upon Animal Bodies. 5 



Muscular motion, that is, the contraction and subse- 

 quent elongation of muscular fibres, we are told, is a 

 totally different power ; which doctrine is founded on 

 the following fact, that the force which is exhibited in 

 muscular action is greater than the power which is ap- 

 plied to produce it. This, however, appears to us to 

 prove no more than this, viz., that the source of this 

 extraordinary re-action in the living muscular fibre can- 

 not be traced, either in the agent which excites it, nor 

 can it be said to depend upon volition ; for the most 

 violent and extraordinary contractions are involuntary, 

 as in cases of somnambulism, hysteria, insanity, &c. 

 But it does not at all destroy the position, that a regular 

 and equal motion of the component parts of the animal 

 body, and a certain degree of temperature, must exist, 

 or this excitement cannot be produced. " Omne quod 

 vivit, sive animal, sive terra editum, id vivit propter in- 

 clusum in eo calorem ; quod autem alitur et crescit, 

 motu quodam utitur certo et equabili, qui quamdiu re- 

 manet in nobis, tamdiu et vita remanet, refrigerato au- 

 tem et extincto calore, occidimus ipsi, et extingui- 

 mur*." 



Muscular action, therefore, though arising from an in- 

 dependent power, is subject to some known laws. 

 The disposition of the living fibre to contract, Dr. 

 Brown very appropriately terms excitability, and, to the 

 foreign agents concerned in its continuance and renova- 

 tion, he applies the general term stimulus. The influ- 

 ence of any stimulus on the excitability of the subject 



* Cicero, Nat. Deorum. 



