EQUILIBRIUM SENSATIONS. 589 



afferent impulses, which change the condition of the 

 co-ordinating locomotor centres, with every position of the 

 head. Or, movements of the endolymph in relation to the 

 wall of the canal may be the stimulus, the current swaying 

 the projecting hairs (Fig. 149).* Place a few small bits of 

 cork in a tumbler of water, and rotate the tumbler; at first 

 the water does not move with it; then it begins to go in 

 the same direction, but more slowly; and, finally, moves at 

 the same angular velocity as the tumbler. Then stop the 

 tumbler, and the water will go on rotating for some time. 

 Now if the head be turned in a horizontal plane similar 

 phenomena will occur in the endolymph of the horizontal 

 canal; if it be bent sidewise in the vertical plane, in the 

 anterior vertical canal; and if nodded, in the posterior verti- 

 cal; the hairs moving with the canal would meet the more 

 stationary water and be pushed and so, possibly, excite the 

 nerves at the deep ends of the cells which bear them, and gen- 

 erate afferent impulses which will cause the general nerve- 

 centres of bodily equilibration to be differently- acted upon 

 in each case, tinder ordinary circumstances the results of 

 these impulses do not become prominent in consciousness 

 as sensations; but they sometimes may. If one spins round 

 for a time, the endolymph takes' up the movement of the 

 canals, as the water in the tumbler does that of the glassy 

 on stopping, the liquid still goes on moving and stimulates 

 the hairs which are now stationary; and we feel giddy, 

 from the ears telling us we are rotating and the eyes that 

 we are not; hence difficulty in standing erect or walking 

 straight. A common trick illustrates this very well; make 

 a person place his forehead on the handle of an umbrella, 

 the other end of which is on the floor, and then walk three 

 or four times round it, rise, and try to go out of a door; 

 he will nearly always fail, being unable to combine his 

 muscles properly on account of the conflicting afferent 

 impulses. If a person, with eyes shut, be laid on a hori- 

 zontal table which is turned, he can at first feel and tell the 

 direction of the rotation; as it continues he loses the feeling, 

 and when the movement stops feels as if he were being turned 



* Page 542. 



