276 ANIMAL FORCES. [ii. 



impression (399, 422, 360), and may likewise result as direct ' 

 norve-actions, from the vis nervosa of external impressions 

 (435). These principles have already been fully established 

 by the details of experiments on decapitated animals, and by 

 an analysis of the phenomena of muscular contractioD. Com- 

 pare §§ 201, 357, 445, 453, &c. 



543. When an internal impression, from external sensations, 

 excites direct sentient actions in mechanical machines, which 

 have not received the external impression, it is reflected at the 

 cerebral origin of the nerve along fibrils which were not 

 impressed (188, 129, iv). If a non-conceptional impression, by 

 means of a direct nerve-action of an external impression, de- 

 velops movements in another machine than that duly im- 

 pressed by the external sensation, or excites them in the same 

 machine by means of other fibrils, it operates exactly as in 

 the preceding case. A non-conceptional primary internal im- i 

 pression produces the same effects under conditions already | 

 stated (436, 496). If, therefore, such an impression excite a 

 nerve-fibril, in the same way as it is excited by the internal 

 impression of an external sensation, then the same changes 

 take place, as a nerve-action, that usually accompanied the 

 felt external impression, and constituted a sentient action of 

 the external sensation. 



544. When external sensations excite incidental sentient 

 actions, the material external sensation impresses the origins 

 of other nerves in the brain, which have not received the 

 external impression (124, 131), since it causes material ideas 

 in the brain for other conceptions (97). Consequently, the 

 incidental sentient actions of external sensations differ only 

 in the mode of causation, from those of other and spontaneous 

 conceptions (219, &c.), and are not really different. But 

 just as in a similar manner felt external impressions, acting 

 through nerves indirectly, induce sentient actions of spon- 

 taneous conceptions, so also unfelt external impressions induce 

 nerve-actions of non-conceptional internal impressions, con- 

 stituting the same movements which the spontaneous sensa- 

 tional conceptions caused by sensation would develop ; provided 

 only, that the unfelt external impressions be so deflected from 

 their course before they reach the cerebral origin of their 

 nerve, as to impress the same nerves as the spontaneous con- 



