308 Chronic Fluorine Intoxication in Domestic Animals.
in sufficient quantity to supply 20 mg. per kg. per day (115). This high toxici-
ty of dissolved fluorides has also been observed in the rat (33, 77). In man,
a steady intake of 01 to 0.15 mg. per kg. body-weight per day in the drinking
water has occasioned mottling of the enamel of the teeth (34). An insuffi-
cient supply or an imbalance of other inorganic constituents of the food has
been observed to influence the toxicity of ingested fluorine, while the addi-
tion of extra calcium phosphate to the rations has been reported to reduce
the toxicity of calcium fluoride for sheep (116).
Simultaneous ingestion of green grass has been shown to reduce the toxi-
city of fluorine for pigs (44, 45) and this was confirmed by experiments on
rats (41). With the latter animals neither vitamin A, vitamin C nor the
minerals in the grass were responsible. Storage of fluorine in the bones was
not diminished.
Simultaneous administration of aluminium chloride reduces the toxicity
of fluorine for rats (48, 90, 105). The effect exerted by fluorine is seemingly
enhanced in poorly nourished sheep (86). A relatively low final concentra-
tion of fluorine in the diet after cooking with water containing fluorine has
been observed to be more toxic for rats than an equal amount of fluorine sup-
plied in the drinking water (77). Simultaneous ingestion of desiccated
thyroid has been observed to increase the toxicity of fluorine for chicks
(88).
The toxic effects of fluorine may be less if the intake is intermittent (85,
101). Grazing animals which, as a rule, consume licks spasmodically accord-
ing to the season are thus less liable to untoward effects than if the fluorine-
containing-phosphate in supplements were regularly ingested. It has been
observed (85) that the food consumption and the weight of a sheep decreased
or increased according to whether fluorine was or was not given. In a like
manner, a decrease in the fluorine intake was observed to lead to the dis-
appearance of the symptoms of diarrhœa, and the reduction in size of the exos-
toses, of the long bones, in calves suffering from chronic fluorosis. Resumption
of the larger fluorine intake led to the reappearance of the symptoms (101).
GENERAL OBSERVATIONS
Although a physiological role has been suggested for fluorine (49) con-
vincing experimental verification is lacking and some evidence contrary to
the view that fluorine is an essential element has been obtained (106). It
is generally accepted that fluorine is universally present in the tissues and
organs of animals, even in foetal bones (42) but this is doubtless incidental
to the ingestion of small amounts of this element in the diet. The flourine
content of the bones of rats fed on a diet almost free from this element has
been reduced to from 6 to 25 parts per million. Fluorine was observed to
be eliminated gradually from the teeth without deleterious effect. As pre-
viously mentioned in this review, the ingestion of flourine by farm animals
which are given access to phosphatic licks presents an extensive problem in
animals husbandry. Careful selection of the calcium phosphate from which
these supplements are prepared is probably the most obvious means of over-
coming the difficulty. All natural phosphate deposits contain fluorine. There
is satisfactory proof, however, that the high fluorine content of fossil bones
and teeth, which occasionally contain over 3 per cent of fluorine, is the result