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OF THE STRUCTURE OF A TOOTH, ETC. 37
It is by far the hardest part of our body ; insomuch that the
Other observers, amongst whom are Huxley and Kolliker,
cement." (1)
although allowing the existence of a thin calcified pellicle (by the
former named ' NasmytJis membrane] by the latter the ' cuticle of the
enamel') on the surface of the enamel, do not recognise in it a prolonga-
tion of the cement. It would appear that the layer in question is
remarkable for its great capability of resisting chemical reagents ; it
differs in this respect from ordinary cement, and is proportionately
better fitted to protect the crown of the tooth. The original surmise
of Nasmyth has, however, received some confirmation from certain
observations recorded by Mr Tomes in his ' System of Dental Surgery.'
This gentleman, in describing the disposition of the cement, writes
" In a few rare instances it may be traced, not only over the terminal
edge of the enamel, but for some little distance upon the coronal portion
of the tooth ; and specimens are now and then found in which it fills
up the deep fissures situated between the tubercles of the molar teeth."
Again, in reference to Nasmyth's membrane, he says : " In several
specimens which have been decalcified after being reduced sufficiently
thin for microscopic examination, this membrane is obviously con-
tinuous with the cementum of the fang ; and in other specimens which
have not been treated with acid, I find the membrane thickened in the
deep depressions of the crowns of molar teeth, and there tenanted by a
distinct lacuna." (2)
As life advances, the cement increases in thickness, especially towards
the apex of the fang. In those cases in which its formation extends
beyond a certain limit, it constitutes the disease known as " dental
exostosis." The inner surface of the cement is so intimately connected
with the dentine, that under a high degree of magnifying power its
boundary line is not very sharply defined. Its external surface, which
is uneven and not unfrequently marked with circular striae, is in close
contact with the alveolar periosteum and the gum ; but it is more
firmly united with the former than with the latter. Its tissue is less
hard than either dentine or enamel : consequently, its surface when
exposed to attrition becomes worn down at an earlier period, as may
be seen in the complex grinders of the Elephant, the Masked Boar, or
Capybara. In chemical composition the cement is almost identical with
bone. The following is its analysis according to Bibra : (3)
In Man. In the Ox.
Organic substance - - - 29-42 32-24
Inorganic substance - - - 70'58 67'76
100-00 100-00
(1) Article Teeth, Todd's Cyclop., p. 867.
(2) Tomes, 'A System of Dental Surgery,' pp. 257, 271 ; 1859.
(3) Manual of Human Microscopic Anatomy, by A. Kolliker, p. 297 ; 1860.
OF THE STRUCTURE OF A TOOTH, ETC. 37
It is by far the hardest part of our body ; insomuch that the
Other observers, amongst whom are Huxley and Kolliker,
cement." (1)
although allowing the existence of a thin calcified pellicle (by the
former named ' NasmytJis membrane] by the latter the ' cuticle of the
enamel') on the surface of the enamel, do not recognise in it a prolonga-
tion of the cement. It would appear that the layer in question is
remarkable for its great capability of resisting chemical reagents ; it
differs in this respect from ordinary cement, and is proportionately
better fitted to protect the crown of the tooth. The original surmise
of Nasmyth has, however, received some confirmation from certain
observations recorded by Mr Tomes in his ' System of Dental Surgery.'
This gentleman, in describing the disposition of the cement, writes
" In a few rare instances it may be traced, not only over the terminal
edge of the enamel, but for some little distance upon the coronal portion
of the tooth ; and specimens are now and then found in which it fills
up the deep fissures situated between the tubercles of the molar teeth."
Again, in reference to Nasmyth's membrane, he says : " In several
specimens which have been decalcified after being reduced sufficiently
thin for microscopic examination, this membrane is obviously con-
tinuous with the cementum of the fang ; and in other specimens which
have not been treated with acid, I find the membrane thickened in the
deep depressions of the crowns of molar teeth, and there tenanted by a
distinct lacuna." (2)
As life advances, the cement increases in thickness, especially towards
the apex of the fang. In those cases in which its formation extends
beyond a certain limit, it constitutes the disease known as " dental
exostosis." The inner surface of the cement is so intimately connected
with the dentine, that under a high degree of magnifying power its
boundary line is not very sharply defined. Its external surface, which
is uneven and not unfrequently marked with circular striae, is in close
contact with the alveolar periosteum and the gum ; but it is more
firmly united with the former than with the latter. Its tissue is less
hard than either dentine or enamel : consequently, its surface when
exposed to attrition becomes worn down at an earlier period, as may
be seen in the complex grinders of the Elephant, the Masked Boar, or
Capybara. In chemical composition the cement is almost identical with
bone. The following is its analysis according to Bibra : (3)
In Man. In the Ox.
Organic substance - - - 29-42 32-24
Inorganic substance - - - 70'58 67'76
100-00 100-00
(1) Article Teeth, Todd's Cyclop., p. 867.
(2) Tomes, 'A System of Dental Surgery,' pp. 257, 271 ; 1859.
(3) Manual of Human Microscopic Anatomy, by A. Kolliker, p. 297 ; 1860.
