Sect. VI. i. i. FIBROUS CONTRACTIONS. n 



SECT. VI. 



OF THE FOUR CLASSES OF FIBROUS MOTIONS. 



I. Origin of fibrous contractions* II. Diftributien of them into four 



clajfes, irritative motions, fenfitiie motions, voluntary motions, and 

 officiate motions, defined. 



1. All the fibrous contractions of animal bodies originate 

 from the fenforium, and refolve themfelves into four clafTes, cor- 

 refpondent with the four powers or motions of the fenforium 

 above defcribed, and from which they have their caufation. 



i. Thefe fibrous contractions were originally caufed by the 

 irritations excited by objects, which are external to the moving 

 organ. As the pulfations of the heart are owing to the irrita- 

 tions excited by the ftimulus of the blood ; and the ideas of per- 

 ception are owing to the irritations excited by external bodies. 



2. But as painful or pleafurable fenfations frequently accom- 

 panied thofe irritations, by habit thefe fibrous contractions be- 

 came caufable by the fenfations, and the irritations ceafed to be 

 neceflary to their production. As the fecretion of tears in grief 

 is caufed by the fenfation of pain ; and the ideas of imagina- 

 tion, as in dreams or delirium, are excited by the pleafure or 

 pain, with which they were formerly accompanied. 



3. But as the efforts of the will frequently accompanied 

 thefe painful or pleafurable fenfations, by habit the fibrous con- 

 tractions became caufable by volition ; and both the irritations 

 and fenfations ceafed to be neceflary to their production. As 

 the deliberate locomotions of the body, and the ideas of recol- 

 lection, as when we will to repeat the alphabet backwards. 



4. But as many of thefe fibrous contractions frequently ac- 

 companied other fibrous contractions, by habit they became 

 caufable by their aflbciations with them ; and the irritations, 

 fenfations, and volition, ceafed to be neceflary to their produc- 

 tion. As the actions of the mufcles of the lower limbs in fen- 

 cing are aflbciated with thofe of the arms"*, and the ideas of fug- 

 geftion are afibcicrted with other ideas, which precede or accom- 

 pany them ; as in repeating carelefsly the alphabet in its ufual 

 order after having began it. 



II. We (hall give the following names to thefe four clafles of 

 fibrous motions, and fubjoin their definitions. 



1. Irritative motions. That exertion or change of the fenfo- 

 rium, which is caufed by the appulfes of external bodies, either 

 fimply fubfides, or is fucceeded by fenf*tiop, or it produces 



* fibrous 



