Sect, XI. i. SENSORIAL ACTIONS. 37 



SECT. XI. 



ADDITIONAL OBSERVATIONS ON THE SENSORIAL POWERS. 



1. Stimulation is cf various kinds, adapted to the organs offenfe, t& 

 the muffles y to hollow membranes, and glands. Some objecls irri- 

 tate our fenjes by repeated impulfes. II. 1. Senfation and volition 

 frequently affetl the whole fenforium. 2. £motions i prffions, ap- 

 petites, 3. Origin of deft re and aver/ion. Criterion of volunta- 

 ry actions, difference of brutes and men. 4. Senfibiliiy and vol- 

 untariiy. III. AJfociations formed before nativity, irritative mo- 

 tions miflakenfor affociated ones. 



Irritation, 



I. The various organs of fen fe require various kinds of flam. 

 ulation to excite them into action ; the particles of light pene- 

 trate the cornea and humours of the eye, and then irritate iht 

 naked retina ; fapid particles, diflblved or difFufed in water or 

 faliva, and odorous ones, mixed or combined with the air, irri- 

 tate the extremities of the nerves of tafte and fmell ; which ei- 

 ther penetrate, or are expanded on the membranes of the tongue 

 and noftrils ; the auditory nerves are ftimulated by the vibra- 

 tions of the atmofphere communicated by means of the tympa- 

 num and of the fluid, whether of air or of water, behind it ; and 

 the nerves of touch by the hardnefs of furrounding bodies, 

 though the cuticle is interpofed between thefe bodies and the 

 medulla of the nerve. 



As the nerves of the fenfes have each their appropriated ob~ 

 jecTs, which ftimulate them into activity ; fo the mufcuhr 

 fibres, which are the terminations of other fets of nerves, have 

 their peculiar objects, which excite them into action ; the !on- 

 gitudinal mufcles are ftimulated into contraction by extension, 

 whence the ftretching or pandiculation after a Icn^ continued 

 pofture, during which they have been kept in a frate of execu- 

 tion ; and the hollow mufcles are excited into action by diflen- 

 tion, as thofe of the rectum and bladder are induced to protrude 

 their contents from their fenfe of the diftention rather than of 

 the acrimony of thofe contents. 



There are other objects adapted to flimulate the nerves, 

 which terminate in variety of membranes, and thofe efpecially 

 which form the terminations of canals ; thus the preparations 

 of mercury particularly affect, the faiivary glands, ipecacuanha 

 ihe ftomach, aloe the fphin&er of the anus, cantharides that of 



the 



