ANIMAL CAUSATION. SECT. IV. i. 



^ pleafing picture of objects, reprefented in 

 miniature on the retina of the eye, feems to have 

 given rife to this illufive oratory ! It was forgot that 

 this reprefentation belongs rather to the laws of 

 light, than to thofe of life ; and may with equal ele- 

 gance be feen in the camera obfcura as in the eye ; 

 and that the picture vaniflies for ever, when the 

 object is withdrawn. 



SECT. IV. 



LAWS OF ANIMAL CAUSATION. 



I. The fibres, which conftitute the mufcles and 

 organs of fenfe, poflefs a power of contraction. 

 The circumftances attending the exertion of this 

 power of CONTRACTION constitute the laws of ani- 

 mal motion, as the circumftances attending the ex- 

 ertion of the power of ATTRACTION conftitute the 

 laws of motion of inanimate matter. 



II. The fpirit of imagination is the immediate 

 caufe of the contraction of animal fibres, it refides 

 in the brain and nerves, and is liable to general or 

 partial diminution or accumulation. 



III. The ftimulus of bodies external to the mov- 

 ing organ is the remote caufe of the original con- 

 tractions of animal fibres. 



IV. A certain quantity of ftimulus produces ir- 

 ritation, which is an exertion of the fpirit of ani- 

 mation exciting the fibres into contraction. 



V. A certain quantity of contraction of animal 

 fibres, if it be perceived at all, produces pleafure ; 



a great- 



