KJJ. 



I 



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CH. II.] NERVE^ACTIONS, EXTERNAL IMPRESSIONS. 227 



from its course, or it must have ganglia, plexuses, or points of 

 division, in which the impression itself may be deflected in its 

 course upwards. In this case, the impression is reflected either 

 in the nerve itself, or on its eff'erent fibrils, or in the ganglia 

 and plexuses, on altogether diff'erent nerves, and thus it passes 

 downwards, as a reflected internal impression, but unfelt, and, 

 as such, can excite nerve-actions in those machines suppliied 

 with the nerves, along which it is reflected. 



422. The conditions, then^ which are requisite to the pro- 

 duction of indirect nerve-actions by an external impression, 

 are — 



i. The external impression must be transmitted upwards, to 

 that point of the nerve where it is reflected, and changed into 

 a non-conceptional, internal impression j as^ for example, to 

 that point where the efferent fibrils of the nerve are excited by 

 the external impression, or where the nerve-fibrils are given off 

 which subserve to the required nerve-action ; or to the ganglia, 

 or to the plexuses which contain them (415, ii). 



ii. Reflexion of the external impression, or its change into a 



n-conceptional impression, must actually take place there, 

 'y in other words, must duly affect the efferent or other fibrils 

 bove mentioned (121). 



iii. This new internal impression must also be transmitted 

 to, and reach, the mechanical machines to which the fibrils are 

 istributed (128, 415). 



The indirect nerve-actions of external impressions are, con- 

 sequently, no other than nerve-actions of non-conceptional in- 

 ternal impressions, originating from external impressions turned 

 back from their course towards the brain, and unfelt. 



423. Although this reflexion of external impressions fre- 

 uently takes place, and always in certain circumstances or- 



ined by nature (48), yet it does not follow that it takes place 

 solutely in every case. On the contrary, it is often seen 

 at an external impression, which excites in certain machines 

 ct or indirect nerve-actions, excites also, at the same time, 

 the same movements in other machines regulated by other 

 nerves ; nay, is even felt, and produces them as sentient actions 

 of the internal impression of the external sensation (363, 364, ii), 



424. An indirect nerve-action from an external impression 

 cannot arise, or is prevented, — 



