166 
D. E. SALMON. 
at pasture. In very rare cases an ulcer had been known to de¬ 
velop when the horse was feeding upon hay; but in the great 
majority of cases, if the horses were taken from the pastures and 
fed upon hay, the sores rapidly healed. 
In February, 1906, a great many horses were seen with large 
ulcers, but on the writer’s return, late in June, no active ulcera¬ 
tions were to be found, though most of the horses presented cica¬ 
trices or partly occluded nostrils. It was not until late in August 
that the first ulcer was seen, and it was a month after that before 
they became common. That is, with the feeding of hay, the re¬ 
moval of the dust from the grass by the snows and rains of 
winter and spring, the changing of the air-currents so that the 
smoke was carried away from the valley, and the appearance of 
the young grass, which was either free from arsenic or carried 
but a small quantity, the ulcers healed and disappeared, and were 
not seen again until the smoke had returned to the valley a suffi¬ 
cient time to once more deposit a considerable quantity of the 
poison. 
Referring to the notes made on the ground, there is found the 
following reference to smoke conditions: 
“ July 28. Observed the smoke going down the valley during 
the whole afternoon. While it has been seen on rare occasions 
since the last week in June drifting in that direction, it has not 
before been observed to cover the lower part of the valley as 
to-day.” 
After this date, the tendency of the smoke was more and 
more to vere around and pass over the valley, sometimes, espe- 
ially at first, but an hour or two during the day, but later it would 
remain several hours at a time. 
With the exception of one ulcer seen in August, and which 
it was alleged developed while the animal was feeding on hay, 
the first ulcers were noted under date of September 26. 
One animal, a buggy horse, had a large sore in the left nos¬ 
tril ; it was not sharply circumscribed, occupied the whole floor 
of the nostril and was covered with a nearly dry crust. There 
Was no discharge and the slight appearance of moisture around 
