118 THE MICROSCOPICAL NEWS. 
pulp, and will stop almost immediately after the instrument is 
removed. Moreover, in preparing a tooth for filling the sensation 
in the fibrils will be found greatest at their ends and away from the 
pulp, just as we should expect in all sensation conductors. We 
know next to nothing of the fibrils from actual observation ; but 
as they are simply prolongations of the formative cells of the pulp, 
we may safely conclude they play the most important part in the 
calcification by which the tubes and sheaths become less as age 
advances. The practical experience of the observant dentist also 
gives further evidence of the character of the fibrils which other 
investigation is unable to make out. When a tooth has been filled 
in the most thorough manner, it will be found that it is subject for 
a time to the influence of heat and cold ; and the more thoroughly 
the cavity is prepared, and the firmer the filling is inserted, the 
more is this apt to be the case. After a time this will cease. There 
can be but one explanation to these phenomena. The removal of 
the decayed part of the tooth exposes the ends of the tubes and 
the contained fibrils. The gold that fills up the cavity is an excel- 
lent conductor of heat and cold. Therefore, so long as the ends 
of the tubes remain open the fibrils are exposed, and the effect of 
heat and cold remains ; but when the fibrils, acting as odontoblasts, 
have thrown out new dentine to fill up the exposed ends of the 
dentinal tubes, the sensation ceases. Although it is not common 
to speak of the fibrils as nerves,—and in the usual sense of that 
term I do not contend they are nerves,—there can be no doubt they 
do convey sensation to all parts of the dentine; and this demonstrates 
to my mind that primitive nerve organisation may be looked for 
where it has not heretofore been suspected, because the nerve 
sheaths have not been made out. 
I have thus, in this very imperfect manner, endeavoured to 
sketch the history, uses, and organisation of the teeth, so as to 
give something like a guide to the student of these organs. In so 
doing I have followed the theory of evolution, as put forth by Dr. 
Darwen; for the simple reason that in no other way I could 
form opinion on this matter. Many may object to some of my 
conclusions, and even the proved facts, for the reason that they 
involve this doctrine. In reply, I can only say that where there is an 
ardent wish to know the truth, a real reverence for things sacred, 
and a profound love for the Divine Creator, as the laws of life are 
studied, and the conclusion accepted that they are revealed through 
the order which evolution indicates, so far from a check being 
given to holy aspirations the mind will have reached a new stand- 
point from which to contemplate the wonderful mysteries of His 
never-ceasing wisdom and goodness. 
