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56 PATHOLOGY OF THE HARD TISSUES OF THE TEETH.
depend upon some change in the body fluids giving oral secre-
tions favoring these results ; but how, by what, and how local-
ized, are the questions. For the present it seems that we have
no certain data in support of the theory connecting it with the
gouty diathesis.
The seventh supposition — that erosion is caused by alka-
line fluids acting upon the basic substance of the tooth, setting
the calcium salts free, which waste away leaving a polished sur-
face — is one of the more recent. It has an individuality of
its own. The supposition that an alkaline condition as affecting
litmus is maintained in these localities for any considerable
part of the time is certainly contrary to my personal obser-
vations, and to much the larger number of recorded observa-
tions in the literature. Further, in Dr. Koch's experimental
work mentioned above, he found that he could not dissolve either
enamel or dentin in alkalies until the calcium salts had been
removed, or partially removed by acids. The enamel partic-
ularly contains so little organic matter that it would seem impos-
sible — first, that its organic matter could be removed in that
way, and second, that if it could be accomplished it would not
effect the disintegration of the tissue. The dentin has a much
larger proportion of organic matter, but direct experiment seems
to show that it has sufficient calcium salts to protect its organic
matter from solution by alkalies. Therefore, until it can be
shown experimentally that in some possible form alkalies will
act to disintegrate these tissues, this supposition must be set
aside.
The eighth supposition, the most recent of all, is set forth
by Preiswerk in his "Zahnheilkunde" ("Operative Dentistry"),
1903, page 200. It is the supposition that erosion is caused by
the same or similar microorganisms as those which cause caries,
but by the action of their enzyme, not by the action of their acid
products. It is well known that a number of the microorgan-
isms of the mouth which form acids in the presence of the carbo-
hydrates, such as sugar or starch, will grow well in nutrient
material devoid of these substances, but in that case will form
no acid products. Preiswerk contends that the human saliva
is normally alkaline, and that it is a mistake to suppose that the
enzyme of these microorganisms is necessarily a peptonoid sub-
stance, as these act in an acid medium. He claims to have found
evidence that in alkaline or neutral conditions their enzyme is
a trypsin similar to the trypsin of the pancreas which acts in
the presence of an alkaline reaction. Under these conditions
this enzyme acts upon the basic substance of the dental tissues,