SECT. VII. 2. IRRITATIVE MOTIONS. 41 



5. Other clafies of our ideas are more frequent- 

 ly excited by our fenfations of pleafure or pain, and 

 others by volition : but that thefe have all been 

 originally excited by ftimuli from external objects, 

 and only vary in their combinations or reparations, 

 has been fully evinced by Mr. Locke : and are by 

 him termed the ideas of perception in contradiilinc- 

 tion to thofe, which he calls the ideas of reflec- 

 tion. 



II. i. Thefe mufcular motions, that are excited 

 by perpetual irritation, are neverthelefs occafion- 

 ally excitable by the fenfations of pleafure or pain, 

 or by volition ; as appears by the palpitation of the 

 heart from fear, the increafed fecretion of faliva at 

 the fight of agreeable food, and the glow on the 

 Ikin of thofe who are amamed. I here is an inftance 

 told in the Philofophical Tr an factions of a man, who 

 could for a time flop the motion of his heart when 

 he pleafed ; and Mr. D. has often told me, he could 

 Ib far increafe the periftaltic motion of his bowels 

 by voluntary efforts, as to produce an evacuation 

 by ftool at any time in half an hour. 



2. In like manner the fenfual motions, or ideas, 

 that are excited by perpetual irritation, are never- 

 thelefs occafionally excited by fenfation or volition ; 

 as in the night, when we liften under the influence 

 of fear, or from voluntary attention, the motions 

 excited in the organ of hearing by the whifpering 

 of the air in our room, the pulfation of our own ar- 

 teries, or the faint beating of a diltant watch, be- 

 come objects of perception. 



ill. Innumerable trains or tribes of other motions 

 are aflbciated with thefe mufcular motions which 

 are excited by irritation ; as by the ftimulus of the 

 blood in the right chamber of the heart, the lungs 

 are induced to expand themfelves ; and the pecto- 

 ral and intercoftal mufcles, and the diaphragm, act 

 at the fame time by their aiTociations with them. 



And 



