264 ANIMAL FORCES. [ii. 



impression not induced by conceptions (490). The obscurity in 

 wbich these changes in the brain are involved, is an apology 

 for the want of experiments. (Compare § 159.) 



506. Except in the example stated, § 504, non-conceptional 

 internal impressions act on the mechanical machines, only so { 

 far as the latter have nerves incorporated with them. Their 

 nerve-actions, as well as the sentient actions of the conceptional 

 impressions, are effected through the nerves (160). 



507. The laws of action on the muscular system of the im- 

 pressions derived from conceptions, are applicable to the in- 

 ternal impressions not derived from conceptions, whether they 

 be primary or reflected in their origin (161, 162, 204). The 

 primary are illustrated § 498 ; those from a reflected external 

 impression §§ 415, 495. 



508. Since non-conceptional impressions act on the muscular 

 system, they must also excite movements of the limbs. Examples 

 of this kind are seen, when a decapitated man, either from the 

 primary internal impression of the sword- stroke in his spinal 

 cord, or from the reflected external impression of the injury, 

 makes those movements, which a conception of danger, or an 

 external sensation of the injury, would have led him to make ; 

 or when an animal, decapitated while moving, still goes on, and 

 continues its former sentient actions in the muscles of locomo- 

 tion, as nerve-actions, &c. 



509. A nerve-action in a muscle from an internal impres- 

 sion implies the transmission of the impression along the nerve, 

 in the direction from the brain downwards to the muscle which 

 is excited to movement. If the movement be the indirect 

 nerve-action of an external impression, it implies that an ex- 

 ternal impression, is reflected in its course upwards to the brain, 

 and transmitted from the point of reflexion downwards, as an 

 internal impression, to the muscle excited to movement (422, 

 496). 



510. The same nerve of a muscle may receive external im- 

 pressions, at the same time that internal impressions on it 

 excite muscular action, and this external impression may be 

 either felt, or develop nerve-actions, without the two antago- 

 nistic impressions impeding each other^s action (487). 



511. When a nerve is tied, divided, or compressed, an in- 

 ternal impression (whether primary or reflected in its origin) if 



