SECT. VII. 2. 2. MOTIONS. 27 



tion of the heart from fear, the increafed fecretion of faiiva at 

 the fight of agreeable food, and the glow on the (kin of thofe 

 who are afhamed. There is an inftance told in the Philofophi- 

 cal TranfatHons of a man, who could for a time flop the mo- 

 tion of his heart when he pleafed ; and Mr. D. has often told 

 me, he could fo 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 ex- 

 cited by perpetual irritation, are neverthelefs occafionally exci- 

 ted by fenfation or volition ; as in the night when we liiten 

 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 arteries, or the 

 faint beating of a diltant watch, become objects of perception. 



III. I. Innumerable trains or tribes of other motions are af- 

 fociated with thefe mufcular motions which are excited by irri- 

 tation ; as by the ftimulus of the blood in the right chamber of 

 the heart, the lungs are induced to expand themfelves j and the 

 pe&oral, and intercoftal mufcles, and the diaphragm, net at the 

 fame time by their aflbciations with them. And when the pha- 

 rinx is irritated by agreeable food, the mufcles of deglutition are 

 brought into a&ion by aflbciation. Thus when a greater light 

 falls on the eye, the iris is brought into action without our at- 

 tention, and the cilinary procefs, when the focus is formed be- 

 fore or behind the retina, by their aflbciations of tlie increaf- 

 ed irritative motions of the organ of vifion. Many common 

 actions of life are produced in a fimilar manner. If a fly fettle 

 on my forehead, whild I am intent on my prefent occupation, 

 I diflodge it with my finger, without exciting my attention or 

 breaking the train of my ideas. 



2. In like manner the irritative ideas fuggeft to us many oth- 

 er trains or tribes of ideas that are aflbciated with them. On 

 this kind of connexion, language, letters, hieroglyphics, and ev- 

 ry kind of iymbol, depend. The fymbnls themfelves produce 

 irritative ideas, or fenfual motions, which we do not attend to ; 

 and other ideas, that are fucceeded by fenfation, are excited by 

 their aflbciation with them. And as thefe irritative ideas make 

 up a part of the chain of our waking thoughts, introducing oth- 

 er ideas that engage our attention, though themfelves are unat- 

 tended to, we find it very difficult to inveftigate by what iteps 

 many of our hourly trains of ideas gain their admittance. 



It may appear paradoxical, that ideas can exift, rind not be at- 

 tended to ; but all our perceptions are ideas excited by irrita- 

 tion, and fucceeded by fenfation. Now when thefe ideas exci- 

 ted 



