644 THE BRAIN. 



striking facts bearing on this matter have been gained by studying the effects 

 of operative interference with certain parts of the internal ear, known as the 

 semicircular canals. 



When in a pigeon the horizontal membranous semicircular canal is cut 

 through, the bird is observed to be continually moving its head from side to 

 side. If one of the vertical canals be cut through, the movements are up 

 and down. The peculiar movements may not be witnessed when the bird is 

 perfectly quiet, but they make their appearance whenever it is disturbed or 

 attempts in any way to stir. When the injury is confined to one canal only, 

 or even to the canals of one side of the head only, the condition after a 

 while passes away; when the canals of both sides have been divided, it 

 becomes much exaggerated, lasts much longer, and in some cases is said to 

 remain permanently. After such injuries it is found that these peculiar 

 movements of the head are associated with what appears to be a great want 

 of coordination of bodily movements. If the bird be thrown into the air, 

 it flutters and falls down in a helpless and confused manner ; it appears to 

 have lost the power of orderly flight. If placed in a balanced position, it 

 may remain for some time quiet, generally with its head in a peculiar pos- 

 ture : but directly it is disturbed, the movements which it attempts to execute 

 are irregular and fall short of their purpose. It has great difficulty in pick- 

 ing up food and in drinking; and in general its behavior very much resem- 

 bles that of a person who is exceedingly dizzy. 



It can hear perfectly well, and therefore the symptoms cannot be regarded 

 as the result of any abnormal auditory sensations, such as a " roaring " in the 

 ears. Besides any such stimulation of the auditory nerve as the result of the 

 section would speedily die away, whereas these phenomena may last for a 

 very considerable time. 



The movements are not occasioned by any partial paralysis, by any want 

 of power in particular muscles or group of muscles ; though removal of 

 the canals of one side has been described as leading to diminished muscular 

 force on the same side of the body, the mere diminution of force is insuffi- 

 cient to explain the phenomena. Nor, on the other hand, are the movements 

 due to any uncontrollable impulse ; a very gentle pressure of the hand suf- 

 fices to stop the movements of the head, and the hand in doing so experi- 

 ences 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 eat with ease if its beak be plunged into water or into a 

 heap of barley ; the slight support of the water or the grain seems 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 ope- 

 ations guided by contact with its own body. 



The amount of disorder thus induced differs in different birds, and some 

 movements are more affected than others. As a general rule, it may be said 

 that the more complex and intricate a movement, the fuller and more del- 

 icate the coordination needed to carry it out successfully, the more markedly 

 is it disordered by the operation ; thus, after injury of the canals, while a 

 pigeon cannot fly, a goose is still able to swim. 



In mammals (rabbits) section of the canals also produces a certain 

 amount of loss of coordination, but much less than that witnessed in birds ; 

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

 movements of the eyeballs, differing in direction and character according 

 to the canal or canals operated upon, becoming, however, prominent. In 

 the frog no deviations of the head are seen, but there is some loss of coordi- 

 nation in the movements of the body. In fishes no effect at all is produced. 



