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THE DECAY OF THE TEETH. 133

covered by him in tlie human mouth, which hquefies dentine
and enamel in pretty much the same manner as the fungus 3Ieru-
lius lacrymans softens the wood of houses or furniture (?).
" We have, consequently, in this process, which I shall call
for sake of brevity destructio dentis vegetativa, a fungus which
softens and destroys dental substances and is nourished by their
chemical elements; this parasite is a true Protococcus dentalis."
Klencke assumed " four kinds of tooth-decay, viz : (1) cen-
tral decay, destructio sive dissolutio dentis centralis—s. inflam-
matoria ; (2) peripheric vegetative decay (caries acuta), destructio
dentis vegetativa, caused by the tooth-fungus Protococcus den-
taUs ; (3) peripheric putrid decay, destructio s. colliquatio dentis
putrida—s. infusoria (caries acuta), caused by infusoria (dental
aniraalcula, denticol^e hominis) (4) disintegration of the tooth,
;
destructio dentis chemica (caries chronica)."
Leber and Rottenstein*^ deserve the credit of having placed
the parasitic theory of caries on a more solid basis. They re-
garded the commencement of caries as a purely chemical pro-
cess ; but as soon as the dentine is superficially decalcified the
elements of the fungus Leptothrix buccalis penetrate the dentinal
tubules, enlarge them, and thereby facilitate the rapid penetration
of the acids. These authors discovered a reaction which for a
long time was thought to be characteristic of Leptothrix buccalis.
The elements of this fungus, treated with a slightly acidulated
solution of iodine in iodide of potassium, show a violet color.
Sections of carious dentine exhibit the same reaction. But, as
I have explained on page 71, Leptothrix buccalis, treated with
iodine, gives no, or at most a yellowish, color. The violet reac-
tion of the accumulations in the mouth, as well as of decayed
dentine, is occasioned by an entirely difi:erent organism.
The communication of Milles and Underwood''^ presented be-
fore the Dental Section of the International Medical Congress
in London, 1881, served to revive the interest in the parasitic
theory of dental decay, which at that time appeared to be on the
wane. They noted the constant presence of micro-organisms in
decayed dentine, and the widening of the tubules produced by
them. They rejected the chemical theory of decay, and stated
their conviction that in the decay of the hard tooth-structures