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188 THE MICRO-ORGANISMS OF THE HUMAN MOUTH.

micrococci, and below this a yellow layer about one-fourth of a
millimeter wide. Besides, the parts in a state of disintegration
are i>:enerally of a yellowish color. In the parts that are only
softened, but not infected, as well as in the masses of l)acteria,
the red color prevails. Xow and then scattered, greatly enlarged
tubules are seen to be filled with shining, yellow, homogeneous
contents, and only under a very high power does its granular
character become evident.
Cross-sections also often present a very peculiar appearance.
They reveal more or less numerous, scattered, greatly enlarged
tubules, filled with red-colored micrococci, and about as many
scattered, enlarged tubules of strongly refractive, homogeneous
yellowish contents (Plate III, Fig. 5). I am not able to state
why these various tubules are so difi:erently afifected by coloring
it occurs in artificial as well as in natural decay.
matter ;
Fuchsine specimens also occasionally exhil)it tubules of deep
red, apparently homogeneous contents. In such cases it may l)e
shown that the specimens have lieen over-stained, which makes
it impossible to distinguish the closely-crowded cocci.

We now come to a series of phenomena which have been
widely discussed, but not yet definitely explained. They are (1)
the thickening of Xeumann's sheaths;
Fig.
(2) the breaking up of the dentinal
fibrils into rods (pipe-stems) (3) the
;
occurrence of granular, not vegetable,
elements in the tubules.

Thickening of Neumann's Sheath.
According to some authors, a thick-
ening of the walls of the dentinal tu-
Thickesisc; of the Dental
bules (Fig. 89), that is, of ISTeumami's
Sheath.
slicaths, is an invariable accompaniment
(Neumann's sheath.)
(Alter wedi.)
of dccay. Accordlug to Xcumanu, this
thickening proceeds until the lumen of the tubules is totally
obliterated, while Tomes assumes only partial obliteration. He
compares a dentinal tubule with its thickened walls to the stem
of a tobacco-pipe.