364 ON THE SO-CALLED “ NERVE 5> OF THE TOOTH. 
this can afford; but it may be interesting to show the part it 
plays in the formation of the dentine. 
About the sixth or seventh week of embryonic life a groove 
is formed in either jaw, at the bottom of which, after the 
lapse of a few weeks, papillae begin to arise, and shortly after 
transverse partitions in this groove shut off and separate each 
papilla, which then becomes the representative of the future 
temporary tooth. About the seventh month of foetal life the 
ossification of the tooth commences, and the dentine is repre¬ 
sented by a cup-shaped scale capping the crown, and ulti¬ 
mately extending down the sides and embracing the whole of 
the upper surface of the pulp. It is at this period of their 
growth that the odontoblasts are most active, for they have 
the development of the dentine before them, and deriving a 
plentiful supply of nutrition from the plexus of blood-vessels 
beneath them, dentine is formed through their agency from 
without inwards, till the pulp being reduced to the size at 
which we generally see it by the gradual formation of the 
dentine, the odontoblasts become dormant, but capable of 
awaking to activity under the influence of certain circum¬ 
stances of irritation; thus if caries attacks a tooth at a par¬ 
ticular spot the tubuli in the dentine, through the fibrillse in 
them, become consolidated at an equal distance from the point 
of attack all round it, and a barrier seems to be thus thrown 
up against the inroads of the advancing enemy; but unless 
such a remedial measure as the careful excavation of the 
carious portion of the tooth and subsequent plugging of the 
cavity be adopted, barrier after barrier may be thrown up but 
to be overcome. Even then the odontoblasts of the pulp 
resist by forming new dentine in its very substance, and it is 
only when inflammation and suppuration destroy the odonto¬ 
blasts that this reparative process is annihilated. In some 
cases of general irritation of the pulp, as where the crown of 
a tooth is worn through by the grinding down and wear of 
mastication, the whole of the pulp may be converted into an 
irregular dentine. Sometimes nodules of ossific matter are 
found in the meshes of the areolar tissue of the pulp, but 
these do not partake of the character of the dentine, but are 
semi-transparent and Structureless, testifying to the amount 
of bone-producing matter in the homogeneous plasma satu¬ 
rating the body of the pulp, but which it is the legitimate 
office of the odontoblasts to build up as dentine. 
There are great and, I fear, almost insuperable difficulties in 
the way of clearly seeing the termination of the nerve fibres 
in the pulp; one can only conjecture at the method in which 
they end. In some specimens two fibres may be seen run- 
