CHAP, vi.] SOME OTHER SENSATIONS. 1435 



of the movement which results differs little from that of a like 

 voluntary movement. If for instance, while our eyes are shut, the 

 wrist be bent by direct stimulation of the flexor muscles, we are 

 aware of the movement and can appreciate its character and 

 amount ; we can even use such an artificial movement to judge 

 of weight and resistance. It is indeed urged that our judgment 

 under such conditions is less secure than when the movement is a 

 voluntary one ; and from this it is argued that our judgment is 

 at least assisted by our appreciation of the central changes by a 

 "sense of the effort" as distinguished from a muscular sense of 

 peripheral origin ; but even this is disputed. We may at least 

 conclude that our appreciation of our movements and muscular 

 efforts is largely, if not wholly, dependent on what may be called 

 n muscular sense which is the outcome of afferent impulses 

 proceeding from the periphery and started in the parts concerned 

 in the movement. 



893. Coming next to the questions, What is the exact nature 

 of these afferent impulses ? In what tissues are they started, and 

 along what paths do they travel ? we find the answers beset with 

 considerable difficulties. Every movement of the body, even a 

 simple one, is in reality a complex affair, and the carrying it out 

 involves changes in several tissues. In the first place therie are 

 changes in one or more muscles, changes of contraction in active 

 movements, of extension and relaxation in passive movements. In 

 the second place there are changes in the skin which during a 

 movement is in one spot stretched, in another relaxed or folded ; 

 and in movements of locomotion the pressure of the foot on the 

 ground is continually changing. In the third place, by far the 

 majority of movements affect a joint, and hence involve changes in 

 the relations of the articular surface, in the capsule and ligaments 

 and in the tendons. All these are possible sources of afferent 

 impulses. 



Now we know that the skin is a source of afferent impulses 

 and so of sensations, namely, the sensations of pressure, of tem- 

 perature and of pain ; and we may fairly suppose that stretching 

 or slackening the skin gives rise to impulses either analogous to 

 those caused by the pressure of an external object or, it may be, 

 of a nature more akin to those which belong to general sensibility. 

 Hence it is possible that these do at least contribute, under 

 normal circumstances, to what as a whole we call the muscular 

 sense. 



Indeed it is maintained by some that these cutaneous impulses 

 furnish the whole basis of what is called the muscular sense, the 

 name on this view being of course erroneous. In attempting to 

 judge of such a view we may appeal on the one hand to our own 

 consciousness, and on the other hand to the phenomena of in- 

 coordinate movements. In a previous part of this work, 643, we 

 dwelt upon the importance of afferent impulses as factors in the 



