Page 192 - My FlipBook

vanced, but did not, I determined to make a complete and
thorough examination of this subject of variations in Hme
salts, or the so-called softness and hardness of teeth; and
I pubHshed the results of these studies in the May number
of the Cosmos, 1895. In these studies the teeth of over
100 persons were examined, selected cases ; those in whom
those who were immune to decay. Those three classes
particularly were the subject of study. I obtained the teeth
in various ways. Some of those who were extracting here
in Chicago upon whom I could depend as to the obser-

vation of persons, collected teeth for me, and others col-
lected teeth for me, and I collected such as I could in my
own practice. So that I collected together a large number
of teeth, those coming from each individual being retained
separately with the history of the individual as to caries,
as to conditions in the mouth, etc. All of these teeth were
examined individually. They were weighed as nearly as pos-
sible in the condition in which they came from the mouth;
they were then dried and weighed to determine the amount
of water contained in them ; then certain parts of teeth were
cut and the dentin incinerated, the animal matter driven
ofif and the lime salts weighed to determine the amount
of lime salts in the teeth. This was done with each indi-
vidual tooth. The results I can give you in a few words. Be-
tween persons immune to decay and persons in whom the
teeth decayed rapidly, the difference in the amount of lime
salts, when footed up in a large nunlber of teeth from each,
amounted to one-half of i per cent. Taken at various times
during the progress of study, sometimes one would be a little
more, sometimes a little less, so that in the outcome of over
100 cases the difference was one-half of i per cent. Now,
most of you have had experience in carving ivory, you
have had experience in cutting dentin of the human teeth.
The difference in the amount of lime salts between the ivory
that you have carved and the human teeth is a little over
20 per cent, the human teeth having that much greater
proportion of Hme salts than the ivory. Now, you can
judge pretty well of the influence that one-half of i per
•cent would have in the hardness or in the possible solubility
.of different teeth. Mind you, this is a comparison as to
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