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170
]y irritated by the contagion of these dead parts, yet it is at
the same time protected by them from several irritating
causes ; and although some increased action may be pro-
duced in this membrane, yet it remains sometimes apparently
free from disease for a long period ; and may be considered
as only in a state of mordid predisposition.
In the second stage when the disease has produced a
greater extension of the carious cavity, and consequently the
admission of a greater quantity of corroding matter, the
dead bony parts in the neighbourhood of the nerve gradually
become softer, and this membrane is more irritated, and ren-
dered more liable to inflammation from the application of any
chemical, mechanical, or other cause.
Still, in this state, the living membrane may frequently
recover from such inflammation, and resist the local irrita-
tion arising from the contact of the dead bony matter, expo-
sure to the saliva, or atmospheric changes for a considerable
time, if the disease is not aggravated by causes of extraor-
dinary violence.
But when the disease has reached its third stage by the
great violence and long continuance of the influence of the
general and local causes, and the repeated return of the in-
flammation and suppuration of the nerve, the disease is fast
approaching its fatal termination, namely, the total destruc-
tion of the lining membrane, and consequent loss of vitality
of the tooth itself; the dead bony structure of which is then
left to be destroyed either by chemical solution, putrefaction,
or absorption.
The rapidity, therefore, of the transition from one stage
to another in complicated caries, depends greatly on the de-
gree of violence of its causes, and its progress is not alwaya
so rapid as is generally supposed, for a period from three to