1892-93.] T)v 'KoheYt's,OYi on Madder- Staining of Dentine. 15 
(B.) Molar Teeth of Lower Jaw. 
First Premolar Tooth : length, 8 mm. ; greatest breadth, 1 *5 
mm. 
(^) External appearance. The upper half of the tooth is unstained, 
hut towards the root the colour gradually deepens and reaches its 
greatest intensity at the free margin of the root (fig. 1, c). 
(f) On section. Here again we see that the upper half is free of 
stain, except at the centre of the tooth, where the staining extends, 
as in the incisor, up to the free grinding surface. It also shows that 
the dentine which immediately surrounds the pulp takes on a deeper 
stain (fig. 1, J). 
The explanation of the staining of these teeth is obvious after 
what I have already shown in my paper on the growth of dentine,* 
and corroborates the conclusions at which I had already arrived. 
The unstained part of the tooth had existed before the animal was 
fed on madder. All the stained parts of the tooth have grown since 
the madder feeding was commenced. The portion showing the 
gradual transition between the unstained and stained parts of the 
tooth marks the lowest part of the tooth at the time when the 
madder was first given, and therefore the more deeply stained part 
below this had grown after that time. 
It is seen in the section that the staining reaches the crown, but 
only at the core or centre of the tooth. This coloured new dentine 
had been developed on the inner surface of the old during the fort- 
night of feeding with madder. At the apex of the pulp-cavity the 
staining is deepest, because in that situation the oldest part of the 
tooth is found, and consequently the deposit of madder-stained 
dentine has been going on longest there. 
These specimens show that the incisors increase in length rela. 
tively much more than the molars. Only about one quarter of the 
length of the incisor tooth is unstained, while in the premolar nearly 
one-half is unstained. The stained dentine was developed during 
the fortnight of madder feeding : in that time as much as three- 
fourths of the length of the incisor had grown, but in the premolar 
only a half. 
* “On the Relation of Nerves to Odontoblasts, and on the Growth of 
Dentine,” Trans. Royal Society of Edinburgh, vol. xxxvi., pt. ii., p. 321 
(1891). 
