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570 — DENTAL EMBRYOLOGY AND HISTOLOGY.
trate the intercellular spaces of the cementoblastic layer, and dentine is
formed around the terminal fibrils, causing an interdigitation of the
dentinal tubules and the enamel-prisms. This interpenetration precedes
the process of calcification of the enamel.
This now brings us to the consideration of the subject of calcification,
which rightly precedes the study of both amelification and ossification.
Calcification.
" Calcification is the process of change into a stony substance contain-
ing much lime, as in the formation of the teeth " (R, Owen). In the
light of the present status of scientific investigation I would change the
above definition as follows : Calcification is that process by which (organic)
tissues become hardened by deposition of salts of calcium in their inter-
cellular substance, as exemplified in the formation of bones and teeth.
The intercellular substance found in organic tissues is fluid, and into
this fluid minute particles of lime salts, in such fine subdivision as not
to be demonstrated by even the highest powers of the microscope, are
deposited in regular systems after the several forms of calcified tissues.
This arrangement is superintended by specialized cells for each particular
structure osteoblasts for bone, odontoblasts for dentine, etc. These cells
secrete lime salts and deposit them in the intercellular substance.
All cells lie embedded in, or are bathed by, a fluid which is more or
less gelatinous in consistency. It is from this surrounding medium that
the cells derive the supply of nom-ishment necessary for the performance
of their functions. Cells are capable of cellular activity in proportion
to the amount of cell-pabulum this fluid contains. I do not say that
cells are active according to the amount of food-supply present, but that
they are capable of putting on cellular activity just in proportion to the
amount of cell-food at hand, and in this way are stimulated to increased
functional activity. Bricks cannot be made without straw, neither can
tissues present increased functional powers without plenty of food with
which to nourish themselves. The presence of an intercellular substance
is of essential importance in the develoimient of tissues. In embryonic
life the quantity of cell-pabulum is very marked. It is at this period
that calcification begins in two forms ossification and amelification;
the first under the superintendency of the connective-tissue group of cells,
and the second a product of the epithelium.
Connective tissue is develojied from the mesoblast, while the epithe-
lium is produced from the ejiiblast. In our former studies we found a
wide difference between the tissues of the two layers, and we shall find
a yet wider difference between their ]iroducts.
Under the calcified products of the connective-tissue group we w^ill
consider bone, cement, and dentine ; under the calcified products of
epithelial tissues, enamel, shells, etc.
The essential difference between the two depends npon the matrix,
and the manner in whicii the lime salts are deposited, rather than upon
the character of the cells Avhich govern the deposition. The general
appearance of cells is dependent, to a very considerable extent, on the
matrix in which they lie, yet an epithelial cell, while presenting varia-
570 — DENTAL EMBRYOLOGY AND HISTOLOGY.
trate the intercellular spaces of the cementoblastic layer, and dentine is
formed around the terminal fibrils, causing an interdigitation of the
dentinal tubules and the enamel-prisms. This interpenetration precedes
the process of calcification of the enamel.
This now brings us to the consideration of the subject of calcification,
which rightly precedes the study of both amelification and ossification.
Calcification.
" Calcification is the process of change into a stony substance contain-
ing much lime, as in the formation of the teeth " (R, Owen). In the
light of the present status of scientific investigation I would change the
above definition as follows : Calcification is that process by which (organic)
tissues become hardened by deposition of salts of calcium in their inter-
cellular substance, as exemplified in the formation of bones and teeth.
The intercellular substance found in organic tissues is fluid, and into
this fluid minute particles of lime salts, in such fine subdivision as not
to be demonstrated by even the highest powers of the microscope, are
deposited in regular systems after the several forms of calcified tissues.
This arrangement is superintended by specialized cells for each particular
structure osteoblasts for bone, odontoblasts for dentine, etc. These cells
secrete lime salts and deposit them in the intercellular substance.
All cells lie embedded in, or are bathed by, a fluid which is more or
less gelatinous in consistency. It is from this surrounding medium that
the cells derive the supply of nom-ishment necessary for the performance
of their functions. Cells are capable of cellular activity in proportion
to the amount of cell-pabulum this fluid contains. I do not say that
cells are active according to the amount of food-supply present, but that
they are capable of putting on cellular activity just in proportion to the
amount of cell-food at hand, and in this way are stimulated to increased
functional activity. Bricks cannot be made without straw, neither can
tissues present increased functional powers without plenty of food with
which to nourish themselves. The presence of an intercellular substance
is of essential importance in the develoimient of tissues. In embryonic
life the quantity of cell-pabulum is very marked. It is at this period
that calcification begins in two forms ossification and amelification;
the first under the superintendency of the connective-tissue group of cells,
and the second a product of the epithelium.
Connective tissue is develojied from the mesoblast, while the epithe-
lium is produced from the ejiiblast. In our former studies we found a
wide difference between the tissues of the two layers, and we shall find
a yet wider difference between their ]iroducts.
Under the calcified products of the connective-tissue group we w^ill
consider bone, cement, and dentine ; under the calcified products of
epithelial tissues, enamel, shells, etc.
The essential difference between the two depends npon the matrix,
and the manner in whicii the lime salts are deposited, rather than upon
the character of the cells Avhich govern the deposition. The general
appearance of cells is dependent, to a very considerable extent, on the
matrix in which they lie, yet an epithelial cell, while presenting varia-
