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50 PATHOLOGY OF THE HABD TISSUES OF THE TEETH.

separated only by the introduction of certain factors supposed
important by one party, but not considered so by another.
The FmsT supposition mentioned seems to have been the
older view. It was clearly expressed by John Hunter in 1778,
by Fox in 1806, by Bell in 1825, and by a number of others fol-
lowing these, and finally by Garretson as late as 1890.
Himter supposes that erosion is due to some certain imper-
fection in the formation of the tissues of the tooth, because of
which the substance gradually wastes away, continually leaving
a smooth surface. His supposition seems to have been that
conditions in after life had nothing especially to do in the matter.
Fox and Bell do not differ materially from this view, but
Bell adds the supposition that in the case of the dish-shaped
areas of erosion, the tissues of the tooth have been deposited
in whorls or such forms as favored this kind of wasting. To-day
such views seem very strange; but we should remember that
when these men wrote nothing was known of the histology of
the teeth, and their view did no violence to facts known in their
time. We now know that such faults in the formation of the
tissues do not occur as the basis of these cases.
The second supposition, i. e., that erosion is caused by fric-
tion, and generally by the tooth brush loaded with abrasive
powders, was held by John Tomes and many others in England,
America and Germany, and is still held by many observers.
According to this view erosion is no disease at all, but is purely
a mechanical injury. Conditions present in quite a number of
the cases seen, if grouped together and considered alone, would
give strong support to this view. These cases nearly all belong
to the more indefinite shapes of the wedge-like forms, and the
cases which occur in the cementum after, or with, recession of
the gum. A number of persons who hold this view describe and
illustrate these forms only. This has led me to suspect that in
some regions, particular forms are more frequently met than
others. It seems certain that in the central part of the United
States one would not observe many cases of the wedge-shaped
areas without finding varieties of form that would be very difiicult
to explain as resulting from abrasion by the tooth brush. When
Charles Tomes edited another edition of his father's work, he
had seen cases that he believed could not have been made with
the tooth brush, and he rewrote the chapter entire. Dr. C. R. E.
Koch (Dental Cosmos, Volume 15, 1873, page 463) tried by every
device he could think of to produce the conditions seen in erosion
by the use of brushes and brush wheels, aided by acids in some