CHAP, vi.] THE BRAIN. 619 



when that sense is deranged, we feel giddy and cannot stand. We 

 have no reason, however, for thinking that the failure to keep 

 upright is due to the feeling of giddiness, in the sense of being 

 a direct result of the condition of the consciousness. On the con- 

 trary, since the peculiar movements characteristic of vertigo may 

 take place in the absence of consciousness without the vertigo 

 being actually felt, we may with security assert that the failure to 

 stand upright and the feeling of giddiness are both concomitant 

 effects of the same disarrangement of the coordinating mechanism. 



It cannot be too much insisted upon that for every bodily 

 movement of any complexity afferent impulses are as essential as 

 the executive efferent impulses. Our movements, as we have 

 already urged, are guided not only by the muscular sense, but also 

 by contact sensations, auditory sensations, visual sensations, and 

 visual perceptions (for the remarks made above concerning the 

 relations of the coordinating mechanism to consciousness do not 

 exclude the possibility of consciousness affecting the mechanism, 

 indeed not only may perceptions enter into the causation of vertigo, 

 but even an imaginary idea may be the sole exciting cause of this 

 condition); and when we say 'they are guided,' we mean that with- 

 out the sensations the movements become impossible. In studying 

 vision we saw repeatedly that the movements of the eyes were 

 directly dependent on vision, and every ball-room affords abundant 

 evidence of the ties between sensations of sound and motions of the 

 limbs. So essential, in fact, are afferent impulses to the develop- 

 ment of complex bodily movements, that we are almost justified in 

 considering every such movement in the light of a reflex action 

 made up of afferent and efferent impulses and central actions, and 

 set going by the influence of some dominant afferent impulse, or 

 by the direct action of those nervous changes, whose psychical cor- 

 relative is what we call the will, on the centre itself. All day long 

 and every day multitudinous afferent impulses, from eye, and ear, 

 and skin, and muscle, and other tissues and organs, are streaming 

 into our nervous system ; and did each afferent impulse issue as its 

 correlative efferent motor impulse, our life would be a prolonged 

 convulsion. As it is, by the checks and counterchecks of cerebral 

 and spinal activities, all these impulses are drilled and marshalled, 

 and kept in hand in orderly array till a movement is called for ; and 

 thus we are able to execute at will the most complex bodily 

 manoeuvres, knowing only why, and unconscious or but dimly 

 conscious how, we carry them out. 



We have ventured to use the phrase ' coordinating centre,' but 

 it must be understood that we have no right to attach more than a 

 general meaning to the words. We cannot, at present at least, 

 define such a centre in the same way that we can the vaso-motor 

 or respiratory centre. When the optic lobes as well as the cerebral 

 hemispheres are removed from the frog, the power of balancing 

 itself is lost ; when such a frog is thrown off its balance by inclining 



