408 CHAPTER 57. 



Such are the usual symptoms and course of the attacks. But the 

 disease does not always progress in the violent way described. Specific 

 ophthalmia may run its course and lenticular cataract may form without 

 any outward or noticeable symptoms. The author has known several 

 such cases among troop horses. It may seem, and it is undoubtedly very 

 strange that a disease producing such destructive changes in an organ 

 can occur without at some time or other giving rise to any noticeable out- 

 ward local or constitutional symptoms ; but it is beyond question some- 

 times the case. 



Iritis or inflammation of the iris seldom occurs as a separate disease. 

 It is usually combined with inflammation of the other structures. 



844. Nature of specific Ophthalmia. 



The disease, it will be seen, is inflammation of the internal structures 

 of the eye. The opacity, which ensues whether in the lens itself or in 

 its capsule, or in the aqueous humour, or in the cornea, is simply the 

 result of the deposit of the exudations from the inflamed blood-vessels. 

 This part of the subject will be referred to again under the head of 

 Cataract. 



845. Causes. 



Specific ophthalmia is commonly regarded as an hereditary disease. 

 The author is not inclined to deny that it may arise directly from heredi- 

 tary taint. Like begets like in most points of conformation, and the 

 progeny of animals with constitutionally diseased eyes are likely enough 

 to inherit the failing. There are also probably many animals with a 

 slight, or very slight, hereditary taint, in which the active disease will be 

 developed with a less amount of stable mismanagement than would produce 

 it in other horses. But in such cases he believes that the predisposition 

 is comparatively rarely developed except under the influence of some 

 exciting cause. In support of this opinion he would urge, that in many 

 years' experience he has but rarely known a case of specific ophthalmia 

 among the troop horses. It is difficult to believe that all those horses 

 can have been free from any taint or hereditary predisposition. 



Whether derived from hereditary taint or otherwise, Specific Oph- 

 thalmia is clearly a constitutional rather than a local disease. In most 

 cases the exciting cause seems to be a vitiated state of the blood pro- 

 duced by any or many causes acting on the organ, especially if it be 

 naturally weak, defective, or predisposed to disease. The ordinary ca,uses 

 of such deterioration of the blood are no doubt foul air, sewer gas, neglect, 

 and general bad stable management. Dark stables are also a predispos- 

 ing cause. The structures of the eye become weakened by want of their 

 natural stimulus, namely, light. 



Such are, in the author's opinion, the usual causes of specific oph- 

 thalmia, where it prevails as an epizooty or even affects a small number 

 of animals. This opinion is borne out by the fact that cases of specific 

 ophthalmia are rare in comparison to what they were in past years, when 



