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 
