Atrophy. Paralysis of the Optic Nerve. 445 



magnesium light, of the reflection from snow, ice, water, sand, 

 or white dust. These exhaust the power of vision by over-stimu- 

 lating it, but whether the blindness is due to fatigue of the retina 

 or of the cerebral ganglia which preside over sight, it is difficult 

 to decide. This form is much more likely to occur in horses 

 which spend most of their time in darkness, as in unlighted 

 stables or mines, when they are suddenly brought into the sun- 

 light. Snow blindness, however, from prolonged exposure, is 

 common in animals as in man, and the case of the staghound 

 reported by Johan, is by no means an isolated one. 



Much more common are factors which act primarily on the 

 nerve centres. Poisoning with lead, poppy, belladonna (sheep 

 and goats, Gerlach) lolium temulentum (KHiver), tobacco, car- 

 bon bisulphide, cryptogams (musty fodder), mushrooms, as- 

 tragalus moUissimus, etc. , abolishes vision more or less perfectly. 

 Common illuminating gas and carbon monoxide have shown this 

 effect on dogs and chickens. Quinia subcutem has induced the 

 condition in dogs (Becker and Eversbusch). More or less com- 

 plete amaurosis is noticed in connection with heat apoplexy in 

 horses and fat cattle. 



Cerebral concussion from blows on the head, knocking the 

 head against a post or wall, or from violent falls induce blind- 

 ness which is to be attributed rather to lesion of the brain. The 

 same remark applies to cases that appear during the progress of 

 brain disease, parasitic or otherwise, to those that occur in con- 

 nection with overloading of the stomach or intestines, and from 

 gestation (Riss). 



In cases appearing after severe depletion, like profuse haemor- 

 rhage, diarrhoea, or diuresis, or excessive secretion of milk 

 (bitch) the anaemia of both eye and brain may be taken into 

 account. 



When amaurosis develops during some inflammatory or in- 

 fectious disease, as in parturition fever in cows, the immediate 

 cause may sometimes be found in embolism of the retinal, or 

 cerebral arteries. 



Symptoms. The most striking feature of amaurosis is the con- 

 stant excessive dilatation of the pupil. This is the same in light 

 and darkness, and in fully developed cases the animal may be 

 taken from perfect darkness to the full glare of sunlight or 



