1892-93.] I)y on Maclder-Staining of Dentine. 19 
down the crown in grinding. The increase in length of the incisor 
teeth being here 5 mm. in fourteen days and 8 mm. in twenty-one 
days is readily seen with the unaided eye, since the newly-formed 
dentine is white while the old is pink. The premolar had also 
gained 4 mm. in length in twenty-one days. These two processes, 
gradual increase in breadth and in length, go on both of them at 
the same time, and both are due to the action of the odontoblasts of 
the “formative ring.” 
The deposition of new dentine on the inner surface of that 
already formed is well seen in these madder-stained teeth. The 
recent dentine appears as a white lining to the tooth in Rabbit 
hTo. II.; while in No. III. it is a white lining so thick that it forms 
the larger part of the tooth. In both cases the white lining is 
thickest at the apex of the pulp-cavity, and thins off towards the 
root. The dentine at the upper part of the pulp-cavity has, during 
the persistent growth of the tooth, travelled up from the root, and 
during its passage there has been a continual deposition of new 
dentine on its inner surface. This accounts for the large amount of 
new dentine at the upper end of the pulp-cavity and the consequent 
obliteration of this cavity in the crown. We can now explain why 
it is that in Rabbit No. III. the stained dentine forms only a thin 
hollow cylinder at the upper part of the tooth. The dentine formed 
during the period of madder feeding had been subsequently so worn 
away that barely half the tooth is stained, the lower part having 
been formed after the madder was stopped. The new white dentine 
had then been deposited on the inner surface of the old stained 
dentine, and had replaced it as it was worn away. Thus we have 
the thin coloured cylinder alone left ; and had the animal been 
allowed to live a week or two longer, this would also have been 
worn away, and the whole tooth would have regained its normal 
white colour. 
I conclude by tendering my best thanks to Professor Rutherford, 
in whose laboratory this work was carried on, and who has kindly 
revised this paper. Both he and Dr J. Berry Haycraft personally 
supervised my work, and rendered me every assistance in the 
execution of it. 
