CHAP, vi.] THE BRAIN. 615 



The movements are not occasioned by any partial paralysis, by 

 any want of power in particular muscles or group of muscles. Nor 

 on the other hand are they due to any uncontrollable impulse; 

 a very gentle pressure of the hand suffices to stop the movements 

 of the head, and the hand in doing so experiences no strain. The 

 assistance of a very slight support enables movements otherwise 

 impossible or most difficult, to be easily executed. Thus, though 

 when left alone the bird has great difficulty in drinking or picking 

 up corn, it will continue to drink or eat with ease if its beak be 

 plunged into water, or into a heap of barley ; the slight support of 

 the water or of the grain being sufficient to steady its movements. 

 In the same way, it can, even without assistance, clean its feathers 

 and scratch its head, its beak and foot being in these operations 

 guided by contact with its own body. 



In mammals (rabbits) section of the canals produces a loss of 

 coordination similar to that witnessed in birds ; but the movements 

 of the head are not so marked, peculiar oscillating movements of 

 the eye-balls (nystagmus), differing in direction and character 

 according to the canal or canals operated upon, becoming however 

 very prominent. In the frog no deviations of the head are seen, 

 but there is, as in other animals, a loss of coordination in the 

 movements of the body. 



Injury to the bony canals alone is insufficient to produce the 

 symptoms ; the membranous canals themselves must be divided or 

 destroyed. 



How are we to explain these remarkable phenomena ? Let us 

 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 move- 

 ments of our bodies or to adapt them to the position of things 

 arouad 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 

 muscular sense would help us when, placed perfectly flat and at 

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

 muscle stirring, we attempted to determine whether the table 

 and we with it were moved or no, or to ascertain how much it 

 and we were turned to the right or to the left. Yet under such 

 circumstances we are not only conscious of a change in our position 

 but some observers have been able to pass a tolerably successful 



