FLUORIDE OF CALCIUM IN WATER. 163 
quite sufficient in many cases, especially if we add to the food, the drink of ani- 
mals as a source of the ingredient in question. But when we find fossilized bones 
containing ten or fifteen per cent. of fluoride of calcium, whilst, at the same 
time, they have lost to a great extent their original structure, and have acquired 
a crystalline or mineralized one, it seems highly probable that Mr MippLEron’s 
belief that water may have infiltrated that salt into them, will prove worthy of 
adoption. I cannot, however, agree with him in thinking, that it is enough to 
shew that water may bring fluoride of calcium to bones, to account for its accu- 
mulation in them. Water, as my own experiments prove, may carry away fluo- 
ride of calcium from osseous remains, as well as transport it tothem. We require 
to account for its detention in bones, as well as for its conveyance to them. From 
an experiment made in the laboratory, as well as from their association in nature, 
I am inclined to think that there is a double phosphate of lime and fluoride of 
calcium, much less soluble than the latter salt is; and that the production of this 
compound fixes the fluoride, and prevents its abstraction by water. Further re- 
searches will decide this point. Till quantitative analyses of a considerable num- 
ber both of recent and fossil bones are made, as to the proportion of fluoride of 
calcium in them, it will be impossible to decide how far individual fossils which 
contain that salt are to be looked upon as coming under Lirpic’s or MIpDLETON’s 
explanation, or as requiring, as many probably will do, a reference to both. 
Some, as already stated, may appear to have lost, instead of gaining, fluoride of 
calcium, during their entombment. 
Allusion was made, in the commencement of the paper, to the possibility of a 
conversion of fluoride of calcium into phosphate of lime having occurred. Few 
would more gladly see the idea of elemental transmutation realized by natural 
phenomenon or laboratory experiment than I should do. I can find nothing, 
however, to support it in the phenomena I have been discussing. 
In conclusion, I would observe, that physiologists will doubtless now be 
tempted to speculate on the possibility of fluorine performing some essential 
function in living animals. Its occasional absence from their bones would not 
disprove that it may be necessary for the perfection of certain organs, though not 
for all. Quantitative analyses appear already to have indicated that the enamel 
of teeth contains more fluorine than any other part of the body. If that result 
shall be confirmed, we may suppose that, if fluorine be furnished when the deve- 
lopment of the teeth is proceeding, it may be wanting at other periods, without 
injury to the animal; just as chloride of sodium must be considered as essential 
to the healthy life of most creatures, though they may be deprived of it for long 
intervals, without death ensuing. 
The small quantity of fluorine found in living structures can be counted no 
argument against its occasional or constant importance. Quantity, is at best, 
but a rude measure of the value of an ingredient, in relation to the necessities 
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