18 Proceedings of Eoyal Society of Edinburgh. [sess. 
stained, and the coloration was deepest at the free extremity 
(fig. 3, c). 
(^) On section. The greater part of the tooth was white. There 
was merely a thin madder-stained line running down each lateral 
border of the tooth from its free extremity for about one-third of its 
length (fig. 3, d). 
The appearances found in the teeth of this last rabbit were only 
further stages of what we have already seen in the teeth of Kabbits 
I. and II. Almost the whole of the old stained dentine had been 
worn away, and what remained of it was merely a thin cylinder at 
the upper part of the tooth, which now consisted almost entirely of 
new dentine which had been formed since the madder was stopped. 
The dentine situated between the lower limit of the madder-stain 
and the base of the tooth was that produced by the ‘‘formative 
ring ’’ during the post-madder period. The large amount of 
unstained dentine surrounding xhe pulp-cavity and extending up to 
the free surface had also been deposited on the inner surface of the 
old in the same space of time. 
Incisor. 
Premolar. 
Rabbit. 
Length. 
mm. 
Breadth. 
mm. 
Length. 
mm. 
Breadth. 
mm. 
I. 
14 
2 
8 
1*5 
II. 
19 
2 
10-5 
3 
III. 
22 
2 '5 
12 
3 
Trom the examination of madder-stained teeth we thus derive 
much information regarding the manner in which persistently grow- 
ing teeth increase or maintain their adult size. It clearly shows 
that as the teeth increase in length so do they in breadth. I have 
shown that this increase in breadth always commences at the root, 
and therefore the breadth is always greatest in this situation. In 
three weeks (compare I. and II.) the breadth of the incisor tooth 
had increased by one-fourth, while in the same time the premolar 
had become twice as broad as before. We see also that the teeth 
increase in length by the addition of new dentine to the lower end, 
and that this growth more than compensates the loss from wearing 
