OF SENSATION IN GENERAL. 855 



being itself adequate to the production of changes in its ordinary nutritive 

 action. 



859. It seems to be by an innate law of our constitution, that these subject- 

 ive sensations, whether originating at the central terminations of nerves, or in 

 the course of their trunks, should be referred by the mind to the ordinary situa- 

 tions of their peripheral terminations; even though these should not exist, or 

 should be destitute of the power of receiving impressions. Thus after amputa- 

 tions, the patients are for some time affected with sensations (originating 

 probably in the cut extremities of the nerves), which they refer to the removed 

 extremities ; the same has been noticed in regard to the eye, as well when it 

 has been completely extirpated, as when its powers have been destroyed by 

 disease. The effects of the Taliacotian operation also exhibit the operation of 

 this law in a curious manner } for until the flap of skin from which the new 

 nose is formed obtains vascular and nervous connections in its new situation, 

 the sensation produced by touching it is referred to the forehead. Another 

 interesting illustration of it may be obtained by the following very simple ex- 

 periment : If the middle finger of either hand be crossed behind the forefinger, 

 so that its extremity is on the radial side of the latter, and the ends of the two 

 fingers thus disposed be rolled over a marble, pea, or other round body, a sen- 

 sation will be produced, which, if uncorrected by reason, would cause the mind 

 to believe in the existence of two distinct bodies; this is due to the impression 

 being made at the same time upon the radial side of the forefinger, and the 

 ulnar side of the middle finger two joints which, in the natural position, are at 

 a considerable distance. 



860. Sensations of a purely subjective nature may excite precisely the same 

 muscular movements, or other changes in the bodily system, as do similar 

 sensations produced by objective realities. Of this we have abundant evidence 

 in the effects of sensations called up by ideas ( 758, 863) ; the following 

 example, however, is peculiarly valuable, a,s showing that the sensation still 

 operates in directing movement, even though there be an intellectual conscious- 

 ness that there is no objective cause for it, and that the movement is conse- 

 quently inappropriate. A lady nearly connected with the Author, having been 

 frightened in childhood by a black cat, which sprang up from beneath her pillow 

 just as she was laying her head upon it, was accustomed for many years after- 

 wards, whenever she was at all indisposed, to see a black cat on the ground 

 before her ; and although perfectly aware of the spectral character of the ap- 

 pearance, yet she could never avoid lifting her foot as if to step over the cat, 

 when it seemed to be lying in her path. 



861. The acuteness with which particular Sensations are felt is influenced in 

 a remarkable degree by the attention they receive from the mind. If the mind 

 be entirely inactive, as in profound sleep, no sensation whatever is produced by 

 ordinary impressions ; and the same is the case when the attention is so com- 

 pletely concentrated upon some object of thought or contemplation that sensa- 

 tions altogether unconnected with it fail to make any impression on the percep- 

 tive consciousness. On the other hand, when the attention is from any cause 

 strongly directed upon them, impressions very feeble in themselves produce 

 sensations of even painful acuteness ; thus, every one knows how much a slight 

 itching of some part of the surface may be magnified by the direction of the 

 thoughts to it, whilst, as soon as they are forced by some stronger impression 

 into another channel, the irritation is no longer felt ; so, too, it must be within 

 the experience of most persons, how vividly sounds are perceived when they 

 break in upon the stillness of the night, being increased in strength, not only 

 by the contrast, but by absorbing the whole attention. An interesting experi- 

 ment is mentioned by Miiller, which shows how completely the mind may be 

 unconscious of impressions communicated to it by one organ of sense, when 



