Page 192 - My FlipBook

166 THE MICRO-ORGANISMS OF THE HUMAN MOUTH.

particularly at the margin of the cavity ragged and in a state of
dissolution. In the last stages of decay we see only a mass
of bacteria (cocci, rods and threads), which is held together by
the remnant of the membrane. The thickening of the mem-
brane is for the most part, I think, due to the accumulations of
bacteria. Sections of enamel in an earl}" stage of caries, after
being stained with fuchsine, clearly show that the membrane is
loosened from the enamel on tlie decayed point, thickened and
invaded by masses of bacteria. The membrane in this condition
affords a matrix, that is, a point of retention, for bacteria, as well
as for very minute particles of food, and thereby accelerates the
progress of decay.

2. Decay of Enamel.
a. Preparation of Specimens.
The preparation of specimens of enamel suited for a study of
the process of decay is very difScult. It is well known that it
is impossible to decalcify enamel and to make sections of it with
the microtome. We are restricted to the study of ground sections,
and these necessarily give but an imperfect idea of the process,
because the largest part of the decayed enamel is lost in grinding.
Various methods have been proposed for the preparation of
microscopically thin ground sections. Whichever method be
applied, we first endeavor to split the tooth with a pair of split-
ting forceps in such a manner that the surface of cleavage passes
approximately through the center of the cavity (which, of course,
does not always succeed) and grind down each half on a rough
corundum-wheel to the thickness of about 1 mm. ; or the whole
tooth is ground down from both sides, until the cavity is reached.
By the latter process we obtain only one lamella, and conse-
quently but one preparation, whereas the former yields two
preparations. These lamellae are then ground under water on a
fine corundum-wheel as thin as possible without destroying too
much 'of the diseased tissue. A smooth, firm cork is best suited
for holding the piece against the wheel.
The method of A. Weil (p. 171) may also be applied to advan-
tage, or we may follow the suggestion of Gysi : "*