as indicative of the Age of the Animal. 
293 
To proceed to the structure of the dentine. This substance 
makes up the great bulk of both the body and fangs of a tooth. 
It is that which gives form and size to the organ, and upon 
which its hardness mainly depends. In the interior of the dentine 
we meet with a cavity of large size compared with the dimensions 
of the tooth, and more particularly of one recently formed. From 
containing a red and pulpy mass, composed chiefly ol blood-vessels 
and nerves, interposed with cells and fdamentous tissue, de- 
signated the tooth pulp, this cavity has been called the pulp cavity. 
It is from the pulp that the tooth receives sensation as well as its 
greatest supply of fluids, which are derived from the blood, for 
its nourishment. Entering the cavity from below and being 
bounded on all sides with dentine, the pulp is secured from 
injury. Thus rude pressure can be borne by a tooth without 
the pulp being damaged : a simple but effectual provision 
to maintain the vitality of the organ. (See A, figs. 2, 13, 
and 14.) 
Dentine approaches very near to Enamel in density ; and che- 
mical analysis shows little difference between these structures.. 
According to Berzelius and Bibra, human Dentine consists of 
-28 parts of animal, and 72 of earthy matter, the latter being 
somewhat less proportionally than in Enamel.* Under the mi- 
croscope Dentine is seen to be composed of an intertubular sub- 
stance, and of numerous tubes which radiate from the pulp cavity 
derived from the dentinal tubuli. These tubuli indeed may be seen to communi- 
cate directly with the interstitial passages of the enamel." — I'liysiuloijical Anatomy, 
Part iii. p. 172. 
In tlie annexed engraving (fig. 5) is given a representation of the dentine and 
enamel, i.i which it is evident that tubes are permeating the latter, and that 
they are connected with those in the dentine. The illustration was taken from 
the tooth of a liorse, and the part here sliown is magnified 2(J0 diameters. In the 
figure the dentinal tubes, marked n, are seen to be passing to the dentinal hwmur, 
D,* (small hollow spaces), which have other tubes, !>♦*, arising from them and 
running into e, the enamel. 
* Quain and Sharpey's Anatomy, vol. ii. p. 974. 
t Fig. 5. Section of enamel and dentine, magnified 200 diameters. D, dentinal 
tubes; d*, dentinal lacunsD; d**, tubes extending from the lacuna: into e, the 
enamel. 
