Page 199 - My FlipBook

MICROSCOPICAL PHENOMENA OF DECAY. 173

higher freezing-point than water, and does not become so hard.
By means of the freezing microtome several hundred very thin
cuts may be prepared in a very few moments.
The objection has been raised to this method that it permits, of
securing sections of the softened dentine only, whereas we may
wish to see what, if any, changes have taken place in the other-
wise normal dentine just at or a little beyond the border of decal-
citication. I do not, however, attach much importance to this
point, because a study of a few preparations soon teaches us
that in the parts indicated.but slight changes, or none at all,
can be detected; besides, it is not difficult, with the help of the
freezing microtome, from such pieces of dentine in which a thin
layer of unsoftened dentine has been cut out along with the de-
cayed, to make a few cuts containing both hard as well as de-
cayed dentine, although the edge of the knife will be somewhat
damaged by it. For the study of the phenomena of transparent
dentine, a number of ground sections should be made from teeth
in which the decay has made but little progress.
Unstained sections must be examined in water. But it is im-
peratively necessary to stain a large number of sections, especially
in order to study the distribution of the bacteria in the tissue and
the manner in which they demolish it.

b. Methods of Staining.

For the purpose of staining the tissue, picro-carmine or picro-
lithio-carmine is, according to my experience, most suitable. The
sections are placed in the concentrated solution for about fifteen
minutes, then in a mixture of alcohol 70, water 29, muriatic acid
1, where they may remain from fifteen minutes to five hours,
then for a short time into alcohol, to which have been added a
few crystals of picric acid (till it turns slightly yellow). They
are then cleared up in oil of cloves, and mounted in Canada bal-
sam or glycerine. The dentinal fibrils and sheaths are colored
red, the basis-substance pink, the bacteria light red, the decom-
posing parts yellow.
For staining the micro-organisms the Imsic aniline colors are
best suited, fuchsine and gentian-violet being, according to my