196 ANIMAL FORCES. [ii. 



action^ through the same nerves. External impressions can pro- 

 duce nerve-actions in their way upwards, before they reach the 

 brain (98, i), and at the same time reach the brain and be felt, 

 although their nerve-actions are independent of the brain and 

 of conceptions (362). The movements which a conceptional 

 internal impression excites as sentient actions, may be equally 

 produced by other internal impressions. Movements may, there- 

 fore, have a twofold origin, for an external impression may be 

 felt and excite sentient actions, which are also excited by it as 

 nerve-actions. In the same way an internal impression may, as 

 the result of conceptions, excite sentient actions, and as the re- 

 sult of an irritant applied to the cerebral origin of the same 

 nerve, or in any part of its course, excite the same movements as 

 nerve-actions. When a nerve going to the trunk of a decapitated 

 animal is irritated, movements like those arising volitionally are 

 excited by the irritation (359). It would be, therefore, erroneous 

 to conclude that movements might not be at the same time both 

 sentient actions and nerve- actions, or that actions exactly similar 

 to sentient actions in every respect may not be exclusively nerve- 

 actions, and vice versa. 



364. The possibility that nerve-actions may be at the same 

 time sentient actions, is manifest from a simple consideration 

 of circumstances. 



i. All animal movements in the mechanical machines (7), 

 consequently all sentient actions and nerve- actions, are produced 

 through the nerves. The impressions of the material ideas also 

 act as stimuli to the nerves (130), and produce the appropriate 

 movements (193) : but any other stimulus acting on the same 

 nerves, either at their cerebral origin or on any part of their 

 course dow nwards, must necessarily have a similar effect (359) ; 

 the two kinds of stimuli may occur therefore simultaneously, 

 and co-operate in exciting the same movements. 



ii. If an external impression produces a sentient action, it 

 must act by producing a material external sensation in the 

 brain, the latter exciting the movement by its internal im- 

 pression on the cerebral origin of the nerves. But if this 

 external impression on its way to the brain be reflected in 

 the ganglia, or at the points where branches are given off, 

 on the same fibrils, as it would have acted on if it had 

 actually reached the brain (48, 151), movements must result 



