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CARIES OF THE TEETH. 49

term contagious, can it be applied to caries of the
teeth.
The color of caries is exceedingly various, from that
of healthy dentine, through every intermediate shade,

to jet black. The rate of the progress is indicated by
the color of the decay, being slower as this is darker,
so that when the decay becomes almost stationary,
the affected portion is usually black. The degrees of
color are differently enumerated by different writers;
as, by Koecker five, by others seven, and so on. Three,
however, are sufficient for our purpose : white, brown,
and black. The sensitiveness of the dentine is greatest
in teeth affected by the white decay, and usually
decreases as the color darkens; though there are

exceptions to this rule ; for occasionally we find teeth
affected by dark decay, that are quite sensitive. The
light-colored decay is more difficult to arrest than the
dark. In many cases of the former, filling seems
hardly to retard its progress ; whereas, in the latter,
by proper filling, the advance of the decay may be
checked altogether. The cause of the dark color of
caries is not perfectly understood ; but is probably

owing to the carbonization of the animal portion.
The opinion is entertained by some, that this dark
material protects the dentine from the influence of
injurious agents. But this is most probably not
correct, at least to any perceivable extent. If the