SECT. XL i; SENSORIAL ACTIONS, 55 



the particles of light penetrate the cornea and hu- 

 mours of the eye, and then irritate the naked reti- 

 na ; fapid particles, diffolved or diffufed in water 

 or faliva, and odorous ones, mixed or combined 

 with the air, irritate the extremities of the nerves 

 of tafle and fmeli j which either penetrate, or are 

 expanded on the membranes of the tongue and nof- 

 trils ; the auditory nerves are ilimulated by the vi- 

 brations of the atmofphere communicated by means 

 of the tympanum 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 cu- 

 ticle is interpofed between thefe bodies and the me- 

 dulla of the nerve. 



As the nerves of the fenfes have each their appro- 

 priated objects, which flimulate them into activity ; 

 fo the mufcular fibres, which are the terminations 

 of other fets of nerves, have their peculiar objects, 

 which excite them into action ; the longitudinal 

 mufcles are ftimulated into contraction by exten- 

 lion, whence the ftretching orpandiculation after a 

 long continued pofture, during which they have 

 been kept in a ftate of extenfion ; and the hollow 

 mufcles are excited into action by diftention, as 

 thofe of the rectum and bladder are induced to pro- 

 trude their contents from their fenfe of the diften- 

 tion rather than of the acrimony of thole con- 

 tents. 



There are other objects adapted to ftimulate the 

 nerves, which terminate in a variety of membranes, 

 and thofe efpecialiy which form the terminations of 

 canals ; thus the preparations of mercury particu- 

 larly affect the falivary glands, ipecacuanha the (to- 

 mach, aloe the fphincter of the anus, cantharides 

 that of the bladder, and laftly every gland of the 

 body appears to be indued with a kind of tafte, by 

 which it felects or forms each its peculiar fluid from 

 the blood j and by which it is irritated into acti- 

 vity. 



Many 



