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MICROSCOPICAL PHENOMENA OF DECAY 101

sheaths of Neumann, or they may be mere casts of tlie enlarged
tubules."
The fact, however, that these rods disappear often completely
as soon as they are brought into contact with dilute sulphuric
acid appears to me to render the view that they are bits of the
dentinal sheaths untenable. The rods are easily isolated by
crushing a section of dentine containing them in a drop of
water on an object-glass. If the specimen be now covered with
a cover-glass and dilute sulphuric acid allowed to flow through
it from the margin in the usual manner, we may clearlv observe,
under a high power (1000 to 1500), how the pieces suddenly dis-
solve, leaving behind a hardly visible granular detritus, and in
Fig. 92. Fig. 94.

\ 'y?

Lj

Rud-shaped Formatiu.ns ix Rod-shaped Formations
Decayed Dentine, (lime formations ?.t in a tubule,
with a central black thread surrounded by microeoc-ci.
(dentinal fibril?). 1101) : 1.
noo:i.
some cases disappearing altogether. In one case I plainly saw
the form represented in Fig. 92 appear at the instant when the
acid came in contact with a larger fragment.
I do not regard it as improbable that the products in question
are lime formations; to me, however, they look more like cylin-
And
drical casts of the dentinal tubules than calcified fibrils.
indeed these pieces, when greatly magnified, are sometimes seen
to contain filaments which may be regarded as the remains of
dentinal fibrils (Fig. 93). The tubular structure may sometimes
be directly ascertained under high power. I have never found
micro-organisms in these rod-like products, but have repeatedly
seen them mixed together with cocci, in much enlarged tulniles