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42 HUNTER OX THE TEETH.
nates insensibly, though not equally low, on all sides of the
dilute hydrochloric acid, which has the effect of removing the granular
masses from that portion of the tissue with which it comes more directly
in contact, whilst in deeper parts the opaque masses become more dis-
tinct in consequence of the removal of all opacity from the superficial
portion. A transverse section thus treated with dilute hydrochloric acid
has the appearance of a portion of honeycomb from which the honey has
been removed. As the result of his observations, Mr Tomes does not
admit that the structure of fully-formed enamel is in the strict sense of
the term " fibrous." " A honeycomb," says this observer, " if the cells
were filled with a material of greater opacity or density than the wax of
which the cells themselves are formed, would not be regarded as fibrous
;
yet the arrangement of the parts would resemble those of the enamel."
To the argument that the cleavage of the enamel demonstrates its
fibrous nature, he replies that the lines of fracture do not run in the
longitudinal interspaces between the fibres, but through the lines of
granular masses. He, however, allows that in the young tooth, during
the process of formation, the fibrous arrangement is sufficiently distinct,
and may be demonstrated by hydrochloric acid. In the most perfectly-
developed enamel, he finds the sheaths of the fibres completely blended ;
the longitudinal and transverse markings are comparatively faint, and
appear under a high magnifying power, with a good light, not as dark,,
but as light lines, enclosing spaces occupied by a more dense and opaque
material. He describes several imperfect forms of development in this
tissue, all of which are to be regarded as predisposing causes of caries :
the fibrous condition may be maintained in consequence of the imperfect
blending or fusion of the sheaths of the fibres ; or the central portion or
contents of the fibre may be imperfectly developed, remaining in the
condition of fine globular masses or granules ; or fine cavities arranged
in single lines may occupy the centre of the fibre—in some cases these
may coalesce, and convert the fibre into a tube ; or, lastly, both
longitudinal and transverse markings may be replaced by a general
granular condition of the tissue. (1)
There can be no doubt that the conjunction of the enamel fibres is
very intimate. Neither intermediate substance nor regular canals have
been demonstrated between them. Cavities, however, frequently exist
in enamel, and they are referrible either to extension of the dentinal
tubes and of elongated cavities produced by the enlargement of the
dentinal tubes into the enamel, or to irregular fissures in the outer and
middle parts of that tissue. These latter are frequently found leading
down from the depressions between the cusps of the molar and premolar
teeth, and are to be placed in the foremost rank amongst the predis-
posing causes of caries.
Like the tubes of dentine, the enamel fibres do not pursue a straight
(1) Tomes, System of Dental Surgery, p. 258—277.