CH. III.] VIS NERVOSA OF INTERNAL IMPRESSIONS. 255 



thereby. This, it would appear, is the normal condition of 

 the heart ; for it is not only not sensitive, but is excited to the 

 most violent movements by external impressions on its nerves 

 (455, 456). It is also excited to movements by the internal 

 impressions of some conceptions (167, 211). Nevertheless, the 

 will exerts no influence over it; and the internal irritation of the 

 trunks of its nerves never causes, so far as has been observed, 

 any internal impression in them, and develops no nerve-actions 

 in it; on the contrary, the hearths action remains unchanged, and, 

 if separated from the body, is not re-excited thereby, although 

 this readily results from an external irritation. {Vide § 515, 

 and Haller^s 'Physiology,' § 101.) If it be conceded that, 

 from natural impediments, the efferent fibrils of the cardiac 

 nerves transmit only few kinds of internal impressions, and are 

 capable only of certain conceptions, being at the same time 

 incapable, for the most part at least, if not wholly, of other 

 kinds, and particularly of non- conception al internal impressions; 

 whilst, on the other hand, the afferent fibrils are readily sus- 

 ceptible of an infinite number of external impressions, we can 

 thus comprehend the phenomena, without having recourse to 

 the erroneous doctrine that the cardiac movements result from 

 an animal motive force innate in the muscular fibre, and inde- 

 pendent of the nerves (380 — 388). 



489. The ordinary natural stimuli of the nerves causing in- 

 ternal impressions, are, — I, the conceptions which produce 

 sentient actions (121, 123) ; and, 2, reflected external impres- 

 sions (399), which excite indirect nerve-actions of external 

 impressions, and, consequently, nerve-actions of non-concep- 

 tional internal impressions (399, 421-2). Both can effect the 

 same movements in the mechanical machines, or one only, as 

 well as both (360, 364). These movements may be nerve- 

 actions, excited by reflected external impressions only, and be 

 as connected and adapted as if they were sentient actions ex- 

 cited by conceptions (438). Nature has endowed sentient 

 animals with both kinds of stimuli, but to those which exhibit 

 no conceptive faculty, she has only given the last mentioned ; 

 and she thereby attains, in both, the same end, namely, to 

 impart to them internal impressions, which, together with the 

 direct vis nervosa of the external impressions, constitute the 

 proper natural incitants of the animal movements of the me- 



