(II. IV.] SUBSTITUTION OF NERVE-ACTIONS. 295 



tions. The apparent instances adduced to the contrary, are 

 really only examples in which the sentient actions are instinctive 

 in their nature, and have arisen from direct external sensations. 



574. The material ideas of the conceptions of the understanding, 

 are not excited like those of sensational conceptions by external 

 impressions (66) ; consequently, they cannot be excited by 

 the vis nervosa of the latter, in the order in which they are 

 developed psychologically. But as all material ideas, and, con- 

 sequently, those of the intellectual conceptions are internal 

 impressions on the cerebral origin of the nerves (121), it follows 

 that their actions may be developed by the vis nervosa of non- 

 conceptional internal impressions (360). Still, as they manifest 

 no visible direct sentient actions (330), except in so far as they 

 are either at the same time sensational (and then the vis nervosa 

 can excite them) or incitements of the mind, and excite the 

 will, it follows that no direct actions of the intellectual con- 

 ceptions can be induced as nerve-actions by the vis nervosa 

 acting through the nerves. 



575. The incidental influence of the understanding on the 

 animal economy arises in various ways (331), and can only be 

 replaced by the vis nervosa acting alone, in so far as it consists 

 in sentient actions from sensational conceptions, or from plea- 

 sure or pain of the desires and aversions, whether sensational 

 or intellectual (574). In so far, however, as the eflPort of the 

 intellectual power involves and disorders the entire organism 

 (331, 332), and an abuse of the cerebral forces must necessarily 

 have this effect, — to this extent the effects of the abuse of the 

 vis nervosa are identical, whether the latter co-operate with the 

 former or not (356 — 360). For example, just as study en- 

 feebles the body, wastes it, and disorders its natural functions, 

 so also does an excessive indulgence of the sensational instincts 

 (261, iv). Thus, an abuse of the sexual instinct has the same 

 injurious effect as excessive study. 



576. The gentle influence which the intellectual conceptions, 

 in so far as they are agreeable, or the contrary, have on the 

 vital movements (333), may be exercised by non-conceptional 

 internal impressions ; and in this way the movements of the 

 muscles which the intellectual desires and aversions, and 

 their satisfaction, develop as direct sentient actions (340), 

 are often incidentally mere nerve-actions of impressions 



