SEC. 2. THE MACHINERY OF COORDINATED 



MOVEMENTS. 



§ 478. We may now direct our attention for a while to some 

 considerations concerning the nature of this complex nervous 

 machinery for the coordination of bodily movements, and espe- 

 cially concerning the part played by afferent impulses. Most 

 of our knowledge on this point has been gained by a study of 

 animals not deprived of, but still possessing their cerebral hemi- 

 spheres, or by deductions from the data of our own experience ; 

 but it is possible in most cases to eliminate from the total results 

 the phenomena which are due to the working of a conscious 

 intelligence. 



Let us first of all turn aside to ourselves and examine the 

 coordination of the movements of our own bodies. When we 

 appeal to our own consciousness we find that our movements 

 are governed and guided by what we may call a sense of equi- 

 librium, by an appreciation of the position of our body and its 

 relations to space. When this sense of equilibrium is disturbed 

 we say we are dizz}^, and we then stagger and reel, being no 

 longer able to coordinate the movements of our bodies or to 

 adapt them to the position of things around us. What is the 

 origin of this sense of equilibrium? By what means are we 

 able to appreciate the position of our body? There can be no 

 doubt that this appreciation is in large measure the product of 

 visual and tactile sensations ; we recognize the relations of our 

 body to the things around us in great measure by sight and 

 touch ; we also learn much by our muscular sense. But there 



is something besides these. Neither sight nor touch nor mus- 

 es o 



cular sense can help us when, placed perfectly flat and at rest 

 on a horizontal rotating table, with the eyes shut and not a 

 muscle stirring, we attempt to determine whether or no the 

 table and we with it are being moved, or to ascertain how much 

 it and we are turned to the right or to the left. Yet under 

 such circumstances we are conscious of a change in our posi- 

 tion, and some observers have been even able to pass a tolerably 

 successful judgment as to the angle through which they have 



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