OF SOFT TISSUE IN THE DENTINAL TUBES. 
519 
normal condition occupied by fibrils of soft tissr e. The above extracts from M. Lent’s 
paper have been made in order to show that he has not recognized the existence of 
permanent tube contents, although he has probably seen the fibrils themselves. 
The nature and office of the dentinal fibrils remain for consideration. If a fibril 
be examined in its natural condition, by the aid of an eighth of an inch object-glass, 
it will be found to consist of an almost structureless tissue, transparent, and of a com- 
paratively low refractive power. In glycerine the fibrils are scarcely visible. At pre- 
sent it admits of doubt whether they are tubular or solid. In some cases there is an 
appearance of tubularity ; but being cylindrical this may be a mere optical effect. 
When accidentally stretched between two fragments of dentine the diameter of the 
fibril becomes much diminished, and when broken across, a minute globule of trans- 
parent but dense fluid may sometimes be seen at the broken end, gathered into a 
more or less spherical form. These appearances may be explained by assuming that 
the fibril consists of a sheath containing a semifluid matter, similar to the white 
fibrillse of nerves ; but whether such a conclusion can be justified admits of doubt. 
The manner in which the dentinal fibrillae terminate in the pulp I am at present 
unable to decide. In favourable specimens they may be traced a short distance into 
the pulp, but whether they are terminated by cells or in any way connect themselves 
with nerves, I am unable to determine. The dimensions of the fibrils are the same 
as those of the interior of the dentinal tubes. 
The conditions under which sensation is manifested in dentine have been already 
stated, together with those under which it is lost, and the difficulty of accounting for 
these phenomena has been pointed out. The recognition of the fibrils of dentine will, 
however, I think, remove the difficulty, and enable the physiologist to explain why 
under certain circumstances that tissue is susceptible of pain, while under other con- 
ditions the sensitiveness is lost. 
That the dentine owes its sensation to the presence of the dentinal fibrils cannot, I 
think, be readily doubted, seeing that if their connexion with the pulp be cut off by 
the destruction of the latter, all sensation is at once lost. It is by no means necessary 
to assume that the dentinal fibrils are actual nerves before allowing them the power 
of communicating sensation. Many animals are endowed with sensation which yet 
possess no demonstrable nervous system ; and we may find many points in the human 
body highly sensitive without our being able to demonstrate nerves in such numbers 
as would account for the pain uniformly experienced from the puncture of a needle, 
upon the supposition that the needle had in each case wounded a nerve. Additional 
evidence in favour of the view that the fibrils possess sensation mav be obtained by 
examining their condition in diseased teeth, and the conditions attendant upon the 
disease. In those cases in which the fibrils are consolidated in the manner already 
described, there is perfect absence of pain when the part is removed, but so soon as 
the instrument reaches the healthy dentine, more or less inconvenience is felt. If, on 
tbe other hand, there is no consolidation of the fibrils, but the piiln is yet living, the 
