and fometimes reverfe. 



One branch of this aflbciation, the capillaries of the fkin, is 

 very irritable by the increafed quantities of cold and heat ; anoth- 

 er branch, that of the lungs, has not the perception of cold 

 and heat, but is liable by direct fympathy to act in concert with 

 the former, as in going into the cold bath. And it is probable 

 the capillaries of the internal membranes are likewife directly 



affected 



