GIDDINESS, NYSTAGMUS, MENIERE'S DISEASE. 605 



behind at a skull, with the semicircular canals exposed (fig. 432). He assumes that the canals 

 are paired organs, and that each pair is connected with rotation or movement of the head in a 

 particular direction.] 



Giddiness. This feeling of false impressions as to the relations of the surround- 

 ings and consequent movements of the body, occurs especially during acquired 

 changes in the normal movements of the eyes, whether Lg j^g 



due to involuntary to and fro movements of the eye- 

 balls (nystagmus), or to paralysis of some eye muscle. 



Active or passive movements of the head or of the 

 body are normally accompanied by simultaneous move- 

 ments of both eyeballs, which are characteristic for 

 every position of the body. The general character of 

 these " compensatory " bilateral movements of the eyes 

 consists in this, that during the various changes in the T p< / \ pp 



position of the head and body, the eyes strive to main- " 



tain their primary passive position. Section of the m of \ q ^ u of 



aqueduct of Sylvius at the level of the corpora qua- the sem i c ircular canals. RS 

 drigemina, of the floor of the fourth ventricle, of and LS, right and left supe- 

 the auditory nucleus, both acustici, as well as de- rior ; L ? an d RP, right and 



struction of both membranous labyrinths, causes dis- * P 08 * 6 * ; P a , Ild RE ' 



,, ,1-1 1 right and left external. 



appearance 01 these movements ; while, conversely, 



stimulation of these parts is followed by bilateral associated movements of the 

 eyeballs. 



Compensatory movements of the eyeballs, under normal circumstances, may be 

 caused reflexly from the membranous labyrinth. Nerve channels, capable of excit- 

 ing reflex movements of both eyes, proceed from both labyrinths, and, indeed, both 

 eyes are affected from both labyrinths. These channels pass through the auditory 

 nerve to the centre (nuclei of the 3rd, 4th, 6th, and 8th cranial nerves), and from 

 the latter efferent fibres pass to the muscles of the eye (Hdgyes). 



Cyon found that stimulation of the horizontal semicircular canal was followed by horizontal 

 nystagmus; of the posterior, by vertical, and of the anterior canal, by diagonal nystagmus. 

 Stimulation of one auditory nerve is followed by rotating nystagmus, and rotation of the body 

 of the animal on its axis towards the stimulated side. 



Poisons. Chloroform and other poisons enfeeble the compensatory movements of the eye- 

 balls, while nicotin and asphyxia suppress them, owing to their action on their nerve-centre. 



It is probable that the disturbances of equilibrium and the feeling of giddiness 

 which follow the passage of a galvanic current through the head between the mastoid 

 processes, are also due to an action upon the semicircular canals of the labyrinth 

 ( 300). Deviation of the eyeballs is produced by such a galvanic current (Hitzig). 

 The same result is produced when the two electrodes are placed in the external 

 auditory meatuses. 



Pathological. Meniere's Disease. The feeling of giddiness, not unfrequently accompanied 

 by tinnitus, which occurs in Meniere's disease, must be referred to an affection of the nerves of 

 the ampullae or their central organs, or of the semicircular canals themselves. By injecting fluid 

 violently into the ear of a rabbit, giddiness, with nystagmus and rotation of the head towards 

 the side operated on, are produced (Baginsky). In cases in man, where the tympanic membrane 

 was defective, Lucae, when employing the so-called ear-air-douche at 0*1 atmosphere, observed 

 abduction of the eyeball with diplopia, giddiness, darkness in front of the eyes, while the 

 respiration was deeper and accelerated. These phenomena must be due to stimulation or ex- 

 haustion of the vestibular branch of the auditory nerve (Hdgyes). In chronic gastric catarrh, 

 a tendency to giddiness is an occasional symptom (Trousseau's gastric giddiness). This may, 

 perhaps, be caused by stimulation of the gastric nerves exciting the vaso-motor nerves of the 

 labyrinth, which must affect the pressure of the endolymph. Analogous giddiness is excited 

 from the larynx (Charcot), and from the urethra (Erlenmeyer). 



[Vertigo or giddiness is a very common symptom in disease, and may be produced by a great 

 many different conditions. It literally means "a turning." As Gowers points out, the most 

 common symptom is that the patient himself has a sense of movement in one or other direction ; 

 or objects may appear to move before him; and more rarely there is actual movement "com- 



