CH. ii.J EXTERNAL IMPRESSIONS. 31 



32. When an impression is received on the terminating fibrils 

 or branches of a nerve, it is termed an external impression (a 

 nerve-feeling from without inwards) (31,403), to distinguish it 

 from an impression passing from within outwards (31, 121), 

 and which must not be confounded with the sense of touch. 

 Whether the impression be made on nerves distributed in the 

 interior of the body or on the exterior, it is the same, provided 

 that when it is propagated, it passes upwards to the brain (31). 

 As to this external impression, experience teaches us, that it is 

 developed in living animals by every touch of the nerve, or by 

 some communicated movement, provided it excites a certain 

 definite, although unknown, change in the medulla of the nerve, 

 and is transmitted upwards to the brain. Every impression on 

 the terminating fibres of a nerve is not an external impression, 

 nor causes one, but only those which so act on the medulla of 

 the nerve, that animal actions directly result (31). For example, 

 light excites no external impression on the most exposed and 

 most delicate nerves of the skin, &c. The most undoubted 

 observations teach us, that animal actions are excited by the 

 agency of contact or movement, not in the investing mem- 

 brane, but in and through the medullary matter of the nerve. 

 (Haller's 'Physiology,' §§365,372,373.) The mode in which 

 the medulla is acted upon by a touch, or any other agent, is 

 purely animal, and difi'ers altogether from the physical and 

 mechanical laws of communicated motion. In every case where 

 a touch of the medulla excites most vivid animal actions, whether 

 they be acts of mind, or motions caused by the animal- sentient 

 forces, or simply by the animal forces (6), there is no perceptible 

 movement in the medulla, nor any change visible therein. Nor 

 are the animal actions resulting from such a touch in proportion 

 to its nature and strength, as when bodies act physically on each 

 other by a blow, pressure, &c.; but often the slightest influences 

 will, in the same nerve, excite the most energetic actions, and 

 a more forcible agent the weakest. Certain agencies cannot 



reach the hrain and are felt, they excite an act of mind, or a Vorstellung, as sensa- 

 tion, perception, desire, &c. All acts of mind necessarily and directly dependent 

 upon such impressions are termed by him sinnlich ; and in this case the word may 

 be rendered by sensational. It must be remembered, however, that the word so 

 used implies causation as well as condition, — vide § 66, and would, I think, be as 

 correctly rendered impressional as sensational. 



