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NATURE AND PROPERTIES OF AMALGAM. 311

has prompted a modification of the gilver-tin formiiloe with the object
of maintaining their original color.
The discolorations are not alone upon the external surfaces of fill-
ings, but frequently (and most frequently in improperly prepared and
filled cavities) the discoloration affects the dentinal walls bounding the
cavity (see Fig. 274).

Fig. 274.

staining of tooth structure with amalgam (Bodecker) : e. enamel : D, d, dentin ; B, border of cav-
ity ; s, solidified dentin along the border of the cavity ; k, reticulum brought forth by the
amalgam. (X 500.)
As shown in the illustration the discoloration may be deep. This
danger is increased by leakage, wlien putrefaction of the protoplasmic
contents of the dentinal tubuH or decomposing albuminous substances
generate H.S, and metallic sulfids are formed in marked quantities.