INTRODUCTION. 



353. Animal forces acting without the co-operation of the 

 conceptive force, are termed nerve-forces (vis nervosa), or 

 purely animal forces (183, 186), and their actions are nerve- 

 actions [Nervenwirkungen], ov purely animal movements. 



354. In virtue of the vis nervosa^ the animal body becomes 

 capable of functions, which cannot be explained either by the 

 mechanical and physical laws of motion, or by the laws of the 

 animal-sentient forces, but which are performed by the animal 

 machines, supplied according to special laws with vital spirits 

 (6,183). To these belong the purely animal movements caused 1 

 by an external impression on the nerves before it excites a 

 material external sensation in the brain (98, i), with which the 

 muscular irritability [Muskelreiz] of Haller must be classed 

 [vide § 388), as well as those excited by internal impressions 

 on the medulla of the nervous system and which excite no con- 

 ceptions ; or by other stimuli than conceptions, including many i 

 actions attributed to nervous irritability [Nervenreiz] by Haller. 

 (See § 386.) 



The following is the plan of this, the Second Part : 

 In Chapter I, the vis nervosa and the nerve-actions are 

 considered generally. In Chapter II, the vis nervosa of the 

 external impression ; and in Chapter III, the vis nervosa of the 

 internal impression in the medulla of the brain and nerves, are 

 considered ; and lastly, in Chapter IV, the relations of the vis 

 nervosa and of the cerebral forces are reviewed. 



