AUDITORY NERVE. 701 



circular canals bring rotatory and angular movements to perception, while the 

 nerve-terminations in the saccule, with the otoliths, do the same for the position 

 of the head with relation to the vertical and the existence of straight translational 

 movements. Vertigo (with nystagmus) cannot be induced in deaf-mutes and 

 animals whose labyrinths have been destroyed, nor in a labyrinthine inverte- 

 brates, and young tadpoles, which are as yet unprovided with semicircular 

 canals. 



The feeling of vertigo, of deception as to spatial relations of the surroundings, 

 and at the same time of oscillation of the body, occurs particularly in connection 

 with acquired alterations in the normal movements of the eyes, whether these 

 consist either in involuntary lateral movements of the eyeballs (nystagmus), or 

 in paralysis of these movements. On active or passive movement of the head 

 or of the body, synchronous movements of the eyeballs take place normally, and 

 these are definite for each position of the body. The general characteristic of 

 these bilateral ocular movements, w r hich may be designated as compensatory, 

 consists in the fact that through them both eyes in the various changes in the 

 position of the head and of the body tend to retain their primary position of 

 rest. Division of the aqueduct of Sylvius at the level of the anterior quadri- 

 geminate bodies, the cerebral portion on the floor of the fourth ventricle, the 

 auditory nuclei, both auditory nerves, as well as destruction of the membranous 

 labyrinth on each side, cause loss of these movements. Irritation of the same 

 parts, conversely, causes bilateral associated ocular movements. It thus appears 

 that compensatory ocular movements are under normal conditions excited re- 

 flexly from the membranous labyrinth. Both labyrinths are connected with both 

 eyes by means of reflex nerve-paths, nerve-fibers passing to each eye from both 

 labyrinths. These pass through the auditory nerve to the center (which extends 

 from the interbrain to the commencement of the spinal cord) and from the center 

 centrifugal fibers pass to the ocular muscles. Destruction of the semicircular 

 canals thus causes change in the normal compensatory ocular movements and in 

 this way gives rise to vertigo. 



Chloroform and other poisons exhaust the compensatory ocular movements. 

 Nicotin and others, as well as asphyxia, suppress them through an action upon 

 the center. Cyon found that irritation of the horizontal semicircular canal causes 

 horizontal nystagmus, irritation of the posterior canal vertical nystagmus and 

 irritation of the anterior canal oblique nystagmus. Irritation of one auditory 

 nerve causes rotatory nystagmus and axial rotation of the animal toward the irri- 

 tated side. 



The thought suggests itself that the disorders of equilibrium, attacks of vertigo 

 and the feeling of apparent movement of external objects that are observed on 

 the passage of a galvanic current through the head between the ears or between 

 the two mastoid processes are due to influences acting on the semicircular canals 

 of the labyrinth. Under such circumstances also oscillation of the eyes takes 

 place, as well as a movement of the head on closure of the circuit at the anode. 



Pathological. The attacks of vertigo of sudden onset occurring in the course 

 of disorders of the labyrinth and of so-called Meniere's disease, the latter not 

 rarely being attended with roaring in the ears, vomiting, staggering gait and 

 marked impairment of hearing, must be referred to an affection of the ampullar 

 nerves or their central organs or of the semicircular canals. The labyrinthine 

 nerves may be affected also reflexly, or in the form of a pure neurosis. Even 

 irritative phenomena upon one side may cause vertigo. Forcible injections into 

 the ears of rabbits also cause attacks of vertigo, with nystagmus and rotation 

 of the head toward the side treated. Also in workmen exposed to greatly 

 increased atmospheric pressure, analogous phenomena appear. In the presence 

 of deficiencies in the tympanic membrane in man Lucae observed, on application 

 of the air-douche to the auditory canal, rotation of the eyes and vertigo. Inflam- 

 mation of the middle ear in man may likewise cause nystagmus with vertigo. 

 In this way is explained the vertigo observed in connection with spasm of the 

 tensor tympani, as a result of which excessive pressure is exerted upon the laby- 

 rinth. Urbantschitsch found that even certain tones are capable of causing in 

 persons occupying the vertical position disturbance of equilibrium and apparent 

 movement. Also transitory derangement of the circulation in the nuclei for the 

 nerves to the ocular muscles is, according to Mendel, often a cause of vertigo. 

 Strabismus, paralysis of ocular muscles, pupillary changes are rare as reflex 

 phenomena from the ear. It is a remarkable fact 'that occasionally a tendency 

 to attacks of vertigo occurs in association with chronic disease of the stomach 



