86.2 ON THE SO-CALLED “ NERVE ” OF THE TOOTH. 
occupied in a recent tooth by transparent structureless fibres 
known as the dentinal fibrillae, the exact office of which is 
but obscurely defined, but they may minister to the nutrition 
and vitality of the tooth, since, wdien from age or disease 
these tubes become consolidated, the fibrous structure is 
replaced by one resembling horn, and, as a consequence, the 
tooth dies, becomes loose and a source of painful irritation. 
If a section of the dentine be made in a direction that shall 
cut across the course of these tubes, each tube will present 
an irregular aperture, and will be seen separated from its 
fellows by an almost equal proportion of intertubular tissue. 
We need not now consider any further the character of the 
dentine, as I shall have to recur to it when speaking of its 
relation to the nerve; but what I have laid before you will 
enable you to understand the meaning of much of the struc¬ 
ture it is our especial object to examine in the central or 
pulp cavity of a tooth. 
If we take a recently extracted healthy tooth and split it 
we shall notice that the pulp cavity is occupied by a pinkish 
fleshy mass about f of an inch long and T Vth of an inch wide 
at its upper and thickest part; it partakes somewhat of the 
external shape of the tooth, being wide in the upper part, and 
tapering towards the tooth : this, then, is what is popularly 
called the “nerve.” In physiological parlance it is termed 
the pulp. The basis of this pulp is composed of areolar 
tissue, whose interstices are filled with a homogeneous 
plasma. 
A microscopical examination of its exterior will reveal an 
infinite number of small points, giving to it an appearance 
not much unlike the cross section of the tubes of the dentine, 
both as regards size and distribution. Having noticed this 
much, recourse must be had to compression before we can 
readily make out the arrangements of its internal structure. 
Before proceeding to flatten it by pressure it may be with¬ 
drawn from its cavity, and allowed to soak in the ammoniacal 
solution of carmine, recommended by our President in his 
book f How to Work with the Microscope •/ let it remain in 
it twenty-four hours, wash aw 7 ay the carmine fluid, and trans¬ 
fer it to glycerine for a few hours; then put it under gentle, 
gradual pressure for some few hours more, when it will be 
rendered sufficiently thin to be easily examined by a \ of an 
inch objective or higher powers. 
Commencing our examination at that part of the pulp 
nearest the apex of the root, we shall notice it entering the 
foramen of the fang as a fine thread, which though so fine 
nevertheless conveys the nerve and the artery into the pulp, 
