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SYSTEMIC CONDITIONS. 121
of the dental profession and of the laity as well, was wrong.
There had never been any substantiation of that interpretation
by careful physical examination of the teeth themselves.
This summary speaks for itself and shows that the greatest
difference in the calcium salts in the dentin, including all exag-
geration that might arise from errors, was 4.35 per cent, and the
usual range of difference was very much less than this. The dif-
ferences due to age are also given, and it is found to be 2.30 per
cent. When we consider that ivory, or the tusk of the elephant,
has 20 per cent less of calcium salts than the human teeth, and
we consider its hardness as compared with the human dentin,
we will see that these slight differences in the amount of calcium
salts can amount to nothing whatever as rendering the teeth
more or less liable to dental caries. It is clearly shown in the
comparison of the amount of calcium salts in the teeth of those
whose teeth decayed badly with the amount in the teeth of those
immune to decay, that there is no difference whatever. Teeth
that decay badly have just as much calcium salts, are just as
heavy and just as hard, as teeth of persons immune to caries.
Therefore, while the fact in regard to caries being severe in
this person's mouth, while the teeth of another person escape
caries entirely, was a perfectly correct observation, to attribute
this to the softness of the teeth in the one and the hardness of
the teeth in the other, was a wrong interpretation; but this
interpretation has become so fixed in the minds of men that it is
very difficult indeed for many of the older men, particularly, to
change their minds upon this point. It is perhaps well for the
human family that opinions so widely held should have great
weight in all matters pertaining to human welfare. They should
not be cast aside without the very best reasons for so doing.
At the close of the paper communicating these results, the
suggestion was strongly made that the causes of immunity and
susceptibility to dental caries would necessarily be found in
conditions of the general system, influencing the qualities of the
mixed fluids of the mouth by which the teeth were surrounded.
The composition of these fluids influences the action of the micro-
organisms growing in them in such a way that caries occurs in
one person and not in another. While the elements entering
in to produce these differences in dental caries might be totally
different from those in systemic conditions controlling suscepti-
bility or immunity to other diseases, the search for them would
be conducted on the same general principles.
The storm of disapproval that arose when these results