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48 HUNTER ON THE TEETH.
substances, viz. calcarious earth and an animal substance, which

the enamel. (1) In connection with this condition, also, Czermak has
pointed out the existence of opaque white line>, forming rings round the
fang: they are, of course, abnormal, and vary in breadth from the
l-50th to the l-100th of an inch. The existence of the contour lines has
been explained by referring them to the darker appearance produced by
a series of secondary curves in successive dentinal tubes, or by a widen-
ing of those tubes
; but it appears more probable that they are due, for
the most part, to the same cause which has produced the interspaces and
the globular condition of the dentine—viz., to the mode in which the
animal material of dentine is calcified, and to occasional arrests in the
process. Mr Salter observes that the contour markings, as well as the
fracture lines, which readily occur in the intermediate normal dentine,
and are parallel to them, exactly correspond to the pulp surface in the
progressive formation of the dentine—are identical, in fact, with the
juncture line of the pulp and internal dentine surface at any particular
time of growth. The existence of interglobular sjiaces and persistent
globules may be, with high probability, attributed to arrest at various
times in the process of calcification. The observations of Czermak led
him to the fact that the organic material of dentine is, during the pro-
cess of calcification, impregnated with earthy salts in globular forms
;
and that, by a deeper process of calcific impregnation, the whole tissue
is imbued with the hardening element, and the globules are fused. It is
easy, therefore, by supposing a temporary interference with this process
from some constitutional cause, to account for the appearances we have
been describing. (2) Some light is, perhaps, thrown on the process of
calcification by some observations of Mr Rainje, quoted in Mr Tomes's
'System of Dental Surgery :' " Mr Eainie finds, that if carbonate of lime
is formed in a thick solution of mucilage or albumen by the decomposi-
tion of carbonate of soda or potash, the newly-formed salt takes a
globular instead of a crystalline form. The globules produced are com-
posed, however, not only of carbonate of lime, but also of a certain
portion of mucilage or albumen in which the combination has taken
place." Phosphate of lime, if produced under similar circumstances,
supposing a small proportion of carbonate of lime be present, will also
assume the globular form. The globules are laminated, and increase by
the addition of new layers on the surface ; and if two or more globules
are in contact, they become fused into one laminated mass by the union
of the laminae which are in contact. "The globules themselves have
been produced by the coalescence of smaller masses, which again are
made up of still smaller spherules of similar material, the Individuality

(1) Salter, op. cit., p. 253.
(2) Vide Suiter, op. cit.