A. W. PEIRCE.
309
of long continued secondary chemical changes. Similarly, the fluorine con-
tent of phosphatic rock cannot be attributed solely to that originally present
in the bird guano or the animal remains which have played a part in the for-
mation of the deposits. It is apparent that the fluorine in the rock phosphates,
like that in fossil bones and teeth, results from long contact with fluorine-
bearing waters which transform the hydroxy-and carbonate-apatites par-
tially or wholly into fluorapatite. In the geologically older continental
deposits, this transformation is more or less complete, while in the more recent
insular deposits the inter action is, as yet only partial (66).
The low fluorine to phosphorus ratio of high grade rocks from Curacao
Island and from Christmas Island, which contain 0.7 and 1.3 per cent of
fluorine, respectively, suggests that calcium phosphate from these sources
should be utilised for compounding phosphatic supplements for stock (79).
If it were economically possible, the large scale adoption of calcination
by steam (29, 79, 96, 97, 98, 109) whereby the fluorine content of rock phos-
phate is reduced almost to zero, would remove entirely the risk of chronic
fluorosis arising from the ingestion of phosphatic supplements over long
periods. Dairy cows have been fed for a period of six years on a mineral
supplement containing 2 mg. fluoride per kg. body weight per day and have
been reported to have suffered no reduction in performance (39). The fact
that the requirements of grazing cattle for phosphatic supplements is seasonal
reduces still further the possibility of the untoward effects of chronic fluorosis.
Where poisoning is the result of contamination of the air, grazing sites
and of water supplied with materials containing fluorine discharged from
factories, careful disposal of the gaseous emanations, dust and liquid effluents
will overcome the trouble. In regions permeated with fluorine, control of
chronic fluorosis appears to be impracticable.
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(2) Anonymous. Ann. Rep. Kentucky Agri. Exp. Stat., 1924, 21
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