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170 THE MICRO-ORGAyiSMS OF THE HUMAN MOUTH.

more or less dislocated. The whole looks f,s if the inter-prismatic
substance were dissolved, i.e., the connection between the prisms
F\n. fiP.

Secondary Examkl-Decay. <». partially deealritiud ouauifl whuh has slightly taken on the
staining matter; /j.zone of infected enamel showin,; mas.-es of bacteiia working their way into
the decalcifying tissue. 70 : 1.
destroyed. Sections of enamel in seeoiidarv decay often show the
bacteria forcing their way between the loosened prisms (Figs. ^^.,
67). About the same result is
Fig. 67.
obtained where normal enamel is
treated wdth diluted acids. The
destruction of the enamel as it
occurs in decay must be regarded
as essentially a parasitico-chemi-
^ cal process. The loosening of the
nm enamel-prisms is caused by acids
concerning whose origin there
can be no doubt; they arise in
the mouth by fermentation of
A Small Portion ok the Border of
Fig. 6fi, showing the invasion of the dis- carbohydrates. The prisms thus
eased enamel by bacilli.
loosened are sometimes mechani-
cally removed ; sometimes they remain on the spot, as in the case