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MICROSCOPICAL PHENOMENA OF DECAY. 189

Leber and Rottenstein, on the other hand, found not a con-
traction, but a distention of the tubules with thickened sheaths.
They examined several teeth made of the ivory of the hippo-
potamus, as well as three human teeth, worn on a plate, which
had become carious in the mouth, and discovered that the
microscopic changes of the dentine described al)ove occur in such
teeth also. Id all cases the tubules were more or less, sometimes
very extensively, dilated by a substance generally stained red by
carmine. The specimens from the ivory teeth particularly pre-
sented these changes in a very high degree.
Opinions vary greatly concerning the cause of this thickening.
Tomes"" considers that "the diseased condition has, perhaps,
undone the work of development and thrown light on the ques-
tion how this was effected; it might almost be said to have re-
stored the outline of the formative cells : the tissue is to a certain
extent broken up into its histological elements. Under the
microscope the section looks as though it might have been built
up of multitudes of tobacco-pipe stems, united by an interven-
ing substance. Such is the condition when disorganization has
advanced up to a certain point; at a later period short lengths of
the walls of the tubes (dentinal sheaths, Zahnscheiden of Neu-
mann) are found isolated ; and finally the whole tissue breaks
down into minute granular particles which are, by degrees,
washed away in the saliva."
Leber and Rottenstein^ do not seem to be satisfied with their
own attempts to explain the thickening of Xeumann's sheaths;
still it seemed to them most probable '• that the thickening of
the walls of the dilated tubules is brought about mechanically
by the compression of the surrounding substance." In their
judgment, the thickening cannot be caused by acids.
I have examined numerous specimens of natural and artificial
decay stained with picrocarmine, fuchsine, haemotoxylin, etc., and
indorse the view of Leber and Rottenstein, that a contraction
of the lumen of the dentinal tubules is seen only in cases where
it existed before the softening commenced. Further, that the
thickening of the dentinal sheath is not a vital process, since
it may be clearly observed in specimens of artificial decay.
This phenomenon might perhaps be explained, in part at least,