1012 SEMICIRCULAR CANALS. [BOOK in. 



Let us now for a while 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 equilibrium, 

 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 dizzy, 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 appre- 

 ciation 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 muscular 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 position, and some observers have been even able to 

 pass a tolerably successful judgment as to the angle through which 

 they have been moved. There can be no doubt that such a 

 judgment is based upon the interpretation by consciousness of 

 afferent impulses which are dependent on the position of the 

 body, but which are not afferent impulses belonging to sensations 

 of touch or sight, or taking part in the muscular sense. And it 

 is urged with great plausibility that the afferent impulses in 

 question are those which we have just referred to as started in 

 the semicircular canals. 



If we admit the existence of such ampullar impulses, if we 

 may venture so to call them, and recognise them as contributing 

 largely not only to our direct perception of the position of the 

 head and thus of the body, but also in a more indirect way to 

 what we have called the sense of equilibrium, we should expect to 

 find that when they are abnormal the sense of equilibrium is 

 disturbed, and that in consequence a failure of coordination in our 

 movements results. And the loss of coordination which we 

 described above as resulting from injury to the semicircular 

 canals has accordingly been attributed to a deficiency or disorder 

 of normal ampullar impulses. 



But we must here distinguish between two things. It seems 

 clear that when the membranous canals are injured or otherwise 

 stimulated afferent impulses are generated which on the one hand 

 may produce peculiar movements of the head, and on the other 

 hand seem able when the injury is large to cause a loss of coordi- 

 nation of bodily movements. But it does not necessarily follow 



