ON THE SO-CALLED “ NERVE OF THE TOOTH 361 
of the animal frame. These fields have been well worked by 
others, it is true, but we reap the harvest of their labours in 
the many manuals on the subject with which our scientific 
libraries abound; but though skilful gleaners in the field of 
scientific investigation leave little for us to gather, yet stray 
facts may still be picked up by diligent and careful, but above 
all, systematic observers. 
I trust that you will deal leniently with me if I presume 
for a moment that you know nothing whatever of the various 
structures entering into the formation of a tooth. I can thus, 
in an elementary manner, recall to your minds the osseous 
elements we meet with in our examination. If a tooth be 
divided lougitudinally the main body of such a section would 
reveal three different substances surrounding a cavity which, 
to a certain extent, partakes of the external shape of the 
tooth; immediately surrounding the cavity, and constituting 
the principal bulk of the tooth, we notice a fibrous silky sub¬ 
stance, called the “ dentine capping that part of the dentine 
which appears above the gum, we see the crystalline, almost 
insensible “ enamel ” designed to protect the highly organized 
and exceedingly sensitive dentine beneath it; we shall also 
observe that the dentine inserted in the jaw, and forming the 
root of the tooth, is clothed with a material of a different ap¬ 
pearance to the other two substances—that is called the 
“cementum.” Of the enamel and cementum, it is not neces¬ 
sary on this occasion to speak, but the important relation 
existing between the “ nerve” and the dentine demands that 
I should enter more into detail in explaining its microscopical 
appearance. In looking at a section of dentine under the 
microscope in a well-developed human tooth, one is reminded 
of those views of the comparative sizes of the rivers of the 
world given in some atlases, only here our rivers are all the 
same diameter and about the same length, and run together 
in parallel waves. If, for the sake of illustration, we speak 
of them as rivers, we should say that they arise beneath the 
enamel by exceedingly fine tributaries, by the confluence of 
which the main stream is gradually enlarged till, flowing on 
towards the centre of the tooth, its “ debouchure” helps to 
make up the walls of the central cavity, which is occupied in 
the living state by the so-called “ nerve.” A closer examina¬ 
tion of our metaphorical rivers with higher magnifying powers 
will show us that they are tapering and undulating tubes, 
and existing so abundantly in the dentine as to impart to it 
that fibrous silky aspect which cannot fail to strike the most 
casual observer. These tubes, which, on the walls of the 
cavity, measure about T o ~ o o~oth of an inch in diameter, are 
