122 HEALTH AND DISEASE 



to jump over a chair which was placed in a doorway. The operation on the 

 second eye was equally satisfactory, and after recovery the animal was used 

 by his owner with other pointers in the field, and was reported to be quite 

 equal to them in his work. 



Dr. Randolph ascertained that several similar cases had been reported in 

 foreign journals. In one case an ass was the subject, with what result is 

 not known; but the fact of the restoration of the lens after removal in 

 dogs, rabbits, and cats renders it at least probable that the same thing 

 might happen in the case of the horse, and the experiment is worth a fair 

 trial, especially when the disease is detected in the very early stage. 



DISEASE OF THE OPTIC NERVE AMAUROSIS 



Total blindness may be the consequence of disease of the optic nerve., or 

 its expanded filaments which form the retina within the globe, without the 

 exhibition of any symptoms which would be apparent in the eye to the 

 ordinary observer. In the disease which is known as amaurosis the retina 

 or expansion of the optic nerve is insusceptible to the action of light, which 

 therefore ceases to be a stimulant to the nerve. Consequently the circular 

 fibres of the iris which close the pupil do not contract, and the pupil 

 remains widely dilated even in the strongest light. The eye is perfectly 

 transparent, and to the inexperienced observer affords no indication of 

 unsoundness. If the disease is limited to one eye it may exist for some 

 time without being detected, but the tendency always is for it to extend 

 to the optic nerve of both eyes, and in that event the horse shows that 

 the sight is defective even in the earlier stages of the malady in a manner 

 sufficiently well defined to attract the attention of the attendant, who 

 will probably examine the eye without finding anything wrong. 



An inspection by a professional man will lead to the discovery of the 

 inactive conditions of the muscular fibres of the iris, but until the disease 

 has advanced so far as to cause total blindness, the iris will still to some 

 extent contract and lessen the size of the pupil in a strong light. The 

 expert will, however, observe that the contraction is very sluggish, but he 

 may hesitate to diagnose the affection as amaurosis unless he is familiar with 

 the use of the ophthalmoscope. With this instrument there will be no diffi- 

 culty in getting a good view of the optic disc, as the deficient sensibility of 

 the nerve structures will render the horse indifferent to the light w T hich is 

 thrown into the interior. On getting a view of the optic disc in an 

 amaurotic eye it will at once be evident that the normal pink tint has 

 been replaced by a white or grayish colour, and the vessels also will be 

 indistinct in consequence of the small quantity of blood circulating in them. 



