OF SOFT TISSUE IN THE DENTINAL TUBES. 
517 
upon the fluid at the exposed ends of the tubes is felt by the pulp at their inner extre- 
mities. This assumption does not, however, account for all the circumstances of the 
case, failing altogether to explain the greater sensibility of the dentine at one part of 
the tooth than at another. 
The want of accordance between the views usually entertained upon the structure 
of dentine and the physiological conditions manifested by that tissue when in con- 
nexion with the body, has wholly arisen from assuming that the dentinal tubes are 
solely for the conveyance of fluid, and that they are otherwise empty. With the hope 
of gaining some further knowledge upon this point, I commenced a series of obser- 
vations, the results of which it is the main purpose of this paper to communicate. 
When these investigations were commenced, I had but little expectation of finding 
that one of the most important parts in dental structure had been overlooked, 
namely, that each dentinal tube is permanently tenanted by a soft fibril, which, after 
passing from the pulp into the tubes, follows their ramifications. 
With proper care in manipulating, nothing is more easy than to demonstrate the 
existence of the dentinal fibrils, in any tooth which has been recently extracted. If 
a thin section be made in the plane of the direction of the tubes, and then placed in 
dilute hydrochloric acid until the whole or a greater part of the lime is removed, and 
the section be afterwards torn in a direction transverse to that of the tubes, many of the 
fibrils will be seen projecting from the torn edges (Plate XXI!^fig. 1). It is desirable, 
in repeating the experiment, to place the decalcified section upon a slide before tear- 
ing, as in moving it from the surface upon which it has been torn, some of the longer 
fibrils may be folded back upon the body of the specimen and thus become obscured. 
Where the separation between the torn surfaces has been but slight, we may often 
see a fibril, unbroken, stretching across from the separated orifices of the tube to 
which it belongs. 
It is not necessary, however, to decalcify dentine in order to show the fibrils. If 
a similar section to that already described be divided with the edge of a knife, many 
of these delicate organs will be seen, but they are usually broken off much shorter, 
many of them scarcely projecting beyond the orifices of the tubes. Again, if a minute 
portion of dentine be cut with a sharp knife from the surface produced by fracturing 
a perfectly fresh tooth, the same appearances will be seen, but not with the same cer- 
tainty and distinctness as in the previous examples. 
In order to demonstrate the connexion of the fibrils with the pulp, fine sections 
should be made with a sharp knife from the edge of the pulp-cavity. In this manner 
I obtained the specimen from which Mr. De Morgan has been kind enough to draw 
the accompanying illustration, showing the fibrils stretching from the pulp to the 
displaced dentine, and some of them passing out on the other side of the fragment 
(fig. 2). That the fibrils proceed from the pulp may be seen by carefully fracturing a 
fresh tooth with as little displacement of the fractured parts as possible; and then, by 
slowly removing the pulp from its place in the tooth, we shall be enabled to examine 
3 Y 2 
