Chap, vi.] SOME OTHER SENSATIONS. 1061 



of the central nervous system, but by the direct electric or other 

 stimulation of the muscles or motor nerves, the muscular sense 

 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 con- 

 clude that our appreciation of our movements and muscular 

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

 called a muscular sense which is the outcome of afferent im- 

 pulses proceeding from the periphery and started in the parts 

 concerned in the movement. 



§ 661. 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 there 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 articu- 

 lar 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 

 temperature 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 im- 

 pulses 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 



