64 PHYSIOLOGY. 



For the contraction of a muscular fibre is excited by being ex- 

 tended ; and a contraction is produced, whilst the stretching 

 power continues to be applied. The same contraction is also 

 excited by various applications, whose mode of action we do 

 not perceive ; but we know them to be such as do not affect in- 

 animate elastics. 



In respect of these causes by which it may be excited, the 

 contractility of muscular fibres hath been called IRRITABILITY. 



LXXXIV. The force of contraction in muscular fibres is 

 often much greater than that of the causes exciting it. 



LXXXV. The contractility of muscular fibres (LXXXIII.) 

 appears especially in living bodies, ceases with life, or soon after, 

 and is probably never produced but with life. Hence it is, that, 

 by some writers, it is called the VITAL POWER, and the muscu- 

 lar fibre endued with it the LIVING SOLID. (Gaub. Patholog. 

 169. 170.) 



LXXXVI. The contractility (LXXXIII., LXXXIV., 

 and LXXXV.) hath been supposed to belong to muscular 

 fibres, independently of their connexion with the other parts of 

 the nervous system ; and, upon that supposition, it hath been 

 called the vis insita. We shall call it the INHERENT POWER. 

 (Holler. Prim. Lin. 400.) " I consider this contractility as oc- 

 curring in living vegetables : to consider vegetable life may be 

 as difficult as that of animals ; but this contractility is the pro- 

 perty of living bodies; and a vegetable is such, in as far as its 

 functions are connected, and depend upon a whole. 



" A muscle cut out of the body and this experiment has been 

 frequently made with the heart for a long time shews itself 

 possessed of moving powers : it shews its irritability, and, when 

 its spontaneous motion has seemingly ceased, it may, by the 

 prick of a needle, or other irritamenta, be made to renew its mo- 

 tion. Now, this power may reside entirely in the muscular 

 fibre itself; and so Dr. Haller and others have supposed, and 

 termed it the vis insita" 



LXXXVI I. The contraction of muscular fibres can be ex- 

 cited by applications made to other parts of the nervous system, 

 as well as to the muscles themselves ; and, as the effects of those 

 applications made to the other parts of the nervous system can 

 be prevented by ligatures made upon the nerves between the 



