522 ON THE PRESENCE OF FIBRILS OF SOFT TISSUE IN THE DENTINAL TUBES. 
These were treated with dilute hydrochloric acid, and were examined at short inter- 
vals after their immersion in the solvent fluid. The acid acted upon the enamel with 
great rapidity ; and in the course of a few minutes the edge corresponding to the 
outer surface of the tooth disappeared, leaving in its place a series of fine flexible 
filaments. More prolonged action of the acid led to a further loss from the surface 
of the enamel, and also to the solution of the part in contact with the dentine. In 
this case the fibrils were seen proceeding from the extremities of the dentinal tubes 
across the space which had been occupied by the enamel, from thence they were 
continued through that portion of the latter structure which yet remained undis- 
solved, and ultimately formed a delicate fringe floating freely in the fluid by which 
the preparation was surrounded. If a section presenting the above conditions be 
again placed in acid the whole of the enamel will be dissolved, leaving the dentine in 
those parts which have been invested with enamel, bordered by a thick fringe of long 
delicate fibrils, each one being continued from the peripheral extremity of a dentinal 
tube. In the dentine the fibrils occupying the tubes were as readily detected as in 
the human tooth, and presented the same general appearances and relations. 
The facility with which the fibrils were demonstrated in the enamel of the teeth of 
the Kangaroo, induced me to select for examination specimens of human teeth in 
which the dentinal tubes are continued for a short distance into the enamel. Under 
similar treatment similar results were obtained. Wherever the dentinal tubes could 
be traced into the enamel, the presence of the contained fibrils could be demonstrated 
by the aid of hydrochloric acid. 
Cavendish Square, 
June \7th, 1856. 
