1892-93.] T>ic 'RohQvisori on Madder-Btaining of Dentine. 17 
cavity becoming obliterated by the deposit of this fresh dentine. 
By examining figs. 1 and 2, one can readily see all the dentine that 
was formed daring the period when madder was given. The small 
portion remaining unstained at the crown of the premolar is a 
portion of the old tooth not yet worn away. It was the lower part 
of the tooth previous to the administration of the madder. The 
axial portion of the upper extremity of this tooth is, however, 
stained, and we find the explanation of this by comparing it with 
the condition of the teeth in Babbit B"o. I. In them the coloration 
extends from the newly-formed dentine inclosing the pulp-cavity up 
to the free surface of the crown, through that which had obliterated 
the upper part of the cavity. But in the premolar of Babbit No. II. 
only the lower end of this axial band of coloured dentine is seen not 
yet worn away. 
The teeth of this second rabbit again exhibit the rapid growth of 
the incisor compared with that of the molar teeth. In the former 
the staining extends up to the crown, while in the latter the crown 
is still unstained, because composed of dentine developed before the 
madder was given. The deeper staining of the dentine on the 
concave side of the incisor may be due to the fact that the inner 
surface of this tooth grows more rapidly than the outer, to compen- 
sate its being worn down more rapidly. It thus requires more 
nutrition, and will therefore absorb more of the circulating madder. 
III. Babbit fed on Madder for two weeks, then on 
Ordinary Food for three weeks. 
(A.) Loioer Incisor. Length, 22 mm.; greatest breadth, 2*5 mm. 
(^) External appearance. Nearly the upper half of the tooth 
was stained, and the staining was deepest at its free extremity. 
Only the edges of the grinding surface of the .tooth were stained 
pink, while the central part was unstained (fig. 3, a). 
(^) On section. Nearly all the dentine was found unstained ; 
only that situated at the periphery of the tooth and at its upper 
part had taken on the madder-stain (fig. 3, h). 
(B.) First Premolar Tooth. Length, 12 mm.; greatest breadth, 
3 mm. 
(1) External appearance. Only the upper third of the tooth was 
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