516 
MR. JOHN TOMES ON THE PRESENCE OF FIBRILS 
foreign bodies, even pressure from the tongue giving pain. The degree of pain is not, 
however, increased by increasing the pressure. Then, again, in operating upon the 
teeth for the removal of carious dentine, it is almost invariably found that the dentine 
immediately below the enamel is much more sensitive than that situated deeper in the 
tooth. 
If the pulp of a tooth be destroyed, either by an instrument or by an escharotic, 
the sensitiveness of the whole of the dentine is immediately lost, no pain being after- 
wards experienced when it is cut either near the enamel or the pulp-cavity. The teeth 
of young subjects are much more sensitive than those of older people, and this is more 
especially the case when they are attacked by caries. 
The dentine of teeth which are rapidly decaying is much more sensitive than that 
of teeth in which the destruction progresses more slowly. The former condition is 
indicated by the light colour of the decomposing part, together with the extent of 
tissue involved ; the latter by the deep brown colour, and the comparative hardness 
of the affected dentine. In certain cases of caries, the softened tissue appears to be 
extremely sensitive, so that the patient can scarcely bear its removal ; but when the 
instrument reaches the comparatively healthy dentine, the pain, although present, is 
much less severe. 
In any case, however, the dentine loses its power of feeling pain if the pulp be 
destroyed ; but if, after the destruction, the pulp-cavity be perfectly filled with gold, 
the tooth, in cases suitable for such an operation, may retain its colour and usefulness 
for a considerable period. The dentine will not, however, recover its sensitiveness. 
These several conditions indicate sufficiently clearly that the sensitiveness of the 
dentine is dependent upon its connexion with the pulp of the tooth, and that it has 
no inherent sensibility in its own hard tissue; although the tissue may remain for a 
considerable period without any manifest change, if the root of the tooth be healthy, 
and the dentine be protected from the influence of the fluids of the mouth. 
After a portion of dentine has been for some time exposed, or if the exposure be 
brought about gradually by the slow wearing away of the enamel, that acute sensi- 
tiveness which has been described is not then found to exist. In parts which have 
been subject to the foregoing conditions, it will on examination be found that the den- 
tinal tubes, the peripheral extremities of which have been exposed, are more or less 
obliterated in some part of their course between the surface and the pulp-cavity. 
On reviewing the various circumstances under which dentine evinces sensibility, 
and those under which that sensibility is lost, it is difficult to avoid the conclusion, 
that the dentinal tubes are in some way the medium through which sensation is dis- 
tributed through the substance of the tissue But if the sole office of the tubes be 
the conveyance of nutrient fluid derived from the pulp, the difficulty of accounting 
for the sensitiveness of the dentine remains, inasmuch as we have no instance of 
sensation being manifested in a fluid. We might seem to get out of the difficulty by 
assuming that the dentinal tubes are constantly filled by fluid, and that pressure made 
