CH. III.] VIS NERVOSA OF INTERNAL IMPRESSIONS. 259 



internal impression, be tied or divided, the function may cease 

 or be interrupted, because the co-operation of the internal im- 

 pression ceases ; although the same function can be renewed, if 

 an external impression be made, or a new internal impression 

 be communicated to the nerve below the ligature or section. 

 If, however, the usual non-conceptional impression stimulus be 

 applied to the nerve near its cerebral origin, whether directly, 

 or whether as an external impression reflected and changed 

 there into a non-conceptional impression, then the presence 

 of the brain and its unbroken connection with the nerves of 

 the machines are requisite to the continuance of the natural 

 functions of the latter; although they may be renewed by a 

 renewed impression, or by the renewal of one or of both im- 

 pressions. Thus, a muscle is enfeebled, or the natural move- 

 ments of the heart, diaphragm, &c., interrupted, so soon as the 

 connection of their nerves with the brain is broken ; yet their 

 functions can be renewed so soon as one of the two kinds of vis 

 nervosa communicates a new impulse, and the heart receives an 

 external impression below the ligature, or the diaphragm an 

 internal impression, or the muscle either or both. 



iii. Nevertheless, the brain and the conceptive force are 

 necessary to these movements of the non-conceptional internal 

 impression, when, to continue in their natural order, they must 

 be at the same time sentient actions ; for the removal of the 

 brain interrupts this natural order, although it does not abolish 

 it irreparably. 



iv. That the brain is necessary to the prolonged continuance 

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

 in so far as its medullary substance supplies vital spirits to the 

 nerves, has been already stated ; it is also necessary in those 

 cases, in which the nerve-action depends on an internal im- 

 pression made near to or at the cerebral origin of the nerve, 

 but not by conceptions. But it is manifest, that in none of 



i these cases, the action of the cerebral forces or of the conceptive 

 force is necessary to nerve-actions, and that even in the in- 

 stances mentioned in par. iii, neither contributes to the sole 

 production of the movements as nerve-actions. 

 495. When an internal impression is not a primary, but a 

 reflected external impression, it causes nerve-actions, as if it 

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