SECT. XI. i. SENSORIAL ACTIONS. 37 



SECT. XI. 



ADDITIONAL OBSERVATIONS ON THE SENSORIAL POWERS. 



I. Stimulation is of various kinds, adapted to the organs of fenfe, to 

 the mufcles t to hollow membranes and glands. Some objecls irri- 

 tate our fenfes by repeated impulfes II. I. Sefifation and volition 

 frequently (iff eft the whole fenforium. 2. Emotions ', pnffions, ap- 

 petites. 3 . Origin of defire and averfton. Criterion of volunta- 

 ry aftionsy difference of brutes and men. 4. Senftbility and vol- 

 untarily. ill. Affbcidtiom formed before nativity , irritative mo- 

 tions mijlaken for officiated ones. 



Irritation. 



I. THE various organs of fenfe require various kinds of ftim- 

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

 trare the cornea and humours of the eye, and then irritate the 

 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 Simulated by the vibra- 

 tions of the atmofphere communicated by means of the tytnpa- 

 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- 

 jedls, which (Itmulate them into activity ; fo the mufcular 

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

 their peculiar objecls, which excite them into aclion; the lon- 

 gitudinal mufcles are Simulated into contraction by extenfion, 

 whence the Sretching or pandiculation after a long continued 

 pofture, during which they have been kept in a date of exten- 

 fion ; and the hollow mufcles are excited into action by diSen- 

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

 their contents from their frnfe of the diflention rather than of 

 the acrimony of thofe contents. 



There are other objecls adapted to Simulate the nerves, 

 which terminate in variety of membranes, and thoie efpecially 

 which form the terminations of canals ; thus the preparations 

 of mercury particularly affect the falivary glands, ipecacuanha 

 the ftomach, aloe the fphindter of the anus, cantharides that of 



the 



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