02 PRODUCTION Sect. XIV. 7 , 



VII. Of the Senfe of Extetifon. 



The organ of touch is properly the fenfe of preflure, but the 

 mufeuiar fibres themfelves conftitute the organ of fenfe, that 

 feels extension. The fenfe of preflure is always attended with 

 the ideas of the figure and folidity of the object, neither of 

 which accompany our perception of extenfion. The whole fet 

 of mufcles, whether they are hollow ones, as the heart, arteries, 

 and ihtefthies, or longitudinal ones attached to bones, contract; 

 themielves, whenever they are ftimulated by forcible elonga- 

 tion ; and it is obfervable, that the white mufcles, which 

 conftitute the arterial fyftem, feem to be excited into contrac- 

 tion from no other kinds of ftimulus, according to the experi- 

 ments of Haller. And hence the violent pain in fome inflam- 

 mations, as in the paronychia, obtains immediate relief by cut- 

 ting the membrane, that was ftretched by the tumour of the 

 fubjacent parts. 



Hence the whole mufeuiar fyftem may be confidered as one 

 organ of fenfe, and the various attitudes of the body, as ideas be- 

 longing to this organ, of many of which we are hourly con- 

 fcious, while many others, like the irritative ideas of the other 

 fenfes, are performed without our attention. 



When the mufcles of the heart ceafe to act, the refluent 

 blood again diftends or elongates them ; and thus irritated they 

 contract as before. The fame happens to the arterial fyftem, 

 and I fuppofe to the capillaries, inteftines, and various glands of 

 the body. 



When the quantity of urine, or of excrement, diftends the 

 bladder, or rectum, thofe parts contract, and exclude their con- 

 tents, and many other mufcles by aflbciation act along with 

 them ; but if thefe evacuations are not foon complied with, 

 pain is produced by a little further extenfion of the mufeuiar fi- 

 bres : a fimilar pain is caufed in the mufcles, when a limb is 

 much extended for the reduction of diflocated bones ; and in 

 tiie punifhment of the rack : and in the painful cramps of the 

 calf of the legy or of other mufcles, for a greater degree of con- 

 traction of a mufcle, than the movement of the two bones, to 

 which its ends are affixed, will admit of, muft give fimilar pain 

 to that, which is produced by extending it beyond its due 

 length. And the pain from punctures or incifions arifes from 

 the diftention of the fibres, as the knife pafles through them ; 

 for it nearly ceafes as foon as the divifion is completed. 



All thefe motions of the mufcles, that are thus naturally ex- 

 cited by the ftimulus of diftending bodies, are alfo liable to be 

 called into ftrong action by their catenation with the irritations 



or 



