DISEASES OF THE EYE. 293 



But on these sewage farms a fresh crop may be cut every fortnight, 

 and the product is precisely that aqueous material which contributes 

 to a lymphatic structure and a low tone of health. The presence of 

 a definite germ in the system has not yet been proved, and in the 

 present state of our knowledge we are only warranted in charging 

 the disease to the deleterious emanations from the marshy soil in 

 which bacterial ferments are constantly producing them. 



Heredity is one of the most potent causes. The lymphatic consti- 

 tution is of course transmitted and with it the proclivity to recur- 

 ring ophthalmia. This is notorious in the case of both parents, male 

 and female. The tendency appears to be stronger, however, if either 

 parent has already suffered. Thus a mare may have borne a number 

 of sound foals, and then fallen a victim to the malady, and all foals 

 subsequently borne have likewise suffered. So it is in the case of the 

 stallion. Reynal even quotes the appearance of the disease in alter- 

 nate generations, the stallion- offspring of blind parents remaining 

 sound through life and yet producing foals which furnish numerous 

 victims of recurrent ophthalmia. On the contrary, the offspring of 

 diseased parents removed to high, dry regions and furnished with 

 wholesome, nourishing rations will nearly all escape. Hence the 

 dealers take colts that are still sound or have had but one attack 

 from the affected low Pyrenees (France) to the unaffected Catalonia 

 (Spain), with confidence that they will escape, and from the Jura 

 Valley to Dauphiny with the same result. 



Yet the hereditary taint is so strong and pernicious that intelligent 

 horsemen everywhere refuse to breed from either horse or mare that 

 has once suffered from recurrent ophthalmia, and the French Govern- 

 ment studs not only reject all unsound stallions, but refuse service to 

 any mare which has suffered with her eyes. It is this avoidance of 

 the hereditary predisposition more than anything else that has re- 

 duced the formerly wide prevalence of this disease in the European 

 countries generally. A consideration for the future of our horses 

 would demand the disuse of all sires that are unlicensed, and the 

 refusal of a license to any sire which has suffered from this or any 

 other communicable constitutional disease. 



Other contributing causes deserve passing mention. Unwholesome 

 feed and a faulty method of feeding undoubtedly predisposes to the 

 disease, and in the same district the carefully fed will escape in far 

 larger proportion than the badly fed ; it is so also with every other 

 condition which undermines the general health. The presence of 

 worms in the intestines, overwork, and debilitating diseases and 

 causes of every kind weaken the vitality and lay the system more 

 open to attack. Thierry long ago showed that the improvement of 

 close, low, dark, damp stables, where the disease had previously pre- 

 vailed, practically banished the affection. Whatever contributes to 



