ORIGINAL ARTICLES. 
ARSENICAL POISONING FROM SMELTER SMOKE IN THE 
DEER LODGE VALLEY, MONTANA. 
By D, E. Salmon, D.V.M., Montevideo, Uruguay, S. A. 
VII. (Conclusion). 
The Poisonous Dose of Arsenic. 
In the articles which have preceded, an effort has been made 
to show the quantity of arsenic deposited on the grass and hay 
of the Deer Lodge Valley, the quantity per 25 pounds of air-dry 
ration, the proportion which was soluble, and the quantity which 
existed in the organs of animals which had died or that were 
sacrificed for examination. Thus, there was found by Swain and 
Harkins in the samples of hay and grass, analyzed in 1906, ar¬ 
senic varying in quantity from 1.7 grains (0.1102 gram) all the 
way to 123.4 grains (7.996 grams) per 25 pounds (11.36 kilos) 
of air-dry substance. It was also demonstrated by Haywood 
that from 22.2 per cent, up to 80.6 per cent, of this arsenic was 
soluble in water. It was, therefore, made plain that adult equine 
and bovine animals might ingest at times as much as 99.5 grains 
(6.447 grams) of water-soluble arsenic per day. However, the 
average quantity of arsenic per 25 pounds air-dry substance 
found by Swain and Harkins in 1906 was 25.2 grains (1.633 
grams), and the average solubility in water, as determined by 
Haywood, was 54.1 per cent. The average daily dose of soluble 
arsenic ingested by adult horses and cattle, as indicated by these 
determinations, was, therefore, 13.62 grains (0.894 gram). 
The question which is naturally suggested by these determi¬ 
nations is, “What is the minimum daily dose of arsenic which 
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