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CABIES OF THE TEETH. 63

Begnard of Paris (1838) defined caries of the teeth as
"destruction of the teeth by decomposition." His contention
was that this destruction took place at the very spot where the
acid was formed, or where the alimentary particles lodged and
decomposed.
This was called the chemical theory of caries of the teeth.
A large body of dentists, both in Europe and America, gave simi-
lar expressions of view at about this time. The idea that inflam-
mation of the dentin had any part in its causation was denied.
Also the statements of Fox, Bell, and many others, that caries
began within the dentin and worked its way outward, were gen-
erally denied. Instead, it was asserted that caries always began
upon the surface of the tooth, or in pits, fissures, etc., that were
open to the surface. The contentions along these differences
of thought were sharp and the lines closely drawn. This brought
about a much closer observation and study of the nature and
form of the physical injuries inflicted by dental caries, and with
this, the opinion became general that caries always began on the
outside of the tooth and worked its way inward, forming a cavity.
During this period also, comparative anatomists and geologists
were studying closely the teeth of the living animals and those
remaining of extinct animals, in which prominent differences
between the structure of the teeth and the bones were ascer-
tained. Owen gave us the word "dentin," distinguishing that
which had before been called tooth bone from true bone.
A knowledge of histology began to be developed. The cell
theory of the construction of organic bodies, animal and vege-
table, was propounded and rapidly assumed the general form
in which it stands at the present time. Makers of microscope
lenses rapidly improved them because of the encouragement and
patronage induced by these studies. In the midst of this, John
Tomes, of London, was studying the microscopic structure — the
histology— of the teeth and bones, and by 1860 this was devel-
oped almost completely as it stands to-day. It is true that since
then much more exactness of method and greater accuracy of
detail has been added. But the full foundation of our knowledge
of dental histology and the development of the teeth was laid by
John Tomes.
It seems that Mr. Tomes began this work with the inflam-
matory theory of caries strongly fixed in his mind. He found,
however, that inflammation could not take place in the teeth.
The histological structure of the teeth was such that there was
no provision for the circulation of blood in the dentin, neither