260 ON THE SES-SES. 



elbow under wliicli runs tlae nerve in question ; and tliug, likewise, it is the foot 

 and toes which are benumbed when, by pressure on that part of the thigh under 

 which lies the nerve running to those members, the feeling is produced which 

 we call being " asleep." Thus, while with the sensations of touch there is con- 

 nected a rigid perception of the point at which the exciting cause operates, there 

 is ^ false perception in the case of the common feeling of pain ; we transfer the 

 place of uneasiness to those parts where the nerves of the irritated member 

 terminate. A striking instance of this erroneous transposition is frequently wit- 

 nessed in cases of amputation; if the ends of the divided nerves in an amputated 

 arm or leg become ii-ritated, it is usual for the patient to feel the pain in the 

 finger or toes of the removed member. The error is easily explained if we in- 

 T-estigate the origin of the localizing sensation. In no sensation, either that of 

 louch or of pain, is the perception of place originally comprised ; we can have 

 as little direct perception of a place as of an object ; we acquire only indirectly 

 and mediately, by help of the sensation, an idea of the place of excitation and of 

 an exciting external object. The origination of both ideas is intimately con- 

 nected. Further on, when we specially consider the sense of place, (Ortsinn,) 

 it will be shown that the localization of a sensation of touch and the perception 

 ■ of space through the sense of touch depend on analogous conditions, as we have 

 already incidentally stated in regard to the perception of space through the sense 

 of sight. In like manner, every sensation of touch has, for each fibre which 

 causes it, a peculiar sign or token from which we learn to form the idea of the . 

 situation of the terminal point of that fibre in the skin, and we soon attain a pro- 

 ficiency which enables us instantaneously to distinguish the local sign which 

 corresponds with the sensation. But the same sign also accompanies the sensa- 

 tion generated by any particular fibre when this is irritated, not at its extremity, 

 but at some point in its passage; no wonder then that the mind is deceived, and 

 •assigns the origin of the sensation to that point to which, by the customary 

 token, it has been taught at first to refer it. Thus the pain communicated by 

 the nerve-fibres of the elbow is referred to all the points in which those collective 

 fibres terminate. That, moreover, it is only the sensations of touch and tem- 

 perature — sensations arising from excitation of the ends of the nerves fn the skin — 

 which relate to outer ohjccts, while the sensations of pain, on the other hand, are 

 -always subjective, may be shown in the following manner, thus establishing a 

 still Avider and substantial difference between the two classes of sensations — 

 that of touch and that of common feeling. "We learn to distinguish external 

 objects as causes of sensation by satisfying ourselves of the endless variations 

 of the sensation arising from the movement of the sensitive parts of our body 

 towards exterior objects, or of those objects towards our organs of sensation. 

 That we am-ive at this knowledge is owing to two essential conditions : first, 

 that our organ of touch, the sensitive surfaces of our skin, are, in the highest 

 degree and the most different directions, movable ; and secondly, that we pos- 

 sess a peculiar, but generally unnoticed sense, which continually apprises us 

 that our limbs are in a state of rest or of .motion ; and if the former, what is 

 their actual position ; if the latter, what is the extent and direction of the move- 

 ment. Close your eyes and execute all possible movements, you will be always 

 and accurately conscious what motion has been performed by each member, 

 what has been at each moment the relative position of each limb in regard to 

 every other. 



To return to the important help afforded by this sixth sense in the operations 

 pertaining to touch : the organs of this sense arc the muscles, each of which in 

 acting, or by the contraction through which the points of attachment at its ends 

 are brought nearer together, produces a sensation whose intensity is proportional 

 to the effort and the extent of the actual contraction. The mind learns to in- 

 terpret these feelings of effort like other sensations; it ascertains that, with every 



