CHAP, ii.] THE BRAIN. 733 



elude that in them too afferent impulses supply the means of 

 coordination. Evidence of a nature similar to that detailed in 

 reference to the cristae of the ampullae may be brought forward, 

 shewing that the maculae of the utricle and saccule play a part 

 analogous to that of the cristae. Indeed it is urged that the 

 otoliths are important agents in this matter, a view which is 

 supported by the result of removing in various invertebrata the 

 bodies called otoliths ; for this is a want of coordination very 

 similar to that which we are discussing. No effects on the 

 coordination of bodily movements have, so far as is at present 

 known, been seen to follow removal of the cochlea alone, or 

 section of the cochlear nerve alone. We are thus led to the 

 view that the whole vestibular nerve (apart from the sense of 

 hearing which we shall discuss later on) is the agent of the 

 special afferent impulses so essential to the coordination of the 

 movements affecting the equilibrium of the body, and we may 

 speak of those impulses as * vestibular ' ; the name ' labyrinthine ' 

 (from the ' labyrinth ' of the ear) has also been suggested for 

 them. 



479. We may here say a few words on the interpretation 

 of the subjective condition which we speak of as giddiness or 

 dizziness or vertigo. We compared the condition of the pigeon 

 after an injury to the semicircular canals to that of a person 

 who is giddy or dizzy, and indeed vertigo is the subjective ex- 

 pression of a disarrangement of the coordination machinery, 

 concerned in the maintenance of bodily equilibrium. It may 

 be brought about in many ways. When a constant current of 

 adequate strength is sent through the. head from ear to ear, we 

 experience a sense of vertigo ; our movements then appear to a 

 bystander to fail in coordination, in fact to resemble those of a 

 pigeon whose semicircular canals have been injured ; and indeed 

 the effects are probably produced in the same way in the two 

 cases. In what is called Meniere's disease attacks of vertigo 

 seem to be associated with disease in the ear, being attributed 

 by many to disorder of the semicircular canals, and cases have 

 been recorded of giddiness as well as deafness resulting from 

 disease of the eighth nerve. Visual sensations are very potent 

 in producing vertigo. Many persons feel giddy when they look 

 at a waterfall; and this is a case in which both the sense of gid- 

 diness and the disarrangement of coordination is the result of 

 the action of a pure sensation and nothing else. In the well- 

 known intense vertigo which is caused by rapid rotation of the 

 body visual sensations play a part when the rotation is carried 

 on with the eyes open, but only a part; for vertigo may be 

 induced, though not so readily, by rotation with the eyes com- 

 pletely shut. In the latter case the vertigo is in part caused by 

 abnormal vestibular impulses, and in the case of some deaf per- 

 sons, that is, persons whose eighth nerve is diseased, is brought 



