694 
W. L. WILLIAMS 
from Kentucky, and bands of thoroughbreds are found, almost 
any animal of which, may be traced back to the illustrious blind 
horse, yet I have not seen a horse in the Rocky Mountains 
affected with periodic opthalmia except newly imported animals 
and these recover promptly unless very far advanced and remain 
permanently free from the disease. My observations in this 
region have been brief and limited, but are in full accord with 
the more extensive experience of Drs. Knowles, Montana ; 
Waugh, California, Arizona, New Mexico and old Mexico; 
Turner, Fort Niobrara, Neb., and other veterinarians and stock 
owners of this region. In fact I have been unable to learn of a 
single case of this disease arising in the entire Rocky Mountain 
region, whereas were heredity a sufficient etiological factor in 
the causation of the disease in this entire region, where careless¬ 
ness in breeding reaches its highest point, should be thoroughly 
over-run with this affection. 
Inbreeding is mentioned too as a fertile cause, yet in the 
large bands of wild horses in this region colts grow up in the 
bands, are left uncastrated and mate promiscuously with parent 
or offspring without producing evil results in this respect. 
Close ill-ventilated stables, especially dark stables, are also 
cited as fruitful causes, but in the northern Rocky Mountains, 
where low temperatures prevail, stables are very dark and un¬ 
sanitary, yet the few horses kept in them are free from the 
disease. 
Others attribute the disease to the ill-effects of bright sun¬ 
light, especially to snow-glare in the winter season, but this 
disease is more of a summer affection, and does not occur so 
largely in winter in any district so far as observed, and were 
snow-glare an important factor the Rocky Mountains should be 
the chief habitude of this disease, since the snow-glare of this 
region is far beyond that of the states where the disease prevails. 
No one living in the Mississippi valley or eastward can begin 
to appreciate the intensity of the snow-glare as seen at high 
altitude in the Rocky Mountains, with its dry, calm atmosphere 
and excessively low temperature during winter. 
