90 PERIODIC OPHTIIALMIA. 



Hereditary Influence, according to some veterinarians, 

 shews itself almost everywhere in the production of ophthalmia ; 

 according to others, its power is of a very ambiguous character. 

 We learn from D'Arboval that most of the French veterinarians 

 believe the disease to be hereditary ; and yet, as he observes, we 

 have in the face of this belief, the facts that foals have issued from 

 ophthalmic parents without inheriting the disease ; while others, 

 whose dams and sires have never had ophthalmia, have themselves 

 contracted it. And, independently of this, it is not evidence alto- 

 gether satisfactory to shew that such a mare breeds foals, or such 

 a stallion gets foals subject to ophthalmia, unless it be at the same 

 time proved that the young animal has not contracted the disease, 

 or the predisposition to take it, from the pasture or climate in which 

 he has been reared : since it has been demonstrated that horses in 

 certain situations — in low, wet, marshy pastures — have had oph- 

 thalmic disorders break out among them, which have ceased on 

 their removal to upland or dry situations*. This is a fact which 

 equally applies to some other specific or malignant disorders — to 

 glanders and farc}^, grease and canker. I feel satisfied, however, 

 myself that we have sufficient testimony on record to prove pe- 

 riodic ophthalmia to be what is called " an hereditary disease ;" 

 and that, therefore, too much precaution cannot be taken by 

 breeders to steer clear of propagating so irremediable an evil. 

 Granting the influence of hereditariness, our next inquiry is. 



Is IT THE Disease itself or only the Predisposition 

 which is transmitted — in other words, can the offspring of ophtlial- 

 mic parents take the disease without being exposed to certain 

 causes, called by us excitants 1 If it be answered, " yes !" how, 

 then, comes it that the disease so much confines its attacks to 

 horses of certain ages, and in certain situations] If, " no!" then 

 the production of the disease under certain conditions and states of 

 excitement can be most satisfactorily accounted for. I, therefore, 



* During the winter of 1840-1, which was an intensely cold one, several of 

 our young horses who were in strawvard close to Windsor came up into 

 stables with ophthalmia : for these twenty years I do not remember to have 

 seen so many cases in so short a time. The disease was, I should say, in this 

 instance clearly endemic. 



