16 Proceedings of Boyal Society of Edinhurgh. [sess. 
II. Young Rabbit fed on Madder for two weeks, and then 
ON Ordinary Food for other two weeks. 
(A.) Lower Incuor. Length, 19 mm.; greatest breadth, 2 mm. 
(1) External appearance. The whole of the tooth was stained of 
a light lake colour, with the exception of the lower fourth, which 
was unstained and white. The staining is more marked towards 
the free extremity, and fades off as it approaches the lower end 
(fig- 2, a). 
(2) On section. The greater part of the cut surface is stained, 
but there is a narrow line of unstained white dentine immediately 
around the pulp-cavity, and this unstained portion is continued 
upwards at the centre of the tooth to its free masticatory surface. 
The unstained band occupies the same position as the stained band 
which reached the free surface in the corresponding tooth of the 
preceding rabbit. The dentine on the concave side of the tooth is 
more deeply stained than that on the convex side. The lower 
fourth of the tooth is unstained (fig. 2, V). 
(B.) First Premolar. Length, 10 ’5 mm.; greatest breadth, 3 mm. 
(1) External appearance. Nearly the whole tooth except the 
lower third is stained. The staining at the upper extremity or 
crown is very faint. The lake colour is deepest about the middle of 
the tooth, and gradually fades off towards either extremity 
(fig. 2, c). 
(2) On section. Immediately around the pulp-cavity there is a 
narrow band of unstained dentine. This is continued up for a 
considerable distance in the core of the tooth, in the position of the 
obliterated pulp-cavity. External to this the rest of the tooth is 
coloured, with the exception of the lower third, and a small part at 
the free extremity surrounding the central stained core (fig. 2, d). 
The lower unstained portion of the tooth is that developed from 
what I have termed the “formative ring,” viz., circle of odonto- 
blasts that are always lowest in position, during the interval be- 
tween the cessation of madder feeding and the death of the animal. 
The narrow strip of unstained dentine around the pulp-cavity is the 
new dentine which had been deposited during the same period on 
the inner surface of the preformed dentine. In the incisor tooth it 
extends upwards to the free surface, the upper part of the pulp- 
