72 Veterinary Medicine. 



the primary cerebral disorder. There is also a special tendency 

 to vertigo in the fat, idle, gorged horse and in those with torpor 

 or other disorder of the liyer occurring in pampered horses in 

 spring and early summer. 



6th. Optic vertigo is a reflex disorder, determined in the ex- 

 citable nerve centres by the visual influence. Thus it has been 

 seen in horses and sheep from the intense glare of the sun's rays, 

 reflected from a lake or river or from white snow or ice, or even 

 from the glistening inner surface of the blinds. The effect is in- 

 tensified if the animal has just emerged from a dark stable or a 

 darker mine. The overdraw check may be a factor by reason of its 

 turning the eyes upward and exposing them continuously to the 

 full glare of the sun. The sense of motion conveyed through the 

 eyes contributes to bring on giddiness and a sense of swimming. 

 In man this is notorious, the sense of nausea and vertigo being 

 precipitated by looking at the nearby, moving objects in cabin 

 or on deck, while it may be retarded by directing the eyes to 

 steady distant objects. As dogs, horses and other animals suffer 

 from seasickness, and even railroad sickness, this attendant fac- 

 tor may be logically accepted. The mere limitation of the field 

 of vision, by the use of blinds, and the disappearance in rapid 

 succession of near objects behind this narrow screen probably has 

 an influence similar to the visible motions in the ship between 

 decks, in cases in which these portions of the harness are mani- 

 fest factors. 



7th. Aural Vertigo is determined by irritations of different 

 kinds affecting the external, middle or internal ear. Experi- 

 mental sections show that this is especially due to injuries of the 

 semicircular canals. If the horizontal canal is divided there are 

 pendulum-like movements of the head alternately to the right 

 and left, also lateral rolling of the eyes. If the: posterior canal is 

 cut there is a vertical movement, or nodding of the head and 

 vertical rolling of the eyes. If the superior vertical canals are 

 injured there are pendulum-like vertical movements of the head 

 and the animal tends to fall forward. Injury to the anterior 

 canal causes diagonal rolling of the eyeball. In destruction of 

 all the canals various pendulum-like movements are performed, 

 and standing often becomes impossible. Stimulation of one 

 auditory nerve is followed by rotation of the eye and rotation 



